1 \input texinfo @c -*-texinfo-*-
5 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
7 @c GNAT DOCUMENTATION o
11 @c GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). o
13 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
15 @setfilename gnat_rm.info
18 Copyright @copyright{} 1995-2008, Free Software Foundation, Inc.
20 Permission is granted to copy, distribute and/or modify this document
21 under the terms of the GNU Free Documentation License, Version 1.2 or
22 any later version published by the Free Software Foundation; with no
23 Invariant Sections, with the Front-Cover Texts being ``GNAT Reference
24 Manual'', and with no Back-Cover Texts. A copy of the license is
25 included in the section entitled ``GNU Free Documentation License''.
29 @set DEFAULTLANGUAGEVERSION Ada 2005
30 @set NONDEFAULTLANGUAGEVERSION Ada 95
32 @settitle GNAT Reference Manual
34 @setchapternewpage odd
37 @include gcc-common.texi
39 @dircategory GNU Ada tools
41 * GNAT Reference Manual: (gnat_rm). Reference Manual for GNU Ada tools.
45 @title GNAT Reference Manual
46 @subtitle GNAT, The GNU Ada Compiler
50 @vskip 0pt plus 1filll
57 @node Top, About This Guide, (dir), (dir)
58 @top GNAT Reference Manual
64 GNAT, The GNU Ada Compiler@*
65 GCC version @value{version-GCC}@*
72 * Implementation Defined Pragmas::
73 * Implementation Defined Attributes::
74 * Implementation Advice::
75 * Implementation Defined Characteristics::
76 * Intrinsic Subprograms::
77 * Representation Clauses and Pragmas::
78 * Standard Library Routines::
79 * The Implementation of Standard I/O::
81 * Interfacing to Other Languages::
82 * Specialized Needs Annexes::
83 * Implementation of Specific Ada Features::
84 * Project File Reference::
85 * Obsolescent Features::
86 * GNU Free Documentation License::
89 --- The Detailed Node Listing ---
93 * What This Reference Manual Contains::
94 * Related Information::
96 Implementation Defined Pragmas
98 * Pragma Abort_Defer::
105 * Pragma Assume_No_Invalid_Values::
107 * Pragma C_Pass_By_Copy::
109 * Pragma Check_Name::
110 * Pragma Check_Policy::
112 * Pragma Common_Object::
113 * Pragma Compile_Time_Error::
114 * Pragma Compile_Time_Warning::
115 * Pragma Complete_Representation::
116 * Pragma Complex_Representation::
117 * Pragma Component_Alignment::
118 * Pragma Convention_Identifier::
120 * Pragma CPP_Constructor::
121 * Pragma CPP_Virtual::
122 * Pragma CPP_Vtable::
124 * Pragma Debug_Policy::
125 * Pragma Detect_Blocking::
126 * Pragma Elaboration_Checks::
128 * Pragma Export_Exception::
129 * Pragma Export_Function::
130 * Pragma Export_Object::
131 * Pragma Export_Procedure::
132 * Pragma Export_Value::
133 * Pragma Export_Valued_Procedure::
134 * Pragma Extend_System::
136 * Pragma External_Name_Casing::
138 * Pragma Favor_Top_Level::
139 * Pragma Finalize_Storage_Only::
140 * Pragma Float_Representation::
142 * Pragma Implemented_By_Entry::
143 * Pragma Implicit_Packing::
144 * Pragma Import_Exception::
145 * Pragma Import_Function::
146 * Pragma Import_Object::
147 * Pragma Import_Procedure::
148 * Pragma Import_Valued_Procedure::
149 * Pragma Initialize_Scalars::
150 * Pragma Inline_Always::
151 * Pragma Inline_Generic::
153 * Pragma Interface_Name::
154 * Pragma Interrupt_Handler::
155 * Pragma Interrupt_State::
156 * Pragma Keep_Names::
159 * Pragma Linker_Alias::
160 * Pragma Linker_Constructor::
161 * Pragma Linker_Destructor::
162 * Pragma Linker_Section::
163 * Pragma Long_Float::
164 * Pragma Machine_Attribute::
166 * Pragma Main_Storage::
169 * Pragma No_Strict_Aliasing ::
170 * Pragma Normalize_Scalars::
171 * Pragma Obsolescent::
172 * Pragma Optimize_Alignment::
174 * Pragma Persistent_BSS::
176 * Pragma Postcondition::
177 * Pragma Precondition::
178 * Pragma Profile (Ravenscar)::
179 * Pragma Profile (Restricted)::
180 * Pragma Psect_Object::
181 * Pragma Pure_Function::
182 * Pragma Restriction_Warnings::
184 * Pragma Source_File_Name::
185 * Pragma Source_File_Name_Project::
186 * Pragma Source_Reference::
187 * Pragma Stream_Convert::
188 * Pragma Style_Checks::
191 * Pragma Suppress_All::
192 * Pragma Suppress_Exception_Locations::
193 * Pragma Suppress_Initialization::
196 * Pragma Task_Storage::
197 * Pragma Thread_Local_Storage::
198 * Pragma Time_Slice::
200 * Pragma Unchecked_Union::
201 * Pragma Unimplemented_Unit::
202 * Pragma Universal_Aliasing ::
203 * Pragma Universal_Data::
204 * Pragma Unmodified::
205 * Pragma Unreferenced::
206 * Pragma Unreferenced_Objects::
207 * Pragma Unreserve_All_Interrupts::
208 * Pragma Unsuppress::
209 * Pragma Use_VADS_Size::
210 * Pragma Validity_Checks::
213 * Pragma Weak_External::
214 * Pragma Wide_Character_Encoding::
216 Implementation Defined Attributes
227 * Default_Bit_Order::
237 * Has_Access_Values::
238 * Has_Discriminants::
245 * Max_Interrupt_Priority::
247 * Maximum_Alignment::
252 * Passed_By_Reference::
265 * Unconstrained_Array::
266 * Universal_Literal_String::
267 * Unrestricted_Access::
273 The Implementation of Standard I/O
275 * Standard I/O Packages::
281 * Wide_Wide_Text_IO::
285 * Filenames encoding::
287 * Operations on C Streams::
288 * Interfacing to C Streams::
292 * Ada.Characters.Latin_9 (a-chlat9.ads)::
293 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
294 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
295 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
296 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
297 * Ada.Command_Line.Environment (a-colien.ads)::
298 * Ada.Command_Line.Remove (a-colire.ads)::
299 * Ada.Command_Line.Response_File (a-clrefi.ads)::
300 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
301 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
302 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
303 * Ada.Exceptions.Traceback (a-exctra.ads)::
304 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
305 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
306 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
307 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
308 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
309 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
310 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
311 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
312 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
313 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
314 * GNAT.Altivec (g-altive.ads)::
315 * GNAT.Altivec.Conversions (g-altcon.ads)::
316 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
317 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
318 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
319 * GNAT.Array_Split (g-arrspl.ads)::
320 * GNAT.AWK (g-awk.ads)::
321 * GNAT.Bounded_Buffers (g-boubuf.ads)::
322 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
323 * GNAT.Bubble_Sort (g-bubsor.ads)::
324 * GNAT.Bubble_Sort_A (g-busora.ads)::
325 * GNAT.Bubble_Sort_G (g-busorg.ads)::
326 * GNAT.Byte_Order_Mark (g-byorma.ads)::
327 * GNAT.Byte_Swapping (g-bytswa.ads)::
328 * GNAT.Calendar (g-calend.ads)::
329 * GNAT.Calendar.Time_IO (g-catiio.ads)::
330 * GNAT.Case_Util (g-casuti.ads)::
331 * GNAT.CGI (g-cgi.ads)::
332 * GNAT.CGI.Cookie (g-cgicoo.ads)::
333 * GNAT.CGI.Debug (g-cgideb.ads)::
334 * GNAT.Command_Line (g-comlin.ads)::
335 * GNAT.Compiler_Version (g-comver.ads)::
336 * GNAT.Ctrl_C (g-ctrl_c.ads)::
337 * GNAT.CRC32 (g-crc32.ads)::
338 * GNAT.Current_Exception (g-curexc.ads)::
339 * GNAT.Debug_Pools (g-debpoo.ads)::
340 * GNAT.Debug_Utilities (g-debuti.ads)::
341 * GNAT.Decode_String (g-decstr.ads)::
342 * GNAT.Decode_UTF8_String (g-deutst.ads)::
343 * GNAT.Directory_Operations (g-dirope.ads)::
344 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
345 * GNAT.Dynamic_HTables (g-dynhta.ads)::
346 * GNAT.Dynamic_Tables (g-dyntab.ads)::
347 * GNAT.Encode_String (g-encstr.ads)::
348 * GNAT.Encode_UTF8_String (g-enutst.ads)::
349 * GNAT.Exception_Actions (g-excact.ads)::
350 * GNAT.Exception_Traces (g-exctra.ads)::
351 * GNAT.Exceptions (g-except.ads)::
352 * GNAT.Expect (g-expect.ads)::
353 * GNAT.Float_Control (g-flocon.ads)::
354 * GNAT.Heap_Sort (g-heasor.ads)::
355 * GNAT.Heap_Sort_A (g-hesora.ads)::
356 * GNAT.Heap_Sort_G (g-hesorg.ads)::
357 * GNAT.HTable (g-htable.ads)::
358 * GNAT.IO (g-io.ads)::
359 * GNAT.IO_Aux (g-io_aux.ads)::
360 * GNAT.Lock_Files (g-locfil.ads)::
361 * GNAT.MD5 (g-md5.ads)::
362 * GNAT.Memory_Dump (g-memdum.ads)::
363 * GNAT.Most_Recent_Exception (g-moreex.ads)::
364 * GNAT.OS_Lib (g-os_lib.ads)::
365 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
366 * GNAT.Random_Numbers (g-rannum.ads)::
367 * GNAT.Regexp (g-regexp.ads)::
368 * GNAT.Registry (g-regist.ads)::
369 * GNAT.Regpat (g-regpat.ads)::
370 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
371 * GNAT.Semaphores (g-semaph.ads)::
372 * GNAT.Serial_Communications (g-sercom.ads)::
373 * GNAT.SHA1 (g-sha1.ads)::
374 * GNAT.Signals (g-signal.ads)::
375 * GNAT.Sockets (g-socket.ads)::
376 * GNAT.Source_Info (g-souinf.ads)::
377 * GNAT.Spelling_Checker (g-speche.ads)::
378 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
379 * GNAT.Spitbol.Patterns (g-spipat.ads)::
380 * GNAT.Spitbol (g-spitbo.ads)::
381 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
382 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
383 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
384 * GNAT.SSE (g-sse.ads)::
385 * GNAT.SSE.Internal_Types (g-ssinty.ads)::
386 * GNAT.SSE.Vector_Types (g-ssvety.ads)::
387 * GNAT.Strings (g-string.ads)::
388 * GNAT.String_Split (g-strspl.ads)::
389 * GNAT.Table (g-table.ads)::
390 * GNAT.Task_Lock (g-tasloc.ads)::
391 * GNAT.Threads (g-thread.ads)::
392 * GNAT.Time_Stamp (g-timsta.ads)::
393 * GNAT.Traceback (g-traceb.ads)::
394 * GNAT.Traceback.Symbolic (g-trasym.ads)::
395 * GNAT.UTF_32 (g-utf_32.ads)::
396 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
397 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
398 * GNAT.Wide_String_Split (g-wistsp.ads)::
399 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
400 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
401 * Interfaces.C.Extensions (i-cexten.ads)::
402 * Interfaces.C.Streams (i-cstrea.ads)::
403 * Interfaces.CPP (i-cpp.ads)::
404 * Interfaces.Packed_Decimal (i-pacdec.ads)::
405 * Interfaces.VxWorks (i-vxwork.ads)::
406 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
407 * System.Address_Image (s-addima.ads)::
408 * System.Assertions (s-assert.ads)::
409 * System.Memory (s-memory.ads)::
410 * System.Partition_Interface (s-parint.ads)::
411 * System.Pool_Global (s-pooglo.ads)::
412 * System.Pool_Local (s-pooloc.ads)::
413 * System.Restrictions (s-restri.ads)::
414 * System.Rident (s-rident.ads)::
415 * System.Strings.Stream_Ops (s-ststop.ads)::
416 * System.Task_Info (s-tasinf.ads)::
417 * System.Wch_Cnv (s-wchcnv.ads)::
418 * System.Wch_Con (s-wchcon.ads)::
422 * Text_IO Stream Pointer Positioning::
423 * Text_IO Reading and Writing Non-Regular Files::
425 * Treating Text_IO Files as Streams::
426 * Text_IO Extensions::
427 * Text_IO Facilities for Unbounded Strings::
431 * Wide_Text_IO Stream Pointer Positioning::
432 * Wide_Text_IO Reading and Writing Non-Regular Files::
436 * Wide_Wide_Text_IO Stream Pointer Positioning::
437 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
439 Interfacing to Other Languages
442 * Interfacing to C++::
443 * Interfacing to COBOL::
444 * Interfacing to Fortran::
445 * Interfacing to non-GNAT Ada code::
447 Specialized Needs Annexes
449 Implementation of Specific Ada Features
450 * Machine Code Insertions::
451 * GNAT Implementation of Tasking::
452 * GNAT Implementation of Shared Passive Packages::
453 * Code Generation for Array Aggregates::
454 * The Size of Discriminated Records with Default Discriminants::
455 * Strict Conformance to the Ada Reference Manual::
457 Project File Reference
461 GNU Free Documentation License
468 @node About This Guide
469 @unnumbered About This Guide
472 This manual contains useful information in writing programs using the
473 @value{EDITION} compiler. It includes information on implementation dependent
474 characteristics of @value{EDITION}, including all the information required by
475 Annex M of the Ada language standard.
477 @value{EDITION} implements Ada 95 and Ada 2005, and it may also be invoked in
478 Ada 83 compatibility mode.
479 By default, @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION},
480 but you can override with a compiler switch
481 to explicitly specify the language version.
482 (Please refer to @ref{Compiling Different Versions of Ada,,, gnat_ugn,
483 @value{EDITION} User's Guide}, for details on these switches.)
484 Throughout this manual, references to ``Ada'' without a year suffix
485 apply to both the Ada 95 and Ada 2005 versions of the language.
487 Ada is designed to be highly portable.
488 In general, a program will have the same effect even when compiled by
489 different compilers on different platforms.
490 However, since Ada is designed to be used in a
491 wide variety of applications, it also contains a number of system
492 dependent features to be used in interfacing to the external world.
493 @cindex Implementation-dependent features
496 Note: Any program that makes use of implementation-dependent features
497 may be non-portable. You should follow good programming practice and
498 isolate and clearly document any sections of your program that make use
499 of these features in a non-portable manner.
502 For ease of exposition, ``GNAT Pro'' will be referred to simply as
503 ``GNAT'' in the remainder of this document.
507 * What This Reference Manual Contains::
509 * Related Information::
512 @node What This Reference Manual Contains
513 @unnumberedsec What This Reference Manual Contains
516 This reference manual contains the following chapters:
520 @ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
521 pragmas, which can be used to extend and enhance the functionality of the
525 @ref{Implementation Defined Attributes}, lists GNAT
526 implementation-dependent attributes which can be used to extend and
527 enhance the functionality of the compiler.
530 @ref{Implementation Advice}, provides information on generally
531 desirable behavior which are not requirements that all compilers must
532 follow since it cannot be provided on all systems, or which may be
533 undesirable on some systems.
536 @ref{Implementation Defined Characteristics}, provides a guide to
537 minimizing implementation dependent features.
540 @ref{Intrinsic Subprograms}, describes the intrinsic subprograms
541 implemented by GNAT, and how they can be imported into user
542 application programs.
545 @ref{Representation Clauses and Pragmas}, describes in detail the
546 way that GNAT represents data, and in particular the exact set
547 of representation clauses and pragmas that is accepted.
550 @ref{Standard Library Routines}, provides a listing of packages and a
551 brief description of the functionality that is provided by Ada's
552 extensive set of standard library routines as implemented by GNAT@.
555 @ref{The Implementation of Standard I/O}, details how the GNAT
556 implementation of the input-output facilities.
559 @ref{The GNAT Library}, is a catalog of packages that complement
560 the Ada predefined library.
563 @ref{Interfacing to Other Languages}, describes how programs
564 written in Ada using GNAT can be interfaced to other programming
567 @ref{Specialized Needs Annexes}, describes the GNAT implementation of all
568 of the specialized needs annexes.
571 @ref{Implementation of Specific Ada Features}, discusses issues related
572 to GNAT's implementation of machine code insertions, tasking, and several
576 @ref{Project File Reference}, presents the syntax and semantics
580 @ref{Obsolescent Features} documents implementation dependent features,
581 including pragmas and attributes, which are considered obsolescent, since
582 there are other preferred ways of achieving the same results. These
583 obsolescent forms are retained for backwards compatibility.
587 @cindex Ada 95 Language Reference Manual
588 @cindex Ada 2005 Language Reference Manual
590 This reference manual assumes a basic familiarity with the Ada 95 language, as
591 described in the International Standard ANSI/ISO/IEC-8652:1995,
593 It does not require knowledge of the new features introduced by Ada 2005,
594 (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1
596 Both reference manuals are included in the GNAT documentation
600 @unnumberedsec Conventions
601 @cindex Conventions, typographical
602 @cindex Typographical conventions
605 Following are examples of the typographical and graphic conventions used
610 @code{Functions}, @code{utility program names}, @code{standard names},
617 @file{File names}, @samp{button names}, and @samp{field names}.
620 @code{Variables}, @env{environment variables}, and @var{metasyntactic
627 [optional information or parameters]
630 Examples are described by text
632 and then shown this way.
637 Commands that are entered by the user are preceded in this manual by the
638 characters @samp{$ } (dollar sign followed by space). If your system uses this
639 sequence as a prompt, then the commands will appear exactly as you see them
640 in the manual. If your system uses some other prompt, then the command will
641 appear with the @samp{$} replaced by whatever prompt character you are using.
643 @node Related Information
644 @unnumberedsec Related Information
646 See the following documents for further information on GNAT:
650 @xref{Top, @value{EDITION} User's Guide, About This Guide, gnat_ugn,
651 @value{EDITION} User's Guide}, which provides information on how to use the
652 GNAT compiler system.
655 @cite{Ada 95 Reference Manual}, which contains all reference
656 material for the Ada 95 programming language.
659 @cite{Ada 95 Annotated Reference Manual}, which is an annotated version
660 of the Ada 95 standard. The annotations describe
661 detailed aspects of the design decision, and in particular contain useful
662 sections on Ada 83 compatibility.
665 @cite{Ada 2005 Reference Manual}, which contains all reference
666 material for the Ada 2005 programming language.
669 @cite{Ada 2005 Annotated Reference Manual}, which is an annotated version
670 of the Ada 2005 standard. The annotations describe
671 detailed aspects of the design decision, and in particular contain useful
672 sections on Ada 83 and Ada 95 compatibility.
675 @cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
676 which contains specific information on compatibility between GNAT and
680 @cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
681 describes in detail the pragmas and attributes provided by the DEC Ada 83
686 @node Implementation Defined Pragmas
687 @chapter Implementation Defined Pragmas
690 Ada defines a set of pragmas that can be used to supply additional
691 information to the compiler. These language defined pragmas are
692 implemented in GNAT and work as described in the Ada Reference Manual.
694 In addition, Ada allows implementations to define additional pragmas
695 whose meaning is defined by the implementation. GNAT provides a number
696 of these implementation-defined pragmas, which can be used to extend
697 and enhance the functionality of the compiler. This section of the GNAT
698 Reference Manual describes these additional pragmas.
700 Note that any program using these pragmas might not be portable to other
701 compilers (although GNAT implements this set of pragmas on all
702 platforms). Therefore if portability to other compilers is an important
703 consideration, the use of these pragmas should be minimized.
706 * Pragma Abort_Defer::
713 * Pragma Assume_No_Invalid_Values::
715 * Pragma C_Pass_By_Copy::
717 * Pragma Check_Name::
718 * Pragma Check_Policy::
720 * Pragma Common_Object::
721 * Pragma Compile_Time_Error::
722 * Pragma Compile_Time_Warning::
723 * Pragma Complete_Representation::
724 * Pragma Complex_Representation::
725 * Pragma Component_Alignment::
726 * Pragma Convention_Identifier::
728 * Pragma CPP_Constructor::
729 * Pragma CPP_Virtual::
730 * Pragma CPP_Vtable::
732 * Pragma Debug_Policy::
733 * Pragma Detect_Blocking::
734 * Pragma Elaboration_Checks::
736 * Pragma Export_Exception::
737 * Pragma Export_Function::
738 * Pragma Export_Object::
739 * Pragma Export_Procedure::
740 * Pragma Export_Value::
741 * Pragma Export_Valued_Procedure::
742 * Pragma Extend_System::
744 * Pragma External_Name_Casing::
746 * Pragma Favor_Top_Level::
747 * Pragma Finalize_Storage_Only::
748 * Pragma Float_Representation::
750 * Pragma Implemented_By_Entry::
751 * Pragma Implicit_Packing::
752 * Pragma Import_Exception::
753 * Pragma Import_Function::
754 * Pragma Import_Object::
755 * Pragma Import_Procedure::
756 * Pragma Import_Valued_Procedure::
757 * Pragma Initialize_Scalars::
758 * Pragma Inline_Always::
759 * Pragma Inline_Generic::
761 * Pragma Interface_Name::
762 * Pragma Interrupt_Handler::
763 * Pragma Interrupt_State::
764 * Pragma Keep_Names::
767 * Pragma Linker_Alias::
768 * Pragma Linker_Constructor::
769 * Pragma Linker_Destructor::
770 * Pragma Linker_Section::
771 * Pragma Long_Float::
772 * Pragma Machine_Attribute::
774 * Pragma Main_Storage::
777 * Pragma No_Strict_Aliasing::
778 * Pragma Normalize_Scalars::
779 * Pragma Obsolescent::
780 * Pragma Optimize_Alignment::
782 * Pragma Persistent_BSS::
784 * Pragma Postcondition::
785 * Pragma Precondition::
786 * Pragma Profile (Ravenscar)::
787 * Pragma Profile (Restricted)::
788 * Pragma Psect_Object::
789 * Pragma Pure_Function::
790 * Pragma Restriction_Warnings::
792 * Pragma Source_File_Name::
793 * Pragma Source_File_Name_Project::
794 * Pragma Source_Reference::
795 * Pragma Stream_Convert::
796 * Pragma Style_Checks::
799 * Pragma Suppress_All::
800 * Pragma Suppress_Exception_Locations::
801 * Pragma Suppress_Initialization::
804 * Pragma Task_Storage::
805 * Pragma Thread_Local_Storage::
806 * Pragma Time_Slice::
808 * Pragma Unchecked_Union::
809 * Pragma Unimplemented_Unit::
810 * Pragma Universal_Aliasing ::
811 * Pragma Universal_Data::
812 * Pragma Unmodified::
813 * Pragma Unreferenced::
814 * Pragma Unreferenced_Objects::
815 * Pragma Unreserve_All_Interrupts::
816 * Pragma Unsuppress::
817 * Pragma Use_VADS_Size::
818 * Pragma Validity_Checks::
821 * Pragma Weak_External::
822 * Pragma Wide_Character_Encoding::
825 @node Pragma Abort_Defer
826 @unnumberedsec Pragma Abort_Defer
828 @cindex Deferring aborts
836 This pragma must appear at the start of the statement sequence of a
837 handled sequence of statements (right after the @code{begin}). It has
838 the effect of deferring aborts for the sequence of statements (but not
839 for the declarations or handlers, if any, associated with this statement
843 @unnumberedsec Pragma Ada_83
852 A configuration pragma that establishes Ada 83 mode for the unit to
853 which it applies, regardless of the mode set by the command line
854 switches. In Ada 83 mode, GNAT attempts to be as compatible with
855 the syntax and semantics of Ada 83, as defined in the original Ada
856 83 Reference Manual as possible. In particular, the keywords added by Ada 95
857 and Ada 2005 are not recognized, optional package bodies are allowed,
858 and generics may name types with unknown discriminants without using
859 the @code{(<>)} notation. In addition, some but not all of the additional
860 restrictions of Ada 83 are enforced.
862 Ada 83 mode is intended for two purposes. Firstly, it allows existing
863 Ada 83 code to be compiled and adapted to GNAT with less effort.
864 Secondly, it aids in keeping code backwards compatible with Ada 83.
865 However, there is no guarantee that code that is processed correctly
866 by GNAT in Ada 83 mode will in fact compile and execute with an Ada
867 83 compiler, since GNAT does not enforce all the additional checks
871 @unnumberedsec Pragma Ada_95
880 A configuration pragma that establishes Ada 95 mode for the unit to which
881 it applies, regardless of the mode set by the command line switches.
882 This mode is set automatically for the @code{Ada} and @code{System}
883 packages and their children, so you need not specify it in these
884 contexts. This pragma is useful when writing a reusable component that
885 itself uses Ada 95 features, but which is intended to be usable from
886 either Ada 83 or Ada 95 programs.
889 @unnumberedsec Pragma Ada_05
898 A configuration pragma that establishes Ada 2005 mode for the unit to which
899 it applies, regardless of the mode set by the command line switches.
900 This mode is set automatically for the @code{Ada} and @code{System}
901 packages and their children, so you need not specify it in these
902 contexts. This pragma is useful when writing a reusable component that
903 itself uses Ada 2005 features, but which is intended to be usable from
904 either Ada 83 or Ada 95 programs.
906 @node Pragma Ada_2005
907 @unnumberedsec Pragma Ada_2005
916 This configuration pragma is a synonym for pragma Ada_05 and has the
917 same syntax and effect.
919 @node Pragma Annotate
920 @unnumberedsec Pragma Annotate
925 pragma Annotate (IDENTIFIER @{, ARG@});
927 ARG ::= NAME | EXPRESSION
931 This pragma is used to annotate programs. @var{identifier} identifies
932 the type of annotation. GNAT verifies that it is an identifier, but does
933 not otherwise analyze it. The @var{arg} argument
934 can be either a string literal or an
935 expression. String literals are assumed to be of type
936 @code{Standard.String}. Names of entities are simply analyzed as entity
937 names. All other expressions are analyzed as expressions, and must be
940 The analyzed pragma is retained in the tree, but not otherwise processed
941 by any part of the GNAT compiler. This pragma is intended for use by
942 external tools, including ASIS@.
945 @unnumberedsec Pragma Assert
952 [, string_EXPRESSION]);
956 The effect of this pragma depends on whether the corresponding command
957 line switch is set to activate assertions. The pragma expands into code
958 equivalent to the following:
961 if assertions-enabled then
962 if not boolean_EXPRESSION then
963 System.Assertions.Raise_Assert_Failure
970 The string argument, if given, is the message that will be associated
971 with the exception occurrence if the exception is raised. If no second
972 argument is given, the default message is @samp{@var{file}:@var{nnn}},
973 where @var{file} is the name of the source file containing the assert,
974 and @var{nnn} is the line number of the assert. A pragma is not a
975 statement, so if a statement sequence contains nothing but a pragma
976 assert, then a null statement is required in addition, as in:
981 pragma Assert (K > 3, "Bad value for K");
987 Note that, as with the @code{if} statement to which it is equivalent, the
988 type of the expression is either @code{Standard.Boolean}, or any type derived
989 from this standard type.
991 If assertions are disabled (switch @option{-gnata} not used), then there
992 is no run-time effect (and in particular, any side effects from the
993 expression will not occur at run time). (The expression is still
994 analyzed at compile time, and may cause types to be frozen if they are
995 mentioned here for the first time).
997 If assertions are enabled, then the given expression is tested, and if
998 it is @code{False} then @code{System.Assertions.Raise_Assert_Failure} is called
999 which results in the raising of @code{Assert_Failure} with the given message.
1001 You should generally avoid side effects in the expression arguments of
1002 this pragma, because these side effects will turn on and off with the
1003 setting of the assertions mode, resulting in assertions that have an
1004 effect on the program. However, the expressions are analyzed for
1005 semantic correctness whether or not assertions are enabled, so turning
1006 assertions on and off cannot affect the legality of a program.
1008 @node Pragma Assume_No_Invalid_Values
1009 @unnumberedsec Pragma Assume_No_Invalid_Values
1010 @findex Assume_No_Invalid_Values
1011 @cindex Invalid representations
1012 @cindex Invalid values
1015 @smallexample @c ada
1016 pragma Assume_No_Invalid_Values (On | Off);
1020 This is a configuration pragma that controls the assumptions made by the
1021 compiler about the occurrence of invalid representations (invalid values)
1024 The default behavior (corresponding to an Off argument for this pragma), is
1025 to assume that values may in general be invalid unless the compiler can
1026 prove they are valid. Consider the following example:
1028 @smallexample @c ada
1029 V1 : Integer range 1 .. 10;
1030 V2 : Integer range 11 .. 20;
1032 for J in V2 .. V1 loop
1038 if V1 and V2 have valid values, then the loop is known at compile
1039 time not to execute since the lower bound must be greater than the
1040 upper bound. However in default mode, no such assumption is made,
1041 and the loop may execute. If @code{Assume_No_Invalid_Values (On)}
1042 is given, the compiler will assume that any occurrence of a variable
1043 other than in an explicit @code{'Valid} test always has a valid
1044 value, and the loop above will be optimized away.
1046 The use of @code{Assume_No_Invalid_Values (On)} is appropriate if
1047 you know your code is free of uninitialized variables and other
1048 possible sources of invalid representations, and may result in
1049 more efficient code. A program that accesses an invalid representation
1050 with this pragma in effect is erroneous, so no guarantees can be made
1053 It is peculiar though permissible to use this pragma in conjunction
1054 with validity checking (-gnatVa). In such cases, accessing invalid
1055 values will generally give an exception, though formally the program
1056 is erroneous so there are no guarantees that this will always be the
1057 case, and it is recommended that these two options not be used together.
1059 @node Pragma Ast_Entry
1060 @unnumberedsec Pragma Ast_Entry
1065 @smallexample @c ada
1066 pragma AST_Entry (entry_IDENTIFIER);
1070 This pragma is implemented only in the OpenVMS implementation of GNAT@. The
1071 argument is the simple name of a single entry; at most one @code{AST_Entry}
1072 pragma is allowed for any given entry. This pragma must be used in
1073 conjunction with the @code{AST_Entry} attribute, and is only allowed after
1074 the entry declaration and in the same task type specification or single task
1075 as the entry to which it applies. This pragma specifies that the given entry
1076 may be used to handle an OpenVMS asynchronous system trap (@code{AST})
1077 resulting from an OpenVMS system service call. The pragma does not affect
1078 normal use of the entry. For further details on this pragma, see the
1079 DEC Ada Language Reference Manual, section 9.12a.
1081 @node Pragma C_Pass_By_Copy
1082 @unnumberedsec Pragma C_Pass_By_Copy
1083 @cindex Passing by copy
1084 @findex C_Pass_By_Copy
1087 @smallexample @c ada
1088 pragma C_Pass_By_Copy
1089 ([Max_Size =>] static_integer_EXPRESSION);
1093 Normally the default mechanism for passing C convention records to C
1094 convention subprograms is to pass them by reference, as suggested by RM
1095 B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
1096 this default, by requiring that record formal parameters be passed by
1097 copy if all of the following conditions are met:
1101 The size of the record type does not exceed the value specified for
1104 The record type has @code{Convention C}.
1106 The formal parameter has this record type, and the subprogram has a
1107 foreign (non-Ada) convention.
1111 If these conditions are met the argument is passed by copy, i.e.@: in a
1112 manner consistent with what C expects if the corresponding formal in the
1113 C prototype is a struct (rather than a pointer to a struct).
1115 You can also pass records by copy by specifying the convention
1116 @code{C_Pass_By_Copy} for the record type, or by using the extended
1117 @code{Import} and @code{Export} pragmas, which allow specification of
1118 passing mechanisms on a parameter by parameter basis.
1121 @unnumberedsec Pragma Check
1123 @cindex Named assertions
1127 @smallexample @c ada
1129 [Name =>] Identifier,
1130 [Check =>] Boolean_EXPRESSION
1131 [, [Message =>] string_EXPRESSION] );
1135 This pragma is similar to the predefined pragma @code{Assert} except that an
1136 extra identifier argument is present. In conjunction with pragma
1137 @code{Check_Policy}, this can be used to define groups of assertions that can
1138 be independently controlled. The identifier @code{Assertion} is special, it
1139 refers to the normal set of pragma @code{Assert} statements. The identifiers
1140 @code{Precondition} and @code{Postcondition} correspond to the pragmas of these
1141 names, so these three names would normally not be used directly in a pragma
1144 Checks introduced by this pragma are normally deactivated by default. They can
1145 be activated either by the command line option @option{-gnata}, which turns on
1146 all checks, or individually controlled using pragma @code{Check_Policy}.
1148 @node Pragma Check_Name
1149 @unnumberedsec Pragma Check_Name
1150 @cindex Defining check names
1151 @cindex Check names, defining
1155 @smallexample @c ada
1156 pragma Check_Name (check_name_IDENTIFIER);
1160 This is a configuration pragma that defines a new implementation
1161 defined check name (unless IDENTIFIER matches one of the predefined
1162 check names, in which case the pragma has no effect). Check names
1163 are global to a partition, so if two or more configuration pragmas
1164 are present in a partition mentioning the same name, only one new
1165 check name is introduced.
1167 An implementation defined check name introduced with this pragma may
1168 be used in only three contexts: @code{pragma Suppress},
1169 @code{pragma Unsuppress},
1170 and as the prefix of a @code{Check_Name'Enabled} attribute reference. For
1171 any of these three cases, the check name must be visible. A check
1172 name is visible if it is in the configuration pragmas applying to
1173 the current unit, or if it appears at the start of any unit that
1174 is part of the dependency set of the current unit (e.g., units that
1175 are mentioned in @code{with} clauses).
1177 @node Pragma Check_Policy
1178 @unnumberedsec Pragma Check_Policy
1179 @cindex Controlling assertions
1180 @cindex Assertions, control
1181 @cindex Check pragma control
1182 @cindex Named assertions
1186 @smallexample @c ada
1188 ([Name =>] Identifier,
1189 [Policy =>] POLICY_IDENTIFIER);
1191 POLICY_IDENTIFIER ::= On | Off | Check | Ignore
1195 This pragma is similar to the predefined pragma @code{Assertion_Policy},
1196 except that it controls sets of named assertions introduced using the
1197 @code{Check} pragmas. It can be used as a configuration pragma or (unlike
1198 @code{Assertion_Policy}) can be used within a declarative part, in which case
1199 it controls the status to the end of the corresponding construct (in a manner
1200 identical to pragma @code{Suppress)}.
1202 The identifier given as the first argument corresponds to a name used in
1203 associated @code{Check} pragmas. For example, if the pragma:
1205 @smallexample @c ada
1206 pragma Check_Policy (Critical_Error, Off);
1210 is given, then subsequent @code{Check} pragmas whose first argument is also
1211 @code{Critical_Error} will be disabled. The special identifier @code{Assertion}
1212 controls the behavior of normal @code{Assert} pragmas (thus a pragma
1213 @code{Check_Policy} with this identifier is similar to the normal
1214 @code{Assertion_Policy} pragma except that it can appear within a
1217 The special identifiers @code{Precondition} and @code{Postcondition} control
1218 the status of preconditions and postconditions. If a @code{Precondition} pragma
1219 is encountered, it is ignored if turned off by a @code{Check_Policy} specifying
1220 that @code{Precondition} checks are @code{Off} or @code{Ignored}. Similarly use
1221 of the name @code{Postcondition} controls whether @code{Postcondition} pragmas
1224 The check policy is @code{Off} to turn off corresponding checks, and @code{On}
1225 to turn on corresponding checks. The default for a set of checks for which no
1226 @code{Check_Policy} is given is @code{Off} unless the compiler switch
1227 @option{-gnata} is given, which turns on all checks by default.
1229 The check policy settings @code{Check} and @code{Ignore} are also recognized
1230 as synonyms for @code{On} and @code{Off}. These synonyms are provided for
1231 compatibility with the standard @code{Assertion_Policy} pragma.
1233 @node Pragma Comment
1234 @unnumberedsec Pragma Comment
1239 @smallexample @c ada
1240 pragma Comment (static_string_EXPRESSION);
1244 This is almost identical in effect to pragma @code{Ident}. It allows the
1245 placement of a comment into the object file and hence into the
1246 executable file if the operating system permits such usage. The
1247 difference is that @code{Comment}, unlike @code{Ident}, has
1248 no limitations on placement of the pragma (it can be placed
1249 anywhere in the main source unit), and if more than one pragma
1250 is used, all comments are retained.
1252 @node Pragma Common_Object
1253 @unnumberedsec Pragma Common_Object
1254 @findex Common_Object
1258 @smallexample @c ada
1259 pragma Common_Object (
1260 [Internal =>] LOCAL_NAME
1261 [, [External =>] EXTERNAL_SYMBOL]
1262 [, [Size =>] EXTERNAL_SYMBOL] );
1266 | static_string_EXPRESSION
1270 This pragma enables the shared use of variables stored in overlaid
1271 linker areas corresponding to the use of @code{COMMON}
1272 in Fortran. The single
1273 object @var{LOCAL_NAME} is assigned to the area designated by
1274 the @var{External} argument.
1275 You may define a record to correspond to a series
1276 of fields. The @var{Size} argument
1277 is syntax checked in GNAT, but otherwise ignored.
1279 @code{Common_Object} is not supported on all platforms. If no
1280 support is available, then the code generator will issue a message
1281 indicating that the necessary attribute for implementation of this
1282 pragma is not available.
1284 @node Pragma Compile_Time_Error
1285 @unnumberedsec Pragma Compile_Time_Error
1286 @findex Compile_Time_Error
1290 @smallexample @c ada
1291 pragma Compile_Time_Error
1292 (boolean_EXPRESSION, static_string_EXPRESSION);
1296 This pragma can be used to generate additional compile time
1298 is particularly useful in generics, where errors can be issued for
1299 specific problematic instantiations. The first parameter is a boolean
1300 expression. The pragma is effective only if the value of this expression
1301 is known at compile time, and has the value True. The set of expressions
1302 whose values are known at compile time includes all static boolean
1303 expressions, and also other values which the compiler can determine
1304 at compile time (e.g., the size of a record type set by an explicit
1305 size representation clause, or the value of a variable which was
1306 initialized to a constant and is known not to have been modified).
1307 If these conditions are met, an error message is generated using
1308 the value given as the second argument. This string value may contain
1309 embedded ASCII.LF characters to break the message into multiple lines.
1311 @node Pragma Compile_Time_Warning
1312 @unnumberedsec Pragma Compile_Time_Warning
1313 @findex Compile_Time_Warning
1317 @smallexample @c ada
1318 pragma Compile_Time_Warning
1319 (boolean_EXPRESSION, static_string_EXPRESSION);
1323 Same as pragma Compile_Time_Error, except a warning is issued instead
1324 of an error message. Note that if this pragma is used in a package that
1325 is with'ed by a client, the client will get the warning even though it
1326 is issued by a with'ed package (normally warnings in with'ed units are
1327 suppressed, but this is a special exception to that rule).
1329 One typical use is within a generic where compile time known characteristics
1330 of formal parameters are tested, and warnings given appropriately. Another use
1331 with a first parameter of True is to warn a client about use of a package,
1332 for example that it is not fully implemented.
1334 @node Pragma Complete_Representation
1335 @unnumberedsec Pragma Complete_Representation
1336 @findex Complete_Representation
1340 @smallexample @c ada
1341 pragma Complete_Representation;
1345 This pragma must appear immediately within a record representation
1346 clause. Typical placements are before the first component clause
1347 or after the last component clause. The effect is to give an error
1348 message if any component is missing a component clause. This pragma
1349 may be used to ensure that a record representation clause is
1350 complete, and that this invariant is maintained if fields are
1351 added to the record in the future.
1353 @node Pragma Complex_Representation
1354 @unnumberedsec Pragma Complex_Representation
1355 @findex Complex_Representation
1359 @smallexample @c ada
1360 pragma Complex_Representation
1361 ([Entity =>] LOCAL_NAME);
1365 The @var{Entity} argument must be the name of a record type which has
1366 two fields of the same floating-point type. The effect of this pragma is
1367 to force gcc to use the special internal complex representation form for
1368 this record, which may be more efficient. Note that this may result in
1369 the code for this type not conforming to standard ABI (application
1370 binary interface) requirements for the handling of record types. For
1371 example, in some environments, there is a requirement for passing
1372 records by pointer, and the use of this pragma may result in passing
1373 this type in floating-point registers.
1375 @node Pragma Component_Alignment
1376 @unnumberedsec Pragma Component_Alignment
1377 @cindex Alignments of components
1378 @findex Component_Alignment
1382 @smallexample @c ada
1383 pragma Component_Alignment (
1384 [Form =>] ALIGNMENT_CHOICE
1385 [, [Name =>] type_LOCAL_NAME]);
1387 ALIGNMENT_CHOICE ::=
1395 Specifies the alignment of components in array or record types.
1396 The meaning of the @var{Form} argument is as follows:
1399 @findex Component_Size
1400 @item Component_Size
1401 Aligns scalar components and subcomponents of the array or record type
1402 on boundaries appropriate to their inherent size (naturally
1403 aligned). For example, 1-byte components are aligned on byte boundaries,
1404 2-byte integer components are aligned on 2-byte boundaries, 4-byte
1405 integer components are aligned on 4-byte boundaries and so on. These
1406 alignment rules correspond to the normal rules for C compilers on all
1407 machines except the VAX@.
1409 @findex Component_Size_4
1410 @item Component_Size_4
1411 Naturally aligns components with a size of four or fewer
1412 bytes. Components that are larger than 4 bytes are placed on the next
1415 @findex Storage_Unit
1417 Specifies that array or record components are byte aligned, i.e.@:
1418 aligned on boundaries determined by the value of the constant
1419 @code{System.Storage_Unit}.
1423 Specifies that array or record components are aligned on default
1424 boundaries, appropriate to the underlying hardware or operating system or
1425 both. For OpenVMS VAX systems, the @code{Default} choice is the same as
1426 the @code{Storage_Unit} choice (byte alignment). For all other systems,
1427 the @code{Default} choice is the same as @code{Component_Size} (natural
1432 If the @code{Name} parameter is present, @var{type_LOCAL_NAME} must
1433 refer to a local record or array type, and the specified alignment
1434 choice applies to the specified type. The use of
1435 @code{Component_Alignment} together with a pragma @code{Pack} causes the
1436 @code{Component_Alignment} pragma to be ignored. The use of
1437 @code{Component_Alignment} together with a record representation clause
1438 is only effective for fields not specified by the representation clause.
1440 If the @code{Name} parameter is absent, the pragma can be used as either
1441 a configuration pragma, in which case it applies to one or more units in
1442 accordance with the normal rules for configuration pragmas, or it can be
1443 used within a declarative part, in which case it applies to types that
1444 are declared within this declarative part, or within any nested scope
1445 within this declarative part. In either case it specifies the alignment
1446 to be applied to any record or array type which has otherwise standard
1449 If the alignment for a record or array type is not specified (using
1450 pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
1451 clause), the GNAT uses the default alignment as described previously.
1453 @node Pragma Convention_Identifier
1454 @unnumberedsec Pragma Convention_Identifier
1455 @findex Convention_Identifier
1456 @cindex Conventions, synonyms
1460 @smallexample @c ada
1461 pragma Convention_Identifier (
1462 [Name =>] IDENTIFIER,
1463 [Convention =>] convention_IDENTIFIER);
1467 This pragma provides a mechanism for supplying synonyms for existing
1468 convention identifiers. The @code{Name} identifier can subsequently
1469 be used as a synonym for the given convention in other pragmas (including
1470 for example pragma @code{Import} or another @code{Convention_Identifier}
1471 pragma). As an example of the use of this, suppose you had legacy code
1472 which used Fortran77 as the identifier for Fortran. Then the pragma:
1474 @smallexample @c ada
1475 pragma Convention_Identifier (Fortran77, Fortran);
1479 would allow the use of the convention identifier @code{Fortran77} in
1480 subsequent code, avoiding the need to modify the sources. As another
1481 example, you could use this to parametrize convention requirements
1482 according to systems. Suppose you needed to use @code{Stdcall} on
1483 windows systems, and @code{C} on some other system, then you could
1484 define a convention identifier @code{Library} and use a single
1485 @code{Convention_Identifier} pragma to specify which convention
1486 would be used system-wide.
1488 @node Pragma CPP_Class
1489 @unnumberedsec Pragma CPP_Class
1491 @cindex Interfacing with C++
1495 @smallexample @c ada
1496 pragma CPP_Class ([Entity =>] LOCAL_NAME);
1500 The argument denotes an entity in the current declarative region that is
1501 declared as a record type. It indicates that the type corresponds to an
1502 externally declared C++ class type, and is to be laid out the same way
1503 that C++ would lay out the type. If the C++ class has virtual primitives
1504 then the record must be declared as a tagged record type.
1506 Types for which @code{CPP_Class} is specified do not have assignment or
1507 equality operators defined (such operations can be imported or declared
1508 as subprograms as required). Initialization is allowed only by constructor
1509 functions (see pragma @code{CPP_Constructor}). Such types are implicitly
1510 limited if not explicitly declared as limited or derived from a limited
1511 type, and an error is issued in that case.
1513 Pragma @code{CPP_Class} is intended primarily for automatic generation
1514 using an automatic binding generator tool.
1515 See @ref{Interfacing to C++} for related information.
1517 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
1518 for backward compatibility but its functionality is available
1519 using pragma @code{Import} with @code{Convention} = @code{CPP}.
1521 @node Pragma CPP_Constructor
1522 @unnumberedsec Pragma CPP_Constructor
1523 @cindex Interfacing with C++
1524 @findex CPP_Constructor
1528 @smallexample @c ada
1529 pragma CPP_Constructor ([Entity =>] LOCAL_NAME
1530 [, [External_Name =>] static_string_EXPRESSION ]
1531 [, [Link_Name =>] static_string_EXPRESSION ]);
1535 This pragma identifies an imported function (imported in the usual way
1536 with pragma @code{Import}) as corresponding to a C++ constructor. If
1537 @code{External_Name} and @code{Link_Name} are not specified then the
1538 @code{Entity} argument is a name that must have been previously mentioned
1539 in a pragma @code{Import} with @code{Convention} = @code{CPP}. Such name
1540 must be of one of the following forms:
1544 @code{function @var{Fname} return @var{T}}
1548 @code{function @var{Fname} return @var{T}'Class}
1551 @code{function @var{Fname} (@dots{}) return @var{T}}
1555 @code{function @var{Fname} (@dots{}) return @var{T}'Class}
1559 where @var{T} is a limited record type imported from C++ with pragma
1560 @code{Import} and @code{Convention} = @code{CPP}.
1562 The first two forms import the default constructor, used when an object
1563 of type @var{T} is created on the Ada side with no explicit constructor.
1564 The latter two forms cover all the non-default constructors of the type.
1565 See the GNAT users guide for details.
1567 If no constructors are imported, it is impossible to create any objects
1568 on the Ada side and the type is implicitly declared abstract.
1570 Pragma @code{CPP_Constructor} is intended primarily for automatic generation
1571 using an automatic binding generator tool.
1572 See @ref{Interfacing to C++} for more related information.
1574 Note: The use of functions returning class-wide types for constructors is
1575 currently obsolete. They are supported for backward compatibility. The
1576 use of functions returning the type T leave the Ada sources more clear
1577 because the imported C++ constructors always return an object of type T;
1578 that is, they never return an object whose type is a descendant of type T.
1580 @node Pragma CPP_Virtual
1581 @unnumberedsec Pragma CPP_Virtual
1582 @cindex Interfacing to C++
1585 This pragma is now obsolete has has no effect because GNAT generates
1586 the same object layout than the G++ compiler.
1588 See @ref{Interfacing to C++} for related information.
1590 @node Pragma CPP_Vtable
1591 @unnumberedsec Pragma CPP_Vtable
1592 @cindex Interfacing with C++
1595 This pragma is now obsolete has has no effect because GNAT generates
1596 the same object layout than the G++ compiler.
1598 See @ref{Interfacing to C++} for related information.
1601 @unnumberedsec Pragma Debug
1606 @smallexample @c ada
1607 pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON);
1609 PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
1611 | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
1615 The procedure call argument has the syntactic form of an expression, meeting
1616 the syntactic requirements for pragmas.
1618 If debug pragmas are not enabled or if the condition is present and evaluates
1619 to False, this pragma has no effect. If debug pragmas are enabled, the
1620 semantics of the pragma is exactly equivalent to the procedure call statement
1621 corresponding to the argument with a terminating semicolon. Pragmas are
1622 permitted in sequences of declarations, so you can use pragma @code{Debug} to
1623 intersperse calls to debug procedures in the middle of declarations. Debug
1624 pragmas can be enabled either by use of the command line switch @option{-gnata}
1625 or by use of the configuration pragma @code{Debug_Policy}.
1627 @node Pragma Debug_Policy
1628 @unnumberedsec Pragma Debug_Policy
1629 @findex Debug_Policy
1633 @smallexample @c ada
1634 pragma Debug_Policy (CHECK | IGNORE);
1638 If the argument is @code{CHECK}, then pragma @code{DEBUG} is enabled.
1639 If the argument is @code{IGNORE}, then pragma @code{DEBUG} is ignored.
1640 This pragma overrides the effect of the @option{-gnata} switch on the
1643 @node Pragma Detect_Blocking
1644 @unnumberedsec Pragma Detect_Blocking
1645 @findex Detect_Blocking
1649 @smallexample @c ada
1650 pragma Detect_Blocking;
1654 This is a configuration pragma that forces the detection of potentially
1655 blocking operations within a protected operation, and to raise Program_Error
1658 @node Pragma Elaboration_Checks
1659 @unnumberedsec Pragma Elaboration_Checks
1660 @cindex Elaboration control
1661 @findex Elaboration_Checks
1665 @smallexample @c ada
1666 pragma Elaboration_Checks (Dynamic | Static);
1670 This is a configuration pragma that provides control over the
1671 elaboration model used by the compilation affected by the
1672 pragma. If the parameter is @code{Dynamic},
1673 then the dynamic elaboration
1674 model described in the Ada Reference Manual is used, as though
1675 the @option{-gnatE} switch had been specified on the command
1676 line. If the parameter is @code{Static}, then the default GNAT static
1677 model is used. This configuration pragma overrides the setting
1678 of the command line. For full details on the elaboration models
1679 used by the GNAT compiler, see @ref{Elaboration Order Handling in GNAT,,,
1680 gnat_ugn, @value{EDITION} User's Guide}.
1682 @node Pragma Eliminate
1683 @unnumberedsec Pragma Eliminate
1684 @cindex Elimination of unused subprograms
1689 @smallexample @c ada
1691 [Unit_Name =>] IDENTIFIER |
1692 SELECTED_COMPONENT);
1695 [Unit_Name =>] IDENTIFIER |
1697 [Entity =>] IDENTIFIER |
1698 SELECTED_COMPONENT |
1700 [,OVERLOADING_RESOLUTION]);
1702 OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
1705 PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
1708 PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES
1710 FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
1711 Result_Type => result_SUBTYPE_NAME]
1713 PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
1714 SUBTYPE_NAME ::= STRING_VALUE
1716 SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
1717 SOURCE_TRACE ::= STRING_VALUE
1719 STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
1723 This pragma indicates that the given entity is not used outside the
1724 compilation unit it is defined in. The entity must be an explicitly declared
1725 subprogram; this includes generic subprogram instances and
1726 subprograms declared in generic package instances.
1728 If the entity to be eliminated is a library level subprogram, then
1729 the first form of pragma @code{Eliminate} is used with only a single argument.
1730 In this form, the @code{Unit_Name} argument specifies the name of the
1731 library level unit to be eliminated.
1733 In all other cases, both @code{Unit_Name} and @code{Entity} arguments
1734 are required. If item is an entity of a library package, then the first
1735 argument specifies the unit name, and the second argument specifies
1736 the particular entity. If the second argument is in string form, it must
1737 correspond to the internal manner in which GNAT stores entity names (see
1738 compilation unit Namet in the compiler sources for details).
1740 The remaining parameters (OVERLOADING_RESOLUTION) are optionally used
1741 to distinguish between overloaded subprograms. If a pragma does not contain
1742 the OVERLOADING_RESOLUTION parameter(s), it is applied to all the overloaded
1743 subprograms denoted by the first two parameters.
1745 Use PARAMETER_AND_RESULT_TYPE_PROFILE to specify the profile of the subprogram
1746 to be eliminated in a manner similar to that used for the extended
1747 @code{Import} and @code{Export} pragmas, except that the subtype names are
1748 always given as strings. At the moment, this form of distinguishing
1749 overloaded subprograms is implemented only partially, so we do not recommend
1750 using it for practical subprogram elimination.
1752 Note that in case of a parameterless procedure its profile is represented
1753 as @code{Parameter_Types => ("")}
1755 Alternatively, the @code{Source_Location} parameter is used to specify
1756 which overloaded alternative is to be eliminated by pointing to the
1757 location of the DEFINING_PROGRAM_UNIT_NAME of this subprogram in the
1758 source text. The string literal (or concatenation of string literals)
1759 given as SOURCE_TRACE must have the following format:
1761 @smallexample @c ada
1762 SOURCE_TRACE ::= SOURCE_LOCATION@{LBRACKET SOURCE_LOCATION RBRACKET@}
1767 SOURCE_LOCATION ::= FILE_NAME:LINE_NUMBER
1768 FILE_NAME ::= STRING_LITERAL
1769 LINE_NUMBER ::= DIGIT @{DIGIT@}
1772 SOURCE_TRACE should be the short name of the source file (with no directory
1773 information), and LINE_NUMBER is supposed to point to the line where the
1774 defining name of the subprogram is located.
1776 For the subprograms that are not a part of generic instantiations, only one
1777 SOURCE_LOCATION is used. If a subprogram is declared in a package
1778 instantiation, SOURCE_TRACE contains two SOURCE_LOCATIONs, the first one is
1779 the location of the (DEFINING_PROGRAM_UNIT_NAME of the) instantiation, and the
1780 second one denotes the declaration of the corresponding subprogram in the
1781 generic package. This approach is recursively used to create SOURCE_LOCATIONs
1782 in case of nested instantiations.
1784 The effect of the pragma is to allow the compiler to eliminate
1785 the code or data associated with the named entity. Any reference to
1786 an eliminated entity outside the compilation unit it is defined in,
1787 causes a compile time or link time error.
1789 The intention of pragma @code{Eliminate} is to allow a program to be compiled
1790 in a system independent manner, with unused entities eliminated, without
1791 the requirement of modifying the source text. Normally the required set
1792 of @code{Eliminate} pragmas is constructed automatically using the gnatelim
1793 tool. Elimination of unused entities local to a compilation unit is
1794 automatic, without requiring the use of pragma @code{Eliminate}.
1796 Note that the reason this pragma takes string literals where names might
1797 be expected is that a pragma @code{Eliminate} can appear in a context where the
1798 relevant names are not visible.
1800 Note that any change in the source files that includes removing, splitting of
1801 adding lines may make the set of Eliminate pragmas using SOURCE_LOCATION
1804 It is legal to use pragma Eliminate where the referenced entity is a
1805 dispatching operation, but it is not clear what this would mean, since
1806 in general the call does not know which entity is actually being called.
1807 Consequently, a pragma Eliminate for a dispatching operation is ignored.
1809 @node Pragma Export_Exception
1810 @unnumberedsec Pragma Export_Exception
1812 @findex Export_Exception
1816 @smallexample @c ada
1817 pragma Export_Exception (
1818 [Internal =>] LOCAL_NAME
1819 [, [External =>] EXTERNAL_SYMBOL]
1820 [, [Form =>] Ada | VMS]
1821 [, [Code =>] static_integer_EXPRESSION]);
1825 | static_string_EXPRESSION
1829 This pragma is implemented only in the OpenVMS implementation of GNAT@. It
1830 causes the specified exception to be propagated outside of the Ada program,
1831 so that it can be handled by programs written in other OpenVMS languages.
1832 This pragma establishes an external name for an Ada exception and makes the
1833 name available to the OpenVMS Linker as a global symbol. For further details
1834 on this pragma, see the
1835 DEC Ada Language Reference Manual, section 13.9a3.2.
1837 @node Pragma Export_Function
1838 @unnumberedsec Pragma Export_Function
1839 @cindex Argument passing mechanisms
1840 @findex Export_Function
1845 @smallexample @c ada
1846 pragma Export_Function (
1847 [Internal =>] LOCAL_NAME
1848 [, [External =>] EXTERNAL_SYMBOL]
1849 [, [Parameter_Types =>] PARAMETER_TYPES]
1850 [, [Result_Type =>] result_SUBTYPE_MARK]
1851 [, [Mechanism =>] MECHANISM]
1852 [, [Result_Mechanism =>] MECHANISM_NAME]);
1856 | static_string_EXPRESSION
1861 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1865 | subtype_Name ' Access
1869 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1871 MECHANISM_ASSOCIATION ::=
1872 [formal_parameter_NAME =>] MECHANISM_NAME
1877 | Descriptor [([Class =>] CLASS_NAME)]
1878 | Short_Descriptor [([Class =>] CLASS_NAME)]
1880 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1884 Use this pragma to make a function externally callable and optionally
1885 provide information on mechanisms to be used for passing parameter and
1886 result values. We recommend, for the purposes of improving portability,
1887 this pragma always be used in conjunction with a separate pragma
1888 @code{Export}, which must precede the pragma @code{Export_Function}.
1889 GNAT does not require a separate pragma @code{Export}, but if none is
1890 present, @code{Convention Ada} is assumed, which is usually
1891 not what is wanted, so it is usually appropriate to use this
1892 pragma in conjunction with a @code{Export} or @code{Convention}
1893 pragma that specifies the desired foreign convention.
1894 Pragma @code{Export_Function}
1895 (and @code{Export}, if present) must appear in the same declarative
1896 region as the function to which they apply.
1898 @var{internal_name} must uniquely designate the function to which the
1899 pragma applies. If more than one function name exists of this name in
1900 the declarative part you must use the @code{Parameter_Types} and
1901 @code{Result_Type} parameters is mandatory to achieve the required
1902 unique designation. @var{subtype_mark}s in these parameters must
1903 exactly match the subtypes in the corresponding function specification,
1904 using positional notation to match parameters with subtype marks.
1905 The form with an @code{'Access} attribute can be used to match an
1906 anonymous access parameter.
1909 @cindex Passing by descriptor
1910 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
1911 The default behavior for Export_Function is to accept either 64bit or
1912 32bit descriptors unless short_descriptor is specified, then only 32bit
1913 descriptors are accepted.
1915 @cindex Suppressing external name
1916 Special treatment is given if the EXTERNAL is an explicit null
1917 string or a static string expressions that evaluates to the null
1918 string. In this case, no external name is generated. This form
1919 still allows the specification of parameter mechanisms.
1921 @node Pragma Export_Object
1922 @unnumberedsec Pragma Export_Object
1923 @findex Export_Object
1927 @smallexample @c ada
1928 pragma Export_Object
1929 [Internal =>] LOCAL_NAME
1930 [, [External =>] EXTERNAL_SYMBOL]
1931 [, [Size =>] EXTERNAL_SYMBOL]
1935 | static_string_EXPRESSION
1939 This pragma designates an object as exported, and apart from the
1940 extended rules for external symbols, is identical in effect to the use of
1941 the normal @code{Export} pragma applied to an object. You may use a
1942 separate Export pragma (and you probably should from the point of view
1943 of portability), but it is not required. @var{Size} is syntax checked,
1944 but otherwise ignored by GNAT@.
1946 @node Pragma Export_Procedure
1947 @unnumberedsec Pragma Export_Procedure
1948 @findex Export_Procedure
1952 @smallexample @c ada
1953 pragma Export_Procedure (
1954 [Internal =>] LOCAL_NAME
1955 [, [External =>] EXTERNAL_SYMBOL]
1956 [, [Parameter_Types =>] PARAMETER_TYPES]
1957 [, [Mechanism =>] MECHANISM]);
1961 | static_string_EXPRESSION
1966 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1970 | subtype_Name ' Access
1974 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1976 MECHANISM_ASSOCIATION ::=
1977 [formal_parameter_NAME =>] MECHANISM_NAME
1982 | Descriptor [([Class =>] CLASS_NAME)]
1983 | Short_Descriptor [([Class =>] CLASS_NAME)]
1985 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1989 This pragma is identical to @code{Export_Function} except that it
1990 applies to a procedure rather than a function and the parameters
1991 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
1992 GNAT does not require a separate pragma @code{Export}, but if none is
1993 present, @code{Convention Ada} is assumed, which is usually
1994 not what is wanted, so it is usually appropriate to use this
1995 pragma in conjunction with a @code{Export} or @code{Convention}
1996 pragma that specifies the desired foreign convention.
1999 @cindex Passing by descriptor
2000 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2001 The default behavior for Export_Procedure is to accept either 64bit or
2002 32bit descriptors unless short_descriptor is specified, then only 32bit
2003 descriptors are accepted.
2005 @cindex Suppressing external name
2006 Special treatment is given if the EXTERNAL is an explicit null
2007 string or a static string expressions that evaluates to the null
2008 string. In this case, no external name is generated. This form
2009 still allows the specification of parameter mechanisms.
2011 @node Pragma Export_Value
2012 @unnumberedsec Pragma Export_Value
2013 @findex Export_Value
2017 @smallexample @c ada
2018 pragma Export_Value (
2019 [Value =>] static_integer_EXPRESSION,
2020 [Link_Name =>] static_string_EXPRESSION);
2024 This pragma serves to export a static integer value for external use.
2025 The first argument specifies the value to be exported. The Link_Name
2026 argument specifies the symbolic name to be associated with the integer
2027 value. This pragma is useful for defining a named static value in Ada
2028 that can be referenced in assembly language units to be linked with
2029 the application. This pragma is currently supported only for the
2030 AAMP target and is ignored for other targets.
2032 @node Pragma Export_Valued_Procedure
2033 @unnumberedsec Pragma Export_Valued_Procedure
2034 @findex Export_Valued_Procedure
2038 @smallexample @c ada
2039 pragma Export_Valued_Procedure (
2040 [Internal =>] LOCAL_NAME
2041 [, [External =>] EXTERNAL_SYMBOL]
2042 [, [Parameter_Types =>] PARAMETER_TYPES]
2043 [, [Mechanism =>] MECHANISM]);
2047 | static_string_EXPRESSION
2052 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2056 | subtype_Name ' Access
2060 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2062 MECHANISM_ASSOCIATION ::=
2063 [formal_parameter_NAME =>] MECHANISM_NAME
2068 | Descriptor [([Class =>] CLASS_NAME)]
2069 | Short_Descriptor [([Class =>] CLASS_NAME)]
2071 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
2075 This pragma is identical to @code{Export_Procedure} except that the
2076 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2077 mode @code{OUT}, and externally the subprogram is treated as a function
2078 with this parameter as the result of the function. GNAT provides for
2079 this capability to allow the use of @code{OUT} and @code{IN OUT}
2080 parameters in interfacing to external functions (which are not permitted
2082 GNAT does not require a separate pragma @code{Export}, but if none is
2083 present, @code{Convention Ada} is assumed, which is almost certainly
2084 not what is wanted since the whole point of this pragma is to interface
2085 with foreign language functions, so it is usually appropriate to use this
2086 pragma in conjunction with a @code{Export} or @code{Convention}
2087 pragma that specifies the desired foreign convention.
2090 @cindex Passing by descriptor
2091 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2092 The default behavior for Export_Valued_Procedure is to accept either 64bit or
2093 32bit descriptors unless short_descriptor is specified, then only 32bit
2094 descriptors are accepted.
2096 @cindex Suppressing external name
2097 Special treatment is given if the EXTERNAL is an explicit null
2098 string or a static string expressions that evaluates to the null
2099 string. In this case, no external name is generated. This form
2100 still allows the specification of parameter mechanisms.
2102 @node Pragma Extend_System
2103 @unnumberedsec Pragma Extend_System
2104 @cindex @code{system}, extending
2106 @findex Extend_System
2110 @smallexample @c ada
2111 pragma Extend_System ([Name =>] IDENTIFIER);
2115 This pragma is used to provide backwards compatibility with other
2116 implementations that extend the facilities of package @code{System}. In
2117 GNAT, @code{System} contains only the definitions that are present in
2118 the Ada RM@. However, other implementations, notably the DEC Ada 83
2119 implementation, provide many extensions to package @code{System}.
2121 For each such implementation accommodated by this pragma, GNAT provides a
2122 package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
2123 implementation, which provides the required additional definitions. You
2124 can use this package in two ways. You can @code{with} it in the normal
2125 way and access entities either by selection or using a @code{use}
2126 clause. In this case no special processing is required.
2128 However, if existing code contains references such as
2129 @code{System.@var{xxx}} where @var{xxx} is an entity in the extended
2130 definitions provided in package @code{System}, you may use this pragma
2131 to extend visibility in @code{System} in a non-standard way that
2132 provides greater compatibility with the existing code. Pragma
2133 @code{Extend_System} is a configuration pragma whose single argument is
2134 the name of the package containing the extended definition
2135 (e.g.@: @code{Aux_DEC} for the DEC Ada case). A unit compiled under
2136 control of this pragma will be processed using special visibility
2137 processing that looks in package @code{System.Aux_@var{xxx}} where
2138 @code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
2139 package @code{System}, but not found in package @code{System}.
2141 You can use this pragma either to access a predefined @code{System}
2142 extension supplied with the compiler, for example @code{Aux_DEC} or
2143 you can construct your own extension unit following the above
2144 definition. Note that such a package is a child of @code{System}
2145 and thus is considered part of the implementation. To compile
2146 it you will have to use the appropriate switch for compiling
2147 system units. @xref{Top, @value{EDITION} User's Guide, About This
2148 Guide,, gnat_ugn, @value{EDITION} User's Guide}, for details.
2150 @node Pragma External
2151 @unnumberedsec Pragma External
2156 @smallexample @c ada
2158 [ Convention =>] convention_IDENTIFIER,
2159 [ Entity =>] LOCAL_NAME
2160 [, [External_Name =>] static_string_EXPRESSION ]
2161 [, [Link_Name =>] static_string_EXPRESSION ]);
2165 This pragma is identical in syntax and semantics to pragma
2166 @code{Export} as defined in the Ada Reference Manual. It is
2167 provided for compatibility with some Ada 83 compilers that
2168 used this pragma for exactly the same purposes as pragma
2169 @code{Export} before the latter was standardized.
2171 @node Pragma External_Name_Casing
2172 @unnumberedsec Pragma External_Name_Casing
2173 @cindex Dec Ada 83 casing compatibility
2174 @cindex External Names, casing
2175 @cindex Casing of External names
2176 @findex External_Name_Casing
2180 @smallexample @c ada
2181 pragma External_Name_Casing (
2182 Uppercase | Lowercase
2183 [, Uppercase | Lowercase | As_Is]);
2187 This pragma provides control over the casing of external names associated
2188 with Import and Export pragmas. There are two cases to consider:
2191 @item Implicit external names
2192 Implicit external names are derived from identifiers. The most common case
2193 arises when a standard Ada Import or Export pragma is used with only two
2196 @smallexample @c ada
2197 pragma Import (C, C_Routine);
2201 Since Ada is a case-insensitive language, the spelling of the identifier in
2202 the Ada source program does not provide any information on the desired
2203 casing of the external name, and so a convention is needed. In GNAT the
2204 default treatment is that such names are converted to all lower case
2205 letters. This corresponds to the normal C style in many environments.
2206 The first argument of pragma @code{External_Name_Casing} can be used to
2207 control this treatment. If @code{Uppercase} is specified, then the name
2208 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2209 then the normal default of all lower case letters will be used.
2211 This same implicit treatment is also used in the case of extended DEC Ada 83
2212 compatible Import and Export pragmas where an external name is explicitly
2213 specified using an identifier rather than a string.
2215 @item Explicit external names
2216 Explicit external names are given as string literals. The most common case
2217 arises when a standard Ada Import or Export pragma is used with three
2220 @smallexample @c ada
2221 pragma Import (C, C_Routine, "C_routine");
2225 In this case, the string literal normally provides the exact casing required
2226 for the external name. The second argument of pragma
2227 @code{External_Name_Casing} may be used to modify this behavior.
2228 If @code{Uppercase} is specified, then the name
2229 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2230 then the name will be forced to all lowercase letters. A specification of
2231 @code{As_Is} provides the normal default behavior in which the casing is
2232 taken from the string provided.
2236 This pragma may appear anywhere that a pragma is valid. In particular, it
2237 can be used as a configuration pragma in the @file{gnat.adc} file, in which
2238 case it applies to all subsequent compilations, or it can be used as a program
2239 unit pragma, in which case it only applies to the current unit, or it can
2240 be used more locally to control individual Import/Export pragmas.
2242 It is primarily intended for use with OpenVMS systems, where many
2243 compilers convert all symbols to upper case by default. For interfacing to
2244 such compilers (e.g.@: the DEC C compiler), it may be convenient to use
2247 @smallexample @c ada
2248 pragma External_Name_Casing (Uppercase, Uppercase);
2252 to enforce the upper casing of all external symbols.
2254 @node Pragma Fast_Math
2255 @unnumberedsec Pragma Fast_Math
2260 @smallexample @c ada
2265 This is a configuration pragma which activates a mode in which speed is
2266 considered more important for floating-point operations than absolutely
2267 accurate adherence to the requirements of the standard. Currently the
2268 following operations are affected:
2271 @item Complex Multiplication
2272 The normal simple formula for complex multiplication can result in intermediate
2273 overflows for numbers near the end of the range. The Ada standard requires that
2274 this situation be detected and corrected by scaling, but in Fast_Math mode such
2275 cases will simply result in overflow. Note that to take advantage of this you
2276 must instantiate your own version of @code{Ada.Numerics.Generic_Complex_Types}
2277 under control of the pragma, rather than use the preinstantiated versions.
2280 @node Pragma Favor_Top_Level
2281 @unnumberedsec Pragma Favor_Top_Level
2282 @findex Favor_Top_Level
2286 @smallexample @c ada
2287 pragma Favor_Top_Level (type_NAME);
2291 The named type must be an access-to-subprogram type. This pragma is an
2292 efficiency hint to the compiler, regarding the use of 'Access or
2293 'Unrestricted_Access on nested (non-library-level) subprograms. The
2294 pragma means that nested subprograms are not used with this type, or
2295 are rare, so that the generated code should be efficient in the
2296 top-level case. When this pragma is used, dynamically generated
2297 trampolines may be used on some targets for nested subprograms.
2298 See also the No_Implicit_Dynamic_Code restriction.
2300 @node Pragma Finalize_Storage_Only
2301 @unnumberedsec Pragma Finalize_Storage_Only
2302 @findex Finalize_Storage_Only
2306 @smallexample @c ada
2307 pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
2311 This pragma allows the compiler not to emit a Finalize call for objects
2312 defined at the library level. This is mostly useful for types where
2313 finalization is only used to deal with storage reclamation since in most
2314 environments it is not necessary to reclaim memory just before terminating
2315 execution, hence the name.
2317 @node Pragma Float_Representation
2318 @unnumberedsec Pragma Float_Representation
2320 @findex Float_Representation
2324 @smallexample @c ada
2325 pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]);
2327 FLOAT_REP ::= VAX_Float | IEEE_Float
2331 In the one argument form, this pragma is a configuration pragma which
2332 allows control over the internal representation chosen for the predefined
2333 floating point types declared in the packages @code{Standard} and
2334 @code{System}. On all systems other than OpenVMS, the argument must
2335 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2336 argument may be @code{VAX_Float} to specify the use of the VAX float
2337 format for the floating-point types in Standard. This requires that
2338 the standard runtime libraries be recompiled. @xref{The GNAT Run-Time
2339 Library Builder gnatlbr,,, gnat_ugn, @value{EDITION} User's Guide
2340 OpenVMS}, for a description of the @code{GNAT LIBRARY} command.
2342 The two argument form specifies the representation to be used for
2343 the specified floating-point type. On all systems other than OpenVMS,
2345 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2346 argument may be @code{VAX_Float} to specify the use of the VAX float
2351 For digits values up to 6, F float format will be used.
2353 For digits values from 7 to 9, G float format will be used.
2355 For digits values from 10 to 15, F float format will be used.
2357 Digits values above 15 are not allowed.
2361 @unnumberedsec Pragma Ident
2366 @smallexample @c ada
2367 pragma Ident (static_string_EXPRESSION);
2371 This pragma provides a string identification in the generated object file,
2372 if the system supports the concept of this kind of identification string.
2373 This pragma is allowed only in the outermost declarative part or
2374 declarative items of a compilation unit. If more than one @code{Ident}
2375 pragma is given, only the last one processed is effective.
2377 On OpenVMS systems, the effect of the pragma is identical to the effect of
2378 the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
2379 maximum allowed length is 31 characters, so if it is important to
2380 maintain compatibility with this compiler, you should obey this length
2383 @node Pragma Implemented_By_Entry
2384 @unnumberedsec Pragma Implemented_By_Entry
2385 @findex Implemented_By_Entry
2389 @smallexample @c ada
2390 pragma Implemented_By_Entry (LOCAL_NAME);
2394 This is a representation pragma which applies to protected, synchronized and
2395 task interface primitives. If the pragma is applied to primitive operation Op
2396 of interface Iface, it is illegal to override Op in a type that implements
2397 Iface, with anything other than an entry.
2399 @smallexample @c ada
2400 type Iface is protected interface;
2401 procedure Do_Something (Object : in out Iface) is abstract;
2402 pragma Implemented_By_Entry (Do_Something);
2404 protected type P is new Iface with
2405 procedure Do_Something; -- Illegal
2408 task type T is new Iface with
2409 entry Do_Something; -- Legal
2414 NOTE: The pragma is still in its design stage by the Ada Rapporteur Group. It
2415 is intended to be used in conjunction with dispatching requeue statements as
2416 described in AI05-0030. Should the ARG decide on an official name and syntax,
2417 this pragma will become language-defined rather than GNAT-specific.
2419 @node Pragma Implicit_Packing
2420 @unnumberedsec Pragma Implicit_Packing
2421 @findex Implicit_Packing
2425 @smallexample @c ada
2426 pragma Implicit_Packing;
2430 This is a configuration pragma that requests implicit packing for packed
2431 arrays for which a size clause is given but no explicit pragma Pack or
2432 specification of Component_Size is present. It also applies to records
2433 where no record representation clause is present. Consider this example:
2435 @smallexample @c ada
2436 type R is array (0 .. 7) of Boolean;
2441 In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause
2442 does not change the layout of a composite object. So the Size clause in the
2443 above example is normally rejected, since the default layout of the array uses
2444 8-bit components, and thus the array requires a minimum of 64 bits.
2446 If this declaration is compiled in a region of code covered by an occurrence
2447 of the configuration pragma Implicit_Packing, then the Size clause in this
2448 and similar examples will cause implicit packing and thus be accepted. For
2449 this implicit packing to occur, the type in question must be an array of small
2450 components whose size is known at compile time, and the Size clause must
2451 specify the exact size that corresponds to the length of the array multiplied
2452 by the size in bits of the component type.
2453 @cindex Array packing
2455 Similarly, the following example shows the use in the record case
2457 @smallexample @c ada
2459 a, b, c, d, e, f, g, h : boolean;
2466 Without a pragma Pack, each Boolean field requires 8 bits, so the
2467 minimum size is 72 bits, but with a pragma Pack, 16 bits would be
2468 sufficient. The use of pragma Implciit_Packing allows this record
2469 declaration to compile without an explicit pragma Pack.
2470 @node Pragma Import_Exception
2471 @unnumberedsec Pragma Import_Exception
2473 @findex Import_Exception
2477 @smallexample @c ada
2478 pragma Import_Exception (
2479 [Internal =>] LOCAL_NAME
2480 [, [External =>] EXTERNAL_SYMBOL]
2481 [, [Form =>] Ada | VMS]
2482 [, [Code =>] static_integer_EXPRESSION]);
2486 | static_string_EXPRESSION
2490 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2491 It allows OpenVMS conditions (for example, from OpenVMS system services or
2492 other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
2493 The pragma specifies that the exception associated with an exception
2494 declaration in an Ada program be defined externally (in non-Ada code).
2495 For further details on this pragma, see the
2496 DEC Ada Language Reference Manual, section 13.9a.3.1.
2498 @node Pragma Import_Function
2499 @unnumberedsec Pragma Import_Function
2500 @findex Import_Function
2504 @smallexample @c ada
2505 pragma Import_Function (
2506 [Internal =>] LOCAL_NAME,
2507 [, [External =>] EXTERNAL_SYMBOL]
2508 [, [Parameter_Types =>] PARAMETER_TYPES]
2509 [, [Result_Type =>] SUBTYPE_MARK]
2510 [, [Mechanism =>] MECHANISM]
2511 [, [Result_Mechanism =>] MECHANISM_NAME]
2512 [, [First_Optional_Parameter =>] IDENTIFIER]);
2516 | static_string_EXPRESSION
2520 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2524 | subtype_Name ' Access
2528 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2530 MECHANISM_ASSOCIATION ::=
2531 [formal_parameter_NAME =>] MECHANISM_NAME
2536 | Descriptor [([Class =>] CLASS_NAME)]
2537 | Short_Descriptor [([Class =>] CLASS_NAME)]
2539 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2543 This pragma is used in conjunction with a pragma @code{Import} to
2544 specify additional information for an imported function. The pragma
2545 @code{Import} (or equivalent pragma @code{Interface}) must precede the
2546 @code{Import_Function} pragma and both must appear in the same
2547 declarative part as the function specification.
2549 The @var{Internal} argument must uniquely designate
2550 the function to which the
2551 pragma applies. If more than one function name exists of this name in
2552 the declarative part you must use the @code{Parameter_Types} and
2553 @var{Result_Type} parameters to achieve the required unique
2554 designation. Subtype marks in these parameters must exactly match the
2555 subtypes in the corresponding function specification, using positional
2556 notation to match parameters with subtype marks.
2557 The form with an @code{'Access} attribute can be used to match an
2558 anonymous access parameter.
2560 You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
2561 parameters to specify passing mechanisms for the
2562 parameters and result. If you specify a single mechanism name, it
2563 applies to all parameters. Otherwise you may specify a mechanism on a
2564 parameter by parameter basis using either positional or named
2565 notation. If the mechanism is not specified, the default mechanism
2569 @cindex Passing by descriptor
2570 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2571 The default behavior for Import_Function is to pass a 64bit descriptor
2572 unless short_descriptor is specified, then a 32bit descriptor is passed.
2574 @code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
2575 It specifies that the designated parameter and all following parameters
2576 are optional, meaning that they are not passed at the generated code
2577 level (this is distinct from the notion of optional parameters in Ada
2578 where the parameters are passed anyway with the designated optional
2579 parameters). All optional parameters must be of mode @code{IN} and have
2580 default parameter values that are either known at compile time
2581 expressions, or uses of the @code{'Null_Parameter} attribute.
2583 @node Pragma Import_Object
2584 @unnumberedsec Pragma Import_Object
2585 @findex Import_Object
2589 @smallexample @c ada
2590 pragma Import_Object
2591 [Internal =>] LOCAL_NAME
2592 [, [External =>] EXTERNAL_SYMBOL]
2593 [, [Size =>] EXTERNAL_SYMBOL]);
2597 | static_string_EXPRESSION
2601 This pragma designates an object as imported, and apart from the
2602 extended rules for external symbols, is identical in effect to the use of
2603 the normal @code{Import} pragma applied to an object. Unlike the
2604 subprogram case, you need not use a separate @code{Import} pragma,
2605 although you may do so (and probably should do so from a portability
2606 point of view). @var{size} is syntax checked, but otherwise ignored by
2609 @node Pragma Import_Procedure
2610 @unnumberedsec Pragma Import_Procedure
2611 @findex Import_Procedure
2615 @smallexample @c ada
2616 pragma Import_Procedure (
2617 [Internal =>] LOCAL_NAME
2618 [, [External =>] EXTERNAL_SYMBOL]
2619 [, [Parameter_Types =>] PARAMETER_TYPES]
2620 [, [Mechanism =>] MECHANISM]
2621 [, [First_Optional_Parameter =>] IDENTIFIER]);
2625 | static_string_EXPRESSION
2629 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2633 | subtype_Name ' Access
2637 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2639 MECHANISM_ASSOCIATION ::=
2640 [formal_parameter_NAME =>] MECHANISM_NAME
2645 | Descriptor [([Class =>] CLASS_NAME)]
2646 | Short_Descriptor [([Class =>] CLASS_NAME)]
2648 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2652 This pragma is identical to @code{Import_Function} except that it
2653 applies to a procedure rather than a function and the parameters
2654 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2656 @node Pragma Import_Valued_Procedure
2657 @unnumberedsec Pragma Import_Valued_Procedure
2658 @findex Import_Valued_Procedure
2662 @smallexample @c ada
2663 pragma Import_Valued_Procedure (
2664 [Internal =>] LOCAL_NAME
2665 [, [External =>] EXTERNAL_SYMBOL]
2666 [, [Parameter_Types =>] PARAMETER_TYPES]
2667 [, [Mechanism =>] MECHANISM]
2668 [, [First_Optional_Parameter =>] IDENTIFIER]);
2672 | static_string_EXPRESSION
2676 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2680 | subtype_Name ' Access
2684 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2686 MECHANISM_ASSOCIATION ::=
2687 [formal_parameter_NAME =>] MECHANISM_NAME
2692 | Descriptor [([Class =>] CLASS_NAME)]
2693 | Short_Descriptor [([Class =>] CLASS_NAME)]
2695 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2699 This pragma is identical to @code{Import_Procedure} except that the
2700 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2701 mode @code{OUT}, and externally the subprogram is treated as a function
2702 with this parameter as the result of the function. The purpose of this
2703 capability is to allow the use of @code{OUT} and @code{IN OUT}
2704 parameters in interfacing to external functions (which are not permitted
2705 in Ada functions). You may optionally use the @code{Mechanism}
2706 parameters to specify passing mechanisms for the parameters.
2707 If you specify a single mechanism name, it applies to all parameters.
2708 Otherwise you may specify a mechanism on a parameter by parameter
2709 basis using either positional or named notation. If the mechanism is not
2710 specified, the default mechanism is used.
2712 Note that it is important to use this pragma in conjunction with a separate
2713 pragma Import that specifies the desired convention, since otherwise the
2714 default convention is Ada, which is almost certainly not what is required.
2716 @node Pragma Initialize_Scalars
2717 @unnumberedsec Pragma Initialize_Scalars
2718 @findex Initialize_Scalars
2719 @cindex debugging with Initialize_Scalars
2723 @smallexample @c ada
2724 pragma Initialize_Scalars;
2728 This pragma is similar to @code{Normalize_Scalars} conceptually but has
2729 two important differences. First, there is no requirement for the pragma
2730 to be used uniformly in all units of a partition, in particular, it is fine
2731 to use this just for some or all of the application units of a partition,
2732 without needing to recompile the run-time library.
2734 In the case where some units are compiled with the pragma, and some without,
2735 then a declaration of a variable where the type is defined in package
2736 Standard or is locally declared will always be subject to initialization,
2737 as will any declaration of a scalar variable. For composite variables,
2738 whether the variable is initialized may also depend on whether the package
2739 in which the type of the variable is declared is compiled with the pragma.
2741 The other important difference is that you can control the value used
2742 for initializing scalar objects. At bind time, you can select several
2743 options for initialization. You can
2744 initialize with invalid values (similar to Normalize_Scalars, though for
2745 Initialize_Scalars it is not always possible to determine the invalid
2746 values in complex cases like signed component fields with non-standard
2747 sizes). You can also initialize with high or
2748 low values, or with a specified bit pattern. See the users guide for binder
2749 options for specifying these cases.
2751 This means that you can compile a program, and then without having to
2752 recompile the program, you can run it with different values being used
2753 for initializing otherwise uninitialized values, to test if your program
2754 behavior depends on the choice. Of course the behavior should not change,
2755 and if it does, then most likely you have an erroneous reference to an
2756 uninitialized value.
2758 It is even possible to change the value at execution time eliminating even
2759 the need to rebind with a different switch using an environment variable.
2760 See the GNAT users guide for details.
2762 Note that pragma @code{Initialize_Scalars} is particularly useful in
2763 conjunction with the enhanced validity checking that is now provided
2764 in GNAT, which checks for invalid values under more conditions.
2765 Using this feature (see description of the @option{-gnatV} flag in the
2766 users guide) in conjunction with pragma @code{Initialize_Scalars}
2767 provides a powerful new tool to assist in the detection of problems
2768 caused by uninitialized variables.
2770 Note: the use of @code{Initialize_Scalars} has a fairly extensive
2771 effect on the generated code. This may cause your code to be
2772 substantially larger. It may also cause an increase in the amount
2773 of stack required, so it is probably a good idea to turn on stack
2774 checking (see description of stack checking in the GNAT users guide)
2775 when using this pragma.
2777 @node Pragma Inline_Always
2778 @unnumberedsec Pragma Inline_Always
2779 @findex Inline_Always
2783 @smallexample @c ada
2784 pragma Inline_Always (NAME [, NAME]);
2788 Similar to pragma @code{Inline} except that inlining is not subject to
2789 the use of option @option{-gnatn} and the inlining happens regardless of
2790 whether this option is used.
2792 @node Pragma Inline_Generic
2793 @unnumberedsec Pragma Inline_Generic
2794 @findex Inline_Generic
2798 @smallexample @c ada
2799 pragma Inline_Generic (generic_package_NAME);
2803 This is implemented for compatibility with DEC Ada 83 and is recognized,
2804 but otherwise ignored, by GNAT@. All generic instantiations are inlined
2805 by default when using GNAT@.
2807 @node Pragma Interface
2808 @unnumberedsec Pragma Interface
2813 @smallexample @c ada
2815 [Convention =>] convention_identifier,
2816 [Entity =>] local_NAME
2817 [, [External_Name =>] static_string_expression]
2818 [, [Link_Name =>] static_string_expression]);
2822 This pragma is identical in syntax and semantics to
2823 the standard Ada pragma @code{Import}. It is provided for compatibility
2824 with Ada 83. The definition is upwards compatible both with pragma
2825 @code{Interface} as defined in the Ada 83 Reference Manual, and also
2826 with some extended implementations of this pragma in certain Ada 83
2829 @node Pragma Interface_Name
2830 @unnumberedsec Pragma Interface_Name
2831 @findex Interface_Name
2835 @smallexample @c ada
2836 pragma Interface_Name (
2837 [Entity =>] LOCAL_NAME
2838 [, [External_Name =>] static_string_EXPRESSION]
2839 [, [Link_Name =>] static_string_EXPRESSION]);
2843 This pragma provides an alternative way of specifying the interface name
2844 for an interfaced subprogram, and is provided for compatibility with Ada
2845 83 compilers that use the pragma for this purpose. You must provide at
2846 least one of @var{External_Name} or @var{Link_Name}.
2848 @node Pragma Interrupt_Handler
2849 @unnumberedsec Pragma Interrupt_Handler
2850 @findex Interrupt_Handler
2854 @smallexample @c ada
2855 pragma Interrupt_Handler (procedure_LOCAL_NAME);
2859 This program unit pragma is supported for parameterless protected procedures
2860 as described in Annex C of the Ada Reference Manual. On the AAMP target
2861 the pragma can also be specified for nonprotected parameterless procedures
2862 that are declared at the library level (which includes procedures
2863 declared at the top level of a library package). In the case of AAMP,
2864 when this pragma is applied to a nonprotected procedure, the instruction
2865 @code{IERET} is generated for returns from the procedure, enabling
2866 maskable interrupts, in place of the normal return instruction.
2868 @node Pragma Interrupt_State
2869 @unnumberedsec Pragma Interrupt_State
2870 @findex Interrupt_State
2874 @smallexample @c ada
2875 pragma Interrupt_State
2877 [State =>] SYSTEM | RUNTIME | USER);
2881 Normally certain interrupts are reserved to the implementation. Any attempt
2882 to attach an interrupt causes Program_Error to be raised, as described in
2883 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
2884 many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
2885 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
2886 interrupt execution. Additionally, signals such as @code{SIGSEGV},
2887 @code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
2888 Ada exceptions, or used to implement run-time functions such as the
2889 @code{abort} statement and stack overflow checking.
2891 Pragma @code{Interrupt_State} provides a general mechanism for overriding
2892 such uses of interrupts. It subsumes the functionality of pragma
2893 @code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
2894 available on OS/2, Windows or VMS. On all other platforms than VxWorks,
2895 it applies to signals; on VxWorks, it applies to vectored hardware interrupts
2896 and may be used to mark interrupts required by the board support package
2899 Interrupts can be in one of three states:
2903 The interrupt is reserved (no Ada handler can be installed), and the
2904 Ada run-time may not install a handler. As a result you are guaranteed
2905 standard system default action if this interrupt is raised.
2909 The interrupt is reserved (no Ada handler can be installed). The run time
2910 is allowed to install a handler for internal control purposes, but is
2911 not required to do so.
2915 The interrupt is unreserved. The user may install a handler to provide
2920 These states are the allowed values of the @code{State} parameter of the
2921 pragma. The @code{Name} parameter is a value of the type
2922 @code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
2923 @code{Ada.Interrupts.Names}.
2925 This is a configuration pragma, and the binder will check that there
2926 are no inconsistencies between different units in a partition in how a
2927 given interrupt is specified. It may appear anywhere a pragma is legal.
2929 The effect is to move the interrupt to the specified state.
2931 By declaring interrupts to be SYSTEM, you guarantee the standard system
2932 action, such as a core dump.
2934 By declaring interrupts to be USER, you guarantee that you can install
2937 Note that certain signals on many operating systems cannot be caught and
2938 handled by applications. In such cases, the pragma is ignored. See the
2939 operating system documentation, or the value of the array @code{Reserved}
2940 declared in the spec of package @code{System.OS_Interface}.
2942 Overriding the default state of signals used by the Ada runtime may interfere
2943 with an application's runtime behavior in the cases of the synchronous signals,
2944 and in the case of the signal used to implement the @code{abort} statement.
2946 @node Pragma Keep_Names
2947 @unnumberedsec Pragma Keep_Names
2952 @smallexample @c ada
2953 pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
2957 The @var{LOCAL_NAME} argument
2958 must refer to an enumeration first subtype
2959 in the current declarative part. The effect is to retain the enumeration
2960 literal names for use by @code{Image} and @code{Value} even if a global
2961 @code{Discard_Names} pragma applies. This is useful when you want to
2962 generally suppress enumeration literal names and for example you therefore
2963 use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
2964 want to retain the names for specific enumeration types.
2966 @node Pragma License
2967 @unnumberedsec Pragma License
2969 @cindex License checking
2973 @smallexample @c ada
2974 pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
2978 This pragma is provided to allow automated checking for appropriate license
2979 conditions with respect to the standard and modified GPL@. A pragma
2980 @code{License}, which is a configuration pragma that typically appears at
2981 the start of a source file or in a separate @file{gnat.adc} file, specifies
2982 the licensing conditions of a unit as follows:
2986 This is used for a unit that can be freely used with no license restrictions.
2987 Examples of such units are public domain units, and units from the Ada
2991 This is used for a unit that is licensed under the unmodified GPL, and which
2992 therefore cannot be @code{with}'ed by a restricted unit.
2995 This is used for a unit licensed under the GNAT modified GPL that includes
2996 a special exception paragraph that specifically permits the inclusion of
2997 the unit in programs without requiring the entire program to be released
3001 This is used for a unit that is restricted in that it is not permitted to
3002 depend on units that are licensed under the GPL@. Typical examples are
3003 proprietary code that is to be released under more restrictive license
3004 conditions. Note that restricted units are permitted to @code{with} units
3005 which are licensed under the modified GPL (this is the whole point of the
3011 Normally a unit with no @code{License} pragma is considered to have an
3012 unknown license, and no checking is done. However, standard GNAT headers
3013 are recognized, and license information is derived from them as follows.
3017 A GNAT license header starts with a line containing 78 hyphens. The following
3018 comment text is searched for the appearance of any of the following strings.
3020 If the string ``GNU General Public License'' is found, then the unit is assumed
3021 to have GPL license, unless the string ``As a special exception'' follows, in
3022 which case the license is assumed to be modified GPL@.
3024 If one of the strings
3025 ``This specification is adapted from the Ada Semantic Interface'' or
3026 ``This specification is derived from the Ada Reference Manual'' is found
3027 then the unit is assumed to be unrestricted.
3031 These default actions means that a program with a restricted license pragma
3032 will automatically get warnings if a GPL unit is inappropriately
3033 @code{with}'ed. For example, the program:
3035 @smallexample @c ada
3038 procedure Secret_Stuff is
3044 if compiled with pragma @code{License} (@code{Restricted}) in a
3045 @file{gnat.adc} file will generate the warning:
3050 >>> license of withed unit "Sem_Ch3" is incompatible
3052 2. with GNAT.Sockets;
3053 3. procedure Secret_Stuff is
3057 Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
3058 compiler and is licensed under the
3059 GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
3060 run time, and is therefore licensed under the modified GPL@.
3062 @node Pragma Link_With
3063 @unnumberedsec Pragma Link_With
3068 @smallexample @c ada
3069 pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
3073 This pragma is provided for compatibility with certain Ada 83 compilers.
3074 It has exactly the same effect as pragma @code{Linker_Options} except
3075 that spaces occurring within one of the string expressions are treated
3076 as separators. For example, in the following case:
3078 @smallexample @c ada
3079 pragma Link_With ("-labc -ldef");
3083 results in passing the strings @code{-labc} and @code{-ldef} as two
3084 separate arguments to the linker. In addition pragma Link_With allows
3085 multiple arguments, with the same effect as successive pragmas.
3087 @node Pragma Linker_Alias
3088 @unnumberedsec Pragma Linker_Alias
3089 @findex Linker_Alias
3093 @smallexample @c ada
3094 pragma Linker_Alias (
3095 [Entity =>] LOCAL_NAME,
3096 [Target =>] static_string_EXPRESSION);
3100 @var{LOCAL_NAME} must refer to an object that is declared at the library
3101 level. This pragma establishes the given entity as a linker alias for the
3102 given target. It is equivalent to @code{__attribute__((alias))} in GNU C
3103 and causes @var{LOCAL_NAME} to be emitted as an alias for the symbol
3104 @var{static_string_EXPRESSION} in the object file, that is to say no space
3105 is reserved for @var{LOCAL_NAME} by the assembler and it will be resolved
3106 to the same address as @var{static_string_EXPRESSION} by the linker.
3108 The actual linker name for the target must be used (e.g.@: the fully
3109 encoded name with qualification in Ada, or the mangled name in C++),
3110 or it must be declared using the C convention with @code{pragma Import}
3111 or @code{pragma Export}.
3113 Not all target machines support this pragma. On some of them it is accepted
3114 only if @code{pragma Weak_External} has been applied to @var{LOCAL_NAME}.
3116 @smallexample @c ada
3117 -- Example of the use of pragma Linker_Alias
3121 pragma Export (C, i);
3123 new_name_for_i : Integer;
3124 pragma Linker_Alias (new_name_for_i, "i");
3128 @node Pragma Linker_Constructor
3129 @unnumberedsec Pragma Linker_Constructor
3130 @findex Linker_Constructor
3134 @smallexample @c ada
3135 pragma Linker_Constructor (procedure_LOCAL_NAME);
3139 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3140 is declared at the library level. A procedure to which this pragma is
3141 applied will be treated as an initialization routine by the linker.
3142 It is equivalent to @code{__attribute__((constructor))} in GNU C and
3143 causes @var{procedure_LOCAL_NAME} to be invoked before the entry point
3144 of the executable is called (or immediately after the shared library is
3145 loaded if the procedure is linked in a shared library), in particular
3146 before the Ada run-time environment is set up.
3148 Because of these specific contexts, the set of operations such a procedure
3149 can perform is very limited and the type of objects it can manipulate is
3150 essentially restricted to the elementary types. In particular, it must only
3151 contain code to which pragma Restrictions (No_Elaboration_Code) applies.
3153 This pragma is used by GNAT to implement auto-initialization of shared Stand
3154 Alone Libraries, which provides a related capability without the restrictions
3155 listed above. Where possible, the use of Stand Alone Libraries is preferable
3156 to the use of this pragma.
3158 @node Pragma Linker_Destructor
3159 @unnumberedsec Pragma Linker_Destructor
3160 @findex Linker_Destructor
3164 @smallexample @c ada
3165 pragma Linker_Destructor (procedure_LOCAL_NAME);
3169 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3170 is declared at the library level. A procedure to which this pragma is
3171 applied will be treated as a finalization routine by the linker.
3172 It is equivalent to @code{__attribute__((destructor))} in GNU C and
3173 causes @var{procedure_LOCAL_NAME} to be invoked after the entry point
3174 of the executable has exited (or immediately before the shared library
3175 is unloaded if the procedure is linked in a shared library), in particular
3176 after the Ada run-time environment is shut down.
3178 See @code{pragma Linker_Constructor} for the set of restrictions that apply
3179 because of these specific contexts.
3181 @node Pragma Linker_Section
3182 @unnumberedsec Pragma Linker_Section
3183 @findex Linker_Section
3187 @smallexample @c ada
3188 pragma Linker_Section (
3189 [Entity =>] LOCAL_NAME,
3190 [Section =>] static_string_EXPRESSION);
3194 @var{LOCAL_NAME} must refer to an object that is declared at the library
3195 level. This pragma specifies the name of the linker section for the given
3196 entity. It is equivalent to @code{__attribute__((section))} in GNU C and
3197 causes @var{LOCAL_NAME} to be placed in the @var{static_string_EXPRESSION}
3198 section of the executable (assuming the linker doesn't rename the section).
3200 The compiler normally places library-level objects in standard sections
3201 depending on their type: procedures and functions generally go in the
3202 @code{.text} section, initialized variables in the @code{.data} section
3203 and uninitialized variables in the @code{.bss} section.
3205 Other, special sections may exist on given target machines to map special
3206 hardware, for example I/O ports or flash memory. This pragma is a means to
3207 defer the final layout of the executable to the linker, thus fully working
3208 at the symbolic level with the compiler.
3210 Some file formats do not support arbitrary sections so not all target
3211 machines support this pragma. The use of this pragma may cause a program
3212 execution to be erroneous if it is used to place an entity into an
3213 inappropriate section (e.g.@: a modified variable into the @code{.text}
3214 section). See also @code{pragma Persistent_BSS}.
3216 @smallexample @c ada
3217 -- Example of the use of pragma Linker_Section
3221 pragma Volatile (Port_A);
3222 pragma Linker_Section (Port_A, ".bss.port_a");
3225 pragma Volatile (Port_B);
3226 pragma Linker_Section (Port_B, ".bss.port_b");
3230 @node Pragma Long_Float
3231 @unnumberedsec Pragma Long_Float
3237 @smallexample @c ada
3238 pragma Long_Float (FLOAT_FORMAT);
3240 FLOAT_FORMAT ::= D_Float | G_Float
3244 This pragma is implemented only in the OpenVMS implementation of GNAT@.
3245 It allows control over the internal representation chosen for the predefined
3246 type @code{Long_Float} and for floating point type representations with
3247 @code{digits} specified in the range 7 through 15.
3248 For further details on this pragma, see the
3249 @cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
3250 this pragma, the standard runtime libraries must be recompiled.
3251 @xref{The GNAT Run-Time Library Builder gnatlbr,,, gnat_ugn,
3252 @value{EDITION} User's Guide OpenVMS}, for a description of the
3253 @code{GNAT LIBRARY} command.
3255 @node Pragma Machine_Attribute
3256 @unnumberedsec Pragma Machine_Attribute
3257 @findex Machine_Attribute
3261 @smallexample @c ada
3262 pragma Machine_Attribute (
3263 [Entity =>] LOCAL_NAME,
3264 [Attribute_Name =>] static_string_EXPRESSION
3265 [, [Info =>] static_EXPRESSION] );
3269 Machine-dependent attributes can be specified for types and/or
3270 declarations. This pragma is semantically equivalent to
3271 @code{__attribute__((@var{attribute_name}))} (if @var{info} is not
3272 specified) or @code{__attribute__((@var{attribute_name}(@var{info})))}
3273 in GNU C, where @code{@var{attribute_name}} is recognized by the
3274 compiler middle-end or the @code{TARGET_ATTRIBUTE_TABLE} machine
3275 specific macro. A string literal for the optional parameter @var{info}
3276 is transformed into an identifier, which may make this pragma unusable
3277 for some attributes. @xref{Target Attributes,, Defining target-specific
3278 uses of @code{__attribute__}, gccint, GNU Compiler Collection (GCC)
3279 Internals}, further information.
3282 @unnumberedsec Pragma Main
3288 @smallexample @c ada
3290 (MAIN_OPTION [, MAIN_OPTION]);
3293 [Stack_Size =>] static_integer_EXPRESSION
3294 | [Task_Stack_Size_Default =>] static_integer_EXPRESSION
3295 | [Time_Slicing_Enabled =>] static_boolean_EXPRESSION
3299 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3300 no effect in GNAT, other than being syntax checked.
3302 @node Pragma Main_Storage
3303 @unnumberedsec Pragma Main_Storage
3305 @findex Main_Storage
3309 @smallexample @c ada
3311 (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
3313 MAIN_STORAGE_OPTION ::=
3314 [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
3315 | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
3319 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3320 no effect in GNAT, other than being syntax checked. Note that the pragma
3321 also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
3323 @node Pragma No_Body
3324 @unnumberedsec Pragma No_Body
3329 @smallexample @c ada
3334 There are a number of cases in which a package spec does not require a body,
3335 and in fact a body is not permitted. GNAT will not permit the spec to be
3336 compiled if there is a body around. The pragma No_Body allows you to provide
3337 a body file, even in a case where no body is allowed. The body file must
3338 contain only comments and a single No_Body pragma. This is recognized by
3339 the compiler as indicating that no body is logically present.
3341 This is particularly useful during maintenance when a package is modified in
3342 such a way that a body needed before is no longer needed. The provision of a
3343 dummy body with a No_Body pragma ensures that there is no interference from
3344 earlier versions of the package body.
3346 @node Pragma No_Return
3347 @unnumberedsec Pragma No_Return
3352 @smallexample @c ada
3353 pragma No_Return (procedure_LOCAL_NAME @{, procedure_LOCAL_NAME@});
3357 Each @var{procedure_LOCAL_NAME} argument must refer to one or more procedure
3358 declarations in the current declarative part. A procedure to which this
3359 pragma is applied may not contain any explicit @code{return} statements.
3360 In addition, if the procedure contains any implicit returns from falling
3361 off the end of a statement sequence, then execution of that implicit
3362 return will cause Program_Error to be raised.
3364 One use of this pragma is to identify procedures whose only purpose is to raise
3365 an exception. Another use of this pragma is to suppress incorrect warnings
3366 about missing returns in functions, where the last statement of a function
3367 statement sequence is a call to such a procedure.
3369 Note that in Ada 2005 mode, this pragma is part of the language, and is
3370 identical in effect to the pragma as implemented in Ada 95 mode.
3372 @node Pragma No_Strict_Aliasing
3373 @unnumberedsec Pragma No_Strict_Aliasing
3374 @findex No_Strict_Aliasing
3378 @smallexample @c ada
3379 pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)];
3383 @var{type_LOCAL_NAME} must refer to an access type
3384 declaration in the current declarative part. The effect is to inhibit
3385 strict aliasing optimization for the given type. The form with no
3386 arguments is a configuration pragma which applies to all access types
3387 declared in units to which the pragma applies. For a detailed
3388 description of the strict aliasing optimization, and the situations
3389 in which it must be suppressed, see @ref{Optimization and Strict
3390 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
3392 @node Pragma Normalize_Scalars
3393 @unnumberedsec Pragma Normalize_Scalars
3394 @findex Normalize_Scalars
3398 @smallexample @c ada
3399 pragma Normalize_Scalars;
3403 This is a language defined pragma which is fully implemented in GNAT@. The
3404 effect is to cause all scalar objects that are not otherwise initialized
3405 to be initialized. The initial values are implementation dependent and
3409 @item Standard.Character
3411 Objects whose root type is Standard.Character are initialized to
3412 Character'Last unless the subtype range excludes NUL (in which case
3413 NUL is used). This choice will always generate an invalid value if
3416 @item Standard.Wide_Character
3418 Objects whose root type is Standard.Wide_Character are initialized to
3419 Wide_Character'Last unless the subtype range excludes NUL (in which case
3420 NUL is used). This choice will always generate an invalid value if
3423 @item Standard.Wide_Wide_Character
3425 Objects whose root type is Standard.Wide_Wide_Character are initialized to
3426 the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in
3427 which case NUL is used). This choice will always generate an invalid value if
3432 Objects of an integer type are treated differently depending on whether
3433 negative values are present in the subtype. If no negative values are
3434 present, then all one bits is used as the initial value except in the
3435 special case where zero is excluded from the subtype, in which case
3436 all zero bits are used. This choice will always generate an invalid
3437 value if one exists.
3439 For subtypes with negative values present, the largest negative number
3440 is used, except in the unusual case where this largest negative number
3441 is in the subtype, and the largest positive number is not, in which case
3442 the largest positive value is used. This choice will always generate
3443 an invalid value if one exists.
3445 @item Floating-Point Types
3446 Objects of all floating-point types are initialized to all 1-bits. For
3447 standard IEEE format, this corresponds to a NaN (not a number) which is
3448 indeed an invalid value.
3450 @item Fixed-Point Types
3451 Objects of all fixed-point types are treated as described above for integers,
3452 with the rules applying to the underlying integer value used to represent
3453 the fixed-point value.
3456 Objects of a modular type are initialized to all one bits, except in
3457 the special case where zero is excluded from the subtype, in which
3458 case all zero bits are used. This choice will always generate an
3459 invalid value if one exists.
3461 @item Enumeration types
3462 Objects of an enumeration type are initialized to all one-bits, i.e.@: to
3463 the value @code{2 ** typ'Size - 1} unless the subtype excludes the literal
3464 whose Pos value is zero, in which case a code of zero is used. This choice
3465 will always generate an invalid value if one exists.
3469 @node Pragma Obsolescent
3470 @unnumberedsec Pragma Obsolescent
3475 @smallexample @c ada
3478 pragma Obsolescent (
3479 [Message =>] static_string_EXPRESSION
3480 [,[Version =>] Ada_05]]);
3482 pragma Obsolescent (
3484 [,[Message =>] static_string_EXPRESSION
3485 [,[Version =>] Ada_05]] );
3489 This pragma can occur immediately following a declaration of an entity,
3490 including the case of a record component. If no Entity argument is present,
3491 then this declaration is the one to which the pragma applies. If an Entity
3492 parameter is present, it must either match the name of the entity in this
3493 declaration, or alternatively, the pragma can immediately follow an enumeration
3494 type declaration, where the Entity argument names one of the enumeration
3497 This pragma is used to indicate that the named entity
3498 is considered obsolescent and should not be used. Typically this is
3499 used when an API must be modified by eventually removing or modifying
3500 existing subprograms or other entities. The pragma can be used at an
3501 intermediate stage when the entity is still present, but will be
3504 The effect of this pragma is to output a warning message on a reference to
3505 an entity thus marked that the subprogram is obsolescent if the appropriate
3506 warning option in the compiler is activated. If the Message parameter is
3507 present, then a second warning message is given containing this text. In
3508 addition, a reference to the eneity is considered to be a violation of pragma
3509 Restrictions (No_Obsolescent_Features).
3511 This pragma can also be used as a program unit pragma for a package,
3512 in which case the entity name is the name of the package, and the
3513 pragma indicates that the entire package is considered
3514 obsolescent. In this case a client @code{with}'ing such a package
3515 violates the restriction, and the @code{with} statement is
3516 flagged with warnings if the warning option is set.
3518 If the Version parameter is present (which must be exactly
3519 the identifier Ada_05, no other argument is allowed), then the
3520 indication of obsolescence applies only when compiling in Ada 2005
3521 mode. This is primarily intended for dealing with the situations
3522 in the predefined library where subprograms or packages
3523 have become defined as obsolescent in Ada 2005
3524 (e.g.@: in Ada.Characters.Handling), but may be used anywhere.
3526 The following examples show typical uses of this pragma:
3528 @smallexample @c ada
3530 pragma Obsolescent (p, Message => "use pp instead of p");
3535 pragma Obsolescent ("use q2new instead");
3537 type R is new integer;
3540 Message => "use RR in Ada 2005",
3550 type E is (a, bc, 'd', quack);
3551 pragma Obsolescent (Entity => bc)
3552 pragma Obsolescent (Entity => 'd')
3555 (a, b : character) return character;
3556 pragma Obsolescent (Entity => "+");
3561 Note that, as for all pragmas, if you use a pragma argument identifier,
3562 then all subsequent parameters must also use a pragma argument identifier.
3563 So if you specify "Entity =>" for the Entity argument, and a Message
3564 argument is present, it must be preceded by "Message =>".
3566 @node Pragma Optimize_Alignment
3567 @unnumberedsec Pragma Optimize_Alignment
3568 @findex Optimize_Alignment
3569 @cindex Alignment, default settings
3573 @smallexample @c ada
3574 pragma Optimize_Alignment (TIME | SPACE | OFF);
3578 This is a configuration pragma which affects the choice of default alignments
3579 for types where no alignment is explicitly specified. There is a time/space
3580 trade-off in the selection of these values. Large alignments result in more
3581 efficient code, at the expense of larger data space, since sizes have to be
3582 increased to match these alignments. Smaller alignments save space, but the
3583 access code is slower. The normal choice of default alignments (which is what
3584 you get if you do not use this pragma, or if you use an argument of OFF),
3585 tries to balance these two requirements.
3587 Specifying SPACE causes smaller default alignments to be chosen in two cases.
3588 First any packed record is given an alignment of 1. Second, if a size is given
3589 for the type, then the alignment is chosen to avoid increasing this size. For
3592 @smallexample @c ada
3602 In the default mode, this type gets an alignment of 4, so that access to the
3603 Integer field X are efficient. But this means that objects of the type end up
3604 with a size of 8 bytes. This is a valid choice, since sizes of objects are
3605 allowed to be bigger than the size of the type, but it can waste space if for
3606 example fields of type R appear in an enclosing record. If the above type is
3607 compiled in @code{Optimize_Alignment (Space)} mode, the alignment is set to 1.
3609 Specifying TIME causes larger default alignments to be chosen in the case of
3610 small types with sizes that are not a power of 2. For example, consider:
3612 @smallexample @c ada
3624 The default alignment for this record is normally 1, but if this type is
3625 compiled in @code{Optimize_Alignment (Time)} mode, then the alignment is set
3626 to 4, which wastes space for objects of the type, since they are now 4 bytes
3627 long, but results in more efficient access when the whole record is referenced.
3629 As noted above, this is a configuration pragma, and there is a requirement
3630 that all units in a partition be compiled with a consistent setting of the
3631 optimization setting. This would normally be achieved by use of a configuration
3632 pragma file containing the appropriate setting. The exception to this rule is
3633 that units with an explicit configuration pragma in the same file as the source
3634 unit are excluded from the consistency check, as are all predefined units. The
3635 latter are compiled by default in pragma Optimize_Alignment (Off) mode if no
3636 pragma appears at the start of the file.
3638 @node Pragma Passive
3639 @unnumberedsec Pragma Passive
3644 @smallexample @c ada
3645 pragma Passive [(Semaphore | No)];
3649 Syntax checked, but otherwise ignored by GNAT@. This is recognized for
3650 compatibility with DEC Ada 83 implementations, where it is used within a
3651 task definition to request that a task be made passive. If the argument
3652 @code{Semaphore} is present, or the argument is omitted, then DEC Ada 83
3653 treats the pragma as an assertion that the containing task is passive
3654 and that optimization of context switch with this task is permitted and
3655 desired. If the argument @code{No} is present, the task must not be
3656 optimized. GNAT does not attempt to optimize any tasks in this manner
3657 (since protected objects are available in place of passive tasks).
3659 @node Pragma Persistent_BSS
3660 @unnumberedsec Pragma Persistent_BSS
3661 @findex Persistent_BSS
3665 @smallexample @c ada
3666 pragma Persistent_BSS [(LOCAL_NAME)]
3670 This pragma allows selected objects to be placed in the @code{.persistent_bss}
3671 section. On some targets the linker and loader provide for special
3672 treatment of this section, allowing a program to be reloaded without
3673 affecting the contents of this data (hence the name persistent).
3675 There are two forms of usage. If an argument is given, it must be the
3676 local name of a library level object, with no explicit initialization
3677 and whose type is potentially persistent. If no argument is given, then
3678 the pragma is a configuration pragma, and applies to all library level
3679 objects with no explicit initialization of potentially persistent types.
3681 A potentially persistent type is a scalar type, or a non-tagged,
3682 non-discriminated record, all of whose components have no explicit
3683 initialization and are themselves of a potentially persistent type,
3684 or an array, all of whose constraints are static, and whose component
3685 type is potentially persistent.
3687 If this pragma is used on a target where this feature is not supported,
3688 then the pragma will be ignored. See also @code{pragma Linker_Section}.
3690 @node Pragma Polling
3691 @unnumberedsec Pragma Polling
3696 @smallexample @c ada
3697 pragma Polling (ON | OFF);
3701 This pragma controls the generation of polling code. This is normally off.
3702 If @code{pragma Polling (ON)} is used then periodic calls are generated to
3703 the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
3704 runtime library, and can be found in file @file{a-excpol.adb}.
3706 Pragma @code{Polling} can appear as a configuration pragma (for example it
3707 can be placed in the @file{gnat.adc} file) to enable polling globally, or it
3708 can be used in the statement or declaration sequence to control polling
3711 A call to the polling routine is generated at the start of every loop and
3712 at the start of every subprogram call. This guarantees that the @code{Poll}
3713 routine is called frequently, and places an upper bound (determined by
3714 the complexity of the code) on the period between two @code{Poll} calls.
3716 The primary purpose of the polling interface is to enable asynchronous
3717 aborts on targets that cannot otherwise support it (for example Windows
3718 NT), but it may be used for any other purpose requiring periodic polling.
3719 The standard version is null, and can be replaced by a user program. This
3720 will require re-compilation of the @code{Ada.Exceptions} package that can
3721 be found in files @file{a-except.ads} and @file{a-except.adb}.
3723 A standard alternative unit (in file @file{4wexcpol.adb} in the standard GNAT
3724 distribution) is used to enable the asynchronous abort capability on
3725 targets that do not normally support the capability. The version of
3726 @code{Poll} in this file makes a call to the appropriate runtime routine
3727 to test for an abort condition.
3729 Note that polling can also be enabled by use of the @option{-gnatP} switch.
3730 @xref{Switches for gcc,,, gnat_ugn, @value{EDITION} User's Guide}, for
3733 @node Pragma Postcondition
3734 @unnumberedsec Pragma Postcondition
3735 @cindex Postconditions
3736 @cindex Checks, postconditions
3737 @findex Postconditions
3741 @smallexample @c ada
3742 pragma Postcondition (
3743 [Check =>] Boolean_Expression
3744 [,[Message =>] String_Expression]);
3748 The @code{Postcondition} pragma allows specification of automatic
3749 postcondition checks for subprograms. These checks are similar to
3750 assertions, but are automatically inserted just prior to the return
3751 statements of the subprogram with which they are associated (including
3752 implicit returns at the end of procedure bodies and associated
3753 exception handlers).
3755 In addition, the boolean expression which is the condition which
3756 must be true may contain references to function'Result in the case
3757 of a function to refer to the returned value.
3759 @code{Postcondition} pragmas may appear either immediate following the
3760 (separate) declaration of a subprogram, or at the start of the
3761 declarations of a subprogram body. Only other pragmas may intervene
3762 (that is appear between the subprogram declaration and its
3763 postconditions, or appear before the postcondition in the
3764 declaration sequence in a subprogram body). In the case of a
3765 postcondition appearing after a subprogram declaration, the
3766 formal arguments of the subprogram are visible, and can be
3767 referenced in the postcondition expressions.
3769 The postconditions are collected and automatically tested just
3770 before any return (implicit or explicit) in the subprogram body.
3771 A postcondition is only recognized if postconditions are active
3772 at the time the pragma is encountered. The compiler switch @option{gnata}
3773 turns on all postconditions by default, and pragma @code{Check_Policy}
3774 with an identifier of @code{Postcondition} can also be used to
3775 control whether postconditions are active.
3777 The general approach is that postconditions are placed in the spec
3778 if they represent functional aspects which make sense to the client.
3779 For example we might have:
3781 @smallexample @c ada
3782 function Direction return Integer;
3783 pragma Postcondition
3784 (Direction'Result = +1
3786 Direction'Result = -1);
3790 which serves to document that the result must be +1 or -1, and
3791 will test that this is the case at run time if postcondition
3794 Postconditions within the subprogram body can be used to
3795 check that some internal aspect of the implementation,
3796 not visible to the client, is operating as expected.
3797 For instance if a square root routine keeps an internal
3798 counter of the number of times it is called, then we
3799 might have the following postcondition:
3801 @smallexample @c ada
3802 Sqrt_Calls : Natural := 0;
3804 function Sqrt (Arg : Float) return Float is
3805 pragma Postcondition
3806 (Sqrt_Calls = Sqrt_Calls'Old + 1);
3812 As this example, shows, the use of the @code{Old} attribute
3813 is often useful in postconditions to refer to the state on
3814 entry to the subprogram.
3816 Note that postconditions are only checked on normal returns
3817 from the subprogram. If an abnormal return results from
3818 raising an exception, then the postconditions are not checked.
3820 If a postcondition fails, then the exception
3821 @code{System.Assertions.Assert_Failure} is raised. If
3822 a message argument was supplied, then the given string
3823 will be used as the exception message. If no message
3824 argument was supplied, then the default message has
3825 the form "Postcondition failed at file:line". The
3826 exception is raised in the context of the subprogram
3827 body, so it is possible to catch postcondition failures
3828 within the subprogram body itself.
3830 Within a package spec, normal visibility rules
3831 in Ada would prevent forward references within a
3832 postcondition pragma to functions defined later in
3833 the same package. This would introduce undesirable
3834 ordering constraints. To avoid this problem, all
3835 postcondition pragmas are analyzed at the end of
3836 the package spec, allowing forward references.
3838 The following example shows that this even allows
3839 mutually recursive postconditions as in:
3841 @smallexample @c ada
3842 package Parity_Functions is
3843 function Odd (X : Natural) return Boolean;
3844 pragma Postcondition
3848 (x /= 0 and then Even (X - 1))));
3850 function Even (X : Natural) return Boolean;
3851 pragma Postcondition
3855 (x /= 1 and then Odd (X - 1))));
3857 end Parity_Functions;
3861 There are no restrictions on the complexity or form of
3862 conditions used within @code{Postcondition} pragmas.
3863 The following example shows that it is even possible
3864 to verify performance behavior.
3866 @smallexample @c ada
3869 Performance : constant Float;
3870 -- Performance constant set by implementation
3871 -- to match target architecture behavior.
3873 procedure Treesort (Arg : String);
3874 -- Sorts characters of argument using N*logN sort
3875 pragma Postcondition
3876 (Float (Clock - Clock'Old) <=
3877 Float (Arg'Length) *
3878 log (Float (Arg'Length)) *
3884 Note: postcondition pragmas associated with subprograms that are
3885 marked as Inline_Always, or those marked as Inline with front-end
3886 inlining (-gnatN option set) are accepted and legality-checked
3887 by the compiler, but are ignored at run-time even if postcondition
3888 checking is enabled.
3890 @node Pragma Precondition
3891 @unnumberedsec Pragma Precondition
3892 @cindex Preconditions
3893 @cindex Checks, preconditions
3894 @findex Preconditions
3898 @smallexample @c ada
3899 pragma Precondition (
3900 [Check =>] Boolean_Expression
3901 [,[Message =>] String_Expression]);
3905 The @code{Precondition} pragma is similar to @code{Postcondition}
3906 except that the corresponding checks take place immediately upon
3907 entry to the subprogram, and if a precondition fails, the exception
3908 is raised in the context of the caller, and the attribute 'Result
3909 cannot be used within the precondition expression.
3911 Otherwise, the placement and visibility rules are identical to those
3912 described for postconditions. The following is an example of use
3913 within a package spec:
3915 @smallexample @c ada
3916 package Math_Functions is
3918 function Sqrt (Arg : Float) return Float;
3919 pragma Precondition (Arg >= 0.0)
3925 @code{Precondition} pragmas may appear either immediate following the
3926 (separate) declaration of a subprogram, or at the start of the
3927 declarations of a subprogram body. Only other pragmas may intervene
3928 (that is appear between the subprogram declaration and its
3929 postconditions, or appear before the postcondition in the
3930 declaration sequence in a subprogram body).
3932 Note: postcondition pragmas associated with subprograms that are
3933 marked as Inline_Always, or those marked as Inline with front-end
3934 inlining (-gnatN option set) are accepted and legality-checked
3935 by the compiler, but are ignored at run-time even if postcondition
3936 checking is enabled.
3940 @node Pragma Profile (Ravenscar)
3941 @unnumberedsec Pragma Profile (Ravenscar)
3946 @smallexample @c ada
3947 pragma Profile (Ravenscar);
3951 A configuration pragma that establishes the following set of configuration
3955 @item Task_Dispatching_Policy (FIFO_Within_Priorities)
3956 [RM D.2.2] Tasks are dispatched following a preemptive
3957 priority-ordered scheduling policy.
3959 @item Locking_Policy (Ceiling_Locking)
3960 [RM D.3] While tasks and interrupts execute a protected action, they inherit
3961 the ceiling priority of the corresponding protected object.
3963 @c @item Detect_Blocking
3964 @c This pragma forces the detection of potentially blocking operations within a
3965 @c protected operation, and to raise Program_Error if that happens.
3969 plus the following set of restrictions:
3972 @item Max_Entry_Queue_Length = 1
3973 Defines the maximum number of calls that are queued on a (protected) entry.
3974 Note that this restrictions is checked at run time. Violation of this
3975 restriction results in the raising of Program_Error exception at the point of
3976 the call. For the Profile (Ravenscar) the value of Max_Entry_Queue_Length is
3977 always 1 and hence no task can be queued on a protected entry.
3979 @item Max_Protected_Entries = 1
3980 [RM D.7] Specifies the maximum number of entries per protected type. The
3981 bounds of every entry family of a protected unit shall be static, or shall be
3982 defined by a discriminant of a subtype whose corresponding bound is static.
3983 For the Profile (Ravenscar) the value of Max_Protected_Entries is always 1.
3985 @item Max_Task_Entries = 0
3986 [RM D.7] Specifies the maximum number of entries
3987 per task. The bounds of every entry family
3988 of a task unit shall be static, or shall be
3989 defined by a discriminant of a subtype whose
3990 corresponding bound is static. A value of zero
3991 indicates that no rendezvous are possible. For
3992 the Profile (Ravenscar), the value of Max_Task_Entries is always
3995 @item No_Abort_Statements
3996 [RM D.7] There are no abort_statements, and there are
3997 no calls to Task_Identification.Abort_Task.
3999 @item No_Asynchronous_Control
4000 There are no semantic dependences on the package
4001 Asynchronous_Task_Control.
4004 There are no semantic dependencies on the package Ada.Calendar.
4006 @item No_Dynamic_Attachment
4007 There is no call to any of the operations defined in package Ada.Interrupts
4008 (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler,
4009 Detach_Handler, and Reference).
4011 @item No_Dynamic_Priorities
4012 [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
4014 @item No_Implicit_Heap_Allocations
4015 [RM D.7] No constructs are allowed to cause implicit heap allocation.
4017 @item No_Local_Protected_Objects
4018 Protected objects and access types that designate
4019 such objects shall be declared only at library level.
4021 @item No_Local_Timing_Events
4022 [RM D.7] All objects of type Ada.Timing_Events.Timing_Event are
4023 declared at the library level.
4025 @item No_Protected_Type_Allocators
4026 There are no allocators for protected types or
4027 types containing protected subcomponents.
4029 @item No_Relative_Delay
4030 There are no delay_relative statements.
4032 @item No_Requeue_Statements
4033 Requeue statements are not allowed.
4035 @item No_Select_Statements
4036 There are no select_statements.
4038 @item No_Specific_Termination_Handlers
4039 [RM D.7] There are no calls to Ada.Task_Termination.Set_Specific_Handler
4040 or to Ada.Task_Termination.Specific_Handler.
4042 @item No_Task_Allocators
4043 [RM D.7] There are no allocators for task types
4044 or types containing task subcomponents.
4046 @item No_Task_Attributes_Package
4047 There are no semantic dependencies on the Ada.Task_Attributes package.
4049 @item No_Task_Hierarchy
4050 [RM D.7] All (non-environment) tasks depend
4051 directly on the environment task of the partition.
4053 @item No_Task_Termination
4054 Tasks which terminate are erroneous.
4056 @item No_Unchecked_Conversion
4057 There are no semantic dependencies on the Ada.Unchecked_Conversion package.
4059 @item No_Unchecked_Deallocation
4060 There are no semantic dependencies on the Ada.Unchecked_Deallocation package.
4062 @item Simple_Barriers
4063 Entry barrier condition expressions shall be either static
4064 boolean expressions or boolean objects which are declared in
4065 the protected type which contains the entry.
4069 This set of configuration pragmas and restrictions correspond to the
4070 definition of the ``Ravenscar Profile'' for limited tasking, devised and
4071 published by the @cite{International Real-Time Ada Workshop}, 1997,
4072 and whose most recent description is available at
4073 @url{http://www-users.cs.york.ac.uk/~burns/ravenscar.ps}.
4075 The original definition of the profile was revised at subsequent IRTAW
4076 meetings. It has been included in the ISO
4077 @cite{Guide for the Use of the Ada Programming Language in High
4078 Integrity Systems}, and has been approved by ISO/IEC/SC22/WG9 for inclusion in
4079 the next revision of the standard. The formal definition given by
4080 the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and
4081 AI-305) available at
4082 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00249.TXT} and
4083 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00305.TXT}
4086 The above set is a superset of the restrictions provided by pragma
4087 @code{Profile (Restricted)}, it includes six additional restrictions
4088 (@code{Simple_Barriers}, @code{No_Select_Statements},
4089 @code{No_Calendar}, @code{No_Implicit_Heap_Allocations},
4090 @code{No_Relative_Delay} and @code{No_Task_Termination}). This means
4091 that pragma @code{Profile (Ravenscar)}, like the pragma
4092 @code{Profile (Restricted)},
4093 automatically causes the use of a simplified,
4094 more efficient version of the tasking run-time system.
4096 @node Pragma Profile (Restricted)
4097 @unnumberedsec Pragma Profile (Restricted)
4098 @findex Restricted Run Time
4102 @smallexample @c ada
4103 pragma Profile (Restricted);
4107 A configuration pragma that establishes the following set of restrictions:
4110 @item No_Abort_Statements
4111 @item No_Entry_Queue
4112 @item No_Task_Hierarchy
4113 @item No_Task_Allocators
4114 @item No_Dynamic_Priorities
4115 @item No_Terminate_Alternatives
4116 @item No_Dynamic_Attachment
4117 @item No_Protected_Type_Allocators
4118 @item No_Local_Protected_Objects
4119 @item No_Requeue_Statements
4120 @item No_Task_Attributes_Package
4121 @item Max_Asynchronous_Select_Nesting = 0
4122 @item Max_Task_Entries = 0
4123 @item Max_Protected_Entries = 1
4124 @item Max_Select_Alternatives = 0
4128 This set of restrictions causes the automatic selection of a simplified
4129 version of the run time that provides improved performance for the
4130 limited set of tasking functionality permitted by this set of restrictions.
4132 @node Pragma Psect_Object
4133 @unnumberedsec Pragma Psect_Object
4134 @findex Psect_Object
4138 @smallexample @c ada
4139 pragma Psect_Object (
4140 [Internal =>] LOCAL_NAME,
4141 [, [External =>] EXTERNAL_SYMBOL]
4142 [, [Size =>] EXTERNAL_SYMBOL]);
4146 | static_string_EXPRESSION
4150 This pragma is identical in effect to pragma @code{Common_Object}.
4152 @node Pragma Pure_Function
4153 @unnumberedsec Pragma Pure_Function
4154 @findex Pure_Function
4158 @smallexample @c ada
4159 pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
4163 This pragma appears in the same declarative part as a function
4164 declaration (or a set of function declarations if more than one
4165 overloaded declaration exists, in which case the pragma applies
4166 to all entities). It specifies that the function @code{Entity} is
4167 to be considered pure for the purposes of code generation. This means
4168 that the compiler can assume that there are no side effects, and
4169 in particular that two calls with identical arguments produce the
4170 same result. It also means that the function can be used in an
4173 Note that, quite deliberately, there are no static checks to try
4174 to ensure that this promise is met, so @code{Pure_Function} can be used
4175 with functions that are conceptually pure, even if they do modify
4176 global variables. For example, a square root function that is
4177 instrumented to count the number of times it is called is still
4178 conceptually pure, and can still be optimized, even though it
4179 modifies a global variable (the count). Memo functions are another
4180 example (where a table of previous calls is kept and consulted to
4181 avoid re-computation).
4184 Note: Most functions in a @code{Pure} package are automatically pure, and
4185 there is no need to use pragma @code{Pure_Function} for such functions. One
4186 exception is any function that has at least one formal of type
4187 @code{System.Address} or a type derived from it. Such functions are not
4188 considered pure by default, since the compiler assumes that the
4189 @code{Address} parameter may be functioning as a pointer and that the
4190 referenced data may change even if the address value does not.
4191 Similarly, imported functions are not considered to be pure by default,
4192 since there is no way of checking that they are in fact pure. The use
4193 of pragma @code{Pure_Function} for such a function will override these default
4194 assumption, and cause the compiler to treat a designated subprogram as pure
4197 Note: If pragma @code{Pure_Function} is applied to a renamed function, it
4198 applies to the underlying renamed function. This can be used to
4199 disambiguate cases of overloading where some but not all functions
4200 in a set of overloaded functions are to be designated as pure.
4202 If pragma @code{Pure_Function} is applied to a library level function, the
4203 function is also considered pure from an optimization point of view, but the
4204 unit is not a Pure unit in the categorization sense. So for example, a function
4205 thus marked is free to @code{with} non-pure units.
4207 @node Pragma Restriction_Warnings
4208 @unnumberedsec Pragma Restriction_Warnings
4209 @findex Restriction_Warnings
4213 @smallexample @c ada
4214 pragma Restriction_Warnings
4215 (restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
4219 This pragma allows a series of restriction identifiers to be
4220 specified (the list of allowed identifiers is the same as for
4221 pragma @code{Restrictions}). For each of these identifiers
4222 the compiler checks for violations of the restriction, but
4223 generates a warning message rather than an error message
4224 if the restriction is violated.
4227 @unnumberedsec Pragma Shared
4231 This pragma is provided for compatibility with Ada 83. The syntax and
4232 semantics are identical to pragma Atomic.
4234 @node Pragma Source_File_Name
4235 @unnumberedsec Pragma Source_File_Name
4236 @findex Source_File_Name
4240 @smallexample @c ada
4241 pragma Source_File_Name (
4242 [Unit_Name =>] unit_NAME,
4243 Spec_File_Name => STRING_LITERAL,
4244 [Index => INTEGER_LITERAL]);
4246 pragma Source_File_Name (
4247 [Unit_Name =>] unit_NAME,
4248 Body_File_Name => STRING_LITERAL,
4249 [Index => INTEGER_LITERAL]);
4253 Use this to override the normal naming convention. It is a configuration
4254 pragma, and so has the usual applicability of configuration pragmas
4255 (i.e.@: it applies to either an entire partition, or to all units in a
4256 compilation, or to a single unit, depending on how it is used.
4257 @var{unit_name} is mapped to @var{file_name_literal}. The identifier for
4258 the second argument is required, and indicates whether this is the file
4259 name for the spec or for the body.
4261 The optional Index argument should be used when a file contains multiple
4262 units, and when you do not want to use @code{gnatchop} to separate then
4263 into multiple files (which is the recommended procedure to limit the
4264 number of recompilation that are needed when some sources change).
4265 For instance, if the source file @file{source.ada} contains
4267 @smallexample @c ada
4279 you could use the following configuration pragmas:
4281 @smallexample @c ada
4282 pragma Source_File_Name
4283 (B, Spec_File_Name => "source.ada", Index => 1);
4284 pragma Source_File_Name
4285 (A, Body_File_Name => "source.ada", Index => 2);
4288 Note that the @code{gnatname} utility can also be used to generate those
4289 configuration pragmas.
4291 Another form of the @code{Source_File_Name} pragma allows
4292 the specification of patterns defining alternative file naming schemes
4293 to apply to all files.
4295 @smallexample @c ada
4296 pragma Source_File_Name
4297 ( [Spec_File_Name =>] STRING_LITERAL
4298 [,[Casing =>] CASING_SPEC]
4299 [,[Dot_Replacement =>] STRING_LITERAL]);
4301 pragma Source_File_Name
4302 ( [Body_File_Name =>] STRING_LITERAL
4303 [,[Casing =>] CASING_SPEC]
4304 [,[Dot_Replacement =>] STRING_LITERAL]);
4306 pragma Source_File_Name
4307 ( [Subunit_File_Name =>] STRING_LITERAL
4308 [,[Casing =>] CASING_SPEC]
4309 [,[Dot_Replacement =>] STRING_LITERAL]);
4311 CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
4315 The first argument is a pattern that contains a single asterisk indicating
4316 the point at which the unit name is to be inserted in the pattern string
4317 to form the file name. The second argument is optional. If present it
4318 specifies the casing of the unit name in the resulting file name string.
4319 The default is lower case. Finally the third argument allows for systematic
4320 replacement of any dots in the unit name by the specified string literal.
4322 A pragma Source_File_Name cannot appear after a
4323 @ref{Pragma Source_File_Name_Project}.
4325 For more details on the use of the @code{Source_File_Name} pragma,
4326 @xref{Using Other File Names,,, gnat_ugn, @value{EDITION} User's Guide},
4327 and @ref{Alternative File Naming Schemes,,, gnat_ugn, @value{EDITION}
4330 @node Pragma Source_File_Name_Project
4331 @unnumberedsec Pragma Source_File_Name_Project
4332 @findex Source_File_Name_Project
4335 This pragma has the same syntax and semantics as pragma Source_File_Name.
4336 It is only allowed as a stand alone configuration pragma.
4337 It cannot appear after a @ref{Pragma Source_File_Name}, and
4338 most importantly, once pragma Source_File_Name_Project appears,
4339 no further Source_File_Name pragmas are allowed.
4341 The intention is that Source_File_Name_Project pragmas are always
4342 generated by the Project Manager in a manner consistent with the naming
4343 specified in a project file, and when naming is controlled in this manner,
4344 it is not permissible to attempt to modify this naming scheme using
4345 Source_File_Name pragmas (which would not be known to the project manager).
4347 @node Pragma Source_Reference
4348 @unnumberedsec Pragma Source_Reference
4349 @findex Source_Reference
4353 @smallexample @c ada
4354 pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
4358 This pragma must appear as the first line of a source file.
4359 @var{integer_literal} is the logical line number of the line following
4360 the pragma line (for use in error messages and debugging
4361 information). @var{string_literal} is a static string constant that
4362 specifies the file name to be used in error messages and debugging
4363 information. This is most notably used for the output of @code{gnatchop}
4364 with the @option{-r} switch, to make sure that the original unchopped
4365 source file is the one referred to.
4367 The second argument must be a string literal, it cannot be a static
4368 string expression other than a string literal. This is because its value
4369 is needed for error messages issued by all phases of the compiler.
4371 @node Pragma Stream_Convert
4372 @unnumberedsec Pragma Stream_Convert
4373 @findex Stream_Convert
4377 @smallexample @c ada
4378 pragma Stream_Convert (
4379 [Entity =>] type_LOCAL_NAME,
4380 [Read =>] function_NAME,
4381 [Write =>] function_NAME);
4385 This pragma provides an efficient way of providing stream functions for
4386 types defined in packages. Not only is it simpler to use than declaring
4387 the necessary functions with attribute representation clauses, but more
4388 significantly, it allows the declaration to made in such a way that the
4389 stream packages are not loaded unless they are needed. The use of
4390 the Stream_Convert pragma adds no overhead at all, unless the stream
4391 attributes are actually used on the designated type.
4393 The first argument specifies the type for which stream functions are
4394 provided. The second parameter provides a function used to read values
4395 of this type. It must name a function whose argument type may be any
4396 subtype, and whose returned type must be the type given as the first
4397 argument to the pragma.
4399 The meaning of the @var{Read}
4400 parameter is that if a stream attribute directly
4401 or indirectly specifies reading of the type given as the first parameter,
4402 then a value of the type given as the argument to the Read function is
4403 read from the stream, and then the Read function is used to convert this
4404 to the required target type.
4406 Similarly the @var{Write} parameter specifies how to treat write attributes
4407 that directly or indirectly apply to the type given as the first parameter.
4408 It must have an input parameter of the type specified by the first parameter,
4409 and the return type must be the same as the input type of the Read function.
4410 The effect is to first call the Write function to convert to the given stream
4411 type, and then write the result type to the stream.
4413 The Read and Write functions must not be overloaded subprograms. If necessary
4414 renamings can be supplied to meet this requirement.
4415 The usage of this attribute is best illustrated by a simple example, taken
4416 from the GNAT implementation of package Ada.Strings.Unbounded:
4418 @smallexample @c ada
4419 function To_Unbounded (S : String)
4420 return Unbounded_String
4421 renames To_Unbounded_String;
4423 pragma Stream_Convert
4424 (Unbounded_String, To_Unbounded, To_String);
4428 The specifications of the referenced functions, as given in the Ada
4429 Reference Manual are:
4431 @smallexample @c ada
4432 function To_Unbounded_String (Source : String)
4433 return Unbounded_String;
4435 function To_String (Source : Unbounded_String)
4440 The effect is that if the value of an unbounded string is written to a stream,
4441 then the representation of the item in the stream is in the same format that
4442 would be used for @code{Standard.String'Output}, and this same representation
4443 is expected when a value of this type is read from the stream. Note that the
4444 value written always includes the bounds, even for Unbounded_String'Write,
4445 since Unbounded_String is not an array type.
4447 @node Pragma Style_Checks
4448 @unnumberedsec Pragma Style_Checks
4449 @findex Style_Checks
4453 @smallexample @c ada
4454 pragma Style_Checks (string_LITERAL | ALL_CHECKS |
4455 On | Off [, LOCAL_NAME]);
4459 This pragma is used in conjunction with compiler switches to control the
4460 built in style checking provided by GNAT@. The compiler switches, if set,
4461 provide an initial setting for the switches, and this pragma may be used
4462 to modify these settings, or the settings may be provided entirely by
4463 the use of the pragma. This pragma can be used anywhere that a pragma
4464 is legal, including use as a configuration pragma (including use in
4465 the @file{gnat.adc} file).
4467 The form with a string literal specifies which style options are to be
4468 activated. These are additive, so they apply in addition to any previously
4469 set style check options. The codes for the options are the same as those
4470 used in the @option{-gnaty} switch to @command{gcc} or @command{gnatmake}.
4471 For example the following two methods can be used to enable
4476 @smallexample @c ada
4477 pragma Style_Checks ("l");
4482 gcc -c -gnatyl @dots{}
4487 The form ALL_CHECKS activates all standard checks (its use is equivalent
4488 to the use of the @code{gnaty} switch with no options. @xref{Top,
4489 @value{EDITION} User's Guide, About This Guide, gnat_ugn,
4490 @value{EDITION} User's Guide}, for details.
4492 The forms with @code{Off} and @code{On}
4493 can be used to temporarily disable style checks
4494 as shown in the following example:
4496 @smallexample @c ada
4500 pragma Style_Checks ("k"); -- requires keywords in lower case
4501 pragma Style_Checks (Off); -- turn off style checks
4502 NULL; -- this will not generate an error message
4503 pragma Style_Checks (On); -- turn style checks back on
4504 NULL; -- this will generate an error message
4508 Finally the two argument form is allowed only if the first argument is
4509 @code{On} or @code{Off}. The effect is to turn of semantic style checks
4510 for the specified entity, as shown in the following example:
4512 @smallexample @c ada
4516 pragma Style_Checks ("r"); -- require consistency of identifier casing
4518 Rf1 : Integer := ARG; -- incorrect, wrong case
4519 pragma Style_Checks (Off, Arg);
4520 Rf2 : Integer := ARG; -- OK, no error
4523 @node Pragma Subtitle
4524 @unnumberedsec Pragma Subtitle
4529 @smallexample @c ada
4530 pragma Subtitle ([Subtitle =>] STRING_LITERAL);
4534 This pragma is recognized for compatibility with other Ada compilers
4535 but is ignored by GNAT@.
4537 @node Pragma Suppress
4538 @unnumberedsec Pragma Suppress
4543 @smallexample @c ada
4544 pragma Suppress (Identifier [, [On =>] Name]);
4548 This is a standard pragma, and supports all the check names required in
4549 the RM. It is included here because GNAT recognizes one additional check
4550 name: @code{Alignment_Check} which can be used to suppress alignment checks
4551 on addresses used in address clauses. Such checks can also be suppressed
4552 by suppressing range checks, but the specific use of @code{Alignment_Check}
4553 allows suppression of alignment checks without suppressing other range checks.
4555 Note that pragma Suppress gives the compiler permission to omit
4556 checks, but does not require the compiler to omit checks. The compiler
4557 will generate checks if they are essentially free, even when they are
4558 suppressed. In particular, if the compiler can prove that a certain
4559 check will necessarily fail, it will generate code to do an
4560 unconditional ``raise'', even if checks are suppressed. The compiler
4563 Of course, run-time checks are omitted whenever the compiler can prove
4564 that they will not fail, whether or not checks are suppressed.
4566 @node Pragma Suppress_All
4567 @unnumberedsec Pragma Suppress_All
4568 @findex Suppress_All
4572 @smallexample @c ada
4573 pragma Suppress_All;
4577 This pragma can only appear immediately following a compilation
4578 unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
4579 which it follows. This pragma is implemented for compatibility with DEC
4580 Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
4581 configuration pragma is the preferred usage in GNAT@.
4583 @node Pragma Suppress_Exception_Locations
4584 @unnumberedsec Pragma Suppress_Exception_Locations
4585 @findex Suppress_Exception_Locations
4589 @smallexample @c ada
4590 pragma Suppress_Exception_Locations;
4594 In normal mode, a raise statement for an exception by default generates
4595 an exception message giving the file name and line number for the location
4596 of the raise. This is useful for debugging and logging purposes, but this
4597 entails extra space for the strings for the messages. The configuration
4598 pragma @code{Suppress_Exception_Locations} can be used to suppress the
4599 generation of these strings, with the result that space is saved, but the
4600 exception message for such raises is null. This configuration pragma may
4601 appear in a global configuration pragma file, or in a specific unit as
4602 usual. It is not required that this pragma be used consistently within
4603 a partition, so it is fine to have some units within a partition compiled
4604 with this pragma and others compiled in normal mode without it.
4606 @node Pragma Suppress_Initialization
4607 @unnumberedsec Pragma Suppress_Initialization
4608 @findex Suppress_Initialization
4609 @cindex Suppressing initialization
4610 @cindex Initialization, suppression of
4614 @smallexample @c ada
4615 pragma Suppress_Initialization ([Entity =>] type_Name);
4619 This pragma suppresses any implicit or explicit initialization
4620 associated with the given type name for all variables of this type.
4622 @node Pragma Task_Info
4623 @unnumberedsec Pragma Task_Info
4628 @smallexample @c ada
4629 pragma Task_Info (EXPRESSION);
4633 This pragma appears within a task definition (like pragma
4634 @code{Priority}) and applies to the task in which it appears. The
4635 argument must be of type @code{System.Task_Info.Task_Info_Type}.
4636 The @code{Task_Info} pragma provides system dependent control over
4637 aspects of tasking implementation, for example, the ability to map
4638 tasks to specific processors. For details on the facilities available
4639 for the version of GNAT that you are using, see the documentation
4640 in the spec of package System.Task_Info in the runtime
4643 @node Pragma Task_Name
4644 @unnumberedsec Pragma Task_Name
4649 @smallexample @c ada
4650 pragma Task_Name (string_EXPRESSION);
4654 This pragma appears within a task definition (like pragma
4655 @code{Priority}) and applies to the task in which it appears. The
4656 argument must be of type String, and provides a name to be used for
4657 the task instance when the task is created. Note that this expression
4658 is not required to be static, and in particular, it can contain
4659 references to task discriminants. This facility can be used to
4660 provide different names for different tasks as they are created,
4661 as illustrated in the example below.
4663 The task name is recorded internally in the run-time structures
4664 and is accessible to tools like the debugger. In addition the
4665 routine @code{Ada.Task_Identification.Image} will return this
4666 string, with a unique task address appended.
4668 @smallexample @c ada
4669 -- Example of the use of pragma Task_Name
4671 with Ada.Task_Identification;
4672 use Ada.Task_Identification;
4673 with Text_IO; use Text_IO;
4676 type Astring is access String;
4678 task type Task_Typ (Name : access String) is
4679 pragma Task_Name (Name.all);
4682 task body Task_Typ is
4683 Nam : constant String := Image (Current_Task);
4685 Put_Line ("-->" & Nam (1 .. 14) & "<--");
4688 type Ptr_Task is access Task_Typ;
4689 Task_Var : Ptr_Task;
4693 new Task_Typ (new String'("This is task 1"));
4695 new Task_Typ (new String'("This is task 2"));
4699 @node Pragma Task_Storage
4700 @unnumberedsec Pragma Task_Storage
4701 @findex Task_Storage
4704 @smallexample @c ada
4705 pragma Task_Storage (
4706 [Task_Type =>] LOCAL_NAME,
4707 [Top_Guard =>] static_integer_EXPRESSION);
4711 This pragma specifies the length of the guard area for tasks. The guard
4712 area is an additional storage area allocated to a task. A value of zero
4713 means that either no guard area is created or a minimal guard area is
4714 created, depending on the target. This pragma can appear anywhere a
4715 @code{Storage_Size} attribute definition clause is allowed for a task
4718 @node Pragma Thread_Local_Storage
4719 @unnumberedsec Pragma Thread_Local_Storage
4720 @findex Thread_Local_Storage
4721 @cindex Task specific storage
4722 @cindex TLS (Thread Local Storage)
4725 @smallexample @c ada
4726 pragma Thread_Local_Storage ([Entity =>] LOCAL_NAME);
4730 This pragma specifies that the specified entity, which must be
4731 a variable declared in a library level package, is to be marked as
4732 "Thread Local Storage" (@code{TLS}). On systems supporting this (which
4733 include Solaris, GNU/Linux and VxWorks 6), this causes each thread
4734 (and hence each Ada task) to see a distinct copy of the variable.
4736 The variable may not have default initialization, and if there is
4737 an explicit initialization, it must be either @code{null} for an
4738 access variable, or a static expression for a scalar variable.
4739 This provides a low level mechanism similar to that provided by
4740 the @code{Ada.Task_Attributes} package, but much more efficient
4741 and is also useful in writing interface code that will interact
4742 with foreign threads.
4744 If this pragma is used on a system where @code{TLS} is not supported,
4745 then an error message will be generated and the program will be rejected.
4747 @node Pragma Time_Slice
4748 @unnumberedsec Pragma Time_Slice
4753 @smallexample @c ada
4754 pragma Time_Slice (static_duration_EXPRESSION);
4758 For implementations of GNAT on operating systems where it is possible
4759 to supply a time slice value, this pragma may be used for this purpose.
4760 It is ignored if it is used in a system that does not allow this control,
4761 or if it appears in other than the main program unit.
4763 Note that the effect of this pragma is identical to the effect of the
4764 DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
4767 @unnumberedsec Pragma Title
4772 @smallexample @c ada
4773 pragma Title (TITLING_OPTION [, TITLING OPTION]);
4776 [Title =>] STRING_LITERAL,
4777 | [Subtitle =>] STRING_LITERAL
4781 Syntax checked but otherwise ignored by GNAT@. This is a listing control
4782 pragma used in DEC Ada 83 implementations to provide a title and/or
4783 subtitle for the program listing. The program listing generated by GNAT
4784 does not have titles or subtitles.
4786 Unlike other pragmas, the full flexibility of named notation is allowed
4787 for this pragma, i.e.@: the parameters may be given in any order if named
4788 notation is used, and named and positional notation can be mixed
4789 following the normal rules for procedure calls in Ada.
4791 @node Pragma Unchecked_Union
4792 @unnumberedsec Pragma Unchecked_Union
4794 @findex Unchecked_Union
4798 @smallexample @c ada
4799 pragma Unchecked_Union (first_subtype_LOCAL_NAME);
4803 This pragma is used to specify a representation of a record type that is
4804 equivalent to a C union. It was introduced as a GNAT implementation defined
4805 pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this
4806 pragma, making it language defined, and GNAT fully implements this extended
4807 version in all language modes (Ada 83, Ada 95, and Ada 2005). For full
4808 details, consult the Ada 2005 Reference Manual, section B.3.3.
4810 @node Pragma Unimplemented_Unit
4811 @unnumberedsec Pragma Unimplemented_Unit
4812 @findex Unimplemented_Unit
4816 @smallexample @c ada
4817 pragma Unimplemented_Unit;
4821 If this pragma occurs in a unit that is processed by the compiler, GNAT
4822 aborts with the message @samp{@var{xxx} not implemented}, where
4823 @var{xxx} is the name of the current compilation unit. This pragma is
4824 intended to allow the compiler to handle unimplemented library units in
4827 The abort only happens if code is being generated. Thus you can use
4828 specs of unimplemented packages in syntax or semantic checking mode.
4830 @node Pragma Universal_Aliasing
4831 @unnumberedsec Pragma Universal_Aliasing
4832 @findex Universal_Aliasing
4836 @smallexample @c ada
4837 pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)];
4841 @var{type_LOCAL_NAME} must refer to a type declaration in the current
4842 declarative part. The effect is to inhibit strict type-based aliasing
4843 optimization for the given type. In other words, the effect is as though
4844 access types designating this type were subject to pragma No_Strict_Aliasing.
4845 For a detailed description of the strict aliasing optimization, and the
4846 situations in which it must be suppressed, @xref{Optimization and Strict
4847 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
4849 @node Pragma Universal_Data
4850 @unnumberedsec Pragma Universal_Data
4851 @findex Universal_Data
4855 @smallexample @c ada
4856 pragma Universal_Data [(library_unit_Name)];
4860 This pragma is supported only for the AAMP target and is ignored for
4861 other targets. The pragma specifies that all library-level objects
4862 (Counter 0 data) associated with the library unit are to be accessed
4863 and updated using universal addressing (24-bit addresses for AAMP5)
4864 rather than the default of 16-bit Data Environment (DENV) addressing.
4865 Use of this pragma will generally result in less efficient code for
4866 references to global data associated with the library unit, but
4867 allows such data to be located anywhere in memory. This pragma is
4868 a library unit pragma, but can also be used as a configuration pragma
4869 (including use in the @file{gnat.adc} file). The functionality
4870 of this pragma is also available by applying the -univ switch on the
4871 compilations of units where universal addressing of the data is desired.
4873 @node Pragma Unmodified
4874 @unnumberedsec Pragma Unmodified
4876 @cindex Warnings, unmodified
4880 @smallexample @c ada
4881 pragma Unmodified (LOCAL_NAME @{, LOCAL_NAME@});
4885 This pragma signals that the assignable entities (variables,
4886 @code{out} parameters, @code{in out} parameters) whose names are listed are
4887 deliberately not assigned in the current source unit. This
4888 suppresses warnings about the
4889 entities being referenced but not assigned, and in addition a warning will be
4890 generated if one of these entities is in fact assigned in the
4891 same unit as the pragma (or in the corresponding body, or one
4894 This is particularly useful for clearly signaling that a particular
4895 parameter is not modified, even though the spec suggests that it might
4898 @node Pragma Unreferenced
4899 @unnumberedsec Pragma Unreferenced
4900 @findex Unreferenced
4901 @cindex Warnings, unreferenced
4905 @smallexample @c ada
4906 pragma Unreferenced (LOCAL_NAME @{, LOCAL_NAME@});
4907 pragma Unreferenced (library_unit_NAME @{, library_unit_NAME@});
4911 This pragma signals that the entities whose names are listed are
4912 deliberately not referenced in the current source unit. This
4913 suppresses warnings about the
4914 entities being unreferenced, and in addition a warning will be
4915 generated if one of these entities is in fact referenced in the
4916 same unit as the pragma (or in the corresponding body, or one
4919 This is particularly useful for clearly signaling that a particular
4920 parameter is not referenced in some particular subprogram implementation
4921 and that this is deliberate. It can also be useful in the case of
4922 objects declared only for their initialization or finalization side
4925 If @code{LOCAL_NAME} identifies more than one matching homonym in the
4926 current scope, then the entity most recently declared is the one to which
4927 the pragma applies. Note that in the case of accept formals, the pragma
4928 Unreferenced may appear immediately after the keyword @code{do} which
4929 allows the indication of whether or not accept formals are referenced
4930 or not to be given individually for each accept statement.
4932 The left hand side of an assignment does not count as a reference for the
4933 purpose of this pragma. Thus it is fine to assign to an entity for which
4934 pragma Unreferenced is given.
4936 Note that if a warning is desired for all calls to a given subprogram,
4937 regardless of whether they occur in the same unit as the subprogram
4938 declaration, then this pragma should not be used (calls from another
4939 unit would not be flagged); pragma Obsolescent can be used instead
4940 for this purpose, see @xref{Pragma Obsolescent}.
4942 The second form of pragma @code{Unreferenced} is used within a context
4943 clause. In this case the arguments must be unit names of units previously
4944 mentioned in @code{with} clauses (similar to the usage of pragma
4945 @code{Elaborate_All}. The effect is to suppress warnings about unreferenced
4946 units and unreferenced entities within these units.
4948 @node Pragma Unreferenced_Objects
4949 @unnumberedsec Pragma Unreferenced_Objects
4950 @findex Unreferenced_Objects
4951 @cindex Warnings, unreferenced
4955 @smallexample @c ada
4956 pragma Unreferenced_Objects (local_subtype_NAME @{, local_subtype_NAME@});
4960 This pragma signals that for the types or subtypes whose names are
4961 listed, objects which are declared with one of these types or subtypes may
4962 not be referenced, and if no references appear, no warnings are given.
4964 This is particularly useful for objects which are declared solely for their
4965 initialization and finalization effect. Such variables are sometimes referred
4966 to as RAII variables (Resource Acquisition Is Initialization). Using this
4967 pragma on the relevant type (most typically a limited controlled type), the
4968 compiler will automatically suppress unwanted warnings about these variables
4969 not being referenced.
4971 @node Pragma Unreserve_All_Interrupts
4972 @unnumberedsec Pragma Unreserve_All_Interrupts
4973 @findex Unreserve_All_Interrupts
4977 @smallexample @c ada
4978 pragma Unreserve_All_Interrupts;
4982 Normally certain interrupts are reserved to the implementation. Any attempt
4983 to attach an interrupt causes Program_Error to be raised, as described in
4984 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
4985 many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
4986 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
4987 interrupt execution.
4989 If the pragma @code{Unreserve_All_Interrupts} appears anywhere in any unit in
4990 a program, then all such interrupts are unreserved. This allows the
4991 program to handle these interrupts, but disables their standard
4992 functions. For example, if this pragma is used, then pressing
4993 @kbd{Ctrl-C} will not automatically interrupt execution. However,
4994 a program can then handle the @code{SIGINT} interrupt as it chooses.
4996 For a full list of the interrupts handled in a specific implementation,
4997 see the source code for the spec of @code{Ada.Interrupts.Names} in
4998 file @file{a-intnam.ads}. This is a target dependent file that contains the
4999 list of interrupts recognized for a given target. The documentation in
5000 this file also specifies what interrupts are affected by the use of
5001 the @code{Unreserve_All_Interrupts} pragma.
5003 For a more general facility for controlling what interrupts can be
5004 handled, see pragma @code{Interrupt_State}, which subsumes the functionality
5005 of the @code{Unreserve_All_Interrupts} pragma.
5007 @node Pragma Unsuppress
5008 @unnumberedsec Pragma Unsuppress
5013 @smallexample @c ada
5014 pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
5018 This pragma undoes the effect of a previous pragma @code{Suppress}. If
5019 there is no corresponding pragma @code{Suppress} in effect, it has no
5020 effect. The range of the effect is the same as for pragma
5021 @code{Suppress}. The meaning of the arguments is identical to that used
5022 in pragma @code{Suppress}.
5024 One important application is to ensure that checks are on in cases where
5025 code depends on the checks for its correct functioning, so that the code
5026 will compile correctly even if the compiler switches are set to suppress
5029 @node Pragma Use_VADS_Size
5030 @unnumberedsec Pragma Use_VADS_Size
5031 @cindex @code{Size}, VADS compatibility
5032 @findex Use_VADS_Size
5036 @smallexample @c ada
5037 pragma Use_VADS_Size;
5041 This is a configuration pragma. In a unit to which it applies, any use
5042 of the 'Size attribute is automatically interpreted as a use of the
5043 'VADS_Size attribute. Note that this may result in incorrect semantic
5044 processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in
5045 the handling of existing code which depends on the interpretation of Size
5046 as implemented in the VADS compiler. See description of the VADS_Size
5047 attribute for further details.
5049 @node Pragma Validity_Checks
5050 @unnumberedsec Pragma Validity_Checks
5051 @findex Validity_Checks
5055 @smallexample @c ada
5056 pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
5060 This pragma is used in conjunction with compiler switches to control the
5061 built-in validity checking provided by GNAT@. The compiler switches, if set
5062 provide an initial setting for the switches, and this pragma may be used
5063 to modify these settings, or the settings may be provided entirely by
5064 the use of the pragma. This pragma can be used anywhere that a pragma
5065 is legal, including use as a configuration pragma (including use in
5066 the @file{gnat.adc} file).
5068 The form with a string literal specifies which validity options are to be
5069 activated. The validity checks are first set to include only the default
5070 reference manual settings, and then a string of letters in the string
5071 specifies the exact set of options required. The form of this string
5072 is exactly as described for the @option{-gnatVx} compiler switch (see the
5073 GNAT users guide for details). For example the following two methods
5074 can be used to enable validity checking for mode @code{in} and
5075 @code{in out} subprogram parameters:
5079 @smallexample @c ada
5080 pragma Validity_Checks ("im");
5085 gcc -c -gnatVim @dots{}
5090 The form ALL_CHECKS activates all standard checks (its use is equivalent
5091 to the use of the @code{gnatva} switch.
5093 The forms with @code{Off} and @code{On}
5094 can be used to temporarily disable validity checks
5095 as shown in the following example:
5097 @smallexample @c ada
5101 pragma Validity_Checks ("c"); -- validity checks for copies
5102 pragma Validity_Checks (Off); -- turn off validity checks
5103 A := B; -- B will not be validity checked
5104 pragma Validity_Checks (On); -- turn validity checks back on
5105 A := C; -- C will be validity checked
5108 @node Pragma Volatile
5109 @unnumberedsec Pragma Volatile
5114 @smallexample @c ada
5115 pragma Volatile (LOCAL_NAME);
5119 This pragma is defined by the Ada Reference Manual, and the GNAT
5120 implementation is fully conformant with this definition. The reason it
5121 is mentioned in this section is that a pragma of the same name was supplied
5122 in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005
5123 implementation of pragma Volatile is upwards compatible with the
5124 implementation in DEC Ada 83.
5126 @node Pragma Warnings
5127 @unnumberedsec Pragma Warnings
5132 @smallexample @c ada
5133 pragma Warnings (On | Off);
5134 pragma Warnings (On | Off, LOCAL_NAME);
5135 pragma Warnings (static_string_EXPRESSION);
5136 pragma Warnings (On | Off, static_string_EXPRESSION);
5140 Normally warnings are enabled, with the output being controlled by
5141 the command line switch. Warnings (@code{Off}) turns off generation of
5142 warnings until a Warnings (@code{On}) is encountered or the end of the
5143 current unit. If generation of warnings is turned off using this
5144 pragma, then no warning messages are output, regardless of the
5145 setting of the command line switches.
5147 The form with a single argument may be used as a configuration pragma.
5149 If the @var{LOCAL_NAME} parameter is present, warnings are suppressed for
5150 the specified entity. This suppression is effective from the point where
5151 it occurs till the end of the extended scope of the variable (similar to
5152 the scope of @code{Suppress}).
5154 The form with a single static_string_EXPRESSION argument provides more precise
5155 control over which warnings are active. The string is a list of letters
5156 specifying which warnings are to be activated and which deactivated. The
5157 code for these letters is the same as the string used in the command
5158 line switch controlling warnings. The following is a brief summary. For
5159 full details see @ref{Warning Message Control,,, gnat_ugn, @value{EDITION}
5163 a turn on all optional warnings (except d h l .o)
5164 A turn off all optional warnings
5165 .a* turn on warnings for failing assertions
5166 .A turn off warnings for failing assertions
5167 b turn on warnings for bad fixed value (not multiple of small)
5168 B* turn off warnings for bad fixed value (not multiple of small)
5169 .b* turn on warnings for biased representation
5170 .B turn off warnings for biased representation
5171 c turn on warnings for constant conditional
5172 C* turn off warnings for constant conditional
5173 .c turn on warnings for unrepped components
5174 .C* turn off warnings for unrepped components
5175 d turn on warnings for implicit dereference
5176 D* turn off warnings for implicit dereference
5177 e treat all warnings as errors
5178 .e turn on every optional warning
5179 f turn on warnings for unreferenced formal
5180 F* turn off warnings for unreferenced formal
5181 g* turn on warnings for unrecognized pragma
5182 G turn off warnings for unrecognized pragma
5183 h turn on warnings for hiding variable
5184 H* turn off warnings for hiding variable
5185 i* turn on warnings for implementation unit
5186 I turn off warnings for implementation unit
5187 j turn on warnings for obsolescent (annex J) feature
5188 J* turn off warnings for obsolescent (annex J) feature
5189 k turn on warnings on constant variable
5190 K* turn off warnings on constant variable
5191 l turn on warnings for missing elaboration pragma
5192 L* turn off warnings for missing elaboration pragma
5193 m turn on warnings for variable assigned but not read
5194 M* turn off warnings for variable assigned but not read
5195 n* normal warning mode (cancels -gnatws/-gnatwe)
5196 o* turn on warnings for address clause overlay
5197 O turn off warnings for address clause overlay
5198 .o turn on warnings for out parameters assigned but not read
5199 .O* turn off warnings for out parameters assigned but not read
5200 p turn on warnings for ineffective pragma Inline in frontend
5201 P* turn off warnings for ineffective pragma Inline in frontend
5202 .p turn on warnings for parameter ordering
5203 .P* turn off warnings for parameter ordering
5204 q* turn on warnings for questionable missing parentheses
5205 Q turn off warnings for questionable missing parentheses
5206 r turn on warnings for redundant construct
5207 R* turn off warnings for redundant construct
5208 .r turn on warnings for object renaming function
5209 .R* turn off warnings for object renaming function
5210 s suppress all warnings
5211 t turn on warnings for tracking deleted code
5212 T* turn off warnings for tracking deleted code
5213 u turn on warnings for unused entity
5214 U* turn off warnings for unused entity
5215 v* turn on warnings for unassigned variable
5216 V turn off warnings for unassigned variable
5217 w* turn on warnings for wrong low bound assumption
5218 W turn off warnings for wrong low bound assumption
5219 .w turn on warnings for unnecessary Warnings Off pragmas
5220 .W* turn off warnings for unnecessary Warnings Off pragmas
5221 x* turn on warnings for export/import
5222 X turn off warnings for export/import
5223 .x turn on warnings for non-local exceptions
5224 .X* turn off warnings for non-local exceptions
5225 y* turn on warnings for Ada 2005 incompatibility
5226 Y turn off warnings for Ada 2005 incompatibility
5227 z* turn on convention/size/align warnings for unchecked conversion
5228 Z turn off convention/size/align warnings for unchecked conversion
5229 * indicates default in above list
5233 The specified warnings will be in effect until the end of the program
5234 or another pragma Warnings is encountered. The effect of the pragma is
5235 cumulative. Initially the set of warnings is the standard default set
5236 as possibly modified by compiler switches. Then each pragma Warning
5237 modifies this set of warnings as specified. This form of the pragma may
5238 also be used as a configuration pragma.
5240 The fourth form, with an On|Off parameter and a string, is used to
5241 control individual messages, based on their text. The string argument
5242 is a pattern that is used to match against the text of individual
5243 warning messages (not including the initial "warning: " tag).
5245 The pattern may contain asterisks, which match zero or more characters in
5246 the message. For example, you can use
5247 @code{pragma Warnings (Off, "*bits of*unused")} to suppress the warning
5248 message @code{warning: 960 bits of "a" unused}. No other regular
5249 expression notations are permitted. All characters other than asterisk in
5250 these three specific cases are treated as literal characters in the match.
5252 There are two ways to use this pragma. The OFF form can be used as a
5253 configuration pragma. The effect is to suppress all warnings (if any)
5254 that match the pattern string throughout the compilation.
5256 The second usage is to suppress a warning locally, and in this case, two
5257 pragmas must appear in sequence:
5259 @smallexample @c ada
5260 pragma Warnings (Off, Pattern);
5261 @dots{} code where given warning is to be suppressed
5262 pragma Warnings (On, Pattern);
5266 In this usage, the pattern string must match in the Off and On pragmas,
5267 and at least one matching warning must be suppressed.
5269 @node Pragma Weak_External
5270 @unnumberedsec Pragma Weak_External
5271 @findex Weak_External
5275 @smallexample @c ada
5276 pragma Weak_External ([Entity =>] LOCAL_NAME);
5280 @var{LOCAL_NAME} must refer to an object that is declared at the library
5281 level. This pragma specifies that the given entity should be marked as a
5282 weak symbol for the linker. It is equivalent to @code{__attribute__((weak))}
5283 in GNU C and causes @var{LOCAL_NAME} to be emitted as a weak symbol instead
5284 of a regular symbol, that is to say a symbol that does not have to be
5285 resolved by the linker if used in conjunction with a pragma Import.
5287 When a weak symbol is not resolved by the linker, its address is set to
5288 zero. This is useful in writing interfaces to external modules that may
5289 or may not be linked in the final executable, for example depending on
5290 configuration settings.
5292 If a program references at run time an entity to which this pragma has been
5293 applied, and the corresponding symbol was not resolved at link time, then
5294 the execution of the program is erroneous. It is not erroneous to take the
5295 Address of such an entity, for example to guard potential references,
5296 as shown in the example below.
5298 Some file formats do not support weak symbols so not all target machines
5299 support this pragma.
5301 @smallexample @c ada
5302 -- Example of the use of pragma Weak_External
5304 package External_Module is
5306 pragma Import (C, key);
5307 pragma Weak_External (key);
5308 function Present return boolean;
5309 end External_Module;
5311 with System; use System;
5312 package body External_Module is
5313 function Present return boolean is
5315 return key'Address /= System.Null_Address;
5317 end External_Module;
5320 @node Pragma Wide_Character_Encoding
5321 @unnumberedsec Pragma Wide_Character_Encoding
5322 @findex Wide_Character_Encoding
5326 @smallexample @c ada
5327 pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL);
5331 This pragma specifies the wide character encoding to be used in program
5332 source text appearing subsequently. It is a configuration pragma, but may
5333 also be used at any point that a pragma is allowed, and it is permissible
5334 to have more than one such pragma in a file, allowing multiple encodings
5335 to appear within the same file.
5337 The argument can be an identifier or a character literal. In the identifier
5338 case, it is one of @code{HEX}, @code{UPPER}, @code{SHIFT_JIS},
5339 @code{EUC}, @code{UTF8}, or @code{BRACKETS}. In the character literal
5340 case it is correspondingly one of the characters @samp{h}, @samp{u},
5341 @samp{s}, @samp{e}, @samp{8}, or @samp{b}.
5343 Note that when the pragma is used within a file, it affects only the
5344 encoding within that file, and does not affect withed units, specs,
5347 @node Implementation Defined Attributes
5348 @chapter Implementation Defined Attributes
5349 Ada defines (throughout the Ada reference manual,
5350 summarized in Annex K),
5351 a set of attributes that provide useful additional functionality in all
5352 areas of the language. These language defined attributes are implemented
5353 in GNAT and work as described in the Ada Reference Manual.
5355 In addition, Ada allows implementations to define additional
5356 attributes whose meaning is defined by the implementation. GNAT provides
5357 a number of these implementation-dependent attributes which can be used
5358 to extend and enhance the functionality of the compiler. This section of
5359 the GNAT reference manual describes these additional attributes.
5361 Note that any program using these attributes may not be portable to
5362 other compilers (although GNAT implements this set of attributes on all
5363 platforms). Therefore if portability to other compilers is an important
5364 consideration, you should minimize the use of these attributes.
5374 * Compiler_Version::
5376 * Default_Bit_Order::
5386 * Has_Access_Values::
5387 * Has_Discriminants::
5394 * Max_Interrupt_Priority::
5396 * Maximum_Alignment::
5401 * Passed_By_Reference::
5414 * Unconstrained_Array::
5415 * Universal_Literal_String::
5416 * Unrestricted_Access::
5424 @unnumberedsec Abort_Signal
5425 @findex Abort_Signal
5427 @code{Standard'Abort_Signal} (@code{Standard} is the only allowed
5428 prefix) provides the entity for the special exception used to signal
5429 task abort or asynchronous transfer of control. Normally this attribute
5430 should only be used in the tasking runtime (it is highly peculiar, and
5431 completely outside the normal semantics of Ada, for a user program to
5432 intercept the abort exception).
5435 @unnumberedsec Address_Size
5436 @cindex Size of @code{Address}
5437 @findex Address_Size
5439 @code{Standard'Address_Size} (@code{Standard} is the only allowed
5440 prefix) is a static constant giving the number of bits in an
5441 @code{Address}. It is the same value as System.Address'Size,
5442 but has the advantage of being static, while a direct
5443 reference to System.Address'Size is non-static because Address
5447 @unnumberedsec Asm_Input
5450 The @code{Asm_Input} attribute denotes a function that takes two
5451 parameters. The first is a string, the second is an expression of the
5452 type designated by the prefix. The first (string) argument is required
5453 to be a static expression, and is the constraint for the parameter,
5454 (e.g.@: what kind of register is required). The second argument is the
5455 value to be used as the input argument. The possible values for the
5456 constant are the same as those used in the RTL, and are dependent on
5457 the configuration file used to built the GCC back end.
5458 @ref{Machine Code Insertions}
5461 @unnumberedsec Asm_Output
5464 The @code{Asm_Output} attribute denotes a function that takes two
5465 parameters. The first is a string, the second is the name of a variable
5466 of the type designated by the attribute prefix. The first (string)
5467 argument is required to be a static expression and designates the
5468 constraint for the parameter (e.g.@: what kind of register is
5469 required). The second argument is the variable to be updated with the
5470 result. The possible values for constraint are the same as those used in
5471 the RTL, and are dependent on the configuration file used to build the
5472 GCC back end. If there are no output operands, then this argument may
5473 either be omitted, or explicitly given as @code{No_Output_Operands}.
5474 @ref{Machine Code Insertions}
5477 @unnumberedsec AST_Entry
5481 This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
5482 the name of an entry, it yields a value of the predefined type AST_Handler
5483 (declared in the predefined package System, as extended by the use of
5484 pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
5485 be called when an AST occurs. For further details, refer to the @cite{DEC Ada
5486 Language Reference Manual}, section 9.12a.
5491 @code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
5492 offset within the storage unit (byte) that contains the first bit of
5493 storage allocated for the object. The value of this attribute is of the
5494 type @code{Universal_Integer}, and is always a non-negative number not
5495 exceeding the value of @code{System.Storage_Unit}.
5497 For an object that is a variable or a constant allocated in a register,
5498 the value is zero. (The use of this attribute does not force the
5499 allocation of a variable to memory).
5501 For an object that is a formal parameter, this attribute applies
5502 to either the matching actual parameter or to a copy of the
5503 matching actual parameter.
5505 For an access object the value is zero. Note that
5506 @code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
5507 designated object. Similarly for a record component
5508 @code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
5509 @code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
5510 are subject to index checks.
5512 This attribute is designed to be compatible with the DEC Ada 83 definition
5513 and implementation of the @code{Bit} attribute.
5516 @unnumberedsec Bit_Position
5517 @findex Bit_Position
5519 @code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
5520 of the fields of the record type, yields the bit
5521 offset within the record contains the first bit of
5522 storage allocated for the object. The value of this attribute is of the
5523 type @code{Universal_Integer}. The value depends only on the field
5524 @var{C} and is independent of the alignment of
5525 the containing record @var{R}.
5527 @node Compiler_Version
5528 @unnumberedsec Compiler_Version
5529 @findex Compiler_Version
5531 @code{Standard'Compiler_Version} (@code{Standard} is the only allowed
5532 prefix) yields a static string identifying the version of the compiler
5533 being used to compile the unit containing the attribute reference. A
5534 typical result would be something like "GNAT Pro 6.3.0w (20090221)".
5537 @unnumberedsec Code_Address
5538 @findex Code_Address
5539 @cindex Subprogram address
5540 @cindex Address of subprogram code
5543 attribute may be applied to subprograms in Ada 95 and Ada 2005, but the
5544 intended effect seems to be to provide
5545 an address value which can be used to call the subprogram by means of
5546 an address clause as in the following example:
5548 @smallexample @c ada
5549 procedure K is @dots{}
5552 for L'Address use K'Address;
5553 pragma Import (Ada, L);
5557 A call to @code{L} is then expected to result in a call to @code{K}@.
5558 In Ada 83, where there were no access-to-subprogram values, this was
5559 a common work-around for getting the effect of an indirect call.
5560 GNAT implements the above use of @code{Address} and the technique
5561 illustrated by the example code works correctly.
5563 However, for some purposes, it is useful to have the address of the start
5564 of the generated code for the subprogram. On some architectures, this is
5565 not necessarily the same as the @code{Address} value described above.
5566 For example, the @code{Address} value may reference a subprogram
5567 descriptor rather than the subprogram itself.
5569 The @code{'Code_Address} attribute, which can only be applied to
5570 subprogram entities, always returns the address of the start of the
5571 generated code of the specified subprogram, which may or may not be
5572 the same value as is returned by the corresponding @code{'Address}
5575 @node Default_Bit_Order
5576 @unnumberedsec Default_Bit_Order
5578 @cindex Little endian
5579 @findex Default_Bit_Order
5581 @code{Standard'Default_Bit_Order} (@code{Standard} is the only
5582 permissible prefix), provides the value @code{System.Default_Bit_Order}
5583 as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
5584 @code{Low_Order_First}). This is used to construct the definition of
5585 @code{Default_Bit_Order} in package @code{System}.
5588 @unnumberedsec Elaborated
5591 The prefix of the @code{'Elaborated} attribute must be a unit name. The
5592 value is a Boolean which indicates whether or not the given unit has been
5593 elaborated. This attribute is primarily intended for internal use by the
5594 generated code for dynamic elaboration checking, but it can also be used
5595 in user programs. The value will always be True once elaboration of all
5596 units has been completed. An exception is for units which need no
5597 elaboration, the value is always False for such units.
5600 @unnumberedsec Elab_Body
5603 This attribute can only be applied to a program unit name. It returns
5604 the entity for the corresponding elaboration procedure for elaborating
5605 the body of the referenced unit. This is used in the main generated
5606 elaboration procedure by the binder and is not normally used in any
5607 other context. However, there may be specialized situations in which it
5608 is useful to be able to call this elaboration procedure from Ada code,
5609 e.g.@: if it is necessary to do selective re-elaboration to fix some
5613 @unnumberedsec Elab_Spec
5616 This attribute can only be applied to a program unit name. It returns
5617 the entity for the corresponding elaboration procedure for elaborating
5618 the spec of the referenced unit. This is used in the main
5619 generated elaboration procedure by the binder and is not normally used
5620 in any other context. However, there may be specialized situations in
5621 which it is useful to be able to call this elaboration procedure from
5622 Ada code, e.g.@: if it is necessary to do selective re-elaboration to fix
5627 @cindex Ada 83 attributes
5630 The @code{Emax} attribute is provided for compatibility with Ada 83. See
5631 the Ada 83 reference manual for an exact description of the semantics of
5635 @unnumberedsec Enabled
5638 The @code{Enabled} attribute allows an application program to check at compile
5639 time to see if the designated check is currently enabled. The prefix is a
5640 simple identifier, referencing any predefined check name (other than
5641 @code{All_Checks}) or a check name introduced by pragma Check_Name. If
5642 no argument is given for the attribute, the check is for the general state
5643 of the check, if an argument is given, then it is an entity name, and the
5644 check indicates whether an @code{Suppress} or @code{Unsuppress} has been
5645 given naming the entity (if not, then the argument is ignored).
5647 Note that instantiations inherit the check status at the point of the
5648 instantiation, so a useful idiom is to have a library package that
5649 introduces a check name with @code{pragma Check_Name}, and then contains
5650 generic packages or subprograms which use the @code{Enabled} attribute
5651 to see if the check is enabled. A user of this package can then issue
5652 a @code{pragma Suppress} or @code{pragma Unsuppress} before instantiating
5653 the package or subprogram, controlling whether the check will be present.
5656 @unnumberedsec Enum_Rep
5657 @cindex Representation of enums
5660 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5661 function with the following spec:
5663 @smallexample @c ada
5664 function @var{S}'Enum_Rep (Arg : @var{S}'Base)
5665 return @i{Universal_Integer};
5669 It is also allowable to apply @code{Enum_Rep} directly to an object of an
5670 enumeration type or to a non-overloaded enumeration
5671 literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
5672 @code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
5673 enumeration literal or object.
5675 The function returns the representation value for the given enumeration
5676 value. This will be equal to value of the @code{Pos} attribute in the
5677 absence of an enumeration representation clause. This is a static
5678 attribute (i.e.@: the result is static if the argument is static).
5680 @code{@var{S}'Enum_Rep} can also be used with integer types and objects,
5681 in which case it simply returns the integer value. The reason for this
5682 is to allow it to be used for @code{(<>)} discrete formal arguments in
5683 a generic unit that can be instantiated with either enumeration types
5684 or integer types. Note that if @code{Enum_Rep} is used on a modular
5685 type whose upper bound exceeds the upper bound of the largest signed
5686 integer type, and the argument is a variable, so that the universal
5687 integer calculation is done at run time, then the call to @code{Enum_Rep}
5688 may raise @code{Constraint_Error}.
5691 @unnumberedsec Enum_Val
5692 @cindex Representation of enums
5695 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5696 function with the following spec:
5698 @smallexample @c ada
5699 function @var{S}'Enum_Rep (Arg : @i{Universal_Integer)
5700 return @var{S}'Base};
5704 The function returns the enumeration value whose representation matches the
5705 argument, or raises Constraint_Error if no enumeration literal of the type
5706 has the matching value.
5707 This will be equal to value of the @code{Val} attribute in the
5708 absence of an enumeration representation clause. This is a static
5709 attribute (i.e.@: the result is static if the argument is static).
5712 @unnumberedsec Epsilon
5713 @cindex Ada 83 attributes
5716 The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
5717 the Ada 83 reference manual for an exact description of the semantics of
5721 @unnumberedsec Fixed_Value
5724 For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
5725 function with the following specification:
5727 @smallexample @c ada
5728 function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
5733 The value returned is the fixed-point value @var{V} such that
5735 @smallexample @c ada
5736 @var{V} = Arg * @var{S}'Small
5740 The effect is thus similar to first converting the argument to the
5741 integer type used to represent @var{S}, and then doing an unchecked
5742 conversion to the fixed-point type. The difference is
5743 that there are full range checks, to ensure that the result is in range.
5744 This attribute is primarily intended for use in implementation of the
5745 input-output functions for fixed-point values.
5747 @node Has_Access_Values
5748 @unnumberedsec Has_Access_Values
5749 @cindex Access values, testing for
5750 @findex Has_Access_Values
5752 The prefix of the @code{Has_Access_Values} attribute is a type. The result
5753 is a Boolean value which is True if the is an access type, or is a composite
5754 type with a component (at any nesting depth) that is an access type, and is
5756 The intended use of this attribute is in conjunction with generic
5757 definitions. If the attribute is applied to a generic private type, it
5758 indicates whether or not the corresponding actual type has access values.
5760 @node Has_Discriminants
5761 @unnumberedsec Has_Discriminants
5762 @cindex Discriminants, testing for
5763 @findex Has_Discriminants
5765 The prefix of the @code{Has_Discriminants} attribute is a type. The result
5766 is a Boolean value which is True if the type has discriminants, and False
5767 otherwise. The intended use of this attribute is in conjunction with generic
5768 definitions. If the attribute is applied to a generic private type, it
5769 indicates whether or not the corresponding actual type has discriminants.
5775 The @code{Img} attribute differs from @code{Image} in that it may be
5776 applied to objects as well as types, in which case it gives the
5777 @code{Image} for the subtype of the object. This is convenient for
5780 @smallexample @c ada
5781 Put_Line ("X = " & X'Img);
5785 has the same meaning as the more verbose:
5787 @smallexample @c ada
5788 Put_Line ("X = " & @var{T}'Image (X));
5792 where @var{T} is the (sub)type of the object @code{X}.
5795 @unnumberedsec Integer_Value
5796 @findex Integer_Value
5798 For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
5799 function with the following spec:
5801 @smallexample @c ada
5802 function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
5807 The value returned is the integer value @var{V}, such that
5809 @smallexample @c ada
5810 Arg = @var{V} * @var{T}'Small
5814 where @var{T} is the type of @code{Arg}.
5815 The effect is thus similar to first doing an unchecked conversion from
5816 the fixed-point type to its corresponding implementation type, and then
5817 converting the result to the target integer type. The difference is
5818 that there are full range checks, to ensure that the result is in range.
5819 This attribute is primarily intended for use in implementation of the
5820 standard input-output functions for fixed-point values.
5823 @unnumberedsec Invalid_Value
5824 @findex Invalid_Value
5826 For every scalar type S, S'Invalid_Value returns an undefined value of the
5827 type. If possible this value is an invalid representation for the type. The
5828 value returned is identical to the value used to initialize an otherwise
5829 uninitialized value of the type if pragma Initialize_Scalars is used,
5830 including the ability to modify the value with the binder -Sxx flag and
5831 relevant environment variables at run time.
5834 @unnumberedsec Large
5835 @cindex Ada 83 attributes
5838 The @code{Large} attribute is provided for compatibility with Ada 83. See
5839 the Ada 83 reference manual for an exact description of the semantics of
5843 @unnumberedsec Machine_Size
5844 @findex Machine_Size
5846 This attribute is identical to the @code{Object_Size} attribute. It is
5847 provided for compatibility with the DEC Ada 83 attribute of this name.
5850 @unnumberedsec Mantissa
5851 @cindex Ada 83 attributes
5854 The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
5855 the Ada 83 reference manual for an exact description of the semantics of
5858 @node Max_Interrupt_Priority
5859 @unnumberedsec Max_Interrupt_Priority
5860 @cindex Interrupt priority, maximum
5861 @findex Max_Interrupt_Priority
5863 @code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
5864 permissible prefix), provides the same value as
5865 @code{System.Max_Interrupt_Priority}.
5868 @unnumberedsec Max_Priority
5869 @cindex Priority, maximum
5870 @findex Max_Priority
5872 @code{Standard'Max_Priority} (@code{Standard} is the only permissible
5873 prefix) provides the same value as @code{System.Max_Priority}.
5875 @node Maximum_Alignment
5876 @unnumberedsec Maximum_Alignment
5877 @cindex Alignment, maximum
5878 @findex Maximum_Alignment
5880 @code{Standard'Maximum_Alignment} (@code{Standard} is the only
5881 permissible prefix) provides the maximum useful alignment value for the
5882 target. This is a static value that can be used to specify the alignment
5883 for an object, guaranteeing that it is properly aligned in all
5886 @node Mechanism_Code
5887 @unnumberedsec Mechanism_Code
5888 @cindex Return values, passing mechanism
5889 @cindex Parameters, passing mechanism
5890 @findex Mechanism_Code
5892 @code{@var{function}'Mechanism_Code} yields an integer code for the
5893 mechanism used for the result of function, and
5894 @code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
5895 used for formal parameter number @var{n} (a static integer value with 1
5896 meaning the first parameter) of @var{subprogram}. The code returned is:
5904 by descriptor (default descriptor class)
5906 by descriptor (UBS: unaligned bit string)
5908 by descriptor (UBSB: aligned bit string with arbitrary bounds)
5910 by descriptor (UBA: unaligned bit array)
5912 by descriptor (S: string, also scalar access type parameter)
5914 by descriptor (SB: string with arbitrary bounds)
5916 by descriptor (A: contiguous array)
5918 by descriptor (NCA: non-contiguous array)
5922 Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
5925 @node Null_Parameter
5926 @unnumberedsec Null_Parameter
5927 @cindex Zero address, passing
5928 @findex Null_Parameter
5930 A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
5931 type or subtype @var{T} allocated at machine address zero. The attribute
5932 is allowed only as the default expression of a formal parameter, or as
5933 an actual expression of a subprogram call. In either case, the
5934 subprogram must be imported.
5936 The identity of the object is represented by the address zero in the
5937 argument list, independent of the passing mechanism (explicit or
5940 This capability is needed to specify that a zero address should be
5941 passed for a record or other composite object passed by reference.
5942 There is no way of indicating this without the @code{Null_Parameter}
5946 @unnumberedsec Object_Size
5947 @cindex Size, used for objects
5950 The size of an object is not necessarily the same as the size of the type
5951 of an object. This is because by default object sizes are increased to be
5952 a multiple of the alignment of the object. For example,
5953 @code{Natural'Size} is
5954 31, but by default objects of type @code{Natural} will have a size of 32 bits.
5955 Similarly, a record containing an integer and a character:
5957 @smallexample @c ada
5965 will have a size of 40 (that is @code{Rec'Size} will be 40. The
5966 alignment will be 4, because of the
5967 integer field, and so the default size of record objects for this type
5968 will be 64 (8 bytes).
5972 @cindex Capturing Old values
5973 @cindex Postconditions
5975 The attribute Prefix'Old can be used within a
5976 subprogram to refer to the value of the prefix on entry. So for
5977 example if you have an argument of a record type X called Arg1,
5978 you can refer to Arg1.Field'Old which yields the value of
5979 Arg1.Field on entry. The implementation simply involves generating
5980 an object declaration which captures the value on entry. Any
5981 prefix is allowed except one of a limited type (since limited
5982 types cannot be copied to capture their values) or a local variable
5983 (since it does not exist at subprogram entry time).
5985 The following example shows the use of 'Old to implement
5986 a test of a postcondition:
5988 @smallexample @c ada
5999 package body Old_Pkg is
6000 Count : Natural := 0;
6004 ... code manipulating the value of Count
6006 pragma Assert (Count = Count'Old + 1);
6012 Note that it is allowed to apply 'Old to a constant entity, but this will
6013 result in a warning, since the old and new values will always be the same.
6015 @node Passed_By_Reference
6016 @unnumberedsec Passed_By_Reference
6017 @cindex Parameters, when passed by reference
6018 @findex Passed_By_Reference
6020 @code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
6021 a value of type @code{Boolean} value that is @code{True} if the type is
6022 normally passed by reference and @code{False} if the type is normally
6023 passed by copy in calls. For scalar types, the result is always @code{False}
6024 and is static. For non-scalar types, the result is non-static.
6027 @unnumberedsec Pool_Address
6028 @cindex Parameters, when passed by reference
6029 @findex Pool_Address
6031 @code{@var{X}'Pool_Address} for any object @var{X} returns the address
6032 of X within its storage pool. This is the same as
6033 @code{@var{X}'Address}, except that for an unconstrained array whose
6034 bounds are allocated just before the first component,
6035 @code{@var{X}'Pool_Address} returns the address of those bounds,
6036 whereas @code{@var{X}'Address} returns the address of the first
6039 Here, we are interpreting ``storage pool'' broadly to mean ``wherever
6040 the object is allocated'', which could be a user-defined storage pool,
6041 the global heap, on the stack, or in a static memory area. For an
6042 object created by @code{new}, @code{@var{Ptr.all}'Pool_Address} is
6043 what is passed to @code{Allocate} and returned from @code{Deallocate}.
6046 @unnumberedsec Range_Length
6047 @findex Range_Length
6049 @code{@var{type}'Range_Length} for any discrete type @var{type} yields
6050 the number of values represented by the subtype (zero for a null
6051 range). The result is static for static subtypes. @code{Range_Length}
6052 applied to the index subtype of a one dimensional array always gives the
6053 same result as @code{Range} applied to the array itself.
6056 @unnumberedsec Safe_Emax
6057 @cindex Ada 83 attributes
6060 The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
6061 the Ada 83 reference manual for an exact description of the semantics of
6065 @unnumberedsec Safe_Large
6066 @cindex Ada 83 attributes
6069 The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
6070 the Ada 83 reference manual for an exact description of the semantics of
6074 @unnumberedsec Small
6075 @cindex Ada 83 attributes
6078 The @code{Small} attribute is defined in Ada 95 (and Ada 2005) only for
6080 GNAT also allows this attribute to be applied to floating-point types
6081 for compatibility with Ada 83. See
6082 the Ada 83 reference manual for an exact description of the semantics of
6083 this attribute when applied to floating-point types.
6086 @unnumberedsec Storage_Unit
6087 @findex Storage_Unit
6089 @code{Standard'Storage_Unit} (@code{Standard} is the only permissible
6090 prefix) provides the same value as @code{System.Storage_Unit}.
6093 @unnumberedsec Stub_Type
6096 The GNAT implementation of remote access-to-classwide types is
6097 organized as described in AARM section E.4 (20.t): a value of an RACW type
6098 (designating a remote object) is represented as a normal access
6099 value, pointing to a "stub" object which in turn contains the
6100 necessary information to contact the designated remote object. A
6101 call on any dispatching operation of such a stub object does the
6102 remote call, if necessary, using the information in the stub object
6103 to locate the target partition, etc.
6105 For a prefix @code{T} that denotes a remote access-to-classwide type,
6106 @code{T'Stub_Type} denotes the type of the corresponding stub objects.
6108 By construction, the layout of @code{T'Stub_Type} is identical to that of
6109 type @code{RACW_Stub_Type} declared in the internal implementation-defined
6110 unit @code{System.Partition_Interface}. Use of this attribute will create
6111 an implicit dependency on this unit.
6114 @unnumberedsec Target_Name
6117 @code{Standard'Target_Name} (@code{Standard} is the only permissible
6118 prefix) provides a static string value that identifies the target
6119 for the current compilation. For GCC implementations, this is the
6120 standard gcc target name without the terminating slash (for
6121 example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
6127 @code{Standard'Tick} (@code{Standard} is the only permissible prefix)
6128 provides the same value as @code{System.Tick},
6131 @unnumberedsec To_Address
6134 The @code{System'To_Address}
6135 (@code{System} is the only permissible prefix)
6136 denotes a function identical to
6137 @code{System.Storage_Elements.To_Address} except that
6138 it is a static attribute. This means that if its argument is
6139 a static expression, then the result of the attribute is a
6140 static expression. The result is that such an expression can be
6141 used in contexts (e.g.@: preelaborable packages) which require a
6142 static expression and where the function call could not be used
6143 (since the function call is always non-static, even if its
6144 argument is static).
6147 @unnumberedsec Type_Class
6150 @code{@var{type}'Type_Class} for any type or subtype @var{type} yields
6151 the value of the type class for the full type of @var{type}. If
6152 @var{type} is a generic formal type, the value is the value for the
6153 corresponding actual subtype. The value of this attribute is of type
6154 @code{System.Aux_DEC.Type_Class}, which has the following definition:
6156 @smallexample @c ada
6158 (Type_Class_Enumeration,
6160 Type_Class_Fixed_Point,
6161 Type_Class_Floating_Point,
6166 Type_Class_Address);
6170 Protected types yield the value @code{Type_Class_Task}, which thus
6171 applies to all concurrent types. This attribute is designed to
6172 be compatible with the DEC Ada 83 attribute of the same name.
6175 @unnumberedsec UET_Address
6178 The @code{UET_Address} attribute can only be used for a prefix which
6179 denotes a library package. It yields the address of the unit exception
6180 table when zero cost exception handling is used. This attribute is
6181 intended only for use within the GNAT implementation. See the unit
6182 @code{Ada.Exceptions} in files @file{a-except.ads} and @file{a-except.adb}
6183 for details on how this attribute is used in the implementation.
6185 @node Unconstrained_Array
6186 @unnumberedsec Unconstrained_Array
6187 @findex Unconstrained_Array
6189 The @code{Unconstrained_Array} attribute can be used with a prefix that
6190 denotes any type or subtype. It is a static attribute that yields
6191 @code{True} if the prefix designates an unconstrained array,
6192 and @code{False} otherwise. In a generic instance, the result is
6193 still static, and yields the result of applying this test to the
6196 @node Universal_Literal_String
6197 @unnumberedsec Universal_Literal_String
6198 @cindex Named numbers, representation of
6199 @findex Universal_Literal_String
6201 The prefix of @code{Universal_Literal_String} must be a named
6202 number. The static result is the string consisting of the characters of
6203 the number as defined in the original source. This allows the user
6204 program to access the actual text of named numbers without intermediate
6205 conversions and without the need to enclose the strings in quotes (which
6206 would preclude their use as numbers). This is used internally for the
6207 construction of values of the floating-point attributes from the file
6208 @file{ttypef.ads}, but may also be used by user programs.
6210 For example, the following program prints the first 50 digits of pi:
6212 @smallexample @c ada
6213 with Text_IO; use Text_IO;
6217 Put (Ada.Numerics.Pi'Universal_Literal_String);
6221 @node Unrestricted_Access
6222 @unnumberedsec Unrestricted_Access
6223 @cindex @code{Access}, unrestricted
6224 @findex Unrestricted_Access
6226 The @code{Unrestricted_Access} attribute is similar to @code{Access}
6227 except that all accessibility and aliased view checks are omitted. This
6228 is a user-beware attribute. It is similar to
6229 @code{Address}, for which it is a desirable replacement where the value
6230 desired is an access type. In other words, its effect is identical to
6231 first applying the @code{Address} attribute and then doing an unchecked
6232 conversion to a desired access type. In GNAT, but not necessarily in
6233 other implementations, the use of static chains for inner level
6234 subprograms means that @code{Unrestricted_Access} applied to a
6235 subprogram yields a value that can be called as long as the subprogram
6236 is in scope (normal Ada accessibility rules restrict this usage).
6238 It is possible to use @code{Unrestricted_Access} for any type, but care
6239 must be exercised if it is used to create pointers to unconstrained
6240 objects. In this case, the resulting pointer has the same scope as the
6241 context of the attribute, and may not be returned to some enclosing
6242 scope. For instance, a function cannot use @code{Unrestricted_Access}
6243 to create a unconstrained pointer and then return that value to the
6247 @unnumberedsec VADS_Size
6248 @cindex @code{Size}, VADS compatibility
6251 The @code{'VADS_Size} attribute is intended to make it easier to port
6252 legacy code which relies on the semantics of @code{'Size} as implemented
6253 by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
6254 same semantic interpretation. In particular, @code{'VADS_Size} applied
6255 to a predefined or other primitive type with no Size clause yields the
6256 Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
6257 typical machines). In addition @code{'VADS_Size} applied to an object
6258 gives the result that would be obtained by applying the attribute to
6259 the corresponding type.
6262 @unnumberedsec Value_Size
6263 @cindex @code{Size}, setting for not-first subtype
6265 @code{@var{type}'Value_Size} is the number of bits required to represent
6266 a value of the given subtype. It is the same as @code{@var{type}'Size},
6267 but, unlike @code{Size}, may be set for non-first subtypes.
6270 @unnumberedsec Wchar_T_Size
6271 @findex Wchar_T_Size
6272 @code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
6273 prefix) provides the size in bits of the C @code{wchar_t} type
6274 primarily for constructing the definition of this type in
6275 package @code{Interfaces.C}.
6278 @unnumberedsec Word_Size
6280 @code{Standard'Word_Size} (@code{Standard} is the only permissible
6281 prefix) provides the value @code{System.Word_Size}.
6283 @c ------------------------
6284 @node Implementation Advice
6285 @chapter Implementation Advice
6287 The main text of the Ada Reference Manual describes the required
6288 behavior of all Ada compilers, and the GNAT compiler conforms to
6291 In addition, there are sections throughout the Ada Reference Manual headed
6292 by the phrase ``Implementation advice''. These sections are not normative,
6293 i.e., they do not specify requirements that all compilers must
6294 follow. Rather they provide advice on generally desirable behavior. You
6295 may wonder why they are not requirements. The most typical answer is
6296 that they describe behavior that seems generally desirable, but cannot
6297 be provided on all systems, or which may be undesirable on some systems.
6299 As far as practical, GNAT follows the implementation advice sections in
6300 the Ada Reference Manual. This chapter contains a table giving the
6301 reference manual section number, paragraph number and several keywords
6302 for each advice. Each entry consists of the text of the advice followed
6303 by the GNAT interpretation of this advice. Most often, this simply says
6304 ``followed'', which means that GNAT follows the advice. However, in a
6305 number of cases, GNAT deliberately deviates from this advice, in which
6306 case the text describes what GNAT does and why.
6308 @cindex Error detection
6309 @unnumberedsec 1.1.3(20): Error Detection
6312 If an implementation detects the use of an unsupported Specialized Needs
6313 Annex feature at run time, it should raise @code{Program_Error} if
6316 Not relevant. All specialized needs annex features are either supported,
6317 or diagnosed at compile time.
6320 @unnumberedsec 1.1.3(31): Child Units
6323 If an implementation wishes to provide implementation-defined
6324 extensions to the functionality of a language-defined library unit, it
6325 should normally do so by adding children to the library unit.
6329 @cindex Bounded errors
6330 @unnumberedsec 1.1.5(12): Bounded Errors
6333 If an implementation detects a bounded error or erroneous
6334 execution, it should raise @code{Program_Error}.
6336 Followed in all cases in which the implementation detects a bounded
6337 error or erroneous execution. Not all such situations are detected at
6341 @unnumberedsec 2.8(16): Pragmas
6344 Normally, implementation-defined pragmas should have no semantic effect
6345 for error-free programs; that is, if the implementation-defined pragmas
6346 are removed from a working program, the program should still be legal,
6347 and should still have the same semantics.
6349 The following implementation defined pragmas are exceptions to this
6361 @item CPP_Constructor
6365 @item Interface_Name
6367 @item Machine_Attribute
6369 @item Unimplemented_Unit
6371 @item Unchecked_Union
6376 In each of the above cases, it is essential to the purpose of the pragma
6377 that this advice not be followed. For details see the separate section
6378 on implementation defined pragmas.
6380 @unnumberedsec 2.8(17-19): Pragmas
6383 Normally, an implementation should not define pragmas that can
6384 make an illegal program legal, except as follows:
6388 A pragma used to complete a declaration, such as a pragma @code{Import};
6392 A pragma used to configure the environment by adding, removing, or
6393 replacing @code{library_items}.
6395 See response to paragraph 16 of this same section.
6397 @cindex Character Sets
6398 @cindex Alternative Character Sets
6399 @unnumberedsec 3.5.2(5): Alternative Character Sets
6402 If an implementation supports a mode with alternative interpretations
6403 for @code{Character} and @code{Wide_Character}, the set of graphic
6404 characters of @code{Character} should nevertheless remain a proper
6405 subset of the set of graphic characters of @code{Wide_Character}. Any
6406 character set ``localizations'' should be reflected in the results of
6407 the subprograms defined in the language-defined package
6408 @code{Characters.Handling} (see A.3) available in such a mode. In a mode with
6409 an alternative interpretation of @code{Character}, the implementation should
6410 also support a corresponding change in what is a legal
6411 @code{identifier_letter}.
6413 Not all wide character modes follow this advice, in particular the JIS
6414 and IEC modes reflect standard usage in Japan, and in these encoding,
6415 the upper half of the Latin-1 set is not part of the wide-character
6416 subset, since the most significant bit is used for wide character
6417 encoding. However, this only applies to the external forms. Internally
6418 there is no such restriction.
6420 @cindex Integer types
6421 @unnumberedsec 3.5.4(28): Integer Types
6425 An implementation should support @code{Long_Integer} in addition to
6426 @code{Integer} if the target machine supports 32-bit (or longer)
6427 arithmetic. No other named integer subtypes are recommended for package
6428 @code{Standard}. Instead, appropriate named integer subtypes should be
6429 provided in the library package @code{Interfaces} (see B.2).
6431 @code{Long_Integer} is supported. Other standard integer types are supported
6432 so this advice is not fully followed. These types
6433 are supported for convenient interface to C, and so that all hardware
6434 types of the machine are easily available.
6435 @unnumberedsec 3.5.4(29): Integer Types
6439 An implementation for a two's complement machine should support
6440 modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
6441 implementation should support a non-binary modules up to @code{Integer'Last}.
6445 @cindex Enumeration values
6446 @unnumberedsec 3.5.5(8): Enumeration Values
6449 For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
6450 subtype, if the value of the operand does not correspond to the internal
6451 code for any enumeration literal of its type (perhaps due to an
6452 un-initialized variable), then the implementation should raise
6453 @code{Program_Error}. This is particularly important for enumeration
6454 types with noncontiguous internal codes specified by an
6455 enumeration_representation_clause.
6460 @unnumberedsec 3.5.7(17): Float Types
6463 An implementation should support @code{Long_Float} in addition to
6464 @code{Float} if the target machine supports 11 or more digits of
6465 precision. No other named floating point subtypes are recommended for
6466 package @code{Standard}. Instead, appropriate named floating point subtypes
6467 should be provided in the library package @code{Interfaces} (see B.2).
6469 @code{Short_Float} and @code{Long_Long_Float} are also provided. The
6470 former provides improved compatibility with other implementations
6471 supporting this type. The latter corresponds to the highest precision
6472 floating-point type supported by the hardware. On most machines, this
6473 will be the same as @code{Long_Float}, but on some machines, it will
6474 correspond to the IEEE extended form. The notable case is all ia32
6475 (x86) implementations, where @code{Long_Long_Float} corresponds to
6476 the 80-bit extended precision format supported in hardware on this
6477 processor. Note that the 128-bit format on SPARC is not supported,
6478 since this is a software rather than a hardware format.
6480 @cindex Multidimensional arrays
6481 @cindex Arrays, multidimensional
6482 @unnumberedsec 3.6.2(11): Multidimensional Arrays
6485 An implementation should normally represent multidimensional arrays in
6486 row-major order, consistent with the notation used for multidimensional
6487 array aggregates (see 4.3.3). However, if a pragma @code{Convention}
6488 (@code{Fortran}, @dots{}) applies to a multidimensional array type, then
6489 column-major order should be used instead (see B.5, ``Interfacing with
6494 @findex Duration'Small
6495 @unnumberedsec 9.6(30-31): Duration'Small
6498 Whenever possible in an implementation, the value of @code{Duration'Small}
6499 should be no greater than 100 microseconds.
6501 Followed. (@code{Duration'Small} = 10**(@minus{}9)).
6505 The time base for @code{delay_relative_statements} should be monotonic;
6506 it need not be the same time base as used for @code{Calendar.Clock}.
6510 @unnumberedsec 10.2.1(12): Consistent Representation
6513 In an implementation, a type declared in a pre-elaborated package should
6514 have the same representation in every elaboration of a given version of
6515 the package, whether the elaborations occur in distinct executions of
6516 the same program, or in executions of distinct programs or partitions
6517 that include the given version.
6519 Followed, except in the case of tagged types. Tagged types involve
6520 implicit pointers to a local copy of a dispatch table, and these pointers
6521 have representations which thus depend on a particular elaboration of the
6522 package. It is not easy to see how it would be possible to follow this
6523 advice without severely impacting efficiency of execution.
6525 @cindex Exception information
6526 @unnumberedsec 11.4.1(19): Exception Information
6529 @code{Exception_Message} by default and @code{Exception_Information}
6530 should produce information useful for
6531 debugging. @code{Exception_Message} should be short, about one
6532 line. @code{Exception_Information} can be long. @code{Exception_Message}
6533 should not include the
6534 @code{Exception_Name}. @code{Exception_Information} should include both
6535 the @code{Exception_Name} and the @code{Exception_Message}.
6537 Followed. For each exception that doesn't have a specified
6538 @code{Exception_Message}, the compiler generates one containing the location
6539 of the raise statement. This location has the form ``file:line'', where
6540 file is the short file name (without path information) and line is the line
6541 number in the file. Note that in the case of the Zero Cost Exception
6542 mechanism, these messages become redundant with the Exception_Information that
6543 contains a full backtrace of the calling sequence, so they are disabled.
6544 To disable explicitly the generation of the source location message, use the
6545 Pragma @code{Discard_Names}.
6547 @cindex Suppression of checks
6548 @cindex Checks, suppression of
6549 @unnumberedsec 11.5(28): Suppression of Checks
6552 The implementation should minimize the code executed for checks that
6553 have been suppressed.
6557 @cindex Representation clauses
6558 @unnumberedsec 13.1 (21-24): Representation Clauses
6561 The recommended level of support for all representation items is
6562 qualified as follows:
6566 An implementation need not support representation items containing
6567 non-static expressions, except that an implementation should support a
6568 representation item for a given entity if each non-static expression in
6569 the representation item is a name that statically denotes a constant
6570 declared before the entity.
6572 Followed. In fact, GNAT goes beyond the recommended level of support
6573 by allowing nonstatic expressions in some representation clauses even
6574 without the need to declare constants initialized with the values of
6578 @smallexample @c ada
6581 for Y'Address use X'Address;>>
6587 An implementation need not support a specification for the @code{Size}
6588 for a given composite subtype, nor the size or storage place for an
6589 object (including a component) of a given composite subtype, unless the
6590 constraints on the subtype and its composite subcomponents (if any) are
6591 all static constraints.
6593 Followed. Size Clauses are not permitted on non-static components, as
6598 An aliased component, or a component whose type is by-reference, should
6599 always be allocated at an addressable location.
6603 @cindex Packed types
6604 @unnumberedsec 13.2(6-8): Packed Types
6607 If a type is packed, then the implementation should try to minimize
6608 storage allocated to objects of the type, possibly at the expense of
6609 speed of accessing components, subject to reasonable complexity in
6610 addressing calculations.
6614 The recommended level of support pragma @code{Pack} is:
6616 For a packed record type, the components should be packed as tightly as
6617 possible subject to the Sizes of the component subtypes, and subject to
6618 any @code{record_representation_clause} that applies to the type; the
6619 implementation may, but need not, reorder components or cross aligned
6620 word boundaries to improve the packing. A component whose @code{Size} is
6621 greater than the word size may be allocated an integral number of words.
6623 Followed. Tight packing of arrays is supported for all component sizes
6624 up to 64-bits. If the array component size is 1 (that is to say, if
6625 the component is a boolean type or an enumeration type with two values)
6626 then values of the type are implicitly initialized to zero. This
6627 happens both for objects of the packed type, and for objects that have a
6628 subcomponent of the packed type.
6632 An implementation should support Address clauses for imported
6636 @cindex @code{Address} clauses
6637 @unnumberedsec 13.3(14-19): Address Clauses
6641 For an array @var{X}, @code{@var{X}'Address} should point at the first
6642 component of the array, and not at the array bounds.
6648 The recommended level of support for the @code{Address} attribute is:
6650 @code{@var{X}'Address} should produce a useful result if @var{X} is an
6651 object that is aliased or of a by-reference type, or is an entity whose
6652 @code{Address} has been specified.
6654 Followed. A valid address will be produced even if none of those
6655 conditions have been met. If necessary, the object is forced into
6656 memory to ensure the address is valid.
6660 An implementation should support @code{Address} clauses for imported
6667 Objects (including subcomponents) that are aliased or of a by-reference
6668 type should be allocated on storage element boundaries.
6674 If the @code{Address} of an object is specified, or it is imported or exported,
6675 then the implementation should not perform optimizations based on
6676 assumptions of no aliases.
6680 @cindex @code{Alignment} clauses
6681 @unnumberedsec 13.3(29-35): Alignment Clauses
6684 The recommended level of support for the @code{Alignment} attribute for
6687 An implementation should support specified Alignments that are factors
6688 and multiples of the number of storage elements per word, subject to the
6695 An implementation need not support specified @code{Alignment}s for
6696 combinations of @code{Size}s and @code{Alignment}s that cannot be easily
6697 loaded and stored by available machine instructions.
6703 An implementation need not support specified @code{Alignment}s that are
6704 greater than the maximum @code{Alignment} the implementation ever returns by
6711 The recommended level of support for the @code{Alignment} attribute for
6714 Same as above, for subtypes, but in addition:
6720 For stand-alone library-level objects of statically constrained
6721 subtypes, the implementation should support all @code{Alignment}s
6722 supported by the target linker. For example, page alignment is likely to
6723 be supported for such objects, but not for subtypes.
6727 @cindex @code{Size} clauses
6728 @unnumberedsec 13.3(42-43): Size Clauses
6731 The recommended level of support for the @code{Size} attribute of
6734 A @code{Size} clause should be supported for an object if the specified
6735 @code{Size} is at least as large as its subtype's @code{Size}, and
6736 corresponds to a size in storage elements that is a multiple of the
6737 object's @code{Alignment} (if the @code{Alignment} is nonzero).
6741 @unnumberedsec 13.3(50-56): Size Clauses
6744 If the @code{Size} of a subtype is specified, and allows for efficient
6745 independent addressability (see 9.10) on the target architecture, then
6746 the @code{Size} of the following objects of the subtype should equal the
6747 @code{Size} of the subtype:
6749 Aliased objects (including components).
6755 @code{Size} clause on a composite subtype should not affect the
6756 internal layout of components.
6758 Followed. But note that this can be overridden by use of the implementation
6759 pragma Implicit_Packing in the case of packed arrays.
6763 The recommended level of support for the @code{Size} attribute of subtypes is:
6767 The @code{Size} (if not specified) of a static discrete or fixed point
6768 subtype should be the number of bits needed to represent each value
6769 belonging to the subtype using an unbiased representation, leaving space
6770 for a sign bit only if the subtype contains negative values. If such a
6771 subtype is a first subtype, then an implementation should support a
6772 specified @code{Size} for it that reflects this representation.
6778 For a subtype implemented with levels of indirection, the @code{Size}
6779 should include the size of the pointers, but not the size of what they
6784 @cindex @code{Component_Size} clauses
6785 @unnumberedsec 13.3(71-73): Component Size Clauses
6788 The recommended level of support for the @code{Component_Size}
6793 An implementation need not support specified @code{Component_Sizes} that are
6794 less than the @code{Size} of the component subtype.
6800 An implementation should support specified @code{Component_Size}s that
6801 are factors and multiples of the word size. For such
6802 @code{Component_Size}s, the array should contain no gaps between
6803 components. For other @code{Component_Size}s (if supported), the array
6804 should contain no gaps between components when packing is also
6805 specified; the implementation should forbid this combination in cases
6806 where it cannot support a no-gaps representation.
6810 @cindex Enumeration representation clauses
6811 @cindex Representation clauses, enumeration
6812 @unnumberedsec 13.4(9-10): Enumeration Representation Clauses
6815 The recommended level of support for enumeration representation clauses
6818 An implementation need not support enumeration representation clauses
6819 for boolean types, but should at minimum support the internal codes in
6820 the range @code{System.Min_Int.System.Max_Int}.
6824 @cindex Record representation clauses
6825 @cindex Representation clauses, records
6826 @unnumberedsec 13.5.1(17-22): Record Representation Clauses
6829 The recommended level of support for
6830 @*@code{record_representation_clauses} is:
6832 An implementation should support storage places that can be extracted
6833 with a load, mask, shift sequence of machine code, and set with a load,
6834 shift, mask, store sequence, given the available machine instructions
6841 A storage place should be supported if its size is equal to the
6842 @code{Size} of the component subtype, and it starts and ends on a
6843 boundary that obeys the @code{Alignment} of the component subtype.
6849 If the default bit ordering applies to the declaration of a given type,
6850 then for a component whose subtype's @code{Size} is less than the word
6851 size, any storage place that does not cross an aligned word boundary
6852 should be supported.
6858 An implementation may reserve a storage place for the tag field of a
6859 tagged type, and disallow other components from overlapping that place.
6861 Followed. The storage place for the tag field is the beginning of the tagged
6862 record, and its size is Address'Size. GNAT will reject an explicit component
6863 clause for the tag field.
6867 An implementation need not support a @code{component_clause} for a
6868 component of an extension part if the storage place is not after the
6869 storage places of all components of the parent type, whether or not
6870 those storage places had been specified.
6872 Followed. The above advice on record representation clauses is followed,
6873 and all mentioned features are implemented.
6875 @cindex Storage place attributes
6876 @unnumberedsec 13.5.2(5): Storage Place Attributes
6879 If a component is represented using some form of pointer (such as an
6880 offset) to the actual data of the component, and this data is contiguous
6881 with the rest of the object, then the storage place attributes should
6882 reflect the place of the actual data, not the pointer. If a component is
6883 allocated discontinuously from the rest of the object, then a warning
6884 should be generated upon reference to one of its storage place
6887 Followed. There are no such components in GNAT@.
6889 @cindex Bit ordering
6890 @unnumberedsec 13.5.3(7-8): Bit Ordering
6893 The recommended level of support for the non-default bit ordering is:
6897 If @code{Word_Size} = @code{Storage_Unit}, then the implementation
6898 should support the non-default bit ordering in addition to the default
6901 Followed. Word size does not equal storage size in this implementation.
6902 Thus non-default bit ordering is not supported.
6904 @cindex @code{Address}, as private type
6905 @unnumberedsec 13.7(37): Address as Private
6908 @code{Address} should be of a private type.
6912 @cindex Operations, on @code{Address}
6913 @cindex @code{Address}, operations of
6914 @unnumberedsec 13.7.1(16): Address Operations
6917 Operations in @code{System} and its children should reflect the target
6918 environment semantics as closely as is reasonable. For example, on most
6919 machines, it makes sense for address arithmetic to ``wrap around''.
6920 Operations that do not make sense should raise @code{Program_Error}.
6922 Followed. Address arithmetic is modular arithmetic that wraps around. No
6923 operation raises @code{Program_Error}, since all operations make sense.
6925 @cindex Unchecked conversion
6926 @unnumberedsec 13.9(14-17): Unchecked Conversion
6929 The @code{Size} of an array object should not include its bounds; hence,
6930 the bounds should not be part of the converted data.
6936 The implementation should not generate unnecessary run-time checks to
6937 ensure that the representation of @var{S} is a representation of the
6938 target type. It should take advantage of the permission to return by
6939 reference when possible. Restrictions on unchecked conversions should be
6940 avoided unless required by the target environment.
6942 Followed. There are no restrictions on unchecked conversion. A warning is
6943 generated if the source and target types do not have the same size since
6944 the semantics in this case may be target dependent.
6948 The recommended level of support for unchecked conversions is:
6952 Unchecked conversions should be supported and should be reversible in
6953 the cases where this clause defines the result. To enable meaningful use
6954 of unchecked conversion, a contiguous representation should be used for
6955 elementary subtypes, for statically constrained array subtypes whose
6956 component subtype is one of the subtypes described in this paragraph,
6957 and for record subtypes without discriminants whose component subtypes
6958 are described in this paragraph.
6962 @cindex Heap usage, implicit
6963 @unnumberedsec 13.11(23-25): Implicit Heap Usage
6966 An implementation should document any cases in which it dynamically
6967 allocates heap storage for a purpose other than the evaluation of an
6970 Followed, the only other points at which heap storage is dynamically
6971 allocated are as follows:
6975 At initial elaboration time, to allocate dynamically sized global
6979 To allocate space for a task when a task is created.
6982 To extend the secondary stack dynamically when needed. The secondary
6983 stack is used for returning variable length results.
6988 A default (implementation-provided) storage pool for an
6989 access-to-constant type should not have overhead to support deallocation of
6996 A storage pool for an anonymous access type should be created at the
6997 point of an allocator for the type, and be reclaimed when the designated
6998 object becomes inaccessible.
7002 @cindex Unchecked deallocation
7003 @unnumberedsec 13.11.2(17): Unchecked De-allocation
7006 For a standard storage pool, @code{Free} should actually reclaim the
7011 @cindex Stream oriented attributes
7012 @unnumberedsec 13.13.2(17): Stream Oriented Attributes
7015 If a stream element is the same size as a storage element, then the
7016 normal in-memory representation should be used by @code{Read} and
7017 @code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
7018 should use the smallest number of stream elements needed to represent
7019 all values in the base range of the scalar type.
7022 Followed. By default, GNAT uses the interpretation suggested by AI-195,
7023 which specifies using the size of the first subtype.
7024 However, such an implementation is based on direct binary
7025 representations and is therefore target- and endianness-dependent.
7026 To address this issue, GNAT also supplies an alternate implementation
7027 of the stream attributes @code{Read} and @code{Write},
7028 which uses the target-independent XDR standard representation
7030 @cindex XDR representation
7031 @cindex @code{Read} attribute
7032 @cindex @code{Write} attribute
7033 @cindex Stream oriented attributes
7034 The XDR implementation is provided as an alternative body of the
7035 @code{System.Stream_Attributes} package, in the file
7036 @file{s-strxdr.adb} in the GNAT library.
7037 There is no @file{s-strxdr.ads} file.
7038 In order to install the XDR implementation, do the following:
7040 @item Replace the default implementation of the
7041 @code{System.Stream_Attributes} package with the XDR implementation.
7042 For example on a Unix platform issue the commands:
7044 $ mv s-stratt.adb s-strold.adb
7045 $ mv s-strxdr.adb s-stratt.adb
7049 Rebuild the GNAT run-time library as documented in
7050 @ref{GNAT and Libraries,,, gnat_ugn, @value{EDITION} User's Guide}.
7053 @unnumberedsec A.1(52): Names of Predefined Numeric Types
7056 If an implementation provides additional named predefined integer types,
7057 then the names should end with @samp{Integer} as in
7058 @samp{Long_Integer}. If an implementation provides additional named
7059 predefined floating point types, then the names should end with
7060 @samp{Float} as in @samp{Long_Float}.
7064 @findex Ada.Characters.Handling
7065 @unnumberedsec A.3.2(49): @code{Ada.Characters.Handling}
7068 If an implementation provides a localized definition of @code{Character}
7069 or @code{Wide_Character}, then the effects of the subprograms in
7070 @code{Characters.Handling} should reflect the localizations. See also
7073 Followed. GNAT provides no such localized definitions.
7075 @cindex Bounded-length strings
7076 @unnumberedsec A.4.4(106): Bounded-Length String Handling
7079 Bounded string objects should not be implemented by implicit pointers
7080 and dynamic allocation.
7082 Followed. No implicit pointers or dynamic allocation are used.
7084 @cindex Random number generation
7085 @unnumberedsec A.5.2(46-47): Random Number Generation
7088 Any storage associated with an object of type @code{Generator} should be
7089 reclaimed on exit from the scope of the object.
7095 If the generator period is sufficiently long in relation to the number
7096 of distinct initiator values, then each possible value of
7097 @code{Initiator} passed to @code{Reset} should initiate a sequence of
7098 random numbers that does not, in a practical sense, overlap the sequence
7099 initiated by any other value. If this is not possible, then the mapping
7100 between initiator values and generator states should be a rapidly
7101 varying function of the initiator value.
7103 Followed. The generator period is sufficiently long for the first
7104 condition here to hold true.
7106 @findex Get_Immediate
7107 @unnumberedsec A.10.7(23): @code{Get_Immediate}
7110 The @code{Get_Immediate} procedures should be implemented with
7111 unbuffered input. For a device such as a keyboard, input should be
7112 @dfn{available} if a key has already been typed, whereas for a disk
7113 file, input should always be available except at end of file. For a file
7114 associated with a keyboard-like device, any line-editing features of the
7115 underlying operating system should be disabled during the execution of
7116 @code{Get_Immediate}.
7118 Followed on all targets except VxWorks. For VxWorks, there is no way to
7119 provide this functionality that does not result in the input buffer being
7120 flushed before the @code{Get_Immediate} call. A special unit
7121 @code{Interfaces.Vxworks.IO} is provided that contains routines to enable
7125 @unnumberedsec B.1(39-41): Pragma @code{Export}
7128 If an implementation supports pragma @code{Export} to a given language,
7129 then it should also allow the main subprogram to be written in that
7130 language. It should support some mechanism for invoking the elaboration
7131 of the Ada library units included in the system, and for invoking the
7132 finalization of the environment task. On typical systems, the
7133 recommended mechanism is to provide two subprograms whose link names are
7134 @code{adainit} and @code{adafinal}. @code{adainit} should contain the
7135 elaboration code for library units. @code{adafinal} should contain the
7136 finalization code. These subprograms should have no effect the second
7137 and subsequent time they are called.
7143 Automatic elaboration of pre-elaborated packages should be
7144 provided when pragma @code{Export} is supported.
7146 Followed when the main program is in Ada. If the main program is in a
7147 foreign language, then
7148 @code{adainit} must be called to elaborate pre-elaborated
7153 For each supported convention @var{L} other than @code{Intrinsic}, an
7154 implementation should support @code{Import} and @code{Export} pragmas
7155 for objects of @var{L}-compatible types and for subprograms, and pragma
7156 @code{Convention} for @var{L}-eligible types and for subprograms,
7157 presuming the other language has corresponding features. Pragma
7158 @code{Convention} need not be supported for scalar types.
7162 @cindex Package @code{Interfaces}
7164 @unnumberedsec B.2(12-13): Package @code{Interfaces}
7167 For each implementation-defined convention identifier, there should be a
7168 child package of package Interfaces with the corresponding name. This
7169 package should contain any declarations that would be useful for
7170 interfacing to the language (implementation) represented by the
7171 convention. Any declarations useful for interfacing to any language on
7172 the given hardware architecture should be provided directly in
7175 Followed. An additional package not defined
7176 in the Ada Reference Manual is @code{Interfaces.CPP}, used
7177 for interfacing to C++.
7181 An implementation supporting an interface to C, COBOL, or Fortran should
7182 provide the corresponding package or packages described in the following
7185 Followed. GNAT provides all the packages described in this section.
7187 @cindex C, interfacing with
7188 @unnumberedsec B.3(63-71): Interfacing with C
7191 An implementation should support the following interface correspondences
7198 An Ada procedure corresponds to a void-returning C function.
7204 An Ada function corresponds to a non-void C function.
7210 An Ada @code{in} scalar parameter is passed as a scalar argument to a C
7217 An Ada @code{in} parameter of an access-to-object type with designated
7218 type @var{T} is passed as a @code{@var{t}*} argument to a C function,
7219 where @var{t} is the C type corresponding to the Ada type @var{T}.
7225 An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
7226 parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
7227 argument to a C function, where @var{t} is the C type corresponding to
7228 the Ada type @var{T}. In the case of an elementary @code{out} or
7229 @code{in out} parameter, a pointer to a temporary copy is used to
7230 preserve by-copy semantics.
7236 An Ada parameter of a record type @var{T}, of any mode, is passed as a
7237 @code{@var{t}*} argument to a C function, where @var{t} is the C
7238 structure corresponding to the Ada type @var{T}.
7240 Followed. This convention may be overridden by the use of the C_Pass_By_Copy
7241 pragma, or Convention, or by explicitly specifying the mechanism for a given
7242 call using an extended import or export pragma.
7246 An Ada parameter of an array type with component type @var{T}, of any
7247 mode, is passed as a @code{@var{t}*} argument to a C function, where
7248 @var{t} is the C type corresponding to the Ada type @var{T}.
7254 An Ada parameter of an access-to-subprogram type is passed as a pointer
7255 to a C function whose prototype corresponds to the designated
7256 subprogram's specification.
7260 @cindex COBOL, interfacing with
7261 @unnumberedsec B.4(95-98): Interfacing with COBOL
7264 An Ada implementation should support the following interface
7265 correspondences between Ada and COBOL@.
7271 An Ada access @var{T} parameter is passed as a @samp{BY REFERENCE} data item of
7272 the COBOL type corresponding to @var{T}.
7278 An Ada in scalar parameter is passed as a @samp{BY CONTENT} data item of
7279 the corresponding COBOL type.
7285 Any other Ada parameter is passed as a @samp{BY REFERENCE} data item of the
7286 COBOL type corresponding to the Ada parameter type; for scalars, a local
7287 copy is used if necessary to ensure by-copy semantics.
7291 @cindex Fortran, interfacing with
7292 @unnumberedsec B.5(22-26): Interfacing with Fortran
7295 An Ada implementation should support the following interface
7296 correspondences between Ada and Fortran:
7302 An Ada procedure corresponds to a Fortran subroutine.
7308 An Ada function corresponds to a Fortran function.
7314 An Ada parameter of an elementary, array, or record type @var{T} is
7315 passed as a @var{T} argument to a Fortran procedure, where @var{T} is
7316 the Fortran type corresponding to the Ada type @var{T}, and where the
7317 INTENT attribute of the corresponding dummy argument matches the Ada
7318 formal parameter mode; the Fortran implementation's parameter passing
7319 conventions are used. For elementary types, a local copy is used if
7320 necessary to ensure by-copy semantics.
7326 An Ada parameter of an access-to-subprogram type is passed as a
7327 reference to a Fortran procedure whose interface corresponds to the
7328 designated subprogram's specification.
7332 @cindex Machine operations
7333 @unnumberedsec C.1(3-5): Access to Machine Operations
7336 The machine code or intrinsic support should allow access to all
7337 operations normally available to assembly language programmers for the
7338 target environment, including privileged instructions, if any.
7344 The interfacing pragmas (see Annex B) should support interface to
7345 assembler; the default assembler should be associated with the
7346 convention identifier @code{Assembler}.
7352 If an entity is exported to assembly language, then the implementation
7353 should allocate it at an addressable location, and should ensure that it
7354 is retained by the linking process, even if not otherwise referenced
7355 from the Ada code. The implementation should assume that any call to a
7356 machine code or assembler subprogram is allowed to read or update every
7357 object that is specified as exported.
7361 @unnumberedsec C.1(10-16): Access to Machine Operations
7364 The implementation should ensure that little or no overhead is
7365 associated with calling intrinsic and machine-code subprograms.
7367 Followed for both intrinsics and machine-code subprograms.
7371 It is recommended that intrinsic subprograms be provided for convenient
7372 access to any machine operations that provide special capabilities or
7373 efficiency and that are not otherwise available through the language
7376 Followed. A full set of machine operation intrinsic subprograms is provided.
7380 Atomic read-modify-write operations---e.g.@:, test and set, compare and
7381 swap, decrement and test, enqueue/dequeue.
7383 Followed on any target supporting such operations.
7387 Standard numeric functions---e.g.@:, sin, log.
7389 Followed on any target supporting such operations.
7393 String manipulation operations---e.g.@:, translate and test.
7395 Followed on any target supporting such operations.
7399 Vector operations---e.g.@:, compare vector against thresholds.
7401 Followed on any target supporting such operations.
7405 Direct operations on I/O ports.
7407 Followed on any target supporting such operations.
7409 @cindex Interrupt support
7410 @unnumberedsec C.3(28): Interrupt Support
7413 If the @code{Ceiling_Locking} policy is not in effect, the
7414 implementation should provide means for the application to specify which
7415 interrupts are to be blocked during protected actions, if the underlying
7416 system allows for a finer-grain control of interrupt blocking.
7418 Followed. The underlying system does not allow for finer-grain control
7419 of interrupt blocking.
7421 @cindex Protected procedure handlers
7422 @unnumberedsec C.3.1(20-21): Protected Procedure Handlers
7425 Whenever possible, the implementation should allow interrupt handlers to
7426 be called directly by the hardware.
7430 This is never possible under IRIX, so this is followed by default.
7432 Followed on any target where the underlying operating system permits
7437 Whenever practical, violations of any
7438 implementation-defined restrictions should be detected before run time.
7440 Followed. Compile time warnings are given when possible.
7442 @cindex Package @code{Interrupts}
7444 @unnumberedsec C.3.2(25): Package @code{Interrupts}
7448 If implementation-defined forms of interrupt handler procedures are
7449 supported, such as protected procedures with parameters, then for each
7450 such form of a handler, a type analogous to @code{Parameterless_Handler}
7451 should be specified in a child package of @code{Interrupts}, with the
7452 same operations as in the predefined package Interrupts.
7456 @cindex Pre-elaboration requirements
7457 @unnumberedsec C.4(14): Pre-elaboration Requirements
7460 It is recommended that pre-elaborated packages be implemented in such a
7461 way that there should be little or no code executed at run time for the
7462 elaboration of entities not already covered by the Implementation
7465 Followed. Executable code is generated in some cases, e.g.@: loops
7466 to initialize large arrays.
7468 @unnumberedsec C.5(8): Pragma @code{Discard_Names}
7472 If the pragma applies to an entity, then the implementation should
7473 reduce the amount of storage used for storing names associated with that
7478 @cindex Package @code{Task_Attributes}
7479 @findex Task_Attributes
7480 @unnumberedsec C.7.2(30): The Package Task_Attributes
7483 Some implementations are targeted to domains in which memory use at run
7484 time must be completely deterministic. For such implementations, it is
7485 recommended that the storage for task attributes will be pre-allocated
7486 statically and not from the heap. This can be accomplished by either
7487 placing restrictions on the number and the size of the task's
7488 attributes, or by using the pre-allocated storage for the first @var{N}
7489 attribute objects, and the heap for the others. In the latter case,
7490 @var{N} should be documented.
7492 Not followed. This implementation is not targeted to such a domain.
7494 @cindex Locking Policies
7495 @unnumberedsec D.3(17): Locking Policies
7499 The implementation should use names that end with @samp{_Locking} for
7500 locking policies defined by the implementation.
7502 Followed. A single implementation-defined locking policy is defined,
7503 whose name (@code{Inheritance_Locking}) follows this suggestion.
7505 @cindex Entry queuing policies
7506 @unnumberedsec D.4(16): Entry Queuing Policies
7509 Names that end with @samp{_Queuing} should be used
7510 for all implementation-defined queuing policies.
7512 Followed. No such implementation-defined queuing policies exist.
7514 @cindex Preemptive abort
7515 @unnumberedsec D.6(9-10): Preemptive Abort
7518 Even though the @code{abort_statement} is included in the list of
7519 potentially blocking operations (see 9.5.1), it is recommended that this
7520 statement be implemented in a way that never requires the task executing
7521 the @code{abort_statement} to block.
7527 On a multi-processor, the delay associated with aborting a task on
7528 another processor should be bounded; the implementation should use
7529 periodic polling, if necessary, to achieve this.
7533 @cindex Tasking restrictions
7534 @unnumberedsec D.7(21): Tasking Restrictions
7537 When feasible, the implementation should take advantage of the specified
7538 restrictions to produce a more efficient implementation.
7540 GNAT currently takes advantage of these restrictions by providing an optimized
7541 run time when the Ravenscar profile and the GNAT restricted run time set
7542 of restrictions are specified. See pragma @code{Profile (Ravenscar)} and
7543 pragma @code{Profile (Restricted)} for more details.
7545 @cindex Time, monotonic
7546 @unnumberedsec D.8(47-49): Monotonic Time
7549 When appropriate, implementations should provide configuration
7550 mechanisms to change the value of @code{Tick}.
7552 Such configuration mechanisms are not appropriate to this implementation
7553 and are thus not supported.
7557 It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
7558 be implemented as transformations of the same time base.
7564 It is recommended that the @dfn{best} time base which exists in
7565 the underlying system be available to the application through
7566 @code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
7570 @cindex Partition communication subsystem
7572 @unnumberedsec E.5(28-29): Partition Communication Subsystem
7575 Whenever possible, the PCS on the called partition should allow for
7576 multiple tasks to call the RPC-receiver with different messages and
7577 should allow them to block until the corresponding subprogram body
7580 Followed by GLADE, a separately supplied PCS that can be used with
7585 The @code{Write} operation on a stream of type @code{Params_Stream_Type}
7586 should raise @code{Storage_Error} if it runs out of space trying to
7587 write the @code{Item} into the stream.
7589 Followed by GLADE, a separately supplied PCS that can be used with
7592 @cindex COBOL support
7593 @unnumberedsec F(7): COBOL Support
7596 If COBOL (respectively, C) is widely supported in the target
7597 environment, implementations supporting the Information Systems Annex
7598 should provide the child package @code{Interfaces.COBOL} (respectively,
7599 @code{Interfaces.C}) specified in Annex B and should support a
7600 @code{convention_identifier} of COBOL (respectively, C) in the interfacing
7601 pragmas (see Annex B), thus allowing Ada programs to interface with
7602 programs written in that language.
7606 @cindex Decimal radix support
7607 @unnumberedsec F.1(2): Decimal Radix Support
7610 Packed decimal should be used as the internal representation for objects
7611 of subtype @var{S} when @var{S}'Machine_Radix = 10.
7613 Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
7617 @unnumberedsec G: Numerics
7620 If Fortran (respectively, C) is widely supported in the target
7621 environment, implementations supporting the Numerics Annex
7622 should provide the child package @code{Interfaces.Fortran} (respectively,
7623 @code{Interfaces.C}) specified in Annex B and should support a
7624 @code{convention_identifier} of Fortran (respectively, C) in the interfacing
7625 pragmas (see Annex B), thus allowing Ada programs to interface with
7626 programs written in that language.
7630 @cindex Complex types
7631 @unnumberedsec G.1.1(56-58): Complex Types
7634 Because the usual mathematical meaning of multiplication of a complex
7635 operand and a real operand is that of the scaling of both components of
7636 the former by the latter, an implementation should not perform this
7637 operation by first promoting the real operand to complex type and then
7638 performing a full complex multiplication. In systems that, in the
7639 future, support an Ada binding to IEC 559:1989, the latter technique
7640 will not generate the required result when one of the components of the
7641 complex operand is infinite. (Explicit multiplication of the infinite
7642 component by the zero component obtained during promotion yields a NaN
7643 that propagates into the final result.) Analogous advice applies in the
7644 case of multiplication of a complex operand and a pure-imaginary
7645 operand, and in the case of division of a complex operand by a real or
7646 pure-imaginary operand.
7652 Similarly, because the usual mathematical meaning of addition of a
7653 complex operand and a real operand is that the imaginary operand remains
7654 unchanged, an implementation should not perform this operation by first
7655 promoting the real operand to complex type and then performing a full
7656 complex addition. In implementations in which the @code{Signed_Zeros}
7657 attribute of the component type is @code{True} (and which therefore
7658 conform to IEC 559:1989 in regard to the handling of the sign of zero in
7659 predefined arithmetic operations), the latter technique will not
7660 generate the required result when the imaginary component of the complex
7661 operand is a negatively signed zero. (Explicit addition of the negative
7662 zero to the zero obtained during promotion yields a positive zero.)
7663 Analogous advice applies in the case of addition of a complex operand
7664 and a pure-imaginary operand, and in the case of subtraction of a
7665 complex operand and a real or pure-imaginary operand.
7671 Implementations in which @code{Real'Signed_Zeros} is @code{True} should
7672 attempt to provide a rational treatment of the signs of zero results and
7673 result components. As one example, the result of the @code{Argument}
7674 function should have the sign of the imaginary component of the
7675 parameter @code{X} when the point represented by that parameter lies on
7676 the positive real axis; as another, the sign of the imaginary component
7677 of the @code{Compose_From_Polar} function should be the same as
7678 (respectively, the opposite of) that of the @code{Argument} parameter when that
7679 parameter has a value of zero and the @code{Modulus} parameter has a
7680 nonnegative (respectively, negative) value.
7684 @cindex Complex elementary functions
7685 @unnumberedsec G.1.2(49): Complex Elementary Functions
7688 Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
7689 @code{True} should attempt to provide a rational treatment of the signs
7690 of zero results and result components. For example, many of the complex
7691 elementary functions have components that are odd functions of one of
7692 the parameter components; in these cases, the result component should
7693 have the sign of the parameter component at the origin. Other complex
7694 elementary functions have zero components whose sign is opposite that of
7695 a parameter component at the origin, or is always positive or always
7700 @cindex Accuracy requirements
7701 @unnumberedsec G.2.4(19): Accuracy Requirements
7704 The versions of the forward trigonometric functions without a
7705 @code{Cycle} parameter should not be implemented by calling the
7706 corresponding version with a @code{Cycle} parameter of
7707 @code{2.0*Numerics.Pi}, since this will not provide the required
7708 accuracy in some portions of the domain. For the same reason, the
7709 version of @code{Log} without a @code{Base} parameter should not be
7710 implemented by calling the corresponding version with a @code{Base}
7711 parameter of @code{Numerics.e}.
7715 @cindex Complex arithmetic accuracy
7716 @cindex Accuracy, complex arithmetic
7717 @unnumberedsec G.2.6(15): Complex Arithmetic Accuracy
7721 The version of the @code{Compose_From_Polar} function without a
7722 @code{Cycle} parameter should not be implemented by calling the
7723 corresponding version with a @code{Cycle} parameter of
7724 @code{2.0*Numerics.Pi}, since this will not provide the required
7725 accuracy in some portions of the domain.
7729 @c -----------------------------------------
7730 @node Implementation Defined Characteristics
7731 @chapter Implementation Defined Characteristics
7734 In addition to the implementation dependent pragmas and attributes, and
7735 the implementation advice, there are a number of other Ada features
7736 that are potentially implementation dependent. These are mentioned
7737 throughout the Ada Reference Manual, and are summarized in annex M@.
7739 A requirement for conforming Ada compilers is that they provide
7740 documentation describing how the implementation deals with each of these
7741 issues. In this chapter, you will find each point in annex M listed
7742 followed by a description in italic font of how GNAT
7746 implementation on IRIX 5.3 operating system or greater
7748 handles the implementation dependence.
7750 You can use this chapter as a guide to minimizing implementation
7751 dependent features in your programs if portability to other compilers
7752 and other operating systems is an important consideration. The numbers
7753 in each section below correspond to the paragraph number in the Ada
7759 @strong{2}. Whether or not each recommendation given in Implementation
7760 Advice is followed. See 1.1.2(37).
7763 @xref{Implementation Advice}.
7768 @strong{3}. Capacity limitations of the implementation. See 1.1.3(3).
7771 The complexity of programs that can be processed is limited only by the
7772 total amount of available virtual memory, and disk space for the
7773 generated object files.
7778 @strong{4}. Variations from the standard that are impractical to avoid
7779 given the implementation's execution environment. See 1.1.3(6).
7782 There are no variations from the standard.
7787 @strong{5}. Which @code{code_statement}s cause external
7788 interactions. See 1.1.3(10).
7791 Any @code{code_statement} can potentially cause external interactions.
7796 @strong{6}. The coded representation for the text of an Ada
7797 program. See 2.1(4).
7800 See separate section on source representation.
7805 @strong{7}. The control functions allowed in comments. See 2.1(14).
7808 See separate section on source representation.
7813 @strong{8}. The representation for an end of line. See 2.2(2).
7816 See separate section on source representation.
7821 @strong{9}. Maximum supported line length and lexical element
7822 length. See 2.2(15).
7825 The maximum line length is 255 characters and the maximum length of a
7826 lexical element is also 255 characters.
7831 @strong{10}. Implementation defined pragmas. See 2.8(14).
7835 @xref{Implementation Defined Pragmas}.
7840 @strong{11}. Effect of pragma @code{Optimize}. See 2.8(27).
7843 Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
7844 parameter, checks that the optimization flag is set, and aborts if it is
7850 @strong{12}. The sequence of characters of the value returned by
7851 @code{@var{S}'Image} when some of the graphic characters of
7852 @code{@var{S}'Wide_Image} are not defined in @code{Character}. See
7856 The sequence of characters is as defined by the wide character encoding
7857 method used for the source. See section on source representation for
7863 @strong{13}. The predefined integer types declared in
7864 @code{Standard}. See 3.5.4(25).
7868 @item Short_Short_Integer
7871 (Short) 16 bit signed
7875 64 bit signed (Alpha OpenVMS only)
7876 32 bit signed (all other targets)
7877 @item Long_Long_Integer
7884 @strong{14}. Any nonstandard integer types and the operators defined
7885 for them. See 3.5.4(26).
7888 There are no nonstandard integer types.
7893 @strong{15}. Any nonstandard real types and the operators defined for
7897 There are no nonstandard real types.
7902 @strong{16}. What combinations of requested decimal precision and range
7903 are supported for floating point types. See 3.5.7(7).
7906 The precision and range is as defined by the IEEE standard.
7911 @strong{17}. The predefined floating point types declared in
7912 @code{Standard}. See 3.5.7(16).
7919 (Short) 32 bit IEEE short
7922 @item Long_Long_Float
7923 64 bit IEEE long (80 bit IEEE long on x86 processors)
7929 @strong{18}. The small of an ordinary fixed point type. See 3.5.9(8).
7932 @code{Fine_Delta} is 2**(@minus{}63)
7937 @strong{19}. What combinations of small, range, and digits are
7938 supported for fixed point types. See 3.5.9(10).
7941 Any combinations are permitted that do not result in a small less than
7942 @code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
7943 If the mantissa is larger than 53 bits on machines where Long_Long_Float
7944 is 64 bits (true of all architectures except ia32), then the output from
7945 Text_IO is accurate to only 53 bits, rather than the full mantissa. This
7946 is because floating-point conversions are used to convert fixed point.
7951 @strong{20}. The result of @code{Tags.Expanded_Name} for types declared
7952 within an unnamed @code{block_statement}. See 3.9(10).
7955 Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
7956 decimal integer are allocated.
7961 @strong{21}. Implementation-defined attributes. See 4.1.4(12).
7964 @xref{Implementation Defined Attributes}.
7969 @strong{22}. Any implementation-defined time types. See 9.6(6).
7972 There are no implementation-defined time types.
7977 @strong{23}. The time base associated with relative delays.
7980 See 9.6(20). The time base used is that provided by the C library
7981 function @code{gettimeofday}.
7986 @strong{24}. The time base of the type @code{Calendar.Time}. See
7990 The time base used is that provided by the C library function
7991 @code{gettimeofday}.
7996 @strong{25}. The time zone used for package @code{Calendar}
7997 operations. See 9.6(24).
8000 The time zone used by package @code{Calendar} is the current system time zone
8001 setting for local time, as accessed by the C library function
8007 @strong{26}. Any limit on @code{delay_until_statements} of
8008 @code{select_statements}. See 9.6(29).
8011 There are no such limits.
8016 @strong{27}. Whether or not two non-overlapping parts of a composite
8017 object are independently addressable, in the case where packing, record
8018 layout, or @code{Component_Size} is specified for the object. See
8022 Separate components are independently addressable if they do not share
8023 overlapping storage units.
8028 @strong{28}. The representation for a compilation. See 10.1(2).
8031 A compilation is represented by a sequence of files presented to the
8032 compiler in a single invocation of the @command{gcc} command.
8037 @strong{29}. Any restrictions on compilations that contain multiple
8038 compilation_units. See 10.1(4).
8041 No single file can contain more than one compilation unit, but any
8042 sequence of files can be presented to the compiler as a single
8048 @strong{30}. The mechanisms for creating an environment and for adding
8049 and replacing compilation units. See 10.1.4(3).
8052 See separate section on compilation model.
8057 @strong{31}. The manner of explicitly assigning library units to a
8058 partition. See 10.2(2).
8061 If a unit contains an Ada main program, then the Ada units for the partition
8062 are determined by recursive application of the rules in the Ada Reference
8063 Manual section 10.2(2-6). In other words, the Ada units will be those that
8064 are needed by the main program, and then this definition of need is applied
8065 recursively to those units, and the partition contains the transitive
8066 closure determined by this relationship. In short, all the necessary units
8067 are included, with no need to explicitly specify the list. If additional
8068 units are required, e.g.@: by foreign language units, then all units must be
8069 mentioned in the context clause of one of the needed Ada units.
8071 If the partition contains no main program, or if the main program is in
8072 a language other than Ada, then GNAT
8073 provides the binder options @option{-z} and @option{-n} respectively, and in
8074 this case a list of units can be explicitly supplied to the binder for
8075 inclusion in the partition (all units needed by these units will also
8076 be included automatically). For full details on the use of these
8077 options, refer to @ref{The GNAT Make Program gnatmake,,, gnat_ugn,
8078 @value{EDITION} User's Guide}.
8083 @strong{32}. The implementation-defined means, if any, of specifying
8084 which compilation units are needed by a given compilation unit. See
8088 The units needed by a given compilation unit are as defined in
8089 the Ada Reference Manual section 10.2(2-6). There are no
8090 implementation-defined pragmas or other implementation-defined
8091 means for specifying needed units.
8096 @strong{33}. The manner of designating the main subprogram of a
8097 partition. See 10.2(7).
8100 The main program is designated by providing the name of the
8101 corresponding @file{ALI} file as the input parameter to the binder.
8106 @strong{34}. The order of elaboration of @code{library_items}. See
8110 The first constraint on ordering is that it meets the requirements of
8111 Chapter 10 of the Ada Reference Manual. This still leaves some
8112 implementation dependent choices, which are resolved by first
8113 elaborating bodies as early as possible (i.e., in preference to specs
8114 where there is a choice), and second by evaluating the immediate with
8115 clauses of a unit to determine the probably best choice, and
8116 third by elaborating in alphabetical order of unit names
8117 where a choice still remains.
8122 @strong{35}. Parameter passing and function return for the main
8123 subprogram. See 10.2(21).
8126 The main program has no parameters. It may be a procedure, or a function
8127 returning an integer type. In the latter case, the returned integer
8128 value is the return code of the program (overriding any value that
8129 may have been set by a call to @code{Ada.Command_Line.Set_Exit_Status}).
8134 @strong{36}. The mechanisms for building and running partitions. See
8138 GNAT itself supports programs with only a single partition. The GNATDIST
8139 tool provided with the GLADE package (which also includes an implementation
8140 of the PCS) provides a completely flexible method for building and running
8141 programs consisting of multiple partitions. See the separate GLADE manual
8147 @strong{37}. The details of program execution, including program
8148 termination. See 10.2(25).
8151 See separate section on compilation model.
8156 @strong{38}. The semantics of any non-active partitions supported by the
8157 implementation. See 10.2(28).
8160 Passive partitions are supported on targets where shared memory is
8161 provided by the operating system. See the GLADE reference manual for
8167 @strong{39}. The information returned by @code{Exception_Message}. See
8171 Exception message returns the null string unless a specific message has
8172 been passed by the program.
8177 @strong{40}. The result of @code{Exceptions.Exception_Name} for types
8178 declared within an unnamed @code{block_statement}. See 11.4.1(12).
8181 Blocks have implementation defined names of the form @code{B@var{nnn}}
8182 where @var{nnn} is an integer.
8187 @strong{41}. The information returned by
8188 @code{Exception_Information}. See 11.4.1(13).
8191 @code{Exception_Information} returns a string in the following format:
8194 @emph{Exception_Name:} nnnnn
8195 @emph{Message:} mmmmm
8197 @emph{Call stack traceback locations:}
8198 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
8206 @code{nnnn} is the fully qualified name of the exception in all upper
8207 case letters. This line is always present.
8210 @code{mmmm} is the message (this line present only if message is non-null)
8213 @code{ppp} is the Process Id value as a decimal integer (this line is
8214 present only if the Process Id is nonzero). Currently we are
8215 not making use of this field.
8218 The Call stack traceback locations line and the following values
8219 are present only if at least one traceback location was recorded.
8220 The values are given in C style format, with lower case letters
8221 for a-f, and only as many digits present as are necessary.
8225 The line terminator sequence at the end of each line, including
8226 the last line is a single @code{LF} character (@code{16#0A#}).
8231 @strong{42}. Implementation-defined check names. See 11.5(27).
8234 The implementation defined check name Alignment_Check controls checking of
8235 address clause values for proper alignment (that is, the address supplied
8236 must be consistent with the alignment of the type).
8238 In addition, a user program can add implementation-defined check names
8239 by means of the pragma Check_Name.
8244 @strong{43}. The interpretation of each aspect of representation. See
8248 See separate section on data representations.
8253 @strong{44}. Any restrictions placed upon representation items. See
8257 See separate section on data representations.
8262 @strong{45}. The meaning of @code{Size} for indefinite subtypes. See
8266 Size for an indefinite subtype is the maximum possible size, except that
8267 for the case of a subprogram parameter, the size of the parameter object
8273 @strong{46}. The default external representation for a type tag. See
8277 The default external representation for a type tag is the fully expanded
8278 name of the type in upper case letters.
8283 @strong{47}. What determines whether a compilation unit is the same in
8284 two different partitions. See 13.3(76).
8287 A compilation unit is the same in two different partitions if and only
8288 if it derives from the same source file.
8293 @strong{48}. Implementation-defined components. See 13.5.1(15).
8296 The only implementation defined component is the tag for a tagged type,
8297 which contains a pointer to the dispatching table.
8302 @strong{49}. If @code{Word_Size} = @code{Storage_Unit}, the default bit
8303 ordering. See 13.5.3(5).
8306 @code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
8307 implementation, so no non-default bit ordering is supported. The default
8308 bit ordering corresponds to the natural endianness of the target architecture.
8313 @strong{50}. The contents of the visible part of package @code{System}
8314 and its language-defined children. See 13.7(2).
8317 See the definition of these packages in files @file{system.ads} and
8318 @file{s-stoele.ads}.
8323 @strong{51}. The contents of the visible part of package
8324 @code{System.Machine_Code}, and the meaning of
8325 @code{code_statements}. See 13.8(7).
8328 See the definition and documentation in file @file{s-maccod.ads}.
8333 @strong{52}. The effect of unchecked conversion. See 13.9(11).
8336 Unchecked conversion between types of the same size
8337 results in an uninterpreted transmission of the bits from one type
8338 to the other. If the types are of unequal sizes, then in the case of
8339 discrete types, a shorter source is first zero or sign extended as
8340 necessary, and a shorter target is simply truncated on the left.
8341 For all non-discrete types, the source is first copied if necessary
8342 to ensure that the alignment requirements of the target are met, then
8343 a pointer is constructed to the source value, and the result is obtained
8344 by dereferencing this pointer after converting it to be a pointer to the
8345 target type. Unchecked conversions where the target subtype is an
8346 unconstrained array are not permitted. If the target alignment is
8347 greater than the source alignment, then a copy of the result is
8348 made with appropriate alignment
8353 @strong{53}. The manner of choosing a storage pool for an access type
8354 when @code{Storage_Pool} is not specified for the type. See 13.11(17).
8357 There are 3 different standard pools used by the compiler when
8358 @code{Storage_Pool} is not specified depending whether the type is local
8359 to a subprogram or defined at the library level and whether
8360 @code{Storage_Size}is specified or not. See documentation in the runtime
8361 library units @code{System.Pool_Global}, @code{System.Pool_Size} and
8362 @code{System.Pool_Local} in files @file{s-poosiz.ads},
8363 @file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
8369 @strong{54}. Whether or not the implementation provides user-accessible
8370 names for the standard pool type(s). See 13.11(17).
8374 See documentation in the sources of the run time mentioned in paragraph
8375 @strong{53} . All these pools are accessible by means of @code{with}'ing
8381 @strong{55}. The meaning of @code{Storage_Size}. See 13.11(18).
8384 @code{Storage_Size} is measured in storage units, and refers to the
8385 total space available for an access type collection, or to the primary
8386 stack space for a task.
8391 @strong{56}. Implementation-defined aspects of storage pools. See
8395 See documentation in the sources of the run time mentioned in paragraph
8396 @strong{53} for details on GNAT-defined aspects of storage pools.
8401 @strong{57}. The set of restrictions allowed in a pragma
8402 @code{Restrictions}. See 13.12(7).
8405 All RM defined Restriction identifiers are implemented. The following
8406 additional restriction identifiers are provided. There are two separate
8407 lists of implementation dependent restriction identifiers. The first
8408 set requires consistency throughout a partition (in other words, if the
8409 restriction identifier is used for any compilation unit in the partition,
8410 then all compilation units in the partition must obey the restriction.
8414 @item Simple_Barriers
8415 @findex Simple_Barriers
8416 This restriction ensures at compile time that barriers in entry declarations
8417 for protected types are restricted to either static boolean expressions or
8418 references to simple boolean variables defined in the private part of the
8419 protected type. No other form of entry barriers is permitted. This is one
8420 of the restrictions of the Ravenscar profile for limited tasking (see also
8421 pragma @code{Profile (Ravenscar)}).
8423 @item Max_Entry_Queue_Length => Expr
8424 @findex Max_Entry_Queue_Length
8425 This restriction is a declaration that any protected entry compiled in
8426 the scope of the restriction has at most the specified number of
8427 tasks waiting on the entry
8428 at any one time, and so no queue is required. This restriction is not
8429 checked at compile time. A program execution is erroneous if an attempt
8430 is made to queue more than the specified number of tasks on such an entry.
8434 This restriction ensures at compile time that there is no implicit or
8435 explicit dependence on the package @code{Ada.Calendar}.
8437 @item No_Default_Initialization
8438 @findex No_Default_Initialization
8440 This restriction prohibits any instance of default initialization of variables.
8441 The binder implements a consistency rule which prevents any unit compiled
8442 without the restriction from with'ing a unit with the restriction (this allows
8443 the generation of initialization procedures to be skipped, since you can be
8444 sure that no call is ever generated to an initialization procedure in a unit
8445 with the restriction active). If used in conjunction with Initialize_Scalars or
8446 Normalize_Scalars, the effect is to prohibit all cases of variables declared
8447 without a specific initializer (including the case of OUT scalar parameters).
8449 @item No_Direct_Boolean_Operators
8450 @findex No_Direct_Boolean_Operators
8451 This restriction ensures that no logical (and/or/xor) are used on
8452 operands of type Boolean (or any type derived
8453 from Boolean). This is intended for use in safety critical programs
8454 where the certification protocol requires the use of short-circuit
8455 (and then, or else) forms for all composite boolean operations.
8457 @item No_Dispatching_Calls
8458 @findex No_Dispatching_Calls
8459 This restriction ensures at compile time that the code generated by the
8460 compiler involves no dispatching calls. The use of this restriction allows the
8461 safe use of record extensions, classwide membership tests and other classwide
8462 features not involving implicit dispatching. This restriction ensures that
8463 the code contains no indirect calls through a dispatching mechanism. Note that
8464 this includes internally-generated calls created by the compiler, for example
8465 in the implementation of class-wide objects assignments. The
8466 membership test is allowed in the presence of this restriction, because its
8467 implementation requires no dispatching.
8468 This restriction is comparable to the official Ada restriction
8469 @code{No_Dispatch} except that it is a bit less restrictive in that it allows
8470 all classwide constructs that do not imply dispatching.
8471 The following example indicates constructs that violate this restriction.
8475 type T is tagged record
8478 procedure P (X : T);
8480 type DT is new T with record
8481 More_Data : Natural;
8483 procedure Q (X : DT);
8487 procedure Example is
8488 procedure Test (O : T'Class) is
8489 N : Natural := O'Size;-- Error: Dispatching call
8490 C : T'Class := O; -- Error: implicit Dispatching Call
8492 if O in DT'Class then -- OK : Membership test
8493 Q (DT (O)); -- OK : Type conversion plus direct call
8495 P (O); -- Error: Dispatching call
8501 P (Obj); -- OK : Direct call
8502 P (T (Obj)); -- OK : Type conversion plus direct call
8503 P (T'Class (Obj)); -- Error: Dispatching call
8505 Test (Obj); -- OK : Type conversion
8507 if Obj in T'Class then -- OK : Membership test
8513 @item No_Dynamic_Attachment
8514 @findex No_Dynamic_Attachment
8515 This restriction ensures that there is no call to any of the operations
8516 defined in package Ada.Interrupts.
8518 @item No_Enumeration_Maps
8519 @findex No_Enumeration_Maps
8520 This restriction ensures at compile time that no operations requiring
8521 enumeration maps are used (that is Image and Value attributes applied
8522 to enumeration types).
8524 @item No_Entry_Calls_In_Elaboration_Code
8525 @findex No_Entry_Calls_In_Elaboration_Code
8526 This restriction ensures at compile time that no task or protected entry
8527 calls are made during elaboration code. As a result of the use of this
8528 restriction, the compiler can assume that no code past an accept statement
8529 in a task can be executed at elaboration time.
8531 @item No_Exception_Handlers
8532 @findex No_Exception_Handlers
8533 This restriction ensures at compile time that there are no explicit
8534 exception handlers. It also indicates that no exception propagation will
8535 be provided. In this mode, exceptions may be raised but will result in
8536 an immediate call to the last chance handler, a routine that the user
8537 must define with the following profile:
8539 @smallexample @c ada
8540 procedure Last_Chance_Handler
8541 (Source_Location : System.Address; Line : Integer);
8542 pragma Export (C, Last_Chance_Handler,
8543 "__gnat_last_chance_handler");
8546 The parameter is a C null-terminated string representing a message to be
8547 associated with the exception (typically the source location of the raise
8548 statement generated by the compiler). The Line parameter when nonzero
8549 represents the line number in the source program where the raise occurs.
8551 @item No_Exception_Propagation
8552 @findex No_Exception_Propagation
8553 This restriction guarantees that exceptions are never propagated to an outer
8554 subprogram scope). The only case in which an exception may be raised is when
8555 the handler is statically in the same subprogram, so that the effect of a raise
8556 is essentially like a goto statement. Any other raise statement (implicit or
8557 explicit) will be considered unhandled. Exception handlers are allowed, but may
8558 not contain an exception occurrence identifier (exception choice). In addition
8559 use of the package GNAT.Current_Exception is not permitted, and reraise
8560 statements (raise with no operand) are not permitted.
8562 @item No_Exception_Registration
8563 @findex No_Exception_Registration
8564 This restriction ensures at compile time that no stream operations for
8565 types Exception_Id or Exception_Occurrence are used. This also makes it
8566 impossible to pass exceptions to or from a partition with this restriction
8567 in a distributed environment. If this exception is active, then the generated
8568 code is simplified by omitting the otherwise-required global registration
8569 of exceptions when they are declared.
8571 @item No_Implicit_Conditionals
8572 @findex No_Implicit_Conditionals
8573 This restriction ensures that the generated code does not contain any
8574 implicit conditionals, either by modifying the generated code where possible,
8575 or by rejecting any construct that would otherwise generate an implicit
8576 conditional. Note that this check does not include run time constraint
8577 checks, which on some targets may generate implicit conditionals as
8578 well. To control the latter, constraint checks can be suppressed in the
8579 normal manner. Constructs generating implicit conditionals include comparisons
8580 of composite objects and the Max/Min attributes.
8582 @item No_Implicit_Dynamic_Code
8583 @findex No_Implicit_Dynamic_Code
8585 This restriction prevents the compiler from building ``trampolines''.
8586 This is a structure that is built on the stack and contains dynamic
8587 code to be executed at run time. On some targets, a trampoline is
8588 built for the following features: @code{Access},
8589 @code{Unrestricted_Access}, or @code{Address} of a nested subprogram;
8590 nested task bodies; primitive operations of nested tagged types.
8591 Trampolines do not work on machines that prevent execution of stack
8592 data. For example, on windows systems, enabling DEP (data execution
8593 protection) will cause trampolines to raise an exception.
8594 Trampolines are also quite slow at run time.
8596 On many targets, trampolines have been largely eliminated. Look at the
8597 version of system.ads for your target --- if it has
8598 Always_Compatible_Rep equal to False, then trampolines are largely
8599 eliminated. In particular, a trampoline is built for the following
8600 features: @code{Address} of a nested subprogram;
8601 @code{Access} or @code{Unrestricted_Access} of a nested subprogram,
8602 but only if pragma Favor_Top_Level applies, or the access type has a
8603 foreign-language convention; primitive operations of nested tagged
8606 @item No_Implicit_Loops
8607 @findex No_Implicit_Loops
8608 This restriction ensures that the generated code does not contain any
8609 implicit @code{for} loops, either by modifying
8610 the generated code where possible,
8611 or by rejecting any construct that would otherwise generate an implicit
8612 @code{for} loop. If this restriction is active, it is possible to build
8613 large array aggregates with all static components without generating an
8614 intermediate temporary, and without generating a loop to initialize individual
8615 components. Otherwise, a loop is created for arrays larger than about 5000
8618 @item No_Initialize_Scalars
8619 @findex No_Initialize_Scalars
8620 This restriction ensures that no unit in the partition is compiled with
8621 pragma Initialize_Scalars. This allows the generation of more efficient
8622 code, and in particular eliminates dummy null initialization routines that
8623 are otherwise generated for some record and array types.
8625 @item No_Local_Protected_Objects
8626 @findex No_Local_Protected_Objects
8627 This restriction ensures at compile time that protected objects are
8628 only declared at the library level.
8630 @item No_Protected_Type_Allocators
8631 @findex No_Protected_Type_Allocators
8632 This restriction ensures at compile time that there are no allocator
8633 expressions that attempt to allocate protected objects.
8635 @item No_Secondary_Stack
8636 @findex No_Secondary_Stack
8637 This restriction ensures at compile time that the generated code does not
8638 contain any reference to the secondary stack. The secondary stack is used
8639 to implement functions returning unconstrained objects (arrays or records)
8642 @item No_Select_Statements
8643 @findex No_Select_Statements
8644 This restriction ensures at compile time no select statements of any kind
8645 are permitted, that is the keyword @code{select} may not appear.
8646 This is one of the restrictions of the Ravenscar
8647 profile for limited tasking (see also pragma @code{Profile (Ravenscar)}).
8649 @item No_Standard_Storage_Pools
8650 @findex No_Standard_Storage_Pools
8651 This restriction ensures at compile time that no access types
8652 use the standard default storage pool. Any access type declared must
8653 have an explicit Storage_Pool attribute defined specifying a
8654 user-defined storage pool.
8658 This restriction ensures at compile/bind time that there are no
8659 stream objects created and no use of stream attributes.
8660 This restriction does not forbid dependences on the package
8661 @code{Ada.Streams}. So it is permissible to with
8662 @code{Ada.Streams} (or another package that does so itself)
8663 as long as no actual stream objects are created and no
8664 stream attributes are used.
8666 Note that the use of restriction allows optimization of tagged types,
8667 since they do not need to worry about dispatching stream operations.
8668 To take maximum advantage of this space-saving optimization, any
8669 unit declaring a tagged type should be compiled with the restriction,
8670 though this is not required.
8672 @item No_Task_Attributes_Package
8673 @findex No_Task_Attributes_Package
8674 This restriction ensures at compile time that there are no implicit or
8675 explicit dependencies on the package @code{Ada.Task_Attributes}.
8677 @item No_Task_Termination
8678 @findex No_Task_Termination
8679 This restriction ensures at compile time that no terminate alternatives
8680 appear in any task body.
8684 This restriction prevents the declaration of tasks or task types throughout
8685 the partition. It is similar in effect to the use of @code{Max_Tasks => 0}
8686 except that violations are caught at compile time and cause an error message
8687 to be output either by the compiler or binder.
8689 @item Static_Priorities
8690 @findex Static_Priorities
8691 This restriction ensures at compile time that all priority expressions
8692 are static, and that there are no dependencies on the package
8693 @code{Ada.Dynamic_Priorities}.
8695 @item Static_Storage_Size
8696 @findex Static_Storage_Size
8697 This restriction ensures at compile time that any expression appearing
8698 in a Storage_Size pragma or attribute definition clause is static.
8703 The second set of implementation dependent restriction identifiers
8704 does not require partition-wide consistency.
8705 The restriction may be enforced for a single
8706 compilation unit without any effect on any of the
8707 other compilation units in the partition.
8711 @item No_Elaboration_Code
8712 @findex No_Elaboration_Code
8713 This restriction ensures at compile time that no elaboration code is
8714 generated. Note that this is not the same condition as is enforced
8715 by pragma @code{Preelaborate}. There are cases in which pragma
8716 @code{Preelaborate} still permits code to be generated (e.g.@: code
8717 to initialize a large array to all zeroes), and there are cases of units
8718 which do not meet the requirements for pragma @code{Preelaborate},
8719 but for which no elaboration code is generated. Generally, it is
8720 the case that preelaborable units will meet the restrictions, with
8721 the exception of large aggregates initialized with an others_clause,
8722 and exception declarations (which generate calls to a run-time
8723 registry procedure). This restriction is enforced on
8724 a unit by unit basis, it need not be obeyed consistently
8725 throughout a partition.
8727 In the case of aggregates with others, if the aggregate has a dynamic
8728 size, there is no way to eliminate the elaboration code (such dynamic
8729 bounds would be incompatible with @code{Preelaborate} in any case). If
8730 the bounds are static, then use of this restriction actually modifies
8731 the code choice of the compiler to avoid generating a loop, and instead
8732 generate the aggregate statically if possible, no matter how many times
8733 the data for the others clause must be repeatedly generated.
8735 It is not possible to precisely document
8736 the constructs which are compatible with this restriction, since,
8737 unlike most other restrictions, this is not a restriction on the
8738 source code, but a restriction on the generated object code. For
8739 example, if the source contains a declaration:
8742 Val : constant Integer := X;
8746 where X is not a static constant, it may be possible, depending
8747 on complex optimization circuitry, for the compiler to figure
8748 out the value of X at compile time, in which case this initialization
8749 can be done by the loader, and requires no initialization code. It
8750 is not possible to document the precise conditions under which the
8751 optimizer can figure this out.
8753 Note that this the implementation of this restriction requires full
8754 code generation. If it is used in conjunction with "semantics only"
8755 checking, then some cases of violations may be missed.
8757 @item No_Entry_Queue
8758 @findex No_Entry_Queue
8759 This restriction is a declaration that any protected entry compiled in
8760 the scope of the restriction has at most one task waiting on the entry
8761 at any one time, and so no queue is required. This restriction is not
8762 checked at compile time. A program execution is erroneous if an attempt
8763 is made to queue a second task on such an entry.
8765 @item No_Implementation_Attributes
8766 @findex No_Implementation_Attributes
8767 This restriction checks at compile time that no GNAT-defined attributes
8768 are present. With this restriction, the only attributes that can be used
8769 are those defined in the Ada Reference Manual.
8771 @item No_Implementation_Pragmas
8772 @findex No_Implementation_Pragmas
8773 This restriction checks at compile time that no GNAT-defined pragmas
8774 are present. With this restriction, the only pragmas that can be used
8775 are those defined in the Ada Reference Manual.
8777 @item No_Implementation_Restrictions
8778 @findex No_Implementation_Restrictions
8779 This restriction checks at compile time that no GNAT-defined restriction
8780 identifiers (other than @code{No_Implementation_Restrictions} itself)
8781 are present. With this restriction, the only other restriction identifiers
8782 that can be used are those defined in the Ada Reference Manual.
8784 @item No_Wide_Characters
8785 @findex No_Wide_Characters
8786 This restriction ensures at compile time that no uses of the types
8787 @code{Wide_Character} or @code{Wide_String} or corresponding wide
8789 appear, and that no wide or wide wide string or character literals
8790 appear in the program (that is literals representing characters not in
8791 type @code{Character}.
8798 @strong{58}. The consequences of violating limitations on
8799 @code{Restrictions} pragmas. See 13.12(9).
8802 Restrictions that can be checked at compile time result in illegalities
8803 if violated. Currently there are no other consequences of violating
8809 @strong{59}. The representation used by the @code{Read} and
8810 @code{Write} attributes of elementary types in terms of stream
8811 elements. See 13.13.2(9).
8814 The representation is the in-memory representation of the base type of
8815 the type, using the number of bits corresponding to the
8816 @code{@var{type}'Size} value, and the natural ordering of the machine.
8821 @strong{60}. The names and characteristics of the numeric subtypes
8822 declared in the visible part of package @code{Standard}. See A.1(3).
8825 See items describing the integer and floating-point types supported.
8830 @strong{61}. The accuracy actually achieved by the elementary
8831 functions. See A.5.1(1).
8834 The elementary functions correspond to the functions available in the C
8835 library. Only fast math mode is implemented.
8840 @strong{62}. The sign of a zero result from some of the operators or
8841 functions in @code{Numerics.Generic_Elementary_Functions}, when
8842 @code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
8845 The sign of zeroes follows the requirements of the IEEE 754 standard on
8851 @strong{63}. The value of
8852 @code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
8855 Maximum image width is 649, see library file @file{a-numran.ads}.
8860 @strong{64}. The value of
8861 @code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
8864 Maximum image width is 80, see library file @file{a-nudira.ads}.
8869 @strong{65}. The algorithms for random number generation. See
8873 The algorithm is documented in the source files @file{a-numran.ads} and
8874 @file{a-numran.adb}.
8879 @strong{66}. The string representation of a random number generator's
8880 state. See A.5.2(38).
8883 See the documentation contained in the file @file{a-numran.adb}.
8888 @strong{67}. The minimum time interval between calls to the
8889 time-dependent Reset procedure that are guaranteed to initiate different
8890 random number sequences. See A.5.2(45).
8893 The minimum period between reset calls to guarantee distinct series of
8894 random numbers is one microsecond.
8899 @strong{68}. The values of the @code{Model_Mantissa},
8900 @code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
8901 @code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
8902 Annex is not supported. See A.5.3(72).
8905 See the source file @file{ttypef.ads} for the values of all numeric
8911 @strong{69}. Any implementation-defined characteristics of the
8912 input-output packages. See A.7(14).
8915 There are no special implementation defined characteristics for these
8921 @strong{70}. The value of @code{Buffer_Size} in @code{Storage_IO}. See
8925 All type representations are contiguous, and the @code{Buffer_Size} is
8926 the value of @code{@var{type}'Size} rounded up to the next storage unit
8932 @strong{71}. External files for standard input, standard output, and
8933 standard error See A.10(5).
8936 These files are mapped onto the files provided by the C streams
8937 libraries. See source file @file{i-cstrea.ads} for further details.
8942 @strong{72}. The accuracy of the value produced by @code{Put}. See
8946 If more digits are requested in the output than are represented by the
8947 precision of the value, zeroes are output in the corresponding least
8948 significant digit positions.
8953 @strong{73}. The meaning of @code{Argument_Count}, @code{Argument}, and
8954 @code{Command_Name}. See A.15(1).
8957 These are mapped onto the @code{argv} and @code{argc} parameters of the
8958 main program in the natural manner.
8963 @strong{74}. Implementation-defined convention names. See B.1(11).
8966 The following convention names are supported
8974 Synonym for Assembler
8976 Synonym for Assembler
8979 @item C_Pass_By_Copy
8980 Allowed only for record types, like C, but also notes that record
8981 is to be passed by copy rather than reference.
8984 @item C_Plus_Plus (or CPP)
8987 Treated the same as C
8989 Treated the same as C
8993 For support of pragma @code{Import} with convention Intrinsic, see
8994 separate section on Intrinsic Subprograms.
8996 Stdcall (used for Windows implementations only). This convention correspond
8997 to the WINAPI (previously called Pascal convention) C/C++ convention under
8998 Windows. A function with this convention cleans the stack before exit.
9004 Stubbed is a special convention used to indicate that the body of the
9005 subprogram will be entirely ignored. Any call to the subprogram
9006 is converted into a raise of the @code{Program_Error} exception. If a
9007 pragma @code{Import} specifies convention @code{stubbed} then no body need
9008 be present at all. This convention is useful during development for the
9009 inclusion of subprograms whose body has not yet been written.
9013 In addition, all otherwise unrecognized convention names are also
9014 treated as being synonymous with convention C@. In all implementations
9015 except for VMS, use of such other names results in a warning. In VMS
9016 implementations, these names are accepted silently.
9021 @strong{75}. The meaning of link names. See B.1(36).
9024 Link names are the actual names used by the linker.
9029 @strong{76}. The manner of choosing link names when neither the link
9030 name nor the address of an imported or exported entity is specified. See
9034 The default linker name is that which would be assigned by the relevant
9035 external language, interpreting the Ada name as being in all lower case
9041 @strong{77}. The effect of pragma @code{Linker_Options}. See B.1(37).
9044 The string passed to @code{Linker_Options} is presented uninterpreted as
9045 an argument to the link command, unless it contains ASCII.NUL characters.
9046 NUL characters if they appear act as argument separators, so for example
9048 @smallexample @c ada
9049 pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef");
9053 causes two separate arguments @code{-labc} and @code{-ldef} to be passed to the
9054 linker. The order of linker options is preserved for a given unit. The final
9055 list of options passed to the linker is in reverse order of the elaboration
9056 order. For example, linker options for a body always appear before the options
9057 from the corresponding package spec.
9062 @strong{78}. The contents of the visible part of package
9063 @code{Interfaces} and its language-defined descendants. See B.2(1).
9066 See files with prefix @file{i-} in the distributed library.
9071 @strong{79}. Implementation-defined children of package
9072 @code{Interfaces}. The contents of the visible part of package
9073 @code{Interfaces}. See B.2(11).
9076 See files with prefix @file{i-} in the distributed library.
9081 @strong{80}. The types @code{Floating}, @code{Long_Floating},
9082 @code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
9083 @code{COBOL_Character}; and the initialization of the variables
9084 @code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
9085 @code{Interfaces.COBOL}. See B.4(50).
9092 (Floating) Long_Float
9097 @item Decimal_Element
9099 @item COBOL_Character
9104 For initialization, see the file @file{i-cobol.ads} in the distributed library.
9109 @strong{81}. Support for access to machine instructions. See C.1(1).
9112 See documentation in file @file{s-maccod.ads} in the distributed library.
9117 @strong{82}. Implementation-defined aspects of access to machine
9118 operations. See C.1(9).
9121 See documentation in file @file{s-maccod.ads} in the distributed library.
9126 @strong{83}. Implementation-defined aspects of interrupts. See C.3(2).
9129 Interrupts are mapped to signals or conditions as appropriate. See
9131 @code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
9132 on the interrupts supported on a particular target.
9137 @strong{84}. Implementation-defined aspects of pre-elaboration. See
9141 GNAT does not permit a partition to be restarted without reloading,
9142 except under control of the debugger.
9147 @strong{85}. The semantics of pragma @code{Discard_Names}. See C.5(7).
9150 Pragma @code{Discard_Names} causes names of enumeration literals to
9151 be suppressed. In the presence of this pragma, the Image attribute
9152 provides the image of the Pos of the literal, and Value accepts
9158 @strong{86}. The result of the @code{Task_Identification.Image}
9159 attribute. See C.7.1(7).
9162 The result of this attribute is a string that identifies
9163 the object or component that denotes a given task. If a variable @code{Var}
9164 has a task type, the image for this task will have the form @code{Var_@var{XXXXXXXX}},
9166 is the hexadecimal representation of the virtual address of the corresponding
9167 task control block. If the variable is an array of tasks, the image of each
9168 task will have the form of an indexed component indicating the position of a
9169 given task in the array, e.g.@: @code{Group(5)_@var{XXXXXXX}}. If the task is a
9170 component of a record, the image of the task will have the form of a selected
9171 component. These rules are fully recursive, so that the image of a task that
9172 is a subcomponent of a composite object corresponds to the expression that
9173 designates this task.
9175 If a task is created by an allocator, its image depends on the context. If the
9176 allocator is part of an object declaration, the rules described above are used
9177 to construct its image, and this image is not affected by subsequent
9178 assignments. If the allocator appears within an expression, the image
9179 includes only the name of the task type.
9181 If the configuration pragma Discard_Names is present, or if the restriction
9182 No_Implicit_Heap_Allocation is in effect, the image reduces to
9183 the numeric suffix, that is to say the hexadecimal representation of the
9184 virtual address of the control block of the task.
9188 @strong{87}. The value of @code{Current_Task} when in a protected entry
9189 or interrupt handler. See C.7.1(17).
9192 Protected entries or interrupt handlers can be executed by any
9193 convenient thread, so the value of @code{Current_Task} is undefined.
9198 @strong{88}. The effect of calling @code{Current_Task} from an entry
9199 body or interrupt handler. See C.7.1(19).
9202 The effect of calling @code{Current_Task} from an entry body or
9203 interrupt handler is to return the identification of the task currently
9209 @strong{89}. Implementation-defined aspects of
9210 @code{Task_Attributes}. See C.7.2(19).
9213 There are no implementation-defined aspects of @code{Task_Attributes}.
9218 @strong{90}. Values of all @code{Metrics}. See D(2).
9221 The metrics information for GNAT depends on the performance of the
9222 underlying operating system. The sources of the run-time for tasking
9223 implementation, together with the output from @option{-gnatG} can be
9224 used to determine the exact sequence of operating systems calls made
9225 to implement various tasking constructs. Together with appropriate
9226 information on the performance of the underlying operating system,
9227 on the exact target in use, this information can be used to determine
9228 the required metrics.
9233 @strong{91}. The declarations of @code{Any_Priority} and
9234 @code{Priority}. See D.1(11).
9237 See declarations in file @file{system.ads}.
9242 @strong{92}. Implementation-defined execution resources. See D.1(15).
9245 There are no implementation-defined execution resources.
9250 @strong{93}. Whether, on a multiprocessor, a task that is waiting for
9251 access to a protected object keeps its processor busy. See D.2.1(3).
9254 On a multi-processor, a task that is waiting for access to a protected
9255 object does not keep its processor busy.
9260 @strong{94}. The affect of implementation defined execution resources
9261 on task dispatching. See D.2.1(9).
9266 Tasks map to IRIX threads, and the dispatching policy is as defined by
9267 the IRIX implementation of threads.
9269 Tasks map to threads in the threads package used by GNAT@. Where possible
9270 and appropriate, these threads correspond to native threads of the
9271 underlying operating system.
9276 @strong{95}. Implementation-defined @code{policy_identifiers} allowed
9277 in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
9280 There are no implementation-defined policy-identifiers allowed in this
9286 @strong{96}. Implementation-defined aspects of priority inversion. See
9290 Execution of a task cannot be preempted by the implementation processing
9291 of delay expirations for lower priority tasks.
9296 @strong{97}. Implementation defined task dispatching. See D.2.2(18).
9301 Tasks map to IRIX threads, and the dispatching policy is as defined by
9302 the IRIX implementation of threads.
9304 The policy is the same as that of the underlying threads implementation.
9309 @strong{98}. Implementation-defined @code{policy_identifiers} allowed
9310 in a pragma @code{Locking_Policy}. See D.3(4).
9313 The only implementation defined policy permitted in GNAT is
9314 @code{Inheritance_Locking}. On targets that support this policy, locking
9315 is implemented by inheritance, i.e.@: the task owning the lock operates
9316 at a priority equal to the highest priority of any task currently
9317 requesting the lock.
9322 @strong{99}. Default ceiling priorities. See D.3(10).
9325 The ceiling priority of protected objects of the type
9326 @code{System.Interrupt_Priority'Last} as described in the Ada
9327 Reference Manual D.3(10),
9332 @strong{100}. The ceiling of any protected object used internally by
9333 the implementation. See D.3(16).
9336 The ceiling priority of internal protected objects is
9337 @code{System.Priority'Last}.
9342 @strong{101}. Implementation-defined queuing policies. See D.4(1).
9345 There are no implementation-defined queuing policies.
9350 @strong{102}. On a multiprocessor, any conditions that cause the
9351 completion of an aborted construct to be delayed later than what is
9352 specified for a single processor. See D.6(3).
9355 The semantics for abort on a multi-processor is the same as on a single
9356 processor, there are no further delays.
9361 @strong{103}. Any operations that implicitly require heap storage
9362 allocation. See D.7(8).
9365 The only operation that implicitly requires heap storage allocation is
9371 @strong{104}. Implementation-defined aspects of pragma
9372 @code{Restrictions}. See D.7(20).
9375 There are no such implementation-defined aspects.
9380 @strong{105}. Implementation-defined aspects of package
9381 @code{Real_Time}. See D.8(17).
9384 There are no implementation defined aspects of package @code{Real_Time}.
9389 @strong{106}. Implementation-defined aspects of
9390 @code{delay_statements}. See D.9(8).
9393 Any difference greater than one microsecond will cause the task to be
9394 delayed (see D.9(7)).
9399 @strong{107}. The upper bound on the duration of interrupt blocking
9400 caused by the implementation. See D.12(5).
9403 The upper bound is determined by the underlying operating system. In
9404 no cases is it more than 10 milliseconds.
9409 @strong{108}. The means for creating and executing distributed
9413 The GLADE package provides a utility GNATDIST for creating and executing
9414 distributed programs. See the GLADE reference manual for further details.
9419 @strong{109}. Any events that can result in a partition becoming
9420 inaccessible. See E.1(7).
9423 See the GLADE reference manual for full details on such events.
9428 @strong{110}. The scheduling policies, treatment of priorities, and
9429 management of shared resources between partitions in certain cases. See
9433 See the GLADE reference manual for full details on these aspects of
9434 multi-partition execution.
9439 @strong{111}. Events that cause the version of a compilation unit to
9443 Editing the source file of a compilation unit, or the source files of
9444 any units on which it is dependent in a significant way cause the version
9445 to change. No other actions cause the version number to change. All changes
9446 are significant except those which affect only layout, capitalization or
9452 @strong{112}. Whether the execution of the remote subprogram is
9453 immediately aborted as a result of cancellation. See E.4(13).
9456 See the GLADE reference manual for details on the effect of abort in
9457 a distributed application.
9462 @strong{113}. Implementation-defined aspects of the PCS@. See E.5(25).
9465 See the GLADE reference manual for a full description of all implementation
9466 defined aspects of the PCS@.
9471 @strong{114}. Implementation-defined interfaces in the PCS@. See
9475 See the GLADE reference manual for a full description of all
9476 implementation defined interfaces.
9481 @strong{115}. The values of named numbers in the package
9482 @code{Decimal}. See F.2(7).
9494 @item Max_Decimal_Digits
9501 @strong{116}. The value of @code{Max_Picture_Length} in the package
9502 @code{Text_IO.Editing}. See F.3.3(16).
9510 @strong{117}. The value of @code{Max_Picture_Length} in the package
9511 @code{Wide_Text_IO.Editing}. See F.3.4(5).
9519 @strong{118}. The accuracy actually achieved by the complex elementary
9520 functions and by other complex arithmetic operations. See G.1(1).
9523 Standard library functions are used for the complex arithmetic
9524 operations. Only fast math mode is currently supported.
9529 @strong{119}. The sign of a zero result (or a component thereof) from
9530 any operator or function in @code{Numerics.Generic_Complex_Types}, when
9531 @code{Real'Signed_Zeros} is True. See G.1.1(53).
9534 The signs of zero values are as recommended by the relevant
9535 implementation advice.
9540 @strong{120}. The sign of a zero result (or a component thereof) from
9541 any operator or function in
9542 @code{Numerics.Generic_Complex_Elementary_Functions}, when
9543 @code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
9546 The signs of zero values are as recommended by the relevant
9547 implementation advice.
9552 @strong{121}. Whether the strict mode or the relaxed mode is the
9553 default. See G.2(2).
9556 The strict mode is the default. There is no separate relaxed mode. GNAT
9557 provides a highly efficient implementation of strict mode.
9562 @strong{122}. The result interval in certain cases of fixed-to-float
9563 conversion. See G.2.1(10).
9566 For cases where the result interval is implementation dependent, the
9567 accuracy is that provided by performing all operations in 64-bit IEEE
9568 floating-point format.
9573 @strong{123}. The result of a floating point arithmetic operation in
9574 overflow situations, when the @code{Machine_Overflows} attribute of the
9575 result type is @code{False}. See G.2.1(13).
9578 Infinite and NaN values are produced as dictated by the IEEE
9579 floating-point standard.
9581 Note that on machines that are not fully compliant with the IEEE
9582 floating-point standard, such as Alpha, the @option{-mieee} compiler flag
9583 must be used for achieving IEEE confirming behavior (although at the cost
9584 of a significant performance penalty), so infinite and NaN values are
9590 @strong{124}. The result interval for division (or exponentiation by a
9591 negative exponent), when the floating point hardware implements division
9592 as multiplication by a reciprocal. See G.2.1(16).
9595 Not relevant, division is IEEE exact.
9600 @strong{125}. The definition of close result set, which determines the
9601 accuracy of certain fixed point multiplications and divisions. See
9605 Operations in the close result set are performed using IEEE long format
9606 floating-point arithmetic. The input operands are converted to
9607 floating-point, the operation is done in floating-point, and the result
9608 is converted to the target type.
9613 @strong{126}. Conditions on a @code{universal_real} operand of a fixed
9614 point multiplication or division for which the result shall be in the
9615 perfect result set. See G.2.3(22).
9618 The result is only defined to be in the perfect result set if the result
9619 can be computed by a single scaling operation involving a scale factor
9620 representable in 64-bits.
9625 @strong{127}. The result of a fixed point arithmetic operation in
9626 overflow situations, when the @code{Machine_Overflows} attribute of the
9627 result type is @code{False}. See G.2.3(27).
9630 Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
9636 @strong{128}. The result of an elementary function reference in
9637 overflow situations, when the @code{Machine_Overflows} attribute of the
9638 result type is @code{False}. See G.2.4(4).
9641 IEEE infinite and Nan values are produced as appropriate.
9646 @strong{129}. The value of the angle threshold, within which certain
9647 elementary functions, complex arithmetic operations, and complex
9648 elementary functions yield results conforming to a maximum relative
9649 error bound. See G.2.4(10).
9652 Information on this subject is not yet available.
9657 @strong{130}. The accuracy of certain elementary functions for
9658 parameters beyond the angle threshold. See G.2.4(10).
9661 Information on this subject is not yet available.
9666 @strong{131}. The result of a complex arithmetic operation or complex
9667 elementary function reference in overflow situations, when the
9668 @code{Machine_Overflows} attribute of the corresponding real type is
9669 @code{False}. See G.2.6(5).
9672 IEEE infinite and Nan values are produced as appropriate.
9677 @strong{132}. The accuracy of certain complex arithmetic operations and
9678 certain complex elementary functions for parameters (or components
9679 thereof) beyond the angle threshold. See G.2.6(8).
9682 Information on those subjects is not yet available.
9687 @strong{133}. Information regarding bounded errors and erroneous
9688 execution. See H.2(1).
9691 Information on this subject is not yet available.
9696 @strong{134}. Implementation-defined aspects of pragma
9697 @code{Inspection_Point}. See H.3.2(8).
9700 Pragma @code{Inspection_Point} ensures that the variable is live and can
9701 be examined by the debugger at the inspection point.
9706 @strong{135}. Implementation-defined aspects of pragma
9707 @code{Restrictions}. See H.4(25).
9710 There are no implementation-defined aspects of pragma @code{Restrictions}. The
9711 use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
9712 generated code. Checks must suppressed by use of pragma @code{Suppress}.
9717 @strong{136}. Any restrictions on pragma @code{Restrictions}. See
9721 There are no restrictions on pragma @code{Restrictions}.
9723 @node Intrinsic Subprograms
9724 @chapter Intrinsic Subprograms
9725 @cindex Intrinsic Subprograms
9728 * Intrinsic Operators::
9729 * Enclosing_Entity::
9730 * Exception_Information::
9731 * Exception_Message::
9739 * Shift_Right_Arithmetic::
9744 GNAT allows a user application program to write the declaration:
9746 @smallexample @c ada
9747 pragma Import (Intrinsic, name);
9751 providing that the name corresponds to one of the implemented intrinsic
9752 subprograms in GNAT, and that the parameter profile of the referenced
9753 subprogram meets the requirements. This chapter describes the set of
9754 implemented intrinsic subprograms, and the requirements on parameter profiles.
9755 Note that no body is supplied; as with other uses of pragma Import, the
9756 body is supplied elsewhere (in this case by the compiler itself). Note
9757 that any use of this feature is potentially non-portable, since the
9758 Ada standard does not require Ada compilers to implement this feature.
9760 @node Intrinsic Operators
9761 @section Intrinsic Operators
9762 @cindex Intrinsic operator
9765 All the predefined numeric operators in package Standard
9766 in @code{pragma Import (Intrinsic,..)}
9767 declarations. In the binary operator case, the operands must have the same
9768 size. The operand or operands must also be appropriate for
9769 the operator. For example, for addition, the operands must
9770 both be floating-point or both be fixed-point, and the
9771 right operand for @code{"**"} must have a root type of
9772 @code{Standard.Integer'Base}.
9773 You can use an intrinsic operator declaration as in the following example:
9775 @smallexample @c ada
9776 type Int1 is new Integer;
9777 type Int2 is new Integer;
9779 function "+" (X1 : Int1; X2 : Int2) return Int1;
9780 function "+" (X1 : Int1; X2 : Int2) return Int2;
9781 pragma Import (Intrinsic, "+");
9785 This declaration would permit ``mixed mode'' arithmetic on items
9786 of the differing types @code{Int1} and @code{Int2}.
9787 It is also possible to specify such operators for private types, if the
9788 full views are appropriate arithmetic types.
9790 @node Enclosing_Entity
9791 @section Enclosing_Entity
9792 @cindex Enclosing_Entity
9794 This intrinsic subprogram is used in the implementation of the
9795 library routine @code{GNAT.Source_Info}. The only useful use of the
9796 intrinsic import in this case is the one in this unit, so an
9797 application program should simply call the function
9798 @code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
9799 the current subprogram, package, task, entry, or protected subprogram.
9801 @node Exception_Information
9802 @section Exception_Information
9803 @cindex Exception_Information'
9805 This intrinsic subprogram is used in the implementation of the
9806 library routine @code{GNAT.Current_Exception}. The only useful
9807 use of the intrinsic import in this case is the one in this unit,
9808 so an application program should simply call the function
9809 @code{GNAT.Current_Exception.Exception_Information} to obtain
9810 the exception information associated with the current exception.
9812 @node Exception_Message
9813 @section Exception_Message
9814 @cindex Exception_Message
9816 This intrinsic subprogram is used in the implementation of the
9817 library routine @code{GNAT.Current_Exception}. The only useful
9818 use of the intrinsic import in this case is the one in this unit,
9819 so an application program should simply call the function
9820 @code{GNAT.Current_Exception.Exception_Message} to obtain
9821 the message associated with the current exception.
9823 @node Exception_Name
9824 @section Exception_Name
9825 @cindex Exception_Name
9827 This intrinsic subprogram is used in the implementation of the
9828 library routine @code{GNAT.Current_Exception}. The only useful
9829 use of the intrinsic import in this case is the one in this unit,
9830 so an application program should simply call the function
9831 @code{GNAT.Current_Exception.Exception_Name} to obtain
9832 the name of the current exception.
9838 This intrinsic subprogram is used in the implementation of the
9839 library routine @code{GNAT.Source_Info}. The only useful use of the
9840 intrinsic import in this case is the one in this unit, so an
9841 application program should simply call the function
9842 @code{GNAT.Source_Info.File} to obtain the name of the current
9849 This intrinsic subprogram is used in the implementation of the
9850 library routine @code{GNAT.Source_Info}. The only useful use of the
9851 intrinsic import in this case is the one in this unit, so an
9852 application program should simply call the function
9853 @code{GNAT.Source_Info.Line} to obtain the number of the current
9857 @section Rotate_Left
9860 In standard Ada, the @code{Rotate_Left} function is available only
9861 for the predefined modular types in package @code{Interfaces}. However, in
9862 GNAT it is possible to define a Rotate_Left function for a user
9863 defined modular type or any signed integer type as in this example:
9865 @smallexample @c ada
9867 (Value : My_Modular_Type;
9869 return My_Modular_Type;
9873 The requirements are that the profile be exactly as in the example
9874 above. The only modifications allowed are in the formal parameter
9875 names, and in the type of @code{Value} and the return type, which
9876 must be the same, and must be either a signed integer type, or
9877 a modular integer type with a binary modulus, and the size must
9878 be 8. 16, 32 or 64 bits.
9881 @section Rotate_Right
9882 @cindex Rotate_Right
9884 A @code{Rotate_Right} function can be defined for any user defined
9885 binary modular integer type, or signed integer type, as described
9886 above for @code{Rotate_Left}.
9892 A @code{Shift_Left} function can be defined for any user defined
9893 binary modular integer type, or signed integer type, as described
9894 above for @code{Rotate_Left}.
9897 @section Shift_Right
9900 A @code{Shift_Right} function can be defined for any user defined
9901 binary modular integer type, or signed integer type, as described
9902 above for @code{Rotate_Left}.
9904 @node Shift_Right_Arithmetic
9905 @section Shift_Right_Arithmetic
9906 @cindex Shift_Right_Arithmetic
9908 A @code{Shift_Right_Arithmetic} function can be defined for any user
9909 defined binary modular integer type, or signed integer type, as described
9910 above for @code{Rotate_Left}.
9912 @node Source_Location
9913 @section Source_Location
9914 @cindex Source_Location
9916 This intrinsic subprogram is used in the implementation of the
9917 library routine @code{GNAT.Source_Info}. The only useful use of the
9918 intrinsic import in this case is the one in this unit, so an
9919 application program should simply call the function
9920 @code{GNAT.Source_Info.Source_Location} to obtain the current
9921 source file location.
9923 @node Representation Clauses and Pragmas
9924 @chapter Representation Clauses and Pragmas
9925 @cindex Representation Clauses
9928 * Alignment Clauses::
9930 * Storage_Size Clauses::
9931 * Size of Variant Record Objects::
9932 * Biased Representation ::
9933 * Value_Size and Object_Size Clauses::
9934 * Component_Size Clauses::
9935 * Bit_Order Clauses::
9936 * Effect of Bit_Order on Byte Ordering::
9937 * Pragma Pack for Arrays::
9938 * Pragma Pack for Records::
9939 * Record Representation Clauses::
9940 * Enumeration Clauses::
9942 * Effect of Convention on Representation::
9943 * Determining the Representations chosen by GNAT::
9947 @cindex Representation Clause
9948 @cindex Representation Pragma
9949 @cindex Pragma, representation
9950 This section describes the representation clauses accepted by GNAT, and
9951 their effect on the representation of corresponding data objects.
9953 GNAT fully implements Annex C (Systems Programming). This means that all
9954 the implementation advice sections in chapter 13 are fully implemented.
9955 However, these sections only require a minimal level of support for
9956 representation clauses. GNAT provides much more extensive capabilities,
9957 and this section describes the additional capabilities provided.
9959 @node Alignment Clauses
9960 @section Alignment Clauses
9961 @cindex Alignment Clause
9964 GNAT requires that all alignment clauses specify a power of 2, and all
9965 default alignments are always a power of 2. The default alignment
9966 values are as follows:
9969 @item @emph{Primitive Types}.
9970 For primitive types, the alignment is the minimum of the actual size of
9971 objects of the type divided by @code{Storage_Unit},
9972 and the maximum alignment supported by the target.
9973 (This maximum alignment is given by the GNAT-specific attribute
9974 @code{Standard'Maximum_Alignment}; see @ref{Maximum_Alignment}.)
9975 @cindex @code{Maximum_Alignment} attribute
9976 For example, for type @code{Long_Float}, the object size is 8 bytes, and the
9977 default alignment will be 8 on any target that supports alignments
9978 this large, but on some targets, the maximum alignment may be smaller
9979 than 8, in which case objects of type @code{Long_Float} will be maximally
9982 @item @emph{Arrays}.
9983 For arrays, the alignment is equal to the alignment of the component type
9984 for the normal case where no packing or component size is given. If the
9985 array is packed, and the packing is effective (see separate section on
9986 packed arrays), then the alignment will be one for long packed arrays,
9987 or arrays whose length is not known at compile time. For short packed
9988 arrays, which are handled internally as modular types, the alignment
9989 will be as described for primitive types, e.g.@: a packed array of length
9990 31 bits will have an object size of four bytes, and an alignment of 4.
9992 @item @emph{Records}.
9993 For the normal non-packed case, the alignment of a record is equal to
9994 the maximum alignment of any of its components. For tagged records, this
9995 includes the implicit access type used for the tag. If a pragma @code{Pack}
9996 is used and all components are packable (see separate section on pragma
9997 @code{Pack}), then the resulting alignment is 1, unless the layout of the
9998 record makes it profitable to increase it.
10000 A special case is when:
10003 the size of the record is given explicitly, or a
10004 full record representation clause is given, and
10006 the size of the record is 2, 4, or 8 bytes.
10009 In this case, an alignment is chosen to match the
10010 size of the record. For example, if we have:
10012 @smallexample @c ada
10013 type Small is record
10016 for Small'Size use 16;
10020 then the default alignment of the record type @code{Small} is 2, not 1. This
10021 leads to more efficient code when the record is treated as a unit, and also
10022 allows the type to specified as @code{Atomic} on architectures requiring
10028 An alignment clause may specify a larger alignment than the default value
10029 up to some maximum value dependent on the target (obtainable by using the
10030 attribute reference @code{Standard'Maximum_Alignment}). It may also specify
10031 a smaller alignment than the default value for enumeration, integer and
10032 fixed point types, as well as for record types, for example
10034 @smallexample @c ada
10039 for V'alignment use 1;
10043 @cindex Alignment, default
10044 The default alignment for the type @code{V} is 4, as a result of the
10045 Integer field in the record, but it is permissible, as shown, to
10046 override the default alignment of the record with a smaller value.
10049 @section Size Clauses
10050 @cindex Size Clause
10053 The default size for a type @code{T} is obtainable through the
10054 language-defined attribute @code{T'Size} and also through the
10055 equivalent GNAT-defined attribute @code{T'Value_Size}.
10056 For objects of type @code{T}, GNAT will generally increase the type size
10057 so that the object size (obtainable through the GNAT-defined attribute
10058 @code{T'Object_Size})
10059 is a multiple of @code{T'Alignment * Storage_Unit}.
10062 @smallexample @c ada
10063 type Smallint is range 1 .. 6;
10072 In this example, @code{Smallint'Size} = @code{Smallint'Value_Size} = 3,
10073 as specified by the RM rules,
10074 but objects of this type will have a size of 8
10075 (@code{Smallint'Object_Size} = 8),
10076 since objects by default occupy an integral number
10077 of storage units. On some targets, notably older
10078 versions of the Digital Alpha, the size of stand
10079 alone objects of this type may be 32, reflecting
10080 the inability of the hardware to do byte load/stores.
10082 Similarly, the size of type @code{Rec} is 40 bits
10083 (@code{Rec'Size} = @code{Rec'Value_Size} = 40), but
10084 the alignment is 4, so objects of this type will have
10085 their size increased to 64 bits so that it is a multiple
10086 of the alignment (in bits). This decision is
10087 in accordance with the specific Implementation Advice in RM 13.3(43):
10090 A @code{Size} clause should be supported for an object if the specified
10091 @code{Size} is at least as large as its subtype's @code{Size}, and corresponds
10092 to a size in storage elements that is a multiple of the object's
10093 @code{Alignment} (if the @code{Alignment} is nonzero).
10097 An explicit size clause may be used to override the default size by
10098 increasing it. For example, if we have:
10100 @smallexample @c ada
10101 type My_Boolean is new Boolean;
10102 for My_Boolean'Size use 32;
10106 then values of this type will always be 32 bits long. In the case of
10107 discrete types, the size can be increased up to 64 bits, with the effect
10108 that the entire specified field is used to hold the value, sign- or
10109 zero-extended as appropriate. If more than 64 bits is specified, then
10110 padding space is allocated after the value, and a warning is issued that
10111 there are unused bits.
10113 Similarly the size of records and arrays may be increased, and the effect
10114 is to add padding bits after the value. This also causes a warning message
10117 The largest Size value permitted in GNAT is 2**31@minus{}1. Since this is a
10118 Size in bits, this corresponds to an object of size 256 megabytes (minus
10119 one). This limitation is true on all targets. The reason for this
10120 limitation is that it improves the quality of the code in many cases
10121 if it is known that a Size value can be accommodated in an object of
10124 @node Storage_Size Clauses
10125 @section Storage_Size Clauses
10126 @cindex Storage_Size Clause
10129 For tasks, the @code{Storage_Size} clause specifies the amount of space
10130 to be allocated for the task stack. This cannot be extended, and if the
10131 stack is exhausted, then @code{Storage_Error} will be raised (if stack
10132 checking is enabled). Use a @code{Storage_Size} attribute definition clause,
10133 or a @code{Storage_Size} pragma in the task definition to set the
10134 appropriate required size. A useful technique is to include in every
10135 task definition a pragma of the form:
10137 @smallexample @c ada
10138 pragma Storage_Size (Default_Stack_Size);
10142 Then @code{Default_Stack_Size} can be defined in a global package, and
10143 modified as required. Any tasks requiring stack sizes different from the
10144 default can have an appropriate alternative reference in the pragma.
10146 You can also use the @option{-d} binder switch to modify the default stack
10149 For access types, the @code{Storage_Size} clause specifies the maximum
10150 space available for allocation of objects of the type. If this space is
10151 exceeded then @code{Storage_Error} will be raised by an allocation attempt.
10152 In the case where the access type is declared local to a subprogram, the
10153 use of a @code{Storage_Size} clause triggers automatic use of a special
10154 predefined storage pool (@code{System.Pool_Size}) that ensures that all
10155 space for the pool is automatically reclaimed on exit from the scope in
10156 which the type is declared.
10158 A special case recognized by the compiler is the specification of a
10159 @code{Storage_Size} of zero for an access type. This means that no
10160 items can be allocated from the pool, and this is recognized at compile
10161 time, and all the overhead normally associated with maintaining a fixed
10162 size storage pool is eliminated. Consider the following example:
10164 @smallexample @c ada
10166 type R is array (Natural) of Character;
10167 type P is access all R;
10168 for P'Storage_Size use 0;
10169 -- Above access type intended only for interfacing purposes
10173 procedure g (m : P);
10174 pragma Import (C, g);
10185 As indicated in this example, these dummy storage pools are often useful in
10186 connection with interfacing where no object will ever be allocated. If you
10187 compile the above example, you get the warning:
10190 p.adb:16:09: warning: allocation from empty storage pool
10191 p.adb:16:09: warning: Storage_Error will be raised at run time
10195 Of course in practice, there will not be any explicit allocators in the
10196 case of such an access declaration.
10198 @node Size of Variant Record Objects
10199 @section Size of Variant Record Objects
10200 @cindex Size, variant record objects
10201 @cindex Variant record objects, size
10204 In the case of variant record objects, there is a question whether Size gives
10205 information about a particular variant, or the maximum size required
10206 for any variant. Consider the following program
10208 @smallexample @c ada
10209 with Text_IO; use Text_IO;
10211 type R1 (A : Boolean := False) is record
10213 when True => X : Character;
10214 when False => null;
10222 Put_Line (Integer'Image (V1'Size));
10223 Put_Line (Integer'Image (V2'Size));
10228 Here we are dealing with a variant record, where the True variant
10229 requires 16 bits, and the False variant requires 8 bits.
10230 In the above example, both V1 and V2 contain the False variant,
10231 which is only 8 bits long. However, the result of running the
10240 The reason for the difference here is that the discriminant value of
10241 V1 is fixed, and will always be False. It is not possible to assign
10242 a True variant value to V1, therefore 8 bits is sufficient. On the
10243 other hand, in the case of V2, the initial discriminant value is
10244 False (from the default), but it is possible to assign a True
10245 variant value to V2, therefore 16 bits must be allocated for V2
10246 in the general case, even fewer bits may be needed at any particular
10247 point during the program execution.
10249 As can be seen from the output of this program, the @code{'Size}
10250 attribute applied to such an object in GNAT gives the actual allocated
10251 size of the variable, which is the largest size of any of the variants.
10252 The Ada Reference Manual is not completely clear on what choice should
10253 be made here, but the GNAT behavior seems most consistent with the
10254 language in the RM@.
10256 In some cases, it may be desirable to obtain the size of the current
10257 variant, rather than the size of the largest variant. This can be
10258 achieved in GNAT by making use of the fact that in the case of a
10259 subprogram parameter, GNAT does indeed return the size of the current
10260 variant (because a subprogram has no way of knowing how much space
10261 is actually allocated for the actual).
10263 Consider the following modified version of the above program:
10265 @smallexample @c ada
10266 with Text_IO; use Text_IO;
10268 type R1 (A : Boolean := False) is record
10270 when True => X : Character;
10271 when False => null;
10277 function Size (V : R1) return Integer is
10283 Put_Line (Integer'Image (V2'Size));
10284 Put_Line (Integer'IMage (Size (V2)));
10286 Put_Line (Integer'Image (V2'Size));
10287 Put_Line (Integer'IMage (Size (V2)));
10292 The output from this program is
10302 Here we see that while the @code{'Size} attribute always returns
10303 the maximum size, regardless of the current variant value, the
10304 @code{Size} function does indeed return the size of the current
10307 @node Biased Representation
10308 @section Biased Representation
10309 @cindex Size for biased representation
10310 @cindex Biased representation
10313 In the case of scalars with a range starting at other than zero, it is
10314 possible in some cases to specify a size smaller than the default minimum
10315 value, and in such cases, GNAT uses an unsigned biased representation,
10316 in which zero is used to represent the lower bound, and successive values
10317 represent successive values of the type.
10319 For example, suppose we have the declaration:
10321 @smallexample @c ada
10322 type Small is range -7 .. -4;
10323 for Small'Size use 2;
10327 Although the default size of type @code{Small} is 4, the @code{Size}
10328 clause is accepted by GNAT and results in the following representation
10332 -7 is represented as 2#00#
10333 -6 is represented as 2#01#
10334 -5 is represented as 2#10#
10335 -4 is represented as 2#11#
10339 Biased representation is only used if the specified @code{Size} clause
10340 cannot be accepted in any other manner. These reduced sizes that force
10341 biased representation can be used for all discrete types except for
10342 enumeration types for which a representation clause is given.
10344 @node Value_Size and Object_Size Clauses
10345 @section Value_Size and Object_Size Clauses
10347 @findex Object_Size
10348 @cindex Size, of objects
10351 In Ada 95 and Ada 2005, @code{T'Size} for a type @code{T} is the minimum
10352 number of bits required to hold values of type @code{T}.
10353 Although this interpretation was allowed in Ada 83, it was not required,
10354 and this requirement in practice can cause some significant difficulties.
10355 For example, in most Ada 83 compilers, @code{Natural'Size} was 32.
10356 However, in Ada 95 and Ada 2005,
10357 @code{Natural'Size} is
10358 typically 31. This means that code may change in behavior when moving
10359 from Ada 83 to Ada 95 or Ada 2005. For example, consider:
10361 @smallexample @c ada
10362 type Rec is record;
10368 at 0 range 0 .. Natural'Size - 1;
10369 at 0 range Natural'Size .. 2 * Natural'Size - 1;
10374 In the above code, since the typical size of @code{Natural} objects
10375 is 32 bits and @code{Natural'Size} is 31, the above code can cause
10376 unexpected inefficient packing in Ada 95 and Ada 2005, and in general
10377 there are cases where the fact that the object size can exceed the
10378 size of the type causes surprises.
10380 To help get around this problem GNAT provides two implementation
10381 defined attributes, @code{Value_Size} and @code{Object_Size}. When
10382 applied to a type, these attributes yield the size of the type
10383 (corresponding to the RM defined size attribute), and the size of
10384 objects of the type respectively.
10386 The @code{Object_Size} is used for determining the default size of
10387 objects and components. This size value can be referred to using the
10388 @code{Object_Size} attribute. The phrase ``is used'' here means that it is
10389 the basis of the determination of the size. The backend is free to
10390 pad this up if necessary for efficiency, e.g.@: an 8-bit stand-alone
10391 character might be stored in 32 bits on a machine with no efficient
10392 byte access instructions such as the Alpha.
10394 The default rules for the value of @code{Object_Size} for
10395 discrete types are as follows:
10399 The @code{Object_Size} for base subtypes reflect the natural hardware
10400 size in bits (run the compiler with @option{-gnatS} to find those values
10401 for numeric types). Enumeration types and fixed-point base subtypes have
10402 8, 16, 32 or 64 bits for this size, depending on the range of values
10406 The @code{Object_Size} of a subtype is the same as the
10407 @code{Object_Size} of
10408 the type from which it is obtained.
10411 The @code{Object_Size} of a derived base type is copied from the parent
10412 base type, and the @code{Object_Size} of a derived first subtype is copied
10413 from the parent first subtype.
10417 The @code{Value_Size} attribute
10418 is the (minimum) number of bits required to store a value
10420 This value is used to determine how tightly to pack
10421 records or arrays with components of this type, and also affects
10422 the semantics of unchecked conversion (unchecked conversions where
10423 the @code{Value_Size} values differ generate a warning, and are potentially
10426 The default rules for the value of @code{Value_Size} are as follows:
10430 The @code{Value_Size} for a base subtype is the minimum number of bits
10431 required to store all values of the type (including the sign bit
10432 only if negative values are possible).
10435 If a subtype statically matches the first subtype of a given type, then it has
10436 by default the same @code{Value_Size} as the first subtype. This is a
10437 consequence of RM 13.1(14) (``if two subtypes statically match,
10438 then their subtype-specific aspects are the same''.)
10441 All other subtypes have a @code{Value_Size} corresponding to the minimum
10442 number of bits required to store all values of the subtype. For
10443 dynamic bounds, it is assumed that the value can range down or up
10444 to the corresponding bound of the ancestor
10448 The RM defined attribute @code{Size} corresponds to the
10449 @code{Value_Size} attribute.
10451 The @code{Size} attribute may be defined for a first-named subtype. This sets
10452 the @code{Value_Size} of
10453 the first-named subtype to the given value, and the
10454 @code{Object_Size} of this first-named subtype to the given value padded up
10455 to an appropriate boundary. It is a consequence of the default rules
10456 above that this @code{Object_Size} will apply to all further subtypes. On the
10457 other hand, @code{Value_Size} is affected only for the first subtype, any
10458 dynamic subtypes obtained from it directly, and any statically matching
10459 subtypes. The @code{Value_Size} of any other static subtypes is not affected.
10461 @code{Value_Size} and
10462 @code{Object_Size} may be explicitly set for any subtype using
10463 an attribute definition clause. Note that the use of these attributes
10464 can cause the RM 13.1(14) rule to be violated. If two access types
10465 reference aliased objects whose subtypes have differing @code{Object_Size}
10466 values as a result of explicit attribute definition clauses, then it
10467 is erroneous to convert from one access subtype to the other.
10469 At the implementation level, Esize stores the Object_Size and the
10470 RM_Size field stores the @code{Value_Size} (and hence the value of the
10471 @code{Size} attribute,
10472 which, as noted above, is equivalent to @code{Value_Size}).
10474 To get a feel for the difference, consider the following examples (note
10475 that in each case the base is @code{Short_Short_Integer} with a size of 8):
10478 Object_Size Value_Size
10480 type x1 is range 0 .. 5; 8 3
10482 type x2 is range 0 .. 5;
10483 for x2'size use 12; 16 12
10485 subtype x3 is x2 range 0 .. 3; 16 2
10487 subtype x4 is x2'base range 0 .. 10; 8 4
10489 subtype x5 is x2 range 0 .. dynamic; 16 3*
10491 subtype x6 is x2'base range 0 .. dynamic; 8 3*
10496 Note: the entries marked ``3*'' are not actually specified by the Ada
10497 Reference Manual, but it seems in the spirit of the RM rules to allocate
10498 the minimum number of bits (here 3, given the range for @code{x2})
10499 known to be large enough to hold the given range of values.
10501 So far, so good, but GNAT has to obey the RM rules, so the question is
10502 under what conditions must the RM @code{Size} be used.
10503 The following is a list
10504 of the occasions on which the RM @code{Size} must be used:
10508 Component size for packed arrays or records
10511 Value of the attribute @code{Size} for a type
10514 Warning about sizes not matching for unchecked conversion
10518 For record types, the @code{Object_Size} is always a multiple of the
10519 alignment of the type (this is true for all types). In some cases the
10520 @code{Value_Size} can be smaller. Consider:
10530 On a typical 32-bit architecture, the X component will be four bytes, and
10531 require four-byte alignment, and the Y component will be one byte. In this
10532 case @code{R'Value_Size} will be 40 (bits) since this is the minimum size
10533 required to store a value of this type, and for example, it is permissible
10534 to have a component of type R in an outer array whose component size is
10535 specified to be 48 bits. However, @code{R'Object_Size} will be 64 (bits),
10536 since it must be rounded up so that this value is a multiple of the
10537 alignment (4 bytes = 32 bits).
10540 For all other types, the @code{Object_Size}
10541 and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
10542 Only @code{Size} may be specified for such types.
10544 @node Component_Size Clauses
10545 @section Component_Size Clauses
10546 @cindex Component_Size Clause
10549 Normally, the value specified in a component size clause must be consistent
10550 with the subtype of the array component with regard to size and alignment.
10551 In other words, the value specified must be at least equal to the size
10552 of this subtype, and must be a multiple of the alignment value.
10554 In addition, component size clauses are allowed which cause the array
10555 to be packed, by specifying a smaller value. A first case is for
10556 component size values in the range 1 through 63. The value specified
10557 must not be smaller than the Size of the subtype. GNAT will accurately
10558 honor all packing requests in this range. For example, if we have:
10560 @smallexample @c ada
10561 type r is array (1 .. 8) of Natural;
10562 for r'Component_Size use 31;
10566 then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
10567 Of course access to the components of such an array is considerably
10568 less efficient than if the natural component size of 32 is used.
10569 A second case is when the subtype of the component is a record type
10570 padded because of its default alignment. For example, if we have:
10572 @smallexample @c ada
10579 type a is array (1 .. 8) of r;
10580 for a'Component_Size use 72;
10584 then the resulting array has a length of 72 bytes, instead of 96 bytes
10585 if the alignment of the record (4) was obeyed.
10587 Note that there is no point in giving both a component size clause
10588 and a pragma Pack for the same array type. if such duplicate
10589 clauses are given, the pragma Pack will be ignored.
10591 @node Bit_Order Clauses
10592 @section Bit_Order Clauses
10593 @cindex Bit_Order Clause
10594 @cindex bit ordering
10595 @cindex ordering, of bits
10598 For record subtypes, GNAT permits the specification of the @code{Bit_Order}
10599 attribute. The specification may either correspond to the default bit
10600 order for the target, in which case the specification has no effect and
10601 places no additional restrictions, or it may be for the non-standard
10602 setting (that is the opposite of the default).
10604 In the case where the non-standard value is specified, the effect is
10605 to renumber bits within each byte, but the ordering of bytes is not
10606 affected. There are certain
10607 restrictions placed on component clauses as follows:
10611 @item Components fitting within a single storage unit.
10613 These are unrestricted, and the effect is merely to renumber bits. For
10614 example if we are on a little-endian machine with @code{Low_Order_First}
10615 being the default, then the following two declarations have exactly
10618 @smallexample @c ada
10621 B : Integer range 1 .. 120;
10625 A at 0 range 0 .. 0;
10626 B at 0 range 1 .. 7;
10631 B : Integer range 1 .. 120;
10634 for R2'Bit_Order use High_Order_First;
10637 A at 0 range 7 .. 7;
10638 B at 0 range 0 .. 6;
10643 The useful application here is to write the second declaration with the
10644 @code{Bit_Order} attribute definition clause, and know that it will be treated
10645 the same, regardless of whether the target is little-endian or big-endian.
10647 @item Components occupying an integral number of bytes.
10649 These are components that exactly fit in two or more bytes. Such component
10650 declarations are allowed, but have no effect, since it is important to realize
10651 that the @code{Bit_Order} specification does not affect the ordering of bytes.
10652 In particular, the following attempt at getting an endian-independent integer
10655 @smallexample @c ada
10660 for R2'Bit_Order use High_Order_First;
10663 A at 0 range 0 .. 31;
10668 This declaration will result in a little-endian integer on a
10669 little-endian machine, and a big-endian integer on a big-endian machine.
10670 If byte flipping is required for interoperability between big- and
10671 little-endian machines, this must be explicitly programmed. This capability
10672 is not provided by @code{Bit_Order}.
10674 @item Components that are positioned across byte boundaries
10676 but do not occupy an integral number of bytes. Given that bytes are not
10677 reordered, such fields would occupy a non-contiguous sequence of bits
10678 in memory, requiring non-trivial code to reassemble. They are for this
10679 reason not permitted, and any component clause specifying such a layout
10680 will be flagged as illegal by GNAT@.
10685 Since the misconception that Bit_Order automatically deals with all
10686 endian-related incompatibilities is a common one, the specification of
10687 a component field that is an integral number of bytes will always
10688 generate a warning. This warning may be suppressed using @code{pragma
10689 Warnings (Off)} if desired. The following section contains additional
10690 details regarding the issue of byte ordering.
10692 @node Effect of Bit_Order on Byte Ordering
10693 @section Effect of Bit_Order on Byte Ordering
10694 @cindex byte ordering
10695 @cindex ordering, of bytes
10698 In this section we will review the effect of the @code{Bit_Order} attribute
10699 definition clause on byte ordering. Briefly, it has no effect at all, but
10700 a detailed example will be helpful. Before giving this
10701 example, let us review the precise
10702 definition of the effect of defining @code{Bit_Order}. The effect of a
10703 non-standard bit order is described in section 15.5.3 of the Ada
10707 2 A bit ordering is a method of interpreting the meaning of
10708 the storage place attributes.
10712 To understand the precise definition of storage place attributes in
10713 this context, we visit section 13.5.1 of the manual:
10716 13 A record_representation_clause (without the mod_clause)
10717 specifies the layout. The storage place attributes (see 13.5.2)
10718 are taken from the values of the position, first_bit, and last_bit
10719 expressions after normalizing those values so that first_bit is
10720 less than Storage_Unit.
10724 The critical point here is that storage places are taken from
10725 the values after normalization, not before. So the @code{Bit_Order}
10726 interpretation applies to normalized values. The interpretation
10727 is described in the later part of the 15.5.3 paragraph:
10730 2 A bit ordering is a method of interpreting the meaning of
10731 the storage place attributes. High_Order_First (known in the
10732 vernacular as ``big endian'') means that the first bit of a
10733 storage element (bit 0) is the most significant bit (interpreting
10734 the sequence of bits that represent a component as an unsigned
10735 integer value). Low_Order_First (known in the vernacular as
10736 ``little endian'') means the opposite: the first bit is the
10741 Note that the numbering is with respect to the bits of a storage
10742 unit. In other words, the specification affects only the numbering
10743 of bits within a single storage unit.
10745 We can make the effect clearer by giving an example.
10747 Suppose that we have an external device which presents two bytes, the first
10748 byte presented, which is the first (low addressed byte) of the two byte
10749 record is called Master, and the second byte is called Slave.
10751 The left most (most significant bit is called Control for each byte, and
10752 the remaining 7 bits are called V1, V2, @dots{} V7, where V7 is the rightmost
10753 (least significant) bit.
10755 On a big-endian machine, we can write the following representation clause
10757 @smallexample @c ada
10758 type Data is record
10759 Master_Control : Bit;
10767 Slave_Control : Bit;
10777 for Data use record
10778 Master_Control at 0 range 0 .. 0;
10779 Master_V1 at 0 range 1 .. 1;
10780 Master_V2 at 0 range 2 .. 2;
10781 Master_V3 at 0 range 3 .. 3;
10782 Master_V4 at 0 range 4 .. 4;
10783 Master_V5 at 0 range 5 .. 5;
10784 Master_V6 at 0 range 6 .. 6;
10785 Master_V7 at 0 range 7 .. 7;
10786 Slave_Control at 1 range 0 .. 0;
10787 Slave_V1 at 1 range 1 .. 1;
10788 Slave_V2 at 1 range 2 .. 2;
10789 Slave_V3 at 1 range 3 .. 3;
10790 Slave_V4 at 1 range 4 .. 4;
10791 Slave_V5 at 1 range 5 .. 5;
10792 Slave_V6 at 1 range 6 .. 6;
10793 Slave_V7 at 1 range 7 .. 7;
10798 Now if we move this to a little endian machine, then the bit ordering within
10799 the byte is backwards, so we have to rewrite the record rep clause as:
10801 @smallexample @c ada
10802 for Data use record
10803 Master_Control at 0 range 7 .. 7;
10804 Master_V1 at 0 range 6 .. 6;
10805 Master_V2 at 0 range 5 .. 5;
10806 Master_V3 at 0 range 4 .. 4;
10807 Master_V4 at 0 range 3 .. 3;
10808 Master_V5 at 0 range 2 .. 2;
10809 Master_V6 at 0 range 1 .. 1;
10810 Master_V7 at 0 range 0 .. 0;
10811 Slave_Control at 1 range 7 .. 7;
10812 Slave_V1 at 1 range 6 .. 6;
10813 Slave_V2 at 1 range 5 .. 5;
10814 Slave_V3 at 1 range 4 .. 4;
10815 Slave_V4 at 1 range 3 .. 3;
10816 Slave_V5 at 1 range 2 .. 2;
10817 Slave_V6 at 1 range 1 .. 1;
10818 Slave_V7 at 1 range 0 .. 0;
10823 It is a nuisance to have to rewrite the clause, especially if
10824 the code has to be maintained on both machines. However,
10825 this is a case that we can handle with the
10826 @code{Bit_Order} attribute if it is implemented.
10827 Note that the implementation is not required on byte addressed
10828 machines, but it is indeed implemented in GNAT.
10829 This means that we can simply use the
10830 first record clause, together with the declaration
10832 @smallexample @c ada
10833 for Data'Bit_Order use High_Order_First;
10837 and the effect is what is desired, namely the layout is exactly the same,
10838 independent of whether the code is compiled on a big-endian or little-endian
10841 The important point to understand is that byte ordering is not affected.
10842 A @code{Bit_Order} attribute definition never affects which byte a field
10843 ends up in, only where it ends up in that byte.
10844 To make this clear, let us rewrite the record rep clause of the previous
10847 @smallexample @c ada
10848 for Data'Bit_Order use High_Order_First;
10849 for Data use record
10850 Master_Control at 0 range 0 .. 0;
10851 Master_V1 at 0 range 1 .. 1;
10852 Master_V2 at 0 range 2 .. 2;
10853 Master_V3 at 0 range 3 .. 3;
10854 Master_V4 at 0 range 4 .. 4;
10855 Master_V5 at 0 range 5 .. 5;
10856 Master_V6 at 0 range 6 .. 6;
10857 Master_V7 at 0 range 7 .. 7;
10858 Slave_Control at 0 range 8 .. 8;
10859 Slave_V1 at 0 range 9 .. 9;
10860 Slave_V2 at 0 range 10 .. 10;
10861 Slave_V3 at 0 range 11 .. 11;
10862 Slave_V4 at 0 range 12 .. 12;
10863 Slave_V5 at 0 range 13 .. 13;
10864 Slave_V6 at 0 range 14 .. 14;
10865 Slave_V7 at 0 range 15 .. 15;
10870 This is exactly equivalent to saying (a repeat of the first example):
10872 @smallexample @c ada
10873 for Data'Bit_Order use High_Order_First;
10874 for Data use record
10875 Master_Control at 0 range 0 .. 0;
10876 Master_V1 at 0 range 1 .. 1;
10877 Master_V2 at 0 range 2 .. 2;
10878 Master_V3 at 0 range 3 .. 3;
10879 Master_V4 at 0 range 4 .. 4;
10880 Master_V5 at 0 range 5 .. 5;
10881 Master_V6 at 0 range 6 .. 6;
10882 Master_V7 at 0 range 7 .. 7;
10883 Slave_Control at 1 range 0 .. 0;
10884 Slave_V1 at 1 range 1 .. 1;
10885 Slave_V2 at 1 range 2 .. 2;
10886 Slave_V3 at 1 range 3 .. 3;
10887 Slave_V4 at 1 range 4 .. 4;
10888 Slave_V5 at 1 range 5 .. 5;
10889 Slave_V6 at 1 range 6 .. 6;
10890 Slave_V7 at 1 range 7 .. 7;
10895 Why are they equivalent? Well take a specific field, the @code{Slave_V2}
10896 field. The storage place attributes are obtained by normalizing the
10897 values given so that the @code{First_Bit} value is less than 8. After
10898 normalizing the values (0,10,10) we get (1,2,2) which is exactly what
10899 we specified in the other case.
10901 Now one might expect that the @code{Bit_Order} attribute might affect
10902 bit numbering within the entire record component (two bytes in this
10903 case, thus affecting which byte fields end up in), but that is not
10904 the way this feature is defined, it only affects numbering of bits,
10905 not which byte they end up in.
10907 Consequently it never makes sense to specify a starting bit number
10908 greater than 7 (for a byte addressable field) if an attribute
10909 definition for @code{Bit_Order} has been given, and indeed it
10910 may be actively confusing to specify such a value, so the compiler
10911 generates a warning for such usage.
10913 If you do need to control byte ordering then appropriate conditional
10914 values must be used. If in our example, the slave byte came first on
10915 some machines we might write:
10917 @smallexample @c ada
10918 Master_Byte_First constant Boolean := @dots{};
10920 Master_Byte : constant Natural :=
10921 1 - Boolean'Pos (Master_Byte_First);
10922 Slave_Byte : constant Natural :=
10923 Boolean'Pos (Master_Byte_First);
10925 for Data'Bit_Order use High_Order_First;
10926 for Data use record
10927 Master_Control at Master_Byte range 0 .. 0;
10928 Master_V1 at Master_Byte range 1 .. 1;
10929 Master_V2 at Master_Byte range 2 .. 2;
10930 Master_V3 at Master_Byte range 3 .. 3;
10931 Master_V4 at Master_Byte range 4 .. 4;
10932 Master_V5 at Master_Byte range 5 .. 5;
10933 Master_V6 at Master_Byte range 6 .. 6;
10934 Master_V7 at Master_Byte range 7 .. 7;
10935 Slave_Control at Slave_Byte range 0 .. 0;
10936 Slave_V1 at Slave_Byte range 1 .. 1;
10937 Slave_V2 at Slave_Byte range 2 .. 2;
10938 Slave_V3 at Slave_Byte range 3 .. 3;
10939 Slave_V4 at Slave_Byte range 4 .. 4;
10940 Slave_V5 at Slave_Byte range 5 .. 5;
10941 Slave_V6 at Slave_Byte range 6 .. 6;
10942 Slave_V7 at Slave_Byte range 7 .. 7;
10947 Now to switch between machines, all that is necessary is
10948 to set the boolean constant @code{Master_Byte_First} in
10949 an appropriate manner.
10951 @node Pragma Pack for Arrays
10952 @section Pragma Pack for Arrays
10953 @cindex Pragma Pack (for arrays)
10956 Pragma @code{Pack} applied to an array has no effect unless the component type
10957 is packable. For a component type to be packable, it must be one of the
10964 Any type whose size is specified with a size clause
10966 Any packed array type with a static size
10968 Any record type padded because of its default alignment
10972 For all these cases, if the component subtype size is in the range
10973 1 through 63, then the effect of the pragma @code{Pack} is exactly as though a
10974 component size were specified giving the component subtype size.
10975 For example if we have:
10977 @smallexample @c ada
10978 type r is range 0 .. 17;
10980 type ar is array (1 .. 8) of r;
10985 Then the component size of @code{ar} will be set to 5 (i.e.@: to @code{r'size},
10986 and the size of the array @code{ar} will be exactly 40 bits.
10988 Note that in some cases this rather fierce approach to packing can produce
10989 unexpected effects. For example, in Ada 95 and Ada 2005,
10990 subtype @code{Natural} typically has a size of 31, meaning that if you
10991 pack an array of @code{Natural}, you get 31-bit
10992 close packing, which saves a few bits, but results in far less efficient
10993 access. Since many other Ada compilers will ignore such a packing request,
10994 GNAT will generate a warning on some uses of pragma @code{Pack} that it guesses
10995 might not be what is intended. You can easily remove this warning by
10996 using an explicit @code{Component_Size} setting instead, which never generates
10997 a warning, since the intention of the programmer is clear in this case.
10999 GNAT treats packed arrays in one of two ways. If the size of the array is
11000 known at compile time and is less than 64 bits, then internally the array
11001 is represented as a single modular type, of exactly the appropriate number
11002 of bits. If the length is greater than 63 bits, or is not known at compile
11003 time, then the packed array is represented as an array of bytes, and the
11004 length is always a multiple of 8 bits.
11006 Note that to represent a packed array as a modular type, the alignment must
11007 be suitable for the modular type involved. For example, on typical machines
11008 a 32-bit packed array will be represented by a 32-bit modular integer with
11009 an alignment of four bytes. If you explicitly override the default alignment
11010 with an alignment clause that is too small, the modular representation
11011 cannot be used. For example, consider the following set of declarations:
11013 @smallexample @c ada
11014 type R is range 1 .. 3;
11015 type S is array (1 .. 31) of R;
11016 for S'Component_Size use 2;
11018 for S'Alignment use 1;
11022 If the alignment clause were not present, then a 62-bit modular
11023 representation would be chosen (typically with an alignment of 4 or 8
11024 bytes depending on the target). But the default alignment is overridden
11025 with the explicit alignment clause. This means that the modular
11026 representation cannot be used, and instead the array of bytes
11027 representation must be used, meaning that the length must be a multiple
11028 of 8. Thus the above set of declarations will result in a diagnostic
11029 rejecting the size clause and noting that the minimum size allowed is 64.
11031 @cindex Pragma Pack (for type Natural)
11032 @cindex Pragma Pack warning
11034 One special case that is worth noting occurs when the base type of the
11035 component size is 8/16/32 and the subtype is one bit less. Notably this
11036 occurs with subtype @code{Natural}. Consider:
11038 @smallexample @c ada
11039 type Arr is array (1 .. 32) of Natural;
11044 In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
11045 since typically @code{Natural'Size} is 32 in Ada 83, and in any case most
11046 Ada 83 compilers did not attempt 31 bit packing.
11048 In Ada 95 and Ada 2005, @code{Natural'Size} is required to be 31. Furthermore,
11049 GNAT really does pack 31-bit subtype to 31 bits. This may result in a
11050 substantial unintended performance penalty when porting legacy Ada 83 code.
11051 To help prevent this, GNAT generates a warning in such cases. If you really
11052 want 31 bit packing in a case like this, you can set the component size
11055 @smallexample @c ada
11056 type Arr is array (1 .. 32) of Natural;
11057 for Arr'Component_Size use 31;
11061 Here 31-bit packing is achieved as required, and no warning is generated,
11062 since in this case the programmer intention is clear.
11064 @node Pragma Pack for Records
11065 @section Pragma Pack for Records
11066 @cindex Pragma Pack (for records)
11069 Pragma @code{Pack} applied to a record will pack the components to reduce
11070 wasted space from alignment gaps and by reducing the amount of space
11071 taken by components. We distinguish between @emph{packable} components and
11072 @emph{non-packable} components.
11073 Components of the following types are considered packable:
11076 All primitive types are packable.
11079 Small packed arrays, whose size does not exceed 64 bits, and where the
11080 size is statically known at compile time, are represented internally
11081 as modular integers, and so they are also packable.
11086 All packable components occupy the exact number of bits corresponding to
11087 their @code{Size} value, and are packed with no padding bits, i.e.@: they
11088 can start on an arbitrary bit boundary.
11090 All other types are non-packable, they occupy an integral number of
11092 are placed at a boundary corresponding to their alignment requirements.
11094 For example, consider the record
11096 @smallexample @c ada
11097 type Rb1 is array (1 .. 13) of Boolean;
11100 type Rb2 is array (1 .. 65) of Boolean;
11115 The representation for the record x2 is as follows:
11117 @smallexample @c ada
11118 for x2'Size use 224;
11120 l1 at 0 range 0 .. 0;
11121 l2 at 0 range 1 .. 64;
11122 l3 at 12 range 0 .. 31;
11123 l4 at 16 range 0 .. 0;
11124 l5 at 16 range 1 .. 13;
11125 l6 at 18 range 0 .. 71;
11130 Studying this example, we see that the packable fields @code{l1}
11132 of length equal to their sizes, and placed at specific bit boundaries (and
11133 not byte boundaries) to
11134 eliminate padding. But @code{l3} is of a non-packable float type, so
11135 it is on the next appropriate alignment boundary.
11137 The next two fields are fully packable, so @code{l4} and @code{l5} are
11138 minimally packed with no gaps. However, type @code{Rb2} is a packed
11139 array that is longer than 64 bits, so it is itself non-packable. Thus
11140 the @code{l6} field is aligned to the next byte boundary, and takes an
11141 integral number of bytes, i.e.@: 72 bits.
11143 @node Record Representation Clauses
11144 @section Record Representation Clauses
11145 @cindex Record Representation Clause
11148 Record representation clauses may be given for all record types, including
11149 types obtained by record extension. Component clauses are allowed for any
11150 static component. The restrictions on component clauses depend on the type
11153 @cindex Component Clause
11154 For all components of an elementary type, the only restriction on component
11155 clauses is that the size must be at least the 'Size value of the type
11156 (actually the Value_Size). There are no restrictions due to alignment,
11157 and such components may freely cross storage boundaries.
11159 Packed arrays with a size up to and including 64 bits are represented
11160 internally using a modular type with the appropriate number of bits, and
11161 thus the same lack of restriction applies. For example, if you declare:
11163 @smallexample @c ada
11164 type R is array (1 .. 49) of Boolean;
11170 then a component clause for a component of type R may start on any
11171 specified bit boundary, and may specify a value of 49 bits or greater.
11173 For packed bit arrays that are longer than 64 bits, there are two
11174 cases. If the component size is a power of 2 (1,2,4,8,16,32 bits),
11175 including the important case of single bits or boolean values, then
11176 there are no limitations on placement of such components, and they
11177 may start and end at arbitrary bit boundaries.
11179 If the component size is not a power of 2 (e.g.@: 3 or 5), then
11180 an array of this type longer than 64 bits must always be placed on
11181 on a storage unit (byte) boundary and occupy an integral number
11182 of storage units (bytes). Any component clause that does not
11183 meet this requirement will be rejected.
11185 Any aliased component, or component of an aliased type, must
11186 have its normal alignment and size. A component clause that
11187 does not meet this requirement will be rejected.
11189 The tag field of a tagged type always occupies an address sized field at
11190 the start of the record. No component clause may attempt to overlay this
11191 tag. When a tagged type appears as a component, the tag field must have
11194 In the case of a record extension T1, of a type T, no component clause applied
11195 to the type T1 can specify a storage location that would overlap the first
11196 T'Size bytes of the record.
11198 For all other component types, including non-bit-packed arrays,
11199 the component can be placed at an arbitrary bit boundary,
11200 so for example, the following is permitted:
11202 @smallexample @c ada
11203 type R is array (1 .. 10) of Boolean;
11212 G at 0 range 0 .. 0;
11213 H at 0 range 1 .. 1;
11214 L at 0 range 2 .. 81;
11215 R at 0 range 82 .. 161;
11220 Note: the above rules apply to recent releases of GNAT 5.
11221 In GNAT 3, there are more severe restrictions on larger components.
11222 For non-primitive types, including packed arrays with a size greater than
11223 64 bits, component clauses must respect the alignment requirement of the
11224 type, in particular, always starting on a byte boundary, and the length
11225 must be a multiple of the storage unit.
11227 @node Enumeration Clauses
11228 @section Enumeration Clauses
11230 The only restriction on enumeration clauses is that the range of values
11231 must be representable. For the signed case, if one or more of the
11232 representation values are negative, all values must be in the range:
11234 @smallexample @c ada
11235 System.Min_Int .. System.Max_Int
11239 For the unsigned case, where all values are nonnegative, the values must
11242 @smallexample @c ada
11243 0 .. System.Max_Binary_Modulus;
11247 A @emph{confirming} representation clause is one in which the values range
11248 from 0 in sequence, i.e.@: a clause that confirms the default representation
11249 for an enumeration type.
11250 Such a confirming representation
11251 is permitted by these rules, and is specially recognized by the compiler so
11252 that no extra overhead results from the use of such a clause.
11254 If an array has an index type which is an enumeration type to which an
11255 enumeration clause has been applied, then the array is stored in a compact
11256 manner. Consider the declarations:
11258 @smallexample @c ada
11259 type r is (A, B, C);
11260 for r use (A => 1, B => 5, C => 10);
11261 type t is array (r) of Character;
11265 The array type t corresponds to a vector with exactly three elements and
11266 has a default size equal to @code{3*Character'Size}. This ensures efficient
11267 use of space, but means that accesses to elements of the array will incur
11268 the overhead of converting representation values to the corresponding
11269 positional values, (i.e.@: the value delivered by the @code{Pos} attribute).
11271 @node Address Clauses
11272 @section Address Clauses
11273 @cindex Address Clause
11275 The reference manual allows a general restriction on representation clauses,
11276 as found in RM 13.1(22):
11279 An implementation need not support representation
11280 items containing nonstatic expressions, except that
11281 an implementation should support a representation item
11282 for a given entity if each nonstatic expression in the
11283 representation item is a name that statically denotes
11284 a constant declared before the entity.
11288 In practice this is applicable only to address clauses, since this is the
11289 only case in which a non-static expression is permitted by the syntax. As
11290 the AARM notes in sections 13.1 (22.a-22.h):
11293 22.a Reason: This is to avoid the following sort of thing:
11295 22.b X : Integer := F(@dots{});
11296 Y : Address := G(@dots{});
11297 for X'Address use Y;
11299 22.c In the above, we have to evaluate the
11300 initialization expression for X before we
11301 know where to put the result. This seems
11302 like an unreasonable implementation burden.
11304 22.d The above code should instead be written
11307 22.e Y : constant Address := G(@dots{});
11308 X : Integer := F(@dots{});
11309 for X'Address use Y;
11311 22.f This allows the expression ``Y'' to be safely
11312 evaluated before X is created.
11314 22.g The constant could be a formal parameter of mode in.
11316 22.h An implementation can support other nonstatic
11317 expressions if it wants to. Expressions of type
11318 Address are hardly ever static, but their value
11319 might be known at compile time anyway in many
11324 GNAT does indeed permit many additional cases of non-static expressions. In
11325 particular, if the type involved is elementary there are no restrictions
11326 (since in this case, holding a temporary copy of the initialization value,
11327 if one is present, is inexpensive). In addition, if there is no implicit or
11328 explicit initialization, then there are no restrictions. GNAT will reject
11329 only the case where all three of these conditions hold:
11334 The type of the item is non-elementary (e.g.@: a record or array).
11337 There is explicit or implicit initialization required for the object.
11338 Note that access values are always implicitly initialized, and also
11339 in GNAT, certain bit-packed arrays (those having a dynamic length or
11340 a length greater than 64) will also be implicitly initialized to zero.
11343 The address value is non-static. Here GNAT is more permissive than the
11344 RM, and allows the address value to be the address of a previously declared
11345 stand-alone variable, as long as it does not itself have an address clause.
11347 @smallexample @c ada
11348 Anchor : Some_Initialized_Type;
11349 Overlay : Some_Initialized_Type;
11350 for Overlay'Address use Anchor'Address;
11354 However, the prefix of the address clause cannot be an array component, or
11355 a component of a discriminated record.
11360 As noted above in section 22.h, address values are typically non-static. In
11361 particular the To_Address function, even if applied to a literal value, is
11362 a non-static function call. To avoid this minor annoyance, GNAT provides
11363 the implementation defined attribute 'To_Address. The following two
11364 expressions have identical values:
11368 @smallexample @c ada
11369 To_Address (16#1234_0000#)
11370 System'To_Address (16#1234_0000#);
11374 except that the second form is considered to be a static expression, and
11375 thus when used as an address clause value is always permitted.
11378 Additionally, GNAT treats as static an address clause that is an
11379 unchecked_conversion of a static integer value. This simplifies the porting
11380 of legacy code, and provides a portable equivalent to the GNAT attribute
11383 Another issue with address clauses is the interaction with alignment
11384 requirements. When an address clause is given for an object, the address
11385 value must be consistent with the alignment of the object (which is usually
11386 the same as the alignment of the type of the object). If an address clause
11387 is given that specifies an inappropriately aligned address value, then the
11388 program execution is erroneous.
11390 Since this source of erroneous behavior can have unfortunate effects, GNAT
11391 checks (at compile time if possible, generating a warning, or at execution
11392 time with a run-time check) that the alignment is appropriate. If the
11393 run-time check fails, then @code{Program_Error} is raised. This run-time
11394 check is suppressed if range checks are suppressed, or if the special GNAT
11395 check Alignment_Check is suppressed, or if
11396 @code{pragma Restrictions (No_Elaboration_Code)} is in effect.
11398 Finally, GNAT does not permit overlaying of objects of controlled types or
11399 composite types containing a controlled component. In most cases, the compiler
11400 can detect an attempt at such overlays and will generate a warning at compile
11401 time and a Program_Error exception at run time.
11404 An address clause cannot be given for an exported object. More
11405 understandably the real restriction is that objects with an address
11406 clause cannot be exported. This is because such variables are not
11407 defined by the Ada program, so there is no external object to export.
11410 It is permissible to give an address clause and a pragma Import for the
11411 same object. In this case, the variable is not really defined by the
11412 Ada program, so there is no external symbol to be linked. The link name
11413 and the external name are ignored in this case. The reason that we allow this
11414 combination is that it provides a useful idiom to avoid unwanted
11415 initializations on objects with address clauses.
11417 When an address clause is given for an object that has implicit or
11418 explicit initialization, then by default initialization takes place. This
11419 means that the effect of the object declaration is to overwrite the
11420 memory at the specified address. This is almost always not what the
11421 programmer wants, so GNAT will output a warning:
11431 for Ext'Address use System'To_Address (16#1234_1234#);
11433 >>> warning: implicit initialization of "Ext" may
11434 modify overlaid storage
11435 >>> warning: use pragma Import for "Ext" to suppress
11436 initialization (RM B(24))
11442 As indicated by the warning message, the solution is to use a (dummy) pragma
11443 Import to suppress this initialization. The pragma tell the compiler that the
11444 object is declared and initialized elsewhere. The following package compiles
11445 without warnings (and the initialization is suppressed):
11447 @smallexample @c ada
11455 for Ext'Address use System'To_Address (16#1234_1234#);
11456 pragma Import (Ada, Ext);
11461 A final issue with address clauses involves their use for overlaying
11462 variables, as in the following example:
11463 @cindex Overlaying of objects
11465 @smallexample @c ada
11468 for B'Address use A'Address;
11472 or alternatively, using the form recommended by the RM:
11474 @smallexample @c ada
11476 Addr : constant Address := A'Address;
11478 for B'Address use Addr;
11482 In both of these cases, @code{A}
11483 and @code{B} become aliased to one another via the
11484 address clause. This use of address clauses to overlay
11485 variables, achieving an effect similar to unchecked
11486 conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005
11487 the effect is implementation defined. Furthermore, the
11488 Ada RM specifically recommends that in a situation
11489 like this, @code{B} should be subject to the following
11490 implementation advice (RM 13.3(19)):
11493 19 If the Address of an object is specified, or it is imported
11494 or exported, then the implementation should not perform
11495 optimizations based on assumptions of no aliases.
11499 GNAT follows this recommendation, and goes further by also applying
11500 this recommendation to the overlaid variable (@code{A}
11501 in the above example) in this case. This means that the overlay
11502 works "as expected", in that a modification to one of the variables
11503 will affect the value of the other.
11505 @node Effect of Convention on Representation
11506 @section Effect of Convention on Representation
11507 @cindex Convention, effect on representation
11510 Normally the specification of a foreign language convention for a type or
11511 an object has no effect on the chosen representation. In particular, the
11512 representation chosen for data in GNAT generally meets the standard system
11513 conventions, and for example records are laid out in a manner that is
11514 consistent with C@. This means that specifying convention C (for example)
11517 There are four exceptions to this general rule:
11521 @item Convention Fortran and array subtypes
11522 If pragma Convention Fortran is specified for an array subtype, then in
11523 accordance with the implementation advice in section 3.6.2(11) of the
11524 Ada Reference Manual, the array will be stored in a Fortran-compatible
11525 column-major manner, instead of the normal default row-major order.
11527 @item Convention C and enumeration types
11528 GNAT normally stores enumeration types in 8, 16, or 32 bits as required
11529 to accommodate all values of the type. For example, for the enumeration
11532 @smallexample @c ada
11533 type Color is (Red, Green, Blue);
11537 8 bits is sufficient to store all values of the type, so by default, objects
11538 of type @code{Color} will be represented using 8 bits. However, normal C
11539 convention is to use 32 bits for all enum values in C, since enum values
11540 are essentially of type int. If pragma @code{Convention C} is specified for an
11541 Ada enumeration type, then the size is modified as necessary (usually to
11542 32 bits) to be consistent with the C convention for enum values.
11544 Note that this treatment applies only to types. If Convention C is given for
11545 an enumeration object, where the enumeration type is not Convention C, then
11546 Object_Size bits are allocated. For example, for a normal enumeration type,
11547 with less than 256 elements, only 8 bits will be allocated for the object.
11548 Since this may be a surprise in terms of what C expects, GNAT will issue a
11549 warning in this situation. The warning can be suppressed by giving an explicit
11550 size clause specifying the desired size.
11552 @item Convention C/Fortran and Boolean types
11553 In C, the usual convention for boolean values, that is values used for
11554 conditions, is that zero represents false, and nonzero values represent
11555 true. In Ada, the normal convention is that two specific values, typically
11556 0/1, are used to represent false/true respectively.
11558 Fortran has a similar convention for @code{LOGICAL} values (any nonzero
11559 value represents true).
11561 To accommodate the Fortran and C conventions, if a pragma Convention specifies
11562 C or Fortran convention for a derived Boolean, as in the following example:
11564 @smallexample @c ada
11565 type C_Switch is new Boolean;
11566 pragma Convention (C, C_Switch);
11570 then the GNAT generated code will treat any nonzero value as true. For truth
11571 values generated by GNAT, the conventional value 1 will be used for True, but
11572 when one of these values is read, any nonzero value is treated as True.
11574 @item Access types on OpenVMS
11575 For 64-bit OpenVMS systems, access types (other than those for unconstrained
11576 arrays) are 64-bits long. An exception to this rule is for the case of
11577 C-convention access types where there is no explicit size clause present (or
11578 inherited for derived types). In this case, GNAT chooses to make these
11579 pointers 32-bits, which provides an easier path for migration of 32-bit legacy
11580 code. size clause specifying 64-bits must be used to obtain a 64-bit pointer.
11584 @node Determining the Representations chosen by GNAT
11585 @section Determining the Representations chosen by GNAT
11586 @cindex Representation, determination of
11587 @cindex @option{-gnatR} switch
11590 Although the descriptions in this section are intended to be complete, it is
11591 often easier to simply experiment to see what GNAT accepts and what the
11592 effect is on the layout of types and objects.
11594 As required by the Ada RM, if a representation clause is not accepted, then
11595 it must be rejected as illegal by the compiler. However, when a
11596 representation clause or pragma is accepted, there can still be questions
11597 of what the compiler actually does. For example, if a partial record
11598 representation clause specifies the location of some components and not
11599 others, then where are the non-specified components placed? Or if pragma
11600 @code{Pack} is used on a record, then exactly where are the resulting
11601 fields placed? The section on pragma @code{Pack} in this chapter can be
11602 used to answer the second question, but it is often easier to just see
11603 what the compiler does.
11605 For this purpose, GNAT provides the option @option{-gnatR}. If you compile
11606 with this option, then the compiler will output information on the actual
11607 representations chosen, in a format similar to source representation
11608 clauses. For example, if we compile the package:
11610 @smallexample @c ada
11612 type r (x : boolean) is tagged record
11614 when True => S : String (1 .. 100);
11615 when False => null;
11619 type r2 is new r (false) with record
11624 y2 at 16 range 0 .. 31;
11631 type x1 is array (1 .. 10) of x;
11632 for x1'component_size use 11;
11634 type ia is access integer;
11636 type Rb1 is array (1 .. 13) of Boolean;
11639 type Rb2 is array (1 .. 65) of Boolean;
11655 using the switch @option{-gnatR} we obtain the following output:
11658 Representation information for unit q
11659 -------------------------------------
11662 for r'Alignment use 4;
11664 x at 4 range 0 .. 7;
11665 _tag at 0 range 0 .. 31;
11666 s at 5 range 0 .. 799;
11669 for r2'Size use 160;
11670 for r2'Alignment use 4;
11672 x at 4 range 0 .. 7;
11673 _tag at 0 range 0 .. 31;
11674 _parent at 0 range 0 .. 63;
11675 y2 at 16 range 0 .. 31;
11679 for x'Alignment use 1;
11681 y at 0 range 0 .. 7;
11684 for x1'Size use 112;
11685 for x1'Alignment use 1;
11686 for x1'Component_Size use 11;
11688 for rb1'Size use 13;
11689 for rb1'Alignment use 2;
11690 for rb1'Component_Size use 1;
11692 for rb2'Size use 72;
11693 for rb2'Alignment use 1;
11694 for rb2'Component_Size use 1;
11696 for x2'Size use 224;
11697 for x2'Alignment use 4;
11699 l1 at 0 range 0 .. 0;
11700 l2 at 0 range 1 .. 64;
11701 l3 at 12 range 0 .. 31;
11702 l4 at 16 range 0 .. 0;
11703 l5 at 16 range 1 .. 13;
11704 l6 at 18 range 0 .. 71;
11709 The Size values are actually the Object_Size, i.e.@: the default size that
11710 will be allocated for objects of the type.
11711 The ?? size for type r indicates that we have a variant record, and the
11712 actual size of objects will depend on the discriminant value.
11714 The Alignment values show the actual alignment chosen by the compiler
11715 for each record or array type.
11717 The record representation clause for type r shows where all fields
11718 are placed, including the compiler generated tag field (whose location
11719 cannot be controlled by the programmer).
11721 The record representation clause for the type extension r2 shows all the
11722 fields present, including the parent field, which is a copy of the fields
11723 of the parent type of r2, i.e.@: r1.
11725 The component size and size clauses for types rb1 and rb2 show
11726 the exact effect of pragma @code{Pack} on these arrays, and the record
11727 representation clause for type x2 shows how pragma @code{Pack} affects
11730 In some cases, it may be useful to cut and paste the representation clauses
11731 generated by the compiler into the original source to fix and guarantee
11732 the actual representation to be used.
11734 @node Standard Library Routines
11735 @chapter Standard Library Routines
11738 The Ada Reference Manual contains in Annex A a full description of an
11739 extensive set of standard library routines that can be used in any Ada
11740 program, and which must be provided by all Ada compilers. They are
11741 analogous to the standard C library used by C programs.
11743 GNAT implements all of the facilities described in annex A, and for most
11744 purposes the description in the Ada Reference Manual, or appropriate Ada
11745 text book, will be sufficient for making use of these facilities.
11747 In the case of the input-output facilities,
11748 @xref{The Implementation of Standard I/O},
11749 gives details on exactly how GNAT interfaces to the
11750 file system. For the remaining packages, the Ada Reference Manual
11751 should be sufficient. The following is a list of the packages included,
11752 together with a brief description of the functionality that is provided.
11754 For completeness, references are included to other predefined library
11755 routines defined in other sections of the Ada Reference Manual (these are
11756 cross-indexed from Annex A).
11760 This is a parent package for all the standard library packages. It is
11761 usually included implicitly in your program, and itself contains no
11762 useful data or routines.
11764 @item Ada.Calendar (9.6)
11765 @code{Calendar} provides time of day access, and routines for
11766 manipulating times and durations.
11768 @item Ada.Characters (A.3.1)
11769 This is a dummy parent package that contains no useful entities
11771 @item Ada.Characters.Handling (A.3.2)
11772 This package provides some basic character handling capabilities,
11773 including classification functions for classes of characters (e.g.@: test
11774 for letters, or digits).
11776 @item Ada.Characters.Latin_1 (A.3.3)
11777 This package includes a complete set of definitions of the characters
11778 that appear in type CHARACTER@. It is useful for writing programs that
11779 will run in international environments. For example, if you want an
11780 upper case E with an acute accent in a string, it is often better to use
11781 the definition of @code{UC_E_Acute} in this package. Then your program
11782 will print in an understandable manner even if your environment does not
11783 support these extended characters.
11785 @item Ada.Command_Line (A.15)
11786 This package provides access to the command line parameters and the name
11787 of the current program (analogous to the use of @code{argc} and @code{argv}
11788 in C), and also allows the exit status for the program to be set in a
11789 system-independent manner.
11791 @item Ada.Decimal (F.2)
11792 This package provides constants describing the range of decimal numbers
11793 implemented, and also a decimal divide routine (analogous to the COBOL
11794 verb DIVIDE @dots{} GIVING @dots{} REMAINDER @dots{})
11796 @item Ada.Direct_IO (A.8.4)
11797 This package provides input-output using a model of a set of records of
11798 fixed-length, containing an arbitrary definite Ada type, indexed by an
11799 integer record number.
11801 @item Ada.Dynamic_Priorities (D.5)
11802 This package allows the priorities of a task to be adjusted dynamically
11803 as the task is running.
11805 @item Ada.Exceptions (11.4.1)
11806 This package provides additional information on exceptions, and also
11807 contains facilities for treating exceptions as data objects, and raising
11808 exceptions with associated messages.
11810 @item Ada.Finalization (7.6)
11811 This package contains the declarations and subprograms to support the
11812 use of controlled types, providing for automatic initialization and
11813 finalization (analogous to the constructors and destructors of C++)
11815 @item Ada.Interrupts (C.3.2)
11816 This package provides facilities for interfacing to interrupts, which
11817 includes the set of signals or conditions that can be raised and
11818 recognized as interrupts.
11820 @item Ada.Interrupts.Names (C.3.2)
11821 This package provides the set of interrupt names (actually signal
11822 or condition names) that can be handled by GNAT@.
11824 @item Ada.IO_Exceptions (A.13)
11825 This package defines the set of exceptions that can be raised by use of
11826 the standard IO packages.
11829 This package contains some standard constants and exceptions used
11830 throughout the numerics packages. Note that the constants pi and e are
11831 defined here, and it is better to use these definitions than rolling
11834 @item Ada.Numerics.Complex_Elementary_Functions
11835 Provides the implementation of standard elementary functions (such as
11836 log and trigonometric functions) operating on complex numbers using the
11837 standard @code{Float} and the @code{Complex} and @code{Imaginary} types
11838 created by the package @code{Numerics.Complex_Types}.
11840 @item Ada.Numerics.Complex_Types
11841 This is a predefined instantiation of
11842 @code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
11843 build the type @code{Complex} and @code{Imaginary}.
11845 @item Ada.Numerics.Discrete_Random
11846 This package provides a random number generator suitable for generating
11847 random integer values from a specified range.
11849 @item Ada.Numerics.Float_Random
11850 This package provides a random number generator suitable for generating
11851 uniformly distributed floating point values.
11853 @item Ada.Numerics.Generic_Complex_Elementary_Functions
11854 This is a generic version of the package that provides the
11855 implementation of standard elementary functions (such as log and
11856 trigonometric functions) for an arbitrary complex type.
11858 The following predefined instantiations of this package are provided:
11862 @code{Ada.Numerics.Short_Complex_Elementary_Functions}
11864 @code{Ada.Numerics.Complex_Elementary_Functions}
11866 @code{Ada.Numerics.Long_Complex_Elementary_Functions}
11869 @item Ada.Numerics.Generic_Complex_Types
11870 This is a generic package that allows the creation of complex types,
11871 with associated complex arithmetic operations.
11873 The following predefined instantiations of this package exist
11876 @code{Ada.Numerics.Short_Complex_Complex_Types}
11878 @code{Ada.Numerics.Complex_Complex_Types}
11880 @code{Ada.Numerics.Long_Complex_Complex_Types}
11883 @item Ada.Numerics.Generic_Elementary_Functions
11884 This is a generic package that provides the implementation of standard
11885 elementary functions (such as log an trigonometric functions) for an
11886 arbitrary float type.
11888 The following predefined instantiations of this package exist
11892 @code{Ada.Numerics.Short_Elementary_Functions}
11894 @code{Ada.Numerics.Elementary_Functions}
11896 @code{Ada.Numerics.Long_Elementary_Functions}
11899 @item Ada.Real_Time (D.8)
11900 This package provides facilities similar to those of @code{Calendar}, but
11901 operating with a finer clock suitable for real time control. Note that
11902 annex D requires that there be no backward clock jumps, and GNAT generally
11903 guarantees this behavior, but of course if the external clock on which
11904 the GNAT runtime depends is deliberately reset by some external event,
11905 then such a backward jump may occur.
11907 @item Ada.Sequential_IO (A.8.1)
11908 This package provides input-output facilities for sequential files,
11909 which can contain a sequence of values of a single type, which can be
11910 any Ada type, including indefinite (unconstrained) types.
11912 @item Ada.Storage_IO (A.9)
11913 This package provides a facility for mapping arbitrary Ada types to and
11914 from a storage buffer. It is primarily intended for the creation of new
11917 @item Ada.Streams (13.13.1)
11918 This is a generic package that provides the basic support for the
11919 concept of streams as used by the stream attributes (@code{Input},
11920 @code{Output}, @code{Read} and @code{Write}).
11922 @item Ada.Streams.Stream_IO (A.12.1)
11923 This package is a specialization of the type @code{Streams} defined in
11924 package @code{Streams} together with a set of operations providing
11925 Stream_IO capability. The Stream_IO model permits both random and
11926 sequential access to a file which can contain an arbitrary set of values
11927 of one or more Ada types.
11929 @item Ada.Strings (A.4.1)
11930 This package provides some basic constants used by the string handling
11933 @item Ada.Strings.Bounded (A.4.4)
11934 This package provides facilities for handling variable length
11935 strings. The bounded model requires a maximum length. It is thus
11936 somewhat more limited than the unbounded model, but avoids the use of
11937 dynamic allocation or finalization.
11939 @item Ada.Strings.Fixed (A.4.3)
11940 This package provides facilities for handling fixed length strings.
11942 @item Ada.Strings.Maps (A.4.2)
11943 This package provides facilities for handling character mappings and
11944 arbitrarily defined subsets of characters. For instance it is useful in
11945 defining specialized translation tables.
11947 @item Ada.Strings.Maps.Constants (A.4.6)
11948 This package provides a standard set of predefined mappings and
11949 predefined character sets. For example, the standard upper to lower case
11950 conversion table is found in this package. Note that upper to lower case
11951 conversion is non-trivial if you want to take the entire set of
11952 characters, including extended characters like E with an acute accent,
11953 into account. You should use the mappings in this package (rather than
11954 adding 32 yourself) to do case mappings.
11956 @item Ada.Strings.Unbounded (A.4.5)
11957 This package provides facilities for handling variable length
11958 strings. The unbounded model allows arbitrary length strings, but
11959 requires the use of dynamic allocation and finalization.
11961 @item Ada.Strings.Wide_Bounded (A.4.7)
11962 @itemx Ada.Strings.Wide_Fixed (A.4.7)
11963 @itemx Ada.Strings.Wide_Maps (A.4.7)
11964 @itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
11965 @itemx Ada.Strings.Wide_Unbounded (A.4.7)
11966 These packages provide analogous capabilities to the corresponding
11967 packages without @samp{Wide_} in the name, but operate with the types
11968 @code{Wide_String} and @code{Wide_Character} instead of @code{String}
11969 and @code{Character}.
11971 @item Ada.Strings.Wide_Wide_Bounded (A.4.7)
11972 @itemx Ada.Strings.Wide_Wide_Fixed (A.4.7)
11973 @itemx Ada.Strings.Wide_Wide_Maps (A.4.7)
11974 @itemx Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
11975 @itemx Ada.Strings.Wide_Wide_Unbounded (A.4.7)
11976 These packages provide analogous capabilities to the corresponding
11977 packages without @samp{Wide_} in the name, but operate with the types
11978 @code{Wide_Wide_String} and @code{Wide_Wide_Character} instead
11979 of @code{String} and @code{Character}.
11981 @item Ada.Synchronous_Task_Control (D.10)
11982 This package provides some standard facilities for controlling task
11983 communication in a synchronous manner.
11986 This package contains definitions for manipulation of the tags of tagged
11989 @item Ada.Task_Attributes
11990 This package provides the capability of associating arbitrary
11991 task-specific data with separate tasks.
11994 This package provides basic text input-output capabilities for
11995 character, string and numeric data. The subpackages of this
11996 package are listed next.
11998 @item Ada.Text_IO.Decimal_IO
11999 Provides input-output facilities for decimal fixed-point types
12001 @item Ada.Text_IO.Enumeration_IO
12002 Provides input-output facilities for enumeration types.
12004 @item Ada.Text_IO.Fixed_IO
12005 Provides input-output facilities for ordinary fixed-point types.
12007 @item Ada.Text_IO.Float_IO
12008 Provides input-output facilities for float types. The following
12009 predefined instantiations of this generic package are available:
12013 @code{Short_Float_Text_IO}
12015 @code{Float_Text_IO}
12017 @code{Long_Float_Text_IO}
12020 @item Ada.Text_IO.Integer_IO
12021 Provides input-output facilities for integer types. The following
12022 predefined instantiations of this generic package are available:
12025 @item Short_Short_Integer
12026 @code{Ada.Short_Short_Integer_Text_IO}
12027 @item Short_Integer
12028 @code{Ada.Short_Integer_Text_IO}
12030 @code{Ada.Integer_Text_IO}
12032 @code{Ada.Long_Integer_Text_IO}
12033 @item Long_Long_Integer
12034 @code{Ada.Long_Long_Integer_Text_IO}
12037 @item Ada.Text_IO.Modular_IO
12038 Provides input-output facilities for modular (unsigned) types
12040 @item Ada.Text_IO.Complex_IO (G.1.3)
12041 This package provides basic text input-output capabilities for complex
12044 @item Ada.Text_IO.Editing (F.3.3)
12045 This package contains routines for edited output, analogous to the use
12046 of pictures in COBOL@. The picture formats used by this package are a
12047 close copy of the facility in COBOL@.
12049 @item Ada.Text_IO.Text_Streams (A.12.2)
12050 This package provides a facility that allows Text_IO files to be treated
12051 as streams, so that the stream attributes can be used for writing
12052 arbitrary data, including binary data, to Text_IO files.
12054 @item Ada.Unchecked_Conversion (13.9)
12055 This generic package allows arbitrary conversion from one type to
12056 another of the same size, providing for breaking the type safety in
12057 special circumstances.
12059 If the types have the same Size (more accurately the same Value_Size),
12060 then the effect is simply to transfer the bits from the source to the
12061 target type without any modification. This usage is well defined, and
12062 for simple types whose representation is typically the same across
12063 all implementations, gives a portable method of performing such
12066 If the types do not have the same size, then the result is implementation
12067 defined, and thus may be non-portable. The following describes how GNAT
12068 handles such unchecked conversion cases.
12070 If the types are of different sizes, and are both discrete types, then
12071 the effect is of a normal type conversion without any constraint checking.
12072 In particular if the result type has a larger size, the result will be
12073 zero or sign extended. If the result type has a smaller size, the result
12074 will be truncated by ignoring high order bits.
12076 If the types are of different sizes, and are not both discrete types,
12077 then the conversion works as though pointers were created to the source
12078 and target, and the pointer value is converted. The effect is that bits
12079 are copied from successive low order storage units and bits of the source
12080 up to the length of the target type.
12082 A warning is issued if the lengths differ, since the effect in this
12083 case is implementation dependent, and the above behavior may not match
12084 that of some other compiler.
12086 A pointer to one type may be converted to a pointer to another type using
12087 unchecked conversion. The only case in which the effect is undefined is
12088 when one or both pointers are pointers to unconstrained array types. In
12089 this case, the bounds information may get incorrectly transferred, and in
12090 particular, GNAT uses double size pointers for such types, and it is
12091 meaningless to convert between such pointer types. GNAT will issue a
12092 warning if the alignment of the target designated type is more strict
12093 than the alignment of the source designated type (since the result may
12094 be unaligned in this case).
12096 A pointer other than a pointer to an unconstrained array type may be
12097 converted to and from System.Address. Such usage is common in Ada 83
12098 programs, but note that Ada.Address_To_Access_Conversions is the
12099 preferred method of performing such conversions in Ada 95 and Ada 2005.
12101 unchecked conversion nor Ada.Address_To_Access_Conversions should be
12102 used in conjunction with pointers to unconstrained objects, since
12103 the bounds information cannot be handled correctly in this case.
12105 @item Ada.Unchecked_Deallocation (13.11.2)
12106 This generic package allows explicit freeing of storage previously
12107 allocated by use of an allocator.
12109 @item Ada.Wide_Text_IO (A.11)
12110 This package is similar to @code{Ada.Text_IO}, except that the external
12111 file supports wide character representations, and the internal types are
12112 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12113 and @code{String}. It contains generic subpackages listed next.
12115 @item Ada.Wide_Text_IO.Decimal_IO
12116 Provides input-output facilities for decimal fixed-point types
12118 @item Ada.Wide_Text_IO.Enumeration_IO
12119 Provides input-output facilities for enumeration types.
12121 @item Ada.Wide_Text_IO.Fixed_IO
12122 Provides input-output facilities for ordinary fixed-point types.
12124 @item Ada.Wide_Text_IO.Float_IO
12125 Provides input-output facilities for float types. The following
12126 predefined instantiations of this generic package are available:
12130 @code{Short_Float_Wide_Text_IO}
12132 @code{Float_Wide_Text_IO}
12134 @code{Long_Float_Wide_Text_IO}
12137 @item Ada.Wide_Text_IO.Integer_IO
12138 Provides input-output facilities for integer types. The following
12139 predefined instantiations of this generic package are available:
12142 @item Short_Short_Integer
12143 @code{Ada.Short_Short_Integer_Wide_Text_IO}
12144 @item Short_Integer
12145 @code{Ada.Short_Integer_Wide_Text_IO}
12147 @code{Ada.Integer_Wide_Text_IO}
12149 @code{Ada.Long_Integer_Wide_Text_IO}
12150 @item Long_Long_Integer
12151 @code{Ada.Long_Long_Integer_Wide_Text_IO}
12154 @item Ada.Wide_Text_IO.Modular_IO
12155 Provides input-output facilities for modular (unsigned) types
12157 @item Ada.Wide_Text_IO.Complex_IO (G.1.3)
12158 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12159 external file supports wide character representations.
12161 @item Ada.Wide_Text_IO.Editing (F.3.4)
12162 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12163 types are @code{Wide_Character} and @code{Wide_String} instead of
12164 @code{Character} and @code{String}.
12166 @item Ada.Wide_Text_IO.Streams (A.12.3)
12167 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12168 types are @code{Wide_Character} and @code{Wide_String} instead of
12169 @code{Character} and @code{String}.
12171 @item Ada.Wide_Wide_Text_IO (A.11)
12172 This package is similar to @code{Ada.Text_IO}, except that the external
12173 file supports wide character representations, and the internal types are
12174 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12175 and @code{String}. It contains generic subpackages listed next.
12177 @item Ada.Wide_Wide_Text_IO.Decimal_IO
12178 Provides input-output facilities for decimal fixed-point types
12180 @item Ada.Wide_Wide_Text_IO.Enumeration_IO
12181 Provides input-output facilities for enumeration types.
12183 @item Ada.Wide_Wide_Text_IO.Fixed_IO
12184 Provides input-output facilities for ordinary fixed-point types.
12186 @item Ada.Wide_Wide_Text_IO.Float_IO
12187 Provides input-output facilities for float types. The following
12188 predefined instantiations of this generic package are available:
12192 @code{Short_Float_Wide_Wide_Text_IO}
12194 @code{Float_Wide_Wide_Text_IO}
12196 @code{Long_Float_Wide_Wide_Text_IO}
12199 @item Ada.Wide_Wide_Text_IO.Integer_IO
12200 Provides input-output facilities for integer types. The following
12201 predefined instantiations of this generic package are available:
12204 @item Short_Short_Integer
12205 @code{Ada.Short_Short_Integer_Wide_Wide_Text_IO}
12206 @item Short_Integer
12207 @code{Ada.Short_Integer_Wide_Wide_Text_IO}
12209 @code{Ada.Integer_Wide_Wide_Text_IO}
12211 @code{Ada.Long_Integer_Wide_Wide_Text_IO}
12212 @item Long_Long_Integer
12213 @code{Ada.Long_Long_Integer_Wide_Wide_Text_IO}
12216 @item Ada.Wide_Wide_Text_IO.Modular_IO
12217 Provides input-output facilities for modular (unsigned) types
12219 @item Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
12220 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12221 external file supports wide character representations.
12223 @item Ada.Wide_Wide_Text_IO.Editing (F.3.4)
12224 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12225 types are @code{Wide_Character} and @code{Wide_String} instead of
12226 @code{Character} and @code{String}.
12228 @item Ada.Wide_Wide_Text_IO.Streams (A.12.3)
12229 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12230 types are @code{Wide_Character} and @code{Wide_String} instead of
12231 @code{Character} and @code{String}.
12236 @node The Implementation of Standard I/O
12237 @chapter The Implementation of Standard I/O
12240 GNAT implements all the required input-output facilities described in
12241 A.6 through A.14. These sections of the Ada Reference Manual describe the
12242 required behavior of these packages from the Ada point of view, and if
12243 you are writing a portable Ada program that does not need to know the
12244 exact manner in which Ada maps to the outside world when it comes to
12245 reading or writing external files, then you do not need to read this
12246 chapter. As long as your files are all regular files (not pipes or
12247 devices), and as long as you write and read the files only from Ada, the
12248 description in the Ada Reference Manual is sufficient.
12250 However, if you want to do input-output to pipes or other devices, such
12251 as the keyboard or screen, or if the files you are dealing with are
12252 either generated by some other language, or to be read by some other
12253 language, then you need to know more about the details of how the GNAT
12254 implementation of these input-output facilities behaves.
12256 In this chapter we give a detailed description of exactly how GNAT
12257 interfaces to the file system. As always, the sources of the system are
12258 available to you for answering questions at an even more detailed level,
12259 but for most purposes the information in this chapter will suffice.
12261 Another reason that you may need to know more about how input-output is
12262 implemented arises when you have a program written in mixed languages
12263 where, for example, files are shared between the C and Ada sections of
12264 the same program. GNAT provides some additional facilities, in the form
12265 of additional child library packages, that facilitate this sharing, and
12266 these additional facilities are also described in this chapter.
12269 * Standard I/O Packages::
12275 * Wide_Wide_Text_IO::
12277 * Text Translation::
12279 * Filenames encoding::
12281 * Operations on C Streams::
12282 * Interfacing to C Streams::
12285 @node Standard I/O Packages
12286 @section Standard I/O Packages
12289 The Standard I/O packages described in Annex A for
12295 Ada.Text_IO.Complex_IO
12297 Ada.Text_IO.Text_Streams
12301 Ada.Wide_Text_IO.Complex_IO
12303 Ada.Wide_Text_IO.Text_Streams
12305 Ada.Wide_Wide_Text_IO
12307 Ada.Wide_Wide_Text_IO.Complex_IO
12309 Ada.Wide_Wide_Text_IO.Text_Streams
12319 are implemented using the C
12320 library streams facility; where
12324 All files are opened using @code{fopen}.
12326 All input/output operations use @code{fread}/@code{fwrite}.
12330 There is no internal buffering of any kind at the Ada library level. The only
12331 buffering is that provided at the system level in the implementation of the
12332 library routines that support streams. This facilitates shared use of these
12333 streams by mixed language programs. Note though that system level buffering is
12334 explicitly enabled at elaboration of the standard I/O packages and that can
12335 have an impact on mixed language programs, in particular those using I/O before
12336 calling the Ada elaboration routine (e.g.@: adainit). It is recommended to call
12337 the Ada elaboration routine before performing any I/O or when impractical,
12338 flush the common I/O streams and in particular Standard_Output before
12339 elaborating the Ada code.
12342 @section FORM Strings
12345 The format of a FORM string in GNAT is:
12348 "keyword=value,keyword=value,@dots{},keyword=value"
12352 where letters may be in upper or lower case, and there are no spaces
12353 between values. The order of the entries is not important. Currently
12354 the following keywords defined.
12357 TEXT_TRANSLATION=[YES|NO]
12359 WCEM=[n|h|u|s|e|8|b]
12360 ENCODING=[UTF8|8BITS]
12364 The use of these parameters is described later in this section.
12370 Direct_IO can only be instantiated for definite types. This is a
12371 restriction of the Ada language, which means that the records are fixed
12372 length (the length being determined by @code{@var{type}'Size}, rounded
12373 up to the next storage unit boundary if necessary).
12375 The records of a Direct_IO file are simply written to the file in index
12376 sequence, with the first record starting at offset zero, and subsequent
12377 records following. There is no control information of any kind. For
12378 example, if 32-bit integers are being written, each record takes
12379 4-bytes, so the record at index @var{K} starts at offset
12380 (@var{K}@minus{}1)*4.
12382 There is no limit on the size of Direct_IO files, they are expanded as
12383 necessary to accommodate whatever records are written to the file.
12385 @node Sequential_IO
12386 @section Sequential_IO
12389 Sequential_IO may be instantiated with either a definite (constrained)
12390 or indefinite (unconstrained) type.
12392 For the definite type case, the elements written to the file are simply
12393 the memory images of the data values with no control information of any
12394 kind. The resulting file should be read using the same type, no validity
12395 checking is performed on input.
12397 For the indefinite type case, the elements written consist of two
12398 parts. First is the size of the data item, written as the memory image
12399 of a @code{Interfaces.C.size_t} value, followed by the memory image of
12400 the data value. The resulting file can only be read using the same
12401 (unconstrained) type. Normal assignment checks are performed on these
12402 read operations, and if these checks fail, @code{Data_Error} is
12403 raised. In particular, in the array case, the lengths must match, and in
12404 the variant record case, if the variable for a particular read operation
12405 is constrained, the discriminants must match.
12407 Note that it is not possible to use Sequential_IO to write variable
12408 length array items, and then read the data back into different length
12409 arrays. For example, the following will raise @code{Data_Error}:
12411 @smallexample @c ada
12412 package IO is new Sequential_IO (String);
12417 IO.Write (F, "hello!")
12418 IO.Reset (F, Mode=>In_File);
12425 On some Ada implementations, this will print @code{hell}, but the program is
12426 clearly incorrect, since there is only one element in the file, and that
12427 element is the string @code{hello!}.
12429 In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved
12430 using Stream_IO, and this is the preferred mechanism. In particular, the
12431 above program fragment rewritten to use Stream_IO will work correctly.
12437 Text_IO files consist of a stream of characters containing the following
12438 special control characters:
12441 LF (line feed, 16#0A#) Line Mark
12442 FF (form feed, 16#0C#) Page Mark
12446 A canonical Text_IO file is defined as one in which the following
12447 conditions are met:
12451 The character @code{LF} is used only as a line mark, i.e.@: to mark the end
12455 The character @code{FF} is used only as a page mark, i.e.@: to mark the
12456 end of a page and consequently can appear only immediately following a
12457 @code{LF} (line mark) character.
12460 The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
12461 (line mark, page mark). In the former case, the page mark is implicitly
12462 assumed to be present.
12466 A file written using Text_IO will be in canonical form provided that no
12467 explicit @code{LF} or @code{FF} characters are written using @code{Put}
12468 or @code{Put_Line}. There will be no @code{FF} character at the end of
12469 the file unless an explicit @code{New_Page} operation was performed
12470 before closing the file.
12472 A canonical Text_IO file that is a regular file (i.e., not a device or a
12473 pipe) can be read using any of the routines in Text_IO@. The
12474 semantics in this case will be exactly as defined in the Ada Reference
12475 Manual, and all the routines in Text_IO are fully implemented.
12477 A text file that does not meet the requirements for a canonical Text_IO
12478 file has one of the following:
12482 The file contains @code{FF} characters not immediately following a
12483 @code{LF} character.
12486 The file contains @code{LF} or @code{FF} characters written by
12487 @code{Put} or @code{Put_Line}, which are not logically considered to be
12488 line marks or page marks.
12491 The file ends in a character other than @code{LF} or @code{FF},
12492 i.e.@: there is no explicit line mark or page mark at the end of the file.
12496 Text_IO can be used to read such non-standard text files but subprograms
12497 to do with line or page numbers do not have defined meanings. In
12498 particular, a @code{FF} character that does not follow a @code{LF}
12499 character may or may not be treated as a page mark from the point of
12500 view of page and line numbering. Every @code{LF} character is considered
12501 to end a line, and there is an implied @code{LF} character at the end of
12505 * Text_IO Stream Pointer Positioning::
12506 * Text_IO Reading and Writing Non-Regular Files::
12508 * Treating Text_IO Files as Streams::
12509 * Text_IO Extensions::
12510 * Text_IO Facilities for Unbounded Strings::
12513 @node Text_IO Stream Pointer Positioning
12514 @subsection Stream Pointer Positioning
12517 @code{Ada.Text_IO} has a definition of current position for a file that
12518 is being read. No internal buffering occurs in Text_IO, and usually the
12519 physical position in the stream used to implement the file corresponds
12520 to this logical position defined by Text_IO@. There are two exceptions:
12524 After a call to @code{End_Of_Page} that returns @code{True}, the stream
12525 is positioned past the @code{LF} (line mark) that precedes the page
12526 mark. Text_IO maintains an internal flag so that subsequent read
12527 operations properly handle the logical position which is unchanged by
12528 the @code{End_Of_Page} call.
12531 After a call to @code{End_Of_File} that returns @code{True}, if the
12532 Text_IO file was positioned before the line mark at the end of file
12533 before the call, then the logical position is unchanged, but the stream
12534 is physically positioned right at the end of file (past the line mark,
12535 and past a possible page mark following the line mark. Again Text_IO
12536 maintains internal flags so that subsequent read operations properly
12537 handle the logical position.
12541 These discrepancies have no effect on the observable behavior of
12542 Text_IO, but if a single Ada stream is shared between a C program and
12543 Ada program, or shared (using @samp{shared=yes} in the form string)
12544 between two Ada files, then the difference may be observable in some
12547 @node Text_IO Reading and Writing Non-Regular Files
12548 @subsection Reading and Writing Non-Regular Files
12551 A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
12552 can be used for reading and writing. Writing is not affected and the
12553 sequence of characters output is identical to the normal file case, but
12554 for reading, the behavior of Text_IO is modified to avoid undesirable
12555 look-ahead as follows:
12557 An input file that is not a regular file is considered to have no page
12558 marks. Any @code{Ascii.FF} characters (the character normally used for a
12559 page mark) appearing in the file are considered to be data
12560 characters. In particular:
12564 @code{Get_Line} and @code{Skip_Line} do not test for a page mark
12565 following a line mark. If a page mark appears, it will be treated as a
12569 This avoids the need to wait for an extra character to be typed or
12570 entered from the pipe to complete one of these operations.
12573 @code{End_Of_Page} always returns @code{False}
12576 @code{End_Of_File} will return @code{False} if there is a page mark at
12577 the end of the file.
12581 Output to non-regular files is the same as for regular files. Page marks
12582 may be written to non-regular files using @code{New_Page}, but as noted
12583 above they will not be treated as page marks on input if the output is
12584 piped to another Ada program.
12586 Another important discrepancy when reading non-regular files is that the end
12587 of file indication is not ``sticky''. If an end of file is entered, e.g.@: by
12588 pressing the @key{EOT} key,
12590 is signaled once (i.e.@: the test @code{End_Of_File}
12591 will yield @code{True}, or a read will
12592 raise @code{End_Error}), but then reading can resume
12593 to read data past that end of
12594 file indication, until another end of file indication is entered.
12596 @node Get_Immediate
12597 @subsection Get_Immediate
12598 @cindex Get_Immediate
12601 Get_Immediate returns the next character (including control characters)
12602 from the input file. In particular, Get_Immediate will return LF or FF
12603 characters used as line marks or page marks. Such operations leave the
12604 file positioned past the control character, and it is thus not treated
12605 as having its normal function. This means that page, line and column
12606 counts after this kind of Get_Immediate call are set as though the mark
12607 did not occur. In the case where a Get_Immediate leaves the file
12608 positioned between the line mark and page mark (which is not normally
12609 possible), it is undefined whether the FF character will be treated as a
12612 @node Treating Text_IO Files as Streams
12613 @subsection Treating Text_IO Files as Streams
12614 @cindex Stream files
12617 The package @code{Text_IO.Streams} allows a Text_IO file to be treated
12618 as a stream. Data written to a Text_IO file in this stream mode is
12619 binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
12620 16#0C# (@code{FF}), the resulting file may have non-standard
12621 format. Similarly if read operations are used to read from a Text_IO
12622 file treated as a stream, then @code{LF} and @code{FF} characters may be
12623 skipped and the effect is similar to that described above for
12624 @code{Get_Immediate}.
12626 @node Text_IO Extensions
12627 @subsection Text_IO Extensions
12628 @cindex Text_IO extensions
12631 A package GNAT.IO_Aux in the GNAT library provides some useful extensions
12632 to the standard @code{Text_IO} package:
12635 @item function File_Exists (Name : String) return Boolean;
12636 Determines if a file of the given name exists.
12638 @item function Get_Line return String;
12639 Reads a string from the standard input file. The value returned is exactly
12640 the length of the line that was read.
12642 @item function Get_Line (File : Ada.Text_IO.File_Type) return String;
12643 Similar, except that the parameter File specifies the file from which
12644 the string is to be read.
12648 @node Text_IO Facilities for Unbounded Strings
12649 @subsection Text_IO Facilities for Unbounded Strings
12650 @cindex Text_IO for unbounded strings
12651 @cindex Unbounded_String, Text_IO operations
12654 The package @code{Ada.Strings.Unbounded.Text_IO}
12655 in library files @code{a-suteio.ads/adb} contains some GNAT-specific
12656 subprograms useful for Text_IO operations on unbounded strings:
12660 @item function Get_Line (File : File_Type) return Unbounded_String;
12661 Reads a line from the specified file
12662 and returns the result as an unbounded string.
12664 @item procedure Put (File : File_Type; U : Unbounded_String);
12665 Writes the value of the given unbounded string to the specified file
12666 Similar to the effect of
12667 @code{Put (To_String (U))} except that an extra copy is avoided.
12669 @item procedure Put_Line (File : File_Type; U : Unbounded_String);
12670 Writes the value of the given unbounded string to the specified file,
12671 followed by a @code{New_Line}.
12672 Similar to the effect of @code{Put_Line (To_String (U))} except
12673 that an extra copy is avoided.
12677 In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
12678 and is optional. If the parameter is omitted, then the standard input or
12679 output file is referenced as appropriate.
12681 The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
12682 files @file{a-swuwti.ads} and @file{a-swuwti.adb} provides similar extended
12683 @code{Wide_Text_IO} functionality for unbounded wide strings.
12685 The package @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library
12686 files @file{a-szuzti.ads} and @file{a-szuzti.adb} provides similar extended
12687 @code{Wide_Wide_Text_IO} functionality for unbounded wide wide strings.
12690 @section Wide_Text_IO
12693 @code{Wide_Text_IO} is similar in most respects to Text_IO, except that
12694 both input and output files may contain special sequences that represent
12695 wide character values. The encoding scheme for a given file may be
12696 specified using a FORM parameter:
12703 as part of the FORM string (WCEM = wide character encoding method),
12704 where @var{x} is one of the following characters
12710 Upper half encoding
12722 The encoding methods match those that
12723 can be used in a source
12724 program, but there is no requirement that the encoding method used for
12725 the source program be the same as the encoding method used for files,
12726 and different files may use different encoding methods.
12728 The default encoding method for the standard files, and for opened files
12729 for which no WCEM parameter is given in the FORM string matches the
12730 wide character encoding specified for the main program (the default
12731 being brackets encoding if no coding method was specified with -gnatW).
12735 In this encoding, a wide character is represented by a five character
12743 where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
12744 characters (using upper case letters) of the wide character code. For
12745 example, ESC A345 is used to represent the wide character with code
12746 16#A345#. This scheme is compatible with use of the full
12747 @code{Wide_Character} set.
12749 @item Upper Half Coding
12750 The wide character with encoding 16#abcd#, where the upper bit is on
12751 (i.e.@: a is in the range 8-F) is represented as two bytes 16#ab# and
12752 16#cd#. The second byte may never be a format control character, but is
12753 not required to be in the upper half. This method can be also used for
12754 shift-JIS or EUC where the internal coding matches the external coding.
12756 @item Shift JIS Coding
12757 A wide character is represented by a two character sequence 16#ab# and
12758 16#cd#, with the restrictions described for upper half encoding as
12759 described above. The internal character code is the corresponding JIS
12760 character according to the standard algorithm for Shift-JIS
12761 conversion. Only characters defined in the JIS code set table can be
12762 used with this encoding method.
12765 A wide character is represented by a two character sequence 16#ab# and
12766 16#cd#, with both characters being in the upper half. The internal
12767 character code is the corresponding JIS character according to the EUC
12768 encoding algorithm. Only characters defined in the JIS code set table
12769 can be used with this encoding method.
12772 A wide character is represented using
12773 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12774 10646-1/Am.2. Depending on the character value, the representation
12775 is a one, two, or three byte sequence:
12778 16#0000#-16#007f#: 2#0xxxxxxx#
12779 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
12780 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12784 where the @var{xxx} bits correspond to the left-padded bits of the
12785 16-bit character value. Note that all lower half ASCII characters
12786 are represented as ASCII bytes and all upper half characters and
12787 other wide characters are represented as sequences of upper-half
12788 (The full UTF-8 scheme allows for encoding 31-bit characters as
12789 6-byte sequences, but in this implementation, all UTF-8 sequences
12790 of four or more bytes length will raise a Constraint_Error, as
12791 will all invalid UTF-8 sequences.)
12793 @item Brackets Coding
12794 In this encoding, a wide character is represented by the following eight
12795 character sequence:
12802 where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
12803 characters (using uppercase letters) of the wide character code. For
12804 example, @code{["A345"]} is used to represent the wide character with code
12806 This scheme is compatible with use of the full Wide_Character set.
12807 On input, brackets coding can also be used for upper half characters,
12808 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12809 is only used for wide characters with a code greater than @code{16#FF#}.
12811 Note that brackets coding is not normally used in the context of
12812 Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as
12813 a portable way of encoding source files. In the context of Wide_Text_IO
12814 or Wide_Wide_Text_IO, it can only be used if the file does not contain
12815 any instance of the left bracket character other than to encode wide
12816 character values using the brackets encoding method. In practice it is
12817 expected that some standard wide character encoding method such
12818 as UTF-8 will be used for text input output.
12820 If brackets notation is used, then any occurrence of a left bracket
12821 in the input file which is not the start of a valid wide character
12822 sequence will cause Constraint_Error to be raised. It is possible to
12823 encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO
12824 input will interpret this as a left bracket.
12826 However, when a left bracket is output, it will be output as a left bracket
12827 and not as ["5B"]. We make this decision because for normal use of
12828 Wide_Text_IO for outputting messages, it is unpleasant to clobber left
12829 brackets. For example, if we write:
12832 Put_Line ("Start of output [first run]");
12836 we really do not want to have the left bracket in this message clobbered so
12837 that the output reads:
12840 Start of output ["5B"]first run]
12844 In practice brackets encoding is reasonably useful for normal Put_Line use
12845 since we won't get confused between left brackets and wide character
12846 sequences in the output. But for input, or when files are written out
12847 and read back in, it really makes better sense to use one of the standard
12848 encoding methods such as UTF-8.
12853 For the coding schemes other than UTF-8, Hex, or Brackets encoding,
12854 not all wide character
12855 values can be represented. An attempt to output a character that cannot
12856 be represented using the encoding scheme for the file causes
12857 Constraint_Error to be raised. An invalid wide character sequence on
12858 input also causes Constraint_Error to be raised.
12861 * Wide_Text_IO Stream Pointer Positioning::
12862 * Wide_Text_IO Reading and Writing Non-Regular Files::
12865 @node Wide_Text_IO Stream Pointer Positioning
12866 @subsection Stream Pointer Positioning
12869 @code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12870 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12873 If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
12874 normal lower ASCII set (i.e.@: a character in the range:
12876 @smallexample @c ada
12877 Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
12881 then although the logical position of the file pointer is unchanged by
12882 the @code{Look_Ahead} call, the stream is physically positioned past the
12883 wide character sequence. Again this is to avoid the need for buffering
12884 or backup, and all @code{Wide_Text_IO} routines check the internal
12885 indication that this situation has occurred so that this is not visible
12886 to a normal program using @code{Wide_Text_IO}. However, this discrepancy
12887 can be observed if the wide text file shares a stream with another file.
12889 @node Wide_Text_IO Reading and Writing Non-Regular Files
12890 @subsection Reading and Writing Non-Regular Files
12893 As in the case of Text_IO, when a non-regular file is read, it is
12894 assumed that the file contains no page marks (any form characters are
12895 treated as data characters), and @code{End_Of_Page} always returns
12896 @code{False}. Similarly, the end of file indication is not sticky, so
12897 it is possible to read beyond an end of file.
12899 @node Wide_Wide_Text_IO
12900 @section Wide_Wide_Text_IO
12903 @code{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that
12904 both input and output files may contain special sequences that represent
12905 wide wide character values. The encoding scheme for a given file may be
12906 specified using a FORM parameter:
12913 as part of the FORM string (WCEM = wide character encoding method),
12914 where @var{x} is one of the following characters
12920 Upper half encoding
12932 The encoding methods match those that
12933 can be used in a source
12934 program, but there is no requirement that the encoding method used for
12935 the source program be the same as the encoding method used for files,
12936 and different files may use different encoding methods.
12938 The default encoding method for the standard files, and for opened files
12939 for which no WCEM parameter is given in the FORM string matches the
12940 wide character encoding specified for the main program (the default
12941 being brackets encoding if no coding method was specified with -gnatW).
12946 A wide character is represented using
12947 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12948 10646-1/Am.2. Depending on the character value, the representation
12949 is a one, two, three, or four byte sequence:
12952 16#000000#-16#00007f#: 2#0xxxxxxx#
12953 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx#
12954 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12955 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
12959 where the @var{xxx} bits correspond to the left-padded bits of the
12960 21-bit character value. Note that all lower half ASCII characters
12961 are represented as ASCII bytes and all upper half characters and
12962 other wide characters are represented as sequences of upper-half
12965 @item Brackets Coding
12966 In this encoding, a wide wide character is represented by the following eight
12967 character sequence if is in wide character range
12973 and by the following ten character sequence if not
12976 [ " a b c d e f " ]
12980 where @code{a}, @code{b}, @code{c}, @code{d}, @code{e}, and @code{f}
12981 are the four or six hexadecimal
12982 characters (using uppercase letters) of the wide wide character code. For
12983 example, @code{["01A345"]} is used to represent the wide wide character
12984 with code @code{16#01A345#}.
12986 This scheme is compatible with use of the full Wide_Wide_Character set.
12987 On input, brackets coding can also be used for upper half characters,
12988 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12989 is only used for wide characters with a code greater than @code{16#FF#}.
12994 If is also possible to use the other Wide_Character encoding methods,
12995 such as Shift-JIS, but the other schemes cannot support the full range
12996 of wide wide characters.
12997 An attempt to output a character that cannot
12998 be represented using the encoding scheme for the file causes
12999 Constraint_Error to be raised. An invalid wide character sequence on
13000 input also causes Constraint_Error to be raised.
13003 * Wide_Wide_Text_IO Stream Pointer Positioning::
13004 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
13007 @node Wide_Wide_Text_IO Stream Pointer Positioning
13008 @subsection Stream Pointer Positioning
13011 @code{Ada.Wide_Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
13012 of stream pointer positioning (@pxref{Text_IO}). There is one additional
13015 If @code{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the
13016 normal lower ASCII set (i.e.@: a character in the range:
13018 @smallexample @c ada
13019 Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
13023 then although the logical position of the file pointer is unchanged by
13024 the @code{Look_Ahead} call, the stream is physically positioned past the
13025 wide character sequence. Again this is to avoid the need for buffering
13026 or backup, and all @code{Wide_Wide_Text_IO} routines check the internal
13027 indication that this situation has occurred so that this is not visible
13028 to a normal program using @code{Wide_Wide_Text_IO}. However, this discrepancy
13029 can be observed if the wide text file shares a stream with another file.
13031 @node Wide_Wide_Text_IO Reading and Writing Non-Regular Files
13032 @subsection Reading and Writing Non-Regular Files
13035 As in the case of Text_IO, when a non-regular file is read, it is
13036 assumed that the file contains no page marks (any form characters are
13037 treated as data characters), and @code{End_Of_Page} always returns
13038 @code{False}. Similarly, the end of file indication is not sticky, so
13039 it is possible to read beyond an end of file.
13045 A stream file is a sequence of bytes, where individual elements are
13046 written to the file as described in the Ada Reference Manual. The type
13047 @code{Stream_Element} is simply a byte. There are two ways to read or
13048 write a stream file.
13052 The operations @code{Read} and @code{Write} directly read or write a
13053 sequence of stream elements with no control information.
13056 The stream attributes applied to a stream file transfer data in the
13057 manner described for stream attributes.
13060 @node Text Translation
13061 @section Text Translation
13064 @samp{Text_Translation=@var{xxx}} may be used as the Form parameter
13065 passed to Text_IO.Create and Text_IO.Open:
13066 @samp{Text_Translation=@var{Yes}} is the default, which means to
13067 translate LF to/from CR/LF on Windows systems.
13068 @samp{Text_Translation=@var{No}} disables this translation; i.e. it
13069 uses binary mode. For output files, @samp{Text_Translation=@var{No}}
13070 may be used to create Unix-style files on
13071 Windows. @samp{Text_Translation=@var{xxx}} has no effect on Unix
13075 @section Shared Files
13078 Section A.14 of the Ada Reference Manual allows implementations to
13079 provide a wide variety of behavior if an attempt is made to access the
13080 same external file with two or more internal files.
13082 To provide a full range of functionality, while at the same time
13083 minimizing the problems of portability caused by this implementation
13084 dependence, GNAT handles file sharing as follows:
13088 In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
13089 to open two or more files with the same full name is considered an error
13090 and is not supported. The exception @code{Use_Error} will be
13091 raised. Note that a file that is not explicitly closed by the program
13092 remains open until the program terminates.
13095 If the form parameter @samp{shared=no} appears in the form string, the
13096 file can be opened or created with its own separate stream identifier,
13097 regardless of whether other files sharing the same external file are
13098 opened. The exact effect depends on how the C stream routines handle
13099 multiple accesses to the same external files using separate streams.
13102 If the form parameter @samp{shared=yes} appears in the form string for
13103 each of two or more files opened using the same full name, the same
13104 stream is shared between these files, and the semantics are as described
13105 in Ada Reference Manual, Section A.14.
13109 When a program that opens multiple files with the same name is ported
13110 from another Ada compiler to GNAT, the effect will be that
13111 @code{Use_Error} is raised.
13113 The documentation of the original compiler and the documentation of the
13114 program should then be examined to determine if file sharing was
13115 expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
13116 and @code{Create} calls as required.
13118 When a program is ported from GNAT to some other Ada compiler, no
13119 special attention is required unless the @samp{shared=@var{xxx}} form
13120 parameter is used in the program. In this case, you must examine the
13121 documentation of the new compiler to see if it supports the required
13122 file sharing semantics, and form strings modified appropriately. Of
13123 course it may be the case that the program cannot be ported if the
13124 target compiler does not support the required functionality. The best
13125 approach in writing portable code is to avoid file sharing (and hence
13126 the use of the @samp{shared=@var{xxx}} parameter in the form string)
13129 One common use of file sharing in Ada 83 is the use of instantiations of
13130 Sequential_IO on the same file with different types, to achieve
13131 heterogeneous input-output. Although this approach will work in GNAT if
13132 @samp{shared=yes} is specified, it is preferable in Ada to use Stream_IO
13133 for this purpose (using the stream attributes)
13135 @node Filenames encoding
13136 @section Filenames encoding
13139 An encoding form parameter can be used to specify the filename
13140 encoding @samp{encoding=@var{xxx}}.
13144 If the form parameter @samp{encoding=utf8} appears in the form string, the
13145 filename must be encoded in UTF-8.
13148 If the form parameter @samp{encoding=8bits} appears in the form
13149 string, the filename must be a standard 8bits string.
13152 In the absence of a @samp{encoding=@var{xxx}} form parameter, the
13153 encoding is controlled by the @samp{GNAT_CODE_PAGE} environment
13154 variable. And if not set @samp{utf8} is assumed.
13158 The current system Windows ANSI code page.
13163 This encoding form parameter is only supported on the Windows
13164 platform. On the other Operating Systems the run-time is supporting
13168 @section Open Modes
13171 @code{Open} and @code{Create} calls result in a call to @code{fopen}
13172 using the mode shown in the following table:
13175 @center @code{Open} and @code{Create} Call Modes
13177 @b{OPEN } @b{CREATE}
13178 Append_File "r+" "w+"
13180 Out_File (Direct_IO) "r+" "w"
13181 Out_File (all other cases) "w" "w"
13182 Inout_File "r+" "w+"
13186 If text file translation is required, then either @samp{b} or @samp{t}
13187 is added to the mode, depending on the setting of Text. Text file
13188 translation refers to the mapping of CR/LF sequences in an external file
13189 to LF characters internally. This mapping only occurs in DOS and
13190 DOS-like systems, and is not relevant to other systems.
13192 A special case occurs with Stream_IO@. As shown in the above table, the
13193 file is initially opened in @samp{r} or @samp{w} mode for the
13194 @code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
13195 subsequently requires switching from reading to writing or vice-versa,
13196 then the file is reopened in @samp{r+} mode to permit the required operation.
13198 @node Operations on C Streams
13199 @section Operations on C Streams
13200 The package @code{Interfaces.C_Streams} provides an Ada program with direct
13201 access to the C library functions for operations on C streams:
13203 @smallexample @c adanocomment
13204 package Interfaces.C_Streams is
13205 -- Note: the reason we do not use the types that are in
13206 -- Interfaces.C is that we want to avoid dragging in the
13207 -- code in this unit if possible.
13208 subtype chars is System.Address;
13209 -- Pointer to null-terminated array of characters
13210 subtype FILEs is System.Address;
13211 -- Corresponds to the C type FILE*
13212 subtype voids is System.Address;
13213 -- Corresponds to the C type void*
13214 subtype int is Integer;
13215 subtype long is Long_Integer;
13216 -- Note: the above types are subtypes deliberately, and it
13217 -- is part of this spec that the above correspondences are
13218 -- guaranteed. This means that it is legitimate to, for
13219 -- example, use Integer instead of int. We provide these
13220 -- synonyms for clarity, but in some cases it may be
13221 -- convenient to use the underlying types (for example to
13222 -- avoid an unnecessary dependency of a spec on the spec
13224 type size_t is mod 2 ** Standard'Address_Size;
13225 NULL_Stream : constant FILEs;
13226 -- Value returned (NULL in C) to indicate an
13227 -- fdopen/fopen/tmpfile error
13228 ----------------------------------
13229 -- Constants Defined in stdio.h --
13230 ----------------------------------
13231 EOF : constant int;
13232 -- Used by a number of routines to indicate error or
13234 IOFBF : constant int;
13235 IOLBF : constant int;
13236 IONBF : constant int;
13237 -- Used to indicate buffering mode for setvbuf call
13238 SEEK_CUR : constant int;
13239 SEEK_END : constant int;
13240 SEEK_SET : constant int;
13241 -- Used to indicate origin for fseek call
13242 function stdin return FILEs;
13243 function stdout return FILEs;
13244 function stderr return FILEs;
13245 -- Streams associated with standard files
13246 --------------------------
13247 -- Standard C functions --
13248 --------------------------
13249 -- The functions selected below are ones that are
13250 -- available in DOS, OS/2, UNIX and Xenix (but not
13251 -- necessarily in ANSI C). These are very thin interfaces
13252 -- which copy exactly the C headers. For more
13253 -- documentation on these functions, see the Microsoft C
13254 -- "Run-Time Library Reference" (Microsoft Press, 1990,
13255 -- ISBN 1-55615-225-6), which includes useful information
13256 -- on system compatibility.
13257 procedure clearerr (stream : FILEs);
13258 function fclose (stream : FILEs) return int;
13259 function fdopen (handle : int; mode : chars) return FILEs;
13260 function feof (stream : FILEs) return int;
13261 function ferror (stream : FILEs) return int;
13262 function fflush (stream : FILEs) return int;
13263 function fgetc (stream : FILEs) return int;
13264 function fgets (strng : chars; n : int; stream : FILEs)
13266 function fileno (stream : FILEs) return int;
13267 function fopen (filename : chars; Mode : chars)
13269 -- Note: to maintain target independence, use
13270 -- text_translation_required, a boolean variable defined in
13271 -- a-sysdep.c to deal with the target dependent text
13272 -- translation requirement. If this variable is set,
13273 -- then b/t should be appended to the standard mode
13274 -- argument to set the text translation mode off or on
13276 function fputc (C : int; stream : FILEs) return int;
13277 function fputs (Strng : chars; Stream : FILEs) return int;
13294 function ftell (stream : FILEs) return long;
13301 function isatty (handle : int) return int;
13302 procedure mktemp (template : chars);
13303 -- The return value (which is just a pointer to template)
13305 procedure rewind (stream : FILEs);
13306 function rmtmp return int;
13314 function tmpfile return FILEs;
13315 function ungetc (c : int; stream : FILEs) return int;
13316 function unlink (filename : chars) return int;
13317 ---------------------
13318 -- Extra functions --
13319 ---------------------
13320 -- These functions supply slightly thicker bindings than
13321 -- those above. They are derived from functions in the
13322 -- C Run-Time Library, but may do a bit more work than
13323 -- just directly calling one of the Library functions.
13324 function is_regular_file (handle : int) return int;
13325 -- Tests if given handle is for a regular file (result 1)
13326 -- or for a non-regular file (pipe or device, result 0).
13327 ---------------------------------
13328 -- Control of Text/Binary Mode --
13329 ---------------------------------
13330 -- If text_translation_required is true, then the following
13331 -- functions may be used to dynamically switch a file from
13332 -- binary to text mode or vice versa. These functions have
13333 -- no effect if text_translation_required is false (i.e.@: in
13334 -- normal UNIX mode). Use fileno to get a stream handle.
13335 procedure set_binary_mode (handle : int);
13336 procedure set_text_mode (handle : int);
13337 ----------------------------
13338 -- Full Path Name support --
13339 ----------------------------
13340 procedure full_name (nam : chars; buffer : chars);
13341 -- Given a NUL terminated string representing a file
13342 -- name, returns in buffer a NUL terminated string
13343 -- representing the full path name for the file name.
13344 -- On systems where it is relevant the drive is also
13345 -- part of the full path name. It is the responsibility
13346 -- of the caller to pass an actual parameter for buffer
13347 -- that is big enough for any full path name. Use
13348 -- max_path_len given below as the size of buffer.
13349 max_path_len : integer;
13350 -- Maximum length of an allowable full path name on the
13351 -- system, including a terminating NUL character.
13352 end Interfaces.C_Streams;
13355 @node Interfacing to C Streams
13356 @section Interfacing to C Streams
13359 The packages in this section permit interfacing Ada files to C Stream
13362 @smallexample @c ada
13363 with Interfaces.C_Streams;
13364 package Ada.Sequential_IO.C_Streams is
13365 function C_Stream (F : File_Type)
13366 return Interfaces.C_Streams.FILEs;
13368 (File : in out File_Type;
13369 Mode : in File_Mode;
13370 C_Stream : in Interfaces.C_Streams.FILEs;
13371 Form : in String := "");
13372 end Ada.Sequential_IO.C_Streams;
13374 with Interfaces.C_Streams;
13375 package Ada.Direct_IO.C_Streams is
13376 function C_Stream (F : File_Type)
13377 return Interfaces.C_Streams.FILEs;
13379 (File : in out File_Type;
13380 Mode : in File_Mode;
13381 C_Stream : in Interfaces.C_Streams.FILEs;
13382 Form : in String := "");
13383 end Ada.Direct_IO.C_Streams;
13385 with Interfaces.C_Streams;
13386 package Ada.Text_IO.C_Streams is
13387 function C_Stream (F : File_Type)
13388 return Interfaces.C_Streams.FILEs;
13390 (File : in out File_Type;
13391 Mode : in File_Mode;
13392 C_Stream : in Interfaces.C_Streams.FILEs;
13393 Form : in String := "");
13394 end Ada.Text_IO.C_Streams;
13396 with Interfaces.C_Streams;
13397 package Ada.Wide_Text_IO.C_Streams is
13398 function C_Stream (F : File_Type)
13399 return Interfaces.C_Streams.FILEs;
13401 (File : in out File_Type;
13402 Mode : in File_Mode;
13403 C_Stream : in Interfaces.C_Streams.FILEs;
13404 Form : in String := "");
13405 end Ada.Wide_Text_IO.C_Streams;
13407 with Interfaces.C_Streams;
13408 package Ada.Wide_Wide_Text_IO.C_Streams is
13409 function C_Stream (F : File_Type)
13410 return Interfaces.C_Streams.FILEs;
13412 (File : in out File_Type;
13413 Mode : in File_Mode;
13414 C_Stream : in Interfaces.C_Streams.FILEs;
13415 Form : in String := "");
13416 end Ada.Wide_Wide_Text_IO.C_Streams;
13418 with Interfaces.C_Streams;
13419 package Ada.Stream_IO.C_Streams is
13420 function C_Stream (F : File_Type)
13421 return Interfaces.C_Streams.FILEs;
13423 (File : in out File_Type;
13424 Mode : in File_Mode;
13425 C_Stream : in Interfaces.C_Streams.FILEs;
13426 Form : in String := "");
13427 end Ada.Stream_IO.C_Streams;
13431 In each of these six packages, the @code{C_Stream} function obtains the
13432 @code{FILE} pointer from a currently opened Ada file. It is then
13433 possible to use the @code{Interfaces.C_Streams} package to operate on
13434 this stream, or the stream can be passed to a C program which can
13435 operate on it directly. Of course the program is responsible for
13436 ensuring that only appropriate sequences of operations are executed.
13438 One particular use of relevance to an Ada program is that the
13439 @code{setvbuf} function can be used to control the buffering of the
13440 stream used by an Ada file. In the absence of such a call the standard
13441 default buffering is used.
13443 The @code{Open} procedures in these packages open a file giving an
13444 existing C Stream instead of a file name. Typically this stream is
13445 imported from a C program, allowing an Ada file to operate on an
13448 @node The GNAT Library
13449 @chapter The GNAT Library
13452 The GNAT library contains a number of general and special purpose packages.
13453 It represents functionality that the GNAT developers have found useful, and
13454 which is made available to GNAT users. The packages described here are fully
13455 supported, and upwards compatibility will be maintained in future releases,
13456 so you can use these facilities with the confidence that the same functionality
13457 will be available in future releases.
13459 The chapter here simply gives a brief summary of the facilities available.
13460 The full documentation is found in the spec file for the package. The full
13461 sources of these library packages, including both spec and body, are provided
13462 with all GNAT releases. For example, to find out the full specifications of
13463 the SPITBOL pattern matching capability, including a full tutorial and
13464 extensive examples, look in the @file{g-spipat.ads} file in the library.
13466 For each entry here, the package name (as it would appear in a @code{with}
13467 clause) is given, followed by the name of the corresponding spec file in
13468 parentheses. The packages are children in four hierarchies, @code{Ada},
13469 @code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
13470 GNAT-specific hierarchy.
13472 Note that an application program should only use packages in one of these
13473 four hierarchies if the package is defined in the Ada Reference Manual,
13474 or is listed in this section of the GNAT Programmers Reference Manual.
13475 All other units should be considered internal implementation units and
13476 should not be directly @code{with}'ed by application code. The use of
13477 a @code{with} statement that references one of these internal implementation
13478 units makes an application potentially dependent on changes in versions
13479 of GNAT, and will generate a warning message.
13482 * Ada.Characters.Latin_9 (a-chlat9.ads)::
13483 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
13484 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
13485 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
13486 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
13487 * Ada.Command_Line.Environment (a-colien.ads)::
13488 * Ada.Command_Line.Remove (a-colire.ads)::
13489 * Ada.Command_Line.Response_File (a-clrefi.ads)::
13490 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
13491 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
13492 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
13493 * Ada.Exceptions.Traceback (a-exctra.ads)::
13494 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
13495 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
13496 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
13497 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
13498 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
13499 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
13500 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
13501 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
13502 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
13503 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
13504 * GNAT.Altivec (g-altive.ads)::
13505 * GNAT.Altivec.Conversions (g-altcon.ads)::
13506 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
13507 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
13508 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
13509 * GNAT.Array_Split (g-arrspl.ads)::
13510 * GNAT.AWK (g-awk.ads)::
13511 * GNAT.Bounded_Buffers (g-boubuf.ads)::
13512 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
13513 * GNAT.Bubble_Sort (g-bubsor.ads)::
13514 * GNAT.Bubble_Sort_A (g-busora.ads)::
13515 * GNAT.Bubble_Sort_G (g-busorg.ads)::
13516 * GNAT.Byte_Order_Mark (g-byorma.ads)::
13517 * GNAT.Byte_Swapping (g-bytswa.ads)::
13518 * GNAT.Calendar (g-calend.ads)::
13519 * GNAT.Calendar.Time_IO (g-catiio.ads)::
13520 * GNAT.Case_Util (g-casuti.ads)::
13521 * GNAT.CGI (g-cgi.ads)::
13522 * GNAT.CGI.Cookie (g-cgicoo.ads)::
13523 * GNAT.CGI.Debug (g-cgideb.ads)::
13524 * GNAT.Command_Line (g-comlin.ads)::
13525 * GNAT.Compiler_Version (g-comver.ads)::
13526 * GNAT.Ctrl_C (g-ctrl_c.ads)::
13527 * GNAT.CRC32 (g-crc32.ads)::
13528 * GNAT.Current_Exception (g-curexc.ads)::
13529 * GNAT.Debug_Pools (g-debpoo.ads)::
13530 * GNAT.Debug_Utilities (g-debuti.ads)::
13531 * GNAT.Decode_String (g-decstr.ads)::
13532 * GNAT.Decode_UTF8_String (g-deutst.ads)::
13533 * GNAT.Directory_Operations (g-dirope.ads)::
13534 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
13535 * GNAT.Dynamic_HTables (g-dynhta.ads)::
13536 * GNAT.Dynamic_Tables (g-dyntab.ads)::
13537 * GNAT.Encode_String (g-encstr.ads)::
13538 * GNAT.Encode_UTF8_String (g-enutst.ads)::
13539 * GNAT.Exception_Actions (g-excact.ads)::
13540 * GNAT.Exception_Traces (g-exctra.ads)::
13541 * GNAT.Exceptions (g-except.ads)::
13542 * GNAT.Expect (g-expect.ads)::
13543 * GNAT.Float_Control (g-flocon.ads)::
13544 * GNAT.Heap_Sort (g-heasor.ads)::
13545 * GNAT.Heap_Sort_A (g-hesora.ads)::
13546 * GNAT.Heap_Sort_G (g-hesorg.ads)::
13547 * GNAT.HTable (g-htable.ads)::
13548 * GNAT.IO (g-io.ads)::
13549 * GNAT.IO_Aux (g-io_aux.ads)::
13550 * GNAT.Lock_Files (g-locfil.ads)::
13551 * GNAT.MD5 (g-md5.ads)::
13552 * GNAT.Memory_Dump (g-memdum.ads)::
13553 * GNAT.Most_Recent_Exception (g-moreex.ads)::
13554 * GNAT.OS_Lib (g-os_lib.ads)::
13555 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
13556 * GNAT.Random_Numbers (g-rannum.ads)::
13557 * GNAT.Regexp (g-regexp.ads)::
13558 * GNAT.Registry (g-regist.ads)::
13559 * GNAT.Regpat (g-regpat.ads)::
13560 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
13561 * GNAT.Semaphores (g-semaph.ads)::
13562 * GNAT.Serial_Communications (g-sercom.ads)::
13563 * GNAT.SHA1 (g-sha1.ads)::
13564 * GNAT.Signals (g-signal.ads)::
13565 * GNAT.Sockets (g-socket.ads)::
13566 * GNAT.Source_Info (g-souinf.ads)::
13567 * GNAT.Spelling_Checker (g-speche.ads)::
13568 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
13569 * GNAT.Spitbol.Patterns (g-spipat.ads)::
13570 * GNAT.Spitbol (g-spitbo.ads)::
13571 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
13572 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
13573 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
13574 * GNAT.SSE (g-sse.ads)::
13575 * GNAT.SSE.Internal_Types (g-ssinty.ads)::
13576 * GNAT.SSE.Vector_Types (g-ssvety.ads)::
13577 * GNAT.Strings (g-string.ads)::
13578 * GNAT.String_Split (g-strspl.ads)::
13579 * GNAT.Table (g-table.ads)::
13580 * GNAT.Task_Lock (g-tasloc.ads)::
13581 * GNAT.Threads (g-thread.ads)::
13582 * GNAT.Time_Stamp (g-timsta.ads)::
13583 * GNAT.Traceback (g-traceb.ads)::
13584 * GNAT.Traceback.Symbolic (g-trasym.ads)::
13585 * GNAT.UTF_32 (g-utf_32.ads)::
13586 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
13587 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
13588 * GNAT.Wide_String_Split (g-wistsp.ads)::
13589 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
13590 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
13591 * Interfaces.C.Extensions (i-cexten.ads)::
13592 * Interfaces.C.Streams (i-cstrea.ads)::
13593 * Interfaces.CPP (i-cpp.ads)::
13594 * Interfaces.Packed_Decimal (i-pacdec.ads)::
13595 * Interfaces.VxWorks (i-vxwork.ads)::
13596 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
13597 * System.Address_Image (s-addima.ads)::
13598 * System.Assertions (s-assert.ads)::
13599 * System.Memory (s-memory.ads)::
13600 * System.Partition_Interface (s-parint.ads)::
13601 * System.Pool_Global (s-pooglo.ads)::
13602 * System.Pool_Local (s-pooloc.ads)::
13603 * System.Restrictions (s-restri.ads)::
13604 * System.Rident (s-rident.ads)::
13605 * System.Strings.Stream_Ops (s-ststop.ads)::
13606 * System.Task_Info (s-tasinf.ads)::
13607 * System.Wch_Cnv (s-wchcnv.ads)::
13608 * System.Wch_Con (s-wchcon.ads)::
13611 @node Ada.Characters.Latin_9 (a-chlat9.ads)
13612 @section @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13613 @cindex @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13614 @cindex Latin_9 constants for Character
13617 This child of @code{Ada.Characters}
13618 provides a set of definitions corresponding to those in the
13619 RM-defined package @code{Ada.Characters.Latin_1} but with the
13620 few modifications required for @code{Latin-9}
13621 The provision of such a package
13622 is specifically authorized by the Ada Reference Manual
13625 @node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
13626 @section @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13627 @cindex @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13628 @cindex Latin_1 constants for Wide_Character
13631 This child of @code{Ada.Characters}
13632 provides a set of definitions corresponding to those in the
13633 RM-defined package @code{Ada.Characters.Latin_1} but with the
13634 types of the constants being @code{Wide_Character}
13635 instead of @code{Character}. The provision of such a package
13636 is specifically authorized by the Ada Reference Manual
13639 @node Ada.Characters.Wide_Latin_9 (a-cwila9.ads)
13640 @section @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13641 @cindex @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13642 @cindex Latin_9 constants for Wide_Character
13645 This child of @code{Ada.Characters}
13646 provides a set of definitions corresponding to those in the
13647 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13648 types of the constants being @code{Wide_Character}
13649 instead of @code{Character}. The provision of such a package
13650 is specifically authorized by the Ada Reference Manual
13653 @node Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)
13654 @section @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13655 @cindex @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13656 @cindex Latin_1 constants for Wide_Wide_Character
13659 This child of @code{Ada.Characters}
13660 provides a set of definitions corresponding to those in the
13661 RM-defined package @code{Ada.Characters.Latin_1} but with the
13662 types of the constants being @code{Wide_Wide_Character}
13663 instead of @code{Character}. The provision of such a package
13664 is specifically authorized by the Ada Reference Manual
13667 @node Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)
13668 @section @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13669 @cindex @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13670 @cindex Latin_9 constants for Wide_Wide_Character
13673 This child of @code{Ada.Characters}
13674 provides a set of definitions corresponding to those in the
13675 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13676 types of the constants being @code{Wide_Wide_Character}
13677 instead of @code{Character}. The provision of such a package
13678 is specifically authorized by the Ada Reference Manual
13681 @node Ada.Command_Line.Environment (a-colien.ads)
13682 @section @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13683 @cindex @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13684 @cindex Environment entries
13687 This child of @code{Ada.Command_Line}
13688 provides a mechanism for obtaining environment values on systems
13689 where this concept makes sense.
13691 @node Ada.Command_Line.Remove (a-colire.ads)
13692 @section @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13693 @cindex @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13694 @cindex Removing command line arguments
13695 @cindex Command line, argument removal
13698 This child of @code{Ada.Command_Line}
13699 provides a mechanism for logically removing
13700 arguments from the argument list. Once removed, an argument is not visible
13701 to further calls on the subprograms in @code{Ada.Command_Line} will not
13702 see the removed argument.
13704 @node Ada.Command_Line.Response_File (a-clrefi.ads)
13705 @section @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13706 @cindex @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13707 @cindex Response file for command line
13708 @cindex Command line, response file
13709 @cindex Command line, handling long command lines
13712 This child of @code{Ada.Command_Line} provides a mechanism facilities for
13713 getting command line arguments from a text file, called a "response file".
13714 Using a response file allow passing a set of arguments to an executable longer
13715 than the maximum allowed by the system on the command line.
13717 @node Ada.Direct_IO.C_Streams (a-diocst.ads)
13718 @section @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13719 @cindex @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13720 @cindex C Streams, Interfacing with Direct_IO
13723 This package provides subprograms that allow interfacing between
13724 C streams and @code{Direct_IO}. The stream identifier can be
13725 extracted from a file opened on the Ada side, and an Ada file
13726 can be constructed from a stream opened on the C side.
13728 @node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
13729 @section @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13730 @cindex @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13731 @cindex Null_Occurrence, testing for
13734 This child subprogram provides a way of testing for the null
13735 exception occurrence (@code{Null_Occurrence}) without raising
13738 @node Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)
13739 @section @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13740 @cindex @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13741 @cindex Null_Occurrence, testing for
13744 This child subprogram is used for handling otherwise unhandled
13745 exceptions (hence the name last chance), and perform clean ups before
13746 terminating the program. Note that this subprogram never returns.
13748 @node Ada.Exceptions.Traceback (a-exctra.ads)
13749 @section @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13750 @cindex @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13751 @cindex Traceback for Exception Occurrence
13754 This child package provides the subprogram (@code{Tracebacks}) to
13755 give a traceback array of addresses based on an exception
13758 @node Ada.Sequential_IO.C_Streams (a-siocst.ads)
13759 @section @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13760 @cindex @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13761 @cindex C Streams, Interfacing with Sequential_IO
13764 This package provides subprograms that allow interfacing between
13765 C streams and @code{Sequential_IO}. The stream identifier can be
13766 extracted from a file opened on the Ada side, and an Ada file
13767 can be constructed from a stream opened on the C side.
13769 @node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
13770 @section @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13771 @cindex @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13772 @cindex C Streams, Interfacing with Stream_IO
13775 This package provides subprograms that allow interfacing between
13776 C streams and @code{Stream_IO}. The stream identifier can be
13777 extracted from a file opened on the Ada side, and an Ada file
13778 can be constructed from a stream opened on the C side.
13780 @node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
13781 @section @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13782 @cindex @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13783 @cindex @code{Unbounded_String}, IO support
13784 @cindex @code{Text_IO}, extensions for unbounded strings
13787 This package provides subprograms for Text_IO for unbounded
13788 strings, avoiding the necessity for an intermediate operation
13789 with ordinary strings.
13791 @node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
13792 @section @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13793 @cindex @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13794 @cindex @code{Unbounded_Wide_String}, IO support
13795 @cindex @code{Text_IO}, extensions for unbounded wide strings
13798 This package provides subprograms for Text_IO for unbounded
13799 wide strings, avoiding the necessity for an intermediate operation
13800 with ordinary wide strings.
13802 @node Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)
13803 @section @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13804 @cindex @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13805 @cindex @code{Unbounded_Wide_Wide_String}, IO support
13806 @cindex @code{Text_IO}, extensions for unbounded wide wide strings
13809 This package provides subprograms for Text_IO for unbounded
13810 wide wide strings, avoiding the necessity for an intermediate operation
13811 with ordinary wide wide strings.
13813 @node Ada.Text_IO.C_Streams (a-tiocst.ads)
13814 @section @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13815 @cindex @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13816 @cindex C Streams, Interfacing with @code{Text_IO}
13819 This package provides subprograms that allow interfacing between
13820 C streams and @code{Text_IO}. The stream identifier can be
13821 extracted from a file opened on the Ada side, and an Ada file
13822 can be constructed from a stream opened on the C side.
13824 @node Ada.Wide_Characters.Unicode (a-wichun.ads)
13825 @section @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13826 @cindex @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13827 @cindex Unicode categorization, Wide_Character
13830 This package provides subprograms that allow categorization of
13831 Wide_Character values according to Unicode categories.
13833 @node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
13834 @section @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13835 @cindex @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13836 @cindex C Streams, Interfacing with @code{Wide_Text_IO}
13839 This package provides subprograms that allow interfacing between
13840 C streams and @code{Wide_Text_IO}. The stream identifier can be
13841 extracted from a file opened on the Ada side, and an Ada file
13842 can be constructed from a stream opened on the C side.
13844 @node Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)
13845 @section @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13846 @cindex @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13847 @cindex Unicode categorization, Wide_Wide_Character
13850 This package provides subprograms that allow categorization of
13851 Wide_Wide_Character values according to Unicode categories.
13853 @node Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)
13854 @section @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13855 @cindex @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13856 @cindex C Streams, Interfacing with @code{Wide_Wide_Text_IO}
13859 This package provides subprograms that allow interfacing between
13860 C streams and @code{Wide_Wide_Text_IO}. The stream identifier can be
13861 extracted from a file opened on the Ada side, and an Ada file
13862 can be constructed from a stream opened on the C side.
13864 @node GNAT.Altivec (g-altive.ads)
13865 @section @code{GNAT.Altivec} (@file{g-altive.ads})
13866 @cindex @code{GNAT.Altivec} (@file{g-altive.ads})
13870 This is the root package of the GNAT AltiVec binding. It provides
13871 definitions of constants and types common to all the versions of the
13874 @node GNAT.Altivec.Conversions (g-altcon.ads)
13875 @section @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13876 @cindex @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13880 This package provides the Vector/View conversion routines.
13882 @node GNAT.Altivec.Vector_Operations (g-alveop.ads)
13883 @section @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13884 @cindex @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13888 This package exposes the Ada interface to the AltiVec operations on
13889 vector objects. A soft emulation is included by default in the GNAT
13890 library. The hard binding is provided as a separate package. This unit
13891 is common to both bindings.
13893 @node GNAT.Altivec.Vector_Types (g-alvety.ads)
13894 @section @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13895 @cindex @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13899 This package exposes the various vector types part of the Ada binding
13900 to AltiVec facilities.
13902 @node GNAT.Altivec.Vector_Views (g-alvevi.ads)
13903 @section @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13904 @cindex @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13908 This package provides public 'View' data types from/to which private
13909 vector representations can be converted via
13910 GNAT.Altivec.Conversions. This allows convenient access to individual
13911 vector elements and provides a simple way to initialize vector
13914 @node GNAT.Array_Split (g-arrspl.ads)
13915 @section @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13916 @cindex @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13917 @cindex Array splitter
13920 Useful array-manipulation routines: given a set of separators, split
13921 an array wherever the separators appear, and provide direct access
13922 to the resulting slices.
13924 @node GNAT.AWK (g-awk.ads)
13925 @section @code{GNAT.AWK} (@file{g-awk.ads})
13926 @cindex @code{GNAT.AWK} (@file{g-awk.ads})
13931 Provides AWK-like parsing functions, with an easy interface for parsing one
13932 or more files containing formatted data. The file is viewed as a database
13933 where each record is a line and a field is a data element in this line.
13935 @node GNAT.Bounded_Buffers (g-boubuf.ads)
13936 @section @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13937 @cindex @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13939 @cindex Bounded Buffers
13942 Provides a concurrent generic bounded buffer abstraction. Instances are
13943 useful directly or as parts of the implementations of other abstractions,
13946 @node GNAT.Bounded_Mailboxes (g-boumai.ads)
13947 @section @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13948 @cindex @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13953 Provides a thread-safe asynchronous intertask mailbox communication facility.
13955 @node GNAT.Bubble_Sort (g-bubsor.ads)
13956 @section @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13957 @cindex @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13959 @cindex Bubble sort
13962 Provides a general implementation of bubble sort usable for sorting arbitrary
13963 data items. Exchange and comparison procedures are provided by passing
13964 access-to-procedure values.
13966 @node GNAT.Bubble_Sort_A (g-busora.ads)
13967 @section @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13968 @cindex @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13970 @cindex Bubble sort
13973 Provides a general implementation of bubble sort usable for sorting arbitrary
13974 data items. Move and comparison procedures are provided by passing
13975 access-to-procedure values. This is an older version, retained for
13976 compatibility. Usually @code{GNAT.Bubble_Sort} will be preferable.
13978 @node GNAT.Bubble_Sort_G (g-busorg.ads)
13979 @section @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13980 @cindex @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13982 @cindex Bubble sort
13985 Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
13986 are provided as generic parameters, this improves efficiency, especially
13987 if the procedures can be inlined, at the expense of duplicating code for
13988 multiple instantiations.
13990 @node GNAT.Byte_Order_Mark (g-byorma.ads)
13991 @section @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13992 @cindex @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13993 @cindex UTF-8 representation
13994 @cindex Wide characte representations
13997 Provides a routine which given a string, reads the start of the string to
13998 see whether it is one of the standard byte order marks (BOM's) which signal
13999 the encoding of the string. The routine includes detection of special XML
14000 sequences for various UCS input formats.
14002 @node GNAT.Byte_Swapping (g-bytswa.ads)
14003 @section @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
14004 @cindex @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
14005 @cindex Byte swapping
14009 General routines for swapping the bytes in 2-, 4-, and 8-byte quantities.
14010 Machine-specific implementations are available in some cases.
14012 @node GNAT.Calendar (g-calend.ads)
14013 @section @code{GNAT.Calendar} (@file{g-calend.ads})
14014 @cindex @code{GNAT.Calendar} (@file{g-calend.ads})
14015 @cindex @code{Calendar}
14018 Extends the facilities provided by @code{Ada.Calendar} to include handling
14019 of days of the week, an extended @code{Split} and @code{Time_Of} capability.
14020 Also provides conversion of @code{Ada.Calendar.Time} values to and from the
14021 C @code{timeval} format.
14023 @node GNAT.Calendar.Time_IO (g-catiio.ads)
14024 @section @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
14025 @cindex @code{Calendar}
14027 @cindex @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
14029 @node GNAT.CRC32 (g-crc32.ads)
14030 @section @code{GNAT.CRC32} (@file{g-crc32.ads})
14031 @cindex @code{GNAT.CRC32} (@file{g-crc32.ads})
14033 @cindex Cyclic Redundancy Check
14036 This package implements the CRC-32 algorithm. For a full description
14037 of this algorithm see
14038 ``Computation of Cyclic Redundancy Checks via Table Look-Up'',
14039 @cite{Communications of the ACM}, Vol.@: 31 No.@: 8, pp.@: 1008-1013,
14040 Aug.@: 1988. Sarwate, D.V@.
14042 @node GNAT.Case_Util (g-casuti.ads)
14043 @section @code{GNAT.Case_Util} (@file{g-casuti.ads})
14044 @cindex @code{GNAT.Case_Util} (@file{g-casuti.ads})
14045 @cindex Casing utilities
14046 @cindex Character handling (@code{GNAT.Case_Util})
14049 A set of simple routines for handling upper and lower casing of strings
14050 without the overhead of the full casing tables
14051 in @code{Ada.Characters.Handling}.
14053 @node GNAT.CGI (g-cgi.ads)
14054 @section @code{GNAT.CGI} (@file{g-cgi.ads})
14055 @cindex @code{GNAT.CGI} (@file{g-cgi.ads})
14056 @cindex CGI (Common Gateway Interface)
14059 This is a package for interfacing a GNAT program with a Web server via the
14060 Common Gateway Interface (CGI)@. Basically this package parses the CGI
14061 parameters, which are a set of key/value pairs sent by the Web server. It
14062 builds a table whose index is the key and provides some services to deal
14065 @node GNAT.CGI.Cookie (g-cgicoo.ads)
14066 @section @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
14067 @cindex @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
14068 @cindex CGI (Common Gateway Interface) cookie support
14069 @cindex Cookie support in CGI
14072 This is a package to interface a GNAT program with a Web server via the
14073 Common Gateway Interface (CGI). It exports services to deal with Web
14074 cookies (piece of information kept in the Web client software).
14076 @node GNAT.CGI.Debug (g-cgideb.ads)
14077 @section @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
14078 @cindex @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
14079 @cindex CGI (Common Gateway Interface) debugging
14082 This is a package to help debugging CGI (Common Gateway Interface)
14083 programs written in Ada.
14085 @node GNAT.Command_Line (g-comlin.ads)
14086 @section @code{GNAT.Command_Line} (@file{g-comlin.ads})
14087 @cindex @code{GNAT.Command_Line} (@file{g-comlin.ads})
14088 @cindex Command line
14091 Provides a high level interface to @code{Ada.Command_Line} facilities,
14092 including the ability to scan for named switches with optional parameters
14093 and expand file names using wild card notations.
14095 @node GNAT.Compiler_Version (g-comver.ads)
14096 @section @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14097 @cindex @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14098 @cindex Compiler Version
14099 @cindex Version, of compiler
14102 Provides a routine for obtaining the version of the compiler used to
14103 compile the program. More accurately this is the version of the binder
14104 used to bind the program (this will normally be the same as the version
14105 of the compiler if a consistent tool set is used to compile all units
14108 @node GNAT.Ctrl_C (g-ctrl_c.ads)
14109 @section @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14110 @cindex @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14114 Provides a simple interface to handle Ctrl-C keyboard events.
14116 @node GNAT.Current_Exception (g-curexc.ads)
14117 @section @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14118 @cindex @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14119 @cindex Current exception
14120 @cindex Exception retrieval
14123 Provides access to information on the current exception that has been raised
14124 without the need for using the Ada 95 / Ada 2005 exception choice parameter
14125 specification syntax.
14126 This is particularly useful in simulating typical facilities for
14127 obtaining information about exceptions provided by Ada 83 compilers.
14129 @node GNAT.Debug_Pools (g-debpoo.ads)
14130 @section @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14131 @cindex @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14133 @cindex Debug pools
14134 @cindex Memory corruption debugging
14137 Provide a debugging storage pools that helps tracking memory corruption
14138 problems. @xref{The GNAT Debug Pool Facility,,, gnat_ugn,
14139 @value{EDITION} User's Guide}.
14141 @node GNAT.Debug_Utilities (g-debuti.ads)
14142 @section @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14143 @cindex @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14147 Provides a few useful utilities for debugging purposes, including conversion
14148 to and from string images of address values. Supports both C and Ada formats
14149 for hexadecimal literals.
14151 @node GNAT.Decode_String (g-decstr.ads)
14152 @section @code{GNAT.Decode_String} (@file{g-decstr.ads})
14153 @cindex @code{GNAT.Decode_String} (@file{g-decstr.ads})
14154 @cindex Decoding strings
14155 @cindex String decoding
14156 @cindex Wide character encoding
14161 A generic package providing routines for decoding wide character and wide wide
14162 character strings encoded as sequences of 8-bit characters using a specified
14163 encoding method. Includes validation routines, and also routines for stepping
14164 to next or previous encoded character in an encoded string.
14165 Useful in conjunction with Unicode character coding. Note there is a
14166 preinstantiation for UTF-8. See next entry.
14168 @node GNAT.Decode_UTF8_String (g-deutst.ads)
14169 @section @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14170 @cindex @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14171 @cindex Decoding strings
14172 @cindex Decoding UTF-8 strings
14173 @cindex UTF-8 string decoding
14174 @cindex Wide character decoding
14179 A preinstantiation of GNAT.Decode_Strings for UTF-8 encoding.
14181 @node GNAT.Directory_Operations (g-dirope.ads)
14182 @section @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14183 @cindex @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14184 @cindex Directory operations
14187 Provides a set of routines for manipulating directories, including changing
14188 the current directory, making new directories, and scanning the files in a
14191 @node GNAT.Directory_Operations.Iteration (g-diopit.ads)
14192 @section @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14193 @cindex @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14194 @cindex Directory operations iteration
14197 A child unit of GNAT.Directory_Operations providing additional operations
14198 for iterating through directories.
14200 @node GNAT.Dynamic_HTables (g-dynhta.ads)
14201 @section @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14202 @cindex @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14203 @cindex Hash tables
14206 A generic implementation of hash tables that can be used to hash arbitrary
14207 data. Provided in two forms, a simple form with built in hash functions,
14208 and a more complex form in which the hash function is supplied.
14211 This package provides a facility similar to that of @code{GNAT.HTable},
14212 except that this package declares a type that can be used to define
14213 dynamic instances of the hash table, while an instantiation of
14214 @code{GNAT.HTable} creates a single instance of the hash table.
14216 @node GNAT.Dynamic_Tables (g-dyntab.ads)
14217 @section @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14218 @cindex @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14219 @cindex Table implementation
14220 @cindex Arrays, extendable
14223 A generic package providing a single dimension array abstraction where the
14224 length of the array can be dynamically modified.
14227 This package provides a facility similar to that of @code{GNAT.Table},
14228 except that this package declares a type that can be used to define
14229 dynamic instances of the table, while an instantiation of
14230 @code{GNAT.Table} creates a single instance of the table type.
14232 @node GNAT.Encode_String (g-encstr.ads)
14233 @section @code{GNAT.Encode_String} (@file{g-encstr.ads})
14234 @cindex @code{GNAT.Encode_String} (@file{g-encstr.ads})
14235 @cindex Encoding strings
14236 @cindex String encoding
14237 @cindex Wide character encoding
14242 A generic package providing routines for encoding wide character and wide
14243 wide character strings as sequences of 8-bit characters using a specified
14244 encoding method. Useful in conjunction with Unicode character coding.
14245 Note there is a preinstantiation for UTF-8. See next entry.
14247 @node GNAT.Encode_UTF8_String (g-enutst.ads)
14248 @section @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14249 @cindex @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14250 @cindex Encoding strings
14251 @cindex Encoding UTF-8 strings
14252 @cindex UTF-8 string encoding
14253 @cindex Wide character encoding
14258 A preinstantiation of GNAT.Encode_Strings for UTF-8 encoding.
14260 @node GNAT.Exception_Actions (g-excact.ads)
14261 @section @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14262 @cindex @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14263 @cindex Exception actions
14266 Provides callbacks when an exception is raised. Callbacks can be registered
14267 for specific exceptions, or when any exception is raised. This
14268 can be used for instance to force a core dump to ease debugging.
14270 @node GNAT.Exception_Traces (g-exctra.ads)
14271 @section @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14272 @cindex @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14273 @cindex Exception traces
14277 Provides an interface allowing to control automatic output upon exception
14280 @node GNAT.Exceptions (g-except.ads)
14281 @section @code{GNAT.Exceptions} (@file{g-expect.ads})
14282 @cindex @code{GNAT.Exceptions} (@file{g-expect.ads})
14283 @cindex Exceptions, Pure
14284 @cindex Pure packages, exceptions
14287 Normally it is not possible to raise an exception with
14288 a message from a subprogram in a pure package, since the
14289 necessary types and subprograms are in @code{Ada.Exceptions}
14290 which is not a pure unit. @code{GNAT.Exceptions} provides a
14291 facility for getting around this limitation for a few
14292 predefined exceptions, and for example allow raising
14293 @code{Constraint_Error} with a message from a pure subprogram.
14295 @node GNAT.Expect (g-expect.ads)
14296 @section @code{GNAT.Expect} (@file{g-expect.ads})
14297 @cindex @code{GNAT.Expect} (@file{g-expect.ads})
14300 Provides a set of subprograms similar to what is available
14301 with the standard Tcl Expect tool.
14302 It allows you to easily spawn and communicate with an external process.
14303 You can send commands or inputs to the process, and compare the output
14304 with some expected regular expression. Currently @code{GNAT.Expect}
14305 is implemented on all native GNAT ports except for OpenVMS@.
14306 It is not implemented for cross ports, and in particular is not
14307 implemented for VxWorks or LynxOS@.
14309 @node GNAT.Float_Control (g-flocon.ads)
14310 @section @code{GNAT.Float_Control} (@file{g-flocon.ads})
14311 @cindex @code{GNAT.Float_Control} (@file{g-flocon.ads})
14312 @cindex Floating-Point Processor
14315 Provides an interface for resetting the floating-point processor into the
14316 mode required for correct semantic operation in Ada. Some third party
14317 library calls may cause this mode to be modified, and the Reset procedure
14318 in this package can be used to reestablish the required mode.
14320 @node GNAT.Heap_Sort (g-heasor.ads)
14321 @section @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14322 @cindex @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14326 Provides a general implementation of heap sort usable for sorting arbitrary
14327 data items. Exchange and comparison procedures are provided by passing
14328 access-to-procedure values. The algorithm used is a modified heap sort
14329 that performs approximately N*log(N) comparisons in the worst case.
14331 @node GNAT.Heap_Sort_A (g-hesora.ads)
14332 @section @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14333 @cindex @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14337 Provides a general implementation of heap sort usable for sorting arbitrary
14338 data items. Move and comparison procedures are provided by passing
14339 access-to-procedure values. The algorithm used is a modified heap sort
14340 that performs approximately N*log(N) comparisons in the worst case.
14341 This differs from @code{GNAT.Heap_Sort} in having a less convenient
14342 interface, but may be slightly more efficient.
14344 @node GNAT.Heap_Sort_G (g-hesorg.ads)
14345 @section @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14346 @cindex @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14350 Similar to @code{Heap_Sort_A} except that the move and sorting procedures
14351 are provided as generic parameters, this improves efficiency, especially
14352 if the procedures can be inlined, at the expense of duplicating code for
14353 multiple instantiations.
14355 @node GNAT.HTable (g-htable.ads)
14356 @section @code{GNAT.HTable} (@file{g-htable.ads})
14357 @cindex @code{GNAT.HTable} (@file{g-htable.ads})
14358 @cindex Hash tables
14361 A generic implementation of hash tables that can be used to hash arbitrary
14362 data. Provides two approaches, one a simple static approach, and the other
14363 allowing arbitrary dynamic hash tables.
14365 @node GNAT.IO (g-io.ads)
14366 @section @code{GNAT.IO} (@file{g-io.ads})
14367 @cindex @code{GNAT.IO} (@file{g-io.ads})
14369 @cindex Input/Output facilities
14372 A simple preelaborable input-output package that provides a subset of
14373 simple Text_IO functions for reading characters and strings from
14374 Standard_Input, and writing characters, strings and integers to either
14375 Standard_Output or Standard_Error.
14377 @node GNAT.IO_Aux (g-io_aux.ads)
14378 @section @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14379 @cindex @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14381 @cindex Input/Output facilities
14383 Provides some auxiliary functions for use with Text_IO, including a test
14384 for whether a file exists, and functions for reading a line of text.
14386 @node GNAT.Lock_Files (g-locfil.ads)
14387 @section @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14388 @cindex @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14389 @cindex File locking
14390 @cindex Locking using files
14393 Provides a general interface for using files as locks. Can be used for
14394 providing program level synchronization.
14396 @node GNAT.MD5 (g-md5.ads)
14397 @section @code{GNAT.MD5} (@file{g-md5.ads})
14398 @cindex @code{GNAT.MD5} (@file{g-md5.ads})
14399 @cindex Message Digest MD5
14402 Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
14404 @node GNAT.Memory_Dump (g-memdum.ads)
14405 @section @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14406 @cindex @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14407 @cindex Dump Memory
14410 Provides a convenient routine for dumping raw memory to either the
14411 standard output or standard error files. Uses GNAT.IO for actual
14414 @node GNAT.Most_Recent_Exception (g-moreex.ads)
14415 @section @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14416 @cindex @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14417 @cindex Exception, obtaining most recent
14420 Provides access to the most recently raised exception. Can be used for
14421 various logging purposes, including duplicating functionality of some
14422 Ada 83 implementation dependent extensions.
14424 @node GNAT.OS_Lib (g-os_lib.ads)
14425 @section @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14426 @cindex @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14427 @cindex Operating System interface
14428 @cindex Spawn capability
14431 Provides a range of target independent operating system interface functions,
14432 including time/date management, file operations, subprocess management,
14433 including a portable spawn procedure, and access to environment variables
14434 and error return codes.
14436 @node GNAT.Perfect_Hash_Generators (g-pehage.ads)
14437 @section @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14438 @cindex @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14439 @cindex Hash functions
14442 Provides a generator of static minimal perfect hash functions. No
14443 collisions occur and each item can be retrieved from the table in one
14444 probe (perfect property). The hash table size corresponds to the exact
14445 size of the key set and no larger (minimal property). The key set has to
14446 be know in advance (static property). The hash functions are also order
14447 preserving. If w2 is inserted after w1 in the generator, their
14448 hashcode are in the same order. These hashing functions are very
14449 convenient for use with realtime applications.
14451 @node GNAT.Random_Numbers (g-rannum.ads)
14452 @section @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14453 @cindex @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14454 @cindex Random number generation
14457 Provides random number capabilities which extend those available in the
14458 standard Ada library and are more convenient to use.
14460 @node GNAT.Regexp (g-regexp.ads)
14461 @section @code{GNAT.Regexp} (@file{g-regexp.ads})
14462 @cindex @code{GNAT.Regexp} (@file{g-regexp.ads})
14463 @cindex Regular expressions
14464 @cindex Pattern matching
14467 A simple implementation of regular expressions, using a subset of regular
14468 expression syntax copied from familiar Unix style utilities. This is the
14469 simples of the three pattern matching packages provided, and is particularly
14470 suitable for ``file globbing'' applications.
14472 @node GNAT.Registry (g-regist.ads)
14473 @section @code{GNAT.Registry} (@file{g-regist.ads})
14474 @cindex @code{GNAT.Registry} (@file{g-regist.ads})
14475 @cindex Windows Registry
14478 This is a high level binding to the Windows registry. It is possible to
14479 do simple things like reading a key value, creating a new key. For full
14480 registry API, but at a lower level of abstraction, refer to the Win32.Winreg
14481 package provided with the Win32Ada binding
14483 @node GNAT.Regpat (g-regpat.ads)
14484 @section @code{GNAT.Regpat} (@file{g-regpat.ads})
14485 @cindex @code{GNAT.Regpat} (@file{g-regpat.ads})
14486 @cindex Regular expressions
14487 @cindex Pattern matching
14490 A complete implementation of Unix-style regular expression matching, copied
14491 from the original V7 style regular expression library written in C by
14492 Henry Spencer (and binary compatible with this C library).
14494 @node GNAT.Secondary_Stack_Info (g-sestin.ads)
14495 @section @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14496 @cindex @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14497 @cindex Secondary Stack Info
14500 Provide the capability to query the high water mark of the current task's
14503 @node GNAT.Semaphores (g-semaph.ads)
14504 @section @code{GNAT.Semaphores} (@file{g-semaph.ads})
14505 @cindex @code{GNAT.Semaphores} (@file{g-semaph.ads})
14509 Provides classic counting and binary semaphores using protected types.
14511 @node GNAT.Serial_Communications (g-sercom.ads)
14512 @section @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14513 @cindex @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14514 @cindex Serial_Communications
14517 Provides a simple interface to send and receive data over a serial
14518 port. This is only supported on GNU/Linux and Windows.
14520 @node GNAT.SHA1 (g-sha1.ads)
14521 @section @code{GNAT.SHA1} (@file{g-sha1.ads})
14522 @cindex @code{GNAT.SHA1} (@file{g-sha1.ads})
14523 @cindex Secure Hash Algorithm SHA-1
14526 Implements the SHA-1 Secure Hash Algorithm as described in RFC 3174.
14528 @node GNAT.Signals (g-signal.ads)
14529 @section @code{GNAT.Signals} (@file{g-signal.ads})
14530 @cindex @code{GNAT.Signals} (@file{g-signal.ads})
14534 Provides the ability to manipulate the blocked status of signals on supported
14537 @node GNAT.Sockets (g-socket.ads)
14538 @section @code{GNAT.Sockets} (@file{g-socket.ads})
14539 @cindex @code{GNAT.Sockets} (@file{g-socket.ads})
14543 A high level and portable interface to develop sockets based applications.
14544 This package is based on the sockets thin binding found in
14545 @code{GNAT.Sockets.Thin}. Currently @code{GNAT.Sockets} is implemented
14546 on all native GNAT ports except for OpenVMS@. It is not implemented
14547 for the LynxOS@ cross port.
14549 @node GNAT.Source_Info (g-souinf.ads)
14550 @section @code{GNAT.Source_Info} (@file{g-souinf.ads})
14551 @cindex @code{GNAT.Source_Info} (@file{g-souinf.ads})
14552 @cindex Source Information
14555 Provides subprograms that give access to source code information known at
14556 compile time, such as the current file name and line number.
14558 @node GNAT.Spelling_Checker (g-speche.ads)
14559 @section @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14560 @cindex @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14561 @cindex Spell checking
14564 Provides a function for determining whether one string is a plausible
14565 near misspelling of another string.
14567 @node GNAT.Spelling_Checker_Generic (g-spchge.ads)
14568 @section @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14569 @cindex @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14570 @cindex Spell checking
14573 Provides a generic function that can be instantiated with a string type for
14574 determining whether one string is a plausible near misspelling of another
14577 @node GNAT.Spitbol.Patterns (g-spipat.ads)
14578 @section @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14579 @cindex @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14580 @cindex SPITBOL pattern matching
14581 @cindex Pattern matching
14584 A complete implementation of SNOBOL4 style pattern matching. This is the
14585 most elaborate of the pattern matching packages provided. It fully duplicates
14586 the SNOBOL4 dynamic pattern construction and matching capabilities, using the
14587 efficient algorithm developed by Robert Dewar for the SPITBOL system.
14589 @node GNAT.Spitbol (g-spitbo.ads)
14590 @section @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14591 @cindex @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14592 @cindex SPITBOL interface
14595 The top level package of the collection of SPITBOL-style functionality, this
14596 package provides basic SNOBOL4 string manipulation functions, such as
14597 Pad, Reverse, Trim, Substr capability, as well as a generic table function
14598 useful for constructing arbitrary mappings from strings in the style of
14599 the SNOBOL4 TABLE function.
14601 @node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
14602 @section @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14603 @cindex @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14604 @cindex Sets of strings
14605 @cindex SPITBOL Tables
14608 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14609 for type @code{Standard.Boolean}, giving an implementation of sets of
14612 @node GNAT.Spitbol.Table_Integer (g-sptain.ads)
14613 @section @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14614 @cindex @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14615 @cindex Integer maps
14617 @cindex SPITBOL Tables
14620 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14621 for type @code{Standard.Integer}, giving an implementation of maps
14622 from string to integer values.
14624 @node GNAT.Spitbol.Table_VString (g-sptavs.ads)
14625 @section @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14626 @cindex @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14627 @cindex String maps
14629 @cindex SPITBOL Tables
14632 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table} for
14633 a variable length string type, giving an implementation of general
14634 maps from strings to strings.
14636 @node GNAT.SSE (g-sse.ads)
14637 @section @code{GNAT.SSE} (@file{g-sse.ads})
14638 @cindex @code{GNAT.SSE} (@file{g-sse.ads})
14641 Root of a set of units aimed at offering Ada bindings to a subset of
14642 the Intel(r) Streaming SIMD Extensions with GNAT on the x86 family of
14643 targets. It exposes vector component types together with a general
14644 introduction to the binding contents and use.
14646 @node GNAT.SSE.Internal_Types (g-ssinty.ads)
14647 @section @code{GNAT.SSE.Internal_Types} (@file{g-ssinty.ads})
14648 @cindex @code{GNAT.SSE.Internal_Types} (@file{g-ssinty.ads})
14651 Low level GCC vector types for direct use of the vector related
14652 builtins, required for the development of higher level bindings to SSE
14653 intrinsic operations.
14655 @node GNAT.SSE.Vector_Types (g-ssvety.ads)
14656 @section @code{GNAT.SSE.Vector_Types} (@file{g-ssvety.ads})
14657 @cindex @code{GNAT.SSE.Vector_Types} (@file{g-ssvety.ads})
14660 SSE vector types for use with SSE related intrinsics.
14662 @node GNAT.Strings (g-string.ads)
14663 @section @code{GNAT.Strings} (@file{g-string.ads})
14664 @cindex @code{GNAT.Strings} (@file{g-string.ads})
14667 Common String access types and related subprograms. Basically it
14668 defines a string access and an array of string access types.
14670 @node GNAT.String_Split (g-strspl.ads)
14671 @section @code{GNAT.String_Split} (@file{g-strspl.ads})
14672 @cindex @code{GNAT.String_Split} (@file{g-strspl.ads})
14673 @cindex String splitter
14676 Useful string manipulation routines: given a set of separators, split
14677 a string wherever the separators appear, and provide direct access
14678 to the resulting slices. This package is instantiated from
14679 @code{GNAT.Array_Split}.
14681 @node GNAT.Table (g-table.ads)
14682 @section @code{GNAT.Table} (@file{g-table.ads})
14683 @cindex @code{GNAT.Table} (@file{g-table.ads})
14684 @cindex Table implementation
14685 @cindex Arrays, extendable
14688 A generic package providing a single dimension array abstraction where the
14689 length of the array can be dynamically modified.
14692 This package provides a facility similar to that of @code{GNAT.Dynamic_Tables},
14693 except that this package declares a single instance of the table type,
14694 while an instantiation of @code{GNAT.Dynamic_Tables} creates a type that can be
14695 used to define dynamic instances of the table.
14697 @node GNAT.Task_Lock (g-tasloc.ads)
14698 @section @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14699 @cindex @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14700 @cindex Task synchronization
14701 @cindex Task locking
14705 A very simple facility for locking and unlocking sections of code using a
14706 single global task lock. Appropriate for use in situations where contention
14707 between tasks is very rarely expected.
14709 @node GNAT.Time_Stamp (g-timsta.ads)
14710 @section @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14711 @cindex @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14713 @cindex Current time
14716 Provides a simple function that returns a string YYYY-MM-DD HH:MM:SS.SS that
14717 represents the current date and time in ISO 8601 format. This is a very simple
14718 routine with minimal code and there are no dependencies on any other unit.
14720 @node GNAT.Threads (g-thread.ads)
14721 @section @code{GNAT.Threads} (@file{g-thread.ads})
14722 @cindex @code{GNAT.Threads} (@file{g-thread.ads})
14723 @cindex Foreign threads
14724 @cindex Threads, foreign
14727 Provides facilities for dealing with foreign threads which need to be known
14728 by the GNAT run-time system. Consult the documentation of this package for
14729 further details if your program has threads that are created by a non-Ada
14730 environment which then accesses Ada code.
14732 @node GNAT.Traceback (g-traceb.ads)
14733 @section @code{GNAT.Traceback} (@file{g-traceb.ads})
14734 @cindex @code{GNAT.Traceback} (@file{g-traceb.ads})
14735 @cindex Trace back facilities
14738 Provides a facility for obtaining non-symbolic traceback information, useful
14739 in various debugging situations.
14741 @node GNAT.Traceback.Symbolic (g-trasym.ads)
14742 @section @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14743 @cindex @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14744 @cindex Trace back facilities
14746 @node GNAT.UTF_32 (g-utf_32.ads)
14747 @section @code{GNAT.UTF_32} (@file{g-table.ads})
14748 @cindex @code{GNAT.UTF_32} (@file{g-table.ads})
14749 @cindex Wide character codes
14752 This is a package intended to be used in conjunction with the
14753 @code{Wide_Character} type in Ada 95 and the
14754 @code{Wide_Wide_Character} type in Ada 2005 (available
14755 in @code{GNAT} in Ada 2005 mode). This package contains
14756 Unicode categorization routines, as well as lexical
14757 categorization routines corresponding to the Ada 2005
14758 lexical rules for identifiers and strings, and also a
14759 lower case to upper case fold routine corresponding to
14760 the Ada 2005 rules for identifier equivalence.
14762 @node GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)
14763 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14764 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14765 @cindex Spell checking
14768 Provides a function for determining whether one wide wide string is a plausible
14769 near misspelling of another wide wide string, where the strings are represented
14770 using the UTF_32_String type defined in System.Wch_Cnv.
14772 @node GNAT.Wide_Spelling_Checker (g-wispch.ads)
14773 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14774 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14775 @cindex Spell checking
14778 Provides a function for determining whether one wide string is a plausible
14779 near misspelling of another wide string.
14781 @node GNAT.Wide_String_Split (g-wistsp.ads)
14782 @section @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14783 @cindex @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14784 @cindex Wide_String splitter
14787 Useful wide string manipulation routines: given a set of separators, split
14788 a wide string wherever the separators appear, and provide direct access
14789 to the resulting slices. This package is instantiated from
14790 @code{GNAT.Array_Split}.
14792 @node GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)
14793 @section @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14794 @cindex @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14795 @cindex Spell checking
14798 Provides a function for determining whether one wide wide string is a plausible
14799 near misspelling of another wide wide string.
14801 @node GNAT.Wide_Wide_String_Split (g-zistsp.ads)
14802 @section @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14803 @cindex @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14804 @cindex Wide_Wide_String splitter
14807 Useful wide wide string manipulation routines: given a set of separators, split
14808 a wide wide string wherever the separators appear, and provide direct access
14809 to the resulting slices. This package is instantiated from
14810 @code{GNAT.Array_Split}.
14812 @node Interfaces.C.Extensions (i-cexten.ads)
14813 @section @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14814 @cindex @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14817 This package contains additional C-related definitions, intended
14818 for use with either manually or automatically generated bindings
14821 @node Interfaces.C.Streams (i-cstrea.ads)
14822 @section @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14823 @cindex @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14824 @cindex C streams, interfacing
14827 This package is a binding for the most commonly used operations
14830 @node Interfaces.CPP (i-cpp.ads)
14831 @section @code{Interfaces.CPP} (@file{i-cpp.ads})
14832 @cindex @code{Interfaces.CPP} (@file{i-cpp.ads})
14833 @cindex C++ interfacing
14834 @cindex Interfacing, to C++
14837 This package provides facilities for use in interfacing to C++. It
14838 is primarily intended to be used in connection with automated tools
14839 for the generation of C++ interfaces.
14841 @node Interfaces.Packed_Decimal (i-pacdec.ads)
14842 @section @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14843 @cindex @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14844 @cindex IBM Packed Format
14845 @cindex Packed Decimal
14848 This package provides a set of routines for conversions to and
14849 from a packed decimal format compatible with that used on IBM
14852 @node Interfaces.VxWorks (i-vxwork.ads)
14853 @section @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14854 @cindex @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14855 @cindex Interfacing to VxWorks
14856 @cindex VxWorks, interfacing
14859 This package provides a limited binding to the VxWorks API.
14860 In particular, it interfaces with the
14861 VxWorks hardware interrupt facilities.
14863 @node Interfaces.VxWorks.IO (i-vxwoio.ads)
14864 @section @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14865 @cindex @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14866 @cindex Interfacing to VxWorks' I/O
14867 @cindex VxWorks, I/O interfacing
14868 @cindex VxWorks, Get_Immediate
14869 @cindex Get_Immediate, VxWorks
14872 This package provides a binding to the ioctl (IO/Control)
14873 function of VxWorks, defining a set of option values and
14874 function codes. A particular use of this package is
14875 to enable the use of Get_Immediate under VxWorks.
14877 @node System.Address_Image (s-addima.ads)
14878 @section @code{System.Address_Image} (@file{s-addima.ads})
14879 @cindex @code{System.Address_Image} (@file{s-addima.ads})
14880 @cindex Address image
14881 @cindex Image, of an address
14884 This function provides a useful debugging
14885 function that gives an (implementation dependent)
14886 string which identifies an address.
14888 @node System.Assertions (s-assert.ads)
14889 @section @code{System.Assertions} (@file{s-assert.ads})
14890 @cindex @code{System.Assertions} (@file{s-assert.ads})
14892 @cindex Assert_Failure, exception
14895 This package provides the declaration of the exception raised
14896 by an run-time assertion failure, as well as the routine that
14897 is used internally to raise this assertion.
14899 @node System.Memory (s-memory.ads)
14900 @section @code{System.Memory} (@file{s-memory.ads})
14901 @cindex @code{System.Memory} (@file{s-memory.ads})
14902 @cindex Memory allocation
14905 This package provides the interface to the low level routines used
14906 by the generated code for allocation and freeing storage for the
14907 default storage pool (analogous to the C routines malloc and free.
14908 It also provides a reallocation interface analogous to the C routine
14909 realloc. The body of this unit may be modified to provide alternative
14910 allocation mechanisms for the default pool, and in addition, direct
14911 calls to this unit may be made for low level allocation uses (for
14912 example see the body of @code{GNAT.Tables}).
14914 @node System.Partition_Interface (s-parint.ads)
14915 @section @code{System.Partition_Interface} (@file{s-parint.ads})
14916 @cindex @code{System.Partition_Interface} (@file{s-parint.ads})
14917 @cindex Partition interfacing functions
14920 This package provides facilities for partition interfacing. It
14921 is used primarily in a distribution context when using Annex E
14924 @node System.Pool_Global (s-pooglo.ads)
14925 @section @code{System.Pool_Global} (@file{s-pooglo.ads})
14926 @cindex @code{System.Pool_Global} (@file{s-pooglo.ads})
14927 @cindex Storage pool, global
14928 @cindex Global storage pool
14931 This package provides a storage pool that is equivalent to the default
14932 storage pool used for access types for which no pool is specifically
14933 declared. It uses malloc/free to allocate/free and does not attempt to
14934 do any automatic reclamation.
14936 @node System.Pool_Local (s-pooloc.ads)
14937 @section @code{System.Pool_Local} (@file{s-pooloc.ads})
14938 @cindex @code{System.Pool_Local} (@file{s-pooloc.ads})
14939 @cindex Storage pool, local
14940 @cindex Local storage pool
14943 This package provides a storage pool that is intended for use with locally
14944 defined access types. It uses malloc/free for allocate/free, and maintains
14945 a list of allocated blocks, so that all storage allocated for the pool can
14946 be freed automatically when the pool is finalized.
14948 @node System.Restrictions (s-restri.ads)
14949 @section @code{System.Restrictions} (@file{s-restri.ads})
14950 @cindex @code{System.Restrictions} (@file{s-restri.ads})
14951 @cindex Run-time restrictions access
14954 This package provides facilities for accessing at run time
14955 the status of restrictions specified at compile time for
14956 the partition. Information is available both with regard
14957 to actual restrictions specified, and with regard to
14958 compiler determined information on which restrictions
14959 are violated by one or more packages in the partition.
14961 @node System.Rident (s-rident.ads)
14962 @section @code{System.Rident} (@file{s-rident.ads})
14963 @cindex @code{System.Rident} (@file{s-rident.ads})
14964 @cindex Restrictions definitions
14967 This package provides definitions of the restrictions
14968 identifiers supported by GNAT, and also the format of
14969 the restrictions provided in package System.Restrictions.
14970 It is not normally necessary to @code{with} this generic package
14971 since the necessary instantiation is included in
14972 package System.Restrictions.
14974 @node System.Strings.Stream_Ops (s-ststop.ads)
14975 @section @code{System.Strings.Stream_Ops} (@file{s-ststop.ads})
14976 @cindex @code{System.Strings.Stream_Ops} (@file{s-ststop.ads})
14977 @cindex Stream operations
14978 @cindex String stream operations
14981 This package provides a set of stream subprograms for standard string types.
14982 It is intended primarily to support implicit use of such subprograms when
14983 stream attributes are applied to string types, but the subprograms in this
14984 package can be used directly by application programs.
14986 @node System.Task_Info (s-tasinf.ads)
14987 @section @code{System.Task_Info} (@file{s-tasinf.ads})
14988 @cindex @code{System.Task_Info} (@file{s-tasinf.ads})
14989 @cindex Task_Info pragma
14992 This package provides target dependent functionality that is used
14993 to support the @code{Task_Info} pragma
14995 @node System.Wch_Cnv (s-wchcnv.ads)
14996 @section @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14997 @cindex @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14998 @cindex Wide Character, Representation
14999 @cindex Wide String, Conversion
15000 @cindex Representation of wide characters
15003 This package provides routines for converting between
15004 wide and wide wide characters and a representation as a value of type
15005 @code{Standard.String}, using a specified wide character
15006 encoding method. It uses definitions in
15007 package @code{System.Wch_Con}.
15009 @node System.Wch_Con (s-wchcon.ads)
15010 @section @code{System.Wch_Con} (@file{s-wchcon.ads})
15011 @cindex @code{System.Wch_Con} (@file{s-wchcon.ads})
15014 This package provides definitions and descriptions of
15015 the various methods used for encoding wide characters
15016 in ordinary strings. These definitions are used by
15017 the package @code{System.Wch_Cnv}.
15019 @node Interfacing to Other Languages
15020 @chapter Interfacing to Other Languages
15022 The facilities in annex B of the Ada Reference Manual are fully
15023 implemented in GNAT, and in addition, a full interface to C++ is
15027 * Interfacing to C::
15028 * Interfacing to C++::
15029 * Interfacing to COBOL::
15030 * Interfacing to Fortran::
15031 * Interfacing to non-GNAT Ada code::
15034 @node Interfacing to C
15035 @section Interfacing to C
15038 Interfacing to C with GNAT can use one of two approaches:
15042 The types in the package @code{Interfaces.C} may be used.
15044 Standard Ada types may be used directly. This may be less portable to
15045 other compilers, but will work on all GNAT compilers, which guarantee
15046 correspondence between the C and Ada types.
15050 Pragma @code{Convention C} may be applied to Ada types, but mostly has no
15051 effect, since this is the default. The following table shows the
15052 correspondence between Ada scalar types and the corresponding C types.
15057 @item Short_Integer
15059 @item Short_Short_Integer
15063 @item Long_Long_Integer
15071 @item Long_Long_Float
15072 This is the longest floating-point type supported by the hardware.
15076 Additionally, there are the following general correspondences between Ada
15080 Ada enumeration types map to C enumeration types directly if pragma
15081 @code{Convention C} is specified, which causes them to have int
15082 length. Without pragma @code{Convention C}, Ada enumeration types map to
15083 8, 16, or 32 bits (i.e.@: C types @code{signed char}, @code{short},
15084 @code{int}, respectively) depending on the number of values passed.
15085 This is the only case in which pragma @code{Convention C} affects the
15086 representation of an Ada type.
15089 Ada access types map to C pointers, except for the case of pointers to
15090 unconstrained types in Ada, which have no direct C equivalent.
15093 Ada arrays map directly to C arrays.
15096 Ada records map directly to C structures.
15099 Packed Ada records map to C structures where all members are bit fields
15100 of the length corresponding to the @code{@var{type}'Size} value in Ada.
15103 @node Interfacing to C++
15104 @section Interfacing to C++
15107 The interface to C++ makes use of the following pragmas, which are
15108 primarily intended to be constructed automatically using a binding generator
15109 tool, although it is possible to construct them by hand. No suitable binding
15110 generator tool is supplied with GNAT though.
15112 Using these pragmas it is possible to achieve complete
15113 inter-operability between Ada tagged types and C++ class definitions.
15114 See @ref{Implementation Defined Pragmas}, for more details.
15117 @item pragma CPP_Class ([Entity =>] @var{LOCAL_NAME})
15118 The argument denotes an entity in the current declarative region that is
15119 declared as a tagged or untagged record type. It indicates that the type
15120 corresponds to an externally declared C++ class type, and is to be laid
15121 out the same way that C++ would lay out the type.
15123 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
15124 for backward compatibility but its functionality is available
15125 using pragma @code{Import} with @code{Convention} = @code{CPP}.
15127 @item pragma CPP_Constructor ([Entity =>] @var{LOCAL_NAME})
15128 This pragma identifies an imported function (imported in the usual way
15129 with pragma @code{Import}) as corresponding to a C++ constructor.
15132 @node Interfacing to COBOL
15133 @section Interfacing to COBOL
15136 Interfacing to COBOL is achieved as described in section B.4 of
15137 the Ada Reference Manual.
15139 @node Interfacing to Fortran
15140 @section Interfacing to Fortran
15143 Interfacing to Fortran is achieved as described in section B.5 of the
15144 Ada Reference Manual. The pragma @code{Convention Fortran}, applied to a
15145 multi-dimensional array causes the array to be stored in column-major
15146 order as required for convenient interface to Fortran.
15148 @node Interfacing to non-GNAT Ada code
15149 @section Interfacing to non-GNAT Ada code
15151 It is possible to specify the convention @code{Ada} in a pragma
15152 @code{Import} or pragma @code{Export}. However this refers to
15153 the calling conventions used by GNAT, which may or may not be
15154 similar enough to those used by some other Ada 83 / Ada 95 / Ada 2005
15155 compiler to allow interoperation.
15157 If arguments types are kept simple, and if the foreign compiler generally
15158 follows system calling conventions, then it may be possible to integrate
15159 files compiled by other Ada compilers, provided that the elaboration
15160 issues are adequately addressed (for example by eliminating the
15161 need for any load time elaboration).
15163 In particular, GNAT running on VMS is designed to
15164 be highly compatible with the DEC Ada 83 compiler, so this is one
15165 case in which it is possible to import foreign units of this type,
15166 provided that the data items passed are restricted to simple scalar
15167 values or simple record types without variants, or simple array
15168 types with fixed bounds.
15170 @node Specialized Needs Annexes
15171 @chapter Specialized Needs Annexes
15174 Ada 95 and Ada 2005 define a number of Specialized Needs Annexes, which are not
15175 required in all implementations. However, as described in this chapter,
15176 GNAT implements all of these annexes:
15179 @item Systems Programming (Annex C)
15180 The Systems Programming Annex is fully implemented.
15182 @item Real-Time Systems (Annex D)
15183 The Real-Time Systems Annex is fully implemented.
15185 @item Distributed Systems (Annex E)
15186 Stub generation is fully implemented in the GNAT compiler. In addition,
15187 a complete compatible PCS is available as part of the GLADE system,
15188 a separate product. When the two
15189 products are used in conjunction, this annex is fully implemented.
15191 @item Information Systems (Annex F)
15192 The Information Systems annex is fully implemented.
15194 @item Numerics (Annex G)
15195 The Numerics Annex is fully implemented.
15197 @item Safety and Security / High-Integrity Systems (Annex H)
15198 The Safety and Security Annex (termed the High-Integrity Systems Annex
15199 in Ada 2005) is fully implemented.
15202 @node Implementation of Specific Ada Features
15203 @chapter Implementation of Specific Ada Features
15206 This chapter describes the GNAT implementation of several Ada language
15210 * Machine Code Insertions::
15211 * GNAT Implementation of Tasking::
15212 * GNAT Implementation of Shared Passive Packages::
15213 * Code Generation for Array Aggregates::
15214 * The Size of Discriminated Records with Default Discriminants::
15215 * Strict Conformance to the Ada Reference Manual::
15218 @node Machine Code Insertions
15219 @section Machine Code Insertions
15220 @cindex Machine Code insertions
15223 Package @code{Machine_Code} provides machine code support as described
15224 in the Ada Reference Manual in two separate forms:
15227 Machine code statements, consisting of qualified expressions that
15228 fit the requirements of RM section 13.8.
15230 An intrinsic callable procedure, providing an alternative mechanism of
15231 including machine instructions in a subprogram.
15235 The two features are similar, and both are closely related to the mechanism
15236 provided by the asm instruction in the GNU C compiler. Full understanding
15237 and use of the facilities in this package requires understanding the asm
15238 instruction, see @ref{Extended Asm,, Assembler Instructions with C Expression
15239 Operands, gcc, Using the GNU Compiler Collection (GCC)}.
15241 Calls to the function @code{Asm} and the procedure @code{Asm} have identical
15242 semantic restrictions and effects as described below. Both are provided so
15243 that the procedure call can be used as a statement, and the function call
15244 can be used to form a code_statement.
15246 The first example given in the GCC documentation is the C @code{asm}
15249 asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
15253 The equivalent can be written for GNAT as:
15255 @smallexample @c ada
15256 Asm ("fsinx %1 %0",
15257 My_Float'Asm_Output ("=f", result),
15258 My_Float'Asm_Input ("f", angle));
15262 The first argument to @code{Asm} is the assembler template, and is
15263 identical to what is used in GNU C@. This string must be a static
15264 expression. The second argument is the output operand list. It is
15265 either a single @code{Asm_Output} attribute reference, or a list of such
15266 references enclosed in parentheses (technically an array aggregate of
15269 The @code{Asm_Output} attribute denotes a function that takes two
15270 parameters. The first is a string, the second is the name of a variable
15271 of the type designated by the attribute prefix. The first (string)
15272 argument is required to be a static expression and designates the
15273 constraint for the parameter (e.g.@: what kind of register is
15274 required). The second argument is the variable to be updated with the
15275 result. The possible values for constraint are the same as those used in
15276 the RTL, and are dependent on the configuration file used to build the
15277 GCC back end. If there are no output operands, then this argument may
15278 either be omitted, or explicitly given as @code{No_Output_Operands}.
15280 The second argument of @code{@var{my_float}'Asm_Output} functions as
15281 though it were an @code{out} parameter, which is a little curious, but
15282 all names have the form of expressions, so there is no syntactic
15283 irregularity, even though normally functions would not be permitted
15284 @code{out} parameters. The third argument is the list of input
15285 operands. It is either a single @code{Asm_Input} attribute reference, or
15286 a list of such references enclosed in parentheses (technically an array
15287 aggregate of such references).
15289 The @code{Asm_Input} attribute denotes a function that takes two
15290 parameters. The first is a string, the second is an expression of the
15291 type designated by the prefix. The first (string) argument is required
15292 to be a static expression, and is the constraint for the parameter,
15293 (e.g.@: what kind of register is required). The second argument is the
15294 value to be used as the input argument. The possible values for the
15295 constant are the same as those used in the RTL, and are dependent on
15296 the configuration file used to built the GCC back end.
15298 If there are no input operands, this argument may either be omitted, or
15299 explicitly given as @code{No_Input_Operands}. The fourth argument, not
15300 present in the above example, is a list of register names, called the
15301 @dfn{clobber} argument. This argument, if given, must be a static string
15302 expression, and is a space or comma separated list of names of registers
15303 that must be considered destroyed as a result of the @code{Asm} call. If
15304 this argument is the null string (the default value), then the code
15305 generator assumes that no additional registers are destroyed.
15307 The fifth argument, not present in the above example, called the
15308 @dfn{volatile} argument, is by default @code{False}. It can be set to
15309 the literal value @code{True} to indicate to the code generator that all
15310 optimizations with respect to the instruction specified should be
15311 suppressed, and that in particular, for an instruction that has outputs,
15312 the instruction will still be generated, even if none of the outputs are
15313 used. @xref{Extended Asm,, Assembler Instructions with C Expression Operands,
15314 gcc, Using the GNU Compiler Collection (GCC)}, for the full description.
15315 Generally it is strongly advisable to use Volatile for any ASM statement
15316 that is missing either input or output operands, or when two or more ASM
15317 statements appear in sequence, to avoid unwanted optimizations. A warning
15318 is generated if this advice is not followed.
15320 The @code{Asm} subprograms may be used in two ways. First the procedure
15321 forms can be used anywhere a procedure call would be valid, and
15322 correspond to what the RM calls ``intrinsic'' routines. Such calls can
15323 be used to intersperse machine instructions with other Ada statements.
15324 Second, the function forms, which return a dummy value of the limited
15325 private type @code{Asm_Insn}, can be used in code statements, and indeed
15326 this is the only context where such calls are allowed. Code statements
15327 appear as aggregates of the form:
15329 @smallexample @c ada
15330 Asm_Insn'(Asm (@dots{}));
15331 Asm_Insn'(Asm_Volatile (@dots{}));
15335 In accordance with RM rules, such code statements are allowed only
15336 within subprograms whose entire body consists of such statements. It is
15337 not permissible to intermix such statements with other Ada statements.
15339 Typically the form using intrinsic procedure calls is more convenient
15340 and more flexible. The code statement form is provided to meet the RM
15341 suggestion that such a facility should be made available. The following
15342 is the exact syntax of the call to @code{Asm}. As usual, if named notation
15343 is used, the arguments may be given in arbitrary order, following the
15344 normal rules for use of positional and named arguments)
15348 [Template =>] static_string_EXPRESSION
15349 [,[Outputs =>] OUTPUT_OPERAND_LIST ]
15350 [,[Inputs =>] INPUT_OPERAND_LIST ]
15351 [,[Clobber =>] static_string_EXPRESSION ]
15352 [,[Volatile =>] static_boolean_EXPRESSION] )
15354 OUTPUT_OPERAND_LIST ::=
15355 [PREFIX.]No_Output_Operands
15356 | OUTPUT_OPERAND_ATTRIBUTE
15357 | (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
15359 OUTPUT_OPERAND_ATTRIBUTE ::=
15360 SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
15362 INPUT_OPERAND_LIST ::=
15363 [PREFIX.]No_Input_Operands
15364 | INPUT_OPERAND_ATTRIBUTE
15365 | (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
15367 INPUT_OPERAND_ATTRIBUTE ::=
15368 SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
15372 The identifiers @code{No_Input_Operands} and @code{No_Output_Operands}
15373 are declared in the package @code{Machine_Code} and must be referenced
15374 according to normal visibility rules. In particular if there is no
15375 @code{use} clause for this package, then appropriate package name
15376 qualification is required.
15378 @node GNAT Implementation of Tasking
15379 @section GNAT Implementation of Tasking
15382 This chapter outlines the basic GNAT approach to tasking (in particular,
15383 a multi-layered library for portability) and discusses issues related
15384 to compliance with the Real-Time Systems Annex.
15387 * Mapping Ada Tasks onto the Underlying Kernel Threads::
15388 * Ensuring Compliance with the Real-Time Annex::
15391 @node Mapping Ada Tasks onto the Underlying Kernel Threads
15392 @subsection Mapping Ada Tasks onto the Underlying Kernel Threads
15395 GNAT's run-time support comprises two layers:
15398 @item GNARL (GNAT Run-time Layer)
15399 @item GNULL (GNAT Low-level Library)
15403 In GNAT, Ada's tasking services rely on a platform and OS independent
15404 layer known as GNARL@. This code is responsible for implementing the
15405 correct semantics of Ada's task creation, rendezvous, protected
15408 GNARL decomposes Ada's tasking semantics into simpler lower level
15409 operations such as create a thread, set the priority of a thread,
15410 yield, create a lock, lock/unlock, etc. The spec for these low-level
15411 operations constitutes GNULLI, the GNULL Interface. This interface is
15412 directly inspired from the POSIX real-time API@.
15414 If the underlying executive or OS implements the POSIX standard
15415 faithfully, the GNULL Interface maps as is to the services offered by
15416 the underlying kernel. Otherwise, some target dependent glue code maps
15417 the services offered by the underlying kernel to the semantics expected
15420 Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
15421 key point is that each Ada task is mapped on a thread in the underlying
15422 kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
15424 In addition Ada task priorities map onto the underlying thread priorities.
15425 Mapping Ada tasks onto the underlying kernel threads has several advantages:
15429 The underlying scheduler is used to schedule the Ada tasks. This
15430 makes Ada tasks as efficient as kernel threads from a scheduling
15434 Interaction with code written in C containing threads is eased
15435 since at the lowest level Ada tasks and C threads map onto the same
15436 underlying kernel concept.
15439 When an Ada task is blocked during I/O the remaining Ada tasks are
15443 On multiprocessor systems Ada tasks can execute in parallel.
15447 Some threads libraries offer a mechanism to fork a new process, with the
15448 child process duplicating the threads from the parent.
15450 support this functionality when the parent contains more than one task.
15451 @cindex Forking a new process
15453 @node Ensuring Compliance with the Real-Time Annex
15454 @subsection Ensuring Compliance with the Real-Time Annex
15455 @cindex Real-Time Systems Annex compliance
15458 Although mapping Ada tasks onto
15459 the underlying threads has significant advantages, it does create some
15460 complications when it comes to respecting the scheduling semantics
15461 specified in the real-time annex (Annex D).
15463 For instance the Annex D requirement for the @code{FIFO_Within_Priorities}
15464 scheduling policy states:
15467 @emph{When the active priority of a ready task that is not running
15468 changes, or the setting of its base priority takes effect, the
15469 task is removed from the ready queue for its old active priority
15470 and is added at the tail of the ready queue for its new active
15471 priority, except in the case where the active priority is lowered
15472 due to the loss of inherited priority, in which case the task is
15473 added at the head of the ready queue for its new active priority.}
15477 While most kernels do put tasks at the end of the priority queue when
15478 a task changes its priority, (which respects the main
15479 FIFO_Within_Priorities requirement), almost none keep a thread at the
15480 beginning of its priority queue when its priority drops from the loss
15481 of inherited priority.
15483 As a result most vendors have provided incomplete Annex D implementations.
15485 The GNAT run-time, has a nice cooperative solution to this problem
15486 which ensures that accurate FIFO_Within_Priorities semantics are
15489 The principle is as follows. When an Ada task T is about to start
15490 running, it checks whether some other Ada task R with the same
15491 priority as T has been suspended due to the loss of priority
15492 inheritance. If this is the case, T yields and is placed at the end of
15493 its priority queue. When R arrives at the front of the queue it
15496 Note that this simple scheme preserves the relative order of the tasks
15497 that were ready to execute in the priority queue where R has been
15500 @node GNAT Implementation of Shared Passive Packages
15501 @section GNAT Implementation of Shared Passive Packages
15502 @cindex Shared passive packages
15505 GNAT fully implements the pragma @code{Shared_Passive} for
15506 @cindex pragma @code{Shared_Passive}
15507 the purpose of designating shared passive packages.
15508 This allows the use of passive partitions in the
15509 context described in the Ada Reference Manual; i.e., for communication
15510 between separate partitions of a distributed application using the
15511 features in Annex E.
15513 @cindex Distribution Systems Annex
15515 However, the implementation approach used by GNAT provides for more
15516 extensive usage as follows:
15519 @item Communication between separate programs
15521 This allows separate programs to access the data in passive
15522 partitions, using protected objects for synchronization where
15523 needed. The only requirement is that the two programs have a
15524 common shared file system. It is even possible for programs
15525 running on different machines with different architectures
15526 (e.g.@: different endianness) to communicate via the data in
15527 a passive partition.
15529 @item Persistence between program runs
15531 The data in a passive package can persist from one run of a
15532 program to another, so that a later program sees the final
15533 values stored by a previous run of the same program.
15538 The implementation approach used is to store the data in files. A
15539 separate stream file is created for each object in the package, and
15540 an access to an object causes the corresponding file to be read or
15543 The environment variable @code{SHARED_MEMORY_DIRECTORY} should be
15544 @cindex @code{SHARED_MEMORY_DIRECTORY} environment variable
15545 set to the directory to be used for these files.
15546 The files in this directory
15547 have names that correspond to their fully qualified names. For
15548 example, if we have the package
15550 @smallexample @c ada
15552 pragma Shared_Passive (X);
15559 and the environment variable is set to @code{/stemp/}, then the files created
15560 will have the names:
15568 These files are created when a value is initially written to the object, and
15569 the files are retained until manually deleted. This provides the persistence
15570 semantics. If no file exists, it means that no partition has assigned a value
15571 to the variable; in this case the initial value declared in the package
15572 will be used. This model ensures that there are no issues in synchronizing
15573 the elaboration process, since elaboration of passive packages elaborates the
15574 initial values, but does not create the files.
15576 The files are written using normal @code{Stream_IO} access.
15577 If you want to be able
15578 to communicate between programs or partitions running on different
15579 architectures, then you should use the XDR versions of the stream attribute
15580 routines, since these are architecture independent.
15582 If active synchronization is required for access to the variables in the
15583 shared passive package, then as described in the Ada Reference Manual, the
15584 package may contain protected objects used for this purpose. In this case
15585 a lock file (whose name is @file{___lock} (three underscores)
15586 is created in the shared memory directory.
15587 @cindex @file{___lock} file (for shared passive packages)
15588 This is used to provide the required locking
15589 semantics for proper protected object synchronization.
15591 As of January 2003, GNAT supports shared passive packages on all platforms
15592 except for OpenVMS.
15594 @node Code Generation for Array Aggregates
15595 @section Code Generation for Array Aggregates
15598 * Static constant aggregates with static bounds::
15599 * Constant aggregates with unconstrained nominal types::
15600 * Aggregates with static bounds::
15601 * Aggregates with non-static bounds::
15602 * Aggregates in assignment statements::
15606 Aggregates have a rich syntax and allow the user to specify the values of
15607 complex data structures by means of a single construct. As a result, the
15608 code generated for aggregates can be quite complex and involve loops, case
15609 statements and multiple assignments. In the simplest cases, however, the
15610 compiler will recognize aggregates whose components and constraints are
15611 fully static, and in those cases the compiler will generate little or no
15612 executable code. The following is an outline of the code that GNAT generates
15613 for various aggregate constructs. For further details, you will find it
15614 useful to examine the output produced by the -gnatG flag to see the expanded
15615 source that is input to the code generator. You may also want to examine
15616 the assembly code generated at various levels of optimization.
15618 The code generated for aggregates depends on the context, the component values,
15619 and the type. In the context of an object declaration the code generated is
15620 generally simpler than in the case of an assignment. As a general rule, static
15621 component values and static subtypes also lead to simpler code.
15623 @node Static constant aggregates with static bounds
15624 @subsection Static constant aggregates with static bounds
15627 For the declarations:
15628 @smallexample @c ada
15629 type One_Dim is array (1..10) of integer;
15630 ar0 : constant One_Dim := (1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
15634 GNAT generates no executable code: the constant ar0 is placed in static memory.
15635 The same is true for constant aggregates with named associations:
15637 @smallexample @c ada
15638 Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1 => 1, 5 .. 10 => 0);
15639 Cr3 : constant One_Dim := (others => 7777);
15643 The same is true for multidimensional constant arrays such as:
15645 @smallexample @c ada
15646 type two_dim is array (1..3, 1..3) of integer;
15647 Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
15651 The same is true for arrays of one-dimensional arrays: the following are
15654 @smallexample @c ada
15655 type ar1b is array (1..3) of boolean;
15656 type ar_ar is array (1..3) of ar1b;
15657 None : constant ar1b := (others => false); -- fully static
15658 None2 : constant ar_ar := (1..3 => None); -- fully static
15662 However, for multidimensional aggregates with named associations, GNAT will
15663 generate assignments and loops, even if all associations are static. The
15664 following two declarations generate a loop for the first dimension, and
15665 individual component assignments for the second dimension:
15667 @smallexample @c ada
15668 Zero1: constant two_dim := (1..3 => (1..3 => 0));
15669 Zero2: constant two_dim := (others => (others => 0));
15672 @node Constant aggregates with unconstrained nominal types
15673 @subsection Constant aggregates with unconstrained nominal types
15676 In such cases the aggregate itself establishes the subtype, so that
15677 associations with @code{others} cannot be used. GNAT determines the
15678 bounds for the actual subtype of the aggregate, and allocates the
15679 aggregate statically as well. No code is generated for the following:
15681 @smallexample @c ada
15682 type One_Unc is array (natural range <>) of integer;
15683 Cr_Unc : constant One_Unc := (12,24,36);
15686 @node Aggregates with static bounds
15687 @subsection Aggregates with static bounds
15690 In all previous examples the aggregate was the initial (and immutable) value
15691 of a constant. If the aggregate initializes a variable, then code is generated
15692 for it as a combination of individual assignments and loops over the target
15693 object. The declarations
15695 @smallexample @c ada
15696 Cr_Var1 : One_Dim := (2, 5, 7, 11, 0, 0, 0, 0, 0, 0);
15697 Cr_Var2 : One_Dim := (others > -1);
15701 generate the equivalent of
15703 @smallexample @c ada
15709 for I in Cr_Var2'range loop
15714 @node Aggregates with non-static bounds
15715 @subsection Aggregates with non-static bounds
15718 If the bounds of the aggregate are not statically compatible with the bounds
15719 of the nominal subtype of the target, then constraint checks have to be
15720 generated on the bounds. For a multidimensional array, constraint checks may
15721 have to be applied to sub-arrays individually, if they do not have statically
15722 compatible subtypes.
15724 @node Aggregates in assignment statements
15725 @subsection Aggregates in assignment statements
15728 In general, aggregate assignment requires the construction of a temporary,
15729 and a copy from the temporary to the target of the assignment. This is because
15730 it is not always possible to convert the assignment into a series of individual
15731 component assignments. For example, consider the simple case:
15733 @smallexample @c ada
15738 This cannot be converted into:
15740 @smallexample @c ada
15746 So the aggregate has to be built first in a separate location, and then
15747 copied into the target. GNAT recognizes simple cases where this intermediate
15748 step is not required, and the assignments can be performed in place, directly
15749 into the target. The following sufficient criteria are applied:
15753 The bounds of the aggregate are static, and the associations are static.
15755 The components of the aggregate are static constants, names of
15756 simple variables that are not renamings, or expressions not involving
15757 indexed components whose operands obey these rules.
15761 If any of these conditions are violated, the aggregate will be built in
15762 a temporary (created either by the front-end or the code generator) and then
15763 that temporary will be copied onto the target.
15766 @node The Size of Discriminated Records with Default Discriminants
15767 @section The Size of Discriminated Records with Default Discriminants
15770 If a discriminated type @code{T} has discriminants with default values, it is
15771 possible to declare an object of this type without providing an explicit
15774 @smallexample @c ada
15776 type Size is range 1..100;
15778 type Rec (D : Size := 15) is record
15779 Name : String (1..D);
15787 Such an object is said to be @emph{unconstrained}.
15788 The discriminant of the object
15789 can be modified by a full assignment to the object, as long as it preserves the
15790 relation between the value of the discriminant, and the value of the components
15793 @smallexample @c ada
15795 Word := (3, "yes");
15797 Word := (5, "maybe");
15799 Word := (5, "no"); -- raises Constraint_Error
15804 In order to support this behavior efficiently, an unconstrained object is
15805 given the maximum size that any value of the type requires. In the case
15806 above, @code{Word} has storage for the discriminant and for
15807 a @code{String} of length 100.
15808 It is important to note that unconstrained objects do not require dynamic
15809 allocation. It would be an improper implementation to place on the heap those
15810 components whose size depends on discriminants. (This improper implementation
15811 was used by some Ada83 compilers, where the @code{Name} component above
15813 been stored as a pointer to a dynamic string). Following the principle that
15814 dynamic storage management should never be introduced implicitly,
15815 an Ada compiler should reserve the full size for an unconstrained declared
15816 object, and place it on the stack.
15818 This maximum size approach
15819 has been a source of surprise to some users, who expect the default
15820 values of the discriminants to determine the size reserved for an
15821 unconstrained object: ``If the default is 15, why should the object occupy
15823 The answer, of course, is that the discriminant may be later modified,
15824 and its full range of values must be taken into account. This is why the
15829 type Rec (D : Positive := 15) is record
15830 Name : String (1..D);
15838 is flagged by the compiler with a warning:
15839 an attempt to create @code{Too_Large} will raise @code{Storage_Error},
15840 because the required size includes @code{Positive'Last}
15841 bytes. As the first example indicates, the proper approach is to declare an
15842 index type of ``reasonable'' range so that unconstrained objects are not too
15845 One final wrinkle: if the object is declared to be @code{aliased}, or if it is
15846 created in the heap by means of an allocator, then it is @emph{not}
15848 it is constrained by the default values of the discriminants, and those values
15849 cannot be modified by full assignment. This is because in the presence of
15850 aliasing all views of the object (which may be manipulated by different tasks,
15851 say) must be consistent, so it is imperative that the object, once created,
15854 @node Strict Conformance to the Ada Reference Manual
15855 @section Strict Conformance to the Ada Reference Manual
15858 The dynamic semantics defined by the Ada Reference Manual impose a set of
15859 run-time checks to be generated. By default, the GNAT compiler will insert many
15860 run-time checks into the compiled code, including most of those required by the
15861 Ada Reference Manual. However, there are three checks that are not enabled
15862 in the default mode for efficiency reasons: arithmetic overflow checking for
15863 integer operations (including division by zero), checks for access before
15864 elaboration on subprogram calls, and stack overflow checking (most operating
15865 systems do not perform this check by default).
15867 Strict conformance to the Ada Reference Manual can be achieved by adding
15868 three compiler options for overflow checking for integer operations
15869 (@option{-gnato}), dynamic checks for access-before-elaboration on subprogram
15870 calls and generic instantiations (@option{-gnatE}), and stack overflow
15871 checking (@option{-fstack-check}).
15873 Note that the result of a floating point arithmetic operation in overflow and
15874 invalid situations, when the @code{Machine_Overflows} attribute of the result
15875 type is @code{False}, is to generate IEEE NaN and infinite values. This is the
15876 case for machines compliant with the IEEE floating-point standard, but on
15877 machines that are not fully compliant with this standard, such as Alpha, the
15878 @option{-mieee} compiler flag must be used for achieving IEEE confirming
15879 behavior (although at the cost of a significant performance penalty), so
15880 infinite and and NaN values are properly generated.
15883 @node Project File Reference
15884 @chapter Project File Reference
15887 This chapter describes the syntax and semantics of project files.
15888 Project files specify the options to be used when building a system.
15889 Project files can specify global settings for all tools,
15890 as well as tool-specific settings.
15891 @xref{Examples of Project Files,,, gnat_ugn, @value{EDITION} User's Guide},
15892 for examples of use.
15896 * Lexical Elements::
15898 * Empty declarations::
15899 * Typed string declarations::
15903 * Project Attributes::
15904 * Attribute References::
15905 * External Values::
15906 * Case Construction::
15908 * Package Renamings::
15910 * Project Extensions::
15911 * Project File Elaboration::
15914 @node Reserved Words
15915 @section Reserved Words
15918 All Ada reserved words are reserved in project files, and cannot be used
15919 as variable names or project names. In addition, the following are
15920 also reserved in project files:
15923 @item @code{extends}
15925 @item @code{external}
15927 @item @code{project}
15931 @node Lexical Elements
15932 @section Lexical Elements
15935 Rules for identifiers are the same as in Ada. Identifiers
15936 are case-insensitive. Strings are case sensitive, except where noted.
15937 Comments have the same form as in Ada.
15947 simple_name @{. simple_name@}
15951 @section Declarations
15954 Declarations introduce new entities that denote types, variables, attributes,
15955 and packages. Some declarations can only appear immediately within a project
15956 declaration. Others can appear within a project or within a package.
15960 declarative_item ::=
15961 simple_declarative_item |
15962 typed_string_declaration |
15963 package_declaration
15965 simple_declarative_item ::=
15966 variable_declaration |
15967 typed_variable_declaration |
15968 attribute_declaration |
15969 case_construction |
15973 @node Empty declarations
15974 @section Empty declarations
15977 empty_declaration ::=
15981 An empty declaration is allowed anywhere a declaration is allowed.
15984 @node Typed string declarations
15985 @section Typed string declarations
15988 Typed strings are sequences of string literals. Typed strings are the only
15989 named types in project files. They are used in case constructions, where they
15990 provide support for conditional attribute definitions.
15994 typed_string_declaration ::=
15995 @b{type} <typed_string_>_simple_name @b{is}
15996 ( string_literal @{, string_literal@} );
16000 A typed string declaration can only appear immediately within a project
16003 All the string literals in a typed string declaration must be distinct.
16009 Variables denote values, and appear as constituents of expressions.
16012 typed_variable_declaration ::=
16013 <typed_variable_>simple_name : <typed_string_>name := string_expression ;
16015 variable_declaration ::=
16016 <variable_>simple_name := expression;
16020 The elaboration of a variable declaration introduces the variable and
16021 assigns to it the value of the expression. The name of the variable is
16022 available after the assignment symbol.
16025 A typed_variable can only be declare once.
16028 a non-typed variable can be declared multiple times.
16031 Before the completion of its first declaration, the value of variable
16032 is the null string.
16035 @section Expressions
16038 An expression is a formula that defines a computation or retrieval of a value.
16039 In a project file the value of an expression is either a string or a list
16040 of strings. A string value in an expression is either a literal, the current
16041 value of a variable, an external value, an attribute reference, or a
16042 concatenation operation.
16055 attribute_reference
16061 ( <string_>expression @{ , <string_>expression @} )
16064 @subsection Concatenation
16066 The following concatenation functions are defined:
16068 @smallexample @c ada
16069 function "&" (X : String; Y : String) return String;
16070 function "&" (X : String_List; Y : String) return String_List;
16071 function "&" (X : String_List; Y : String_List) return String_List;
16075 @section Attributes
16078 An attribute declaration defines a property of a project or package. This
16079 property can later be queried by means of an attribute reference.
16080 Attribute values are strings or string lists.
16082 Some attributes are associative arrays. These attributes are mappings whose
16083 domain is a set of strings. These attributes are declared one association
16084 at a time, by specifying a point in the domain and the corresponding image
16085 of the attribute. They may also be declared as a full associative array,
16086 getting the same associations as the corresponding attribute in an imported
16087 or extended project.
16089 Attributes that are not associative arrays are called simple attributes.
16093 attribute_declaration ::=
16094 full_associative_array_declaration |
16095 @b{for} attribute_designator @b{use} expression ;
16097 full_associative_array_declaration ::=
16098 @b{for} <associative_array_attribute_>simple_name @b{use}
16099 <project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
16101 attribute_designator ::=
16102 <simple_attribute_>simple_name |
16103 <associative_array_attribute_>simple_name ( string_literal )
16107 Some attributes are project-specific, and can only appear immediately within
16108 a project declaration. Others are package-specific, and can only appear within
16109 the proper package.
16111 The expression in an attribute definition must be a string or a string_list.
16112 The string literal appearing in the attribute_designator of an associative
16113 array attribute is case-insensitive.
16115 @node Project Attributes
16116 @section Project Attributes
16119 The following attributes apply to a project. All of them are simple
16124 Expression must be a path name. The attribute defines the
16125 directory in which the object files created by the build are to be placed. If
16126 not specified, object files are placed in the project directory.
16129 Expression must be a path name. The attribute defines the
16130 directory in which the executables created by the build are to be placed.
16131 If not specified, executables are placed in the object directory.
16134 Expression must be a list of path names. The attribute
16135 defines the directories in which the source files for the project are to be
16136 found. If not specified, source files are found in the project directory.
16137 If a string in the list ends with "/**", then the directory that precedes
16138 "/**" and all of its subdirectories (recursively) are included in the list
16139 of source directories.
16141 @item Excluded_Source_Dirs
16142 Expression must be a list of strings. Each entry designates a directory that
16143 is not to be included in the list of source directories of the project.
16144 This is normally used when there are strings ending with "/**" in the value
16145 of attribute Source_Dirs.
16148 Expression must be a list of file names. The attribute
16149 defines the individual files, in the project directory, which are to be used
16150 as sources for the project. File names are path_names that contain no directory
16151 information. If the project has no sources the attribute must be declared
16152 explicitly with an empty list.
16154 @item Excluded_Source_Files (Locally_Removed_Files)
16155 Expression must be a list of strings that are legal file names.
16156 Each file name must designate a source that would normally be a source file
16157 in the source directories of the project or, if the project file is an
16158 extending project file, inherited by the current project file. It cannot
16159 designate an immediate source that is not inherited. Each of the source files
16160 in the list are not considered to be sources of the project file: they are not
16161 inherited. Attribute Locally_Removed_Files is obsolescent, attribute
16162 Excluded_Source_Files is preferred.
16164 @item Source_List_File
16165 Expression must a single path name. The attribute
16166 defines a text file that contains a list of source file names to be used
16167 as sources for the project
16170 Expression must be a path name. The attribute defines the
16171 directory in which a library is to be built. The directory must exist, must
16172 be distinct from the project's object directory, and must be writable.
16175 Expression must be a string that is a legal file name,
16176 without extension. The attribute defines a string that is used to generate
16177 the name of the library to be built by the project.
16180 Argument must be a string value that must be one of the
16181 following @code{"static"}, @code{"dynamic"} or @code{"relocatable"}. This
16182 string is case-insensitive. If this attribute is not specified, the library is
16183 a static library. Otherwise, the library may be dynamic or relocatable. This
16184 distinction is operating-system dependent.
16186 @item Library_Version
16187 Expression must be a string value whose interpretation
16188 is platform dependent. On UNIX, it is used only for dynamic/relocatable
16189 libraries as the internal name of the library (the @code{"soname"}). If the
16190 library file name (built from the @code{Library_Name}) is different from the
16191 @code{Library_Version}, then the library file will be a symbolic link to the
16192 actual file whose name will be @code{Library_Version}.
16194 @item Library_Interface
16195 Expression must be a string list. Each element of the string list
16196 must designate a unit of the project.
16197 If this attribute is present in a Library Project File, then the project
16198 file is a Stand-alone Library_Project_File.
16200 @item Library_Auto_Init
16201 Expression must be a single string "true" or "false", case-insensitive.
16202 If this attribute is present in a Stand-alone Library Project File,
16203 it indicates if initialization is automatic when the dynamic library
16206 @item Library_Options
16207 Expression must be a string list. Indicates additional switches that
16208 are to be used when building a shared library.
16211 Expression must be a single string. Designates an alternative to "gcc"
16212 for building shared libraries.
16214 @item Library_Src_Dir
16215 Expression must be a path name. The attribute defines the
16216 directory in which the sources of the interfaces of a Stand-alone Library will
16217 be copied. The directory must exist, must be distinct from the project's
16218 object directory and source directories of all projects in the project tree,
16219 and must be writable.
16221 @item Library_Src_Dir
16222 Expression must be a path name. The attribute defines the
16223 directory in which the ALI files of a Library will
16224 be copied. The directory must exist, must be distinct from the project's
16225 object directory and source directories of all projects in the project tree,
16226 and must be writable.
16228 @item Library_Symbol_File
16229 Expression must be a single string. Its value is the single file name of a
16230 symbol file to be created when building a stand-alone library when the
16231 symbol policy is either "compliant", "controlled" or "restricted",
16232 on platforms that support symbol control, such as VMS. When symbol policy
16233 is "direct", then a file with this name must exist in the object directory.
16235 @item Library_Reference_Symbol_File
16236 Expression must be a single string. Its value is the path name of a
16237 reference symbol file that is read when the symbol policy is either
16238 "compliant" or "controlled", on platforms that support symbol control,
16239 such as VMS, when building a stand-alone library. The path may be an absolute
16240 path or a path relative to the project directory.
16242 @item Library_Symbol_Policy
16243 Expression must be a single string. Its case-insensitive value can only be
16244 "autonomous", "default", "compliant", "controlled", "restricted" or "direct".
16246 This attribute is not taken into account on all platforms. It controls the
16247 policy for exported symbols and, on some platforms (like VMS) that have the
16248 notions of major and minor IDs built in the library files, it controls
16249 the setting of these IDs.
16251 "autonomous" or "default": exported symbols are not controlled.
16253 "compliant": if attribute Library_Reference_Symbol_File is not defined, then
16254 it is equivalent to policy "autonomous". If there are exported symbols in
16255 the reference symbol file that are not in the object files of the interfaces,
16256 the major ID of the library is increased. If there are symbols in the
16257 object files of the interfaces that are not in the reference symbol file,
16258 these symbols are put at the end of the list in the newly created symbol file
16259 and the minor ID is increased.
16261 "controlled": the attribute Library_Reference_Symbol_File must be defined.
16262 The library will fail to build if the exported symbols in the object files of
16263 the interfaces do not match exactly the symbol in the symbol file.
16265 "restricted": The attribute Library_Symbol_File must be defined. The library
16266 will fail to build if there are symbols in the symbol file that are not in
16267 the exported symbols of the object files of the interfaces. Additional symbols
16268 in the object files are not added to the symbol file.
16270 "direct": The attribute Library_Symbol_File must be defined and must designate
16271 an existing file in the object directory. This symbol file is passed directly
16272 to the underlying linker without any symbol processing.
16275 Expression must be a list of strings that are legal file names.
16276 These file names designate existing compilation units in the source directory
16277 that are legal main subprograms.
16279 When a project file is elaborated, as part of the execution of a gnatmake
16280 command, one or several executables are built and placed in the Exec_Dir.
16281 If the gnatmake command does not include explicit file names, the executables
16282 that are built correspond to the files specified by this attribute.
16284 @item Externally_Built
16285 Expression must be a single string. Its value must be either "true" of "false",
16286 case-insensitive. The default is "false". When the value of this attribute is
16287 "true", no attempt is made to compile the sources or to build the library,
16288 when the project is a library project.
16290 @item Main_Language
16291 This is a simple attribute. Its value is a string that specifies the
16292 language of the main program.
16295 Expression must be a string list. Each string designates
16296 a programming language that is known to GNAT. The strings are case-insensitive.
16300 @node Attribute References
16301 @section Attribute References
16304 Attribute references are used to retrieve the value of previously defined
16305 attribute for a package or project.
16308 attribute_reference ::=
16309 attribute_prefix ' <simple_attribute_>simple_name [ ( string_literal ) ]
16311 attribute_prefix ::=
16313 <project_simple_name | package_identifier |
16314 <project_>simple_name . package_identifier
16318 If an attribute has not been specified for a given package or project, its
16319 value is the null string or the empty list.
16321 @node External Values
16322 @section External Values
16325 An external value is an expression whose value is obtained from the command
16326 that invoked the processing of the current project file (typically a
16332 @b{external} ( string_literal [, string_literal] )
16336 The first string_literal is the string to be used on the command line or
16337 in the environment to specify the external value. The second string_literal,
16338 if present, is the default to use if there is no specification for this
16339 external value either on the command line or in the environment.
16341 @node Case Construction
16342 @section Case Construction
16345 A case construction supports attribute and variable declarations that depend
16346 on the value of a previously declared variable.
16350 case_construction ::=
16351 @b{case} <typed_variable_>name @b{is}
16356 @b{when} discrete_choice_list =>
16357 @{case_construction |
16358 attribute_declaration |
16359 variable_declaration |
16360 empty_declaration@}
16362 discrete_choice_list ::=
16363 string_literal @{| string_literal@} |
16368 Inside a case construction, variable declarations must be for variables that
16369 have already been declared before the case construction.
16371 All choices in a choice list must be distinct. The choice lists of two
16372 distinct alternatives must be disjoint. Unlike Ada, the choice lists of all
16373 alternatives do not need to include all values of the type. An @code{others}
16374 choice must appear last in the list of alternatives.
16380 A package provides a grouping of variable declarations and attribute
16381 declarations to be used when invoking various GNAT tools. The name of
16382 the package indicates the tool(s) to which it applies.
16386 package_declaration ::=
16387 package_spec | package_renaming
16390 @b{package} package_identifier @b{is}
16391 @{simple_declarative_item@}
16392 @b{end} package_identifier ;
16394 package_identifier ::=
16395 @code{Naming} | @code{Builder} | @code{Compiler} | @code{Binder} |
16396 @code{Linker} | @code{Finder} | @code{Cross_Reference} |
16397 @code{gnatls} | @code{IDE} | @code{Pretty_Printer}
16400 @subsection Package Naming
16403 The attributes of a @code{Naming} package specifies the naming conventions
16404 that apply to the source files in a project. When invoking other GNAT tools,
16405 they will use the sources in the source directories that satisfy these
16406 naming conventions.
16408 The following attributes apply to a @code{Naming} package:
16412 This is a simple attribute whose value is a string. Legal values of this
16413 string are @code{"lowercase"}, @code{"uppercase"} or @code{"mixedcase"}.
16414 These strings are themselves case insensitive.
16417 If @code{Casing} is not specified, then the default is @code{"lowercase"}.
16419 @item Dot_Replacement
16420 This is a simple attribute whose string value satisfies the following
16424 @item It must not be empty
16425 @item It cannot start or end with an alphanumeric character
16426 @item It cannot be a single underscore
16427 @item It cannot start with an underscore followed by an alphanumeric
16428 @item It cannot contain a dot @code{'.'} if longer than one character
16432 If @code{Dot_Replacement} is not specified, then the default is @code{"-"}.
16435 This is an associative array attribute, defined on language names,
16436 whose image is a string that must satisfy the following
16440 @item It must not be empty
16441 @item It cannot start with an alphanumeric character
16442 @item It cannot start with an underscore followed by an alphanumeric character
16446 For Ada, the attribute denotes the suffix used in file names that contain
16447 library unit declarations, that is to say units that are package and
16448 subprogram declarations. If @code{Spec_Suffix ("Ada")} is not
16449 specified, then the default is @code{".ads"}.
16451 For C and C++, the attribute denotes the suffix used in file names that
16452 contain prototypes.
16455 This is an associative array attribute defined on language names,
16456 whose image is a string that must satisfy the following
16460 @item It must not be empty
16461 @item It cannot start with an alphanumeric character
16462 @item It cannot start with an underscore followed by an alphanumeric character
16463 @item It cannot be a suffix of @code{Spec_Suffix}
16467 For Ada, the attribute denotes the suffix used in file names that contain
16468 library bodies, that is to say units that are package and subprogram bodies.
16469 If @code{Body_Suffix ("Ada")} is not specified, then the default is
16472 For C and C++, the attribute denotes the suffix used in file names that contain
16475 @item Separate_Suffix
16476 This is a simple attribute whose value satisfies the same conditions as
16477 @code{Body_Suffix}.
16479 This attribute is specific to Ada. It denotes the suffix used in file names
16480 that contain separate bodies. If it is not specified, then it defaults to same
16481 value as @code{Body_Suffix ("Ada")}.
16484 This is an associative array attribute, specific to Ada, defined over
16485 compilation unit names. The image is a string that is the name of the file
16486 that contains that library unit. The file name is case sensitive if the
16487 conventions of the host operating system require it.
16490 This is an associative array attribute, specific to Ada, defined over
16491 compilation unit names. The image is a string that is the name of the file
16492 that contains the library unit body for the named unit. The file name is case
16493 sensitive if the conventions of the host operating system require it.
16495 @item Specification_Exceptions
16496 This is an associative array attribute defined on language names,
16497 whose value is a list of strings.
16499 This attribute is not significant for Ada.
16501 For C and C++, each string in the list denotes the name of a file that
16502 contains prototypes, but whose suffix is not necessarily the
16503 @code{Spec_Suffix} for the language.
16505 @item Implementation_Exceptions
16506 This is an associative array attribute defined on language names,
16507 whose value is a list of strings.
16509 This attribute is not significant for Ada.
16511 For C and C++, each string in the list denotes the name of a file that
16512 contains source code, but whose suffix is not necessarily the
16513 @code{Body_Suffix} for the language.
16516 The following attributes of package @code{Naming} are obsolescent. They are
16517 kept as synonyms of other attributes for compatibility with previous versions
16518 of the Project Manager.
16521 @item Specification_Suffix
16522 This is a synonym of @code{Spec_Suffix}.
16524 @item Implementation_Suffix
16525 This is a synonym of @code{Body_Suffix}.
16527 @item Specification
16528 This is a synonym of @code{Spec}.
16530 @item Implementation
16531 This is a synonym of @code{Body}.
16534 @subsection package Compiler
16537 The attributes of the @code{Compiler} package specify the compilation options
16538 to be used by the underlying compiler.
16541 @item Default_Switches
16542 This is an associative array attribute. Its
16543 domain is a set of language names. Its range is a string list that
16544 specifies the compilation options to be used when compiling a component
16545 written in that language, for which no file-specific switches have been
16549 This is an associative array attribute. Its domain is
16550 a set of file names. Its range is a string list that specifies the
16551 compilation options to be used when compiling the named file. If a file
16552 is not specified in the Switches attribute, it is compiled with the
16553 options specified by Default_Switches of its language, if defined.
16555 @item Local_Configuration_Pragmas.
16556 This is a simple attribute, whose
16557 value is a path name that designates a file containing configuration pragmas
16558 to be used for all invocations of the compiler for immediate sources of the
16562 @subsection package Builder
16565 The attributes of package @code{Builder} specify the compilation, binding, and
16566 linking options to be used when building an executable for a project. The
16567 following attributes apply to package @code{Builder}:
16570 @item Default_Switches
16571 This is an associative array attribute. Its
16572 domain is a set of language names. Its range is a string list that
16573 specifies options to be used when building a main
16574 written in that language, for which no file-specific switches have been
16578 This is an associative array attribute. Its domain is
16579 a set of file names. Its range is a string list that specifies
16580 options to be used when building the named main file. If a main file
16581 is not specified in the Switches attribute, it is built with the
16582 options specified by Default_Switches of its language, if defined.
16584 @item Global_Configuration_Pragmas
16585 This is a simple attribute, whose
16586 value is a path name that designates a file that contains configuration pragmas
16587 to be used in every build of an executable. If both local and global
16588 configuration pragmas are specified, a compilation makes use of both sets.
16592 This is an associative array attribute. Its domain is
16593 a set of main source file names. Its range is a simple string that specifies
16594 the executable file name to be used when linking the specified main source.
16595 If a main source is not specified in the Executable attribute, the executable
16596 file name is deducted from the main source file name.
16597 This attribute has no effect if its value is the empty string.
16599 @item Executable_Suffix
16600 This is a simple attribute whose value is the suffix to be added to
16601 the executables that don't have an attribute Executable specified.
16604 @subsection package Gnatls
16607 The attributes of package @code{Gnatls} specify the tool options to be used
16608 when invoking the library browser @command{gnatls}.
16609 The following attributes apply to package @code{Gnatls}:
16613 This is a single attribute with a string list value. Each nonempty string
16614 in the list is an option when invoking @code{gnatls}.
16617 @subsection package Binder
16620 The attributes of package @code{Binder} specify the options to be used
16621 when invoking the binder in the construction of an executable.
16622 The following attributes apply to package @code{Binder}:
16625 @item Default_Switches
16626 This is an associative array attribute. Its
16627 domain is a set of language names. Its range is a string list that
16628 specifies options to be used when binding a main
16629 written in that language, for which no file-specific switches have been
16633 This is an associative array attribute. Its domain is
16634 a set of file names. Its range is a string list that specifies
16635 options to be used when binding the named main file. If a main file
16636 is not specified in the Switches attribute, it is bound with the
16637 options specified by Default_Switches of its language, if defined.
16640 @subsection package Linker
16643 The attributes of package @code{Linker} specify the options to be used when
16644 invoking the linker in the construction of an executable.
16645 The following attributes apply to package @code{Linker}:
16648 @item Default_Switches
16649 This is an associative array attribute. Its
16650 domain is a set of language names. Its range is a string list that
16651 specifies options to be used when linking a main
16652 written in that language, for which no file-specific switches have been
16656 This is an associative array attribute. Its domain is
16657 a set of file names. Its range is a string list that specifies
16658 options to be used when linking the named main file. If a main file
16659 is not specified in the Switches attribute, it is linked with the
16660 options specified by Default_Switches of its language, if defined.
16662 @item Linker_Options
16663 This is a string list attribute. Its value specifies additional options that
16664 be given to the linker when linking an executable. This attribute is not
16665 used in the main project, only in projects imported directly or indirectly.
16669 @subsection package Cross_Reference
16672 The attributes of package @code{Cross_Reference} specify the tool options
16674 when invoking the library tool @command{gnatxref}.
16675 The following attributes apply to package @code{Cross_Reference}:
16678 @item Default_Switches
16679 This is an associative array attribute. Its
16680 domain is a set of language names. Its range is a string list that
16681 specifies options to be used when calling @command{gnatxref} on a source
16682 written in that language, for which no file-specific switches have been
16686 This is an associative array attribute. Its domain is
16687 a set of file names. Its range is a string list that specifies
16688 options to be used when calling @command{gnatxref} on the named main source.
16689 If a source is not specified in the Switches attribute, @command{gnatxref} will
16690 be called with the options specified by Default_Switches of its language,
16694 @subsection package Finder
16697 The attributes of package @code{Finder} specify the tool options to be used
16698 when invoking the search tool @command{gnatfind}.
16699 The following attributes apply to package @code{Finder}:
16702 @item Default_Switches
16703 This is an associative array attribute. Its
16704 domain is a set of language names. Its range is a string list that
16705 specifies options to be used when calling @command{gnatfind} on a source
16706 written in that language, for which no file-specific switches have been
16710 This is an associative array attribute. Its domain is
16711 a set of file names. Its range is a string list that specifies
16712 options to be used when calling @command{gnatfind} on the named main source.
16713 If a source is not specified in the Switches attribute, @command{gnatfind} will
16714 be called with the options specified by Default_Switches of its language,
16718 @subsection package Pretty_Printer
16721 The attributes of package @code{Pretty_Printer}
16722 specify the tool options to be used
16723 when invoking the formatting tool @command{gnatpp}.
16724 The following attributes apply to package @code{Pretty_Printer}:
16727 @item Default_switches
16728 This is an associative array attribute. Its
16729 domain is a set of language names. Its range is a string list that
16730 specifies options to be used when calling @command{gnatpp} on a source
16731 written in that language, for which no file-specific switches have been
16735 This is an associative array attribute. Its domain is
16736 a set of file names. Its range is a string list that specifies
16737 options to be used when calling @command{gnatpp} on the named main source.
16738 If a source is not specified in the Switches attribute, @command{gnatpp} will
16739 be called with the options specified by Default_Switches of its language,
16743 @subsection package gnatstub
16746 The attributes of package @code{gnatstub}
16747 specify the tool options to be used
16748 when invoking the tool @command{gnatstub}.
16749 The following attributes apply to package @code{gnatstub}:
16752 @item Default_switches
16753 This is an associative array attribute. Its
16754 domain is a set of language names. Its range is a string list that
16755 specifies options to be used when calling @command{gnatstub} on a source
16756 written in that language, for which no file-specific switches have been
16760 This is an associative array attribute. Its domain is
16761 a set of file names. Its range is a string list that specifies
16762 options to be used when calling @command{gnatstub} on the named main source.
16763 If a source is not specified in the Switches attribute, @command{gnatpp} will
16764 be called with the options specified by Default_Switches of its language,
16768 @subsection package Eliminate
16771 The attributes of package @code{Eliminate}
16772 specify the tool options to be used
16773 when invoking the tool @command{gnatelim}.
16774 The following attributes apply to package @code{Eliminate}:
16777 @item Default_switches
16778 This is an associative array attribute. Its
16779 domain is a set of language names. Its range is a string list that
16780 specifies options to be used when calling @command{gnatelim} on a source
16781 written in that language, for which no file-specific switches have been
16785 This is an associative array attribute. Its domain is
16786 a set of file names. Its range is a string list that specifies
16787 options to be used when calling @command{gnatelim} on the named main source.
16788 If a source is not specified in the Switches attribute, @command{gnatelim} will
16789 be called with the options specified by Default_Switches of its language,
16793 @subsection package Metrics
16796 The attributes of package @code{Metrics}
16797 specify the tool options to be used
16798 when invoking the tool @command{gnatmetric}.
16799 The following attributes apply to package @code{Metrics}:
16802 @item Default_switches
16803 This is an associative array attribute. Its
16804 domain is a set of language names. Its range is a string list that
16805 specifies options to be used when calling @command{gnatmetric} on a source
16806 written in that language, for which no file-specific switches have been
16810 This is an associative array attribute. Its domain is
16811 a set of file names. Its range is a string list that specifies
16812 options to be used when calling @command{gnatmetric} on the named main source.
16813 If a source is not specified in the Switches attribute, @command{gnatmetric}
16814 will be called with the options specified by Default_Switches of its language,
16818 @subsection package IDE
16821 The attributes of package @code{IDE} specify the options to be used when using
16822 an Integrated Development Environment such as @command{GPS}.
16826 This is a simple attribute. Its value is a string that designates the remote
16827 host in a cross-compilation environment, to be used for remote compilation and
16828 debugging. This field should not be specified when running on the local
16832 This is a simple attribute. Its value is a string that specifies the
16833 name of IP address of the embedded target in a cross-compilation environment,
16834 on which the program should execute.
16836 @item Communication_Protocol
16837 This is a simple string attribute. Its value is the name of the protocol
16838 to use to communicate with the target in a cross-compilation environment,
16839 e.g.@: @code{"wtx"} or @code{"vxworks"}.
16841 @item Compiler_Command
16842 This is an associative array attribute, whose domain is a language name. Its
16843 value is string that denotes the command to be used to invoke the compiler.
16844 The value of @code{Compiler_Command ("Ada")} is expected to be compatible with
16845 gnatmake, in particular in the handling of switches.
16847 @item Debugger_Command
16848 This is simple attribute, Its value is a string that specifies the name of
16849 the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
16851 @item Default_Switches
16852 This is an associative array attribute. Its indexes are the name of the
16853 external tools that the GNAT Programming System (GPS) is supporting. Its
16854 value is a list of switches to use when invoking that tool.
16857 This is a simple attribute. Its value is a string that specifies the name
16858 of the @command{gnatls} utility to be used to retrieve information about the
16859 predefined path; e.g., @code{"gnatls"}, @code{"powerpc-wrs-vxworks-gnatls"}.
16862 This is a simple attribute. Its value is a string used to specify the
16863 Version Control System (VCS) to be used for this project, e.g.@: CVS, RCS
16864 ClearCase or Perforce.
16866 @item VCS_File_Check
16867 This is a simple attribute. Its value is a string that specifies the
16868 command used by the VCS to check the validity of a file, either
16869 when the user explicitly asks for a check, or as a sanity check before
16870 doing the check-in.
16872 @item VCS_Log_Check
16873 This is a simple attribute. Its value is a string that specifies
16874 the command used by the VCS to check the validity of a log file.
16876 @item VCS_Repository_Root
16877 The VCS repository root path. This is used to create tags or branches
16878 of the repository. For subversion the value should be the @code{URL}
16879 as specified to check-out the working copy of the repository.
16881 @item VCS_Patch_Root
16882 The local root directory to use for building patch file. All patch chunks
16883 will be relative to this path. The root project directory is used if
16884 this value is not defined.
16888 @node Package Renamings
16889 @section Package Renamings
16892 A package can be defined by a renaming declaration. The new package renames
16893 a package declared in a different project file, and has the same attributes
16894 as the package it renames.
16897 package_renaming ::==
16898 @b{package} package_identifier @b{renames}
16899 <project_>simple_name.package_identifier ;
16903 The package_identifier of the renamed package must be the same as the
16904 package_identifier. The project whose name is the prefix of the renamed
16905 package must contain a package declaration with this name. This project
16906 must appear in the context_clause of the enclosing project declaration,
16907 or be the parent project of the enclosing child project.
16913 A project file specifies a set of rules for constructing a software system.
16914 A project file can be self-contained, or depend on other project files.
16915 Dependencies are expressed through a context clause that names other projects.
16921 context_clause project_declaration
16923 project_declaration ::=
16924 simple_project_declaration | project_extension
16926 simple_project_declaration ::=
16927 @b{project} <project_>simple_name @b{is}
16928 @{declarative_item@}
16929 @b{end} <project_>simple_name;
16935 [@b{limited}] @b{with} path_name @{ , path_name @} ;
16942 A path name denotes a project file. A path name can be absolute or relative.
16943 An absolute path name includes a sequence of directories, in the syntax of
16944 the host operating system, that identifies uniquely the project file in the
16945 file system. A relative path name identifies the project file, relative
16946 to the directory that contains the current project, or relative to a
16947 directory listed in the environment variable ADA_PROJECT_PATH.
16948 Path names are case sensitive if file names in the host operating system
16949 are case sensitive.
16951 The syntax of the environment variable ADA_PROJECT_PATH is a list of
16952 directory names separated by colons (semicolons on Windows).
16954 A given project name can appear only once in a context_clause.
16956 It is illegal for a project imported by a context clause to refer, directly
16957 or indirectly, to the project in which this context clause appears (the
16958 dependency graph cannot contain cycles), except when one of the with_clause
16959 in the cycle is a @code{limited with}.
16961 @node Project Extensions
16962 @section Project Extensions
16965 A project extension introduces a new project, which inherits the declarations
16966 of another project.
16970 project_extension ::=
16971 @b{project} <project_>simple_name @b{extends} path_name @b{is}
16972 @{declarative_item@}
16973 @b{end} <project_>simple_name;
16977 The project extension declares a child project. The child project inherits
16978 all the declarations and all the files of the parent project, These inherited
16979 declaration can be overridden in the child project, by means of suitable
16982 @node Project File Elaboration
16983 @section Project File Elaboration
16986 A project file is processed as part of the invocation of a gnat tool that
16987 uses the project option. Elaboration of the process file consists in the
16988 sequential elaboration of all its declarations. The computed values of
16989 attributes and variables in the project are then used to establish the
16990 environment in which the gnat tool will execute.
16992 @node Obsolescent Features
16993 @chapter Obsolescent Features
16996 This chapter describes features that are provided by GNAT, but are
16997 considered obsolescent since there are preferred ways of achieving
16998 the same effect. These features are provided solely for historical
16999 compatibility purposes.
17002 * pragma No_Run_Time::
17003 * pragma Ravenscar::
17004 * pragma Restricted_Run_Time::
17007 @node pragma No_Run_Time
17008 @section pragma No_Run_Time
17010 The pragma @code{No_Run_Time} is used to achieve an affect similar
17011 to the use of the "Zero Foot Print" configurable run time, but without
17012 requiring a specially configured run time. The result of using this
17013 pragma, which must be used for all units in a partition, is to restrict
17014 the use of any language features requiring run-time support code. The
17015 preferred usage is to use an appropriately configured run-time that
17016 includes just those features that are to be made accessible.
17018 @node pragma Ravenscar
17019 @section pragma Ravenscar
17021 The pragma @code{Ravenscar} has exactly the same effect as pragma
17022 @code{Profile (Ravenscar)}. The latter usage is preferred since it
17023 is part of the new Ada 2005 standard.
17025 @node pragma Restricted_Run_Time
17026 @section pragma Restricted_Run_Time
17028 The pragma @code{Restricted_Run_Time} has exactly the same effect as
17029 pragma @code{Profile (Restricted)}. The latter usage is
17030 preferred since the Ada 2005 pragma @code{Profile} is intended for
17031 this kind of implementation dependent addition.
17034 @c GNU Free Documentation License
17036 @node Index,,GNU Free Documentation License, Top