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
226 * Default_Bit_Order::
236 * Has_Access_Values::
237 * Has_Discriminants::
244 * Max_Interrupt_Priority::
246 * Maximum_Alignment::
251 * Passed_By_Reference::
264 * Unconstrained_Array::
265 * Universal_Literal_String::
266 * Unrestricted_Access::
272 The Implementation of Standard I/O
274 * Standard I/O Packages::
280 * Wide_Wide_Text_IO::
284 * Filenames encoding::
286 * Operations on C Streams::
287 * Interfacing to C Streams::
291 * Ada.Characters.Latin_9 (a-chlat9.ads)::
292 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
293 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
294 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
295 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
296 * Ada.Command_Line.Environment (a-colien.ads)::
297 * Ada.Command_Line.Remove (a-colire.ads)::
298 * Ada.Command_Line.Response_File (a-clrefi.ads)::
299 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
300 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
301 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
302 * Ada.Exceptions.Traceback (a-exctra.ads)::
303 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
304 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
305 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
306 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
307 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
308 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
309 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
310 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
311 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
312 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
313 * GNAT.Altivec (g-altive.ads)::
314 * GNAT.Altivec.Conversions (g-altcon.ads)::
315 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
316 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
317 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
318 * GNAT.Array_Split (g-arrspl.ads)::
319 * GNAT.AWK (g-awk.ads)::
320 * GNAT.Bounded_Buffers (g-boubuf.ads)::
321 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
322 * GNAT.Bubble_Sort (g-bubsor.ads)::
323 * GNAT.Bubble_Sort_A (g-busora.ads)::
324 * GNAT.Bubble_Sort_G (g-busorg.ads)::
325 * GNAT.Byte_Order_Mark (g-byorma.ads)::
326 * GNAT.Byte_Swapping (g-bytswa.ads)::
327 * GNAT.Calendar (g-calend.ads)::
328 * GNAT.Calendar.Time_IO (g-catiio.ads)::
329 * GNAT.Case_Util (g-casuti.ads)::
330 * GNAT.CGI (g-cgi.ads)::
331 * GNAT.CGI.Cookie (g-cgicoo.ads)::
332 * GNAT.CGI.Debug (g-cgideb.ads)::
333 * GNAT.Command_Line (g-comlin.ads)::
334 * GNAT.Compiler_Version (g-comver.ads)::
335 * GNAT.Ctrl_C (g-ctrl_c.ads)::
336 * GNAT.CRC32 (g-crc32.ads)::
337 * GNAT.Current_Exception (g-curexc.ads)::
338 * GNAT.Debug_Pools (g-debpoo.ads)::
339 * GNAT.Debug_Utilities (g-debuti.ads)::
340 * GNAT.Decode_String (g-decstr.ads)::
341 * GNAT.Decode_UTF8_String (g-deutst.ads)::
342 * GNAT.Directory_Operations (g-dirope.ads)::
343 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
344 * GNAT.Dynamic_HTables (g-dynhta.ads)::
345 * GNAT.Dynamic_Tables (g-dyntab.ads)::
346 * GNAT.Encode_String (g-encstr.ads)::
347 * GNAT.Encode_UTF8_String (g-enutst.ads)::
348 * GNAT.Exception_Actions (g-excact.ads)::
349 * GNAT.Exception_Traces (g-exctra.ads)::
350 * GNAT.Exceptions (g-except.ads)::
351 * GNAT.Expect (g-expect.ads)::
352 * GNAT.Float_Control (g-flocon.ads)::
353 * GNAT.Heap_Sort (g-heasor.ads)::
354 * GNAT.Heap_Sort_A (g-hesora.ads)::
355 * GNAT.Heap_Sort_G (g-hesorg.ads)::
356 * GNAT.HTable (g-htable.ads)::
357 * GNAT.IO (g-io.ads)::
358 * GNAT.IO_Aux (g-io_aux.ads)::
359 * GNAT.Lock_Files (g-locfil.ads)::
360 * GNAT.MD5 (g-md5.ads)::
361 * GNAT.Memory_Dump (g-memdum.ads)::
362 * GNAT.Most_Recent_Exception (g-moreex.ads)::
363 * GNAT.OS_Lib (g-os_lib.ads)::
364 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
365 * GNAT.Random_Numbers (g-rannum.ads)::
366 * GNAT.Regexp (g-regexp.ads)::
367 * GNAT.Registry (g-regist.ads)::
368 * GNAT.Regpat (g-regpat.ads)::
369 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
370 * GNAT.Semaphores (g-semaph.ads)::
371 * GNAT.Serial_Communications (g-sercom.ads)::
372 * GNAT.SHA1 (g-sha1.ads)::
373 * GNAT.Signals (g-signal.ads)::
374 * GNAT.Sockets (g-socket.ads)::
375 * GNAT.Source_Info (g-souinf.ads)::
376 * GNAT.Spelling_Checker (g-speche.ads)::
377 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
378 * GNAT.Spitbol.Patterns (g-spipat.ads)::
379 * GNAT.Spitbol (g-spitbo.ads)::
380 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
381 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
382 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
383 * GNAT.Strings (g-string.ads)::
384 * GNAT.String_Split (g-strspl.ads)::
385 * GNAT.Table (g-table.ads)::
386 * GNAT.Task_Lock (g-tasloc.ads)::
387 * GNAT.Threads (g-thread.ads)::
388 * GNAT.Time_Stamp (g-timsta.ads)::
389 * GNAT.Traceback (g-traceb.ads)::
390 * GNAT.Traceback.Symbolic (g-trasym.ads)::
391 * GNAT.UTF_32 (g-utf_32.ads)::
392 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
393 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
394 * GNAT.Wide_String_Split (g-wistsp.ads)::
395 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
396 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
397 * Interfaces.C.Extensions (i-cexten.ads)::
398 * Interfaces.C.Streams (i-cstrea.ads)::
399 * Interfaces.CPP (i-cpp.ads)::
400 * Interfaces.Packed_Decimal (i-pacdec.ads)::
401 * Interfaces.VxWorks (i-vxwork.ads)::
402 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
403 * System.Address_Image (s-addima.ads)::
404 * System.Assertions (s-assert.ads)::
405 * System.Memory (s-memory.ads)::
406 * System.Partition_Interface (s-parint.ads)::
407 * System.Pool_Global (s-pooglo.ads)::
408 * System.Pool_Local (s-pooloc.ads)::
409 * System.Restrictions (s-restri.ads)::
410 * System.Rident (s-rident.ads)::
411 * System.Task_Info (s-tasinf.ads)::
412 * System.Wch_Cnv (s-wchcnv.ads)::
413 * System.Wch_Con (s-wchcon.ads)::
417 * Text_IO Stream Pointer Positioning::
418 * Text_IO Reading and Writing Non-Regular Files::
420 * Treating Text_IO Files as Streams::
421 * Text_IO Extensions::
422 * Text_IO Facilities for Unbounded Strings::
426 * Wide_Text_IO Stream Pointer Positioning::
427 * Wide_Text_IO Reading and Writing Non-Regular Files::
431 * Wide_Wide_Text_IO Stream Pointer Positioning::
432 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
434 Interfacing to Other Languages
437 * Interfacing to C++::
438 * Interfacing to COBOL::
439 * Interfacing to Fortran::
440 * Interfacing to non-GNAT Ada code::
442 Specialized Needs Annexes
444 Implementation of Specific Ada Features
445 * Machine Code Insertions::
446 * GNAT Implementation of Tasking::
447 * GNAT Implementation of Shared Passive Packages::
448 * Code Generation for Array Aggregates::
449 * The Size of Discriminated Records with Default Discriminants::
450 * Strict Conformance to the Ada Reference Manual::
452 Project File Reference
456 GNU Free Documentation License
463 @node About This Guide
464 @unnumbered About This Guide
467 This manual contains useful information in writing programs using the
468 @value{EDITION} compiler. It includes information on implementation dependent
469 characteristics of @value{EDITION}, including all the information required by
470 Annex M of the Ada language standard.
472 @value{EDITION} implements Ada 95 and Ada 2005, and it may also be invoked in
473 Ada 83 compatibility mode.
474 By default, @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION},
475 but you can override with a compiler switch
476 to explicitly specify the language version.
477 (Please refer to @ref{Compiling Different Versions of Ada,,, gnat_ugn,
478 @value{EDITION} User's Guide}, for details on these switches.)
479 Throughout this manual, references to ``Ada'' without a year suffix
480 apply to both the Ada 95 and Ada 2005 versions of the language.
482 Ada is designed to be highly portable.
483 In general, a program will have the same effect even when compiled by
484 different compilers on different platforms.
485 However, since Ada is designed to be used in a
486 wide variety of applications, it also contains a number of system
487 dependent features to be used in interfacing to the external world.
488 @cindex Implementation-dependent features
491 Note: Any program that makes use of implementation-dependent features
492 may be non-portable. You should follow good programming practice and
493 isolate and clearly document any sections of your program that make use
494 of these features in a non-portable manner.
497 For ease of exposition, ``GNAT Pro'' will be referred to simply as
498 ``GNAT'' in the remainder of this document.
502 * What This Reference Manual Contains::
504 * Related Information::
507 @node What This Reference Manual Contains
508 @unnumberedsec What This Reference Manual Contains
511 This reference manual contains the following chapters:
515 @ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
516 pragmas, which can be used to extend and enhance the functionality of the
520 @ref{Implementation Defined Attributes}, lists GNAT
521 implementation-dependent attributes which can be used to extend and
522 enhance the functionality of the compiler.
525 @ref{Implementation Advice}, provides information on generally
526 desirable behavior which are not requirements that all compilers must
527 follow since it cannot be provided on all systems, or which may be
528 undesirable on some systems.
531 @ref{Implementation Defined Characteristics}, provides a guide to
532 minimizing implementation dependent features.
535 @ref{Intrinsic Subprograms}, describes the intrinsic subprograms
536 implemented by GNAT, and how they can be imported into user
537 application programs.
540 @ref{Representation Clauses and Pragmas}, describes in detail the
541 way that GNAT represents data, and in particular the exact set
542 of representation clauses and pragmas that is accepted.
545 @ref{Standard Library Routines}, provides a listing of packages and a
546 brief description of the functionality that is provided by Ada's
547 extensive set of standard library routines as implemented by GNAT@.
550 @ref{The Implementation of Standard I/O}, details how the GNAT
551 implementation of the input-output facilities.
554 @ref{The GNAT Library}, is a catalog of packages that complement
555 the Ada predefined library.
558 @ref{Interfacing to Other Languages}, describes how programs
559 written in Ada using GNAT can be interfaced to other programming
562 @ref{Specialized Needs Annexes}, describes the GNAT implementation of all
563 of the specialized needs annexes.
566 @ref{Implementation of Specific Ada Features}, discusses issues related
567 to GNAT's implementation of machine code insertions, tasking, and several
571 @ref{Project File Reference}, presents the syntax and semantics
575 @ref{Obsolescent Features} documents implementation dependent features,
576 including pragmas and attributes, which are considered obsolescent, since
577 there are other preferred ways of achieving the same results. These
578 obsolescent forms are retained for backwards compatibility.
582 @cindex Ada 95 Language Reference Manual
583 @cindex Ada 2005 Language Reference Manual
585 This reference manual assumes a basic familiarity with the Ada 95 language, as
586 described in the International Standard ANSI/ISO/IEC-8652:1995,
588 It does not require knowledge of the new features introduced by Ada 2005,
589 (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1
591 Both reference manuals are included in the GNAT documentation
595 @unnumberedsec Conventions
596 @cindex Conventions, typographical
597 @cindex Typographical conventions
600 Following are examples of the typographical and graphic conventions used
605 @code{Functions}, @code{utility program names}, @code{standard names},
612 @file{File names}, @samp{button names}, and @samp{field names}.
615 @code{Variables}, @env{environment variables}, and @var{metasyntactic
622 [optional information or parameters]
625 Examples are described by text
627 and then shown this way.
632 Commands that are entered by the user are preceded in this manual by the
633 characters @samp{$ } (dollar sign followed by space). If your system uses this
634 sequence as a prompt, then the commands will appear exactly as you see them
635 in the manual. If your system uses some other prompt, then the command will
636 appear with the @samp{$} replaced by whatever prompt character you are using.
638 @node Related Information
639 @unnumberedsec Related Information
641 See the following documents for further information on GNAT:
645 @xref{Top, @value{EDITION} User's Guide, About This Guide, gnat_ugn,
646 @value{EDITION} User's Guide}, which provides information on how to use the
647 GNAT compiler system.
650 @cite{Ada 95 Reference Manual}, which contains all reference
651 material for the Ada 95 programming language.
654 @cite{Ada 95 Annotated Reference Manual}, which is an annotated version
655 of the Ada 95 standard. The annotations describe
656 detailed aspects of the design decision, and in particular contain useful
657 sections on Ada 83 compatibility.
660 @cite{Ada 2005 Reference Manual}, which contains all reference
661 material for the Ada 2005 programming language.
664 @cite{Ada 2005 Annotated Reference Manual}, which is an annotated version
665 of the Ada 2005 standard. The annotations describe
666 detailed aspects of the design decision, and in particular contain useful
667 sections on Ada 83 and Ada 95 compatibility.
670 @cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
671 which contains specific information on compatibility between GNAT and
675 @cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
676 describes in detail the pragmas and attributes provided by the DEC Ada 83
681 @node Implementation Defined Pragmas
682 @chapter Implementation Defined Pragmas
685 Ada defines a set of pragmas that can be used to supply additional
686 information to the compiler. These language defined pragmas are
687 implemented in GNAT and work as described in the Ada Reference Manual.
689 In addition, Ada allows implementations to define additional pragmas
690 whose meaning is defined by the implementation. GNAT provides a number
691 of these implementation-defined pragmas, which can be used to extend
692 and enhance the functionality of the compiler. This section of the GNAT
693 Reference Manual describes these additional pragmas.
695 Note that any program using these pragmas might not be portable to other
696 compilers (although GNAT implements this set of pragmas on all
697 platforms). Therefore if portability to other compilers is an important
698 consideration, the use of these pragmas should be minimized.
701 * Pragma Abort_Defer::
708 * Pragma Assume_No_Invalid_Values::
710 * Pragma C_Pass_By_Copy::
712 * Pragma Check_Name::
713 * Pragma Check_Policy::
715 * Pragma Common_Object::
716 * Pragma Compile_Time_Error::
717 * Pragma Compile_Time_Warning::
718 * Pragma Complete_Representation::
719 * Pragma Complex_Representation::
720 * Pragma Component_Alignment::
721 * Pragma Convention_Identifier::
723 * Pragma CPP_Constructor::
724 * Pragma CPP_Virtual::
725 * Pragma CPP_Vtable::
727 * Pragma Debug_Policy::
728 * Pragma Detect_Blocking::
729 * Pragma Elaboration_Checks::
731 * Pragma Export_Exception::
732 * Pragma Export_Function::
733 * Pragma Export_Object::
734 * Pragma Export_Procedure::
735 * Pragma Export_Value::
736 * Pragma Export_Valued_Procedure::
737 * Pragma Extend_System::
739 * Pragma External_Name_Casing::
741 * Pragma Favor_Top_Level::
742 * Pragma Finalize_Storage_Only::
743 * Pragma Float_Representation::
745 * Pragma Implemented_By_Entry::
746 * Pragma Implicit_Packing::
747 * Pragma Import_Exception::
748 * Pragma Import_Function::
749 * Pragma Import_Object::
750 * Pragma Import_Procedure::
751 * Pragma Import_Valued_Procedure::
752 * Pragma Initialize_Scalars::
753 * Pragma Inline_Always::
754 * Pragma Inline_Generic::
756 * Pragma Interface_Name::
757 * Pragma Interrupt_Handler::
758 * Pragma Interrupt_State::
759 * Pragma Keep_Names::
762 * Pragma Linker_Alias::
763 * Pragma Linker_Constructor::
764 * Pragma Linker_Destructor::
765 * Pragma Linker_Section::
766 * Pragma Long_Float::
767 * Pragma Machine_Attribute::
769 * Pragma Main_Storage::
772 * Pragma No_Strict_Aliasing::
773 * Pragma Normalize_Scalars::
774 * Pragma Obsolescent::
775 * Pragma Optimize_Alignment::
777 * Pragma Persistent_BSS::
779 * Pragma Postcondition::
780 * Pragma Precondition::
781 * Pragma Profile (Ravenscar)::
782 * Pragma Profile (Restricted)::
783 * Pragma Psect_Object::
784 * Pragma Pure_Function::
785 * Pragma Restriction_Warnings::
787 * Pragma Source_File_Name::
788 * Pragma Source_File_Name_Project::
789 * Pragma Source_Reference::
790 * Pragma Stream_Convert::
791 * Pragma Style_Checks::
794 * Pragma Suppress_All::
795 * Pragma Suppress_Exception_Locations::
796 * Pragma Suppress_Initialization::
799 * Pragma Task_Storage::
800 * Pragma Thread_Local_Storage::
801 * Pragma Time_Slice::
803 * Pragma Unchecked_Union::
804 * Pragma Unimplemented_Unit::
805 * Pragma Universal_Aliasing ::
806 * Pragma Universal_Data::
807 * Pragma Unmodified::
808 * Pragma Unreferenced::
809 * Pragma Unreferenced_Objects::
810 * Pragma Unreserve_All_Interrupts::
811 * Pragma Unsuppress::
812 * Pragma Use_VADS_Size::
813 * Pragma Validity_Checks::
816 * Pragma Weak_External::
817 * Pragma Wide_Character_Encoding::
820 @node Pragma Abort_Defer
821 @unnumberedsec Pragma Abort_Defer
823 @cindex Deferring aborts
831 This pragma must appear at the start of the statement sequence of a
832 handled sequence of statements (right after the @code{begin}). It has
833 the effect of deferring aborts for the sequence of statements (but not
834 for the declarations or handlers, if any, associated with this statement
838 @unnumberedsec Pragma Ada_83
847 A configuration pragma that establishes Ada 83 mode for the unit to
848 which it applies, regardless of the mode set by the command line
849 switches. In Ada 83 mode, GNAT attempts to be as compatible with
850 the syntax and semantics of Ada 83, as defined in the original Ada
851 83 Reference Manual as possible. In particular, the keywords added by Ada 95
852 and Ada 2005 are not recognized, optional package bodies are allowed,
853 and generics may name types with unknown discriminants without using
854 the @code{(<>)} notation. In addition, some but not all of the additional
855 restrictions of Ada 83 are enforced.
857 Ada 83 mode is intended for two purposes. Firstly, it allows existing
858 Ada 83 code to be compiled and adapted to GNAT with less effort.
859 Secondly, it aids in keeping code backwards compatible with Ada 83.
860 However, there is no guarantee that code that is processed correctly
861 by GNAT in Ada 83 mode will in fact compile and execute with an Ada
862 83 compiler, since GNAT does not enforce all the additional checks
866 @unnumberedsec Pragma Ada_95
875 A configuration pragma that establishes Ada 95 mode for the unit to which
876 it applies, regardless of the mode set by the command line switches.
877 This mode is set automatically for the @code{Ada} and @code{System}
878 packages and their children, so you need not specify it in these
879 contexts. This pragma is useful when writing a reusable component that
880 itself uses Ada 95 features, but which is intended to be usable from
881 either Ada 83 or Ada 95 programs.
884 @unnumberedsec Pragma Ada_05
893 A configuration pragma that establishes Ada 2005 mode for the unit to which
894 it applies, regardless of the mode set by the command line switches.
895 This mode is set automatically for the @code{Ada} and @code{System}
896 packages and their children, so you need not specify it in these
897 contexts. This pragma is useful when writing a reusable component that
898 itself uses Ada 2005 features, but which is intended to be usable from
899 either Ada 83 or Ada 95 programs.
901 @node Pragma Ada_2005
902 @unnumberedsec Pragma Ada_2005
911 This configuration pragma is a synonym for pragma Ada_05 and has the
912 same syntax and effect.
914 @node Pragma Annotate
915 @unnumberedsec Pragma Annotate
920 pragma Annotate (IDENTIFIER @{, ARG@});
922 ARG ::= NAME | EXPRESSION
926 This pragma is used to annotate programs. @var{identifier} identifies
927 the type of annotation. GNAT verifies that it is an identifier, but does
928 not otherwise analyze it. The @var{arg} argument
929 can be either a string literal or an
930 expression. String literals are assumed to be of type
931 @code{Standard.String}. Names of entities are simply analyzed as entity
932 names. All other expressions are analyzed as expressions, and must be
935 The analyzed pragma is retained in the tree, but not otherwise processed
936 by any part of the GNAT compiler. This pragma is intended for use by
937 external tools, including ASIS@.
940 @unnumberedsec Pragma Assert
947 [, string_EXPRESSION]);
951 The effect of this pragma depends on whether the corresponding command
952 line switch is set to activate assertions. The pragma expands into code
953 equivalent to the following:
956 if assertions-enabled then
957 if not boolean_EXPRESSION then
958 System.Assertions.Raise_Assert_Failure
965 The string argument, if given, is the message that will be associated
966 with the exception occurrence if the exception is raised. If no second
967 argument is given, the default message is @samp{@var{file}:@var{nnn}},
968 where @var{file} is the name of the source file containing the assert,
969 and @var{nnn} is the line number of the assert. A pragma is not a
970 statement, so if a statement sequence contains nothing but a pragma
971 assert, then a null statement is required in addition, as in:
976 pragma Assert (K > 3, "Bad value for K");
982 Note that, as with the @code{if} statement to which it is equivalent, the
983 type of the expression is either @code{Standard.Boolean}, or any type derived
984 from this standard type.
986 If assertions are disabled (switch @option{-gnata} not used), then there
987 is no run-time effect (and in particular, any side effects from the
988 expression will not occur at run time). (The expression is still
989 analyzed at compile time, and may cause types to be frozen if they are
990 mentioned here for the first time).
992 If assertions are enabled, then the given expression is tested, and if
993 it is @code{False} then @code{System.Assertions.Raise_Assert_Failure} is called
994 which results in the raising of @code{Assert_Failure} with the given message.
996 You should generally avoid side effects in the expression arguments of
997 this pragma, because these side effects will turn on and off with the
998 setting of the assertions mode, resulting in assertions that have an
999 effect on the program. However, the expressions are analyzed for
1000 semantic correctness whether or not assertions are enabled, so turning
1001 assertions on and off cannot affect the legality of a program.
1003 @node Pragma Assume_No_Invalid_Values
1004 @unnumberedsec Pragma Assume_No_Invalid_Values
1005 @findex Assume_No_Invalid_Values
1006 @cindex Invalid representations
1007 @cindex Invalid values
1010 @smallexample @c ada
1011 pragma Assume_No_Invalid_Values (On | Off);
1015 This is a configuration pragma that controls the assumptions made by the
1016 compiler about the occurrence of invalid representations (invalid values)
1019 The default behavior (corresponding to an Off argument for this pragma), is
1020 to assume that values may in general be invalid unless the compiler can
1021 prove they are valid. Consider the following example:
1023 @smallexample @c ada
1024 V1 : Integer range 1 .. 10;
1025 V2 : Integer range 11 .. 20;
1027 for J in V2 .. V1 loop
1033 if V1 and V2 have valid values, then the loop is known at compile
1034 time not to execute since the lower bound must be greater than the
1035 upper bound. However in default mode, no such assumption is made,
1036 and the loop may execute. If @code{Assume_No_Invalid_Values (On)}
1037 is given, the compiler will assume that any occurrence of a variable
1038 other than in an explicit @code{'Valid} test always has a valid
1039 value, and the loop above will be optimized away.
1041 The use of @code{Assume_No_Invalid_Values (On)} is appropriate if
1042 you know your code is free of uninitialized variables and other
1043 possible sources of invalid representations, and may result in
1044 more efficient code.
1046 @node Pragma Ast_Entry
1047 @unnumberedsec Pragma Ast_Entry
1052 @smallexample @c ada
1053 pragma AST_Entry (entry_IDENTIFIER);
1057 This pragma is implemented only in the OpenVMS implementation of GNAT@. The
1058 argument is the simple name of a single entry; at most one @code{AST_Entry}
1059 pragma is allowed for any given entry. This pragma must be used in
1060 conjunction with the @code{AST_Entry} attribute, and is only allowed after
1061 the entry declaration and in the same task type specification or single task
1062 as the entry to which it applies. This pragma specifies that the given entry
1063 may be used to handle an OpenVMS asynchronous system trap (@code{AST})
1064 resulting from an OpenVMS system service call. The pragma does not affect
1065 normal use of the entry. For further details on this pragma, see the
1066 DEC Ada Language Reference Manual, section 9.12a.
1068 @node Pragma C_Pass_By_Copy
1069 @unnumberedsec Pragma C_Pass_By_Copy
1070 @cindex Passing by copy
1071 @findex C_Pass_By_Copy
1074 @smallexample @c ada
1075 pragma C_Pass_By_Copy
1076 ([Max_Size =>] static_integer_EXPRESSION);
1080 Normally the default mechanism for passing C convention records to C
1081 convention subprograms is to pass them by reference, as suggested by RM
1082 B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
1083 this default, by requiring that record formal parameters be passed by
1084 copy if all of the following conditions are met:
1088 The size of the record type does not exceed the value specified for
1091 The record type has @code{Convention C}.
1093 The formal parameter has this record type, and the subprogram has a
1094 foreign (non-Ada) convention.
1098 If these conditions are met the argument is passed by copy, i.e.@: in a
1099 manner consistent with what C expects if the corresponding formal in the
1100 C prototype is a struct (rather than a pointer to a struct).
1102 You can also pass records by copy by specifying the convention
1103 @code{C_Pass_By_Copy} for the record type, or by using the extended
1104 @code{Import} and @code{Export} pragmas, which allow specification of
1105 passing mechanisms on a parameter by parameter basis.
1108 @unnumberedsec Pragma Check
1110 @cindex Named assertions
1114 @smallexample @c ada
1116 [Name =>] Identifier,
1117 [Check =>] Boolean_EXPRESSION
1118 [, [Message =>] string_EXPRESSION] );
1122 This pragma is similar to the predefined pragma @code{Assert} except that an
1123 extra identifier argument is present. In conjunction with pragma
1124 @code{Check_Policy}, this can be used to define groups of assertions that can
1125 be independently controlled. The identifier @code{Assertion} is special, it
1126 refers to the normal set of pragma @code{Assert} statements. The identifiers
1127 @code{Precondition} and @code{Postcondition} correspond to the pragmas of these
1128 names, so these three names would normally not be used directly in a pragma
1131 Checks introduced by this pragma are normally deactivated by default. They can
1132 be activated either by the command line option @option{-gnata}, which turns on
1133 all checks, or individually controlled using pragma @code{Check_Policy}.
1135 @node Pragma Check_Name
1136 @unnumberedsec Pragma Check_Name
1137 @cindex Defining check names
1138 @cindex Check names, defining
1142 @smallexample @c ada
1143 pragma Check_Name (check_name_IDENTIFIER);
1147 This is a configuration pragma that defines a new implementation
1148 defined check name (unless IDENTIFIER matches one of the predefined
1149 check names, in which case the pragma has no effect). Check names
1150 are global to a partition, so if two or more configuration pragmas
1151 are present in a partition mentioning the same name, only one new
1152 check name is introduced.
1154 An implementation defined check name introduced with this pragma may
1155 be used in only three contexts: @code{pragma Suppress},
1156 @code{pragma Unsuppress},
1157 and as the prefix of a @code{Check_Name'Enabled} attribute reference. For
1158 any of these three cases, the check name must be visible. A check
1159 name is visible if it is in the configuration pragmas applying to
1160 the current unit, or if it appears at the start of any unit that
1161 is part of the dependency set of the current unit (e.g., units that
1162 are mentioned in @code{with} clauses).
1164 @node Pragma Check_Policy
1165 @unnumberedsec Pragma Check_Policy
1166 @cindex Controlling assertions
1167 @cindex Assertions, control
1168 @cindex Check pragma control
1169 @cindex Named assertions
1173 @smallexample @c ada
1175 ([Name =>] Identifier,
1176 [Policy =>] POLICY_IDENTIFIER);
1178 POLICY_IDENTIFIER ::= On | Off | Check | Ignore
1182 This pragma is similar to the predefined pragma @code{Assertion_Policy},
1183 except that it controls sets of named assertions introduced using the
1184 @code{Check} pragmas. It can be used as a configuration pragma or (unlike
1185 @code{Assertion_Policy}) can be used within a declarative part, in which case
1186 it controls the status to the end of the corresponding construct (in a manner
1187 identical to pragma @code{Suppress)}.
1189 The identifier given as the first argument corresponds to a name used in
1190 associated @code{Check} pragmas. For example, if the pragma:
1192 @smallexample @c ada
1193 pragma Check_Policy (Critical_Error, Off);
1197 is given, then subsequent @code{Check} pragmas whose first argument is also
1198 @code{Critical_Error} will be disabled. The special identifier @code{Assertion}
1199 controls the behavior of normal @code{Assert} pragmas (thus a pragma
1200 @code{Check_Policy} with this identifier is similar to the normal
1201 @code{Assertion_Policy} pragma except that it can appear within a
1204 The special identifiers @code{Precondition} and @code{Postcondition} control
1205 the status of preconditions and postconditions. If a @code{Precondition} pragma
1206 is encountered, it is ignored if turned off by a @code{Check_Policy} specifying
1207 that @code{Precondition} checks are @code{Off} or @code{Ignored}. Similarly use
1208 of the name @code{Postcondition} controls whether @code{Postcondition} pragmas
1211 The check policy is @code{Off} to turn off corresponding checks, and @code{On}
1212 to turn on corresponding checks. The default for a set of checks for which no
1213 @code{Check_Policy} is given is @code{Off} unless the compiler switch
1214 @option{-gnata} is given, which turns on all checks by default.
1216 The check policy settings @code{Check} and @code{Ignore} are also recognized
1217 as synonyms for @code{On} and @code{Off}. These synonyms are provided for
1218 compatibility with the standard @code{Assertion_Policy} pragma.
1220 @node Pragma Comment
1221 @unnumberedsec Pragma Comment
1226 @smallexample @c ada
1227 pragma Comment (static_string_EXPRESSION);
1231 This is almost identical in effect to pragma @code{Ident}. It allows the
1232 placement of a comment into the object file and hence into the
1233 executable file if the operating system permits such usage. The
1234 difference is that @code{Comment}, unlike @code{Ident}, has
1235 no limitations on placement of the pragma (it can be placed
1236 anywhere in the main source unit), and if more than one pragma
1237 is used, all comments are retained.
1239 @node Pragma Common_Object
1240 @unnumberedsec Pragma Common_Object
1241 @findex Common_Object
1245 @smallexample @c ada
1246 pragma Common_Object (
1247 [Internal =>] LOCAL_NAME
1248 [, [External =>] EXTERNAL_SYMBOL]
1249 [, [Size =>] EXTERNAL_SYMBOL] );
1253 | static_string_EXPRESSION
1257 This pragma enables the shared use of variables stored in overlaid
1258 linker areas corresponding to the use of @code{COMMON}
1259 in Fortran. The single
1260 object @var{LOCAL_NAME} is assigned to the area designated by
1261 the @var{External} argument.
1262 You may define a record to correspond to a series
1263 of fields. The @var{Size} argument
1264 is syntax checked in GNAT, but otherwise ignored.
1266 @code{Common_Object} is not supported on all platforms. If no
1267 support is available, then the code generator will issue a message
1268 indicating that the necessary attribute for implementation of this
1269 pragma is not available.
1271 @node Pragma Compile_Time_Error
1272 @unnumberedsec Pragma Compile_Time_Error
1273 @findex Compile_Time_Error
1277 @smallexample @c ada
1278 pragma Compile_Time_Error
1279 (boolean_EXPRESSION, static_string_EXPRESSION);
1283 This pragma can be used to generate additional compile time
1285 is particularly useful in generics, where errors can be issued for
1286 specific problematic instantiations. The first parameter is a boolean
1287 expression. The pragma is effective only if the value of this expression
1288 is known at compile time, and has the value True. The set of expressions
1289 whose values are known at compile time includes all static boolean
1290 expressions, and also other values which the compiler can determine
1291 at compile time (e.g., the size of a record type set by an explicit
1292 size representation clause, or the value of a variable which was
1293 initialized to a constant and is known not to have been modified).
1294 If these conditions are met, an error message is generated using
1295 the value given as the second argument. This string value may contain
1296 embedded ASCII.LF characters to break the message into multiple lines.
1298 @node Pragma Compile_Time_Warning
1299 @unnumberedsec Pragma Compile_Time_Warning
1300 @findex Compile_Time_Warning
1304 @smallexample @c ada
1305 pragma Compile_Time_Warning
1306 (boolean_EXPRESSION, static_string_EXPRESSION);
1310 Same as pragma Compile_Time_Error, except a warning is issued instead
1311 of an error message. Note that if this pragma is used in a package that
1312 is with'ed by a client, the client will get the warning even though it
1313 is issued by a with'ed package (normally warnings in with'ed units are
1314 suppressed, but this is a special exception to that rule).
1316 One typical use is within a generic where compile time known characteristics
1317 of formal parameters are tested, and warnings given appropriately. Another use
1318 with a first parameter of True is to warn a client about use of a package,
1319 for example that it is not fully implemented.
1321 @node Pragma Complete_Representation
1322 @unnumberedsec Pragma Complete_Representation
1323 @findex Complete_Representation
1327 @smallexample @c ada
1328 pragma Complete_Representation;
1332 This pragma must appear immediately within a record representation
1333 clause. Typical placements are before the first component clause
1334 or after the last component clause. The effect is to give an error
1335 message if any component is missing a component clause. This pragma
1336 may be used to ensure that a record representation clause is
1337 complete, and that this invariant is maintained if fields are
1338 added to the record in the future.
1340 @node Pragma Complex_Representation
1341 @unnumberedsec Pragma Complex_Representation
1342 @findex Complex_Representation
1346 @smallexample @c ada
1347 pragma Complex_Representation
1348 ([Entity =>] LOCAL_NAME);
1352 The @var{Entity} argument must be the name of a record type which has
1353 two fields of the same floating-point type. The effect of this pragma is
1354 to force gcc to use the special internal complex representation form for
1355 this record, which may be more efficient. Note that this may result in
1356 the code for this type not conforming to standard ABI (application
1357 binary interface) requirements for the handling of record types. For
1358 example, in some environments, there is a requirement for passing
1359 records by pointer, and the use of this pragma may result in passing
1360 this type in floating-point registers.
1362 @node Pragma Component_Alignment
1363 @unnumberedsec Pragma Component_Alignment
1364 @cindex Alignments of components
1365 @findex Component_Alignment
1369 @smallexample @c ada
1370 pragma Component_Alignment (
1371 [Form =>] ALIGNMENT_CHOICE
1372 [, [Name =>] type_LOCAL_NAME]);
1374 ALIGNMENT_CHOICE ::=
1382 Specifies the alignment of components in array or record types.
1383 The meaning of the @var{Form} argument is as follows:
1386 @findex Component_Size
1387 @item Component_Size
1388 Aligns scalar components and subcomponents of the array or record type
1389 on boundaries appropriate to their inherent size (naturally
1390 aligned). For example, 1-byte components are aligned on byte boundaries,
1391 2-byte integer components are aligned on 2-byte boundaries, 4-byte
1392 integer components are aligned on 4-byte boundaries and so on. These
1393 alignment rules correspond to the normal rules for C compilers on all
1394 machines except the VAX@.
1396 @findex Component_Size_4
1397 @item Component_Size_4
1398 Naturally aligns components with a size of four or fewer
1399 bytes. Components that are larger than 4 bytes are placed on the next
1402 @findex Storage_Unit
1404 Specifies that array or record components are byte aligned, i.e.@:
1405 aligned on boundaries determined by the value of the constant
1406 @code{System.Storage_Unit}.
1410 Specifies that array or record components are aligned on default
1411 boundaries, appropriate to the underlying hardware or operating system or
1412 both. For OpenVMS VAX systems, the @code{Default} choice is the same as
1413 the @code{Storage_Unit} choice (byte alignment). For all other systems,
1414 the @code{Default} choice is the same as @code{Component_Size} (natural
1419 If the @code{Name} parameter is present, @var{type_LOCAL_NAME} must
1420 refer to a local record or array type, and the specified alignment
1421 choice applies to the specified type. The use of
1422 @code{Component_Alignment} together with a pragma @code{Pack} causes the
1423 @code{Component_Alignment} pragma to be ignored. The use of
1424 @code{Component_Alignment} together with a record representation clause
1425 is only effective for fields not specified by the representation clause.
1427 If the @code{Name} parameter is absent, the pragma can be used as either
1428 a configuration pragma, in which case it applies to one or more units in
1429 accordance with the normal rules for configuration pragmas, or it can be
1430 used within a declarative part, in which case it applies to types that
1431 are declared within this declarative part, or within any nested scope
1432 within this declarative part. In either case it specifies the alignment
1433 to be applied to any record or array type which has otherwise standard
1436 If the alignment for a record or array type is not specified (using
1437 pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
1438 clause), the GNAT uses the default alignment as described previously.
1440 @node Pragma Convention_Identifier
1441 @unnumberedsec Pragma Convention_Identifier
1442 @findex Convention_Identifier
1443 @cindex Conventions, synonyms
1447 @smallexample @c ada
1448 pragma Convention_Identifier (
1449 [Name =>] IDENTIFIER,
1450 [Convention =>] convention_IDENTIFIER);
1454 This pragma provides a mechanism for supplying synonyms for existing
1455 convention identifiers. The @code{Name} identifier can subsequently
1456 be used as a synonym for the given convention in other pragmas (including
1457 for example pragma @code{Import} or another @code{Convention_Identifier}
1458 pragma). As an example of the use of this, suppose you had legacy code
1459 which used Fortran77 as the identifier for Fortran. Then the pragma:
1461 @smallexample @c ada
1462 pragma Convention_Identifier (Fortran77, Fortran);
1466 would allow the use of the convention identifier @code{Fortran77} in
1467 subsequent code, avoiding the need to modify the sources. As another
1468 example, you could use this to parametrize convention requirements
1469 according to systems. Suppose you needed to use @code{Stdcall} on
1470 windows systems, and @code{C} on some other system, then you could
1471 define a convention identifier @code{Library} and use a single
1472 @code{Convention_Identifier} pragma to specify which convention
1473 would be used system-wide.
1475 @node Pragma CPP_Class
1476 @unnumberedsec Pragma CPP_Class
1478 @cindex Interfacing with C++
1482 @smallexample @c ada
1483 pragma CPP_Class ([Entity =>] LOCAL_NAME);
1487 The argument denotes an entity in the current declarative region that is
1488 declared as a tagged record type. It indicates that the type corresponds
1489 to an externally declared C++ class type, and is to be laid out the same
1490 way that C++ would lay out the type.
1492 Types for which @code{CPP_Class} is specified do not have assignment or
1493 equality operators defined (such operations can be imported or declared
1494 as subprograms as required). Initialization is allowed only by constructor
1495 functions (see pragma @code{CPP_Constructor}). Such types are implicitly
1496 limited if not explicitly declared as limited or derived from a limited
1497 type, and a warning is issued in that case.
1499 Pragma @code{CPP_Class} is intended primarily for automatic generation
1500 using an automatic binding generator tool.
1501 See @ref{Interfacing to C++} for related information.
1503 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
1504 for backward compatibility but its functionality is available
1505 using pragma @code{Import} with @code{Convention} = @code{CPP}.
1507 @node Pragma CPP_Constructor
1508 @unnumberedsec Pragma CPP_Constructor
1509 @cindex Interfacing with C++
1510 @findex CPP_Constructor
1514 @smallexample @c ada
1515 pragma CPP_Constructor ([Entity =>] LOCAL_NAME
1516 [, [External_Name =>] static_string_EXPRESSION ]
1517 [, [Link_Name =>] static_string_EXPRESSION ]);
1521 This pragma identifies an imported function (imported in the usual way
1522 with pragma @code{Import}) as corresponding to a C++ constructor. If
1523 @code{External_Name} and @code{Link_Name} are not specified then the
1524 @code{Entity} argument is a name that must have been previously mentioned
1525 in a pragma @code{Import} with @code{Convention} = @code{CPP}. Such name
1526 must be of one of the following forms:
1530 @code{function @var{Fname} return @var{T}'Class}
1533 @code{function @var{Fname} (@dots{}) return @var{T}'Class}
1537 where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.
1539 The first form is the default constructor, used when an object of type
1540 @var{T} is created on the Ada side with no explicit constructor. Other
1541 constructors (including the copy constructor, which is simply a special
1542 case of the second form in which the one and only argument is of type
1543 @var{T}), can only appear in two contexts:
1547 On the right side of an initialization of an object of type @var{T}.
1549 In an extension aggregate for an object of a type derived from @var{T}.
1553 Although the constructor is described as a function that returns a value
1554 on the Ada side, it is typically a procedure with an extra implicit
1555 argument (the object being initialized) at the implementation
1556 level. GNAT issues the appropriate call, whatever it is, to get the
1557 object properly initialized.
1559 In the case of derived objects, you may use one of two possible forms
1560 for declaring and creating an object:
1563 @item @code{New_Object : Derived_T}
1564 @item @code{New_Object : Derived_T := (@var{constructor-call with} @dots{})}
1568 In the first case the default constructor is called and extension fields
1569 if any are initialized according to the default initialization
1570 expressions in the Ada declaration. In the second case, the given
1571 constructor is called and the extension aggregate indicates the explicit
1572 values of the extension fields.
1574 If no constructors are imported, it is impossible to create any objects
1575 on the Ada side. If no default constructor is imported, only the
1576 initialization forms using an explicit call to a constructor are
1579 Pragma @code{CPP_Constructor} is intended primarily for automatic generation
1580 using an automatic binding generator tool.
1581 See @ref{Interfacing to C++} for more related information.
1583 @node Pragma CPP_Virtual
1584 @unnumberedsec Pragma CPP_Virtual
1585 @cindex Interfacing to C++
1588 This pragma is now obsolete has has no effect because GNAT generates
1589 the same object layout than the G++ compiler.
1591 See @ref{Interfacing to C++} for related information.
1593 @node Pragma CPP_Vtable
1594 @unnumberedsec Pragma CPP_Vtable
1595 @cindex Interfacing with C++
1598 This pragma is now obsolete has has no effect because GNAT generates
1599 the same object layout than the G++ compiler.
1601 See @ref{Interfacing to C++} for related information.
1604 @unnumberedsec Pragma Debug
1609 @smallexample @c ada
1610 pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON);
1612 PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
1614 | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
1618 The procedure call argument has the syntactic form of an expression, meeting
1619 the syntactic requirements for pragmas.
1621 If debug pragmas are not enabled or if the condition is present and evaluates
1622 to False, this pragma has no effect. If debug pragmas are enabled, the
1623 semantics of the pragma is exactly equivalent to the procedure call statement
1624 corresponding to the argument with a terminating semicolon. Pragmas are
1625 permitted in sequences of declarations, so you can use pragma @code{Debug} to
1626 intersperse calls to debug procedures in the middle of declarations. Debug
1627 pragmas can be enabled either by use of the command line switch @option{-gnata}
1628 or by use of the configuration pragma @code{Debug_Policy}.
1630 @node Pragma Debug_Policy
1631 @unnumberedsec Pragma Debug_Policy
1632 @findex Debug_Policy
1636 @smallexample @c ada
1637 pragma Debug_Policy (CHECK | IGNORE);
1641 If the argument is @code{CHECK}, then pragma @code{DEBUG} is enabled.
1642 If the argument is @code{IGNORE}, then pragma @code{DEBUG} is ignored.
1643 This pragma overrides the effect of the @option{-gnata} switch on the
1646 @node Pragma Detect_Blocking
1647 @unnumberedsec Pragma Detect_Blocking
1648 @findex Detect_Blocking
1652 @smallexample @c ada
1653 pragma Detect_Blocking;
1657 This is a configuration pragma that forces the detection of potentially
1658 blocking operations within a protected operation, and to raise Program_Error
1661 @node Pragma Elaboration_Checks
1662 @unnumberedsec Pragma Elaboration_Checks
1663 @cindex Elaboration control
1664 @findex Elaboration_Checks
1668 @smallexample @c ada
1669 pragma Elaboration_Checks (Dynamic | Static);
1673 This is a configuration pragma that provides control over the
1674 elaboration model used by the compilation affected by the
1675 pragma. If the parameter is @code{Dynamic},
1676 then the dynamic elaboration
1677 model described in the Ada Reference Manual is used, as though
1678 the @option{-gnatE} switch had been specified on the command
1679 line. If the parameter is @code{Static}, then the default GNAT static
1680 model is used. This configuration pragma overrides the setting
1681 of the command line. For full details on the elaboration models
1682 used by the GNAT compiler, see @ref{Elaboration Order Handling in GNAT,,,
1683 gnat_ugn, @value{EDITION} User's Guide}.
1685 @node Pragma Eliminate
1686 @unnumberedsec Pragma Eliminate
1687 @cindex Elimination of unused subprograms
1692 @smallexample @c ada
1694 [Unit_Name =>] IDENTIFIER |
1695 SELECTED_COMPONENT);
1698 [Unit_Name =>] IDENTIFIER |
1700 [Entity =>] IDENTIFIER |
1701 SELECTED_COMPONENT |
1703 [,OVERLOADING_RESOLUTION]);
1705 OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
1708 PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
1711 PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES
1713 FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
1714 Result_Type => result_SUBTYPE_NAME]
1716 PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
1717 SUBTYPE_NAME ::= STRING_VALUE
1719 SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
1720 SOURCE_TRACE ::= STRING_VALUE
1722 STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
1726 This pragma indicates that the given entity is not used outside the
1727 compilation unit it is defined in. The entity must be an explicitly declared
1728 subprogram; this includes generic subprogram instances and
1729 subprograms declared in generic package instances.
1731 If the entity to be eliminated is a library level subprogram, then
1732 the first form of pragma @code{Eliminate} is used with only a single argument.
1733 In this form, the @code{Unit_Name} argument specifies the name of the
1734 library level unit to be eliminated.
1736 In all other cases, both @code{Unit_Name} and @code{Entity} arguments
1737 are required. If item is an entity of a library package, then the first
1738 argument specifies the unit name, and the second argument specifies
1739 the particular entity. If the second argument is in string form, it must
1740 correspond to the internal manner in which GNAT stores entity names (see
1741 compilation unit Namet in the compiler sources for details).
1743 The remaining parameters (OVERLOADING_RESOLUTION) are optionally used
1744 to distinguish between overloaded subprograms. If a pragma does not contain
1745 the OVERLOADING_RESOLUTION parameter(s), it is applied to all the overloaded
1746 subprograms denoted by the first two parameters.
1748 Use PARAMETER_AND_RESULT_TYPE_PROFILE to specify the profile of the subprogram
1749 to be eliminated in a manner similar to that used for the extended
1750 @code{Import} and @code{Export} pragmas, except that the subtype names are
1751 always given as strings. At the moment, this form of distinguishing
1752 overloaded subprograms is implemented only partially, so we do not recommend
1753 using it for practical subprogram elimination.
1755 Note that in case of a parameterless procedure its profile is represented
1756 as @code{Parameter_Types => ("")}
1758 Alternatively, the @code{Source_Location} parameter is used to specify
1759 which overloaded alternative is to be eliminated by pointing to the
1760 location of the DEFINING_PROGRAM_UNIT_NAME of this subprogram in the
1761 source text. The string literal (or concatenation of string literals)
1762 given as SOURCE_TRACE must have the following format:
1764 @smallexample @c ada
1765 SOURCE_TRACE ::= SOURCE_LOCATION@{LBRACKET SOURCE_LOCATION RBRACKET@}
1770 SOURCE_LOCATION ::= FILE_NAME:LINE_NUMBER
1771 FILE_NAME ::= STRING_LITERAL
1772 LINE_NUMBER ::= DIGIT @{DIGIT@}
1775 SOURCE_TRACE should be the short name of the source file (with no directory
1776 information), and LINE_NUMBER is supposed to point to the line where the
1777 defining name of the subprogram is located.
1779 For the subprograms that are not a part of generic instantiations, only one
1780 SOURCE_LOCATION is used. If a subprogram is declared in a package
1781 instantiation, SOURCE_TRACE contains two SOURCE_LOCATIONs, the first one is
1782 the location of the (DEFINING_PROGRAM_UNIT_NAME of the) instantiation, and the
1783 second one denotes the declaration of the corresponding subprogram in the
1784 generic package. This approach is recursively used to create SOURCE_LOCATIONs
1785 in case of nested instantiations.
1787 The effect of the pragma is to allow the compiler to eliminate
1788 the code or data associated with the named entity. Any reference to
1789 an eliminated entity outside the compilation unit it is defined in,
1790 causes a compile time or link time error.
1792 The intention of pragma @code{Eliminate} is to allow a program to be compiled
1793 in a system independent manner, with unused entities eliminated, without
1794 the requirement of modifying the source text. Normally the required set
1795 of @code{Eliminate} pragmas is constructed automatically using the gnatelim
1796 tool. Elimination of unused entities local to a compilation unit is
1797 automatic, without requiring the use of pragma @code{Eliminate}.
1799 Note that the reason this pragma takes string literals where names might
1800 be expected is that a pragma @code{Eliminate} can appear in a context where the
1801 relevant names are not visible.
1803 Note that any change in the source files that includes removing, splitting of
1804 adding lines may make the set of Eliminate pragmas using SOURCE_LOCATION
1807 It is legal to use pragma Eliminate where the referenced entity is a
1808 dispatching operation, but it is not clear what this would mean, since
1809 in general the call does not know which entity is actually being called.
1810 Consequently, a pragma Eliminate for a dispatching operation is ignored.
1812 @node Pragma Export_Exception
1813 @unnumberedsec Pragma Export_Exception
1815 @findex Export_Exception
1819 @smallexample @c ada
1820 pragma Export_Exception (
1821 [Internal =>] LOCAL_NAME
1822 [, [External =>] EXTERNAL_SYMBOL]
1823 [, [Form =>] Ada | VMS]
1824 [, [Code =>] static_integer_EXPRESSION]);
1828 | static_string_EXPRESSION
1832 This pragma is implemented only in the OpenVMS implementation of GNAT@. It
1833 causes the specified exception to be propagated outside of the Ada program,
1834 so that it can be handled by programs written in other OpenVMS languages.
1835 This pragma establishes an external name for an Ada exception and makes the
1836 name available to the OpenVMS Linker as a global symbol. For further details
1837 on this pragma, see the
1838 DEC Ada Language Reference Manual, section 13.9a3.2.
1840 @node Pragma Export_Function
1841 @unnumberedsec Pragma Export_Function
1842 @cindex Argument passing mechanisms
1843 @findex Export_Function
1848 @smallexample @c ada
1849 pragma Export_Function (
1850 [Internal =>] LOCAL_NAME
1851 [, [External =>] EXTERNAL_SYMBOL]
1852 [, [Parameter_Types =>] PARAMETER_TYPES]
1853 [, [Result_Type =>] result_SUBTYPE_MARK]
1854 [, [Mechanism =>] MECHANISM]
1855 [, [Result_Mechanism =>] MECHANISM_NAME]);
1859 | static_string_EXPRESSION
1864 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1868 | subtype_Name ' Access
1872 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1874 MECHANISM_ASSOCIATION ::=
1875 [formal_parameter_NAME =>] MECHANISM_NAME
1880 | Descriptor [([Class =>] CLASS_NAME)]
1881 | Short_Descriptor [([Class =>] CLASS_NAME)]
1883 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1887 Use this pragma to make a function externally callable and optionally
1888 provide information on mechanisms to be used for passing parameter and
1889 result values. We recommend, for the purposes of improving portability,
1890 this pragma always be used in conjunction with a separate pragma
1891 @code{Export}, which must precede the pragma @code{Export_Function}.
1892 GNAT does not require a separate pragma @code{Export}, but if none is
1893 present, @code{Convention Ada} is assumed, which is usually
1894 not what is wanted, so it is usually appropriate to use this
1895 pragma in conjunction with a @code{Export} or @code{Convention}
1896 pragma that specifies the desired foreign convention.
1897 Pragma @code{Export_Function}
1898 (and @code{Export}, if present) must appear in the same declarative
1899 region as the function to which they apply.
1901 @var{internal_name} must uniquely designate the function to which the
1902 pragma applies. If more than one function name exists of this name in
1903 the declarative part you must use the @code{Parameter_Types} and
1904 @code{Result_Type} parameters is mandatory to achieve the required
1905 unique designation. @var{subtype_mark}s in these parameters must
1906 exactly match the subtypes in the corresponding function specification,
1907 using positional notation to match parameters with subtype marks.
1908 The form with an @code{'Access} attribute can be used to match an
1909 anonymous access parameter.
1912 @cindex Passing by descriptor
1913 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
1914 The default behavior for Export_Function is to accept either 64bit or
1915 32bit descriptors unless short_descriptor is specified, then only 32bit
1916 descriptors are accepted.
1918 @cindex Suppressing external name
1919 Special treatment is given if the EXTERNAL is an explicit null
1920 string or a static string expressions that evaluates to the null
1921 string. In this case, no external name is generated. This form
1922 still allows the specification of parameter mechanisms.
1924 @node Pragma Export_Object
1925 @unnumberedsec Pragma Export_Object
1926 @findex Export_Object
1930 @smallexample @c ada
1931 pragma Export_Object
1932 [Internal =>] LOCAL_NAME
1933 [, [External =>] EXTERNAL_SYMBOL]
1934 [, [Size =>] EXTERNAL_SYMBOL]
1938 | static_string_EXPRESSION
1942 This pragma designates an object as exported, and apart from the
1943 extended rules for external symbols, is identical in effect to the use of
1944 the normal @code{Export} pragma applied to an object. You may use a
1945 separate Export pragma (and you probably should from the point of view
1946 of portability), but it is not required. @var{Size} is syntax checked,
1947 but otherwise ignored by GNAT@.
1949 @node Pragma Export_Procedure
1950 @unnumberedsec Pragma Export_Procedure
1951 @findex Export_Procedure
1955 @smallexample @c ada
1956 pragma Export_Procedure (
1957 [Internal =>] LOCAL_NAME
1958 [, [External =>] EXTERNAL_SYMBOL]
1959 [, [Parameter_Types =>] PARAMETER_TYPES]
1960 [, [Mechanism =>] MECHANISM]);
1964 | static_string_EXPRESSION
1969 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1973 | subtype_Name ' Access
1977 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1979 MECHANISM_ASSOCIATION ::=
1980 [formal_parameter_NAME =>] MECHANISM_NAME
1985 | Descriptor [([Class =>] CLASS_NAME)]
1986 | Short_Descriptor [([Class =>] CLASS_NAME)]
1988 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1992 This pragma is identical to @code{Export_Function} except that it
1993 applies to a procedure rather than a function and the parameters
1994 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
1995 GNAT does not require a separate pragma @code{Export}, but if none is
1996 present, @code{Convention Ada} is assumed, which is usually
1997 not what is wanted, so it is usually appropriate to use this
1998 pragma in conjunction with a @code{Export} or @code{Convention}
1999 pragma that specifies the desired foreign convention.
2002 @cindex Passing by descriptor
2003 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2004 The default behavior for Export_Procedure is to accept either 64bit or
2005 32bit descriptors unless short_descriptor is specified, then only 32bit
2006 descriptors are accepted.
2008 @cindex Suppressing external name
2009 Special treatment is given if the EXTERNAL is an explicit null
2010 string or a static string expressions that evaluates to the null
2011 string. In this case, no external name is generated. This form
2012 still allows the specification of parameter mechanisms.
2014 @node Pragma Export_Value
2015 @unnumberedsec Pragma Export_Value
2016 @findex Export_Value
2020 @smallexample @c ada
2021 pragma Export_Value (
2022 [Value =>] static_integer_EXPRESSION,
2023 [Link_Name =>] static_string_EXPRESSION);
2027 This pragma serves to export a static integer value for external use.
2028 The first argument specifies the value to be exported. The Link_Name
2029 argument specifies the symbolic name to be associated with the integer
2030 value. This pragma is useful for defining a named static value in Ada
2031 that can be referenced in assembly language units to be linked with
2032 the application. This pragma is currently supported only for the
2033 AAMP target and is ignored for other targets.
2035 @node Pragma Export_Valued_Procedure
2036 @unnumberedsec Pragma Export_Valued_Procedure
2037 @findex Export_Valued_Procedure
2041 @smallexample @c ada
2042 pragma Export_Valued_Procedure (
2043 [Internal =>] LOCAL_NAME
2044 [, [External =>] EXTERNAL_SYMBOL]
2045 [, [Parameter_Types =>] PARAMETER_TYPES]
2046 [, [Mechanism =>] MECHANISM]);
2050 | static_string_EXPRESSION
2055 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2059 | subtype_Name ' Access
2063 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2065 MECHANISM_ASSOCIATION ::=
2066 [formal_parameter_NAME =>] MECHANISM_NAME
2071 | Descriptor [([Class =>] CLASS_NAME)]
2072 | Short_Descriptor [([Class =>] CLASS_NAME)]
2074 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
2078 This pragma is identical to @code{Export_Procedure} except that the
2079 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2080 mode @code{OUT}, and externally the subprogram is treated as a function
2081 with this parameter as the result of the function. GNAT provides for
2082 this capability to allow the use of @code{OUT} and @code{IN OUT}
2083 parameters in interfacing to external functions (which are not permitted
2085 GNAT does not require a separate pragma @code{Export}, but if none is
2086 present, @code{Convention Ada} is assumed, which is almost certainly
2087 not what is wanted since the whole point of this pragma is to interface
2088 with foreign language functions, so it is usually appropriate to use this
2089 pragma in conjunction with a @code{Export} or @code{Convention}
2090 pragma that specifies the desired foreign convention.
2093 @cindex Passing by descriptor
2094 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2095 The default behavior for Export_Valued_Procedure is to accept either 64bit or
2096 32bit descriptors unless short_descriptor is specified, then only 32bit
2097 descriptors are accepted.
2099 @cindex Suppressing external name
2100 Special treatment is given if the EXTERNAL is an explicit null
2101 string or a static string expressions that evaluates to the null
2102 string. In this case, no external name is generated. This form
2103 still allows the specification of parameter mechanisms.
2105 @node Pragma Extend_System
2106 @unnumberedsec Pragma Extend_System
2107 @cindex @code{system}, extending
2109 @findex Extend_System
2113 @smallexample @c ada
2114 pragma Extend_System ([Name =>] IDENTIFIER);
2118 This pragma is used to provide backwards compatibility with other
2119 implementations that extend the facilities of package @code{System}. In
2120 GNAT, @code{System} contains only the definitions that are present in
2121 the Ada RM@. However, other implementations, notably the DEC Ada 83
2122 implementation, provide many extensions to package @code{System}.
2124 For each such implementation accommodated by this pragma, GNAT provides a
2125 package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
2126 implementation, which provides the required additional definitions. You
2127 can use this package in two ways. You can @code{with} it in the normal
2128 way and access entities either by selection or using a @code{use}
2129 clause. In this case no special processing is required.
2131 However, if existing code contains references such as
2132 @code{System.@var{xxx}} where @var{xxx} is an entity in the extended
2133 definitions provided in package @code{System}, you may use this pragma
2134 to extend visibility in @code{System} in a non-standard way that
2135 provides greater compatibility with the existing code. Pragma
2136 @code{Extend_System} is a configuration pragma whose single argument is
2137 the name of the package containing the extended definition
2138 (e.g.@: @code{Aux_DEC} for the DEC Ada case). A unit compiled under
2139 control of this pragma will be processed using special visibility
2140 processing that looks in package @code{System.Aux_@var{xxx}} where
2141 @code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
2142 package @code{System}, but not found in package @code{System}.
2144 You can use this pragma either to access a predefined @code{System}
2145 extension supplied with the compiler, for example @code{Aux_DEC} or
2146 you can construct your own extension unit following the above
2147 definition. Note that such a package is a child of @code{System}
2148 and thus is considered part of the implementation. To compile
2149 it you will have to use the appropriate switch for compiling
2150 system units. @xref{Top, @value{EDITION} User's Guide, About This
2151 Guide,, gnat_ugn, @value{EDITION} User's Guide}, for details.
2153 @node Pragma External
2154 @unnumberedsec Pragma External
2159 @smallexample @c ada
2161 [ Convention =>] convention_IDENTIFIER,
2162 [ Entity =>] LOCAL_NAME
2163 [, [External_Name =>] static_string_EXPRESSION ]
2164 [, [Link_Name =>] static_string_EXPRESSION ]);
2168 This pragma is identical in syntax and semantics to pragma
2169 @code{Export} as defined in the Ada Reference Manual. It is
2170 provided for compatibility with some Ada 83 compilers that
2171 used this pragma for exactly the same purposes as pragma
2172 @code{Export} before the latter was standardized.
2174 @node Pragma External_Name_Casing
2175 @unnumberedsec Pragma External_Name_Casing
2176 @cindex Dec Ada 83 casing compatibility
2177 @cindex External Names, casing
2178 @cindex Casing of External names
2179 @findex External_Name_Casing
2183 @smallexample @c ada
2184 pragma External_Name_Casing (
2185 Uppercase | Lowercase
2186 [, Uppercase | Lowercase | As_Is]);
2190 This pragma provides control over the casing of external names associated
2191 with Import and Export pragmas. There are two cases to consider:
2194 @item Implicit external names
2195 Implicit external names are derived from identifiers. The most common case
2196 arises when a standard Ada Import or Export pragma is used with only two
2199 @smallexample @c ada
2200 pragma Import (C, C_Routine);
2204 Since Ada is a case-insensitive language, the spelling of the identifier in
2205 the Ada source program does not provide any information on the desired
2206 casing of the external name, and so a convention is needed. In GNAT the
2207 default treatment is that such names are converted to all lower case
2208 letters. This corresponds to the normal C style in many environments.
2209 The first argument of pragma @code{External_Name_Casing} can be used to
2210 control this treatment. If @code{Uppercase} is specified, then the name
2211 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2212 then the normal default of all lower case letters will be used.
2214 This same implicit treatment is also used in the case of extended DEC Ada 83
2215 compatible Import and Export pragmas where an external name is explicitly
2216 specified using an identifier rather than a string.
2218 @item Explicit external names
2219 Explicit external names are given as string literals. The most common case
2220 arises when a standard Ada Import or Export pragma is used with three
2223 @smallexample @c ada
2224 pragma Import (C, C_Routine, "C_routine");
2228 In this case, the string literal normally provides the exact casing required
2229 for the external name. The second argument of pragma
2230 @code{External_Name_Casing} may be used to modify this behavior.
2231 If @code{Uppercase} is specified, then the name
2232 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2233 then the name will be forced to all lowercase letters. A specification of
2234 @code{As_Is} provides the normal default behavior in which the casing is
2235 taken from the string provided.
2239 This pragma may appear anywhere that a pragma is valid. In particular, it
2240 can be used as a configuration pragma in the @file{gnat.adc} file, in which
2241 case it applies to all subsequent compilations, or it can be used as a program
2242 unit pragma, in which case it only applies to the current unit, or it can
2243 be used more locally to control individual Import/Export pragmas.
2245 It is primarily intended for use with OpenVMS systems, where many
2246 compilers convert all symbols to upper case by default. For interfacing to
2247 such compilers (e.g.@: the DEC C compiler), it may be convenient to use
2250 @smallexample @c ada
2251 pragma External_Name_Casing (Uppercase, Uppercase);
2255 to enforce the upper casing of all external symbols.
2257 @node Pragma Fast_Math
2258 @unnumberedsec Pragma Fast_Math
2263 @smallexample @c ada
2268 This is a configuration pragma which activates a mode in which speed is
2269 considered more important for floating-point operations than absolutely
2270 accurate adherence to the requirements of the standard. Currently the
2271 following operations are affected:
2274 @item Complex Multiplication
2275 The normal simple formula for complex multiplication can result in intermediate
2276 overflows for numbers near the end of the range. The Ada standard requires that
2277 this situation be detected and corrected by scaling, but in Fast_Math mode such
2278 cases will simply result in overflow. Note that to take advantage of this you
2279 must instantiate your own version of @code{Ada.Numerics.Generic_Complex_Types}
2280 under control of the pragma, rather than use the preinstantiated versions.
2283 @node Pragma Favor_Top_Level
2284 @unnumberedsec Pragma Favor_Top_Level
2285 @findex Favor_Top_Level
2289 @smallexample @c ada
2290 pragma Favor_Top_Level (type_NAME);
2294 The named type must be an access-to-subprogram type. This pragma is an
2295 efficiency hint to the compiler, regarding the use of 'Access or
2296 'Unrestricted_Access on nested (non-library-level) subprograms. The
2297 pragma means that nested subprograms are not used with this type, or
2298 are rare, so that the generated code should be efficient in the
2299 top-level case. When this pragma is used, dynamically generated
2300 trampolines may be used on some targets for nested subprograms.
2301 See also the No_Implicit_Dynamic_Code restriction.
2303 @node Pragma Finalize_Storage_Only
2304 @unnumberedsec Pragma Finalize_Storage_Only
2305 @findex Finalize_Storage_Only
2309 @smallexample @c ada
2310 pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
2314 This pragma allows the compiler not to emit a Finalize call for objects
2315 defined at the library level. This is mostly useful for types where
2316 finalization is only used to deal with storage reclamation since in most
2317 environments it is not necessary to reclaim memory just before terminating
2318 execution, hence the name.
2320 @node Pragma Float_Representation
2321 @unnumberedsec Pragma Float_Representation
2323 @findex Float_Representation
2327 @smallexample @c ada
2328 pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]);
2330 FLOAT_REP ::= VAX_Float | IEEE_Float
2334 In the one argument form, this pragma is a configuration pragma which
2335 allows control over the internal representation chosen for the predefined
2336 floating point types declared in the packages @code{Standard} and
2337 @code{System}. On all systems other than OpenVMS, the argument must
2338 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2339 argument may be @code{VAX_Float} to specify the use of the VAX float
2340 format for the floating-point types in Standard. This requires that
2341 the standard runtime libraries be recompiled. @xref{The GNAT Run-Time
2342 Library Builder gnatlbr,,, gnat_ugn, @value{EDITION} User's Guide
2343 OpenVMS}, for a description of the @code{GNAT LIBRARY} command.
2345 The two argument form specifies the representation to be used for
2346 the specified floating-point type. On all systems other than OpenVMS,
2348 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2349 argument may be @code{VAX_Float} to specify the use of the VAX float
2354 For digits values up to 6, F float format will be used.
2356 For digits values from 7 to 9, G float format will be used.
2358 For digits values from 10 to 15, F float format will be used.
2360 Digits values above 15 are not allowed.
2364 @unnumberedsec Pragma Ident
2369 @smallexample @c ada
2370 pragma Ident (static_string_EXPRESSION);
2374 This pragma provides a string identification in the generated object file,
2375 if the system supports the concept of this kind of identification string.
2376 This pragma is allowed only in the outermost declarative part or
2377 declarative items of a compilation unit. If more than one @code{Ident}
2378 pragma is given, only the last one processed is effective.
2380 On OpenVMS systems, the effect of the pragma is identical to the effect of
2381 the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
2382 maximum allowed length is 31 characters, so if it is important to
2383 maintain compatibility with this compiler, you should obey this length
2386 @node Pragma Implemented_By_Entry
2387 @unnumberedsec Pragma Implemented_By_Entry
2388 @findex Implemented_By_Entry
2392 @smallexample @c ada
2393 pragma Implemented_By_Entry (LOCAL_NAME);
2397 This is a representation pragma which applies to protected, synchronized and
2398 task interface primitives. If the pragma is applied to primitive operation Op
2399 of interface Iface, it is illegal to override Op in a type that implements
2400 Iface, with anything other than an entry.
2402 @smallexample @c ada
2403 type Iface is protected interface;
2404 procedure Do_Something (Object : in out Iface) is abstract;
2405 pragma Implemented_By_Entry (Do_Something);
2407 protected type P is new Iface with
2408 procedure Do_Something; -- Illegal
2411 task type T is new Iface with
2412 entry Do_Something; -- Legal
2417 NOTE: The pragma is still in its design stage by the Ada Rapporteur Group. It
2418 is intended to be used in conjunction with dispatching requeue statements as
2419 described in AI05-0030. Should the ARG decide on an official name and syntax,
2420 this pragma will become language-defined rather than GNAT-specific.
2422 @node Pragma Implicit_Packing
2423 @unnumberedsec Pragma Implicit_Packing
2424 @findex Implicit_Packing
2428 @smallexample @c ada
2429 pragma Implicit_Packing;
2433 This is a configuration pragma that requests implicit packing for packed
2434 arrays for which a size clause is given but no explicit pragma Pack or
2435 specification of Component_Size is present. Consider this example:
2437 @smallexample @c ada
2438 type R is array (0 .. 7) of Boolean;
2443 In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause
2444 does not change the layout of a composite object. So the Size clause in the
2445 above example is normally rejected, since the default layout of the array uses
2446 8-bit components, and thus the array requires a minimum of 64 bits.
2448 If this declaration is compiled in a region of code covered by an occurrence
2449 of the configuration pragma Implicit_Packing, then the Size clause in this
2450 and similar examples will cause implicit packing and thus be accepted. For
2451 this implicit packing to occur, the type in question must be an array of small
2452 components whose size is known at compile time, and the Size clause must
2453 specify the exact size that corresponds to the length of the array multiplied
2454 by the size in bits of the component type.
2455 @cindex Array packing
2457 @node Pragma Import_Exception
2458 @unnumberedsec Pragma Import_Exception
2460 @findex Import_Exception
2464 @smallexample @c ada
2465 pragma Import_Exception (
2466 [Internal =>] LOCAL_NAME
2467 [, [External =>] EXTERNAL_SYMBOL]
2468 [, [Form =>] Ada | VMS]
2469 [, [Code =>] static_integer_EXPRESSION]);
2473 | static_string_EXPRESSION
2477 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2478 It allows OpenVMS conditions (for example, from OpenVMS system services or
2479 other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
2480 The pragma specifies that the exception associated with an exception
2481 declaration in an Ada program be defined externally (in non-Ada code).
2482 For further details on this pragma, see the
2483 DEC Ada Language Reference Manual, section 13.9a.3.1.
2485 @node Pragma Import_Function
2486 @unnumberedsec Pragma Import_Function
2487 @findex Import_Function
2491 @smallexample @c ada
2492 pragma Import_Function (
2493 [Internal =>] LOCAL_NAME,
2494 [, [External =>] EXTERNAL_SYMBOL]
2495 [, [Parameter_Types =>] PARAMETER_TYPES]
2496 [, [Result_Type =>] SUBTYPE_MARK]
2497 [, [Mechanism =>] MECHANISM]
2498 [, [Result_Mechanism =>] MECHANISM_NAME]
2499 [, [First_Optional_Parameter =>] IDENTIFIER]);
2503 | static_string_EXPRESSION
2507 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2511 | subtype_Name ' Access
2515 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2517 MECHANISM_ASSOCIATION ::=
2518 [formal_parameter_NAME =>] MECHANISM_NAME
2523 | Descriptor [([Class =>] CLASS_NAME)]
2524 | Short_Descriptor [([Class =>] CLASS_NAME)]
2526 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2530 This pragma is used in conjunction with a pragma @code{Import} to
2531 specify additional information for an imported function. The pragma
2532 @code{Import} (or equivalent pragma @code{Interface}) must precede the
2533 @code{Import_Function} pragma and both must appear in the same
2534 declarative part as the function specification.
2536 The @var{Internal} argument must uniquely designate
2537 the function to which the
2538 pragma applies. If more than one function name exists of this name in
2539 the declarative part you must use the @code{Parameter_Types} and
2540 @var{Result_Type} parameters to achieve the required unique
2541 designation. Subtype marks in these parameters must exactly match the
2542 subtypes in the corresponding function specification, using positional
2543 notation to match parameters with subtype marks.
2544 The form with an @code{'Access} attribute can be used to match an
2545 anonymous access parameter.
2547 You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
2548 parameters to specify passing mechanisms for the
2549 parameters and result. If you specify a single mechanism name, it
2550 applies to all parameters. Otherwise you may specify a mechanism on a
2551 parameter by parameter basis using either positional or named
2552 notation. If the mechanism is not specified, the default mechanism
2556 @cindex Passing by descriptor
2557 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2558 The default behavior for Import_Function is to pass a 64bit descriptor
2559 unless short_descriptor is specified, then a 32bit descriptor is passed.
2561 @code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
2562 It specifies that the designated parameter and all following parameters
2563 are optional, meaning that they are not passed at the generated code
2564 level (this is distinct from the notion of optional parameters in Ada
2565 where the parameters are passed anyway with the designated optional
2566 parameters). All optional parameters must be of mode @code{IN} and have
2567 default parameter values that are either known at compile time
2568 expressions, or uses of the @code{'Null_Parameter} attribute.
2570 @node Pragma Import_Object
2571 @unnumberedsec Pragma Import_Object
2572 @findex Import_Object
2576 @smallexample @c ada
2577 pragma Import_Object
2578 [Internal =>] LOCAL_NAME
2579 [, [External =>] EXTERNAL_SYMBOL]
2580 [, [Size =>] EXTERNAL_SYMBOL]);
2584 | static_string_EXPRESSION
2588 This pragma designates an object as imported, and apart from the
2589 extended rules for external symbols, is identical in effect to the use of
2590 the normal @code{Import} pragma applied to an object. Unlike the
2591 subprogram case, you need not use a separate @code{Import} pragma,
2592 although you may do so (and probably should do so from a portability
2593 point of view). @var{size} is syntax checked, but otherwise ignored by
2596 @node Pragma Import_Procedure
2597 @unnumberedsec Pragma Import_Procedure
2598 @findex Import_Procedure
2602 @smallexample @c ada
2603 pragma Import_Procedure (
2604 [Internal =>] LOCAL_NAME
2605 [, [External =>] EXTERNAL_SYMBOL]
2606 [, [Parameter_Types =>] PARAMETER_TYPES]
2607 [, [Mechanism =>] MECHANISM]
2608 [, [First_Optional_Parameter =>] IDENTIFIER]);
2612 | static_string_EXPRESSION
2616 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2620 | subtype_Name ' Access
2624 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2626 MECHANISM_ASSOCIATION ::=
2627 [formal_parameter_NAME =>] MECHANISM_NAME
2632 | Descriptor [([Class =>] CLASS_NAME)]
2633 | Short_Descriptor [([Class =>] CLASS_NAME)]
2635 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2639 This pragma is identical to @code{Import_Function} except that it
2640 applies to a procedure rather than a function and the parameters
2641 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2643 @node Pragma Import_Valued_Procedure
2644 @unnumberedsec Pragma Import_Valued_Procedure
2645 @findex Import_Valued_Procedure
2649 @smallexample @c ada
2650 pragma Import_Valued_Procedure (
2651 [Internal =>] LOCAL_NAME
2652 [, [External =>] EXTERNAL_SYMBOL]
2653 [, [Parameter_Types =>] PARAMETER_TYPES]
2654 [, [Mechanism =>] MECHANISM]
2655 [, [First_Optional_Parameter =>] IDENTIFIER]);
2659 | static_string_EXPRESSION
2663 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2667 | subtype_Name ' Access
2671 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2673 MECHANISM_ASSOCIATION ::=
2674 [formal_parameter_NAME =>] MECHANISM_NAME
2679 | Descriptor [([Class =>] CLASS_NAME)]
2680 | Short_Descriptor [([Class =>] CLASS_NAME)]
2682 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2686 This pragma is identical to @code{Import_Procedure} except that the
2687 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2688 mode @code{OUT}, and externally the subprogram is treated as a function
2689 with this parameter as the result of the function. The purpose of this
2690 capability is to allow the use of @code{OUT} and @code{IN OUT}
2691 parameters in interfacing to external functions (which are not permitted
2692 in Ada functions). You may optionally use the @code{Mechanism}
2693 parameters to specify passing mechanisms for the parameters.
2694 If you specify a single mechanism name, it applies to all parameters.
2695 Otherwise you may specify a mechanism on a parameter by parameter
2696 basis using either positional or named notation. If the mechanism is not
2697 specified, the default mechanism is used.
2699 Note that it is important to use this pragma in conjunction with a separate
2700 pragma Import that specifies the desired convention, since otherwise the
2701 default convention is Ada, which is almost certainly not what is required.
2703 @node Pragma Initialize_Scalars
2704 @unnumberedsec Pragma Initialize_Scalars
2705 @findex Initialize_Scalars
2706 @cindex debugging with Initialize_Scalars
2710 @smallexample @c ada
2711 pragma Initialize_Scalars;
2715 This pragma is similar to @code{Normalize_Scalars} conceptually but has
2716 two important differences. First, there is no requirement for the pragma
2717 to be used uniformly in all units of a partition, in particular, it is fine
2718 to use this just for some or all of the application units of a partition,
2719 without needing to recompile the run-time library.
2721 In the case where some units are compiled with the pragma, and some without,
2722 then a declaration of a variable where the type is defined in package
2723 Standard or is locally declared will always be subject to initialization,
2724 as will any declaration of a scalar variable. For composite variables,
2725 whether the variable is initialized may also depend on whether the package
2726 in which the type of the variable is declared is compiled with the pragma.
2728 The other important difference is that you can control the value used
2729 for initializing scalar objects. At bind time, you can select several
2730 options for initialization. You can
2731 initialize with invalid values (similar to Normalize_Scalars, though for
2732 Initialize_Scalars it is not always possible to determine the invalid
2733 values in complex cases like signed component fields with non-standard
2734 sizes). You can also initialize with high or
2735 low values, or with a specified bit pattern. See the users guide for binder
2736 options for specifying these cases.
2738 This means that you can compile a program, and then without having to
2739 recompile the program, you can run it with different values being used
2740 for initializing otherwise uninitialized values, to test if your program
2741 behavior depends on the choice. Of course the behavior should not change,
2742 and if it does, then most likely you have an erroneous reference to an
2743 uninitialized value.
2745 It is even possible to change the value at execution time eliminating even
2746 the need to rebind with a different switch using an environment variable.
2747 See the GNAT users guide for details.
2749 Note that pragma @code{Initialize_Scalars} is particularly useful in
2750 conjunction with the enhanced validity checking that is now provided
2751 in GNAT, which checks for invalid values under more conditions.
2752 Using this feature (see description of the @option{-gnatV} flag in the
2753 users guide) in conjunction with pragma @code{Initialize_Scalars}
2754 provides a powerful new tool to assist in the detection of problems
2755 caused by uninitialized variables.
2757 Note: the use of @code{Initialize_Scalars} has a fairly extensive
2758 effect on the generated code. This may cause your code to be
2759 substantially larger. It may also cause an increase in the amount
2760 of stack required, so it is probably a good idea to turn on stack
2761 checking (see description of stack checking in the GNAT users guide)
2762 when using this pragma.
2764 @node Pragma Inline_Always
2765 @unnumberedsec Pragma Inline_Always
2766 @findex Inline_Always
2770 @smallexample @c ada
2771 pragma Inline_Always (NAME [, NAME]);
2775 Similar to pragma @code{Inline} except that inlining is not subject to
2776 the use of option @option{-gnatn} and the inlining happens regardless of
2777 whether this option is used.
2779 @node Pragma Inline_Generic
2780 @unnumberedsec Pragma Inline_Generic
2781 @findex Inline_Generic
2785 @smallexample @c ada
2786 pragma Inline_Generic (generic_package_NAME);
2790 This is implemented for compatibility with DEC Ada 83 and is recognized,
2791 but otherwise ignored, by GNAT@. All generic instantiations are inlined
2792 by default when using GNAT@.
2794 @node Pragma Interface
2795 @unnumberedsec Pragma Interface
2800 @smallexample @c ada
2802 [Convention =>] convention_identifier,
2803 [Entity =>] local_NAME
2804 [, [External_Name =>] static_string_expression]
2805 [, [Link_Name =>] static_string_expression]);
2809 This pragma is identical in syntax and semantics to
2810 the standard Ada pragma @code{Import}. It is provided for compatibility
2811 with Ada 83. The definition is upwards compatible both with pragma
2812 @code{Interface} as defined in the Ada 83 Reference Manual, and also
2813 with some extended implementations of this pragma in certain Ada 83
2816 @node Pragma Interface_Name
2817 @unnumberedsec Pragma Interface_Name
2818 @findex Interface_Name
2822 @smallexample @c ada
2823 pragma Interface_Name (
2824 [Entity =>] LOCAL_NAME
2825 [, [External_Name =>] static_string_EXPRESSION]
2826 [, [Link_Name =>] static_string_EXPRESSION]);
2830 This pragma provides an alternative way of specifying the interface name
2831 for an interfaced subprogram, and is provided for compatibility with Ada
2832 83 compilers that use the pragma for this purpose. You must provide at
2833 least one of @var{External_Name} or @var{Link_Name}.
2835 @node Pragma Interrupt_Handler
2836 @unnumberedsec Pragma Interrupt_Handler
2837 @findex Interrupt_Handler
2841 @smallexample @c ada
2842 pragma Interrupt_Handler (procedure_LOCAL_NAME);
2846 This program unit pragma is supported for parameterless protected procedures
2847 as described in Annex C of the Ada Reference Manual. On the AAMP target
2848 the pragma can also be specified for nonprotected parameterless procedures
2849 that are declared at the library level (which includes procedures
2850 declared at the top level of a library package). In the case of AAMP,
2851 when this pragma is applied to a nonprotected procedure, the instruction
2852 @code{IERET} is generated for returns from the procedure, enabling
2853 maskable interrupts, in place of the normal return instruction.
2855 @node Pragma Interrupt_State
2856 @unnumberedsec Pragma Interrupt_State
2857 @findex Interrupt_State
2861 @smallexample @c ada
2862 pragma Interrupt_State
2864 [State =>] SYSTEM | RUNTIME | USER);
2868 Normally certain interrupts are reserved to the implementation. Any attempt
2869 to attach an interrupt causes Program_Error to be raised, as described in
2870 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
2871 many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
2872 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
2873 interrupt execution. Additionally, signals such as @code{SIGSEGV},
2874 @code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
2875 Ada exceptions, or used to implement run-time functions such as the
2876 @code{abort} statement and stack overflow checking.
2878 Pragma @code{Interrupt_State} provides a general mechanism for overriding
2879 such uses of interrupts. It subsumes the functionality of pragma
2880 @code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
2881 available on OS/2, Windows or VMS. On all other platforms than VxWorks,
2882 it applies to signals; on VxWorks, it applies to vectored hardware interrupts
2883 and may be used to mark interrupts required by the board support package
2886 Interrupts can be in one of three states:
2890 The interrupt is reserved (no Ada handler can be installed), and the
2891 Ada run-time may not install a handler. As a result you are guaranteed
2892 standard system default action if this interrupt is raised.
2896 The interrupt is reserved (no Ada handler can be installed). The run time
2897 is allowed to install a handler for internal control purposes, but is
2898 not required to do so.
2902 The interrupt is unreserved. The user may install a handler to provide
2907 These states are the allowed values of the @code{State} parameter of the
2908 pragma. The @code{Name} parameter is a value of the type
2909 @code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
2910 @code{Ada.Interrupts.Names}.
2912 This is a configuration pragma, and the binder will check that there
2913 are no inconsistencies between different units in a partition in how a
2914 given interrupt is specified. It may appear anywhere a pragma is legal.
2916 The effect is to move the interrupt to the specified state.
2918 By declaring interrupts to be SYSTEM, you guarantee the standard system
2919 action, such as a core dump.
2921 By declaring interrupts to be USER, you guarantee that you can install
2924 Note that certain signals on many operating systems cannot be caught and
2925 handled by applications. In such cases, the pragma is ignored. See the
2926 operating system documentation, or the value of the array @code{Reserved}
2927 declared in the spec of package @code{System.OS_Interface}.
2929 Overriding the default state of signals used by the Ada runtime may interfere
2930 with an application's runtime behavior in the cases of the synchronous signals,
2931 and in the case of the signal used to implement the @code{abort} statement.
2933 @node Pragma Keep_Names
2934 @unnumberedsec Pragma Keep_Names
2939 @smallexample @c ada
2940 pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
2944 The @var{LOCAL_NAME} argument
2945 must refer to an enumeration first subtype
2946 in the current declarative part. The effect is to retain the enumeration
2947 literal names for use by @code{Image} and @code{Value} even if a global
2948 @code{Discard_Names} pragma applies. This is useful when you want to
2949 generally suppress enumeration literal names and for example you therefore
2950 use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
2951 want to retain the names for specific enumeration types.
2953 @node Pragma License
2954 @unnumberedsec Pragma License
2956 @cindex License checking
2960 @smallexample @c ada
2961 pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
2965 This pragma is provided to allow automated checking for appropriate license
2966 conditions with respect to the standard and modified GPL@. A pragma
2967 @code{License}, which is a configuration pragma that typically appears at
2968 the start of a source file or in a separate @file{gnat.adc} file, specifies
2969 the licensing conditions of a unit as follows:
2973 This is used for a unit that can be freely used with no license restrictions.
2974 Examples of such units are public domain units, and units from the Ada
2978 This is used for a unit that is licensed under the unmodified GPL, and which
2979 therefore cannot be @code{with}'ed by a restricted unit.
2982 This is used for a unit licensed under the GNAT modified GPL that includes
2983 a special exception paragraph that specifically permits the inclusion of
2984 the unit in programs without requiring the entire program to be released
2988 This is used for a unit that is restricted in that it is not permitted to
2989 depend on units that are licensed under the GPL@. Typical examples are
2990 proprietary code that is to be released under more restrictive license
2991 conditions. Note that restricted units are permitted to @code{with} units
2992 which are licensed under the modified GPL (this is the whole point of the
2998 Normally a unit with no @code{License} pragma is considered to have an
2999 unknown license, and no checking is done. However, standard GNAT headers
3000 are recognized, and license information is derived from them as follows.
3004 A GNAT license header starts with a line containing 78 hyphens. The following
3005 comment text is searched for the appearance of any of the following strings.
3007 If the string ``GNU General Public License'' is found, then the unit is assumed
3008 to have GPL license, unless the string ``As a special exception'' follows, in
3009 which case the license is assumed to be modified GPL@.
3011 If one of the strings
3012 ``This specification is adapted from the Ada Semantic Interface'' or
3013 ``This specification is derived from the Ada Reference Manual'' is found
3014 then the unit is assumed to be unrestricted.
3018 These default actions means that a program with a restricted license pragma
3019 will automatically get warnings if a GPL unit is inappropriately
3020 @code{with}'ed. For example, the program:
3022 @smallexample @c ada
3025 procedure Secret_Stuff is
3031 if compiled with pragma @code{License} (@code{Restricted}) in a
3032 @file{gnat.adc} file will generate the warning:
3037 >>> license of withed unit "Sem_Ch3" is incompatible
3039 2. with GNAT.Sockets;
3040 3. procedure Secret_Stuff is
3044 Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
3045 compiler and is licensed under the
3046 GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
3047 run time, and is therefore licensed under the modified GPL@.
3049 @node Pragma Link_With
3050 @unnumberedsec Pragma Link_With
3055 @smallexample @c ada
3056 pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
3060 This pragma is provided for compatibility with certain Ada 83 compilers.
3061 It has exactly the same effect as pragma @code{Linker_Options} except
3062 that spaces occurring within one of the string expressions are treated
3063 as separators. For example, in the following case:
3065 @smallexample @c ada
3066 pragma Link_With ("-labc -ldef");
3070 results in passing the strings @code{-labc} and @code{-ldef} as two
3071 separate arguments to the linker. In addition pragma Link_With allows
3072 multiple arguments, with the same effect as successive pragmas.
3074 @node Pragma Linker_Alias
3075 @unnumberedsec Pragma Linker_Alias
3076 @findex Linker_Alias
3080 @smallexample @c ada
3081 pragma Linker_Alias (
3082 [Entity =>] LOCAL_NAME,
3083 [Target =>] static_string_EXPRESSION);
3087 @var{LOCAL_NAME} must refer to an object that is declared at the library
3088 level. This pragma establishes the given entity as a linker alias for the
3089 given target. It is equivalent to @code{__attribute__((alias))} in GNU C
3090 and causes @var{LOCAL_NAME} to be emitted as an alias for the symbol
3091 @var{static_string_EXPRESSION} in the object file, that is to say no space
3092 is reserved for @var{LOCAL_NAME} by the assembler and it will be resolved
3093 to the same address as @var{static_string_EXPRESSION} by the linker.
3095 The actual linker name for the target must be used (e.g.@: the fully
3096 encoded name with qualification in Ada, or the mangled name in C++),
3097 or it must be declared using the C convention with @code{pragma Import}
3098 or @code{pragma Export}.
3100 Not all target machines support this pragma. On some of them it is accepted
3101 only if @code{pragma Weak_External} has been applied to @var{LOCAL_NAME}.
3103 @smallexample @c ada
3104 -- Example of the use of pragma Linker_Alias
3108 pragma Export (C, i);
3110 new_name_for_i : Integer;
3111 pragma Linker_Alias (new_name_for_i, "i");
3115 @node Pragma Linker_Constructor
3116 @unnumberedsec Pragma Linker_Constructor
3117 @findex Linker_Constructor
3121 @smallexample @c ada
3122 pragma Linker_Constructor (procedure_LOCAL_NAME);
3126 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3127 is declared at the library level. A procedure to which this pragma is
3128 applied will be treated as an initialization routine by the linker.
3129 It is equivalent to @code{__attribute__((constructor))} in GNU C and
3130 causes @var{procedure_LOCAL_NAME} to be invoked before the entry point
3131 of the executable is called (or immediately after the shared library is
3132 loaded if the procedure is linked in a shared library), in particular
3133 before the Ada run-time environment is set up.
3135 Because of these specific contexts, the set of operations such a procedure
3136 can perform is very limited and the type of objects it can manipulate is
3137 essentially restricted to the elementary types. In particular, it must only
3138 contain code to which pragma Restrictions (No_Elaboration_Code) applies.
3140 This pragma is used by GNAT to implement auto-initialization of shared Stand
3141 Alone Libraries, which provides a related capability without the restrictions
3142 listed above. Where possible, the use of Stand Alone Libraries is preferable
3143 to the use of this pragma.
3145 @node Pragma Linker_Destructor
3146 @unnumberedsec Pragma Linker_Destructor
3147 @findex Linker_Destructor
3151 @smallexample @c ada
3152 pragma Linker_Destructor (procedure_LOCAL_NAME);
3156 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3157 is declared at the library level. A procedure to which this pragma is
3158 applied will be treated as a finalization routine by the linker.
3159 It is equivalent to @code{__attribute__((destructor))} in GNU C and
3160 causes @var{procedure_LOCAL_NAME} to be invoked after the entry point
3161 of the executable has exited (or immediately before the shared library
3162 is unloaded if the procedure is linked in a shared library), in particular
3163 after the Ada run-time environment is shut down.
3165 See @code{pragma Linker_Constructor} for the set of restrictions that apply
3166 because of these specific contexts.
3168 @node Pragma Linker_Section
3169 @unnumberedsec Pragma Linker_Section
3170 @findex Linker_Section
3174 @smallexample @c ada
3175 pragma Linker_Section (
3176 [Entity =>] LOCAL_NAME,
3177 [Section =>] static_string_EXPRESSION);
3181 @var{LOCAL_NAME} must refer to an object that is declared at the library
3182 level. This pragma specifies the name of the linker section for the given
3183 entity. It is equivalent to @code{__attribute__((section))} in GNU C and
3184 causes @var{LOCAL_NAME} to be placed in the @var{static_string_EXPRESSION}
3185 section of the executable (assuming the linker doesn't rename the section).
3187 The compiler normally places library-level objects in standard sections
3188 depending on their type: procedures and functions generally go in the
3189 @code{.text} section, initialized variables in the @code{.data} section
3190 and uninitialized variables in the @code{.bss} section.
3192 Other, special sections may exist on given target machines to map special
3193 hardware, for example I/O ports or flash memory. This pragma is a means to
3194 defer the final layout of the executable to the linker, thus fully working
3195 at the symbolic level with the compiler.
3197 Some file formats do not support arbitrary sections so not all target
3198 machines support this pragma. The use of this pragma may cause a program
3199 execution to be erroneous if it is used to place an entity into an
3200 inappropriate section (e.g.@: a modified variable into the @code{.text}
3201 section). See also @code{pragma Persistent_BSS}.
3203 @smallexample @c ada
3204 -- Example of the use of pragma Linker_Section
3208 pragma Volatile (Port_A);
3209 pragma Linker_Section (Port_A, ".bss.port_a");
3212 pragma Volatile (Port_B);
3213 pragma Linker_Section (Port_B, ".bss.port_b");
3217 @node Pragma Long_Float
3218 @unnumberedsec Pragma Long_Float
3224 @smallexample @c ada
3225 pragma Long_Float (FLOAT_FORMAT);
3227 FLOAT_FORMAT ::= D_Float | G_Float
3231 This pragma is implemented only in the OpenVMS implementation of GNAT@.
3232 It allows control over the internal representation chosen for the predefined
3233 type @code{Long_Float} and for floating point type representations with
3234 @code{digits} specified in the range 7 through 15.
3235 For further details on this pragma, see the
3236 @cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
3237 this pragma, the standard runtime libraries must be recompiled.
3238 @xref{The GNAT Run-Time Library Builder gnatlbr,,, gnat_ugn,
3239 @value{EDITION} User's Guide OpenVMS}, for a description of the
3240 @code{GNAT LIBRARY} command.
3242 @node Pragma Machine_Attribute
3243 @unnumberedsec Pragma Machine_Attribute
3244 @findex Machine_Attribute
3248 @smallexample @c ada
3249 pragma Machine_Attribute (
3250 [Entity =>] LOCAL_NAME,
3251 [Attribute_Name =>] static_string_EXPRESSION
3252 [, [Info =>] static_string_EXPRESSION] );
3256 Machine-dependent attributes can be specified for types and/or
3257 declarations. This pragma is semantically equivalent to
3258 @code{__attribute__((@var{attribute_name}))} (if @var{info} is not
3259 specified) or @code{__attribute__((@var{attribute_name}(@var{info})))}
3260 in GNU C, where @code{@var{attribute_name}} is recognized by the
3261 target macro @code{TARGET_ATTRIBUTE_TABLE} which is defined for each
3262 machine. The optional parameter @var{info} is transformed into an
3263 identifier, which may make this pragma unusable for some attributes
3264 (parameter of some attributes must be a number or a string).
3265 @xref{Target Attributes,, Defining target-specific uses of
3266 @code{__attribute__}, gccint, GNU Compiler Colletion (GCC) Internals},
3267 further information. It is not possible to specify
3268 attributes defined by other languages, only attributes defined by the
3269 machine the code is intended to run on.
3272 @unnumberedsec Pragma Main
3278 @smallexample @c ada
3280 (MAIN_OPTION [, MAIN_OPTION]);
3283 [Stack_Size =>] static_integer_EXPRESSION
3284 | [Task_Stack_Size_Default =>] static_integer_EXPRESSION
3285 | [Time_Slicing_Enabled =>] static_boolean_EXPRESSION
3289 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3290 no effect in GNAT, other than being syntax checked.
3292 @node Pragma Main_Storage
3293 @unnumberedsec Pragma Main_Storage
3295 @findex Main_Storage
3299 @smallexample @c ada
3301 (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
3303 MAIN_STORAGE_OPTION ::=
3304 [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
3305 | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
3309 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3310 no effect in GNAT, other than being syntax checked. Note that the pragma
3311 also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
3313 @node Pragma No_Body
3314 @unnumberedsec Pragma No_Body
3319 @smallexample @c ada
3324 There are a number of cases in which a package spec does not require a body,
3325 and in fact a body is not permitted. GNAT will not permit the spec to be
3326 compiled if there is a body around. The pragma No_Body allows you to provide
3327 a body file, even in a case where no body is allowed. The body file must
3328 contain only comments and a single No_Body pragma. This is recognized by
3329 the compiler as indicating that no body is logically present.
3331 This is particularly useful during maintenance when a package is modified in
3332 such a way that a body needed before is no longer needed. The provision of a
3333 dummy body with a No_Body pragma ensures that there is no interference from
3334 earlier versions of the package body.
3336 @node Pragma No_Return
3337 @unnumberedsec Pragma No_Return
3342 @smallexample @c ada
3343 pragma No_Return (procedure_LOCAL_NAME @{, procedure_LOCAL_NAME@});
3347 Each @var{procedure_LOCAL_NAME} argument must refer to one or more procedure
3348 declarations in the current declarative part. A procedure to which this
3349 pragma is applied may not contain any explicit @code{return} statements.
3350 In addition, if the procedure contains any implicit returns from falling
3351 off the end of a statement sequence, then execution of that implicit
3352 return will cause Program_Error to be raised.
3354 One use of this pragma is to identify procedures whose only purpose is to raise
3355 an exception. Another use of this pragma is to suppress incorrect warnings
3356 about missing returns in functions, where the last statement of a function
3357 statement sequence is a call to such a procedure.
3359 Note that in Ada 2005 mode, this pragma is part of the language, and is
3360 identical in effect to the pragma as implemented in Ada 95 mode.
3362 @node Pragma No_Strict_Aliasing
3363 @unnumberedsec Pragma No_Strict_Aliasing
3364 @findex No_Strict_Aliasing
3368 @smallexample @c ada
3369 pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)];
3373 @var{type_LOCAL_NAME} must refer to an access type
3374 declaration in the current declarative part. The effect is to inhibit
3375 strict aliasing optimization for the given type. The form with no
3376 arguments is a configuration pragma which applies to all access types
3377 declared in units to which the pragma applies. For a detailed
3378 description of the strict aliasing optimization, and the situations
3379 in which it must be suppressed, see @ref{Optimization and Strict
3380 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
3382 @node Pragma Normalize_Scalars
3383 @unnumberedsec Pragma Normalize_Scalars
3384 @findex Normalize_Scalars
3388 @smallexample @c ada
3389 pragma Normalize_Scalars;
3393 This is a language defined pragma which is fully implemented in GNAT@. The
3394 effect is to cause all scalar objects that are not otherwise initialized
3395 to be initialized. The initial values are implementation dependent and
3399 @item Standard.Character
3401 Objects whose root type is Standard.Character are initialized to
3402 Character'Last unless the subtype range excludes NUL (in which case
3403 NUL is used). This choice will always generate an invalid value if
3406 @item Standard.Wide_Character
3408 Objects whose root type is Standard.Wide_Character are initialized to
3409 Wide_Character'Last unless the subtype range excludes NUL (in which case
3410 NUL is used). This choice will always generate an invalid value if
3413 @item Standard.Wide_Wide_Character
3415 Objects whose root type is Standard.Wide_Wide_Character are initialized to
3416 the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in
3417 which case NUL is used). This choice will always generate an invalid value if
3422 Objects of an integer type are treated differently depending on whether
3423 negative values are present in the subtype. If no negative values are
3424 present, then all one bits is used as the initial value except in the
3425 special case where zero is excluded from the subtype, in which case
3426 all zero bits are used. This choice will always generate an invalid
3427 value if one exists.
3429 For subtypes with negative values present, the largest negative number
3430 is used, except in the unusual case where this largest negative number
3431 is in the subtype, and the largest positive number is not, in which case
3432 the largest positive value is used. This choice will always generate
3433 an invalid value if one exists.
3435 @item Floating-Point Types
3436 Objects of all floating-point types are initialized to all 1-bits. For
3437 standard IEEE format, this corresponds to a NaN (not a number) which is
3438 indeed an invalid value.
3440 @item Fixed-Point Types
3441 Objects of all fixed-point types are treated as described above for integers,
3442 with the rules applying to the underlying integer value used to represent
3443 the fixed-point value.
3446 Objects of a modular type are initialized to all one bits, except in
3447 the special case where zero is excluded from the subtype, in which
3448 case all zero bits are used. This choice will always generate an
3449 invalid value if one exists.
3451 @item Enumeration types
3452 Objects of an enumeration type are initialized to all one-bits, i.e.@: to
3453 the value @code{2 ** typ'Size - 1} unless the subtype excludes the literal
3454 whose Pos value is zero, in which case a code of zero is used. This choice
3455 will always generate an invalid value if one exists.
3459 @node Pragma Obsolescent
3460 @unnumberedsec Pragma Obsolescent
3465 @smallexample @c ada
3468 pragma Obsolescent (
3469 [Message =>] static_string_EXPRESSION
3470 [,[Version =>] Ada_05]]);
3472 pragma Obsolescent (
3474 [,[Message =>] static_string_EXPRESSION
3475 [,[Version =>] Ada_05]] );
3479 This pragma can occur immediately following a declaration of an entity,
3480 including the case of a record component. If no Entity argument is present,
3481 then this declaration is the one to which the pragma applies. If an Entity
3482 parameter is present, it must either match the name of the entity in this
3483 declaration, or alternatively, the pragma can immediately follow an enumeration
3484 type declaration, where the Entity argument names one of the enumeration
3487 This pragma is used to indicate that the named entity
3488 is considered obsolescent and should not be used. Typically this is
3489 used when an API must be modified by eventually removing or modifying
3490 existing subprograms or other entities. The pragma can be used at an
3491 intermediate stage when the entity is still present, but will be
3494 The effect of this pragma is to output a warning message on a reference to
3495 an entity thus marked that the subprogram is obsolescent if the appropriate
3496 warning option in the compiler is activated. If the Message parameter is
3497 present, then a second warning message is given containing this text. In
3498 addition, a reference to the eneity is considered to be a violation of pragma
3499 Restrictions (No_Obsolescent_Features).
3501 This pragma can also be used as a program unit pragma for a package,
3502 in which case the entity name is the name of the package, and the
3503 pragma indicates that the entire package is considered
3504 obsolescent. In this case a client @code{with}'ing such a package
3505 violates the restriction, and the @code{with} statement is
3506 flagged with warnings if the warning option is set.
3508 If the Version parameter is present (which must be exactly
3509 the identifier Ada_05, no other argument is allowed), then the
3510 indication of obsolescence applies only when compiling in Ada 2005
3511 mode. This is primarily intended for dealing with the situations
3512 in the predefined library where subprograms or packages
3513 have become defined as obsolescent in Ada 2005
3514 (e.g.@: in Ada.Characters.Handling), but may be used anywhere.
3516 The following examples show typical uses of this pragma:
3518 @smallexample @c ada
3520 pragma Obsolescent (p, Message => "use pp instead of p");
3525 pragma Obsolescent ("use q2new instead");
3527 type R is new integer;
3530 Message => "use RR in Ada 2005",
3540 type E is (a, bc, 'd', quack);
3541 pragma Obsolescent (Entity => bc)
3542 pragma Obsolescent (Entity => 'd')
3545 (a, b : character) return character;
3546 pragma Obsolescent (Entity => "+");
3551 Note that, as for all pragmas, if you use a pragma argument identifier,
3552 then all subsequent parameters must also use a pragma argument identifier.
3553 So if you specify "Entity =>" for the Entity argument, and a Message
3554 argument is present, it must be preceded by "Message =>".
3556 @node Pragma Optimize_Alignment
3557 @unnumberedsec Pragma Optimize_Alignment
3558 @findex Optimize_Alignment
3559 @cindex Alignment, default settings
3563 @smallexample @c ada
3564 pragma Optimize_Alignment (TIME | SPACE | OFF);
3568 This is a configuration pragma which affects the choice of default alignments
3569 for types where no alignment is explicitly specified. There is a time/space
3570 trade-off in the selection of these values. Large alignments result in more
3571 efficient code, at the expense of larger data space, since sizes have to be
3572 increased to match these alignments. Smaller alignments save space, but the
3573 access code is slower. The normal choice of default alignments (which is what
3574 you get if you do not use this pragma, or if you use an argument of OFF),
3575 tries to balance these two requirements.
3577 Specifying SPACE causes smaller default alignments to be chosen in two cases.
3578 First any packed record is given an alignment of 1. Second, if a size is given
3579 for the type, then the alignment is chosen to avoid increasing this size. For
3582 @smallexample @c ada
3592 In the default mode, this type gets an alignment of 4, so that access to the
3593 Integer field X are efficient. But this means that objects of the type end up
3594 with a size of 8 bytes. This is a valid choice, since sizes of objects are
3595 allowed to be bigger than the size of the type, but it can waste space if for
3596 example fields of type R appear in an enclosing record. If the above type is
3597 compiled in @code{Optimize_Alignment (Space)} mode, the alignment is set to 1.
3599 Specifying TIME causes larger default alignments to be chosen in the case of
3600 small types with sizes that are not a power of 2. For example, consider:
3602 @smallexample @c ada
3614 The default alignment for this record is normally 1, but if this type is
3615 compiled in @code{Optimize_Alignment (Time)} mode, then the alignment is set
3616 to 4, which wastes space for objects of the type, since they are now 4 bytes
3617 long, but results in more efficient access when the whole record is referenced.
3619 As noted above, this is a configuration pragma, and there is a requirement
3620 that all units in a partition be compiled with a consistent setting of the
3621 optimization setting. This would normally be achieved by use of a configuration
3622 pragma file containing the appropriate setting. The exception to this rule is
3623 that units with an explicit configuration pragma in the same file as the source
3624 unit are excluded from the consistency check, as are all predefined units. The
3625 latter are compiled by default in pragma Optimize_Alignment (Off) mode if no
3626 pragma appears at the start of the file.
3628 @node Pragma Passive
3629 @unnumberedsec Pragma Passive
3634 @smallexample @c ada
3635 pragma Passive [(Semaphore | No)];
3639 Syntax checked, but otherwise ignored by GNAT@. This is recognized for
3640 compatibility with DEC Ada 83 implementations, where it is used within a
3641 task definition to request that a task be made passive. If the argument
3642 @code{Semaphore} is present, or the argument is omitted, then DEC Ada 83
3643 treats the pragma as an assertion that the containing task is passive
3644 and that optimization of context switch with this task is permitted and
3645 desired. If the argument @code{No} is present, the task must not be
3646 optimized. GNAT does not attempt to optimize any tasks in this manner
3647 (since protected objects are available in place of passive tasks).
3649 @node Pragma Persistent_BSS
3650 @unnumberedsec Pragma Persistent_BSS
3651 @findex Persistent_BSS
3655 @smallexample @c ada
3656 pragma Persistent_BSS [(LOCAL_NAME)]
3660 This pragma allows selected objects to be placed in the @code{.persistent_bss}
3661 section. On some targets the linker and loader provide for special
3662 treatment of this section, allowing a program to be reloaded without
3663 affecting the contents of this data (hence the name persistent).
3665 There are two forms of usage. If an argument is given, it must be the
3666 local name of a library level object, with no explicit initialization
3667 and whose type is potentially persistent. If no argument is given, then
3668 the pragma is a configuration pragma, and applies to all library level
3669 objects with no explicit initialization of potentially persistent types.
3671 A potentially persistent type is a scalar type, or a non-tagged,
3672 non-discriminated record, all of whose components have no explicit
3673 initialization and are themselves of a potentially persistent type,
3674 or an array, all of whose constraints are static, and whose component
3675 type is potentially persistent.
3677 If this pragma is used on a target where this feature is not supported,
3678 then the pragma will be ignored. See also @code{pragma Linker_Section}.
3680 @node Pragma Polling
3681 @unnumberedsec Pragma Polling
3686 @smallexample @c ada
3687 pragma Polling (ON | OFF);
3691 This pragma controls the generation of polling code. This is normally off.
3692 If @code{pragma Polling (ON)} is used then periodic calls are generated to
3693 the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
3694 runtime library, and can be found in file @file{a-excpol.adb}.
3696 Pragma @code{Polling} can appear as a configuration pragma (for example it
3697 can be placed in the @file{gnat.adc} file) to enable polling globally, or it
3698 can be used in the statement or declaration sequence to control polling
3701 A call to the polling routine is generated at the start of every loop and
3702 at the start of every subprogram call. This guarantees that the @code{Poll}
3703 routine is called frequently, and places an upper bound (determined by
3704 the complexity of the code) on the period between two @code{Poll} calls.
3706 The primary purpose of the polling interface is to enable asynchronous
3707 aborts on targets that cannot otherwise support it (for example Windows
3708 NT), but it may be used for any other purpose requiring periodic polling.
3709 The standard version is null, and can be replaced by a user program. This
3710 will require re-compilation of the @code{Ada.Exceptions} package that can
3711 be found in files @file{a-except.ads} and @file{a-except.adb}.
3713 A standard alternative unit (in file @file{4wexcpol.adb} in the standard GNAT
3714 distribution) is used to enable the asynchronous abort capability on
3715 targets that do not normally support the capability. The version of
3716 @code{Poll} in this file makes a call to the appropriate runtime routine
3717 to test for an abort condition.
3719 Note that polling can also be enabled by use of the @option{-gnatP} switch.
3720 @xref{Switches for gcc,,, gnat_ugn, @value{EDITION} User's Guide}, for
3723 @node Pragma Postcondition
3724 @unnumberedsec Pragma Postcondition
3725 @cindex Postconditions
3726 @cindex Checks, postconditions
3727 @findex Postconditions
3731 @smallexample @c ada
3732 pragma Postcondition (
3733 [Check =>] Boolean_Expression
3734 [,[Message =>] String_Expression]);
3738 The @code{Postcondition} pragma allows specification of automatic
3739 postcondition checks for subprograms. These checks are similar to
3740 assertions, but are automatically inserted just prior to the return
3741 statements of the subprogram with which they are associated (including
3742 implicit returns at the end of procedure bodies and associated
3743 exception handlers).
3745 In addition, the boolean expression which is the condition which
3746 must be true may contain references to function'Result in the case
3747 of a function to refer to the returned value.
3749 @code{Postcondition} pragmas may appear either immediate following the
3750 (separate) declaration of a subprogram, or at the start of the
3751 declarations of a subprogram body. Only other pragmas may intervene
3752 (that is appear between the subprogram declaration and its
3753 postconditions, or appear before the postcondition in the
3754 declaration sequence in a subprogram body). In the case of a
3755 postcondition appearing after a subprogram declaration, the
3756 formal arguments of the subprogram are visible, and can be
3757 referenced in the postcondition expressions.
3759 The postconditions are collected and automatically tested just
3760 before any return (implicit or explicit) in the subprogram body.
3761 A postcondition is only recognized if postconditions are active
3762 at the time the pragma is encountered. The compiler switch @option{gnata}
3763 turns on all postconditions by default, and pragma @code{Check_Policy}
3764 with an identifier of @code{Postcondition} can also be used to
3765 control whether postconditions are active.
3767 The general approach is that postconditions are placed in the spec
3768 if they represent functional aspects which make sense to the client.
3769 For example we might have:
3771 @smallexample @c ada
3772 function Direction return Integer;
3773 pragma Postcondition
3774 (Direction'Result = +1
3776 Direction'Result = -1);
3780 which serves to document that the result must be +1 or -1, and
3781 will test that this is the case at run time if postcondition
3784 Postconditions within the subprogram body can be used to
3785 check that some internal aspect of the implementation,
3786 not visible to the client, is operating as expected.
3787 For instance if a square root routine keeps an internal
3788 counter of the number of times it is called, then we
3789 might have the following postcondition:
3791 @smallexample @c ada
3792 Sqrt_Calls : Natural := 0;
3794 function Sqrt (Arg : Float) return Float is
3795 pragma Postcondition
3796 (Sqrt_Calls = Sqrt_Calls'Old + 1);
3802 As this example, shows, the use of the @code{Old} attribute
3803 is often useful in postconditions to refer to the state on
3804 entry to the subprogram.
3806 Note that postconditions are only checked on normal returns
3807 from the subprogram. If an abnormal return results from
3808 raising an exception, then the postconditions are not checked.
3810 If a postcondition fails, then the exception
3811 @code{System.Assertions.Assert_Failure} is raised. If
3812 a message argument was supplied, then the given string
3813 will be used as the exception message. If no message
3814 argument was supplied, then the default message has
3815 the form "Postcondition failed at file:line". The
3816 exception is raised in the context of the subprogram
3817 body, so it is possible to catch postcondition failures
3818 within the subprogram body itself.
3820 Within a package spec, normal visibility rules
3821 in Ada would prevent forward references within a
3822 postcondition pragma to functions defined later in
3823 the same package. This would introduce undesirable
3824 ordering constraints. To avoid this problem, all
3825 postcondition pragmas are analyzed at the end of
3826 the package spec, allowing forward references.
3828 The following example shows that this even allows
3829 mutually recursive postconditions as in:
3831 @smallexample @c ada
3832 package Parity_Functions is
3833 function Odd (X : Natural) return Boolean;
3834 pragma Postcondition
3838 (x /= 0 and then Even (X - 1))));
3840 function Even (X : Natural) return Boolean;
3841 pragma Postcondition
3845 (x /= 1 and then Odd (X - 1))));
3847 end Parity_Functions;
3851 There are no restrictions on the complexity or form of
3852 conditions used within @code{Postcondition} pragmas.
3853 The following example shows that it is even possible
3854 to verify performance behavior.
3856 @smallexample @c ada
3859 Performance : constant Float;
3860 -- Performance constant set by implementation
3861 -- to match target architecture behavior.
3863 procedure Treesort (Arg : String);
3864 -- Sorts characters of argument using N*logN sort
3865 pragma Postcondition
3866 (Float (Clock - Clock'Old) <=
3867 Float (Arg'Length) *
3868 log (Float (Arg'Length)) *
3874 Note: postcondition pragmas associated with subprograms that are
3875 marked as Inline_Always, or those marked as Inline with front-end
3876 inlining (-gnatN option set) are accepted and legality-checked
3877 by the compiler, but are ignored at run-time even if postcondition
3878 checking is enabled.
3880 @node Pragma Precondition
3881 @unnumberedsec Pragma Precondition
3882 @cindex Preconditions
3883 @cindex Checks, preconditions
3884 @findex Preconditions
3888 @smallexample @c ada
3889 pragma Precondition (
3890 [Check =>] Boolean_Expression
3891 [,[Message =>] String_Expression]);
3895 The @code{Precondition} pragma is similar to @code{Postcondition}
3896 except that the corresponding checks take place immediately upon
3897 entry to the subprogram, and if a precondition fails, the exception
3898 is raised in the context of the caller, and the attribute 'Result
3899 cannot be used within the precondition expression.
3901 Otherwise, the placement and visibility rules are identical to those
3902 described for postconditions. The following is an example of use
3903 within a package spec:
3905 @smallexample @c ada
3906 package Math_Functions is
3908 function Sqrt (Arg : Float) return Float;
3909 pragma Precondition (Arg >= 0.0)
3915 @code{Precondition} pragmas may appear either immediate following the
3916 (separate) declaration of a subprogram, or at the start of the
3917 declarations of a subprogram body. Only other pragmas may intervene
3918 (that is appear between the subprogram declaration and its
3919 postconditions, or appear before the postcondition in the
3920 declaration sequence in a subprogram body).
3922 Note: postcondition pragmas associated with subprograms that are
3923 marked as Inline_Always, or those marked as Inline with front-end
3924 inlining (-gnatN option set) are accepted and legality-checked
3925 by the compiler, but are ignored at run-time even if postcondition
3926 checking is enabled.
3930 @node Pragma Profile (Ravenscar)
3931 @unnumberedsec Pragma Profile (Ravenscar)
3936 @smallexample @c ada
3937 pragma Profile (Ravenscar);
3941 A configuration pragma that establishes the following set of configuration
3945 @item Task_Dispatching_Policy (FIFO_Within_Priorities)
3946 [RM D.2.2] Tasks are dispatched following a preemptive
3947 priority-ordered scheduling policy.
3949 @item Locking_Policy (Ceiling_Locking)
3950 [RM D.3] While tasks and interrupts execute a protected action, they inherit
3951 the ceiling priority of the corresponding protected object.
3953 @c @item Detect_Blocking
3954 @c This pragma forces the detection of potentially blocking operations within a
3955 @c protected operation, and to raise Program_Error if that happens.
3959 plus the following set of restrictions:
3962 @item Max_Entry_Queue_Length = 1
3963 Defines the maximum number of calls that are queued on a (protected) entry.
3964 Note that this restrictions is checked at run time. Violation of this
3965 restriction results in the raising of Program_Error exception at the point of
3966 the call. For the Profile (Ravenscar) the value of Max_Entry_Queue_Length is
3967 always 1 and hence no task can be queued on a protected entry.
3969 @item Max_Protected_Entries = 1
3970 [RM D.7] Specifies the maximum number of entries per protected type. The
3971 bounds of every entry family of a protected unit shall be static, or shall be
3972 defined by a discriminant of a subtype whose corresponding bound is static.
3973 For the Profile (Ravenscar) the value of Max_Protected_Entries is always 1.
3975 @item Max_Task_Entries = 0
3976 [RM D.7] Specifies the maximum number of entries
3977 per task. The bounds of every entry family
3978 of a task unit shall be static, or shall be
3979 defined by a discriminant of a subtype whose
3980 corresponding bound is static. A value of zero
3981 indicates that no rendezvous are possible. For
3982 the Profile (Ravenscar), the value of Max_Task_Entries is always
3985 @item No_Abort_Statements
3986 [RM D.7] There are no abort_statements, and there are
3987 no calls to Task_Identification.Abort_Task.
3989 @item No_Asynchronous_Control
3990 There are no semantic dependences on the package
3991 Asynchronous_Task_Control.
3994 There are no semantic dependencies on the package Ada.Calendar.
3996 @item No_Dynamic_Attachment
3997 There is no call to any of the operations defined in package Ada.Interrupts
3998 (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler,
3999 Detach_Handler, and Reference).
4001 @item No_Dynamic_Priorities
4002 [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
4004 @item No_Implicit_Heap_Allocations
4005 [RM D.7] No constructs are allowed to cause implicit heap allocation.
4007 @item No_Local_Protected_Objects
4008 Protected objects and access types that designate
4009 such objects shall be declared only at library level.
4011 @item No_Local_Timing_Events
4012 [RM D.7] All objects of type Ada.Timing_Events.Timing_Event are
4013 declared at the library level.
4015 @item No_Protected_Type_Allocators
4016 There are no allocators for protected types or
4017 types containing protected subcomponents.
4019 @item No_Relative_Delay
4020 There are no delay_relative statements.
4022 @item No_Requeue_Statements
4023 Requeue statements are not allowed.
4025 @item No_Select_Statements
4026 There are no select_statements.
4028 @item No_Specific_Termination_Handlers
4029 [RM D.7] There are no calls to Ada.Task_Termination.Set_Specific_Handler
4030 or to Ada.Task_Termination.Specific_Handler.
4032 @item No_Task_Allocators
4033 [RM D.7] There are no allocators for task types
4034 or types containing task subcomponents.
4036 @item No_Task_Attributes_Package
4037 There are no semantic dependencies on the Ada.Task_Attributes package.
4039 @item No_Task_Hierarchy
4040 [RM D.7] All (non-environment) tasks depend
4041 directly on the environment task of the partition.
4043 @item No_Task_Termination
4044 Tasks which terminate are erroneous.
4046 @item No_Unchecked_Conversion
4047 There are no semantic dependencies on the Ada.Unchecked_Conversion package.
4049 @item No_Unchecked_Deallocation
4050 There are no semantic dependencies on the Ada.Unchecked_Deallocation package.
4052 @item Simple_Barriers
4053 Entry barrier condition expressions shall be either static
4054 boolean expressions or boolean objects which are declared in
4055 the protected type which contains the entry.
4059 This set of configuration pragmas and restrictions correspond to the
4060 definition of the ``Ravenscar Profile'' for limited tasking, devised and
4061 published by the @cite{International Real-Time Ada Workshop}, 1997,
4062 and whose most recent description is available at
4063 @url{http://www-users.cs.york.ac.uk/~burns/ravenscar.ps}.
4065 The original definition of the profile was revised at subsequent IRTAW
4066 meetings. It has been included in the ISO
4067 @cite{Guide for the Use of the Ada Programming Language in High
4068 Integrity Systems}, and has been approved by ISO/IEC/SC22/WG9 for inclusion in
4069 the next revision of the standard. The formal definition given by
4070 the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and
4071 AI-305) available at
4072 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00249.TXT} and
4073 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00305.TXT}
4076 The above set is a superset of the restrictions provided by pragma
4077 @code{Profile (Restricted)}, it includes six additional restrictions
4078 (@code{Simple_Barriers}, @code{No_Select_Statements},
4079 @code{No_Calendar}, @code{No_Implicit_Heap_Allocations},
4080 @code{No_Relative_Delay} and @code{No_Task_Termination}). This means
4081 that pragma @code{Profile (Ravenscar)}, like the pragma
4082 @code{Profile (Restricted)},
4083 automatically causes the use of a simplified,
4084 more efficient version of the tasking run-time system.
4086 @node Pragma Profile (Restricted)
4087 @unnumberedsec Pragma Profile (Restricted)
4088 @findex Restricted Run Time
4092 @smallexample @c ada
4093 pragma Profile (Restricted);
4097 A configuration pragma that establishes the following set of restrictions:
4100 @item No_Abort_Statements
4101 @item No_Entry_Queue
4102 @item No_Task_Hierarchy
4103 @item No_Task_Allocators
4104 @item No_Dynamic_Priorities
4105 @item No_Terminate_Alternatives
4106 @item No_Dynamic_Attachment
4107 @item No_Protected_Type_Allocators
4108 @item No_Local_Protected_Objects
4109 @item No_Requeue_Statements
4110 @item No_Task_Attributes_Package
4111 @item Max_Asynchronous_Select_Nesting = 0
4112 @item Max_Task_Entries = 0
4113 @item Max_Protected_Entries = 1
4114 @item Max_Select_Alternatives = 0
4118 This set of restrictions causes the automatic selection of a simplified
4119 version of the run time that provides improved performance for the
4120 limited set of tasking functionality permitted by this set of restrictions.
4122 @node Pragma Psect_Object
4123 @unnumberedsec Pragma Psect_Object
4124 @findex Psect_Object
4128 @smallexample @c ada
4129 pragma Psect_Object (
4130 [Internal =>] LOCAL_NAME,
4131 [, [External =>] EXTERNAL_SYMBOL]
4132 [, [Size =>] EXTERNAL_SYMBOL]);
4136 | static_string_EXPRESSION
4140 This pragma is identical in effect to pragma @code{Common_Object}.
4142 @node Pragma Pure_Function
4143 @unnumberedsec Pragma Pure_Function
4144 @findex Pure_Function
4148 @smallexample @c ada
4149 pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
4153 This pragma appears in the same declarative part as a function
4154 declaration (or a set of function declarations if more than one
4155 overloaded declaration exists, in which case the pragma applies
4156 to all entities). It specifies that the function @code{Entity} is
4157 to be considered pure for the purposes of code generation. This means
4158 that the compiler can assume that there are no side effects, and
4159 in particular that two calls with identical arguments produce the
4160 same result. It also means that the function can be used in an
4163 Note that, quite deliberately, there are no static checks to try
4164 to ensure that this promise is met, so @code{Pure_Function} can be used
4165 with functions that are conceptually pure, even if they do modify
4166 global variables. For example, a square root function that is
4167 instrumented to count the number of times it is called is still
4168 conceptually pure, and can still be optimized, even though it
4169 modifies a global variable (the count). Memo functions are another
4170 example (where a table of previous calls is kept and consulted to
4171 avoid re-computation).
4174 Note: Most functions in a @code{Pure} package are automatically pure, and
4175 there is no need to use pragma @code{Pure_Function} for such functions. One
4176 exception is any function that has at least one formal of type
4177 @code{System.Address} or a type derived from it. Such functions are not
4178 considered pure by default, since the compiler assumes that the
4179 @code{Address} parameter may be functioning as a pointer and that the
4180 referenced data may change even if the address value does not.
4181 Similarly, imported functions are not considered to be pure by default,
4182 since there is no way of checking that they are in fact pure. The use
4183 of pragma @code{Pure_Function} for such a function will override these default
4184 assumption, and cause the compiler to treat a designated subprogram as pure
4187 Note: If pragma @code{Pure_Function} is applied to a renamed function, it
4188 applies to the underlying renamed function. This can be used to
4189 disambiguate cases of overloading where some but not all functions
4190 in a set of overloaded functions are to be designated as pure.
4192 If pragma @code{Pure_Function} is applied to a library level function, the
4193 function is also considered pure from an optimization point of view, but the
4194 unit is not a Pure unit in the categorization sense. So for example, a function
4195 thus marked is free to @code{with} non-pure units.
4197 @node Pragma Restriction_Warnings
4198 @unnumberedsec Pragma Restriction_Warnings
4199 @findex Restriction_Warnings
4203 @smallexample @c ada
4204 pragma Restriction_Warnings
4205 (restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
4209 This pragma allows a series of restriction identifiers to be
4210 specified (the list of allowed identifiers is the same as for
4211 pragma @code{Restrictions}). For each of these identifiers
4212 the compiler checks for violations of the restriction, but
4213 generates a warning message rather than an error message
4214 if the restriction is violated.
4217 @unnumberedsec Pragma Shared
4221 This pragma is provided for compatibility with Ada 83. The syntax and
4222 semantics are identical to pragma Atomic.
4224 @node Pragma Source_File_Name
4225 @unnumberedsec Pragma Source_File_Name
4226 @findex Source_File_Name
4230 @smallexample @c ada
4231 pragma Source_File_Name (
4232 [Unit_Name =>] unit_NAME,
4233 Spec_File_Name => STRING_LITERAL);
4235 pragma Source_File_Name (
4236 [Unit_Name =>] unit_NAME,
4237 Body_File_Name => STRING_LITERAL);
4241 Use this to override the normal naming convention. It is a configuration
4242 pragma, and so has the usual applicability of configuration pragmas
4243 (i.e.@: it applies to either an entire partition, or to all units in a
4244 compilation, or to a single unit, depending on how it is used.
4245 @var{unit_name} is mapped to @var{file_name_literal}. The identifier for
4246 the second argument is required, and indicates whether this is the file
4247 name for the spec or for the body.
4249 Another form of the @code{Source_File_Name} pragma allows
4250 the specification of patterns defining alternative file naming schemes
4251 to apply to all files.
4253 @smallexample @c ada
4254 pragma Source_File_Name
4255 ( [Spec_File_Name =>] STRING_LITERAL
4256 [,[Casing =>] CASING_SPEC]
4257 [,[Dot_Replacement =>] STRING_LITERAL]);
4259 pragma Source_File_Name
4260 ( [Body_File_Name =>] STRING_LITERAL
4261 [,[Casing =>] CASING_SPEC]
4262 [,[Dot_Replacement =>] STRING_LITERAL]);
4264 pragma Source_File_Name
4265 ( [Subunit_File_Name =>] STRING_LITERAL
4266 [,[Casing =>] CASING_SPEC]
4267 [,[Dot_Replacement =>] STRING_LITERAL]);
4269 CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
4273 The first argument is a pattern that contains a single asterisk indicating
4274 the point at which the unit name is to be inserted in the pattern string
4275 to form the file name. The second argument is optional. If present it
4276 specifies the casing of the unit name in the resulting file name string.
4277 The default is lower case. Finally the third argument allows for systematic
4278 replacement of any dots in the unit name by the specified string literal.
4280 A pragma Source_File_Name cannot appear after a
4281 @ref{Pragma Source_File_Name_Project}.
4283 For more details on the use of the @code{Source_File_Name} pragma,
4284 @xref{Using Other File Names,,, gnat_ugn, @value{EDITION} User's Guide},
4285 and @ref{Alternative File Naming Schemes,,, gnat_ugn, @value{EDITION}
4288 @node Pragma Source_File_Name_Project
4289 @unnumberedsec Pragma Source_File_Name_Project
4290 @findex Source_File_Name_Project
4293 This pragma has the same syntax and semantics as pragma Source_File_Name.
4294 It is only allowed as a stand alone configuration pragma.
4295 It cannot appear after a @ref{Pragma Source_File_Name}, and
4296 most importantly, once pragma Source_File_Name_Project appears,
4297 no further Source_File_Name pragmas are allowed.
4299 The intention is that Source_File_Name_Project pragmas are always
4300 generated by the Project Manager in a manner consistent with the naming
4301 specified in a project file, and when naming is controlled in this manner,
4302 it is not permissible to attempt to modify this naming scheme using
4303 Source_File_Name pragmas (which would not be known to the project manager).
4305 @node Pragma Source_Reference
4306 @unnumberedsec Pragma Source_Reference
4307 @findex Source_Reference
4311 @smallexample @c ada
4312 pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
4316 This pragma must appear as the first line of a source file.
4317 @var{integer_literal} is the logical line number of the line following
4318 the pragma line (for use in error messages and debugging
4319 information). @var{string_literal} is a static string constant that
4320 specifies the file name to be used in error messages and debugging
4321 information. This is most notably used for the output of @code{gnatchop}
4322 with the @option{-r} switch, to make sure that the original unchopped
4323 source file is the one referred to.
4325 The second argument must be a string literal, it cannot be a static
4326 string expression other than a string literal. This is because its value
4327 is needed for error messages issued by all phases of the compiler.
4329 @node Pragma Stream_Convert
4330 @unnumberedsec Pragma Stream_Convert
4331 @findex Stream_Convert
4335 @smallexample @c ada
4336 pragma Stream_Convert (
4337 [Entity =>] type_LOCAL_NAME,
4338 [Read =>] function_NAME,
4339 [Write =>] function_NAME);
4343 This pragma provides an efficient way of providing stream functions for
4344 types defined in packages. Not only is it simpler to use than declaring
4345 the necessary functions with attribute representation clauses, but more
4346 significantly, it allows the declaration to made in such a way that the
4347 stream packages are not loaded unless they are needed. The use of
4348 the Stream_Convert pragma adds no overhead at all, unless the stream
4349 attributes are actually used on the designated type.
4351 The first argument specifies the type for which stream functions are
4352 provided. The second parameter provides a function used to read values
4353 of this type. It must name a function whose argument type may be any
4354 subtype, and whose returned type must be the type given as the first
4355 argument to the pragma.
4357 The meaning of the @var{Read}
4358 parameter is that if a stream attribute directly
4359 or indirectly specifies reading of the type given as the first parameter,
4360 then a value of the type given as the argument to the Read function is
4361 read from the stream, and then the Read function is used to convert this
4362 to the required target type.
4364 Similarly the @var{Write} parameter specifies how to treat write attributes
4365 that directly or indirectly apply to the type given as the first parameter.
4366 It must have an input parameter of the type specified by the first parameter,
4367 and the return type must be the same as the input type of the Read function.
4368 The effect is to first call the Write function to convert to the given stream
4369 type, and then write the result type to the stream.
4371 The Read and Write functions must not be overloaded subprograms. If necessary
4372 renamings can be supplied to meet this requirement.
4373 The usage of this attribute is best illustrated by a simple example, taken
4374 from the GNAT implementation of package Ada.Strings.Unbounded:
4376 @smallexample @c ada
4377 function To_Unbounded (S : String)
4378 return Unbounded_String
4379 renames To_Unbounded_String;
4381 pragma Stream_Convert
4382 (Unbounded_String, To_Unbounded, To_String);
4386 The specifications of the referenced functions, as given in the Ada
4387 Reference Manual are:
4389 @smallexample @c ada
4390 function To_Unbounded_String (Source : String)
4391 return Unbounded_String;
4393 function To_String (Source : Unbounded_String)
4398 The effect is that if the value of an unbounded string is written to a
4399 stream, then the representation of the item in the stream is in the same
4400 format used for @code{Standard.String}, and this same representation is
4401 expected when a value of this type is read from the stream.
4403 @node Pragma Style_Checks
4404 @unnumberedsec Pragma Style_Checks
4405 @findex Style_Checks
4409 @smallexample @c ada
4410 pragma Style_Checks (string_LITERAL | ALL_CHECKS |
4411 On | Off [, LOCAL_NAME]);
4415 This pragma is used in conjunction with compiler switches to control the
4416 built in style checking provided by GNAT@. The compiler switches, if set,
4417 provide an initial setting for the switches, and this pragma may be used
4418 to modify these settings, or the settings may be provided entirely by
4419 the use of the pragma. This pragma can be used anywhere that a pragma
4420 is legal, including use as a configuration pragma (including use in
4421 the @file{gnat.adc} file).
4423 The form with a string literal specifies which style options are to be
4424 activated. These are additive, so they apply in addition to any previously
4425 set style check options. The codes for the options are the same as those
4426 used in the @option{-gnaty} switch to @command{gcc} or @command{gnatmake}.
4427 For example the following two methods can be used to enable
4432 @smallexample @c ada
4433 pragma Style_Checks ("l");
4438 gcc -c -gnatyl @dots{}
4443 The form ALL_CHECKS activates all standard checks (its use is equivalent
4444 to the use of the @code{gnaty} switch with no options. @xref{Top,
4445 @value{EDITION} User's Guide, About This Guide, gnat_ugn,
4446 @value{EDITION} User's Guide}, for details.
4448 The forms with @code{Off} and @code{On}
4449 can be used to temporarily disable style checks
4450 as shown in the following example:
4452 @smallexample @c ada
4456 pragma Style_Checks ("k"); -- requires keywords in lower case
4457 pragma Style_Checks (Off); -- turn off style checks
4458 NULL; -- this will not generate an error message
4459 pragma Style_Checks (On); -- turn style checks back on
4460 NULL; -- this will generate an error message
4464 Finally the two argument form is allowed only if the first argument is
4465 @code{On} or @code{Off}. The effect is to turn of semantic style checks
4466 for the specified entity, as shown in the following example:
4468 @smallexample @c ada
4472 pragma Style_Checks ("r"); -- require consistency of identifier casing
4474 Rf1 : Integer := ARG; -- incorrect, wrong case
4475 pragma Style_Checks (Off, Arg);
4476 Rf2 : Integer := ARG; -- OK, no error
4479 @node Pragma Subtitle
4480 @unnumberedsec Pragma Subtitle
4485 @smallexample @c ada
4486 pragma Subtitle ([Subtitle =>] STRING_LITERAL);
4490 This pragma is recognized for compatibility with other Ada compilers
4491 but is ignored by GNAT@.
4493 @node Pragma Suppress
4494 @unnumberedsec Pragma Suppress
4499 @smallexample @c ada
4500 pragma Suppress (Identifier [, [On =>] Name]);
4504 This is a standard pragma, and supports all the check names required in
4505 the RM. It is included here because GNAT recognizes one additional check
4506 name: @code{Alignment_Check} which can be used to suppress alignment checks
4507 on addresses used in address clauses. Such checks can also be suppressed
4508 by suppressing range checks, but the specific use of @code{Alignment_Check}
4509 allows suppression of alignment checks without suppressing other range checks.
4511 Note that pragma Suppress gives the compiler permission to omit
4512 checks, but does not require the compiler to omit checks. The compiler
4513 will generate checks if they are essentially free, even when they are
4514 suppressed. In particular, if the compiler can prove that a certain
4515 check will necessarily fail, it will generate code to do an
4516 unconditional ``raise'', even if checks are suppressed. The compiler
4519 Of course, run-time checks are omitted whenever the compiler can prove
4520 that they will not fail, whether or not checks are suppressed.
4522 @node Pragma Suppress_All
4523 @unnumberedsec Pragma Suppress_All
4524 @findex Suppress_All
4528 @smallexample @c ada
4529 pragma Suppress_All;
4533 This pragma can only appear immediately following a compilation
4534 unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
4535 which it follows. This pragma is implemented for compatibility with DEC
4536 Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
4537 configuration pragma is the preferred usage in GNAT@.
4539 @node Pragma Suppress_Exception_Locations
4540 @unnumberedsec Pragma Suppress_Exception_Locations
4541 @findex Suppress_Exception_Locations
4545 @smallexample @c ada
4546 pragma Suppress_Exception_Locations;
4550 In normal mode, a raise statement for an exception by default generates
4551 an exception message giving the file name and line number for the location
4552 of the raise. This is useful for debugging and logging purposes, but this
4553 entails extra space for the strings for the messages. The configuration
4554 pragma @code{Suppress_Exception_Locations} can be used to suppress the
4555 generation of these strings, with the result that space is saved, but the
4556 exception message for such raises is null. This configuration pragma may
4557 appear in a global configuration pragma file, or in a specific unit as
4558 usual. It is not required that this pragma be used consistently within
4559 a partition, so it is fine to have some units within a partition compiled
4560 with this pragma and others compiled in normal mode without it.
4562 @node Pragma Suppress_Initialization
4563 @unnumberedsec Pragma Suppress_Initialization
4564 @findex Suppress_Initialization
4565 @cindex Suppressing initialization
4566 @cindex Initialization, suppression of
4570 @smallexample @c ada
4571 pragma Suppress_Initialization ([Entity =>] type_Name);
4575 This pragma suppresses any implicit or explicit initialization
4576 associated with the given type name for all variables of this type.
4578 @node Pragma Task_Info
4579 @unnumberedsec Pragma Task_Info
4584 @smallexample @c ada
4585 pragma Task_Info (EXPRESSION);
4589 This pragma appears within a task definition (like pragma
4590 @code{Priority}) and applies to the task in which it appears. The
4591 argument must be of type @code{System.Task_Info.Task_Info_Type}.
4592 The @code{Task_Info} pragma provides system dependent control over
4593 aspects of tasking implementation, for example, the ability to map
4594 tasks to specific processors. For details on the facilities available
4595 for the version of GNAT that you are using, see the documentation
4596 in the spec of package System.Task_Info in the runtime
4599 @node Pragma Task_Name
4600 @unnumberedsec Pragma Task_Name
4605 @smallexample @c ada
4606 pragma Task_Name (string_EXPRESSION);
4610 This pragma appears within a task definition (like pragma
4611 @code{Priority}) and applies to the task in which it appears. The
4612 argument must be of type String, and provides a name to be used for
4613 the task instance when the task is created. Note that this expression
4614 is not required to be static, and in particular, it can contain
4615 references to task discriminants. This facility can be used to
4616 provide different names for different tasks as they are created,
4617 as illustrated in the example below.
4619 The task name is recorded internally in the run-time structures
4620 and is accessible to tools like the debugger. In addition the
4621 routine @code{Ada.Task_Identification.Image} will return this
4622 string, with a unique task address appended.
4624 @smallexample @c ada
4625 -- Example of the use of pragma Task_Name
4627 with Ada.Task_Identification;
4628 use Ada.Task_Identification;
4629 with Text_IO; use Text_IO;
4632 type Astring is access String;
4634 task type Task_Typ (Name : access String) is
4635 pragma Task_Name (Name.all);
4638 task body Task_Typ is
4639 Nam : constant String := Image (Current_Task);
4641 Put_Line ("-->" & Nam (1 .. 14) & "<--");
4644 type Ptr_Task is access Task_Typ;
4645 Task_Var : Ptr_Task;
4649 new Task_Typ (new String'("This is task 1"));
4651 new Task_Typ (new String'("This is task 2"));
4655 @node Pragma Task_Storage
4656 @unnumberedsec Pragma Task_Storage
4657 @findex Task_Storage
4660 @smallexample @c ada
4661 pragma Task_Storage (
4662 [Task_Type =>] LOCAL_NAME,
4663 [Top_Guard =>] static_integer_EXPRESSION);
4667 This pragma specifies the length of the guard area for tasks. The guard
4668 area is an additional storage area allocated to a task. A value of zero
4669 means that either no guard area is created or a minimal guard area is
4670 created, depending on the target. This pragma can appear anywhere a
4671 @code{Storage_Size} attribute definition clause is allowed for a task
4674 @node Pragma Thread_Local_Storage
4675 @unnumberedsec Pragma Thread_Local_Storage
4676 @findex Thread_Local_Storage
4677 @cindex Task specific storage
4678 @cindex TLS (Thread Local Storage)
4681 @smallexample @c ada
4682 pragma Thread_Local_Storage ([Entity =>] LOCAL_NAME);
4686 This pragma specifies that the specified entity, which must be
4687 a variable declared in a library level package, is to be marked as
4688 "Thread Local Storage" (@code{TLS}). On systems supporting this (which
4689 include Solaris, GNU/Linux and VxWorks 6), this causes each thread
4690 (and hence each Ada task) to see a distinct copy of the variable.
4692 The variable may not have default initialization, and if there is
4693 an explicit initialization, it must be either @code{null} for an
4694 access variable, or a static expression for a scalar variable.
4695 This provides a low level mechanism similar to that provided by
4696 the @code{Ada.Task_Attributes} package, but much more efficient
4697 and is also useful in writing interface code that will interact
4698 with foreign threads.
4700 If this pragma is used on a system where @code{TLS} is not supported,
4701 then an error message will be generated and the program will be rejected.
4703 @node Pragma Time_Slice
4704 @unnumberedsec Pragma Time_Slice
4709 @smallexample @c ada
4710 pragma Time_Slice (static_duration_EXPRESSION);
4714 For implementations of GNAT on operating systems where it is possible
4715 to supply a time slice value, this pragma may be used for this purpose.
4716 It is ignored if it is used in a system that does not allow this control,
4717 or if it appears in other than the main program unit.
4719 Note that the effect of this pragma is identical to the effect of the
4720 DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
4723 @unnumberedsec Pragma Title
4728 @smallexample @c ada
4729 pragma Title (TITLING_OPTION [, TITLING OPTION]);
4732 [Title =>] STRING_LITERAL,
4733 | [Subtitle =>] STRING_LITERAL
4737 Syntax checked but otherwise ignored by GNAT@. This is a listing control
4738 pragma used in DEC Ada 83 implementations to provide a title and/or
4739 subtitle for the program listing. The program listing generated by GNAT
4740 does not have titles or subtitles.
4742 Unlike other pragmas, the full flexibility of named notation is allowed
4743 for this pragma, i.e.@: the parameters may be given in any order if named
4744 notation is used, and named and positional notation can be mixed
4745 following the normal rules for procedure calls in Ada.
4747 @node Pragma Unchecked_Union
4748 @unnumberedsec Pragma Unchecked_Union
4750 @findex Unchecked_Union
4754 @smallexample @c ada
4755 pragma Unchecked_Union (first_subtype_LOCAL_NAME);
4759 This pragma is used to specify a representation of a record type that is
4760 equivalent to a C union. It was introduced as a GNAT implementation defined
4761 pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this
4762 pragma, making it language defined, and GNAT fully implements this extended
4763 version in all language modes (Ada 83, Ada 95, and Ada 2005). For full
4764 details, consult the Ada 2005 Reference Manual, section B.3.3.
4766 @node Pragma Unimplemented_Unit
4767 @unnumberedsec Pragma Unimplemented_Unit
4768 @findex Unimplemented_Unit
4772 @smallexample @c ada
4773 pragma Unimplemented_Unit;
4777 If this pragma occurs in a unit that is processed by the compiler, GNAT
4778 aborts with the message @samp{@var{xxx} not implemented}, where
4779 @var{xxx} is the name of the current compilation unit. This pragma is
4780 intended to allow the compiler to handle unimplemented library units in
4783 The abort only happens if code is being generated. Thus you can use
4784 specs of unimplemented packages in syntax or semantic checking mode.
4786 @node Pragma Universal_Aliasing
4787 @unnumberedsec Pragma Universal_Aliasing
4788 @findex Universal_Aliasing
4792 @smallexample @c ada
4793 pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)];
4797 @var{type_LOCAL_NAME} must refer to a type declaration in the current
4798 declarative part. The effect is to inhibit strict type-based aliasing
4799 optimization for the given type. In other words, the effect is as though
4800 access types designating this type were subject to pragma No_Strict_Aliasing.
4801 For a detailed description of the strict aliasing optimization, and the
4802 situations in which it must be suppressed, @xref{Optimization and Strict
4803 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
4805 @node Pragma Universal_Data
4806 @unnumberedsec Pragma Universal_Data
4807 @findex Universal_Data
4811 @smallexample @c ada
4812 pragma Universal_Data [(library_unit_Name)];
4816 This pragma is supported only for the AAMP target and is ignored for
4817 other targets. The pragma specifies that all library-level objects
4818 (Counter 0 data) associated with the library unit are to be accessed
4819 and updated using universal addressing (24-bit addresses for AAMP5)
4820 rather than the default of 16-bit Data Environment (DENV) addressing.
4821 Use of this pragma will generally result in less efficient code for
4822 references to global data associated with the library unit, but
4823 allows such data to be located anywhere in memory. This pragma is
4824 a library unit pragma, but can also be used as a configuration pragma
4825 (including use in the @file{gnat.adc} file). The functionality
4826 of this pragma is also available by applying the -univ switch on the
4827 compilations of units where universal addressing of the data is desired.
4829 @node Pragma Unmodified
4830 @unnumberedsec Pragma Unmodified
4832 @cindex Warnings, unmodified
4836 @smallexample @c ada
4837 pragma Unmodified (LOCAL_NAME @{, LOCAL_NAME@});
4841 This pragma signals that the assignable entities (variables,
4842 @code{out} parameters, @code{in out} parameters) whose names are listed are
4843 deliberately not assigned in the current source unit. This
4844 suppresses warnings about the
4845 entities being referenced but not assigned, and in addition a warning will be
4846 generated if one of these entities is in fact assigned in the
4847 same unit as the pragma (or in the corresponding body, or one
4850 This is particularly useful for clearly signaling that a particular
4851 parameter is not modified, even though the spec suggests that it might
4854 @node Pragma Unreferenced
4855 @unnumberedsec Pragma Unreferenced
4856 @findex Unreferenced
4857 @cindex Warnings, unreferenced
4861 @smallexample @c ada
4862 pragma Unreferenced (LOCAL_NAME @{, LOCAL_NAME@});
4863 pragma Unreferenced (library_unit_NAME @{, library_unit_NAME@});
4867 This pragma signals that the entities whose names are listed are
4868 deliberately not referenced in the current source unit. This
4869 suppresses warnings about the
4870 entities being unreferenced, and in addition a warning will be
4871 generated if one of these entities is in fact referenced in the
4872 same unit as the pragma (or in the corresponding body, or one
4875 This is particularly useful for clearly signaling that a particular
4876 parameter is not referenced in some particular subprogram implementation
4877 and that this is deliberate. It can also be useful in the case of
4878 objects declared only for their initialization or finalization side
4881 If @code{LOCAL_NAME} identifies more than one matching homonym in the
4882 current scope, then the entity most recently declared is the one to which
4883 the pragma applies. Note that in the case of accept formals, the pragma
4884 Unreferenced may appear immediately after the keyword @code{do} which
4885 allows the indication of whether or not accept formals are referenced
4886 or not to be given individually for each accept statement.
4888 The left hand side of an assignment does not count as a reference for the
4889 purpose of this pragma. Thus it is fine to assign to an entity for which
4890 pragma Unreferenced is given.
4892 Note that if a warning is desired for all calls to a given subprogram,
4893 regardless of whether they occur in the same unit as the subprogram
4894 declaration, then this pragma should not be used (calls from another
4895 unit would not be flagged); pragma Obsolescent can be used instead
4896 for this purpose, see @xref{Pragma Obsolescent}.
4898 The second form of pragma @code{Unreferenced} is used within a context
4899 clause. In this case the arguments must be unit names of units previously
4900 mentioned in @code{with} clauses (similar to the usage of pragma
4901 @code{Elaborate_All}. The effect is to suppress warnings about unreferenced
4902 units and unreferenced entities within these units.
4904 @node Pragma Unreferenced_Objects
4905 @unnumberedsec Pragma Unreferenced_Objects
4906 @findex Unreferenced_Objects
4907 @cindex Warnings, unreferenced
4911 @smallexample @c ada
4912 pragma Unreferenced_Objects (local_subtype_NAME @{, local_subtype_NAME@});
4916 This pragma signals that for the types or subtypes whose names are
4917 listed, objects which are declared with one of these types or subtypes may
4918 not be referenced, and if no references appear, no warnings are given.
4920 This is particularly useful for objects which are declared solely for their
4921 initialization and finalization effect. Such variables are sometimes referred
4922 to as RAII variables (Resource Acquisition Is Initialization). Using this
4923 pragma on the relevant type (most typically a limited controlled type), the
4924 compiler will automatically suppress unwanted warnings about these variables
4925 not being referenced.
4927 @node Pragma Unreserve_All_Interrupts
4928 @unnumberedsec Pragma Unreserve_All_Interrupts
4929 @findex Unreserve_All_Interrupts
4933 @smallexample @c ada
4934 pragma Unreserve_All_Interrupts;
4938 Normally certain interrupts are reserved to the implementation. Any attempt
4939 to attach an interrupt causes Program_Error to be raised, as described in
4940 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
4941 many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
4942 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
4943 interrupt execution.
4945 If the pragma @code{Unreserve_All_Interrupts} appears anywhere in any unit in
4946 a program, then all such interrupts are unreserved. This allows the
4947 program to handle these interrupts, but disables their standard
4948 functions. For example, if this pragma is used, then pressing
4949 @kbd{Ctrl-C} will not automatically interrupt execution. However,
4950 a program can then handle the @code{SIGINT} interrupt as it chooses.
4952 For a full list of the interrupts handled in a specific implementation,
4953 see the source code for the spec of @code{Ada.Interrupts.Names} in
4954 file @file{a-intnam.ads}. This is a target dependent file that contains the
4955 list of interrupts recognized for a given target. The documentation in
4956 this file also specifies what interrupts are affected by the use of
4957 the @code{Unreserve_All_Interrupts} pragma.
4959 For a more general facility for controlling what interrupts can be
4960 handled, see pragma @code{Interrupt_State}, which subsumes the functionality
4961 of the @code{Unreserve_All_Interrupts} pragma.
4963 @node Pragma Unsuppress
4964 @unnumberedsec Pragma Unsuppress
4969 @smallexample @c ada
4970 pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
4974 This pragma undoes the effect of a previous pragma @code{Suppress}. If
4975 there is no corresponding pragma @code{Suppress} in effect, it has no
4976 effect. The range of the effect is the same as for pragma
4977 @code{Suppress}. The meaning of the arguments is identical to that used
4978 in pragma @code{Suppress}.
4980 One important application is to ensure that checks are on in cases where
4981 code depends on the checks for its correct functioning, so that the code
4982 will compile correctly even if the compiler switches are set to suppress
4985 @node Pragma Use_VADS_Size
4986 @unnumberedsec Pragma Use_VADS_Size
4987 @cindex @code{Size}, VADS compatibility
4988 @findex Use_VADS_Size
4992 @smallexample @c ada
4993 pragma Use_VADS_Size;
4997 This is a configuration pragma. In a unit to which it applies, any use
4998 of the 'Size attribute is automatically interpreted as a use of the
4999 'VADS_Size attribute. Note that this may result in incorrect semantic
5000 processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in
5001 the handling of existing code which depends on the interpretation of Size
5002 as implemented in the VADS compiler. See description of the VADS_Size
5003 attribute for further details.
5005 @node Pragma Validity_Checks
5006 @unnumberedsec Pragma Validity_Checks
5007 @findex Validity_Checks
5011 @smallexample @c ada
5012 pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
5016 This pragma is used in conjunction with compiler switches to control the
5017 built-in validity checking provided by GNAT@. The compiler switches, if set
5018 provide an initial setting for the switches, and this pragma may be used
5019 to modify these settings, or the settings may be provided entirely by
5020 the use of the pragma. This pragma can be used anywhere that a pragma
5021 is legal, including use as a configuration pragma (including use in
5022 the @file{gnat.adc} file).
5024 The form with a string literal specifies which validity options are to be
5025 activated. The validity checks are first set to include only the default
5026 reference manual settings, and then a string of letters in the string
5027 specifies the exact set of options required. The form of this string
5028 is exactly as described for the @option{-gnatVx} compiler switch (see the
5029 GNAT users guide for details). For example the following two methods
5030 can be used to enable validity checking for mode @code{in} and
5031 @code{in out} subprogram parameters:
5035 @smallexample @c ada
5036 pragma Validity_Checks ("im");
5041 gcc -c -gnatVim @dots{}
5046 The form ALL_CHECKS activates all standard checks (its use is equivalent
5047 to the use of the @code{gnatva} switch.
5049 The forms with @code{Off} and @code{On}
5050 can be used to temporarily disable validity checks
5051 as shown in the following example:
5053 @smallexample @c ada
5057 pragma Validity_Checks ("c"); -- validity checks for copies
5058 pragma Validity_Checks (Off); -- turn off validity checks
5059 A := B; -- B will not be validity checked
5060 pragma Validity_Checks (On); -- turn validity checks back on
5061 A := C; -- C will be validity checked
5064 @node Pragma Volatile
5065 @unnumberedsec Pragma Volatile
5070 @smallexample @c ada
5071 pragma Volatile (LOCAL_NAME);
5075 This pragma is defined by the Ada Reference Manual, and the GNAT
5076 implementation is fully conformant with this definition. The reason it
5077 is mentioned in this section is that a pragma of the same name was supplied
5078 in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005
5079 implementation of pragma Volatile is upwards compatible with the
5080 implementation in DEC Ada 83.
5082 @node Pragma Warnings
5083 @unnumberedsec Pragma Warnings
5088 @smallexample @c ada
5089 pragma Warnings (On | Off);
5090 pragma Warnings (On | Off, LOCAL_NAME);
5091 pragma Warnings (static_string_EXPRESSION);
5092 pragma Warnings (On | Off, static_string_EXPRESSION);
5096 Normally warnings are enabled, with the output being controlled by
5097 the command line switch. Warnings (@code{Off}) turns off generation of
5098 warnings until a Warnings (@code{On}) is encountered or the end of the
5099 current unit. If generation of warnings is turned off using this
5100 pragma, then no warning messages are output, regardless of the
5101 setting of the command line switches.
5103 The form with a single argument may be used as a configuration pragma.
5105 If the @var{LOCAL_NAME} parameter is present, warnings are suppressed for
5106 the specified entity. This suppression is effective from the point where
5107 it occurs till the end of the extended scope of the variable (similar to
5108 the scope of @code{Suppress}).
5110 The form with a single static_string_EXPRESSION argument provides more precise
5111 control over which warnings are active. The string is a list of letters
5112 specifying which warnings are to be activated and which deactivated. The
5113 code for these letters is the same as the string used in the command
5114 line switch controlling warnings. The following is a brief summary. For
5115 full details see @ref{Warning Message Control,,, gnat_ugn, @value{EDITION}
5119 a turn on all optional warnings (except d h l .o)
5120 A turn off all optional warnings
5121 .a* turn on warnings for failing assertions
5122 .A turn off warnings for failing assertions
5123 b turn on warnings for bad fixed value (not multiple of small)
5124 B* turn off warnings for bad fixed value (not multiple of small)
5125 c turn on warnings for constant conditional
5126 C* turn off warnings for constant conditional
5127 .c turn on warnings for unrepped components
5128 .C* turn off warnings for unrepped components
5129 d turn on warnings for implicit dereference
5130 D* turn off warnings for implicit dereference
5131 e treat all warnings as errors
5132 f turn on warnings for unreferenced formal
5133 F* turn off warnings for unreferenced formal
5134 g* turn on warnings for unrecognized pragma
5135 G turn off warnings for unrecognized pragma
5136 h turn on warnings for hiding variable
5137 H* turn off warnings for hiding variable
5138 i* turn on warnings for implementation unit
5139 I turn off warnings for implementation unit
5140 j turn on warnings for obsolescent (annex J) feature
5141 J* turn off warnings for obsolescent (annex J) feature
5142 k turn on warnings on constant variable
5143 K* turn off warnings on constant variable
5144 l turn on warnings for missing elaboration pragma
5145 L* turn off warnings for missing elaboration pragma
5146 m turn on warnings for variable assigned but not read
5147 M* turn off warnings for variable assigned but not read
5148 n* normal warning mode (cancels -gnatws/-gnatwe)
5149 o* turn on warnings for address clause overlay
5150 O turn off warnings for address clause overlay
5151 .o turn on warnings for out parameters assigned but not read
5152 .O* turn off warnings for out parameters assigned but not read
5153 p turn on warnings for ineffective pragma Inline in frontend
5154 P* turn off warnings for ineffective pragma Inline in frontend
5155 q* turn on warnings for questionable missing parentheses
5156 Q turn off warnings for questionable missing parentheses
5157 r turn on warnings for redundant construct
5158 R* turn off warnings for redundant construct
5159 .r turn on warnings for object renaming function
5160 .R* turn off warnings for object renaming function
5161 s suppress all warnings
5162 t turn on warnings for tracking deleted code
5163 T* turn off warnings for tracking deleted code
5164 u turn on warnings for unused entity
5165 U* turn off warnings for unused entity
5166 v* turn on warnings for unassigned variable
5167 V turn off warnings for unassigned variable
5168 w* turn on warnings for wrong low bound assumption
5169 W turn off warnings for wrong low bound assumption
5170 x* turn on warnings for export/import
5171 X turn off warnings for export/import
5172 .x turn on warnings for non-local exceptions
5173 .X* turn off warnings for non-local exceptions
5174 y* turn on warnings for Ada 2005 incompatibility
5175 Y turn off warnings for Ada 2005 incompatibility
5176 z* turn on convention/size/align warnings for unchecked conversion
5177 Z turn off convention/size/align warnings for unchecked conversion
5178 * indicates default in above list
5182 The specified warnings will be in effect until the end of the program
5183 or another pragma Warnings is encountered. The effect of the pragma is
5184 cumulative. Initially the set of warnings is the standard default set
5185 as possibly modified by compiler switches. Then each pragma Warning
5186 modifies this set of warnings as specified. This form of the pragma may
5187 also be used as a configuration pragma.
5189 The fourth form, with an On|Off parameter and a string, is used to
5190 control individual messages, based on their text. The string argument
5191 is a pattern that is used to match against the text of individual
5192 warning messages (not including the initial "warnings: " tag).
5194 The pattern may contain asterisks which match zero or more characters in
5195 the message. For example, you can use
5196 @code{pragma Warnings (Off, "*bits of*unused")} to suppress the warning
5197 message @code{warning: 960 bits of "a" unused}. No other regular
5198 expression notations are permitted. All characters other than asterisk in
5199 these three specific cases are treated as literal characters in the match.
5201 There are two ways to use this pragma. The OFF form can be used as a
5202 configuration pragma. The effect is to suppress all warnings (if any)
5203 that match the pattern string throughout the compilation.
5205 The second usage is to suppress a warning locally, and in this case, two
5206 pragmas must appear in sequence:
5208 @smallexample @c ada
5209 pragma Warnings (Off, Pattern);
5210 @dots{} code where given warning is to be suppressed
5211 pragma Warnings (On, Pattern);
5215 In this usage, the pattern string must match in the Off and On pragmas,
5216 and at least one matching warning must be suppressed.
5218 @node Pragma Weak_External
5219 @unnumberedsec Pragma Weak_External
5220 @findex Weak_External
5224 @smallexample @c ada
5225 pragma Weak_External ([Entity =>] LOCAL_NAME);
5229 @var{LOCAL_NAME} must refer to an object that is declared at the library
5230 level. This pragma specifies that the given entity should be marked as a
5231 weak symbol for the linker. It is equivalent to @code{__attribute__((weak))}
5232 in GNU C and causes @var{LOCAL_NAME} to be emitted as a weak symbol instead
5233 of a regular symbol, that is to say a symbol that does not have to be
5234 resolved by the linker if used in conjunction with a pragma Import.
5236 When a weak symbol is not resolved by the linker, its address is set to
5237 zero. This is useful in writing interfaces to external modules that may
5238 or may not be linked in the final executable, for example depending on
5239 configuration settings.
5241 If a program references at run time an entity to which this pragma has been
5242 applied, and the corresponding symbol was not resolved at link time, then
5243 the execution of the program is erroneous. It is not erroneous to take the
5244 Address of such an entity, for example to guard potential references,
5245 as shown in the example below.
5247 Some file formats do not support weak symbols so not all target machines
5248 support this pragma.
5250 @smallexample @c ada
5251 -- Example of the use of pragma Weak_External
5253 package External_Module is
5255 pragma Import (C, key);
5256 pragma Weak_External (key);
5257 function Present return boolean;
5258 end External_Module;
5260 with System; use System;
5261 package body External_Module is
5262 function Present return boolean is
5264 return key'Address /= System.Null_Address;
5266 end External_Module;
5269 @node Pragma Wide_Character_Encoding
5270 @unnumberedsec Pragma Wide_Character_Encoding
5271 @findex Wide_Character_Encoding
5275 @smallexample @c ada
5276 pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL);
5280 This pragma specifies the wide character encoding to be used in program
5281 source text appearing subsequently. It is a configuration pragma, but may
5282 also be used at any point that a pragma is allowed, and it is permissible
5283 to have more than one such pragma in a file, allowing multiple encodings
5284 to appear within the same file.
5286 The argument can be an identifier or a character literal. In the identifier
5287 case, it is one of @code{HEX}, @code{UPPER}, @code{SHIFT_JIS},
5288 @code{EUC}, @code{UTF8}, or @code{BRACKETS}. In the character literal
5289 case it is correspondingly one of the characters @samp{h}, @samp{u},
5290 @samp{s}, @samp{e}, @samp{8}, or @samp{b}.
5292 Note that when the pragma is used within a file, it affects only the
5293 encoding within that file, and does not affect withed units, specs,
5296 @node Implementation Defined Attributes
5297 @chapter Implementation Defined Attributes
5298 Ada defines (throughout the Ada reference manual,
5299 summarized in Annex K),
5300 a set of attributes that provide useful additional functionality in all
5301 areas of the language. These language defined attributes are implemented
5302 in GNAT and work as described in the Ada Reference Manual.
5304 In addition, Ada allows implementations to define additional
5305 attributes whose meaning is defined by the implementation. GNAT provides
5306 a number of these implementation-dependent attributes which can be used
5307 to extend and enhance the functionality of the compiler. This section of
5308 the GNAT reference manual describes these additional attributes.
5310 Note that any program using these attributes may not be portable to
5311 other compilers (although GNAT implements this set of attributes on all
5312 platforms). Therefore if portability to other compilers is an important
5313 consideration, you should minimize the use of these attributes.
5324 * Default_Bit_Order::
5334 * Has_Access_Values::
5335 * Has_Discriminants::
5342 * Max_Interrupt_Priority::
5344 * Maximum_Alignment::
5349 * Passed_By_Reference::
5362 * Unconstrained_Array::
5363 * Universal_Literal_String::
5364 * Unrestricted_Access::
5372 @unnumberedsec Abort_Signal
5373 @findex Abort_Signal
5375 @code{Standard'Abort_Signal} (@code{Standard} is the only allowed
5376 prefix) provides the entity for the special exception used to signal
5377 task abort or asynchronous transfer of control. Normally this attribute
5378 should only be used in the tasking runtime (it is highly peculiar, and
5379 completely outside the normal semantics of Ada, for a user program to
5380 intercept the abort exception).
5383 @unnumberedsec Address_Size
5384 @cindex Size of @code{Address}
5385 @findex Address_Size
5387 @code{Standard'Address_Size} (@code{Standard} is the only allowed
5388 prefix) is a static constant giving the number of bits in an
5389 @code{Address}. It is the same value as System.Address'Size,
5390 but has the advantage of being static, while a direct
5391 reference to System.Address'Size is non-static because Address
5395 @unnumberedsec Asm_Input
5398 The @code{Asm_Input} attribute denotes a function that takes two
5399 parameters. The first is a string, the second is an expression of the
5400 type designated by the prefix. The first (string) argument is required
5401 to be a static expression, and is the constraint for the parameter,
5402 (e.g.@: what kind of register is required). The second argument is the
5403 value to be used as the input argument. The possible values for the
5404 constant are the same as those used in the RTL, and are dependent on
5405 the configuration file used to built the GCC back end.
5406 @ref{Machine Code Insertions}
5409 @unnumberedsec Asm_Output
5412 The @code{Asm_Output} attribute denotes a function that takes two
5413 parameters. The first is a string, the second is the name of a variable
5414 of the type designated by the attribute prefix. The first (string)
5415 argument is required to be a static expression and designates the
5416 constraint for the parameter (e.g.@: what kind of register is
5417 required). The second argument is the variable to be updated with the
5418 result. The possible values for constraint are the same as those used in
5419 the RTL, and are dependent on the configuration file used to build the
5420 GCC back end. If there are no output operands, then this argument may
5421 either be omitted, or explicitly given as @code{No_Output_Operands}.
5422 @ref{Machine Code Insertions}
5425 @unnumberedsec AST_Entry
5429 This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
5430 the name of an entry, it yields a value of the predefined type AST_Handler
5431 (declared in the predefined package System, as extended by the use of
5432 pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
5433 be called when an AST occurs. For further details, refer to the @cite{DEC Ada
5434 Language Reference Manual}, section 9.12a.
5439 @code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
5440 offset within the storage unit (byte) that contains the first bit of
5441 storage allocated for the object. The value of this attribute is of the
5442 type @code{Universal_Integer}, and is always a non-negative number not
5443 exceeding the value of @code{System.Storage_Unit}.
5445 For an object that is a variable or a constant allocated in a register,
5446 the value is zero. (The use of this attribute does not force the
5447 allocation of a variable to memory).
5449 For an object that is a formal parameter, this attribute applies
5450 to either the matching actual parameter or to a copy of the
5451 matching actual parameter.
5453 For an access object the value is zero. Note that
5454 @code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
5455 designated object. Similarly for a record component
5456 @code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
5457 @code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
5458 are subject to index checks.
5460 This attribute is designed to be compatible with the DEC Ada 83 definition
5461 and implementation of the @code{Bit} attribute.
5464 @unnumberedsec Bit_Position
5465 @findex Bit_Position
5467 @code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
5468 of the fields of the record type, yields the bit
5469 offset within the record contains the first bit of
5470 storage allocated for the object. The value of this attribute is of the
5471 type @code{Universal_Integer}. The value depends only on the field
5472 @var{C} and is independent of the alignment of
5473 the containing record @var{R}.
5476 @unnumberedsec Code_Address
5477 @findex Code_Address
5478 @cindex Subprogram address
5479 @cindex Address of subprogram code
5482 attribute may be applied to subprograms in Ada 95 and Ada 2005, but the
5483 intended effect seems to be to provide
5484 an address value which can be used to call the subprogram by means of
5485 an address clause as in the following example:
5487 @smallexample @c ada
5488 procedure K is @dots{}
5491 for L'Address use K'Address;
5492 pragma Import (Ada, L);
5496 A call to @code{L} is then expected to result in a call to @code{K}@.
5497 In Ada 83, where there were no access-to-subprogram values, this was
5498 a common work-around for getting the effect of an indirect call.
5499 GNAT implements the above use of @code{Address} and the technique
5500 illustrated by the example code works correctly.
5502 However, for some purposes, it is useful to have the address of the start
5503 of the generated code for the subprogram. On some architectures, this is
5504 not necessarily the same as the @code{Address} value described above.
5505 For example, the @code{Address} value may reference a subprogram
5506 descriptor rather than the subprogram itself.
5508 The @code{'Code_Address} attribute, which can only be applied to
5509 subprogram entities, always returns the address of the start of the
5510 generated code of the specified subprogram, which may or may not be
5511 the same value as is returned by the corresponding @code{'Address}
5514 @node Default_Bit_Order
5515 @unnumberedsec Default_Bit_Order
5517 @cindex Little endian
5518 @findex Default_Bit_Order
5520 @code{Standard'Default_Bit_Order} (@code{Standard} is the only
5521 permissible prefix), provides the value @code{System.Default_Bit_Order}
5522 as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
5523 @code{Low_Order_First}). This is used to construct the definition of
5524 @code{Default_Bit_Order} in package @code{System}.
5527 @unnumberedsec Elaborated
5530 The prefix of the @code{'Elaborated} attribute must be a unit name. The
5531 value is a Boolean which indicates whether or not the given unit has been
5532 elaborated. This attribute is primarily intended for internal use by the
5533 generated code for dynamic elaboration checking, but it can also be used
5534 in user programs. The value will always be True once elaboration of all
5535 units has been completed. An exception is for units which need no
5536 elaboration, the value is always False for such units.
5539 @unnumberedsec Elab_Body
5542 This attribute can only be applied to a program unit name. It returns
5543 the entity for the corresponding elaboration procedure for elaborating
5544 the body of the referenced unit. This is used in the main generated
5545 elaboration procedure by the binder and is not normally used in any
5546 other context. However, there may be specialized situations in which it
5547 is useful to be able to call this elaboration procedure from Ada code,
5548 e.g.@: if it is necessary to do selective re-elaboration to fix some
5552 @unnumberedsec Elab_Spec
5555 This attribute can only be applied to a program unit name. It returns
5556 the entity for the corresponding elaboration procedure for elaborating
5557 the spec of the referenced unit. This is used in the main
5558 generated elaboration procedure by the binder and is not normally used
5559 in any other context. However, there may be specialized situations in
5560 which it is useful to be able to call this elaboration procedure from
5561 Ada code, e.g.@: if it is necessary to do selective re-elaboration to fix
5566 @cindex Ada 83 attributes
5569 The @code{Emax} attribute is provided for compatibility with Ada 83. See
5570 the Ada 83 reference manual for an exact description of the semantics of
5574 @unnumberedsec Enabled
5577 The @code{Enabled} attribute allows an application program to check at compile
5578 time to see if the designated check is currently enabled. The prefix is a
5579 simple identifier, referencing any predefined check name (other than
5580 @code{All_Checks}) or a check name introduced by pragma Check_Name. If
5581 no argument is given for the attribute, the check is for the general state
5582 of the check, if an argument is given, then it is an entity name, and the
5583 check indicates whether an @code{Suppress} or @code{Unsuppress} has been
5584 given naming the entity (if not, then the argument is ignored).
5586 Note that instantiations inherit the check status at the point of the
5587 instantiation, so a useful idiom is to have a library package that
5588 introduces a check name with @code{pragma Check_Name}, and then contains
5589 generic packages or subprograms which use the @code{Enabled} attribute
5590 to see if the check is enabled. A user of this package can then issue
5591 a @code{pragma Suppress} or @code{pragma Unsuppress} before instantiating
5592 the package or subprogram, controlling whether the check will be present.
5595 @unnumberedsec Enum_Rep
5596 @cindex Representation of enums
5599 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5600 function with the following spec:
5602 @smallexample @c ada
5603 function @var{S}'Enum_Rep (Arg : @var{S}'Base)
5604 return @i{Universal_Integer};
5608 It is also allowable to apply @code{Enum_Rep} directly to an object of an
5609 enumeration type or to a non-overloaded enumeration
5610 literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
5611 @code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
5612 enumeration literal or object.
5614 The function returns the representation value for the given enumeration
5615 value. This will be equal to value of the @code{Pos} attribute in the
5616 absence of an enumeration representation clause. This is a static
5617 attribute (i.e.@: the result is static if the argument is static).
5619 @code{@var{S}'Enum_Rep} can also be used with integer types and objects,
5620 in which case it simply returns the integer value. The reason for this
5621 is to allow it to be used for @code{(<>)} discrete formal arguments in
5622 a generic unit that can be instantiated with either enumeration types
5623 or integer types. Note that if @code{Enum_Rep} is used on a modular
5624 type whose upper bound exceeds the upper bound of the largest signed
5625 integer type, and the argument is a variable, so that the universal
5626 integer calculation is done at run time, then the call to @code{Enum_Rep}
5627 may raise @code{Constraint_Error}.
5630 @unnumberedsec Enum_Val
5631 @cindex Representation of enums
5634 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5635 function with the following spec:
5637 @smallexample @c ada
5638 function @var{S}'Enum_Rep (Arg : @i{Universal_Integer)
5639 return @var{S}'Base};
5643 The function returns the enumeration value whose representation matches the
5644 argument, or raises Constraint_Error if no enumeration literal of the type
5645 has the matching value.
5646 This will be equal to value of the @code{Val} attribute in the
5647 absence of an enumeration representation clause. This is a static
5648 attribute (i.e.@: the result is static if the argument is static).
5651 @unnumberedsec Epsilon
5652 @cindex Ada 83 attributes
5655 The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
5656 the Ada 83 reference manual for an exact description of the semantics of
5660 @unnumberedsec Fixed_Value
5663 For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
5664 function with the following specification:
5666 @smallexample @c ada
5667 function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
5672 The value returned is the fixed-point value @var{V} such that
5674 @smallexample @c ada
5675 @var{V} = Arg * @var{S}'Small
5679 The effect is thus similar to first converting the argument to the
5680 integer type used to represent @var{S}, and then doing an unchecked
5681 conversion to the fixed-point type. The difference is
5682 that there are full range checks, to ensure that the result is in range.
5683 This attribute is primarily intended for use in implementation of the
5684 input-output functions for fixed-point values.
5686 @node Has_Access_Values
5687 @unnumberedsec Has_Access_Values
5688 @cindex Access values, testing for
5689 @findex Has_Access_Values
5691 The prefix of the @code{Has_Access_Values} attribute is a type. The result
5692 is a Boolean value which is True if the is an access type, or is a composite
5693 type with a component (at any nesting depth) that is an access type, and is
5695 The intended use of this attribute is in conjunction with generic
5696 definitions. If the attribute is applied to a generic private type, it
5697 indicates whether or not the corresponding actual type has access values.
5699 @node Has_Discriminants
5700 @unnumberedsec Has_Discriminants
5701 @cindex Discriminants, testing for
5702 @findex Has_Discriminants
5704 The prefix of the @code{Has_Discriminants} attribute is a type. The result
5705 is a Boolean value which is True if the type has discriminants, and False
5706 otherwise. The intended use of this attribute is in conjunction with generic
5707 definitions. If the attribute is applied to a generic private type, it
5708 indicates whether or not the corresponding actual type has discriminants.
5714 The @code{Img} attribute differs from @code{Image} in that it may be
5715 applied to objects as well as types, in which case it gives the
5716 @code{Image} for the subtype of the object. This is convenient for
5719 @smallexample @c ada
5720 Put_Line ("X = " & X'Img);
5724 has the same meaning as the more verbose:
5726 @smallexample @c ada
5727 Put_Line ("X = " & @var{T}'Image (X));
5731 where @var{T} is the (sub)type of the object @code{X}.
5734 @unnumberedsec Integer_Value
5735 @findex Integer_Value
5737 For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
5738 function with the following spec:
5740 @smallexample @c ada
5741 function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
5746 The value returned is the integer value @var{V}, such that
5748 @smallexample @c ada
5749 Arg = @var{V} * @var{T}'Small
5753 where @var{T} is the type of @code{Arg}.
5754 The effect is thus similar to first doing an unchecked conversion from
5755 the fixed-point type to its corresponding implementation type, and then
5756 converting the result to the target integer type. The difference is
5757 that there are full range checks, to ensure that the result is in range.
5758 This attribute is primarily intended for use in implementation of the
5759 standard input-output functions for fixed-point values.
5762 @unnumberedsec Invalid_Value
5763 @findex Invalid_Value
5765 For every scalar type S, S'Invalid_Value returns an undefined value of the
5766 type. If possible this value is an invalid representation for the type. The
5767 value returned is identical to the value used to initialize an otherwise
5768 uninitialized value of the type if pragma Initialize_Scalars is used,
5769 including the ability to modify the value with the binder -Sxx flag and
5770 relevant environment variables at run time.
5773 @unnumberedsec Large
5774 @cindex Ada 83 attributes
5777 The @code{Large} attribute is provided for compatibility with Ada 83. See
5778 the Ada 83 reference manual for an exact description of the semantics of
5782 @unnumberedsec Machine_Size
5783 @findex Machine_Size
5785 This attribute is identical to the @code{Object_Size} attribute. It is
5786 provided for compatibility with the DEC Ada 83 attribute of this name.
5789 @unnumberedsec Mantissa
5790 @cindex Ada 83 attributes
5793 The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
5794 the Ada 83 reference manual for an exact description of the semantics of
5797 @node Max_Interrupt_Priority
5798 @unnumberedsec Max_Interrupt_Priority
5799 @cindex Interrupt priority, maximum
5800 @findex Max_Interrupt_Priority
5802 @code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
5803 permissible prefix), provides the same value as
5804 @code{System.Max_Interrupt_Priority}.
5807 @unnumberedsec Max_Priority
5808 @cindex Priority, maximum
5809 @findex Max_Priority
5811 @code{Standard'Max_Priority} (@code{Standard} is the only permissible
5812 prefix) provides the same value as @code{System.Max_Priority}.
5814 @node Maximum_Alignment
5815 @unnumberedsec Maximum_Alignment
5816 @cindex Alignment, maximum
5817 @findex Maximum_Alignment
5819 @code{Standard'Maximum_Alignment} (@code{Standard} is the only
5820 permissible prefix) provides the maximum useful alignment value for the
5821 target. This is a static value that can be used to specify the alignment
5822 for an object, guaranteeing that it is properly aligned in all
5825 @node Mechanism_Code
5826 @unnumberedsec Mechanism_Code
5827 @cindex Return values, passing mechanism
5828 @cindex Parameters, passing mechanism
5829 @findex Mechanism_Code
5831 @code{@var{function}'Mechanism_Code} yields an integer code for the
5832 mechanism used for the result of function, and
5833 @code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
5834 used for formal parameter number @var{n} (a static integer value with 1
5835 meaning the first parameter) of @var{subprogram}. The code returned is:
5843 by descriptor (default descriptor class)
5845 by descriptor (UBS: unaligned bit string)
5847 by descriptor (UBSB: aligned bit string with arbitrary bounds)
5849 by descriptor (UBA: unaligned bit array)
5851 by descriptor (S: string, also scalar access type parameter)
5853 by descriptor (SB: string with arbitrary bounds)
5855 by descriptor (A: contiguous array)
5857 by descriptor (NCA: non-contiguous array)
5861 Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
5864 @node Null_Parameter
5865 @unnumberedsec Null_Parameter
5866 @cindex Zero address, passing
5867 @findex Null_Parameter
5869 A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
5870 type or subtype @var{T} allocated at machine address zero. The attribute
5871 is allowed only as the default expression of a formal parameter, or as
5872 an actual expression of a subprogram call. In either case, the
5873 subprogram must be imported.
5875 The identity of the object is represented by the address zero in the
5876 argument list, independent of the passing mechanism (explicit or
5879 This capability is needed to specify that a zero address should be
5880 passed for a record or other composite object passed by reference.
5881 There is no way of indicating this without the @code{Null_Parameter}
5885 @unnumberedsec Object_Size
5886 @cindex Size, used for objects
5889 The size of an object is not necessarily the same as the size of the type
5890 of an object. This is because by default object sizes are increased to be
5891 a multiple of the alignment of the object. For example,
5892 @code{Natural'Size} is
5893 31, but by default objects of type @code{Natural} will have a size of 32 bits.
5894 Similarly, a record containing an integer and a character:
5896 @smallexample @c ada
5904 will have a size of 40 (that is @code{Rec'Size} will be 40. The
5905 alignment will be 4, because of the
5906 integer field, and so the default size of record objects for this type
5907 will be 64 (8 bytes).
5911 @cindex Capturing Old values
5912 @cindex Postconditions
5914 The attribute Prefix'Old can be used within a
5915 subprogram to refer to the value of the prefix on entry. So for
5916 example if you have an argument of a record type X called Arg1,
5917 you can refer to Arg1.Field'Old which yields the value of
5918 Arg1.Field on entry. The implementation simply involves generating
5919 an object declaration which captures the value on entry. Any
5920 prefix is allowed except one of a limited type (since limited
5921 types cannot be copied to capture their values) or a local variable
5922 (since it does not exist at subprogram entry time).
5924 The following example shows the use of 'Old to implement
5925 a test of a postcondition:
5927 @smallexample @c ada
5938 package body Old_Pkg is
5939 Count : Natural := 0;
5943 ... code manipulating the value of Count
5945 pragma Assert (Count = Count'Old + 1);
5951 Note that it is allowed to apply 'Old to a constant entity, but this will
5952 result in a warning, since the old and new values will always be the same.
5954 @node Passed_By_Reference
5955 @unnumberedsec Passed_By_Reference
5956 @cindex Parameters, when passed by reference
5957 @findex Passed_By_Reference
5959 @code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
5960 a value of type @code{Boolean} value that is @code{True} if the type is
5961 normally passed by reference and @code{False} if the type is normally
5962 passed by copy in calls. For scalar types, the result is always @code{False}
5963 and is static. For non-scalar types, the result is non-static.
5966 @unnumberedsec Pool_Address
5967 @cindex Parameters, when passed by reference
5968 @findex Pool_Address
5970 @code{@var{X}'Pool_Address} for any object @var{X} returns the address
5971 of X within its storage pool. This is the same as
5972 @code{@var{X}'Address}, except that for an unconstrained array whose
5973 bounds are allocated just before the first component,
5974 @code{@var{X}'Pool_Address} returns the address of those bounds,
5975 whereas @code{@var{X}'Address} returns the address of the first
5978 Here, we are interpreting ``storage pool'' broadly to mean ``wherever
5979 the object is allocated'', which could be a user-defined storage pool,
5980 the global heap, on the stack, or in a static memory area. For an
5981 object created by @code{new}, @code{@var{Ptr.all}'Pool_Address} is
5982 what is passed to @code{Allocate} and returned from @code{Deallocate}.
5985 @unnumberedsec Range_Length
5986 @findex Range_Length
5988 @code{@var{type}'Range_Length} for any discrete type @var{type} yields
5989 the number of values represented by the subtype (zero for a null
5990 range). The result is static for static subtypes. @code{Range_Length}
5991 applied to the index subtype of a one dimensional array always gives the
5992 same result as @code{Range} applied to the array itself.
5995 @unnumberedsec Safe_Emax
5996 @cindex Ada 83 attributes
5999 The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
6000 the Ada 83 reference manual for an exact description of the semantics of
6004 @unnumberedsec Safe_Large
6005 @cindex Ada 83 attributes
6008 The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
6009 the Ada 83 reference manual for an exact description of the semantics of
6013 @unnumberedsec Small
6014 @cindex Ada 83 attributes
6017 The @code{Small} attribute is defined in Ada 95 (and Ada 2005) only for
6019 GNAT also allows this attribute to be applied to floating-point types
6020 for compatibility with Ada 83. See
6021 the Ada 83 reference manual for an exact description of the semantics of
6022 this attribute when applied to floating-point types.
6025 @unnumberedsec Storage_Unit
6026 @findex Storage_Unit
6028 @code{Standard'Storage_Unit} (@code{Standard} is the only permissible
6029 prefix) provides the same value as @code{System.Storage_Unit}.
6032 @unnumberedsec Stub_Type
6035 The GNAT implementation of remote access-to-classwide types is
6036 organized as described in AARM section E.4 (20.t): a value of an RACW type
6037 (designating a remote object) is represented as a normal access
6038 value, pointing to a "stub" object which in turn contains the
6039 necessary information to contact the designated remote object. A
6040 call on any dispatching operation of such a stub object does the
6041 remote call, if necessary, using the information in the stub object
6042 to locate the target partition, etc.
6044 For a prefix @code{T} that denotes a remote access-to-classwide type,
6045 @code{T'Stub_Type} denotes the type of the corresponding stub objects.
6047 By construction, the layout of @code{T'Stub_Type} is identical to that of
6048 type @code{RACW_Stub_Type} declared in the internal implementation-defined
6049 unit @code{System.Partition_Interface}. Use of this attribute will create
6050 an implicit dependency on this unit.
6053 @unnumberedsec Target_Name
6056 @code{Standard'Target_Name} (@code{Standard} is the only permissible
6057 prefix) provides a static string value that identifies the target
6058 for the current compilation. For GCC implementations, this is the
6059 standard gcc target name without the terminating slash (for
6060 example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
6066 @code{Standard'Tick} (@code{Standard} is the only permissible prefix)
6067 provides the same value as @code{System.Tick},
6070 @unnumberedsec To_Address
6073 The @code{System'To_Address}
6074 (@code{System} is the only permissible prefix)
6075 denotes a function identical to
6076 @code{System.Storage_Elements.To_Address} except that
6077 it is a static attribute. This means that if its argument is
6078 a static expression, then the result of the attribute is a
6079 static expression. The result is that such an expression can be
6080 used in contexts (e.g.@: preelaborable packages) which require a
6081 static expression and where the function call could not be used
6082 (since the function call is always non-static, even if its
6083 argument is static).
6086 @unnumberedsec Type_Class
6089 @code{@var{type}'Type_Class} for any type or subtype @var{type} yields
6090 the value of the type class for the full type of @var{type}. If
6091 @var{type} is a generic formal type, the value is the value for the
6092 corresponding actual subtype. The value of this attribute is of type
6093 @code{System.Aux_DEC.Type_Class}, which has the following definition:
6095 @smallexample @c ada
6097 (Type_Class_Enumeration,
6099 Type_Class_Fixed_Point,
6100 Type_Class_Floating_Point,
6105 Type_Class_Address);
6109 Protected types yield the value @code{Type_Class_Task}, which thus
6110 applies to all concurrent types. This attribute is designed to
6111 be compatible with the DEC Ada 83 attribute of the same name.
6114 @unnumberedsec UET_Address
6117 The @code{UET_Address} attribute can only be used for a prefix which
6118 denotes a library package. It yields the address of the unit exception
6119 table when zero cost exception handling is used. This attribute is
6120 intended only for use within the GNAT implementation. See the unit
6121 @code{Ada.Exceptions} in files @file{a-except.ads} and @file{a-except.adb}
6122 for details on how this attribute is used in the implementation.
6124 @node Unconstrained_Array
6125 @unnumberedsec Unconstrained_Array
6126 @findex Unconstrained_Array
6128 The @code{Unconstrained_Array} attribute can be used with a prefix that
6129 denotes any type or subtype. It is a static attribute that yields
6130 @code{True} if the prefix designates an unconstrained array,
6131 and @code{False} otherwise. In a generic instance, the result is
6132 still static, and yields the result of applying this test to the
6135 @node Universal_Literal_String
6136 @unnumberedsec Universal_Literal_String
6137 @cindex Named numbers, representation of
6138 @findex Universal_Literal_String
6140 The prefix of @code{Universal_Literal_String} must be a named
6141 number. The static result is the string consisting of the characters of
6142 the number as defined in the original source. This allows the user
6143 program to access the actual text of named numbers without intermediate
6144 conversions and without the need to enclose the strings in quotes (which
6145 would preclude their use as numbers). This is used internally for the
6146 construction of values of the floating-point attributes from the file
6147 @file{ttypef.ads}, but may also be used by user programs.
6149 For example, the following program prints the first 50 digits of pi:
6151 @smallexample @c ada
6152 with Text_IO; use Text_IO;
6156 Put (Ada.Numerics.Pi'Universal_Literal_String);
6160 @node Unrestricted_Access
6161 @unnumberedsec Unrestricted_Access
6162 @cindex @code{Access}, unrestricted
6163 @findex Unrestricted_Access
6165 The @code{Unrestricted_Access} attribute is similar to @code{Access}
6166 except that all accessibility and aliased view checks are omitted. This
6167 is a user-beware attribute. It is similar to
6168 @code{Address}, for which it is a desirable replacement where the value
6169 desired is an access type. In other words, its effect is identical to
6170 first applying the @code{Address} attribute and then doing an unchecked
6171 conversion to a desired access type. In GNAT, but not necessarily in
6172 other implementations, the use of static chains for inner level
6173 subprograms means that @code{Unrestricted_Access} applied to a
6174 subprogram yields a value that can be called as long as the subprogram
6175 is in scope (normal Ada accessibility rules restrict this usage).
6177 It is possible to use @code{Unrestricted_Access} for any type, but care
6178 must be exercised if it is used to create pointers to unconstrained
6179 objects. In this case, the resulting pointer has the same scope as the
6180 context of the attribute, and may not be returned to some enclosing
6181 scope. For instance, a function cannot use @code{Unrestricted_Access}
6182 to create a unconstrained pointer and then return that value to the
6186 @unnumberedsec VADS_Size
6187 @cindex @code{Size}, VADS compatibility
6190 The @code{'VADS_Size} attribute is intended to make it easier to port
6191 legacy code which relies on the semantics of @code{'Size} as implemented
6192 by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
6193 same semantic interpretation. In particular, @code{'VADS_Size} applied
6194 to a predefined or other primitive type with no Size clause yields the
6195 Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
6196 typical machines). In addition @code{'VADS_Size} applied to an object
6197 gives the result that would be obtained by applying the attribute to
6198 the corresponding type.
6201 @unnumberedsec Value_Size
6202 @cindex @code{Size}, setting for not-first subtype
6204 @code{@var{type}'Value_Size} is the number of bits required to represent
6205 a value of the given subtype. It is the same as @code{@var{type}'Size},
6206 but, unlike @code{Size}, may be set for non-first subtypes.
6209 @unnumberedsec Wchar_T_Size
6210 @findex Wchar_T_Size
6211 @code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
6212 prefix) provides the size in bits of the C @code{wchar_t} type
6213 primarily for constructing the definition of this type in
6214 package @code{Interfaces.C}.
6217 @unnumberedsec Word_Size
6219 @code{Standard'Word_Size} (@code{Standard} is the only permissible
6220 prefix) provides the value @code{System.Word_Size}.
6222 @c ------------------------
6223 @node Implementation Advice
6224 @chapter Implementation Advice
6226 The main text of the Ada Reference Manual describes the required
6227 behavior of all Ada compilers, and the GNAT compiler conforms to
6230 In addition, there are sections throughout the Ada Reference Manual headed
6231 by the phrase ``Implementation advice''. These sections are not normative,
6232 i.e., they do not specify requirements that all compilers must
6233 follow. Rather they provide advice on generally desirable behavior. You
6234 may wonder why they are not requirements. The most typical answer is
6235 that they describe behavior that seems generally desirable, but cannot
6236 be provided on all systems, or which may be undesirable on some systems.
6238 As far as practical, GNAT follows the implementation advice sections in
6239 the Ada Reference Manual. This chapter contains a table giving the
6240 reference manual section number, paragraph number and several keywords
6241 for each advice. Each entry consists of the text of the advice followed
6242 by the GNAT interpretation of this advice. Most often, this simply says
6243 ``followed'', which means that GNAT follows the advice. However, in a
6244 number of cases, GNAT deliberately deviates from this advice, in which
6245 case the text describes what GNAT does and why.
6247 @cindex Error detection
6248 @unnumberedsec 1.1.3(20): Error Detection
6251 If an implementation detects the use of an unsupported Specialized Needs
6252 Annex feature at run time, it should raise @code{Program_Error} if
6255 Not relevant. All specialized needs annex features are either supported,
6256 or diagnosed at compile time.
6259 @unnumberedsec 1.1.3(31): Child Units
6262 If an implementation wishes to provide implementation-defined
6263 extensions to the functionality of a language-defined library unit, it
6264 should normally do so by adding children to the library unit.
6268 @cindex Bounded errors
6269 @unnumberedsec 1.1.5(12): Bounded Errors
6272 If an implementation detects a bounded error or erroneous
6273 execution, it should raise @code{Program_Error}.
6275 Followed in all cases in which the implementation detects a bounded
6276 error or erroneous execution. Not all such situations are detected at
6280 @unnumberedsec 2.8(16): Pragmas
6283 Normally, implementation-defined pragmas should have no semantic effect
6284 for error-free programs; that is, if the implementation-defined pragmas
6285 are removed from a working program, the program should still be legal,
6286 and should still have the same semantics.
6288 The following implementation defined pragmas are exceptions to this
6300 @item CPP_Constructor
6304 @item Interface_Name
6306 @item Machine_Attribute
6308 @item Unimplemented_Unit
6310 @item Unchecked_Union
6315 In each of the above cases, it is essential to the purpose of the pragma
6316 that this advice not be followed. For details see the separate section
6317 on implementation defined pragmas.
6319 @unnumberedsec 2.8(17-19): Pragmas
6322 Normally, an implementation should not define pragmas that can
6323 make an illegal program legal, except as follows:
6327 A pragma used to complete a declaration, such as a pragma @code{Import};
6331 A pragma used to configure the environment by adding, removing, or
6332 replacing @code{library_items}.
6334 See response to paragraph 16 of this same section.
6336 @cindex Character Sets
6337 @cindex Alternative Character Sets
6338 @unnumberedsec 3.5.2(5): Alternative Character Sets
6341 If an implementation supports a mode with alternative interpretations
6342 for @code{Character} and @code{Wide_Character}, the set of graphic
6343 characters of @code{Character} should nevertheless remain a proper
6344 subset of the set of graphic characters of @code{Wide_Character}. Any
6345 character set ``localizations'' should be reflected in the results of
6346 the subprograms defined in the language-defined package
6347 @code{Characters.Handling} (see A.3) available in such a mode. In a mode with
6348 an alternative interpretation of @code{Character}, the implementation should
6349 also support a corresponding change in what is a legal
6350 @code{identifier_letter}.
6352 Not all wide character modes follow this advice, in particular the JIS
6353 and IEC modes reflect standard usage in Japan, and in these encoding,
6354 the upper half of the Latin-1 set is not part of the wide-character
6355 subset, since the most significant bit is used for wide character
6356 encoding. However, this only applies to the external forms. Internally
6357 there is no such restriction.
6359 @cindex Integer types
6360 @unnumberedsec 3.5.4(28): Integer Types
6364 An implementation should support @code{Long_Integer} in addition to
6365 @code{Integer} if the target machine supports 32-bit (or longer)
6366 arithmetic. No other named integer subtypes are recommended for package
6367 @code{Standard}. Instead, appropriate named integer subtypes should be
6368 provided in the library package @code{Interfaces} (see B.2).
6370 @code{Long_Integer} is supported. Other standard integer types are supported
6371 so this advice is not fully followed. These types
6372 are supported for convenient interface to C, and so that all hardware
6373 types of the machine are easily available.
6374 @unnumberedsec 3.5.4(29): Integer Types
6378 An implementation for a two's complement machine should support
6379 modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
6380 implementation should support a non-binary modules up to @code{Integer'Last}.
6384 @cindex Enumeration values
6385 @unnumberedsec 3.5.5(8): Enumeration Values
6388 For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
6389 subtype, if the value of the operand does not correspond to the internal
6390 code for any enumeration literal of its type (perhaps due to an
6391 un-initialized variable), then the implementation should raise
6392 @code{Program_Error}. This is particularly important for enumeration
6393 types with noncontiguous internal codes specified by an
6394 enumeration_representation_clause.
6399 @unnumberedsec 3.5.7(17): Float Types
6402 An implementation should support @code{Long_Float} in addition to
6403 @code{Float} if the target machine supports 11 or more digits of
6404 precision. No other named floating point subtypes are recommended for
6405 package @code{Standard}. Instead, appropriate named floating point subtypes
6406 should be provided in the library package @code{Interfaces} (see B.2).
6408 @code{Short_Float} and @code{Long_Long_Float} are also provided. The
6409 former provides improved compatibility with other implementations
6410 supporting this type. The latter corresponds to the highest precision
6411 floating-point type supported by the hardware. On most machines, this
6412 will be the same as @code{Long_Float}, but on some machines, it will
6413 correspond to the IEEE extended form. The notable case is all ia32
6414 (x86) implementations, where @code{Long_Long_Float} corresponds to
6415 the 80-bit extended precision format supported in hardware on this
6416 processor. Note that the 128-bit format on SPARC is not supported,
6417 since this is a software rather than a hardware format.
6419 @cindex Multidimensional arrays
6420 @cindex Arrays, multidimensional
6421 @unnumberedsec 3.6.2(11): Multidimensional Arrays
6424 An implementation should normally represent multidimensional arrays in
6425 row-major order, consistent with the notation used for multidimensional
6426 array aggregates (see 4.3.3). However, if a pragma @code{Convention}
6427 (@code{Fortran}, @dots{}) applies to a multidimensional array type, then
6428 column-major order should be used instead (see B.5, ``Interfacing with
6433 @findex Duration'Small
6434 @unnumberedsec 9.6(30-31): Duration'Small
6437 Whenever possible in an implementation, the value of @code{Duration'Small}
6438 should be no greater than 100 microseconds.
6440 Followed. (@code{Duration'Small} = 10**(@minus{}9)).
6444 The time base for @code{delay_relative_statements} should be monotonic;
6445 it need not be the same time base as used for @code{Calendar.Clock}.
6449 @unnumberedsec 10.2.1(12): Consistent Representation
6452 In an implementation, a type declared in a pre-elaborated package should
6453 have the same representation in every elaboration of a given version of
6454 the package, whether the elaborations occur in distinct executions of
6455 the same program, or in executions of distinct programs or partitions
6456 that include the given version.
6458 Followed, except in the case of tagged types. Tagged types involve
6459 implicit pointers to a local copy of a dispatch table, and these pointers
6460 have representations which thus depend on a particular elaboration of the
6461 package. It is not easy to see how it would be possible to follow this
6462 advice without severely impacting efficiency of execution.
6464 @cindex Exception information
6465 @unnumberedsec 11.4.1(19): Exception Information
6468 @code{Exception_Message} by default and @code{Exception_Information}
6469 should produce information useful for
6470 debugging. @code{Exception_Message} should be short, about one
6471 line. @code{Exception_Information} can be long. @code{Exception_Message}
6472 should not include the
6473 @code{Exception_Name}. @code{Exception_Information} should include both
6474 the @code{Exception_Name} and the @code{Exception_Message}.
6476 Followed. For each exception that doesn't have a specified
6477 @code{Exception_Message}, the compiler generates one containing the location
6478 of the raise statement. This location has the form ``file:line'', where
6479 file is the short file name (without path information) and line is the line
6480 number in the file. Note that in the case of the Zero Cost Exception
6481 mechanism, these messages become redundant with the Exception_Information that
6482 contains a full backtrace of the calling sequence, so they are disabled.
6483 To disable explicitly the generation of the source location message, use the
6484 Pragma @code{Discard_Names}.
6486 @cindex Suppression of checks
6487 @cindex Checks, suppression of
6488 @unnumberedsec 11.5(28): Suppression of Checks
6491 The implementation should minimize the code executed for checks that
6492 have been suppressed.
6496 @cindex Representation clauses
6497 @unnumberedsec 13.1 (21-24): Representation Clauses
6500 The recommended level of support for all representation items is
6501 qualified as follows:
6505 An implementation need not support representation items containing
6506 non-static expressions, except that an implementation should support a
6507 representation item for a given entity if each non-static expression in
6508 the representation item is a name that statically denotes a constant
6509 declared before the entity.
6511 Followed. In fact, GNAT goes beyond the recommended level of support
6512 by allowing nonstatic expressions in some representation clauses even
6513 without the need to declare constants initialized with the values of
6517 @smallexample @c ada
6520 for Y'Address use X'Address;>>
6526 An implementation need not support a specification for the @code{Size}
6527 for a given composite subtype, nor the size or storage place for an
6528 object (including a component) of a given composite subtype, unless the
6529 constraints on the subtype and its composite subcomponents (if any) are
6530 all static constraints.
6532 Followed. Size Clauses are not permitted on non-static components, as
6537 An aliased component, or a component whose type is by-reference, should
6538 always be allocated at an addressable location.
6542 @cindex Packed types
6543 @unnumberedsec 13.2(6-8): Packed Types
6546 If a type is packed, then the implementation should try to minimize
6547 storage allocated to objects of the type, possibly at the expense of
6548 speed of accessing components, subject to reasonable complexity in
6549 addressing calculations.
6553 The recommended level of support pragma @code{Pack} is:
6555 For a packed record type, the components should be packed as tightly as
6556 possible subject to the Sizes of the component subtypes, and subject to
6557 any @code{record_representation_clause} that applies to the type; the
6558 implementation may, but need not, reorder components or cross aligned
6559 word boundaries to improve the packing. A component whose @code{Size} is
6560 greater than the word size may be allocated an integral number of words.
6562 Followed. Tight packing of arrays is supported for all component sizes
6563 up to 64-bits. If the array component size is 1 (that is to say, if
6564 the component is a boolean type or an enumeration type with two values)
6565 then values of the type are implicitly initialized to zero. This
6566 happens both for objects of the packed type, and for objects that have a
6567 subcomponent of the packed type.
6571 An implementation should support Address clauses for imported
6575 @cindex @code{Address} clauses
6576 @unnumberedsec 13.3(14-19): Address Clauses
6580 For an array @var{X}, @code{@var{X}'Address} should point at the first
6581 component of the array, and not at the array bounds.
6587 The recommended level of support for the @code{Address} attribute is:
6589 @code{@var{X}'Address} should produce a useful result if @var{X} is an
6590 object that is aliased or of a by-reference type, or is an entity whose
6591 @code{Address} has been specified.
6593 Followed. A valid address will be produced even if none of those
6594 conditions have been met. If necessary, the object is forced into
6595 memory to ensure the address is valid.
6599 An implementation should support @code{Address} clauses for imported
6606 Objects (including subcomponents) that are aliased or of a by-reference
6607 type should be allocated on storage element boundaries.
6613 If the @code{Address} of an object is specified, or it is imported or exported,
6614 then the implementation should not perform optimizations based on
6615 assumptions of no aliases.
6619 @cindex @code{Alignment} clauses
6620 @unnumberedsec 13.3(29-35): Alignment Clauses
6623 The recommended level of support for the @code{Alignment} attribute for
6626 An implementation should support specified Alignments that are factors
6627 and multiples of the number of storage elements per word, subject to the
6634 An implementation need not support specified @code{Alignment}s for
6635 combinations of @code{Size}s and @code{Alignment}s that cannot be easily
6636 loaded and stored by available machine instructions.
6642 An implementation need not support specified @code{Alignment}s that are
6643 greater than the maximum @code{Alignment} the implementation ever returns by
6650 The recommended level of support for the @code{Alignment} attribute for
6653 Same as above, for subtypes, but in addition:
6659 For stand-alone library-level objects of statically constrained
6660 subtypes, the implementation should support all @code{Alignment}s
6661 supported by the target linker. For example, page alignment is likely to
6662 be supported for such objects, but not for subtypes.
6666 @cindex @code{Size} clauses
6667 @unnumberedsec 13.3(42-43): Size Clauses
6670 The recommended level of support for the @code{Size} attribute of
6673 A @code{Size} clause should be supported for an object if the specified
6674 @code{Size} is at least as large as its subtype's @code{Size}, and
6675 corresponds to a size in storage elements that is a multiple of the
6676 object's @code{Alignment} (if the @code{Alignment} is nonzero).
6680 @unnumberedsec 13.3(50-56): Size Clauses
6683 If the @code{Size} of a subtype is specified, and allows for efficient
6684 independent addressability (see 9.10) on the target architecture, then
6685 the @code{Size} of the following objects of the subtype should equal the
6686 @code{Size} of the subtype:
6688 Aliased objects (including components).
6694 @code{Size} clause on a composite subtype should not affect the
6695 internal layout of components.
6697 Followed. But note that this can be overridden by use of the implementation
6698 pragma Implicit_Packing in the case of packed arrays.
6702 The recommended level of support for the @code{Size} attribute of subtypes is:
6706 The @code{Size} (if not specified) of a static discrete or fixed point
6707 subtype should be the number of bits needed to represent each value
6708 belonging to the subtype using an unbiased representation, leaving space
6709 for a sign bit only if the subtype contains negative values. If such a
6710 subtype is a first subtype, then an implementation should support a
6711 specified @code{Size} for it that reflects this representation.
6717 For a subtype implemented with levels of indirection, the @code{Size}
6718 should include the size of the pointers, but not the size of what they
6723 @cindex @code{Component_Size} clauses
6724 @unnumberedsec 13.3(71-73): Component Size Clauses
6727 The recommended level of support for the @code{Component_Size}
6732 An implementation need not support specified @code{Component_Sizes} that are
6733 less than the @code{Size} of the component subtype.
6739 An implementation should support specified @code{Component_Size}s that
6740 are factors and multiples of the word size. For such
6741 @code{Component_Size}s, the array should contain no gaps between
6742 components. For other @code{Component_Size}s (if supported), the array
6743 should contain no gaps between components when packing is also
6744 specified; the implementation should forbid this combination in cases
6745 where it cannot support a no-gaps representation.
6749 @cindex Enumeration representation clauses
6750 @cindex Representation clauses, enumeration
6751 @unnumberedsec 13.4(9-10): Enumeration Representation Clauses
6754 The recommended level of support for enumeration representation clauses
6757 An implementation need not support enumeration representation clauses
6758 for boolean types, but should at minimum support the internal codes in
6759 the range @code{System.Min_Int.System.Max_Int}.
6763 @cindex Record representation clauses
6764 @cindex Representation clauses, records
6765 @unnumberedsec 13.5.1(17-22): Record Representation Clauses
6768 The recommended level of support for
6769 @*@code{record_representation_clauses} is:
6771 An implementation should support storage places that can be extracted
6772 with a load, mask, shift sequence of machine code, and set with a load,
6773 shift, mask, store sequence, given the available machine instructions
6780 A storage place should be supported if its size is equal to the
6781 @code{Size} of the component subtype, and it starts and ends on a
6782 boundary that obeys the @code{Alignment} of the component subtype.
6788 If the default bit ordering applies to the declaration of a given type,
6789 then for a component whose subtype's @code{Size} is less than the word
6790 size, any storage place that does not cross an aligned word boundary
6791 should be supported.
6797 An implementation may reserve a storage place for the tag field of a
6798 tagged type, and disallow other components from overlapping that place.
6800 Followed. The storage place for the tag field is the beginning of the tagged
6801 record, and its size is Address'Size. GNAT will reject an explicit component
6802 clause for the tag field.
6806 An implementation need not support a @code{component_clause} for a
6807 component of an extension part if the storage place is not after the
6808 storage places of all components of the parent type, whether or not
6809 those storage places had been specified.
6811 Followed. The above advice on record representation clauses is followed,
6812 and all mentioned features are implemented.
6814 @cindex Storage place attributes
6815 @unnumberedsec 13.5.2(5): Storage Place Attributes
6818 If a component is represented using some form of pointer (such as an
6819 offset) to the actual data of the component, and this data is contiguous
6820 with the rest of the object, then the storage place attributes should
6821 reflect the place of the actual data, not the pointer. If a component is
6822 allocated discontinuously from the rest of the object, then a warning
6823 should be generated upon reference to one of its storage place
6826 Followed. There are no such components in GNAT@.
6828 @cindex Bit ordering
6829 @unnumberedsec 13.5.3(7-8): Bit Ordering
6832 The recommended level of support for the non-default bit ordering is:
6836 If @code{Word_Size} = @code{Storage_Unit}, then the implementation
6837 should support the non-default bit ordering in addition to the default
6840 Followed. Word size does not equal storage size in this implementation.
6841 Thus non-default bit ordering is not supported.
6843 @cindex @code{Address}, as private type
6844 @unnumberedsec 13.7(37): Address as Private
6847 @code{Address} should be of a private type.
6851 @cindex Operations, on @code{Address}
6852 @cindex @code{Address}, operations of
6853 @unnumberedsec 13.7.1(16): Address Operations
6856 Operations in @code{System} and its children should reflect the target
6857 environment semantics as closely as is reasonable. For example, on most
6858 machines, it makes sense for address arithmetic to ``wrap around''.
6859 Operations that do not make sense should raise @code{Program_Error}.
6861 Followed. Address arithmetic is modular arithmetic that wraps around. No
6862 operation raises @code{Program_Error}, since all operations make sense.
6864 @cindex Unchecked conversion
6865 @unnumberedsec 13.9(14-17): Unchecked Conversion
6868 The @code{Size} of an array object should not include its bounds; hence,
6869 the bounds should not be part of the converted data.
6875 The implementation should not generate unnecessary run-time checks to
6876 ensure that the representation of @var{S} is a representation of the
6877 target type. It should take advantage of the permission to return by
6878 reference when possible. Restrictions on unchecked conversions should be
6879 avoided unless required by the target environment.
6881 Followed. There are no restrictions on unchecked conversion. A warning is
6882 generated if the source and target types do not have the same size since
6883 the semantics in this case may be target dependent.
6887 The recommended level of support for unchecked conversions is:
6891 Unchecked conversions should be supported and should be reversible in
6892 the cases where this clause defines the result. To enable meaningful use
6893 of unchecked conversion, a contiguous representation should be used for
6894 elementary subtypes, for statically constrained array subtypes whose
6895 component subtype is one of the subtypes described in this paragraph,
6896 and for record subtypes without discriminants whose component subtypes
6897 are described in this paragraph.
6901 @cindex Heap usage, implicit
6902 @unnumberedsec 13.11(23-25): Implicit Heap Usage
6905 An implementation should document any cases in which it dynamically
6906 allocates heap storage for a purpose other than the evaluation of an
6909 Followed, the only other points at which heap storage is dynamically
6910 allocated are as follows:
6914 At initial elaboration time, to allocate dynamically sized global
6918 To allocate space for a task when a task is created.
6921 To extend the secondary stack dynamically when needed. The secondary
6922 stack is used for returning variable length results.
6927 A default (implementation-provided) storage pool for an
6928 access-to-constant type should not have overhead to support deallocation of
6935 A storage pool for an anonymous access type should be created at the
6936 point of an allocator for the type, and be reclaimed when the designated
6937 object becomes inaccessible.
6941 @cindex Unchecked deallocation
6942 @unnumberedsec 13.11.2(17): Unchecked De-allocation
6945 For a standard storage pool, @code{Free} should actually reclaim the
6950 @cindex Stream oriented attributes
6951 @unnumberedsec 13.13.2(17): Stream Oriented Attributes
6954 If a stream element is the same size as a storage element, then the
6955 normal in-memory representation should be used by @code{Read} and
6956 @code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
6957 should use the smallest number of stream elements needed to represent
6958 all values in the base range of the scalar type.
6961 Followed. By default, GNAT uses the interpretation suggested by AI-195,
6962 which specifies using the size of the first subtype.
6963 However, such an implementation is based on direct binary
6964 representations and is therefore target- and endianness-dependent.
6965 To address this issue, GNAT also supplies an alternate implementation
6966 of the stream attributes @code{Read} and @code{Write},
6967 which uses the target-independent XDR standard representation
6969 @cindex XDR representation
6970 @cindex @code{Read} attribute
6971 @cindex @code{Write} attribute
6972 @cindex Stream oriented attributes
6973 The XDR implementation is provided as an alternative body of the
6974 @code{System.Stream_Attributes} package, in the file
6975 @file{s-strxdr.adb} in the GNAT library.
6976 There is no @file{s-strxdr.ads} file.
6977 In order to install the XDR implementation, do the following:
6979 @item Replace the default implementation of the
6980 @code{System.Stream_Attributes} package with the XDR implementation.
6981 For example on a Unix platform issue the commands:
6983 $ mv s-stratt.adb s-strold.adb
6984 $ mv s-strxdr.adb s-stratt.adb
6988 Rebuild the GNAT run-time library as documented in
6989 @ref{GNAT and Libraries,,, gnat_ugn, @value{EDITION} User's Guide}.
6992 @unnumberedsec A.1(52): Names of Predefined Numeric Types
6995 If an implementation provides additional named predefined integer types,
6996 then the names should end with @samp{Integer} as in
6997 @samp{Long_Integer}. If an implementation provides additional named
6998 predefined floating point types, then the names should end with
6999 @samp{Float} as in @samp{Long_Float}.
7003 @findex Ada.Characters.Handling
7004 @unnumberedsec A.3.2(49): @code{Ada.Characters.Handling}
7007 If an implementation provides a localized definition of @code{Character}
7008 or @code{Wide_Character}, then the effects of the subprograms in
7009 @code{Characters.Handling} should reflect the localizations. See also
7012 Followed. GNAT provides no such localized definitions.
7014 @cindex Bounded-length strings
7015 @unnumberedsec A.4.4(106): Bounded-Length String Handling
7018 Bounded string objects should not be implemented by implicit pointers
7019 and dynamic allocation.
7021 Followed. No implicit pointers or dynamic allocation are used.
7023 @cindex Random number generation
7024 @unnumberedsec A.5.2(46-47): Random Number Generation
7027 Any storage associated with an object of type @code{Generator} should be
7028 reclaimed on exit from the scope of the object.
7034 If the generator period is sufficiently long in relation to the number
7035 of distinct initiator values, then each possible value of
7036 @code{Initiator} passed to @code{Reset} should initiate a sequence of
7037 random numbers that does not, in a practical sense, overlap the sequence
7038 initiated by any other value. If this is not possible, then the mapping
7039 between initiator values and generator states should be a rapidly
7040 varying function of the initiator value.
7042 Followed. The generator period is sufficiently long for the first
7043 condition here to hold true.
7045 @findex Get_Immediate
7046 @unnumberedsec A.10.7(23): @code{Get_Immediate}
7049 The @code{Get_Immediate} procedures should be implemented with
7050 unbuffered input. For a device such as a keyboard, input should be
7051 @dfn{available} if a key has already been typed, whereas for a disk
7052 file, input should always be available except at end of file. For a file
7053 associated with a keyboard-like device, any line-editing features of the
7054 underlying operating system should be disabled during the execution of
7055 @code{Get_Immediate}.
7057 Followed on all targets except VxWorks. For VxWorks, there is no way to
7058 provide this functionality that does not result in the input buffer being
7059 flushed before the @code{Get_Immediate} call. A special unit
7060 @code{Interfaces.Vxworks.IO} is provided that contains routines to enable
7064 @unnumberedsec B.1(39-41): Pragma @code{Export}
7067 If an implementation supports pragma @code{Export} to a given language,
7068 then it should also allow the main subprogram to be written in that
7069 language. It should support some mechanism for invoking the elaboration
7070 of the Ada library units included in the system, and for invoking the
7071 finalization of the environment task. On typical systems, the
7072 recommended mechanism is to provide two subprograms whose link names are
7073 @code{adainit} and @code{adafinal}. @code{adainit} should contain the
7074 elaboration code for library units. @code{adafinal} should contain the
7075 finalization code. These subprograms should have no effect the second
7076 and subsequent time they are called.
7082 Automatic elaboration of pre-elaborated packages should be
7083 provided when pragma @code{Export} is supported.
7085 Followed when the main program is in Ada. If the main program is in a
7086 foreign language, then
7087 @code{adainit} must be called to elaborate pre-elaborated
7092 For each supported convention @var{L} other than @code{Intrinsic}, an
7093 implementation should support @code{Import} and @code{Export} pragmas
7094 for objects of @var{L}-compatible types and for subprograms, and pragma
7095 @code{Convention} for @var{L}-eligible types and for subprograms,
7096 presuming the other language has corresponding features. Pragma
7097 @code{Convention} need not be supported for scalar types.
7101 @cindex Package @code{Interfaces}
7103 @unnumberedsec B.2(12-13): Package @code{Interfaces}
7106 For each implementation-defined convention identifier, there should be a
7107 child package of package Interfaces with the corresponding name. This
7108 package should contain any declarations that would be useful for
7109 interfacing to the language (implementation) represented by the
7110 convention. Any declarations useful for interfacing to any language on
7111 the given hardware architecture should be provided directly in
7114 Followed. An additional package not defined
7115 in the Ada Reference Manual is @code{Interfaces.CPP}, used
7116 for interfacing to C++.
7120 An implementation supporting an interface to C, COBOL, or Fortran should
7121 provide the corresponding package or packages described in the following
7124 Followed. GNAT provides all the packages described in this section.
7126 @cindex C, interfacing with
7127 @unnumberedsec B.3(63-71): Interfacing with C
7130 An implementation should support the following interface correspondences
7137 An Ada procedure corresponds to a void-returning C function.
7143 An Ada function corresponds to a non-void C function.
7149 An Ada @code{in} scalar parameter is passed as a scalar argument to a C
7156 An Ada @code{in} parameter of an access-to-object type with designated
7157 type @var{T} is passed as a @code{@var{t}*} argument to a C function,
7158 where @var{t} is the C type corresponding to the Ada type @var{T}.
7164 An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
7165 parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
7166 argument to a C function, where @var{t} is the C type corresponding to
7167 the Ada type @var{T}. In the case of an elementary @code{out} or
7168 @code{in out} parameter, a pointer to a temporary copy is used to
7169 preserve by-copy semantics.
7175 An Ada parameter of a record type @var{T}, of any mode, is passed as a
7176 @code{@var{t}*} argument to a C function, where @var{t} is the C
7177 structure corresponding to the Ada type @var{T}.
7179 Followed. This convention may be overridden by the use of the C_Pass_By_Copy
7180 pragma, or Convention, or by explicitly specifying the mechanism for a given
7181 call using an extended import or export pragma.
7185 An Ada parameter of an array type with component type @var{T}, of any
7186 mode, is passed as a @code{@var{t}*} argument to a C function, where
7187 @var{t} is the C type corresponding to the Ada type @var{T}.
7193 An Ada parameter of an access-to-subprogram type is passed as a pointer
7194 to a C function whose prototype corresponds to the designated
7195 subprogram's specification.
7199 @cindex COBOL, interfacing with
7200 @unnumberedsec B.4(95-98): Interfacing with COBOL
7203 An Ada implementation should support the following interface
7204 correspondences between Ada and COBOL@.
7210 An Ada access @var{T} parameter is passed as a @samp{BY REFERENCE} data item of
7211 the COBOL type corresponding to @var{T}.
7217 An Ada in scalar parameter is passed as a @samp{BY CONTENT} data item of
7218 the corresponding COBOL type.
7224 Any other Ada parameter is passed as a @samp{BY REFERENCE} data item of the
7225 COBOL type corresponding to the Ada parameter type; for scalars, a local
7226 copy is used if necessary to ensure by-copy semantics.
7230 @cindex Fortran, interfacing with
7231 @unnumberedsec B.5(22-26): Interfacing with Fortran
7234 An Ada implementation should support the following interface
7235 correspondences between Ada and Fortran:
7241 An Ada procedure corresponds to a Fortran subroutine.
7247 An Ada function corresponds to a Fortran function.
7253 An Ada parameter of an elementary, array, or record type @var{T} is
7254 passed as a @var{T} argument to a Fortran procedure, where @var{T} is
7255 the Fortran type corresponding to the Ada type @var{T}, and where the
7256 INTENT attribute of the corresponding dummy argument matches the Ada
7257 formal parameter mode; the Fortran implementation's parameter passing
7258 conventions are used. For elementary types, a local copy is used if
7259 necessary to ensure by-copy semantics.
7265 An Ada parameter of an access-to-subprogram type is passed as a
7266 reference to a Fortran procedure whose interface corresponds to the
7267 designated subprogram's specification.
7271 @cindex Machine operations
7272 @unnumberedsec C.1(3-5): Access to Machine Operations
7275 The machine code or intrinsic support should allow access to all
7276 operations normally available to assembly language programmers for the
7277 target environment, including privileged instructions, if any.
7283 The interfacing pragmas (see Annex B) should support interface to
7284 assembler; the default assembler should be associated with the
7285 convention identifier @code{Assembler}.
7291 If an entity is exported to assembly language, then the implementation
7292 should allocate it at an addressable location, and should ensure that it
7293 is retained by the linking process, even if not otherwise referenced
7294 from the Ada code. The implementation should assume that any call to a
7295 machine code or assembler subprogram is allowed to read or update every
7296 object that is specified as exported.
7300 @unnumberedsec C.1(10-16): Access to Machine Operations
7303 The implementation should ensure that little or no overhead is
7304 associated with calling intrinsic and machine-code subprograms.
7306 Followed for both intrinsics and machine-code subprograms.
7310 It is recommended that intrinsic subprograms be provided for convenient
7311 access to any machine operations that provide special capabilities or
7312 efficiency and that are not otherwise available through the language
7315 Followed. A full set of machine operation intrinsic subprograms is provided.
7319 Atomic read-modify-write operations---e.g.@:, test and set, compare and
7320 swap, decrement and test, enqueue/dequeue.
7322 Followed on any target supporting such operations.
7326 Standard numeric functions---e.g.@:, sin, log.
7328 Followed on any target supporting such operations.
7332 String manipulation operations---e.g.@:, translate and test.
7334 Followed on any target supporting such operations.
7338 Vector operations---e.g.@:, compare vector against thresholds.
7340 Followed on any target supporting such operations.
7344 Direct operations on I/O ports.
7346 Followed on any target supporting such operations.
7348 @cindex Interrupt support
7349 @unnumberedsec C.3(28): Interrupt Support
7352 If the @code{Ceiling_Locking} policy is not in effect, the
7353 implementation should provide means for the application to specify which
7354 interrupts are to be blocked during protected actions, if the underlying
7355 system allows for a finer-grain control of interrupt blocking.
7357 Followed. The underlying system does not allow for finer-grain control
7358 of interrupt blocking.
7360 @cindex Protected procedure handlers
7361 @unnumberedsec C.3.1(20-21): Protected Procedure Handlers
7364 Whenever possible, the implementation should allow interrupt handlers to
7365 be called directly by the hardware.
7369 This is never possible under IRIX, so this is followed by default.
7371 Followed on any target where the underlying operating system permits
7376 Whenever practical, violations of any
7377 implementation-defined restrictions should be detected before run time.
7379 Followed. Compile time warnings are given when possible.
7381 @cindex Package @code{Interrupts}
7383 @unnumberedsec C.3.2(25): Package @code{Interrupts}
7387 If implementation-defined forms of interrupt handler procedures are
7388 supported, such as protected procedures with parameters, then for each
7389 such form of a handler, a type analogous to @code{Parameterless_Handler}
7390 should be specified in a child package of @code{Interrupts}, with the
7391 same operations as in the predefined package Interrupts.
7395 @cindex Pre-elaboration requirements
7396 @unnumberedsec C.4(14): Pre-elaboration Requirements
7399 It is recommended that pre-elaborated packages be implemented in such a
7400 way that there should be little or no code executed at run time for the
7401 elaboration of entities not already covered by the Implementation
7404 Followed. Executable code is generated in some cases, e.g.@: loops
7405 to initialize large arrays.
7407 @unnumberedsec C.5(8): Pragma @code{Discard_Names}
7411 If the pragma applies to an entity, then the implementation should
7412 reduce the amount of storage used for storing names associated with that
7417 @cindex Package @code{Task_Attributes}
7418 @findex Task_Attributes
7419 @unnumberedsec C.7.2(30): The Package Task_Attributes
7422 Some implementations are targeted to domains in which memory use at run
7423 time must be completely deterministic. For such implementations, it is
7424 recommended that the storage for task attributes will be pre-allocated
7425 statically and not from the heap. This can be accomplished by either
7426 placing restrictions on the number and the size of the task's
7427 attributes, or by using the pre-allocated storage for the first @var{N}
7428 attribute objects, and the heap for the others. In the latter case,
7429 @var{N} should be documented.
7431 Not followed. This implementation is not targeted to such a domain.
7433 @cindex Locking Policies
7434 @unnumberedsec D.3(17): Locking Policies
7438 The implementation should use names that end with @samp{_Locking} for
7439 locking policies defined by the implementation.
7441 Followed. A single implementation-defined locking policy is defined,
7442 whose name (@code{Inheritance_Locking}) follows this suggestion.
7444 @cindex Entry queuing policies
7445 @unnumberedsec D.4(16): Entry Queuing Policies
7448 Names that end with @samp{_Queuing} should be used
7449 for all implementation-defined queuing policies.
7451 Followed. No such implementation-defined queuing policies exist.
7453 @cindex Preemptive abort
7454 @unnumberedsec D.6(9-10): Preemptive Abort
7457 Even though the @code{abort_statement} is included in the list of
7458 potentially blocking operations (see 9.5.1), it is recommended that this
7459 statement be implemented in a way that never requires the task executing
7460 the @code{abort_statement} to block.
7466 On a multi-processor, the delay associated with aborting a task on
7467 another processor should be bounded; the implementation should use
7468 periodic polling, if necessary, to achieve this.
7472 @cindex Tasking restrictions
7473 @unnumberedsec D.7(21): Tasking Restrictions
7476 When feasible, the implementation should take advantage of the specified
7477 restrictions to produce a more efficient implementation.
7479 GNAT currently takes advantage of these restrictions by providing an optimized
7480 run time when the Ravenscar profile and the GNAT restricted run time set
7481 of restrictions are specified. See pragma @code{Profile (Ravenscar)} and
7482 pragma @code{Profile (Restricted)} for more details.
7484 @cindex Time, monotonic
7485 @unnumberedsec D.8(47-49): Monotonic Time
7488 When appropriate, implementations should provide configuration
7489 mechanisms to change the value of @code{Tick}.
7491 Such configuration mechanisms are not appropriate to this implementation
7492 and are thus not supported.
7496 It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
7497 be implemented as transformations of the same time base.
7503 It is recommended that the @dfn{best} time base which exists in
7504 the underlying system be available to the application through
7505 @code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
7509 @cindex Partition communication subsystem
7511 @unnumberedsec E.5(28-29): Partition Communication Subsystem
7514 Whenever possible, the PCS on the called partition should allow for
7515 multiple tasks to call the RPC-receiver with different messages and
7516 should allow them to block until the corresponding subprogram body
7519 Followed by GLADE, a separately supplied PCS that can be used with
7524 The @code{Write} operation on a stream of type @code{Params_Stream_Type}
7525 should raise @code{Storage_Error} if it runs out of space trying to
7526 write the @code{Item} into the stream.
7528 Followed by GLADE, a separately supplied PCS that can be used with
7531 @cindex COBOL support
7532 @unnumberedsec F(7): COBOL Support
7535 If COBOL (respectively, C) is widely supported in the target
7536 environment, implementations supporting the Information Systems Annex
7537 should provide the child package @code{Interfaces.COBOL} (respectively,
7538 @code{Interfaces.C}) specified in Annex B and should support a
7539 @code{convention_identifier} of COBOL (respectively, C) in the interfacing
7540 pragmas (see Annex B), thus allowing Ada programs to interface with
7541 programs written in that language.
7545 @cindex Decimal radix support
7546 @unnumberedsec F.1(2): Decimal Radix Support
7549 Packed decimal should be used as the internal representation for objects
7550 of subtype @var{S} when @var{S}'Machine_Radix = 10.
7552 Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
7556 @unnumberedsec G: Numerics
7559 If Fortran (respectively, C) is widely supported in the target
7560 environment, implementations supporting the Numerics Annex
7561 should provide the child package @code{Interfaces.Fortran} (respectively,
7562 @code{Interfaces.C}) specified in Annex B and should support a
7563 @code{convention_identifier} of Fortran (respectively, C) in the interfacing
7564 pragmas (see Annex B), thus allowing Ada programs to interface with
7565 programs written in that language.
7569 @cindex Complex types
7570 @unnumberedsec G.1.1(56-58): Complex Types
7573 Because the usual mathematical meaning of multiplication of a complex
7574 operand and a real operand is that of the scaling of both components of
7575 the former by the latter, an implementation should not perform this
7576 operation by first promoting the real operand to complex type and then
7577 performing a full complex multiplication. In systems that, in the
7578 future, support an Ada binding to IEC 559:1989, the latter technique
7579 will not generate the required result when one of the components of the
7580 complex operand is infinite. (Explicit multiplication of the infinite
7581 component by the zero component obtained during promotion yields a NaN
7582 that propagates into the final result.) Analogous advice applies in the
7583 case of multiplication of a complex operand and a pure-imaginary
7584 operand, and in the case of division of a complex operand by a real or
7585 pure-imaginary operand.
7591 Similarly, because the usual mathematical meaning of addition of a
7592 complex operand and a real operand is that the imaginary operand remains
7593 unchanged, an implementation should not perform this operation by first
7594 promoting the real operand to complex type and then performing a full
7595 complex addition. In implementations in which the @code{Signed_Zeros}
7596 attribute of the component type is @code{True} (and which therefore
7597 conform to IEC 559:1989 in regard to the handling of the sign of zero in
7598 predefined arithmetic operations), the latter technique will not
7599 generate the required result when the imaginary component of the complex
7600 operand is a negatively signed zero. (Explicit addition of the negative
7601 zero to the zero obtained during promotion yields a positive zero.)
7602 Analogous advice applies in the case of addition of a complex operand
7603 and a pure-imaginary operand, and in the case of subtraction of a
7604 complex operand and a real or pure-imaginary operand.
7610 Implementations in which @code{Real'Signed_Zeros} is @code{True} should
7611 attempt to provide a rational treatment of the signs of zero results and
7612 result components. As one example, the result of the @code{Argument}
7613 function should have the sign of the imaginary component of the
7614 parameter @code{X} when the point represented by that parameter lies on
7615 the positive real axis; as another, the sign of the imaginary component
7616 of the @code{Compose_From_Polar} function should be the same as
7617 (respectively, the opposite of) that of the @code{Argument} parameter when that
7618 parameter has a value of zero and the @code{Modulus} parameter has a
7619 nonnegative (respectively, negative) value.
7623 @cindex Complex elementary functions
7624 @unnumberedsec G.1.2(49): Complex Elementary Functions
7627 Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
7628 @code{True} should attempt to provide a rational treatment of the signs
7629 of zero results and result components. For example, many of the complex
7630 elementary functions have components that are odd functions of one of
7631 the parameter components; in these cases, the result component should
7632 have the sign of the parameter component at the origin. Other complex
7633 elementary functions have zero components whose sign is opposite that of
7634 a parameter component at the origin, or is always positive or always
7639 @cindex Accuracy requirements
7640 @unnumberedsec G.2.4(19): Accuracy Requirements
7643 The versions of the forward trigonometric functions without a
7644 @code{Cycle} parameter should not be implemented by calling the
7645 corresponding version with a @code{Cycle} parameter of
7646 @code{2.0*Numerics.Pi}, since this will not provide the required
7647 accuracy in some portions of the domain. For the same reason, the
7648 version of @code{Log} without a @code{Base} parameter should not be
7649 implemented by calling the corresponding version with a @code{Base}
7650 parameter of @code{Numerics.e}.
7654 @cindex Complex arithmetic accuracy
7655 @cindex Accuracy, complex arithmetic
7656 @unnumberedsec G.2.6(15): Complex Arithmetic Accuracy
7660 The version of the @code{Compose_From_Polar} function without a
7661 @code{Cycle} parameter should not be implemented by calling the
7662 corresponding version with a @code{Cycle} parameter of
7663 @code{2.0*Numerics.Pi}, since this will not provide the required
7664 accuracy in some portions of the domain.
7668 @c -----------------------------------------
7669 @node Implementation Defined Characteristics
7670 @chapter Implementation Defined Characteristics
7673 In addition to the implementation dependent pragmas and attributes, and
7674 the implementation advice, there are a number of other Ada features
7675 that are potentially implementation dependent. These are mentioned
7676 throughout the Ada Reference Manual, and are summarized in annex M@.
7678 A requirement for conforming Ada compilers is that they provide
7679 documentation describing how the implementation deals with each of these
7680 issues. In this chapter, you will find each point in annex M listed
7681 followed by a description in italic font of how GNAT
7685 implementation on IRIX 5.3 operating system or greater
7687 handles the implementation dependence.
7689 You can use this chapter as a guide to minimizing implementation
7690 dependent features in your programs if portability to other compilers
7691 and other operating systems is an important consideration. The numbers
7692 in each section below correspond to the paragraph number in the Ada
7698 @strong{2}. Whether or not each recommendation given in Implementation
7699 Advice is followed. See 1.1.2(37).
7702 @xref{Implementation Advice}.
7707 @strong{3}. Capacity limitations of the implementation. See 1.1.3(3).
7710 The complexity of programs that can be processed is limited only by the
7711 total amount of available virtual memory, and disk space for the
7712 generated object files.
7717 @strong{4}. Variations from the standard that are impractical to avoid
7718 given the implementation's execution environment. See 1.1.3(6).
7721 There are no variations from the standard.
7726 @strong{5}. Which @code{code_statement}s cause external
7727 interactions. See 1.1.3(10).
7730 Any @code{code_statement} can potentially cause external interactions.
7735 @strong{6}. The coded representation for the text of an Ada
7736 program. See 2.1(4).
7739 See separate section on source representation.
7744 @strong{7}. The control functions allowed in comments. See 2.1(14).
7747 See separate section on source representation.
7752 @strong{8}. The representation for an end of line. See 2.2(2).
7755 See separate section on source representation.
7760 @strong{9}. Maximum supported line length and lexical element
7761 length. See 2.2(15).
7764 The maximum line length is 255 characters and the maximum length of a
7765 lexical element is also 255 characters.
7770 @strong{10}. Implementation defined pragmas. See 2.8(14).
7774 @xref{Implementation Defined Pragmas}.
7779 @strong{11}. Effect of pragma @code{Optimize}. See 2.8(27).
7782 Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
7783 parameter, checks that the optimization flag is set, and aborts if it is
7789 @strong{12}. The sequence of characters of the value returned by
7790 @code{@var{S}'Image} when some of the graphic characters of
7791 @code{@var{S}'Wide_Image} are not defined in @code{Character}. See
7795 The sequence of characters is as defined by the wide character encoding
7796 method used for the source. See section on source representation for
7802 @strong{13}. The predefined integer types declared in
7803 @code{Standard}. See 3.5.4(25).
7807 @item Short_Short_Integer
7810 (Short) 16 bit signed
7814 64 bit signed (Alpha OpenVMS only)
7815 32 bit signed (all other targets)
7816 @item Long_Long_Integer
7823 @strong{14}. Any nonstandard integer types and the operators defined
7824 for them. See 3.5.4(26).
7827 There are no nonstandard integer types.
7832 @strong{15}. Any nonstandard real types and the operators defined for
7836 There are no nonstandard real types.
7841 @strong{16}. What combinations of requested decimal precision and range
7842 are supported for floating point types. See 3.5.7(7).
7845 The precision and range is as defined by the IEEE standard.
7850 @strong{17}. The predefined floating point types declared in
7851 @code{Standard}. See 3.5.7(16).
7858 (Short) 32 bit IEEE short
7861 @item Long_Long_Float
7862 64 bit IEEE long (80 bit IEEE long on x86 processors)
7868 @strong{18}. The small of an ordinary fixed point type. See 3.5.9(8).
7871 @code{Fine_Delta} is 2**(@minus{}63)
7876 @strong{19}. What combinations of small, range, and digits are
7877 supported for fixed point types. See 3.5.9(10).
7880 Any combinations are permitted that do not result in a small less than
7881 @code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
7882 If the mantissa is larger than 53 bits on machines where Long_Long_Float
7883 is 64 bits (true of all architectures except ia32), then the output from
7884 Text_IO is accurate to only 53 bits, rather than the full mantissa. This
7885 is because floating-point conversions are used to convert fixed point.
7890 @strong{20}. The result of @code{Tags.Expanded_Name} for types declared
7891 within an unnamed @code{block_statement}. See 3.9(10).
7894 Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
7895 decimal integer are allocated.
7900 @strong{21}. Implementation-defined attributes. See 4.1.4(12).
7903 @xref{Implementation Defined Attributes}.
7908 @strong{22}. Any implementation-defined time types. See 9.6(6).
7911 There are no implementation-defined time types.
7916 @strong{23}. The time base associated with relative delays.
7919 See 9.6(20). The time base used is that provided by the C library
7920 function @code{gettimeofday}.
7925 @strong{24}. The time base of the type @code{Calendar.Time}. See
7929 The time base used is that provided by the C library function
7930 @code{gettimeofday}.
7935 @strong{25}. The time zone used for package @code{Calendar}
7936 operations. See 9.6(24).
7939 The time zone used by package @code{Calendar} is the current system time zone
7940 setting for local time, as accessed by the C library function
7946 @strong{26}. Any limit on @code{delay_until_statements} of
7947 @code{select_statements}. See 9.6(29).
7950 There are no such limits.
7955 @strong{27}. Whether or not two non-overlapping parts of a composite
7956 object are independently addressable, in the case where packing, record
7957 layout, or @code{Component_Size} is specified for the object. See
7961 Separate components are independently addressable if they do not share
7962 overlapping storage units.
7967 @strong{28}. The representation for a compilation. See 10.1(2).
7970 A compilation is represented by a sequence of files presented to the
7971 compiler in a single invocation of the @command{gcc} command.
7976 @strong{29}. Any restrictions on compilations that contain multiple
7977 compilation_units. See 10.1(4).
7980 No single file can contain more than one compilation unit, but any
7981 sequence of files can be presented to the compiler as a single
7987 @strong{30}. The mechanisms for creating an environment and for adding
7988 and replacing compilation units. See 10.1.4(3).
7991 See separate section on compilation model.
7996 @strong{31}. The manner of explicitly assigning library units to a
7997 partition. See 10.2(2).
8000 If a unit contains an Ada main program, then the Ada units for the partition
8001 are determined by recursive application of the rules in the Ada Reference
8002 Manual section 10.2(2-6). In other words, the Ada units will be those that
8003 are needed by the main program, and then this definition of need is applied
8004 recursively to those units, and the partition contains the transitive
8005 closure determined by this relationship. In short, all the necessary units
8006 are included, with no need to explicitly specify the list. If additional
8007 units are required, e.g.@: by foreign language units, then all units must be
8008 mentioned in the context clause of one of the needed Ada units.
8010 If the partition contains no main program, or if the main program is in
8011 a language other than Ada, then GNAT
8012 provides the binder options @option{-z} and @option{-n} respectively, and in
8013 this case a list of units can be explicitly supplied to the binder for
8014 inclusion in the partition (all units needed by these units will also
8015 be included automatically). For full details on the use of these
8016 options, refer to @ref{The GNAT Make Program gnatmake,,, gnat_ugn,
8017 @value{EDITION} User's Guide}.
8022 @strong{32}. The implementation-defined means, if any, of specifying
8023 which compilation units are needed by a given compilation unit. See
8027 The units needed by a given compilation unit are as defined in
8028 the Ada Reference Manual section 10.2(2-6). There are no
8029 implementation-defined pragmas or other implementation-defined
8030 means for specifying needed units.
8035 @strong{33}. The manner of designating the main subprogram of a
8036 partition. See 10.2(7).
8039 The main program is designated by providing the name of the
8040 corresponding @file{ALI} file as the input parameter to the binder.
8045 @strong{34}. The order of elaboration of @code{library_items}. See
8049 The first constraint on ordering is that it meets the requirements of
8050 Chapter 10 of the Ada Reference Manual. This still leaves some
8051 implementation dependent choices, which are resolved by first
8052 elaborating bodies as early as possible (i.e., in preference to specs
8053 where there is a choice), and second by evaluating the immediate with
8054 clauses of a unit to determine the probably best choice, and
8055 third by elaborating in alphabetical order of unit names
8056 where a choice still remains.
8061 @strong{35}. Parameter passing and function return for the main
8062 subprogram. See 10.2(21).
8065 The main program has no parameters. It may be a procedure, or a function
8066 returning an integer type. In the latter case, the returned integer
8067 value is the return code of the program (overriding any value that
8068 may have been set by a call to @code{Ada.Command_Line.Set_Exit_Status}).
8073 @strong{36}. The mechanisms for building and running partitions. See
8077 GNAT itself supports programs with only a single partition. The GNATDIST
8078 tool provided with the GLADE package (which also includes an implementation
8079 of the PCS) provides a completely flexible method for building and running
8080 programs consisting of multiple partitions. See the separate GLADE manual
8086 @strong{37}. The details of program execution, including program
8087 termination. See 10.2(25).
8090 See separate section on compilation model.
8095 @strong{38}. The semantics of any non-active partitions supported by the
8096 implementation. See 10.2(28).
8099 Passive partitions are supported on targets where shared memory is
8100 provided by the operating system. See the GLADE reference manual for
8106 @strong{39}. The information returned by @code{Exception_Message}. See
8110 Exception message returns the null string unless a specific message has
8111 been passed by the program.
8116 @strong{40}. The result of @code{Exceptions.Exception_Name} for types
8117 declared within an unnamed @code{block_statement}. See 11.4.1(12).
8120 Blocks have implementation defined names of the form @code{B@var{nnn}}
8121 where @var{nnn} is an integer.
8126 @strong{41}. The information returned by
8127 @code{Exception_Information}. See 11.4.1(13).
8130 @code{Exception_Information} returns a string in the following format:
8133 @emph{Exception_Name:} nnnnn
8134 @emph{Message:} mmmmm
8136 @emph{Call stack traceback locations:}
8137 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
8145 @code{nnnn} is the fully qualified name of the exception in all upper
8146 case letters. This line is always present.
8149 @code{mmmm} is the message (this line present only if message is non-null)
8152 @code{ppp} is the Process Id value as a decimal integer (this line is
8153 present only if the Process Id is nonzero). Currently we are
8154 not making use of this field.
8157 The Call stack traceback locations line and the following values
8158 are present only if at least one traceback location was recorded.
8159 The values are given in C style format, with lower case letters
8160 for a-f, and only as many digits present as are necessary.
8164 The line terminator sequence at the end of each line, including
8165 the last line is a single @code{LF} character (@code{16#0A#}).
8170 @strong{42}. Implementation-defined check names. See 11.5(27).
8173 The implementation defined check name Alignment_Check controls checking of
8174 address clause values for proper alignment (that is, the address supplied
8175 must be consistent with the alignment of the type).
8177 In addition, a user program can add implementation-defined check names
8178 by means of the pragma Check_Name.
8183 @strong{43}. The interpretation of each aspect of representation. See
8187 See separate section on data representations.
8192 @strong{44}. Any restrictions placed upon representation items. See
8196 See separate section on data representations.
8201 @strong{45}. The meaning of @code{Size} for indefinite subtypes. See
8205 Size for an indefinite subtype is the maximum possible size, except that
8206 for the case of a subprogram parameter, the size of the parameter object
8212 @strong{46}. The default external representation for a type tag. See
8216 The default external representation for a type tag is the fully expanded
8217 name of the type in upper case letters.
8222 @strong{47}. What determines whether a compilation unit is the same in
8223 two different partitions. See 13.3(76).
8226 A compilation unit is the same in two different partitions if and only
8227 if it derives from the same source file.
8232 @strong{48}. Implementation-defined components. See 13.5.1(15).
8235 The only implementation defined component is the tag for a tagged type,
8236 which contains a pointer to the dispatching table.
8241 @strong{49}. If @code{Word_Size} = @code{Storage_Unit}, the default bit
8242 ordering. See 13.5.3(5).
8245 @code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
8246 implementation, so no non-default bit ordering is supported. The default
8247 bit ordering corresponds to the natural endianness of the target architecture.
8252 @strong{50}. The contents of the visible part of package @code{System}
8253 and its language-defined children. See 13.7(2).
8256 See the definition of these packages in files @file{system.ads} and
8257 @file{s-stoele.ads}.
8262 @strong{51}. The contents of the visible part of package
8263 @code{System.Machine_Code}, and the meaning of
8264 @code{code_statements}. See 13.8(7).
8267 See the definition and documentation in file @file{s-maccod.ads}.
8272 @strong{52}. The effect of unchecked conversion. See 13.9(11).
8275 Unchecked conversion between types of the same size
8276 results in an uninterpreted transmission of the bits from one type
8277 to the other. If the types are of unequal sizes, then in the case of
8278 discrete types, a shorter source is first zero or sign extended as
8279 necessary, and a shorter target is simply truncated on the left.
8280 For all non-discrete types, the source is first copied if necessary
8281 to ensure that the alignment requirements of the target are met, then
8282 a pointer is constructed to the source value, and the result is obtained
8283 by dereferencing this pointer after converting it to be a pointer to the
8284 target type. Unchecked conversions where the target subtype is an
8285 unconstrained array are not permitted. If the target alignment is
8286 greater than the source alignment, then a copy of the result is
8287 made with appropriate alignment
8292 @strong{53}. The manner of choosing a storage pool for an access type
8293 when @code{Storage_Pool} is not specified for the type. See 13.11(17).
8296 There are 3 different standard pools used by the compiler when
8297 @code{Storage_Pool} is not specified depending whether the type is local
8298 to a subprogram or defined at the library level and whether
8299 @code{Storage_Size}is specified or not. See documentation in the runtime
8300 library units @code{System.Pool_Global}, @code{System.Pool_Size} and
8301 @code{System.Pool_Local} in files @file{s-poosiz.ads},
8302 @file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
8308 @strong{54}. Whether or not the implementation provides user-accessible
8309 names for the standard pool type(s). See 13.11(17).
8313 See documentation in the sources of the run time mentioned in paragraph
8314 @strong{53} . All these pools are accessible by means of @code{with}'ing
8320 @strong{55}. The meaning of @code{Storage_Size}. See 13.11(18).
8323 @code{Storage_Size} is measured in storage units, and refers to the
8324 total space available for an access type collection, or to the primary
8325 stack space for a task.
8330 @strong{56}. Implementation-defined aspects of storage pools. See
8334 See documentation in the sources of the run time mentioned in paragraph
8335 @strong{53} for details on GNAT-defined aspects of storage pools.
8340 @strong{57}. The set of restrictions allowed in a pragma
8341 @code{Restrictions}. See 13.12(7).
8344 All RM defined Restriction identifiers are implemented. The following
8345 additional restriction identifiers are provided. There are two separate
8346 lists of implementation dependent restriction identifiers. The first
8347 set requires consistency throughout a partition (in other words, if the
8348 restriction identifier is used for any compilation unit in the partition,
8349 then all compilation units in the partition must obey the restriction.
8353 @item Simple_Barriers
8354 @findex Simple_Barriers
8355 This restriction ensures at compile time that barriers in entry declarations
8356 for protected types are restricted to either static boolean expressions or
8357 references to simple boolean variables defined in the private part of the
8358 protected type. No other form of entry barriers is permitted. This is one
8359 of the restrictions of the Ravenscar profile for limited tasking (see also
8360 pragma @code{Profile (Ravenscar)}).
8362 @item Max_Entry_Queue_Length => Expr
8363 @findex Max_Entry_Queue_Length
8364 This restriction is a declaration that any protected entry compiled in
8365 the scope of the restriction has at most the specified number of
8366 tasks waiting on the entry
8367 at any one time, and so no queue is required. This restriction is not
8368 checked at compile time. A program execution is erroneous if an attempt
8369 is made to queue more than the specified number of tasks on such an entry.
8373 This restriction ensures at compile time that there is no implicit or
8374 explicit dependence on the package @code{Ada.Calendar}.
8376 @item No_Default_Initialization
8377 @findex No_Default_Initialization
8379 This restriction prohibits any instance of default initialization of variables.
8380 The binder implements a consistency rule which prevents any unit compiled
8381 without the restriction from with'ing a unit with the restriction (this allows
8382 the generation of initialization procedures to be skipped, since you can be
8383 sure that no call is ever generated to an initialization procedure in a unit
8384 with the restriction active). If used in conjunction with Initialize_Scalars or
8385 Normalize_Scalars, the effect is to prohibit all cases of variables declared
8386 without a specific initializer (including the case of OUT scalar parameters).
8388 @item No_Direct_Boolean_Operators
8389 @findex No_Direct_Boolean_Operators
8390 This restriction ensures that no logical (and/or/xor) or comparison
8391 operators are used on operands of type Boolean (or any type derived
8392 from Boolean). This is intended for use in safety critical programs
8393 where the certification protocol requires the use of short-circuit
8394 (and then, or else) forms for all composite boolean operations.
8396 @item No_Dispatching_Calls
8397 @findex No_Dispatching_Calls
8398 This restriction ensures at compile time that the code generated by the
8399 compiler involves no dispatching calls. The use of this restriction allows the
8400 safe use of record extensions, classwide membership tests and other classwide
8401 features not involving implicit dispatching. This restriction ensures that
8402 the code contains no indirect calls through a dispatching mechanism. Note that
8403 this includes internally-generated calls created by the compiler, for example
8404 in the implementation of class-wide objects assignments. The
8405 membership test is allowed in the presence of this restriction, because its
8406 implementation requires no dispatching.
8407 This restriction is comparable to the official Ada restriction
8408 @code{No_Dispatch} except that it is a bit less restrictive in that it allows
8409 all classwide constructs that do not imply dispatching.
8410 The following example indicates constructs that violate this restriction.
8414 type T is tagged record
8417 procedure P (X : T);
8419 type DT is new T with record
8420 More_Data : Natural;
8422 procedure Q (X : DT);
8426 procedure Example is
8427 procedure Test (O : T'Class) is
8428 N : Natural := O'Size;-- Error: Dispatching call
8429 C : T'Class := O; -- Error: implicit Dispatching Call
8431 if O in DT'Class then -- OK : Membership test
8432 Q (DT (O)); -- OK : Type conversion plus direct call
8434 P (O); -- Error: Dispatching call
8440 P (Obj); -- OK : Direct call
8441 P (T (Obj)); -- OK : Type conversion plus direct call
8442 P (T'Class (Obj)); -- Error: Dispatching call
8444 Test (Obj); -- OK : Type conversion
8446 if Obj in T'Class then -- OK : Membership test
8452 @item No_Dynamic_Attachment
8453 @findex No_Dynamic_Attachment
8454 This restriction ensures that there is no call to any of the operations
8455 defined in package Ada.Interrupts.
8457 @item No_Enumeration_Maps
8458 @findex No_Enumeration_Maps
8459 This restriction ensures at compile time that no operations requiring
8460 enumeration maps are used (that is Image and Value attributes applied
8461 to enumeration types).
8463 @item No_Entry_Calls_In_Elaboration_Code
8464 @findex No_Entry_Calls_In_Elaboration_Code
8465 This restriction ensures at compile time that no task or protected entry
8466 calls are made during elaboration code. As a result of the use of this
8467 restriction, the compiler can assume that no code past an accept statement
8468 in a task can be executed at elaboration time.
8470 @item No_Exception_Handlers
8471 @findex No_Exception_Handlers
8472 This restriction ensures at compile time that there are no explicit
8473 exception handlers. It also indicates that no exception propagation will
8474 be provided. In this mode, exceptions may be raised but will result in
8475 an immediate call to the last chance handler, a routine that the user
8476 must define with the following profile:
8478 @smallexample @c ada
8479 procedure Last_Chance_Handler
8480 (Source_Location : System.Address; Line : Integer);
8481 pragma Export (C, Last_Chance_Handler,
8482 "__gnat_last_chance_handler");
8485 The parameter is a C null-terminated string representing a message to be
8486 associated with the exception (typically the source location of the raise
8487 statement generated by the compiler). The Line parameter when nonzero
8488 represents the line number in the source program where the raise occurs.
8490 @item No_Exception_Propagation
8491 @findex No_Exception_Propagation
8492 This restriction guarantees that exceptions are never propagated to an outer
8493 subprogram scope). The only case in which an exception may be raised is when
8494 the handler is statically in the same subprogram, so that the effect of a raise
8495 is essentially like a goto statement. Any other raise statement (implicit or
8496 explicit) will be considered unhandled. Exception handlers are allowed, but may
8497 not contain an exception occurrence identifier (exception choice). In addition
8498 use of the package GNAT.Current_Exception is not permitted, and reraise
8499 statements (raise with no operand) are not permitted.
8501 @item No_Exception_Registration
8502 @findex No_Exception_Registration
8503 This restriction ensures at compile time that no stream operations for
8504 types Exception_Id or Exception_Occurrence are used. This also makes it
8505 impossible to pass exceptions to or from a partition with this restriction
8506 in a distributed environment. If this exception is active, then the generated
8507 code is simplified by omitting the otherwise-required global registration
8508 of exceptions when they are declared.
8510 @item No_Implicit_Conditionals
8511 @findex No_Implicit_Conditionals
8512 This restriction ensures that the generated code does not contain any
8513 implicit conditionals, either by modifying the generated code where possible,
8514 or by rejecting any construct that would otherwise generate an implicit
8515 conditional. Note that this check does not include run time constraint
8516 checks, which on some targets may generate implicit conditionals as
8517 well. To control the latter, constraint checks can be suppressed in the
8518 normal manner. Constructs generating implicit conditionals include comparisons
8519 of composite objects and the Max/Min attributes.
8521 @item No_Implicit_Dynamic_Code
8522 @findex No_Implicit_Dynamic_Code
8524 This restriction prevents the compiler from building ``trampolines''.
8525 This is a structure that is built on the stack and contains dynamic
8526 code to be executed at run time. On some targets, a trampoline is
8527 built for the following features: @code{Access},
8528 @code{Unrestricted_Access}, or @code{Address} of a nested subprogram;
8529 nested task bodies; primitive operations of nested tagged types.
8530 Trampolines do not work on machines that prevent execution of stack
8531 data. For example, on windows systems, enabling DEP (data execution
8532 protection) will cause trampolines to raise an exception.
8533 Trampolines are also quite slow at run time.
8535 On many targets, trampolines have been largely eliminated. Look at the
8536 version of system.ads for your target --- if it has
8537 Always_Compatible_Rep equal to False, then trampolines are largely
8538 eliminated. In particular, a trampoline is built for the following
8539 features: @code{Address} of a nested subprogram;
8540 @code{Access} or @code{Unrestricted_Access} of a nested subprogram,
8541 but only if pragma Favor_Top_Level applies, or the access type has a
8542 foreign-language convention; primitive operations of nested tagged
8545 @item No_Implicit_Loops
8546 @findex No_Implicit_Loops
8547 This restriction ensures that the generated code does not contain any
8548 implicit @code{for} loops, either by modifying
8549 the generated code where possible,
8550 or by rejecting any construct that would otherwise generate an implicit
8551 @code{for} loop. If this restriction is active, it is possible to build
8552 large array aggregates with all static components without generating an
8553 intermediate temporary, and without generating a loop to initialize individual
8554 components. Otherwise, a loop is created for arrays larger than about 5000
8557 @item No_Initialize_Scalars
8558 @findex No_Initialize_Scalars
8559 This restriction ensures that no unit in the partition is compiled with
8560 pragma Initialize_Scalars. This allows the generation of more efficient
8561 code, and in particular eliminates dummy null initialization routines that
8562 are otherwise generated for some record and array types.
8564 @item No_Local_Protected_Objects
8565 @findex No_Local_Protected_Objects
8566 This restriction ensures at compile time that protected objects are
8567 only declared at the library level.
8569 @item No_Protected_Type_Allocators
8570 @findex No_Protected_Type_Allocators
8571 This restriction ensures at compile time that there are no allocator
8572 expressions that attempt to allocate protected objects.
8574 @item No_Secondary_Stack
8575 @findex No_Secondary_Stack
8576 This restriction ensures at compile time that the generated code does not
8577 contain any reference to the secondary stack. The secondary stack is used
8578 to implement functions returning unconstrained objects (arrays or records)
8581 @item No_Select_Statements
8582 @findex No_Select_Statements
8583 This restriction ensures at compile time no select statements of any kind
8584 are permitted, that is the keyword @code{select} may not appear.
8585 This is one of the restrictions of the Ravenscar
8586 profile for limited tasking (see also pragma @code{Profile (Ravenscar)}).
8588 @item No_Standard_Storage_Pools
8589 @findex No_Standard_Storage_Pools
8590 This restriction ensures at compile time that no access types
8591 use the standard default storage pool. Any access type declared must
8592 have an explicit Storage_Pool attribute defined specifying a
8593 user-defined storage pool.
8597 This restriction ensures at compile/bind time that there are no
8598 stream objects created and no use of stream attributes.
8599 This restriction does not forbid dependences on the package
8600 @code{Ada.Streams}. So it is permissible to with
8601 @code{Ada.Streams} (or another package that does so itself)
8602 as long as no actual stream objects are created and no
8603 stream attributes are used.
8605 @item No_Task_Attributes_Package
8606 @findex No_Task_Attributes_Package
8607 This restriction ensures at compile time that there are no implicit or
8608 explicit dependencies on the package @code{Ada.Task_Attributes}.
8610 @item No_Task_Termination
8611 @findex No_Task_Termination
8612 This restriction ensures at compile time that no terminate alternatives
8613 appear in any task body.
8617 This restriction prevents the declaration of tasks or task types throughout
8618 the partition. It is similar in effect to the use of @code{Max_Tasks => 0}
8619 except that violations are caught at compile time and cause an error message
8620 to be output either by the compiler or binder.
8622 @item Static_Priorities
8623 @findex Static_Priorities
8624 This restriction ensures at compile time that all priority expressions
8625 are static, and that there are no dependencies on the package
8626 @code{Ada.Dynamic_Priorities}.
8628 @item Static_Storage_Size
8629 @findex Static_Storage_Size
8630 This restriction ensures at compile time that any expression appearing
8631 in a Storage_Size pragma or attribute definition clause is static.
8636 The second set of implementation dependent restriction identifiers
8637 does not require partition-wide consistency.
8638 The restriction may be enforced for a single
8639 compilation unit without any effect on any of the
8640 other compilation units in the partition.
8644 @item No_Elaboration_Code
8645 @findex No_Elaboration_Code
8646 This restriction ensures at compile time that no elaboration code is
8647 generated. Note that this is not the same condition as is enforced
8648 by pragma @code{Preelaborate}. There are cases in which pragma
8649 @code{Preelaborate} still permits code to be generated (e.g.@: code
8650 to initialize a large array to all zeroes), and there are cases of units
8651 which do not meet the requirements for pragma @code{Preelaborate},
8652 but for which no elaboration code is generated. Generally, it is
8653 the case that preelaborable units will meet the restrictions, with
8654 the exception of large aggregates initialized with an others_clause,
8655 and exception declarations (which generate calls to a run-time
8656 registry procedure). This restriction is enforced on
8657 a unit by unit basis, it need not be obeyed consistently
8658 throughout a partition.
8660 In the case of aggregates with others, if the aggregate has a dynamic
8661 size, there is no way to eliminate the elaboration code (such dynamic
8662 bounds would be incompatible with @code{Preelaborate} in any case). If
8663 the bounds are static, then use of this restriction actually modifies
8664 the code choice of the compiler to avoid generating a loop, and instead
8665 generate the aggregate statically if possible, no matter how many times
8666 the data for the others clause must be repeatedly generated.
8668 It is not possible to precisely document
8669 the constructs which are compatible with this restriction, since,
8670 unlike most other restrictions, this is not a restriction on the
8671 source code, but a restriction on the generated object code. For
8672 example, if the source contains a declaration:
8675 Val : constant Integer := X;
8679 where X is not a static constant, it may be possible, depending
8680 on complex optimization circuitry, for the compiler to figure
8681 out the value of X at compile time, in which case this initialization
8682 can be done by the loader, and requires no initialization code. It
8683 is not possible to document the precise conditions under which the
8684 optimizer can figure this out.
8686 Note that this the implementation of this restriction requires full
8687 code generation. If it is used in conjunction with "semantics only"
8688 checking, then some cases of violations may be missed.
8690 @item No_Entry_Queue
8691 @findex No_Entry_Queue
8692 This restriction is a declaration that any protected entry compiled in
8693 the scope of the restriction has at most one task waiting on the entry
8694 at any one time, and so no queue is required. This restriction is not
8695 checked at compile time. A program execution is erroneous if an attempt
8696 is made to queue a second task on such an entry.
8698 @item No_Implementation_Attributes
8699 @findex No_Implementation_Attributes
8700 This restriction checks at compile time that no GNAT-defined attributes
8701 are present. With this restriction, the only attributes that can be used
8702 are those defined in the Ada Reference Manual.
8704 @item No_Implementation_Pragmas
8705 @findex No_Implementation_Pragmas
8706 This restriction checks at compile time that no GNAT-defined pragmas
8707 are present. With this restriction, the only pragmas that can be used
8708 are those defined in the Ada Reference Manual.
8710 @item No_Implementation_Restrictions
8711 @findex No_Implementation_Restrictions
8712 This restriction checks at compile time that no GNAT-defined restriction
8713 identifiers (other than @code{No_Implementation_Restrictions} itself)
8714 are present. With this restriction, the only other restriction identifiers
8715 that can be used are those defined in the Ada Reference Manual.
8717 @item No_Wide_Characters
8718 @findex No_Wide_Characters
8719 This restriction ensures at compile time that no uses of the types
8720 @code{Wide_Character} or @code{Wide_String} or corresponding wide
8722 appear, and that no wide or wide wide string or character literals
8723 appear in the program (that is literals representing characters not in
8724 type @code{Character}.
8731 @strong{58}. The consequences of violating limitations on
8732 @code{Restrictions} pragmas. See 13.12(9).
8735 Restrictions that can be checked at compile time result in illegalities
8736 if violated. Currently there are no other consequences of violating
8742 @strong{59}. The representation used by the @code{Read} and
8743 @code{Write} attributes of elementary types in terms of stream
8744 elements. See 13.13.2(9).
8747 The representation is the in-memory representation of the base type of
8748 the type, using the number of bits corresponding to the
8749 @code{@var{type}'Size} value, and the natural ordering of the machine.
8754 @strong{60}. The names and characteristics of the numeric subtypes
8755 declared in the visible part of package @code{Standard}. See A.1(3).
8758 See items describing the integer and floating-point types supported.
8763 @strong{61}. The accuracy actually achieved by the elementary
8764 functions. See A.5.1(1).
8767 The elementary functions correspond to the functions available in the C
8768 library. Only fast math mode is implemented.
8773 @strong{62}. The sign of a zero result from some of the operators or
8774 functions in @code{Numerics.Generic_Elementary_Functions}, when
8775 @code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
8778 The sign of zeroes follows the requirements of the IEEE 754 standard on
8784 @strong{63}. The value of
8785 @code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
8788 Maximum image width is 649, see library file @file{a-numran.ads}.
8793 @strong{64}. The value of
8794 @code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
8797 Maximum image width is 80, see library file @file{a-nudira.ads}.
8802 @strong{65}. The algorithms for random number generation. See
8806 The algorithm is documented in the source files @file{a-numran.ads} and
8807 @file{a-numran.adb}.
8812 @strong{66}. The string representation of a random number generator's
8813 state. See A.5.2(38).
8816 See the documentation contained in the file @file{a-numran.adb}.
8821 @strong{67}. The minimum time interval between calls to the
8822 time-dependent Reset procedure that are guaranteed to initiate different
8823 random number sequences. See A.5.2(45).
8826 The minimum period between reset calls to guarantee distinct series of
8827 random numbers is one microsecond.
8832 @strong{68}. The values of the @code{Model_Mantissa},
8833 @code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
8834 @code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
8835 Annex is not supported. See A.5.3(72).
8838 See the source file @file{ttypef.ads} for the values of all numeric
8844 @strong{69}. Any implementation-defined characteristics of the
8845 input-output packages. See A.7(14).
8848 There are no special implementation defined characteristics for these
8854 @strong{70}. The value of @code{Buffer_Size} in @code{Storage_IO}. See
8858 All type representations are contiguous, and the @code{Buffer_Size} is
8859 the value of @code{@var{type}'Size} rounded up to the next storage unit
8865 @strong{71}. External files for standard input, standard output, and
8866 standard error See A.10(5).
8869 These files are mapped onto the files provided by the C streams
8870 libraries. See source file @file{i-cstrea.ads} for further details.
8875 @strong{72}. The accuracy of the value produced by @code{Put}. See
8879 If more digits are requested in the output than are represented by the
8880 precision of the value, zeroes are output in the corresponding least
8881 significant digit positions.
8886 @strong{73}. The meaning of @code{Argument_Count}, @code{Argument}, and
8887 @code{Command_Name}. See A.15(1).
8890 These are mapped onto the @code{argv} and @code{argc} parameters of the
8891 main program in the natural manner.
8896 @strong{74}. Implementation-defined convention names. See B.1(11).
8899 The following convention names are supported
8907 Synonym for Assembler
8909 Synonym for Assembler
8912 @item C_Pass_By_Copy
8913 Allowed only for record types, like C, but also notes that record
8914 is to be passed by copy rather than reference.
8917 @item C_Plus_Plus (or CPP)
8920 Treated the same as C
8922 Treated the same as C
8926 For support of pragma @code{Import} with convention Intrinsic, see
8927 separate section on Intrinsic Subprograms.
8929 Stdcall (used for Windows implementations only). This convention correspond
8930 to the WINAPI (previously called Pascal convention) C/C++ convention under
8931 Windows. A function with this convention cleans the stack before exit.
8937 Stubbed is a special convention used to indicate that the body of the
8938 subprogram will be entirely ignored. Any call to the subprogram
8939 is converted into a raise of the @code{Program_Error} exception. If a
8940 pragma @code{Import} specifies convention @code{stubbed} then no body need
8941 be present at all. This convention is useful during development for the
8942 inclusion of subprograms whose body has not yet been written.
8946 In addition, all otherwise unrecognized convention names are also
8947 treated as being synonymous with convention C@. In all implementations
8948 except for VMS, use of such other names results in a warning. In VMS
8949 implementations, these names are accepted silently.
8954 @strong{75}. The meaning of link names. See B.1(36).
8957 Link names are the actual names used by the linker.
8962 @strong{76}. The manner of choosing link names when neither the link
8963 name nor the address of an imported or exported entity is specified. See
8967 The default linker name is that which would be assigned by the relevant
8968 external language, interpreting the Ada name as being in all lower case
8974 @strong{77}. The effect of pragma @code{Linker_Options}. See B.1(37).
8977 The string passed to @code{Linker_Options} is presented uninterpreted as
8978 an argument to the link command, unless it contains ASCII.NUL characters.
8979 NUL characters if they appear act as argument separators, so for example
8981 @smallexample @c ada
8982 pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef");
8986 causes two separate arguments @code{-labc} and @code{-ldef} to be passed to the
8987 linker. The order of linker options is preserved for a given unit. The final
8988 list of options passed to the linker is in reverse order of the elaboration
8989 order. For example, linker options for a body always appear before the options
8990 from the corresponding package spec.
8995 @strong{78}. The contents of the visible part of package
8996 @code{Interfaces} and its language-defined descendants. See B.2(1).
8999 See files with prefix @file{i-} in the distributed library.
9004 @strong{79}. Implementation-defined children of package
9005 @code{Interfaces}. The contents of the visible part of package
9006 @code{Interfaces}. See B.2(11).
9009 See files with prefix @file{i-} in the distributed library.
9014 @strong{80}. The types @code{Floating}, @code{Long_Floating},
9015 @code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
9016 @code{COBOL_Character}; and the initialization of the variables
9017 @code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
9018 @code{Interfaces.COBOL}. See B.4(50).
9025 (Floating) Long_Float
9030 @item Decimal_Element
9032 @item COBOL_Character
9037 For initialization, see the file @file{i-cobol.ads} in the distributed library.
9042 @strong{81}. Support for access to machine instructions. See C.1(1).
9045 See documentation in file @file{s-maccod.ads} in the distributed library.
9050 @strong{82}. Implementation-defined aspects of access to machine
9051 operations. See C.1(9).
9054 See documentation in file @file{s-maccod.ads} in the distributed library.
9059 @strong{83}. Implementation-defined aspects of interrupts. See C.3(2).
9062 Interrupts are mapped to signals or conditions as appropriate. See
9064 @code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
9065 on the interrupts supported on a particular target.
9070 @strong{84}. Implementation-defined aspects of pre-elaboration. See
9074 GNAT does not permit a partition to be restarted without reloading,
9075 except under control of the debugger.
9080 @strong{85}. The semantics of pragma @code{Discard_Names}. See C.5(7).
9083 Pragma @code{Discard_Names} causes names of enumeration literals to
9084 be suppressed. In the presence of this pragma, the Image attribute
9085 provides the image of the Pos of the literal, and Value accepts
9091 @strong{86}. The result of the @code{Task_Identification.Image}
9092 attribute. See C.7.1(7).
9095 The result of this attribute is a string that identifies
9096 the object or component that denotes a given task. If a variable @code{Var}
9097 has a task type, the image for this task will have the form @code{Var_@var{XXXXXXXX}},
9099 is the hexadecimal representation of the virtual address of the corresponding
9100 task control block. If the variable is an array of tasks, the image of each
9101 task will have the form of an indexed component indicating the position of a
9102 given task in the array, e.g.@: @code{Group(5)_@var{XXXXXXX}}. If the task is a
9103 component of a record, the image of the task will have the form of a selected
9104 component. These rules are fully recursive, so that the image of a task that
9105 is a subcomponent of a composite object corresponds to the expression that
9106 designates this task.
9108 If a task is created by an allocator, its image depends on the context. If the
9109 allocator is part of an object declaration, the rules described above are used
9110 to construct its image, and this image is not affected by subsequent
9111 assignments. If the allocator appears within an expression, the image
9112 includes only the name of the task type.
9114 If the configuration pragma Discard_Names is present, or if the restriction
9115 No_Implicit_Heap_Allocation is in effect, the image reduces to
9116 the numeric suffix, that is to say the hexadecimal representation of the
9117 virtual address of the control block of the task.
9121 @strong{87}. The value of @code{Current_Task} when in a protected entry
9122 or interrupt handler. See C.7.1(17).
9125 Protected entries or interrupt handlers can be executed by any
9126 convenient thread, so the value of @code{Current_Task} is undefined.
9131 @strong{88}. The effect of calling @code{Current_Task} from an entry
9132 body or interrupt handler. See C.7.1(19).
9135 The effect of calling @code{Current_Task} from an entry body or
9136 interrupt handler is to return the identification of the task currently
9142 @strong{89}. Implementation-defined aspects of
9143 @code{Task_Attributes}. See C.7.2(19).
9146 There are no implementation-defined aspects of @code{Task_Attributes}.
9151 @strong{90}. Values of all @code{Metrics}. See D(2).
9154 The metrics information for GNAT depends on the performance of the
9155 underlying operating system. The sources of the run-time for tasking
9156 implementation, together with the output from @option{-gnatG} can be
9157 used to determine the exact sequence of operating systems calls made
9158 to implement various tasking constructs. Together with appropriate
9159 information on the performance of the underlying operating system,
9160 on the exact target in use, this information can be used to determine
9161 the required metrics.
9166 @strong{91}. The declarations of @code{Any_Priority} and
9167 @code{Priority}. See D.1(11).
9170 See declarations in file @file{system.ads}.
9175 @strong{92}. Implementation-defined execution resources. See D.1(15).
9178 There are no implementation-defined execution resources.
9183 @strong{93}. Whether, on a multiprocessor, a task that is waiting for
9184 access to a protected object keeps its processor busy. See D.2.1(3).
9187 On a multi-processor, a task that is waiting for access to a protected
9188 object does not keep its processor busy.
9193 @strong{94}. The affect of implementation defined execution resources
9194 on task dispatching. See D.2.1(9).
9199 Tasks map to IRIX threads, and the dispatching policy is as defined by
9200 the IRIX implementation of threads.
9202 Tasks map to threads in the threads package used by GNAT@. Where possible
9203 and appropriate, these threads correspond to native threads of the
9204 underlying operating system.
9209 @strong{95}. Implementation-defined @code{policy_identifiers} allowed
9210 in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
9213 There are no implementation-defined policy-identifiers allowed in this
9219 @strong{96}. Implementation-defined aspects of priority inversion. See
9223 Execution of a task cannot be preempted by the implementation processing
9224 of delay expirations for lower priority tasks.
9229 @strong{97}. Implementation defined task dispatching. See D.2.2(18).
9234 Tasks map to IRIX threads, and the dispatching policy is as defined by
9235 the IRIX implementation of threads.
9237 The policy is the same as that of the underlying threads implementation.
9242 @strong{98}. Implementation-defined @code{policy_identifiers} allowed
9243 in a pragma @code{Locking_Policy}. See D.3(4).
9246 The only implementation defined policy permitted in GNAT is
9247 @code{Inheritance_Locking}. On targets that support this policy, locking
9248 is implemented by inheritance, i.e.@: the task owning the lock operates
9249 at a priority equal to the highest priority of any task currently
9250 requesting the lock.
9255 @strong{99}. Default ceiling priorities. See D.3(10).
9258 The ceiling priority of protected objects of the type
9259 @code{System.Interrupt_Priority'Last} as described in the Ada
9260 Reference Manual D.3(10),
9265 @strong{100}. The ceiling of any protected object used internally by
9266 the implementation. See D.3(16).
9269 The ceiling priority of internal protected objects is
9270 @code{System.Priority'Last}.
9275 @strong{101}. Implementation-defined queuing policies. See D.4(1).
9278 There are no implementation-defined queuing policies.
9283 @strong{102}. On a multiprocessor, any conditions that cause the
9284 completion of an aborted construct to be delayed later than what is
9285 specified for a single processor. See D.6(3).
9288 The semantics for abort on a multi-processor is the same as on a single
9289 processor, there are no further delays.
9294 @strong{103}. Any operations that implicitly require heap storage
9295 allocation. See D.7(8).
9298 The only operation that implicitly requires heap storage allocation is
9304 @strong{104}. Implementation-defined aspects of pragma
9305 @code{Restrictions}. See D.7(20).
9308 There are no such implementation-defined aspects.
9313 @strong{105}. Implementation-defined aspects of package
9314 @code{Real_Time}. See D.8(17).
9317 There are no implementation defined aspects of package @code{Real_Time}.
9322 @strong{106}. Implementation-defined aspects of
9323 @code{delay_statements}. See D.9(8).
9326 Any difference greater than one microsecond will cause the task to be
9327 delayed (see D.9(7)).
9332 @strong{107}. The upper bound on the duration of interrupt blocking
9333 caused by the implementation. See D.12(5).
9336 The upper bound is determined by the underlying operating system. In
9337 no cases is it more than 10 milliseconds.
9342 @strong{108}. The means for creating and executing distributed
9346 The GLADE package provides a utility GNATDIST for creating and executing
9347 distributed programs. See the GLADE reference manual for further details.
9352 @strong{109}. Any events that can result in a partition becoming
9353 inaccessible. See E.1(7).
9356 See the GLADE reference manual for full details on such events.
9361 @strong{110}. The scheduling policies, treatment of priorities, and
9362 management of shared resources between partitions in certain cases. See
9366 See the GLADE reference manual for full details on these aspects of
9367 multi-partition execution.
9372 @strong{111}. Events that cause the version of a compilation unit to
9376 Editing the source file of a compilation unit, or the source files of
9377 any units on which it is dependent in a significant way cause the version
9378 to change. No other actions cause the version number to change. All changes
9379 are significant except those which affect only layout, capitalization or
9385 @strong{112}. Whether the execution of the remote subprogram is
9386 immediately aborted as a result of cancellation. See E.4(13).
9389 See the GLADE reference manual for details on the effect of abort in
9390 a distributed application.
9395 @strong{113}. Implementation-defined aspects of the PCS@. See E.5(25).
9398 See the GLADE reference manual for a full description of all implementation
9399 defined aspects of the PCS@.
9404 @strong{114}. Implementation-defined interfaces in the PCS@. See
9408 See the GLADE reference manual for a full description of all
9409 implementation defined interfaces.
9414 @strong{115}. The values of named numbers in the package
9415 @code{Decimal}. See F.2(7).
9427 @item Max_Decimal_Digits
9434 @strong{116}. The value of @code{Max_Picture_Length} in the package
9435 @code{Text_IO.Editing}. See F.3.3(16).
9443 @strong{117}. The value of @code{Max_Picture_Length} in the package
9444 @code{Wide_Text_IO.Editing}. See F.3.4(5).
9452 @strong{118}. The accuracy actually achieved by the complex elementary
9453 functions and by other complex arithmetic operations. See G.1(1).
9456 Standard library functions are used for the complex arithmetic
9457 operations. Only fast math mode is currently supported.
9462 @strong{119}. The sign of a zero result (or a component thereof) from
9463 any operator or function in @code{Numerics.Generic_Complex_Types}, when
9464 @code{Real'Signed_Zeros} is True. See G.1.1(53).
9467 The signs of zero values are as recommended by the relevant
9468 implementation advice.
9473 @strong{120}. The sign of a zero result (or a component thereof) from
9474 any operator or function in
9475 @code{Numerics.Generic_Complex_Elementary_Functions}, when
9476 @code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
9479 The signs of zero values are as recommended by the relevant
9480 implementation advice.
9485 @strong{121}. Whether the strict mode or the relaxed mode is the
9486 default. See G.2(2).
9489 The strict mode is the default. There is no separate relaxed mode. GNAT
9490 provides a highly efficient implementation of strict mode.
9495 @strong{122}. The result interval in certain cases of fixed-to-float
9496 conversion. See G.2.1(10).
9499 For cases where the result interval is implementation dependent, the
9500 accuracy is that provided by performing all operations in 64-bit IEEE
9501 floating-point format.
9506 @strong{123}. The result of a floating point arithmetic operation in
9507 overflow situations, when the @code{Machine_Overflows} attribute of the
9508 result type is @code{False}. See G.2.1(13).
9511 Infinite and NaN values are produced as dictated by the IEEE
9512 floating-point standard.
9514 Note that on machines that are not fully compliant with the IEEE
9515 floating-point standard, such as Alpha, the @option{-mieee} compiler flag
9516 must be used for achieving IEEE confirming behavior (although at the cost
9517 of a significant performance penalty), so infinite and NaN values are
9523 @strong{124}. The result interval for division (or exponentiation by a
9524 negative exponent), when the floating point hardware implements division
9525 as multiplication by a reciprocal. See G.2.1(16).
9528 Not relevant, division is IEEE exact.
9533 @strong{125}. The definition of close result set, which determines the
9534 accuracy of certain fixed point multiplications and divisions. See
9538 Operations in the close result set are performed using IEEE long format
9539 floating-point arithmetic. The input operands are converted to
9540 floating-point, the operation is done in floating-point, and the result
9541 is converted to the target type.
9546 @strong{126}. Conditions on a @code{universal_real} operand of a fixed
9547 point multiplication or division for which the result shall be in the
9548 perfect result set. See G.2.3(22).
9551 The result is only defined to be in the perfect result set if the result
9552 can be computed by a single scaling operation involving a scale factor
9553 representable in 64-bits.
9558 @strong{127}. The result of a fixed point arithmetic operation in
9559 overflow situations, when the @code{Machine_Overflows} attribute of the
9560 result type is @code{False}. See G.2.3(27).
9563 Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
9569 @strong{128}. The result of an elementary function reference in
9570 overflow situations, when the @code{Machine_Overflows} attribute of the
9571 result type is @code{False}. See G.2.4(4).
9574 IEEE infinite and Nan values are produced as appropriate.
9579 @strong{129}. The value of the angle threshold, within which certain
9580 elementary functions, complex arithmetic operations, and complex
9581 elementary functions yield results conforming to a maximum relative
9582 error bound. See G.2.4(10).
9585 Information on this subject is not yet available.
9590 @strong{130}. The accuracy of certain elementary functions for
9591 parameters beyond the angle threshold. See G.2.4(10).
9594 Information on this subject is not yet available.
9599 @strong{131}. The result of a complex arithmetic operation or complex
9600 elementary function reference in overflow situations, when the
9601 @code{Machine_Overflows} attribute of the corresponding real type is
9602 @code{False}. See G.2.6(5).
9605 IEEE infinite and Nan values are produced as appropriate.
9610 @strong{132}. The accuracy of certain complex arithmetic operations and
9611 certain complex elementary functions for parameters (or components
9612 thereof) beyond the angle threshold. See G.2.6(8).
9615 Information on those subjects is not yet available.
9620 @strong{133}. Information regarding bounded errors and erroneous
9621 execution. See H.2(1).
9624 Information on this subject is not yet available.
9629 @strong{134}. Implementation-defined aspects of pragma
9630 @code{Inspection_Point}. See H.3.2(8).
9633 Pragma @code{Inspection_Point} ensures that the variable is live and can
9634 be examined by the debugger at the inspection point.
9639 @strong{135}. Implementation-defined aspects of pragma
9640 @code{Restrictions}. See H.4(25).
9643 There are no implementation-defined aspects of pragma @code{Restrictions}. The
9644 use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
9645 generated code. Checks must suppressed by use of pragma @code{Suppress}.
9650 @strong{136}. Any restrictions on pragma @code{Restrictions}. See
9654 There are no restrictions on pragma @code{Restrictions}.
9656 @node Intrinsic Subprograms
9657 @chapter Intrinsic Subprograms
9658 @cindex Intrinsic Subprograms
9661 * Intrinsic Operators::
9662 * Enclosing_Entity::
9663 * Exception_Information::
9664 * Exception_Message::
9672 * Shift_Right_Arithmetic::
9677 GNAT allows a user application program to write the declaration:
9679 @smallexample @c ada
9680 pragma Import (Intrinsic, name);
9684 providing that the name corresponds to one of the implemented intrinsic
9685 subprograms in GNAT, and that the parameter profile of the referenced
9686 subprogram meets the requirements. This chapter describes the set of
9687 implemented intrinsic subprograms, and the requirements on parameter profiles.
9688 Note that no body is supplied; as with other uses of pragma Import, the
9689 body is supplied elsewhere (in this case by the compiler itself). Note
9690 that any use of this feature is potentially non-portable, since the
9691 Ada standard does not require Ada compilers to implement this feature.
9693 @node Intrinsic Operators
9694 @section Intrinsic Operators
9695 @cindex Intrinsic operator
9698 All the predefined numeric operators in package Standard
9699 in @code{pragma Import (Intrinsic,..)}
9700 declarations. In the binary operator case, the operands must have the same
9701 size. The operand or operands must also be appropriate for
9702 the operator. For example, for addition, the operands must
9703 both be floating-point or both be fixed-point, and the
9704 right operand for @code{"**"} must have a root type of
9705 @code{Standard.Integer'Base}.
9706 You can use an intrinsic operator declaration as in the following example:
9708 @smallexample @c ada
9709 type Int1 is new Integer;
9710 type Int2 is new Integer;
9712 function "+" (X1 : Int1; X2 : Int2) return Int1;
9713 function "+" (X1 : Int1; X2 : Int2) return Int2;
9714 pragma Import (Intrinsic, "+");
9718 This declaration would permit ``mixed mode'' arithmetic on items
9719 of the differing types @code{Int1} and @code{Int2}.
9720 It is also possible to specify such operators for private types, if the
9721 full views are appropriate arithmetic types.
9723 @node Enclosing_Entity
9724 @section Enclosing_Entity
9725 @cindex Enclosing_Entity
9727 This intrinsic subprogram is used in the implementation of the
9728 library routine @code{GNAT.Source_Info}. The only useful use of the
9729 intrinsic import in this case is the one in this unit, so an
9730 application program should simply call the function
9731 @code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
9732 the current subprogram, package, task, entry, or protected subprogram.
9734 @node Exception_Information
9735 @section Exception_Information
9736 @cindex Exception_Information'
9738 This intrinsic subprogram is used in the implementation of the
9739 library routine @code{GNAT.Current_Exception}. The only useful
9740 use of the intrinsic import in this case is the one in this unit,
9741 so an application program should simply call the function
9742 @code{GNAT.Current_Exception.Exception_Information} to obtain
9743 the exception information associated with the current exception.
9745 @node Exception_Message
9746 @section Exception_Message
9747 @cindex Exception_Message
9749 This intrinsic subprogram is used in the implementation of the
9750 library routine @code{GNAT.Current_Exception}. The only useful
9751 use of the intrinsic import in this case is the one in this unit,
9752 so an application program should simply call the function
9753 @code{GNAT.Current_Exception.Exception_Message} to obtain
9754 the message associated with the current exception.
9756 @node Exception_Name
9757 @section Exception_Name
9758 @cindex Exception_Name
9760 This intrinsic subprogram is used in the implementation of the
9761 library routine @code{GNAT.Current_Exception}. The only useful
9762 use of the intrinsic import in this case is the one in this unit,
9763 so an application program should simply call the function
9764 @code{GNAT.Current_Exception.Exception_Name} to obtain
9765 the name of the current exception.
9771 This intrinsic subprogram is used in the implementation of the
9772 library routine @code{GNAT.Source_Info}. The only useful use of the
9773 intrinsic import in this case is the one in this unit, so an
9774 application program should simply call the function
9775 @code{GNAT.Source_Info.File} to obtain the name of the current
9782 This intrinsic subprogram is used in the implementation of the
9783 library routine @code{GNAT.Source_Info}. The only useful use of the
9784 intrinsic import in this case is the one in this unit, so an
9785 application program should simply call the function
9786 @code{GNAT.Source_Info.Line} to obtain the number of the current
9790 @section Rotate_Left
9793 In standard Ada, the @code{Rotate_Left} function is available only
9794 for the predefined modular types in package @code{Interfaces}. However, in
9795 GNAT it is possible to define a Rotate_Left function for a user
9796 defined modular type or any signed integer type as in this example:
9798 @smallexample @c ada
9800 (Value : My_Modular_Type;
9802 return My_Modular_Type;
9806 The requirements are that the profile be exactly as in the example
9807 above. The only modifications allowed are in the formal parameter
9808 names, and in the type of @code{Value} and the return type, which
9809 must be the same, and must be either a signed integer type, or
9810 a modular integer type with a binary modulus, and the size must
9811 be 8. 16, 32 or 64 bits.
9814 @section Rotate_Right
9815 @cindex Rotate_Right
9817 A @code{Rotate_Right} function can be defined for any user defined
9818 binary modular integer type, or signed integer type, as described
9819 above for @code{Rotate_Left}.
9825 A @code{Shift_Left} function can be defined for any user defined
9826 binary modular integer type, or signed integer type, as described
9827 above for @code{Rotate_Left}.
9830 @section Shift_Right
9833 A @code{Shift_Right} function can be defined for any user defined
9834 binary modular integer type, or signed integer type, as described
9835 above for @code{Rotate_Left}.
9837 @node Shift_Right_Arithmetic
9838 @section Shift_Right_Arithmetic
9839 @cindex Shift_Right_Arithmetic
9841 A @code{Shift_Right_Arithmetic} function can be defined for any user
9842 defined binary modular integer type, or signed integer type, as described
9843 above for @code{Rotate_Left}.
9845 @node Source_Location
9846 @section Source_Location
9847 @cindex Source_Location
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.Source_Location} to obtain the current
9854 source file location.
9856 @node Representation Clauses and Pragmas
9857 @chapter Representation Clauses and Pragmas
9858 @cindex Representation Clauses
9861 * Alignment Clauses::
9863 * Storage_Size Clauses::
9864 * Size of Variant Record Objects::
9865 * Biased Representation ::
9866 * Value_Size and Object_Size Clauses::
9867 * Component_Size Clauses::
9868 * Bit_Order Clauses::
9869 * Effect of Bit_Order on Byte Ordering::
9870 * Pragma Pack for Arrays::
9871 * Pragma Pack for Records::
9872 * Record Representation Clauses::
9873 * Enumeration Clauses::
9875 * Effect of Convention on Representation::
9876 * Determining the Representations chosen by GNAT::
9880 @cindex Representation Clause
9881 @cindex Representation Pragma
9882 @cindex Pragma, representation
9883 This section describes the representation clauses accepted by GNAT, and
9884 their effect on the representation of corresponding data objects.
9886 GNAT fully implements Annex C (Systems Programming). This means that all
9887 the implementation advice sections in chapter 13 are fully implemented.
9888 However, these sections only require a minimal level of support for
9889 representation clauses. GNAT provides much more extensive capabilities,
9890 and this section describes the additional capabilities provided.
9892 @node Alignment Clauses
9893 @section Alignment Clauses
9894 @cindex Alignment Clause
9897 GNAT requires that all alignment clauses specify a power of 2, and all
9898 default alignments are always a power of 2. The default alignment
9899 values are as follows:
9902 @item @emph{Primitive Types}.
9903 For primitive types, the alignment is the minimum of the actual size of
9904 objects of the type divided by @code{Storage_Unit},
9905 and the maximum alignment supported by the target.
9906 (This maximum alignment is given by the GNAT-specific attribute
9907 @code{Standard'Maximum_Alignment}; see @ref{Maximum_Alignment}.)
9908 @cindex @code{Maximum_Alignment} attribute
9909 For example, for type @code{Long_Float}, the object size is 8 bytes, and the
9910 default alignment will be 8 on any target that supports alignments
9911 this large, but on some targets, the maximum alignment may be smaller
9912 than 8, in which case objects of type @code{Long_Float} will be maximally
9915 @item @emph{Arrays}.
9916 For arrays, the alignment is equal to the alignment of the component type
9917 for the normal case where no packing or component size is given. If the
9918 array is packed, and the packing is effective (see separate section on
9919 packed arrays), then the alignment will be one for long packed arrays,
9920 or arrays whose length is not known at compile time. For short packed
9921 arrays, which are handled internally as modular types, the alignment
9922 will be as described for primitive types, e.g.@: a packed array of length
9923 31 bits will have an object size of four bytes, and an alignment of 4.
9925 @item @emph{Records}.
9926 For the normal non-packed case, the alignment of a record is equal to
9927 the maximum alignment of any of its components. For tagged records, this
9928 includes the implicit access type used for the tag. If a pragma @code{Pack}
9929 is used and all components are packable (see separate section on pragma
9930 @code{Pack}), then the resulting alignment is 1, unless the layout of the
9931 record makes it profitable to increase it.
9933 A special case is when:
9936 the size of the record is given explicitly, or a
9937 full record representation clause is given, and
9939 the size of the record is 2, 4, or 8 bytes.
9942 In this case, an alignment is chosen to match the
9943 size of the record. For example, if we have:
9945 @smallexample @c ada
9946 type Small is record
9949 for Small'Size use 16;
9953 then the default alignment of the record type @code{Small} is 2, not 1. This
9954 leads to more efficient code when the record is treated as a unit, and also
9955 allows the type to specified as @code{Atomic} on architectures requiring
9961 An alignment clause may specify a larger alignment than the default value
9962 up to some maximum value dependent on the target (obtainable by using the
9963 attribute reference @code{Standard'Maximum_Alignment}). It may also specify
9964 a smaller alignment than the default value for enumeration, integer and
9965 fixed point types, as well as for record types, for example
9967 @smallexample @c ada
9972 for V'alignment use 1;
9976 @cindex Alignment, default
9977 The default alignment for the type @code{V} is 4, as a result of the
9978 Integer field in the record, but it is permissible, as shown, to
9979 override the default alignment of the record with a smaller value.
9982 @section Size Clauses
9986 The default size for a type @code{T} is obtainable through the
9987 language-defined attribute @code{T'Size} and also through the
9988 equivalent GNAT-defined attribute @code{T'Value_Size}.
9989 For objects of type @code{T}, GNAT will generally increase the type size
9990 so that the object size (obtainable through the GNAT-defined attribute
9991 @code{T'Object_Size})
9992 is a multiple of @code{T'Alignment * Storage_Unit}.
9995 @smallexample @c ada
9996 type Smallint is range 1 .. 6;
10005 In this example, @code{Smallint'Size} = @code{Smallint'Value_Size} = 3,
10006 as specified by the RM rules,
10007 but objects of this type will have a size of 8
10008 (@code{Smallint'Object_Size} = 8),
10009 since objects by default occupy an integral number
10010 of storage units. On some targets, notably older
10011 versions of the Digital Alpha, the size of stand
10012 alone objects of this type may be 32, reflecting
10013 the inability of the hardware to do byte load/stores.
10015 Similarly, the size of type @code{Rec} is 40 bits
10016 (@code{Rec'Size} = @code{Rec'Value_Size} = 40), but
10017 the alignment is 4, so objects of this type will have
10018 their size increased to 64 bits so that it is a multiple
10019 of the alignment (in bits). This decision is
10020 in accordance with the specific Implementation Advice in RM 13.3(43):
10023 A @code{Size} clause should be supported for an object if the specified
10024 @code{Size} is at least as large as its subtype's @code{Size}, and corresponds
10025 to a size in storage elements that is a multiple of the object's
10026 @code{Alignment} (if the @code{Alignment} is nonzero).
10030 An explicit size clause may be used to override the default size by
10031 increasing it. For example, if we have:
10033 @smallexample @c ada
10034 type My_Boolean is new Boolean;
10035 for My_Boolean'Size use 32;
10039 then values of this type will always be 32 bits long. In the case of
10040 discrete types, the size can be increased up to 64 bits, with the effect
10041 that the entire specified field is used to hold the value, sign- or
10042 zero-extended as appropriate. If more than 64 bits is specified, then
10043 padding space is allocated after the value, and a warning is issued that
10044 there are unused bits.
10046 Similarly the size of records and arrays may be increased, and the effect
10047 is to add padding bits after the value. This also causes a warning message
10050 The largest Size value permitted in GNAT is 2**31@minus{}1. Since this is a
10051 Size in bits, this corresponds to an object of size 256 megabytes (minus
10052 one). This limitation is true on all targets. The reason for this
10053 limitation is that it improves the quality of the code in many cases
10054 if it is known that a Size value can be accommodated in an object of
10057 @node Storage_Size Clauses
10058 @section Storage_Size Clauses
10059 @cindex Storage_Size Clause
10062 For tasks, the @code{Storage_Size} clause specifies the amount of space
10063 to be allocated for the task stack. This cannot be extended, and if the
10064 stack is exhausted, then @code{Storage_Error} will be raised (if stack
10065 checking is enabled). Use a @code{Storage_Size} attribute definition clause,
10066 or a @code{Storage_Size} pragma in the task definition to set the
10067 appropriate required size. A useful technique is to include in every
10068 task definition a pragma of the form:
10070 @smallexample @c ada
10071 pragma Storage_Size (Default_Stack_Size);
10075 Then @code{Default_Stack_Size} can be defined in a global package, and
10076 modified as required. Any tasks requiring stack sizes different from the
10077 default can have an appropriate alternative reference in the pragma.
10079 You can also use the @option{-d} binder switch to modify the default stack
10082 For access types, the @code{Storage_Size} clause specifies the maximum
10083 space available for allocation of objects of the type. If this space is
10084 exceeded then @code{Storage_Error} will be raised by an allocation attempt.
10085 In the case where the access type is declared local to a subprogram, the
10086 use of a @code{Storage_Size} clause triggers automatic use of a special
10087 predefined storage pool (@code{System.Pool_Size}) that ensures that all
10088 space for the pool is automatically reclaimed on exit from the scope in
10089 which the type is declared.
10091 A special case recognized by the compiler is the specification of a
10092 @code{Storage_Size} of zero for an access type. This means that no
10093 items can be allocated from the pool, and this is recognized at compile
10094 time, and all the overhead normally associated with maintaining a fixed
10095 size storage pool is eliminated. Consider the following example:
10097 @smallexample @c ada
10099 type R is array (Natural) of Character;
10100 type P is access all R;
10101 for P'Storage_Size use 0;
10102 -- Above access type intended only for interfacing purposes
10106 procedure g (m : P);
10107 pragma Import (C, g);
10118 As indicated in this example, these dummy storage pools are often useful in
10119 connection with interfacing where no object will ever be allocated. If you
10120 compile the above example, you get the warning:
10123 p.adb:16:09: warning: allocation from empty storage pool
10124 p.adb:16:09: warning: Storage_Error will be raised at run time
10128 Of course in practice, there will not be any explicit allocators in the
10129 case of such an access declaration.
10131 @node Size of Variant Record Objects
10132 @section Size of Variant Record Objects
10133 @cindex Size, variant record objects
10134 @cindex Variant record objects, size
10137 In the case of variant record objects, there is a question whether Size gives
10138 information about a particular variant, or the maximum size required
10139 for any variant. Consider the following program
10141 @smallexample @c ada
10142 with Text_IO; use Text_IO;
10144 type R1 (A : Boolean := False) is record
10146 when True => X : Character;
10147 when False => null;
10155 Put_Line (Integer'Image (V1'Size));
10156 Put_Line (Integer'Image (V2'Size));
10161 Here we are dealing with a variant record, where the True variant
10162 requires 16 bits, and the False variant requires 8 bits.
10163 In the above example, both V1 and V2 contain the False variant,
10164 which is only 8 bits long. However, the result of running the
10173 The reason for the difference here is that the discriminant value of
10174 V1 is fixed, and will always be False. It is not possible to assign
10175 a True variant value to V1, therefore 8 bits is sufficient. On the
10176 other hand, in the case of V2, the initial discriminant value is
10177 False (from the default), but it is possible to assign a True
10178 variant value to V2, therefore 16 bits must be allocated for V2
10179 in the general case, even fewer bits may be needed at any particular
10180 point during the program execution.
10182 As can be seen from the output of this program, the @code{'Size}
10183 attribute applied to such an object in GNAT gives the actual allocated
10184 size of the variable, which is the largest size of any of the variants.
10185 The Ada Reference Manual is not completely clear on what choice should
10186 be made here, but the GNAT behavior seems most consistent with the
10187 language in the RM@.
10189 In some cases, it may be desirable to obtain the size of the current
10190 variant, rather than the size of the largest variant. This can be
10191 achieved in GNAT by making use of the fact that in the case of a
10192 subprogram parameter, GNAT does indeed return the size of the current
10193 variant (because a subprogram has no way of knowing how much space
10194 is actually allocated for the actual).
10196 Consider the following modified version of the above program:
10198 @smallexample @c ada
10199 with Text_IO; use Text_IO;
10201 type R1 (A : Boolean := False) is record
10203 when True => X : Character;
10204 when False => null;
10210 function Size (V : R1) return Integer is
10216 Put_Line (Integer'Image (V2'Size));
10217 Put_Line (Integer'IMage (Size (V2)));
10219 Put_Line (Integer'Image (V2'Size));
10220 Put_Line (Integer'IMage (Size (V2)));
10225 The output from this program is
10235 Here we see that while the @code{'Size} attribute always returns
10236 the maximum size, regardless of the current variant value, the
10237 @code{Size} function does indeed return the size of the current
10240 @node Biased Representation
10241 @section Biased Representation
10242 @cindex Size for biased representation
10243 @cindex Biased representation
10246 In the case of scalars with a range starting at other than zero, it is
10247 possible in some cases to specify a size smaller than the default minimum
10248 value, and in such cases, GNAT uses an unsigned biased representation,
10249 in which zero is used to represent the lower bound, and successive values
10250 represent successive values of the type.
10252 For example, suppose we have the declaration:
10254 @smallexample @c ada
10255 type Small is range -7 .. -4;
10256 for Small'Size use 2;
10260 Although the default size of type @code{Small} is 4, the @code{Size}
10261 clause is accepted by GNAT and results in the following representation
10265 -7 is represented as 2#00#
10266 -6 is represented as 2#01#
10267 -5 is represented as 2#10#
10268 -4 is represented as 2#11#
10272 Biased representation is only used if the specified @code{Size} clause
10273 cannot be accepted in any other manner. These reduced sizes that force
10274 biased representation can be used for all discrete types except for
10275 enumeration types for which a representation clause is given.
10277 @node Value_Size and Object_Size Clauses
10278 @section Value_Size and Object_Size Clauses
10280 @findex Object_Size
10281 @cindex Size, of objects
10284 In Ada 95 and Ada 2005, @code{T'Size} for a type @code{T} is the minimum
10285 number of bits required to hold values of type @code{T}.
10286 Although this interpretation was allowed in Ada 83, it was not required,
10287 and this requirement in practice can cause some significant difficulties.
10288 For example, in most Ada 83 compilers, @code{Natural'Size} was 32.
10289 However, in Ada 95 and Ada 2005,
10290 @code{Natural'Size} is
10291 typically 31. This means that code may change in behavior when moving
10292 from Ada 83 to Ada 95 or Ada 2005. For example, consider:
10294 @smallexample @c ada
10295 type Rec is record;
10301 at 0 range 0 .. Natural'Size - 1;
10302 at 0 range Natural'Size .. 2 * Natural'Size - 1;
10307 In the above code, since the typical size of @code{Natural} objects
10308 is 32 bits and @code{Natural'Size} is 31, the above code can cause
10309 unexpected inefficient packing in Ada 95 and Ada 2005, and in general
10310 there are cases where the fact that the object size can exceed the
10311 size of the type causes surprises.
10313 To help get around this problem GNAT provides two implementation
10314 defined attributes, @code{Value_Size} and @code{Object_Size}. When
10315 applied to a type, these attributes yield the size of the type
10316 (corresponding to the RM defined size attribute), and the size of
10317 objects of the type respectively.
10319 The @code{Object_Size} is used for determining the default size of
10320 objects and components. This size value can be referred to using the
10321 @code{Object_Size} attribute. The phrase ``is used'' here means that it is
10322 the basis of the determination of the size. The backend is free to
10323 pad this up if necessary for efficiency, e.g.@: an 8-bit stand-alone
10324 character might be stored in 32 bits on a machine with no efficient
10325 byte access instructions such as the Alpha.
10327 The default rules for the value of @code{Object_Size} for
10328 discrete types are as follows:
10332 The @code{Object_Size} for base subtypes reflect the natural hardware
10333 size in bits (run the compiler with @option{-gnatS} to find those values
10334 for numeric types). Enumeration types and fixed-point base subtypes have
10335 8, 16, 32 or 64 bits for this size, depending on the range of values
10339 The @code{Object_Size} of a subtype is the same as the
10340 @code{Object_Size} of
10341 the type from which it is obtained.
10344 The @code{Object_Size} of a derived base type is copied from the parent
10345 base type, and the @code{Object_Size} of a derived first subtype is copied
10346 from the parent first subtype.
10350 The @code{Value_Size} attribute
10351 is the (minimum) number of bits required to store a value
10353 This value is used to determine how tightly to pack
10354 records or arrays with components of this type, and also affects
10355 the semantics of unchecked conversion (unchecked conversions where
10356 the @code{Value_Size} values differ generate a warning, and are potentially
10359 The default rules for the value of @code{Value_Size} are as follows:
10363 The @code{Value_Size} for a base subtype is the minimum number of bits
10364 required to store all values of the type (including the sign bit
10365 only if negative values are possible).
10368 If a subtype statically matches the first subtype of a given type, then it has
10369 by default the same @code{Value_Size} as the first subtype. This is a
10370 consequence of RM 13.1(14) (``if two subtypes statically match,
10371 then their subtype-specific aspects are the same''.)
10374 All other subtypes have a @code{Value_Size} corresponding to the minimum
10375 number of bits required to store all values of the subtype. For
10376 dynamic bounds, it is assumed that the value can range down or up
10377 to the corresponding bound of the ancestor
10381 The RM defined attribute @code{Size} corresponds to the
10382 @code{Value_Size} attribute.
10384 The @code{Size} attribute may be defined for a first-named subtype. This sets
10385 the @code{Value_Size} of
10386 the first-named subtype to the given value, and the
10387 @code{Object_Size} of this first-named subtype to the given value padded up
10388 to an appropriate boundary. It is a consequence of the default rules
10389 above that this @code{Object_Size} will apply to all further subtypes. On the
10390 other hand, @code{Value_Size} is affected only for the first subtype, any
10391 dynamic subtypes obtained from it directly, and any statically matching
10392 subtypes. The @code{Value_Size} of any other static subtypes is not affected.
10394 @code{Value_Size} and
10395 @code{Object_Size} may be explicitly set for any subtype using
10396 an attribute definition clause. Note that the use of these attributes
10397 can cause the RM 13.1(14) rule to be violated. If two access types
10398 reference aliased objects whose subtypes have differing @code{Object_Size}
10399 values as a result of explicit attribute definition clauses, then it
10400 is erroneous to convert from one access subtype to the other.
10402 At the implementation level, Esize stores the Object_Size and the
10403 RM_Size field stores the @code{Value_Size} (and hence the value of the
10404 @code{Size} attribute,
10405 which, as noted above, is equivalent to @code{Value_Size}).
10407 To get a feel for the difference, consider the following examples (note
10408 that in each case the base is @code{Short_Short_Integer} with a size of 8):
10411 Object_Size Value_Size
10413 type x1 is range 0 .. 5; 8 3
10415 type x2 is range 0 .. 5;
10416 for x2'size use 12; 16 12
10418 subtype x3 is x2 range 0 .. 3; 16 2
10420 subtype x4 is x2'base range 0 .. 10; 8 4
10422 subtype x5 is x2 range 0 .. dynamic; 16 3*
10424 subtype x6 is x2'base range 0 .. dynamic; 8 3*
10429 Note: the entries marked ``3*'' are not actually specified by the Ada
10430 Reference Manual, but it seems in the spirit of the RM rules to allocate
10431 the minimum number of bits (here 3, given the range for @code{x2})
10432 known to be large enough to hold the given range of values.
10434 So far, so good, but GNAT has to obey the RM rules, so the question is
10435 under what conditions must the RM @code{Size} be used.
10436 The following is a list
10437 of the occasions on which the RM @code{Size} must be used:
10441 Component size for packed arrays or records
10444 Value of the attribute @code{Size} for a type
10447 Warning about sizes not matching for unchecked conversion
10451 For record types, the @code{Object_Size} is always a multiple of the
10452 alignment of the type (this is true for all types). In some cases the
10453 @code{Value_Size} can be smaller. Consider:
10463 On a typical 32-bit architecture, the X component will be four bytes, and
10464 require four-byte alignment, and the Y component will be one byte. In this
10465 case @code{R'Value_Size} will be 40 (bits) since this is the minimum size
10466 required to store a value of this type, and for example, it is permissible
10467 to have a component of type R in an outer record whose component size is
10468 specified to be 48 bits. However, @code{R'Object_Size} will be 64 (bits),
10469 since it must be rounded up so that this value is a multiple of the
10470 alignment (4 bytes = 32 bits).
10473 For all other types, the @code{Object_Size}
10474 and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
10475 Only @code{Size} may be specified for such types.
10477 @node Component_Size Clauses
10478 @section Component_Size Clauses
10479 @cindex Component_Size Clause
10482 Normally, the value specified in a component size clause must be consistent
10483 with the subtype of the array component with regard to size and alignment.
10484 In other words, the value specified must be at least equal to the size
10485 of this subtype, and must be a multiple of the alignment value.
10487 In addition, component size clauses are allowed which cause the array
10488 to be packed, by specifying a smaller value. A first case is for
10489 component size values in the range 1 through 63. The value specified
10490 must not be smaller than the Size of the subtype. GNAT will accurately
10491 honor all packing requests in this range. For example, if we have:
10493 @smallexample @c ada
10494 type r is array (1 .. 8) of Natural;
10495 for r'Component_Size use 31;
10499 then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
10500 Of course access to the components of such an array is considerably
10501 less efficient than if the natural component size of 32 is used.
10502 A second case is when the subtype of the component is a record type
10503 padded because of its default alignment. For example, if we have:
10505 @smallexample @c ada
10512 type a is array (1 .. 8) of r;
10513 for a'Component_Size use 72;
10517 then the resulting array has a length of 72 bytes, instead of 96 bytes
10518 if the alignment of the record (4) was obeyed.
10520 Note that there is no point in giving both a component size clause
10521 and a pragma Pack for the same array type. if such duplicate
10522 clauses are given, the pragma Pack will be ignored.
10524 @node Bit_Order Clauses
10525 @section Bit_Order Clauses
10526 @cindex Bit_Order Clause
10527 @cindex bit ordering
10528 @cindex ordering, of bits
10531 For record subtypes, GNAT permits the specification of the @code{Bit_Order}
10532 attribute. The specification may either correspond to the default bit
10533 order for the target, in which case the specification has no effect and
10534 places no additional restrictions, or it may be for the non-standard
10535 setting (that is the opposite of the default).
10537 In the case where the non-standard value is specified, the effect is
10538 to renumber bits within each byte, but the ordering of bytes is not
10539 affected. There are certain
10540 restrictions placed on component clauses as follows:
10544 @item Components fitting within a single storage unit.
10546 These are unrestricted, and the effect is merely to renumber bits. For
10547 example if we are on a little-endian machine with @code{Low_Order_First}
10548 being the default, then the following two declarations have exactly
10551 @smallexample @c ada
10554 B : Integer range 1 .. 120;
10558 A at 0 range 0 .. 0;
10559 B at 0 range 1 .. 7;
10564 B : Integer range 1 .. 120;
10567 for R2'Bit_Order use High_Order_First;
10570 A at 0 range 7 .. 7;
10571 B at 0 range 0 .. 6;
10576 The useful application here is to write the second declaration with the
10577 @code{Bit_Order} attribute definition clause, and know that it will be treated
10578 the same, regardless of whether the target is little-endian or big-endian.
10580 @item Components occupying an integral number of bytes.
10582 These are components that exactly fit in two or more bytes. Such component
10583 declarations are allowed, but have no effect, since it is important to realize
10584 that the @code{Bit_Order} specification does not affect the ordering of bytes.
10585 In particular, the following attempt at getting an endian-independent integer
10588 @smallexample @c ada
10593 for R2'Bit_Order use High_Order_First;
10596 A at 0 range 0 .. 31;
10601 This declaration will result in a little-endian integer on a
10602 little-endian machine, and a big-endian integer on a big-endian machine.
10603 If byte flipping is required for interoperability between big- and
10604 little-endian machines, this must be explicitly programmed. This capability
10605 is not provided by @code{Bit_Order}.
10607 @item Components that are positioned across byte boundaries
10609 but do not occupy an integral number of bytes. Given that bytes are not
10610 reordered, such fields would occupy a non-contiguous sequence of bits
10611 in memory, requiring non-trivial code to reassemble. They are for this
10612 reason not permitted, and any component clause specifying such a layout
10613 will be flagged as illegal by GNAT@.
10618 Since the misconception that Bit_Order automatically deals with all
10619 endian-related incompatibilities is a common one, the specification of
10620 a component field that is an integral number of bytes will always
10621 generate a warning. This warning may be suppressed using @code{pragma
10622 Warnings (Off)} if desired. The following section contains additional
10623 details regarding the issue of byte ordering.
10625 @node Effect of Bit_Order on Byte Ordering
10626 @section Effect of Bit_Order on Byte Ordering
10627 @cindex byte ordering
10628 @cindex ordering, of bytes
10631 In this section we will review the effect of the @code{Bit_Order} attribute
10632 definition clause on byte ordering. Briefly, it has no effect at all, but
10633 a detailed example will be helpful. Before giving this
10634 example, let us review the precise
10635 definition of the effect of defining @code{Bit_Order}. The effect of a
10636 non-standard bit order is described in section 15.5.3 of the Ada
10640 2 A bit ordering is a method of interpreting the meaning of
10641 the storage place attributes.
10645 To understand the precise definition of storage place attributes in
10646 this context, we visit section 13.5.1 of the manual:
10649 13 A record_representation_clause (without the mod_clause)
10650 specifies the layout. The storage place attributes (see 13.5.2)
10651 are taken from the values of the position, first_bit, and last_bit
10652 expressions after normalizing those values so that first_bit is
10653 less than Storage_Unit.
10657 The critical point here is that storage places are taken from
10658 the values after normalization, not before. So the @code{Bit_Order}
10659 interpretation applies to normalized values. The interpretation
10660 is described in the later part of the 15.5.3 paragraph:
10663 2 A bit ordering is a method of interpreting the meaning of
10664 the storage place attributes. High_Order_First (known in the
10665 vernacular as ``big endian'') means that the first bit of a
10666 storage element (bit 0) is the most significant bit (interpreting
10667 the sequence of bits that represent a component as an unsigned
10668 integer value). Low_Order_First (known in the vernacular as
10669 ``little endian'') means the opposite: the first bit is the
10674 Note that the numbering is with respect to the bits of a storage
10675 unit. In other words, the specification affects only the numbering
10676 of bits within a single storage unit.
10678 We can make the effect clearer by giving an example.
10680 Suppose that we have an external device which presents two bytes, the first
10681 byte presented, which is the first (low addressed byte) of the two byte
10682 record is called Master, and the second byte is called Slave.
10684 The left most (most significant bit is called Control for each byte, and
10685 the remaining 7 bits are called V1, V2, @dots{} V7, where V7 is the rightmost
10686 (least significant) bit.
10688 On a big-endian machine, we can write the following representation clause
10690 @smallexample @c ada
10691 type Data is record
10692 Master_Control : Bit;
10700 Slave_Control : Bit;
10710 for Data use record
10711 Master_Control at 0 range 0 .. 0;
10712 Master_V1 at 0 range 1 .. 1;
10713 Master_V2 at 0 range 2 .. 2;
10714 Master_V3 at 0 range 3 .. 3;
10715 Master_V4 at 0 range 4 .. 4;
10716 Master_V5 at 0 range 5 .. 5;
10717 Master_V6 at 0 range 6 .. 6;
10718 Master_V7 at 0 range 7 .. 7;
10719 Slave_Control at 1 range 0 .. 0;
10720 Slave_V1 at 1 range 1 .. 1;
10721 Slave_V2 at 1 range 2 .. 2;
10722 Slave_V3 at 1 range 3 .. 3;
10723 Slave_V4 at 1 range 4 .. 4;
10724 Slave_V5 at 1 range 5 .. 5;
10725 Slave_V6 at 1 range 6 .. 6;
10726 Slave_V7 at 1 range 7 .. 7;
10731 Now if we move this to a little endian machine, then the bit ordering within
10732 the byte is backwards, so we have to rewrite the record rep clause as:
10734 @smallexample @c ada
10735 for Data use record
10736 Master_Control at 0 range 7 .. 7;
10737 Master_V1 at 0 range 6 .. 6;
10738 Master_V2 at 0 range 5 .. 5;
10739 Master_V3 at 0 range 4 .. 4;
10740 Master_V4 at 0 range 3 .. 3;
10741 Master_V5 at 0 range 2 .. 2;
10742 Master_V6 at 0 range 1 .. 1;
10743 Master_V7 at 0 range 0 .. 0;
10744 Slave_Control at 1 range 7 .. 7;
10745 Slave_V1 at 1 range 6 .. 6;
10746 Slave_V2 at 1 range 5 .. 5;
10747 Slave_V3 at 1 range 4 .. 4;
10748 Slave_V4 at 1 range 3 .. 3;
10749 Slave_V5 at 1 range 2 .. 2;
10750 Slave_V6 at 1 range 1 .. 1;
10751 Slave_V7 at 1 range 0 .. 0;
10756 It is a nuisance to have to rewrite the clause, especially if
10757 the code has to be maintained on both machines. However,
10758 this is a case that we can handle with the
10759 @code{Bit_Order} attribute if it is implemented.
10760 Note that the implementation is not required on byte addressed
10761 machines, but it is indeed implemented in GNAT.
10762 This means that we can simply use the
10763 first record clause, together with the declaration
10765 @smallexample @c ada
10766 for Data'Bit_Order use High_Order_First;
10770 and the effect is what is desired, namely the layout is exactly the same,
10771 independent of whether the code is compiled on a big-endian or little-endian
10774 The important point to understand is that byte ordering is not affected.
10775 A @code{Bit_Order} attribute definition never affects which byte a field
10776 ends up in, only where it ends up in that byte.
10777 To make this clear, let us rewrite the record rep clause of the previous
10780 @smallexample @c ada
10781 for Data'Bit_Order use High_Order_First;
10782 for Data use record
10783 Master_Control at 0 range 0 .. 0;
10784 Master_V1 at 0 range 1 .. 1;
10785 Master_V2 at 0 range 2 .. 2;
10786 Master_V3 at 0 range 3 .. 3;
10787 Master_V4 at 0 range 4 .. 4;
10788 Master_V5 at 0 range 5 .. 5;
10789 Master_V6 at 0 range 6 .. 6;
10790 Master_V7 at 0 range 7 .. 7;
10791 Slave_Control at 0 range 8 .. 8;
10792 Slave_V1 at 0 range 9 .. 9;
10793 Slave_V2 at 0 range 10 .. 10;
10794 Slave_V3 at 0 range 11 .. 11;
10795 Slave_V4 at 0 range 12 .. 12;
10796 Slave_V5 at 0 range 13 .. 13;
10797 Slave_V6 at 0 range 14 .. 14;
10798 Slave_V7 at 0 range 15 .. 15;
10803 This is exactly equivalent to saying (a repeat of the first example):
10805 @smallexample @c ada
10806 for Data'Bit_Order use High_Order_First;
10807 for Data use record
10808 Master_Control at 0 range 0 .. 0;
10809 Master_V1 at 0 range 1 .. 1;
10810 Master_V2 at 0 range 2 .. 2;
10811 Master_V3 at 0 range 3 .. 3;
10812 Master_V4 at 0 range 4 .. 4;
10813 Master_V5 at 0 range 5 .. 5;
10814 Master_V6 at 0 range 6 .. 6;
10815 Master_V7 at 0 range 7 .. 7;
10816 Slave_Control at 1 range 0 .. 0;
10817 Slave_V1 at 1 range 1 .. 1;
10818 Slave_V2 at 1 range 2 .. 2;
10819 Slave_V3 at 1 range 3 .. 3;
10820 Slave_V4 at 1 range 4 .. 4;
10821 Slave_V5 at 1 range 5 .. 5;
10822 Slave_V6 at 1 range 6 .. 6;
10823 Slave_V7 at 1 range 7 .. 7;
10828 Why are they equivalent? Well take a specific field, the @code{Slave_V2}
10829 field. The storage place attributes are obtained by normalizing the
10830 values given so that the @code{First_Bit} value is less than 8. After
10831 normalizing the values (0,10,10) we get (1,2,2) which is exactly what
10832 we specified in the other case.
10834 Now one might expect that the @code{Bit_Order} attribute might affect
10835 bit numbering within the entire record component (two bytes in this
10836 case, thus affecting which byte fields end up in), but that is not
10837 the way this feature is defined, it only affects numbering of bits,
10838 not which byte they end up in.
10840 Consequently it never makes sense to specify a starting bit number
10841 greater than 7 (for a byte addressable field) if an attribute
10842 definition for @code{Bit_Order} has been given, and indeed it
10843 may be actively confusing to specify such a value, so the compiler
10844 generates a warning for such usage.
10846 If you do need to control byte ordering then appropriate conditional
10847 values must be used. If in our example, the slave byte came first on
10848 some machines we might write:
10850 @smallexample @c ada
10851 Master_Byte_First constant Boolean := @dots{};
10853 Master_Byte : constant Natural :=
10854 1 - Boolean'Pos (Master_Byte_First);
10855 Slave_Byte : constant Natural :=
10856 Boolean'Pos (Master_Byte_First);
10858 for Data'Bit_Order use High_Order_First;
10859 for Data use record
10860 Master_Control at Master_Byte range 0 .. 0;
10861 Master_V1 at Master_Byte range 1 .. 1;
10862 Master_V2 at Master_Byte range 2 .. 2;
10863 Master_V3 at Master_Byte range 3 .. 3;
10864 Master_V4 at Master_Byte range 4 .. 4;
10865 Master_V5 at Master_Byte range 5 .. 5;
10866 Master_V6 at Master_Byte range 6 .. 6;
10867 Master_V7 at Master_Byte range 7 .. 7;
10868 Slave_Control at Slave_Byte range 0 .. 0;
10869 Slave_V1 at Slave_Byte range 1 .. 1;
10870 Slave_V2 at Slave_Byte range 2 .. 2;
10871 Slave_V3 at Slave_Byte range 3 .. 3;
10872 Slave_V4 at Slave_Byte range 4 .. 4;
10873 Slave_V5 at Slave_Byte range 5 .. 5;
10874 Slave_V6 at Slave_Byte range 6 .. 6;
10875 Slave_V7 at Slave_Byte range 7 .. 7;
10880 Now to switch between machines, all that is necessary is
10881 to set the boolean constant @code{Master_Byte_First} in
10882 an appropriate manner.
10884 @node Pragma Pack for Arrays
10885 @section Pragma Pack for Arrays
10886 @cindex Pragma Pack (for arrays)
10889 Pragma @code{Pack} applied to an array has no effect unless the component type
10890 is packable. For a component type to be packable, it must be one of the
10897 Any type whose size is specified with a size clause
10899 Any packed array type with a static size
10901 Any record type padded because of its default alignment
10905 For all these cases, if the component subtype size is in the range
10906 1 through 63, then the effect of the pragma @code{Pack} is exactly as though a
10907 component size were specified giving the component subtype size.
10908 For example if we have:
10910 @smallexample @c ada
10911 type r is range 0 .. 17;
10913 type ar is array (1 .. 8) of r;
10918 Then the component size of @code{ar} will be set to 5 (i.e.@: to @code{r'size},
10919 and the size of the array @code{ar} will be exactly 40 bits.
10921 Note that in some cases this rather fierce approach to packing can produce
10922 unexpected effects. For example, in Ada 95 and Ada 2005,
10923 subtype @code{Natural} typically has a size of 31, meaning that if you
10924 pack an array of @code{Natural}, you get 31-bit
10925 close packing, which saves a few bits, but results in far less efficient
10926 access. Since many other Ada compilers will ignore such a packing request,
10927 GNAT will generate a warning on some uses of pragma @code{Pack} that it guesses
10928 might not be what is intended. You can easily remove this warning by
10929 using an explicit @code{Component_Size} setting instead, which never generates
10930 a warning, since the intention of the programmer is clear in this case.
10932 GNAT treats packed arrays in one of two ways. If the size of the array is
10933 known at compile time and is less than 64 bits, then internally the array
10934 is represented as a single modular type, of exactly the appropriate number
10935 of bits. If the length is greater than 63 bits, or is not known at compile
10936 time, then the packed array is represented as an array of bytes, and the
10937 length is always a multiple of 8 bits.
10939 Note that to represent a packed array as a modular type, the alignment must
10940 be suitable for the modular type involved. For example, on typical machines
10941 a 32-bit packed array will be represented by a 32-bit modular integer with
10942 an alignment of four bytes. If you explicitly override the default alignment
10943 with an alignment clause that is too small, the modular representation
10944 cannot be used. For example, consider the following set of declarations:
10946 @smallexample @c ada
10947 type R is range 1 .. 3;
10948 type S is array (1 .. 31) of R;
10949 for S'Component_Size use 2;
10951 for S'Alignment use 1;
10955 If the alignment clause were not present, then a 62-bit modular
10956 representation would be chosen (typically with an alignment of 4 or 8
10957 bytes depending on the target). But the default alignment is overridden
10958 with the explicit alignment clause. This means that the modular
10959 representation cannot be used, and instead the array of bytes
10960 representation must be used, meaning that the length must be a multiple
10961 of 8. Thus the above set of declarations will result in a diagnostic
10962 rejecting the size clause and noting that the minimum size allowed is 64.
10964 @cindex Pragma Pack (for type Natural)
10965 @cindex Pragma Pack warning
10967 One special case that is worth noting occurs when the base type of the
10968 component size is 8/16/32 and the subtype is one bit less. Notably this
10969 occurs with subtype @code{Natural}. Consider:
10971 @smallexample @c ada
10972 type Arr is array (1 .. 32) of Natural;
10977 In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
10978 since typically @code{Natural'Size} is 32 in Ada 83, and in any case most
10979 Ada 83 compilers did not attempt 31 bit packing.
10981 In Ada 95 and Ada 2005, @code{Natural'Size} is required to be 31. Furthermore,
10982 GNAT really does pack 31-bit subtype to 31 bits. This may result in a
10983 substantial unintended performance penalty when porting legacy Ada 83 code.
10984 To help prevent this, GNAT generates a warning in such cases. If you really
10985 want 31 bit packing in a case like this, you can set the component size
10988 @smallexample @c ada
10989 type Arr is array (1 .. 32) of Natural;
10990 for Arr'Component_Size use 31;
10994 Here 31-bit packing is achieved as required, and no warning is generated,
10995 since in this case the programmer intention is clear.
10997 @node Pragma Pack for Records
10998 @section Pragma Pack for Records
10999 @cindex Pragma Pack (for records)
11002 Pragma @code{Pack} applied to a record will pack the components to reduce
11003 wasted space from alignment gaps and by reducing the amount of space
11004 taken by components. We distinguish between @emph{packable} components and
11005 @emph{non-packable} components.
11006 Components of the following types are considered packable:
11009 All primitive types are packable.
11012 Small packed arrays, whose size does not exceed 64 bits, and where the
11013 size is statically known at compile time, are represented internally
11014 as modular integers, and so they are also packable.
11019 All packable components occupy the exact number of bits corresponding to
11020 their @code{Size} value, and are packed with no padding bits, i.e.@: they
11021 can start on an arbitrary bit boundary.
11023 All other types are non-packable, they occupy an integral number of
11025 are placed at a boundary corresponding to their alignment requirements.
11027 For example, consider the record
11029 @smallexample @c ada
11030 type Rb1 is array (1 .. 13) of Boolean;
11033 type Rb2 is array (1 .. 65) of Boolean;
11048 The representation for the record x2 is as follows:
11050 @smallexample @c ada
11051 for x2'Size use 224;
11053 l1 at 0 range 0 .. 0;
11054 l2 at 0 range 1 .. 64;
11055 l3 at 12 range 0 .. 31;
11056 l4 at 16 range 0 .. 0;
11057 l5 at 16 range 1 .. 13;
11058 l6 at 18 range 0 .. 71;
11063 Studying this example, we see that the packable fields @code{l1}
11065 of length equal to their sizes, and placed at specific bit boundaries (and
11066 not byte boundaries) to
11067 eliminate padding. But @code{l3} is of a non-packable float type, so
11068 it is on the next appropriate alignment boundary.
11070 The next two fields are fully packable, so @code{l4} and @code{l5} are
11071 minimally packed with no gaps. However, type @code{Rb2} is a packed
11072 array that is longer than 64 bits, so it is itself non-packable. Thus
11073 the @code{l6} field is aligned to the next byte boundary, and takes an
11074 integral number of bytes, i.e.@: 72 bits.
11076 @node Record Representation Clauses
11077 @section Record Representation Clauses
11078 @cindex Record Representation Clause
11081 Record representation clauses may be given for all record types, including
11082 types obtained by record extension. Component clauses are allowed for any
11083 static component. The restrictions on component clauses depend on the type
11086 @cindex Component Clause
11087 For all components of an elementary type, the only restriction on component
11088 clauses is that the size must be at least the 'Size value of the type
11089 (actually the Value_Size). There are no restrictions due to alignment,
11090 and such components may freely cross storage boundaries.
11092 Packed arrays with a size up to and including 64 bits are represented
11093 internally using a modular type with the appropriate number of bits, and
11094 thus the same lack of restriction applies. For example, if you declare:
11096 @smallexample @c ada
11097 type R is array (1 .. 49) of Boolean;
11103 then a component clause for a component of type R may start on any
11104 specified bit boundary, and may specify a value of 49 bits or greater.
11106 For packed bit arrays that are longer than 64 bits, there are two
11107 cases. If the component size is a power of 2 (1,2,4,8,16,32 bits),
11108 including the important case of single bits or boolean values, then
11109 there are no limitations on placement of such components, and they
11110 may start and end at arbitrary bit boundaries.
11112 If the component size is not a power of 2 (e.g.@: 3 or 5), then
11113 an array of this type longer than 64 bits must always be placed on
11114 on a storage unit (byte) boundary and occupy an integral number
11115 of storage units (bytes). Any component clause that does not
11116 meet this requirement will be rejected.
11118 Any aliased component, or component of an aliased type, must
11119 have its normal alignment and size. A component clause that
11120 does not meet this requirement will be rejected.
11122 The tag field of a tagged type always occupies an address sized field at
11123 the start of the record. No component clause may attempt to overlay this
11124 tag. When a tagged type appears as a component, the tag field must have
11127 In the case of a record extension T1, of a type T, no component clause applied
11128 to the type T1 can specify a storage location that would overlap the first
11129 T'Size bytes of the record.
11131 For all other component types, including non-bit-packed arrays,
11132 the component can be placed at an arbitrary bit boundary,
11133 so for example, the following is permitted:
11135 @smallexample @c ada
11136 type R is array (1 .. 10) of Boolean;
11145 G at 0 range 0 .. 0;
11146 H at 0 range 1 .. 1;
11147 L at 0 range 2 .. 81;
11148 R at 0 range 82 .. 161;
11153 Note: the above rules apply to recent releases of GNAT 5.
11154 In GNAT 3, there are more severe restrictions on larger components.
11155 For non-primitive types, including packed arrays with a size greater than
11156 64 bits, component clauses must respect the alignment requirement of the
11157 type, in particular, always starting on a byte boundary, and the length
11158 must be a multiple of the storage unit.
11160 @node Enumeration Clauses
11161 @section Enumeration Clauses
11163 The only restriction on enumeration clauses is that the range of values
11164 must be representable. For the signed case, if one or more of the
11165 representation values are negative, all values must be in the range:
11167 @smallexample @c ada
11168 System.Min_Int .. System.Max_Int
11172 For the unsigned case, where all values are nonnegative, the values must
11175 @smallexample @c ada
11176 0 .. System.Max_Binary_Modulus;
11180 A @emph{confirming} representation clause is one in which the values range
11181 from 0 in sequence, i.e.@: a clause that confirms the default representation
11182 for an enumeration type.
11183 Such a confirming representation
11184 is permitted by these rules, and is specially recognized by the compiler so
11185 that no extra overhead results from the use of such a clause.
11187 If an array has an index type which is an enumeration type to which an
11188 enumeration clause has been applied, then the array is stored in a compact
11189 manner. Consider the declarations:
11191 @smallexample @c ada
11192 type r is (A, B, C);
11193 for r use (A => 1, B => 5, C => 10);
11194 type t is array (r) of Character;
11198 The array type t corresponds to a vector with exactly three elements and
11199 has a default size equal to @code{3*Character'Size}. This ensures efficient
11200 use of space, but means that accesses to elements of the array will incur
11201 the overhead of converting representation values to the corresponding
11202 positional values, (i.e.@: the value delivered by the @code{Pos} attribute).
11204 @node Address Clauses
11205 @section Address Clauses
11206 @cindex Address Clause
11208 The reference manual allows a general restriction on representation clauses,
11209 as found in RM 13.1(22):
11212 An implementation need not support representation
11213 items containing nonstatic expressions, except that
11214 an implementation should support a representation item
11215 for a given entity if each nonstatic expression in the
11216 representation item is a name that statically denotes
11217 a constant declared before the entity.
11221 In practice this is applicable only to address clauses, since this is the
11222 only case in which a non-static expression is permitted by the syntax. As
11223 the AARM notes in sections 13.1 (22.a-22.h):
11226 22.a Reason: This is to avoid the following sort of thing:
11228 22.b X : Integer := F(@dots{});
11229 Y : Address := G(@dots{});
11230 for X'Address use Y;
11232 22.c In the above, we have to evaluate the
11233 initialization expression for X before we
11234 know where to put the result. This seems
11235 like an unreasonable implementation burden.
11237 22.d The above code should instead be written
11240 22.e Y : constant Address := G(@dots{});
11241 X : Integer := F(@dots{});
11242 for X'Address use Y;
11244 22.f This allows the expression ``Y'' to be safely
11245 evaluated before X is created.
11247 22.g The constant could be a formal parameter of mode in.
11249 22.h An implementation can support other nonstatic
11250 expressions if it wants to. Expressions of type
11251 Address are hardly ever static, but their value
11252 might be known at compile time anyway in many
11257 GNAT does indeed permit many additional cases of non-static expressions. In
11258 particular, if the type involved is elementary there are no restrictions
11259 (since in this case, holding a temporary copy of the initialization value,
11260 if one is present, is inexpensive). In addition, if there is no implicit or
11261 explicit initialization, then there are no restrictions. GNAT will reject
11262 only the case where all three of these conditions hold:
11267 The type of the item is non-elementary (e.g.@: a record or array).
11270 There is explicit or implicit initialization required for the object.
11271 Note that access values are always implicitly initialized, and also
11272 in GNAT, certain bit-packed arrays (those having a dynamic length or
11273 a length greater than 64) will also be implicitly initialized to zero.
11276 The address value is non-static. Here GNAT is more permissive than the
11277 RM, and allows the address value to be the address of a previously declared
11278 stand-alone variable, as long as it does not itself have an address clause.
11280 @smallexample @c ada
11281 Anchor : Some_Initialized_Type;
11282 Overlay : Some_Initialized_Type;
11283 for Overlay'Address use Anchor'Address;
11287 However, the prefix of the address clause cannot be an array component, or
11288 a component of a discriminated record.
11293 As noted above in section 22.h, address values are typically non-static. In
11294 particular the To_Address function, even if applied to a literal value, is
11295 a non-static function call. To avoid this minor annoyance, GNAT provides
11296 the implementation defined attribute 'To_Address. The following two
11297 expressions have identical values:
11301 @smallexample @c ada
11302 To_Address (16#1234_0000#)
11303 System'To_Address (16#1234_0000#);
11307 except that the second form is considered to be a static expression, and
11308 thus when used as an address clause value is always permitted.
11311 Additionally, GNAT treats as static an address clause that is an
11312 unchecked_conversion of a static integer value. This simplifies the porting
11313 of legacy code, and provides a portable equivalent to the GNAT attribute
11316 Another issue with address clauses is the interaction with alignment
11317 requirements. When an address clause is given for an object, the address
11318 value must be consistent with the alignment of the object (which is usually
11319 the same as the alignment of the type of the object). If an address clause
11320 is given that specifies an inappropriately aligned address value, then the
11321 program execution is erroneous.
11323 Since this source of erroneous behavior can have unfortunate effects, GNAT
11324 checks (at compile time if possible, generating a warning, or at execution
11325 time with a run-time check) that the alignment is appropriate. If the
11326 run-time check fails, then @code{Program_Error} is raised. This run-time
11327 check is suppressed if range checks are suppressed, or if the special GNAT
11328 check Alignment_Check is suppressed, or if
11329 @code{pragma Restrictions (No_Elaboration_Code)} is in effect.
11331 Finally, GNAT does not permit overlaying of objects of controlled types or
11332 composite types containing a controlled component. In most cases, the compiler
11333 can detect an attempt at such overlays and will generate a warning at compile
11334 time and a Program_Error exception at run time.
11337 An address clause cannot be given for an exported object. More
11338 understandably the real restriction is that objects with an address
11339 clause cannot be exported. This is because such variables are not
11340 defined by the Ada program, so there is no external object to export.
11343 It is permissible to give an address clause and a pragma Import for the
11344 same object. In this case, the variable is not really defined by the
11345 Ada program, so there is no external symbol to be linked. The link name
11346 and the external name are ignored in this case. The reason that we allow this
11347 combination is that it provides a useful idiom to avoid unwanted
11348 initializations on objects with address clauses.
11350 When an address clause is given for an object that has implicit or
11351 explicit initialization, then by default initialization takes place. This
11352 means that the effect of the object declaration is to overwrite the
11353 memory at the specified address. This is almost always not what the
11354 programmer wants, so GNAT will output a warning:
11364 for Ext'Address use System'To_Address (16#1234_1234#);
11366 >>> warning: implicit initialization of "Ext" may
11367 modify overlaid storage
11368 >>> warning: use pragma Import for "Ext" to suppress
11369 initialization (RM B(24))
11375 As indicated by the warning message, the solution is to use a (dummy) pragma
11376 Import to suppress this initialization. The pragma tell the compiler that the
11377 object is declared and initialized elsewhere. The following package compiles
11378 without warnings (and the initialization is suppressed):
11380 @smallexample @c ada
11388 for Ext'Address use System'To_Address (16#1234_1234#);
11389 pragma Import (Ada, Ext);
11394 A final issue with address clauses involves their use for overlaying
11395 variables, as in the following example:
11396 @cindex Overlaying of objects
11398 @smallexample @c ada
11401 for B'Address use A'Address;
11405 or alternatively, using the form recommended by the RM:
11407 @smallexample @c ada
11409 Addr : constant Address := A'Address;
11411 for B'Address use Addr;
11415 In both of these cases, @code{A}
11416 and @code{B} become aliased to one another via the
11417 address clause. This use of address clauses to overlay
11418 variables, achieving an effect similar to unchecked
11419 conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005
11420 the effect is implementation defined. Furthermore, the
11421 Ada RM specifically recommends that in a situation
11422 like this, @code{B} should be subject to the following
11423 implementation advice (RM 13.3(19)):
11426 19 If the Address of an object is specified, or it is imported
11427 or exported, then the implementation should not perform
11428 optimizations based on assumptions of no aliases.
11432 GNAT follows this recommendation, and goes further by also applying
11433 this recommendation to the overlaid variable (@code{A}
11434 in the above example) in this case. This means that the overlay
11435 works "as expected", in that a modification to one of the variables
11436 will affect the value of the other.
11438 @node Effect of Convention on Representation
11439 @section Effect of Convention on Representation
11440 @cindex Convention, effect on representation
11443 Normally the specification of a foreign language convention for a type or
11444 an object has no effect on the chosen representation. In particular, the
11445 representation chosen for data in GNAT generally meets the standard system
11446 conventions, and for example records are laid out in a manner that is
11447 consistent with C@. This means that specifying convention C (for example)
11450 There are four exceptions to this general rule:
11454 @item Convention Fortran and array subtypes
11455 If pragma Convention Fortran is specified for an array subtype, then in
11456 accordance with the implementation advice in section 3.6.2(11) of the
11457 Ada Reference Manual, the array will be stored in a Fortran-compatible
11458 column-major manner, instead of the normal default row-major order.
11460 @item Convention C and enumeration types
11461 GNAT normally stores enumeration types in 8, 16, or 32 bits as required
11462 to accommodate all values of the type. For example, for the enumeration
11465 @smallexample @c ada
11466 type Color is (Red, Green, Blue);
11470 8 bits is sufficient to store all values of the type, so by default, objects
11471 of type @code{Color} will be represented using 8 bits. However, normal C
11472 convention is to use 32 bits for all enum values in C, since enum values
11473 are essentially of type int. If pragma @code{Convention C} is specified for an
11474 Ada enumeration type, then the size is modified as necessary (usually to
11475 32 bits) to be consistent with the C convention for enum values.
11477 Note that this treatment applies only to types. If Convention C is given for
11478 an enumeration object, where the enumeration type is not Convention C, then
11479 Object_Size bits are allocated. For example, for a normal enumeration type,
11480 with less than 256 elements, only 8 bits will be allocated for the object.
11481 Since this may be a surprise in terms of what C expects, GNAT will issue a
11482 warning in this situation. The warning can be suppressed by giving an explicit
11483 size clause specifying the desired size.
11485 @item Convention C/Fortran and Boolean types
11486 In C, the usual convention for boolean values, that is values used for
11487 conditions, is that zero represents false, and nonzero values represent
11488 true. In Ada, the normal convention is that two specific values, typically
11489 0/1, are used to represent false/true respectively.
11491 Fortran has a similar convention for @code{LOGICAL} values (any nonzero
11492 value represents true).
11494 To accommodate the Fortran and C conventions, if a pragma Convention specifies
11495 C or Fortran convention for a derived Boolean, as in the following example:
11497 @smallexample @c ada
11498 type C_Switch is new Boolean;
11499 pragma Convention (C, C_Switch);
11503 then the GNAT generated code will treat any nonzero value as true. For truth
11504 values generated by GNAT, the conventional value 1 will be used for True, but
11505 when one of these values is read, any nonzero value is treated as True.
11507 @item Access types on OpenVMS
11508 For 64-bit OpenVMS systems, access types (other than those for unconstrained
11509 arrays) are 64-bits long. An exception to this rule is for the case of
11510 C-convention access types where there is no explicit size clause present (or
11511 inherited for derived types). In this case, GNAT chooses to make these
11512 pointers 32-bits, which provides an easier path for migration of 32-bit legacy
11513 code. size clause specifying 64-bits must be used to obtain a 64-bit pointer.
11517 @node Determining the Representations chosen by GNAT
11518 @section Determining the Representations chosen by GNAT
11519 @cindex Representation, determination of
11520 @cindex @option{-gnatR} switch
11523 Although the descriptions in this section are intended to be complete, it is
11524 often easier to simply experiment to see what GNAT accepts and what the
11525 effect is on the layout of types and objects.
11527 As required by the Ada RM, if a representation clause is not accepted, then
11528 it must be rejected as illegal by the compiler. However, when a
11529 representation clause or pragma is accepted, there can still be questions
11530 of what the compiler actually does. For example, if a partial record
11531 representation clause specifies the location of some components and not
11532 others, then where are the non-specified components placed? Or if pragma
11533 @code{Pack} is used on a record, then exactly where are the resulting
11534 fields placed? The section on pragma @code{Pack} in this chapter can be
11535 used to answer the second question, but it is often easier to just see
11536 what the compiler does.
11538 For this purpose, GNAT provides the option @option{-gnatR}. If you compile
11539 with this option, then the compiler will output information on the actual
11540 representations chosen, in a format similar to source representation
11541 clauses. For example, if we compile the package:
11543 @smallexample @c ada
11545 type r (x : boolean) is tagged record
11547 when True => S : String (1 .. 100);
11548 when False => null;
11552 type r2 is new r (false) with record
11557 y2 at 16 range 0 .. 31;
11564 type x1 is array (1 .. 10) of x;
11565 for x1'component_size use 11;
11567 type ia is access integer;
11569 type Rb1 is array (1 .. 13) of Boolean;
11572 type Rb2 is array (1 .. 65) of Boolean;
11588 using the switch @option{-gnatR} we obtain the following output:
11591 Representation information for unit q
11592 -------------------------------------
11595 for r'Alignment use 4;
11597 x at 4 range 0 .. 7;
11598 _tag at 0 range 0 .. 31;
11599 s at 5 range 0 .. 799;
11602 for r2'Size use 160;
11603 for r2'Alignment use 4;
11605 x at 4 range 0 .. 7;
11606 _tag at 0 range 0 .. 31;
11607 _parent at 0 range 0 .. 63;
11608 y2 at 16 range 0 .. 31;
11612 for x'Alignment use 1;
11614 y at 0 range 0 .. 7;
11617 for x1'Size use 112;
11618 for x1'Alignment use 1;
11619 for x1'Component_Size use 11;
11621 for rb1'Size use 13;
11622 for rb1'Alignment use 2;
11623 for rb1'Component_Size use 1;
11625 for rb2'Size use 72;
11626 for rb2'Alignment use 1;
11627 for rb2'Component_Size use 1;
11629 for x2'Size use 224;
11630 for x2'Alignment use 4;
11632 l1 at 0 range 0 .. 0;
11633 l2 at 0 range 1 .. 64;
11634 l3 at 12 range 0 .. 31;
11635 l4 at 16 range 0 .. 0;
11636 l5 at 16 range 1 .. 13;
11637 l6 at 18 range 0 .. 71;
11642 The Size values are actually the Object_Size, i.e.@: the default size that
11643 will be allocated for objects of the type.
11644 The ?? size for type r indicates that we have a variant record, and the
11645 actual size of objects will depend on the discriminant value.
11647 The Alignment values show the actual alignment chosen by the compiler
11648 for each record or array type.
11650 The record representation clause for type r shows where all fields
11651 are placed, including the compiler generated tag field (whose location
11652 cannot be controlled by the programmer).
11654 The record representation clause for the type extension r2 shows all the
11655 fields present, including the parent field, which is a copy of the fields
11656 of the parent type of r2, i.e.@: r1.
11658 The component size and size clauses for types rb1 and rb2 show
11659 the exact effect of pragma @code{Pack} on these arrays, and the record
11660 representation clause for type x2 shows how pragma @code{Pack} affects
11663 In some cases, it may be useful to cut and paste the representation clauses
11664 generated by the compiler into the original source to fix and guarantee
11665 the actual representation to be used.
11667 @node Standard Library Routines
11668 @chapter Standard Library Routines
11671 The Ada Reference Manual contains in Annex A a full description of an
11672 extensive set of standard library routines that can be used in any Ada
11673 program, and which must be provided by all Ada compilers. They are
11674 analogous to the standard C library used by C programs.
11676 GNAT implements all of the facilities described in annex A, and for most
11677 purposes the description in the Ada Reference Manual, or appropriate Ada
11678 text book, will be sufficient for making use of these facilities.
11680 In the case of the input-output facilities,
11681 @xref{The Implementation of Standard I/O},
11682 gives details on exactly how GNAT interfaces to the
11683 file system. For the remaining packages, the Ada Reference Manual
11684 should be sufficient. The following is a list of the packages included,
11685 together with a brief description of the functionality that is provided.
11687 For completeness, references are included to other predefined library
11688 routines defined in other sections of the Ada Reference Manual (these are
11689 cross-indexed from Annex A).
11693 This is a parent package for all the standard library packages. It is
11694 usually included implicitly in your program, and itself contains no
11695 useful data or routines.
11697 @item Ada.Calendar (9.6)
11698 @code{Calendar} provides time of day access, and routines for
11699 manipulating times and durations.
11701 @item Ada.Characters (A.3.1)
11702 This is a dummy parent package that contains no useful entities
11704 @item Ada.Characters.Handling (A.3.2)
11705 This package provides some basic character handling capabilities,
11706 including classification functions for classes of characters (e.g.@: test
11707 for letters, or digits).
11709 @item Ada.Characters.Latin_1 (A.3.3)
11710 This package includes a complete set of definitions of the characters
11711 that appear in type CHARACTER@. It is useful for writing programs that
11712 will run in international environments. For example, if you want an
11713 upper case E with an acute accent in a string, it is often better to use
11714 the definition of @code{UC_E_Acute} in this package. Then your program
11715 will print in an understandable manner even if your environment does not
11716 support these extended characters.
11718 @item Ada.Command_Line (A.15)
11719 This package provides access to the command line parameters and the name
11720 of the current program (analogous to the use of @code{argc} and @code{argv}
11721 in C), and also allows the exit status for the program to be set in a
11722 system-independent manner.
11724 @item Ada.Decimal (F.2)
11725 This package provides constants describing the range of decimal numbers
11726 implemented, and also a decimal divide routine (analogous to the COBOL
11727 verb DIVIDE @dots{} GIVING @dots{} REMAINDER @dots{})
11729 @item Ada.Direct_IO (A.8.4)
11730 This package provides input-output using a model of a set of records of
11731 fixed-length, containing an arbitrary definite Ada type, indexed by an
11732 integer record number.
11734 @item Ada.Dynamic_Priorities (D.5)
11735 This package allows the priorities of a task to be adjusted dynamically
11736 as the task is running.
11738 @item Ada.Exceptions (11.4.1)
11739 This package provides additional information on exceptions, and also
11740 contains facilities for treating exceptions as data objects, and raising
11741 exceptions with associated messages.
11743 @item Ada.Finalization (7.6)
11744 This package contains the declarations and subprograms to support the
11745 use of controlled types, providing for automatic initialization and
11746 finalization (analogous to the constructors and destructors of C++)
11748 @item Ada.Interrupts (C.3.2)
11749 This package provides facilities for interfacing to interrupts, which
11750 includes the set of signals or conditions that can be raised and
11751 recognized as interrupts.
11753 @item Ada.Interrupts.Names (C.3.2)
11754 This package provides the set of interrupt names (actually signal
11755 or condition names) that can be handled by GNAT@.
11757 @item Ada.IO_Exceptions (A.13)
11758 This package defines the set of exceptions that can be raised by use of
11759 the standard IO packages.
11762 This package contains some standard constants and exceptions used
11763 throughout the numerics packages. Note that the constants pi and e are
11764 defined here, and it is better to use these definitions than rolling
11767 @item Ada.Numerics.Complex_Elementary_Functions
11768 Provides the implementation of standard elementary functions (such as
11769 log and trigonometric functions) operating on complex numbers using the
11770 standard @code{Float} and the @code{Complex} and @code{Imaginary} types
11771 created by the package @code{Numerics.Complex_Types}.
11773 @item Ada.Numerics.Complex_Types
11774 This is a predefined instantiation of
11775 @code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
11776 build the type @code{Complex} and @code{Imaginary}.
11778 @item Ada.Numerics.Discrete_Random
11779 This package provides a random number generator suitable for generating
11780 random integer values from a specified range.
11782 @item Ada.Numerics.Float_Random
11783 This package provides a random number generator suitable for generating
11784 uniformly distributed floating point values.
11786 @item Ada.Numerics.Generic_Complex_Elementary_Functions
11787 This is a generic version of the package that provides the
11788 implementation of standard elementary functions (such as log and
11789 trigonometric functions) for an arbitrary complex type.
11791 The following predefined instantiations of this package are provided:
11795 @code{Ada.Numerics.Short_Complex_Elementary_Functions}
11797 @code{Ada.Numerics.Complex_Elementary_Functions}
11799 @code{Ada.Numerics.Long_Complex_Elementary_Functions}
11802 @item Ada.Numerics.Generic_Complex_Types
11803 This is a generic package that allows the creation of complex types,
11804 with associated complex arithmetic operations.
11806 The following predefined instantiations of this package exist
11809 @code{Ada.Numerics.Short_Complex_Complex_Types}
11811 @code{Ada.Numerics.Complex_Complex_Types}
11813 @code{Ada.Numerics.Long_Complex_Complex_Types}
11816 @item Ada.Numerics.Generic_Elementary_Functions
11817 This is a generic package that provides the implementation of standard
11818 elementary functions (such as log an trigonometric functions) for an
11819 arbitrary float type.
11821 The following predefined instantiations of this package exist
11825 @code{Ada.Numerics.Short_Elementary_Functions}
11827 @code{Ada.Numerics.Elementary_Functions}
11829 @code{Ada.Numerics.Long_Elementary_Functions}
11832 @item Ada.Real_Time (D.8)
11833 This package provides facilities similar to those of @code{Calendar}, but
11834 operating with a finer clock suitable for real time control. Note that
11835 annex D requires that there be no backward clock jumps, and GNAT generally
11836 guarantees this behavior, but of course if the external clock on which
11837 the GNAT runtime depends is deliberately reset by some external event,
11838 then such a backward jump may occur.
11840 @item Ada.Sequential_IO (A.8.1)
11841 This package provides input-output facilities for sequential files,
11842 which can contain a sequence of values of a single type, which can be
11843 any Ada type, including indefinite (unconstrained) types.
11845 @item Ada.Storage_IO (A.9)
11846 This package provides a facility for mapping arbitrary Ada types to and
11847 from a storage buffer. It is primarily intended for the creation of new
11850 @item Ada.Streams (13.13.1)
11851 This is a generic package that provides the basic support for the
11852 concept of streams as used by the stream attributes (@code{Input},
11853 @code{Output}, @code{Read} and @code{Write}).
11855 @item Ada.Streams.Stream_IO (A.12.1)
11856 This package is a specialization of the type @code{Streams} defined in
11857 package @code{Streams} together with a set of operations providing
11858 Stream_IO capability. The Stream_IO model permits both random and
11859 sequential access to a file which can contain an arbitrary set of values
11860 of one or more Ada types.
11862 @item Ada.Strings (A.4.1)
11863 This package provides some basic constants used by the string handling
11866 @item Ada.Strings.Bounded (A.4.4)
11867 This package provides facilities for handling variable length
11868 strings. The bounded model requires a maximum length. It is thus
11869 somewhat more limited than the unbounded model, but avoids the use of
11870 dynamic allocation or finalization.
11872 @item Ada.Strings.Fixed (A.4.3)
11873 This package provides facilities for handling fixed length strings.
11875 @item Ada.Strings.Maps (A.4.2)
11876 This package provides facilities for handling character mappings and
11877 arbitrarily defined subsets of characters. For instance it is useful in
11878 defining specialized translation tables.
11880 @item Ada.Strings.Maps.Constants (A.4.6)
11881 This package provides a standard set of predefined mappings and
11882 predefined character sets. For example, the standard upper to lower case
11883 conversion table is found in this package. Note that upper to lower case
11884 conversion is non-trivial if you want to take the entire set of
11885 characters, including extended characters like E with an acute accent,
11886 into account. You should use the mappings in this package (rather than
11887 adding 32 yourself) to do case mappings.
11889 @item Ada.Strings.Unbounded (A.4.5)
11890 This package provides facilities for handling variable length
11891 strings. The unbounded model allows arbitrary length strings, but
11892 requires the use of dynamic allocation and finalization.
11894 @item Ada.Strings.Wide_Bounded (A.4.7)
11895 @itemx Ada.Strings.Wide_Fixed (A.4.7)
11896 @itemx Ada.Strings.Wide_Maps (A.4.7)
11897 @itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
11898 @itemx Ada.Strings.Wide_Unbounded (A.4.7)
11899 These packages provide analogous capabilities to the corresponding
11900 packages without @samp{Wide_} in the name, but operate with the types
11901 @code{Wide_String} and @code{Wide_Character} instead of @code{String}
11902 and @code{Character}.
11904 @item Ada.Strings.Wide_Wide_Bounded (A.4.7)
11905 @itemx Ada.Strings.Wide_Wide_Fixed (A.4.7)
11906 @itemx Ada.Strings.Wide_Wide_Maps (A.4.7)
11907 @itemx Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
11908 @itemx Ada.Strings.Wide_Wide_Unbounded (A.4.7)
11909 These packages provide analogous capabilities to the corresponding
11910 packages without @samp{Wide_} in the name, but operate with the types
11911 @code{Wide_Wide_String} and @code{Wide_Wide_Character} instead
11912 of @code{String} and @code{Character}.
11914 @item Ada.Synchronous_Task_Control (D.10)
11915 This package provides some standard facilities for controlling task
11916 communication in a synchronous manner.
11919 This package contains definitions for manipulation of the tags of tagged
11922 @item Ada.Task_Attributes
11923 This package provides the capability of associating arbitrary
11924 task-specific data with separate tasks.
11927 This package provides basic text input-output capabilities for
11928 character, string and numeric data. The subpackages of this
11929 package are listed next.
11931 @item Ada.Text_IO.Decimal_IO
11932 Provides input-output facilities for decimal fixed-point types
11934 @item Ada.Text_IO.Enumeration_IO
11935 Provides input-output facilities for enumeration types.
11937 @item Ada.Text_IO.Fixed_IO
11938 Provides input-output facilities for ordinary fixed-point types.
11940 @item Ada.Text_IO.Float_IO
11941 Provides input-output facilities for float types. The following
11942 predefined instantiations of this generic package are available:
11946 @code{Short_Float_Text_IO}
11948 @code{Float_Text_IO}
11950 @code{Long_Float_Text_IO}
11953 @item Ada.Text_IO.Integer_IO
11954 Provides input-output facilities for integer types. The following
11955 predefined instantiations of this generic package are available:
11958 @item Short_Short_Integer
11959 @code{Ada.Short_Short_Integer_Text_IO}
11960 @item Short_Integer
11961 @code{Ada.Short_Integer_Text_IO}
11963 @code{Ada.Integer_Text_IO}
11965 @code{Ada.Long_Integer_Text_IO}
11966 @item Long_Long_Integer
11967 @code{Ada.Long_Long_Integer_Text_IO}
11970 @item Ada.Text_IO.Modular_IO
11971 Provides input-output facilities for modular (unsigned) types
11973 @item Ada.Text_IO.Complex_IO (G.1.3)
11974 This package provides basic text input-output capabilities for complex
11977 @item Ada.Text_IO.Editing (F.3.3)
11978 This package contains routines for edited output, analogous to the use
11979 of pictures in COBOL@. The picture formats used by this package are a
11980 close copy of the facility in COBOL@.
11982 @item Ada.Text_IO.Text_Streams (A.12.2)
11983 This package provides a facility that allows Text_IO files to be treated
11984 as streams, so that the stream attributes can be used for writing
11985 arbitrary data, including binary data, to Text_IO files.
11987 @item Ada.Unchecked_Conversion (13.9)
11988 This generic package allows arbitrary conversion from one type to
11989 another of the same size, providing for breaking the type safety in
11990 special circumstances.
11992 If the types have the same Size (more accurately the same Value_Size),
11993 then the effect is simply to transfer the bits from the source to the
11994 target type without any modification. This usage is well defined, and
11995 for simple types whose representation is typically the same across
11996 all implementations, gives a portable method of performing such
11999 If the types do not have the same size, then the result is implementation
12000 defined, and thus may be non-portable. The following describes how GNAT
12001 handles such unchecked conversion cases.
12003 If the types are of different sizes, and are both discrete types, then
12004 the effect is of a normal type conversion without any constraint checking.
12005 In particular if the result type has a larger size, the result will be
12006 zero or sign extended. If the result type has a smaller size, the result
12007 will be truncated by ignoring high order bits.
12009 If the types are of different sizes, and are not both discrete types,
12010 then the conversion works as though pointers were created to the source
12011 and target, and the pointer value is converted. The effect is that bits
12012 are copied from successive low order storage units and bits of the source
12013 up to the length of the target type.
12015 A warning is issued if the lengths differ, since the effect in this
12016 case is implementation dependent, and the above behavior may not match
12017 that of some other compiler.
12019 A pointer to one type may be converted to a pointer to another type using
12020 unchecked conversion. The only case in which the effect is undefined is
12021 when one or both pointers are pointers to unconstrained array types. In
12022 this case, the bounds information may get incorrectly transferred, and in
12023 particular, GNAT uses double size pointers for such types, and it is
12024 meaningless to convert between such pointer types. GNAT will issue a
12025 warning if the alignment of the target designated type is more strict
12026 than the alignment of the source designated type (since the result may
12027 be unaligned in this case).
12029 A pointer other than a pointer to an unconstrained array type may be
12030 converted to and from System.Address. Such usage is common in Ada 83
12031 programs, but note that Ada.Address_To_Access_Conversions is the
12032 preferred method of performing such conversions in Ada 95 and Ada 2005.
12034 unchecked conversion nor Ada.Address_To_Access_Conversions should be
12035 used in conjunction with pointers to unconstrained objects, since
12036 the bounds information cannot be handled correctly in this case.
12038 @item Ada.Unchecked_Deallocation (13.11.2)
12039 This generic package allows explicit freeing of storage previously
12040 allocated by use of an allocator.
12042 @item Ada.Wide_Text_IO (A.11)
12043 This package is similar to @code{Ada.Text_IO}, except that the external
12044 file supports wide character representations, and the internal types are
12045 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12046 and @code{String}. It contains generic subpackages listed next.
12048 @item Ada.Wide_Text_IO.Decimal_IO
12049 Provides input-output facilities for decimal fixed-point types
12051 @item Ada.Wide_Text_IO.Enumeration_IO
12052 Provides input-output facilities for enumeration types.
12054 @item Ada.Wide_Text_IO.Fixed_IO
12055 Provides input-output facilities for ordinary fixed-point types.
12057 @item Ada.Wide_Text_IO.Float_IO
12058 Provides input-output facilities for float types. The following
12059 predefined instantiations of this generic package are available:
12063 @code{Short_Float_Wide_Text_IO}
12065 @code{Float_Wide_Text_IO}
12067 @code{Long_Float_Wide_Text_IO}
12070 @item Ada.Wide_Text_IO.Integer_IO
12071 Provides input-output facilities for integer types. The following
12072 predefined instantiations of this generic package are available:
12075 @item Short_Short_Integer
12076 @code{Ada.Short_Short_Integer_Wide_Text_IO}
12077 @item Short_Integer
12078 @code{Ada.Short_Integer_Wide_Text_IO}
12080 @code{Ada.Integer_Wide_Text_IO}
12082 @code{Ada.Long_Integer_Wide_Text_IO}
12083 @item Long_Long_Integer
12084 @code{Ada.Long_Long_Integer_Wide_Text_IO}
12087 @item Ada.Wide_Text_IO.Modular_IO
12088 Provides input-output facilities for modular (unsigned) types
12090 @item Ada.Wide_Text_IO.Complex_IO (G.1.3)
12091 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12092 external file supports wide character representations.
12094 @item Ada.Wide_Text_IO.Editing (F.3.4)
12095 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12096 types are @code{Wide_Character} and @code{Wide_String} instead of
12097 @code{Character} and @code{String}.
12099 @item Ada.Wide_Text_IO.Streams (A.12.3)
12100 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12101 types are @code{Wide_Character} and @code{Wide_String} instead of
12102 @code{Character} and @code{String}.
12104 @item Ada.Wide_Wide_Text_IO (A.11)
12105 This package is similar to @code{Ada.Text_IO}, except that the external
12106 file supports wide character representations, and the internal types are
12107 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
12108 and @code{String}. It contains generic subpackages listed next.
12110 @item Ada.Wide_Wide_Text_IO.Decimal_IO
12111 Provides input-output facilities for decimal fixed-point types
12113 @item Ada.Wide_Wide_Text_IO.Enumeration_IO
12114 Provides input-output facilities for enumeration types.
12116 @item Ada.Wide_Wide_Text_IO.Fixed_IO
12117 Provides input-output facilities for ordinary fixed-point types.
12119 @item Ada.Wide_Wide_Text_IO.Float_IO
12120 Provides input-output facilities for float types. The following
12121 predefined instantiations of this generic package are available:
12125 @code{Short_Float_Wide_Wide_Text_IO}
12127 @code{Float_Wide_Wide_Text_IO}
12129 @code{Long_Float_Wide_Wide_Text_IO}
12132 @item Ada.Wide_Wide_Text_IO.Integer_IO
12133 Provides input-output facilities for integer types. The following
12134 predefined instantiations of this generic package are available:
12137 @item Short_Short_Integer
12138 @code{Ada.Short_Short_Integer_Wide_Wide_Text_IO}
12139 @item Short_Integer
12140 @code{Ada.Short_Integer_Wide_Wide_Text_IO}
12142 @code{Ada.Integer_Wide_Wide_Text_IO}
12144 @code{Ada.Long_Integer_Wide_Wide_Text_IO}
12145 @item Long_Long_Integer
12146 @code{Ada.Long_Long_Integer_Wide_Wide_Text_IO}
12149 @item Ada.Wide_Wide_Text_IO.Modular_IO
12150 Provides input-output facilities for modular (unsigned) types
12152 @item Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
12153 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12154 external file supports wide character representations.
12156 @item Ada.Wide_Wide_Text_IO.Editing (F.3.4)
12157 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12158 types are @code{Wide_Character} and @code{Wide_String} instead of
12159 @code{Character} and @code{String}.
12161 @item Ada.Wide_Wide_Text_IO.Streams (A.12.3)
12162 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12163 types are @code{Wide_Character} and @code{Wide_String} instead of
12164 @code{Character} and @code{String}.
12169 @node The Implementation of Standard I/O
12170 @chapter The Implementation of Standard I/O
12173 GNAT implements all the required input-output facilities described in
12174 A.6 through A.14. These sections of the Ada Reference Manual describe the
12175 required behavior of these packages from the Ada point of view, and if
12176 you are writing a portable Ada program that does not need to know the
12177 exact manner in which Ada maps to the outside world when it comes to
12178 reading or writing external files, then you do not need to read this
12179 chapter. As long as your files are all regular files (not pipes or
12180 devices), and as long as you write and read the files only from Ada, the
12181 description in the Ada Reference Manual is sufficient.
12183 However, if you want to do input-output to pipes or other devices, such
12184 as the keyboard or screen, or if the files you are dealing with are
12185 either generated by some other language, or to be read by some other
12186 language, then you need to know more about the details of how the GNAT
12187 implementation of these input-output facilities behaves.
12189 In this chapter we give a detailed description of exactly how GNAT
12190 interfaces to the file system. As always, the sources of the system are
12191 available to you for answering questions at an even more detailed level,
12192 but for most purposes the information in this chapter will suffice.
12194 Another reason that you may need to know more about how input-output is
12195 implemented arises when you have a program written in mixed languages
12196 where, for example, files are shared between the C and Ada sections of
12197 the same program. GNAT provides some additional facilities, in the form
12198 of additional child library packages, that facilitate this sharing, and
12199 these additional facilities are also described in this chapter.
12202 * Standard I/O Packages::
12208 * Wide_Wide_Text_IO::
12210 * Text Translation::
12212 * Filenames encoding::
12214 * Operations on C Streams::
12215 * Interfacing to C Streams::
12218 @node Standard I/O Packages
12219 @section Standard I/O Packages
12222 The Standard I/O packages described in Annex A for
12228 Ada.Text_IO.Complex_IO
12230 Ada.Text_IO.Text_Streams
12234 Ada.Wide_Text_IO.Complex_IO
12236 Ada.Wide_Text_IO.Text_Streams
12238 Ada.Wide_Wide_Text_IO
12240 Ada.Wide_Wide_Text_IO.Complex_IO
12242 Ada.Wide_Wide_Text_IO.Text_Streams
12252 are implemented using the C
12253 library streams facility; where
12257 All files are opened using @code{fopen}.
12259 All input/output operations use @code{fread}/@code{fwrite}.
12263 There is no internal buffering of any kind at the Ada library level. The only
12264 buffering is that provided at the system level in the implementation of the
12265 library routines that support streams. This facilitates shared use of these
12266 streams by mixed language programs. Note though that system level buffering is
12267 explicitly enabled at elaboration of the standard I/O packages and that can
12268 have an impact on mixed language programs, in particular those using I/O before
12269 calling the Ada elaboration routine (e.g.@: adainit). It is recommended to call
12270 the Ada elaboration routine before performing any I/O or when impractical,
12271 flush the common I/O streams and in particular Standard_Output before
12272 elaborating the Ada code.
12275 @section FORM Strings
12278 The format of a FORM string in GNAT is:
12281 "keyword=value,keyword=value,@dots{},keyword=value"
12285 where letters may be in upper or lower case, and there are no spaces
12286 between values. The order of the entries is not important. Currently
12287 the following keywords defined.
12290 TEXT_TRANSLATION=[YES|NO]
12292 WCEM=[n|h|u|s|e|8|b]
12293 ENCODING=[UTF8|8BITS]
12297 The use of these parameters is described later in this section.
12303 Direct_IO can only be instantiated for definite types. This is a
12304 restriction of the Ada language, which means that the records are fixed
12305 length (the length being determined by @code{@var{type}'Size}, rounded
12306 up to the next storage unit boundary if necessary).
12308 The records of a Direct_IO file are simply written to the file in index
12309 sequence, with the first record starting at offset zero, and subsequent
12310 records following. There is no control information of any kind. For
12311 example, if 32-bit integers are being written, each record takes
12312 4-bytes, so the record at index @var{K} starts at offset
12313 (@var{K}@minus{}1)*4.
12315 There is no limit on the size of Direct_IO files, they are expanded as
12316 necessary to accommodate whatever records are written to the file.
12318 @node Sequential_IO
12319 @section Sequential_IO
12322 Sequential_IO may be instantiated with either a definite (constrained)
12323 or indefinite (unconstrained) type.
12325 For the definite type case, the elements written to the file are simply
12326 the memory images of the data values with no control information of any
12327 kind. The resulting file should be read using the same type, no validity
12328 checking is performed on input.
12330 For the indefinite type case, the elements written consist of two
12331 parts. First is the size of the data item, written as the memory image
12332 of a @code{Interfaces.C.size_t} value, followed by the memory image of
12333 the data value. The resulting file can only be read using the same
12334 (unconstrained) type. Normal assignment checks are performed on these
12335 read operations, and if these checks fail, @code{Data_Error} is
12336 raised. In particular, in the array case, the lengths must match, and in
12337 the variant record case, if the variable for a particular read operation
12338 is constrained, the discriminants must match.
12340 Note that it is not possible to use Sequential_IO to write variable
12341 length array items, and then read the data back into different length
12342 arrays. For example, the following will raise @code{Data_Error}:
12344 @smallexample @c ada
12345 package IO is new Sequential_IO (String);
12350 IO.Write (F, "hello!")
12351 IO.Reset (F, Mode=>In_File);
12358 On some Ada implementations, this will print @code{hell}, but the program is
12359 clearly incorrect, since there is only one element in the file, and that
12360 element is the string @code{hello!}.
12362 In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved
12363 using Stream_IO, and this is the preferred mechanism. In particular, the
12364 above program fragment rewritten to use Stream_IO will work correctly.
12370 Text_IO files consist of a stream of characters containing the following
12371 special control characters:
12374 LF (line feed, 16#0A#) Line Mark
12375 FF (form feed, 16#0C#) Page Mark
12379 A canonical Text_IO file is defined as one in which the following
12380 conditions are met:
12384 The character @code{LF} is used only as a line mark, i.e.@: to mark the end
12388 The character @code{FF} is used only as a page mark, i.e.@: to mark the
12389 end of a page and consequently can appear only immediately following a
12390 @code{LF} (line mark) character.
12393 The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
12394 (line mark, page mark). In the former case, the page mark is implicitly
12395 assumed to be present.
12399 A file written using Text_IO will be in canonical form provided that no
12400 explicit @code{LF} or @code{FF} characters are written using @code{Put}
12401 or @code{Put_Line}. There will be no @code{FF} character at the end of
12402 the file unless an explicit @code{New_Page} operation was performed
12403 before closing the file.
12405 A canonical Text_IO file that is a regular file (i.e., not a device or a
12406 pipe) can be read using any of the routines in Text_IO@. The
12407 semantics in this case will be exactly as defined in the Ada Reference
12408 Manual, and all the routines in Text_IO are fully implemented.
12410 A text file that does not meet the requirements for a canonical Text_IO
12411 file has one of the following:
12415 The file contains @code{FF} characters not immediately following a
12416 @code{LF} character.
12419 The file contains @code{LF} or @code{FF} characters written by
12420 @code{Put} or @code{Put_Line}, which are not logically considered to be
12421 line marks or page marks.
12424 The file ends in a character other than @code{LF} or @code{FF},
12425 i.e.@: there is no explicit line mark or page mark at the end of the file.
12429 Text_IO can be used to read such non-standard text files but subprograms
12430 to do with line or page numbers do not have defined meanings. In
12431 particular, a @code{FF} character that does not follow a @code{LF}
12432 character may or may not be treated as a page mark from the point of
12433 view of page and line numbering. Every @code{LF} character is considered
12434 to end a line, and there is an implied @code{LF} character at the end of
12438 * Text_IO Stream Pointer Positioning::
12439 * Text_IO Reading and Writing Non-Regular Files::
12441 * Treating Text_IO Files as Streams::
12442 * Text_IO Extensions::
12443 * Text_IO Facilities for Unbounded Strings::
12446 @node Text_IO Stream Pointer Positioning
12447 @subsection Stream Pointer Positioning
12450 @code{Ada.Text_IO} has a definition of current position for a file that
12451 is being read. No internal buffering occurs in Text_IO, and usually the
12452 physical position in the stream used to implement the file corresponds
12453 to this logical position defined by Text_IO@. There are two exceptions:
12457 After a call to @code{End_Of_Page} that returns @code{True}, the stream
12458 is positioned past the @code{LF} (line mark) that precedes the page
12459 mark. Text_IO maintains an internal flag so that subsequent read
12460 operations properly handle the logical position which is unchanged by
12461 the @code{End_Of_Page} call.
12464 After a call to @code{End_Of_File} that returns @code{True}, if the
12465 Text_IO file was positioned before the line mark at the end of file
12466 before the call, then the logical position is unchanged, but the stream
12467 is physically positioned right at the end of file (past the line mark,
12468 and past a possible page mark following the line mark. Again Text_IO
12469 maintains internal flags so that subsequent read operations properly
12470 handle the logical position.
12474 These discrepancies have no effect on the observable behavior of
12475 Text_IO, but if a single Ada stream is shared between a C program and
12476 Ada program, or shared (using @samp{shared=yes} in the form string)
12477 between two Ada files, then the difference may be observable in some
12480 @node Text_IO Reading and Writing Non-Regular Files
12481 @subsection Reading and Writing Non-Regular Files
12484 A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
12485 can be used for reading and writing. Writing is not affected and the
12486 sequence of characters output is identical to the normal file case, but
12487 for reading, the behavior of Text_IO is modified to avoid undesirable
12488 look-ahead as follows:
12490 An input file that is not a regular file is considered to have no page
12491 marks. Any @code{Ascii.FF} characters (the character normally used for a
12492 page mark) appearing in the file are considered to be data
12493 characters. In particular:
12497 @code{Get_Line} and @code{Skip_Line} do not test for a page mark
12498 following a line mark. If a page mark appears, it will be treated as a
12502 This avoids the need to wait for an extra character to be typed or
12503 entered from the pipe to complete one of these operations.
12506 @code{End_Of_Page} always returns @code{False}
12509 @code{End_Of_File} will return @code{False} if there is a page mark at
12510 the end of the file.
12514 Output to non-regular files is the same as for regular files. Page marks
12515 may be written to non-regular files using @code{New_Page}, but as noted
12516 above they will not be treated as page marks on input if the output is
12517 piped to another Ada program.
12519 Another important discrepancy when reading non-regular files is that the end
12520 of file indication is not ``sticky''. If an end of file is entered, e.g.@: by
12521 pressing the @key{EOT} key,
12523 is signaled once (i.e.@: the test @code{End_Of_File}
12524 will yield @code{True}, or a read will
12525 raise @code{End_Error}), but then reading can resume
12526 to read data past that end of
12527 file indication, until another end of file indication is entered.
12529 @node Get_Immediate
12530 @subsection Get_Immediate
12531 @cindex Get_Immediate
12534 Get_Immediate returns the next character (including control characters)
12535 from the input file. In particular, Get_Immediate will return LF or FF
12536 characters used as line marks or page marks. Such operations leave the
12537 file positioned past the control character, and it is thus not treated
12538 as having its normal function. This means that page, line and column
12539 counts after this kind of Get_Immediate call are set as though the mark
12540 did not occur. In the case where a Get_Immediate leaves the file
12541 positioned between the line mark and page mark (which is not normally
12542 possible), it is undefined whether the FF character will be treated as a
12545 @node Treating Text_IO Files as Streams
12546 @subsection Treating Text_IO Files as Streams
12547 @cindex Stream files
12550 The package @code{Text_IO.Streams} allows a Text_IO file to be treated
12551 as a stream. Data written to a Text_IO file in this stream mode is
12552 binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
12553 16#0C# (@code{FF}), the resulting file may have non-standard
12554 format. Similarly if read operations are used to read from a Text_IO
12555 file treated as a stream, then @code{LF} and @code{FF} characters may be
12556 skipped and the effect is similar to that described above for
12557 @code{Get_Immediate}.
12559 @node Text_IO Extensions
12560 @subsection Text_IO Extensions
12561 @cindex Text_IO extensions
12564 A package GNAT.IO_Aux in the GNAT library provides some useful extensions
12565 to the standard @code{Text_IO} package:
12568 @item function File_Exists (Name : String) return Boolean;
12569 Determines if a file of the given name exists.
12571 @item function Get_Line return String;
12572 Reads a string from the standard input file. The value returned is exactly
12573 the length of the line that was read.
12575 @item function Get_Line (File : Ada.Text_IO.File_Type) return String;
12576 Similar, except that the parameter File specifies the file from which
12577 the string is to be read.
12581 @node Text_IO Facilities for Unbounded Strings
12582 @subsection Text_IO Facilities for Unbounded Strings
12583 @cindex Text_IO for unbounded strings
12584 @cindex Unbounded_String, Text_IO operations
12587 The package @code{Ada.Strings.Unbounded.Text_IO}
12588 in library files @code{a-suteio.ads/adb} contains some GNAT-specific
12589 subprograms useful for Text_IO operations on unbounded strings:
12593 @item function Get_Line (File : File_Type) return Unbounded_String;
12594 Reads a line from the specified file
12595 and returns the result as an unbounded string.
12597 @item procedure Put (File : File_Type; U : Unbounded_String);
12598 Writes the value of the given unbounded string to the specified file
12599 Similar to the effect of
12600 @code{Put (To_String (U))} except that an extra copy is avoided.
12602 @item procedure Put_Line (File : File_Type; U : Unbounded_String);
12603 Writes the value of the given unbounded string to the specified file,
12604 followed by a @code{New_Line}.
12605 Similar to the effect of @code{Put_Line (To_String (U))} except
12606 that an extra copy is avoided.
12610 In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
12611 and is optional. If the parameter is omitted, then the standard input or
12612 output file is referenced as appropriate.
12614 The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
12615 files @file{a-swuwti.ads} and @file{a-swuwti.adb} provides similar extended
12616 @code{Wide_Text_IO} functionality for unbounded wide strings.
12618 The package @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library
12619 files @file{a-szuzti.ads} and @file{a-szuzti.adb} provides similar extended
12620 @code{Wide_Wide_Text_IO} functionality for unbounded wide wide strings.
12623 @section Wide_Text_IO
12626 @code{Wide_Text_IO} is similar in most respects to Text_IO, except that
12627 both input and output files may contain special sequences that represent
12628 wide character values. The encoding scheme for a given file may be
12629 specified using a FORM parameter:
12636 as part of the FORM string (WCEM = wide character encoding method),
12637 where @var{x} is one of the following characters
12643 Upper half encoding
12655 The encoding methods match those that
12656 can be used in a source
12657 program, but there is no requirement that the encoding method used for
12658 the source program be the same as the encoding method used for files,
12659 and different files may use different encoding methods.
12661 The default encoding method for the standard files, and for opened files
12662 for which no WCEM parameter is given in the FORM string matches the
12663 wide character encoding specified for the main program (the default
12664 being brackets encoding if no coding method was specified with -gnatW).
12668 In this encoding, a wide character is represented by a five character
12676 where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
12677 characters (using upper case letters) of the wide character code. For
12678 example, ESC A345 is used to represent the wide character with code
12679 16#A345#. This scheme is compatible with use of the full
12680 @code{Wide_Character} set.
12682 @item Upper Half Coding
12683 The wide character with encoding 16#abcd#, where the upper bit is on
12684 (i.e.@: a is in the range 8-F) is represented as two bytes 16#ab# and
12685 16#cd#. The second byte may never be a format control character, but is
12686 not required to be in the upper half. This method can be also used for
12687 shift-JIS or EUC where the internal coding matches the external coding.
12689 @item Shift JIS Coding
12690 A wide character is represented by a two character sequence 16#ab# and
12691 16#cd#, with the restrictions described for upper half encoding as
12692 described above. The internal character code is the corresponding JIS
12693 character according to the standard algorithm for Shift-JIS
12694 conversion. Only characters defined in the JIS code set table can be
12695 used with this encoding method.
12698 A wide character is represented by a two character sequence 16#ab# and
12699 16#cd#, with both characters being in the upper half. The internal
12700 character code is the corresponding JIS character according to the EUC
12701 encoding algorithm. Only characters defined in the JIS code set table
12702 can be used with this encoding method.
12705 A wide character is represented using
12706 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12707 10646-1/Am.2. Depending on the character value, the representation
12708 is a one, two, or three byte sequence:
12711 16#0000#-16#007f#: 2#0xxxxxxx#
12712 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
12713 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12717 where the @var{xxx} bits correspond to the left-padded bits of the
12718 16-bit character value. Note that all lower half ASCII characters
12719 are represented as ASCII bytes and all upper half characters and
12720 other wide characters are represented as sequences of upper-half
12721 (The full UTF-8 scheme allows for encoding 31-bit characters as
12722 6-byte sequences, but in this implementation, all UTF-8 sequences
12723 of four or more bytes length will raise a Constraint_Error, as
12724 will all invalid UTF-8 sequences.)
12726 @item Brackets Coding
12727 In this encoding, a wide character is represented by the following eight
12728 character sequence:
12735 where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
12736 characters (using uppercase letters) of the wide character code. For
12737 example, @code{["A345"]} is used to represent the wide character with code
12739 This scheme is compatible with use of the full Wide_Character set.
12740 On input, brackets coding can also be used for upper half characters,
12741 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12742 is only used for wide characters with a code greater than @code{16#FF#}.
12744 Note that brackets coding is not normally used in the context of
12745 Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as
12746 a portable way of encoding source files. In the context of Wide_Text_IO
12747 or Wide_Wide_Text_IO, it can only be used if the file does not contain
12748 any instance of the left bracket character other than to encode wide
12749 character values using the brackets encoding method. In practice it is
12750 expected that some standard wide character encoding method such
12751 as UTF-8 will be used for text input output.
12753 If brackets notation is used, then any occurrence of a left bracket
12754 in the input file which is not the start of a valid wide character
12755 sequence will cause Constraint_Error to be raised. It is possible to
12756 encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO
12757 input will interpret this as a left bracket.
12759 However, when a left bracket is output, it will be output as a left bracket
12760 and not as ["5B"]. We make this decision because for normal use of
12761 Wide_Text_IO for outputting messages, it is unpleasant to clobber left
12762 brackets. For example, if we write:
12765 Put_Line ("Start of output [first run]");
12769 we really do not want to have the left bracket in this message clobbered so
12770 that the output reads:
12773 Start of output ["5B"]first run]
12777 In practice brackets encoding is reasonably useful for normal Put_Line use
12778 since we won't get confused between left brackets and wide character
12779 sequences in the output. But for input, or when files are written out
12780 and read back in, it really makes better sense to use one of the standard
12781 encoding methods such as UTF-8.
12786 For the coding schemes other than UTF-8, Hex, or Brackets encoding,
12787 not all wide character
12788 values can be represented. An attempt to output a character that cannot
12789 be represented using the encoding scheme for the file causes
12790 Constraint_Error to be raised. An invalid wide character sequence on
12791 input also causes Constraint_Error to be raised.
12794 * Wide_Text_IO Stream Pointer Positioning::
12795 * Wide_Text_IO Reading and Writing Non-Regular Files::
12798 @node Wide_Text_IO Stream Pointer Positioning
12799 @subsection Stream Pointer Positioning
12802 @code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12803 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12806 If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
12807 normal lower ASCII set (i.e.@: a character in the range:
12809 @smallexample @c ada
12810 Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
12814 then although the logical position of the file pointer is unchanged by
12815 the @code{Look_Ahead} call, the stream is physically positioned past the
12816 wide character sequence. Again this is to avoid the need for buffering
12817 or backup, and all @code{Wide_Text_IO} routines check the internal
12818 indication that this situation has occurred so that this is not visible
12819 to a normal program using @code{Wide_Text_IO}. However, this discrepancy
12820 can be observed if the wide text file shares a stream with another file.
12822 @node Wide_Text_IO Reading and Writing Non-Regular Files
12823 @subsection Reading and Writing Non-Regular Files
12826 As in the case of Text_IO, when a non-regular file is read, it is
12827 assumed that the file contains no page marks (any form characters are
12828 treated as data characters), and @code{End_Of_Page} always returns
12829 @code{False}. Similarly, the end of file indication is not sticky, so
12830 it is possible to read beyond an end of file.
12832 @node Wide_Wide_Text_IO
12833 @section Wide_Wide_Text_IO
12836 @code{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that
12837 both input and output files may contain special sequences that represent
12838 wide wide character values. The encoding scheme for a given file may be
12839 specified using a FORM parameter:
12846 as part of the FORM string (WCEM = wide character encoding method),
12847 where @var{x} is one of the following characters
12853 Upper half encoding
12865 The encoding methods match those that
12866 can be used in a source
12867 program, but there is no requirement that the encoding method used for
12868 the source program be the same as the encoding method used for files,
12869 and different files may use different encoding methods.
12871 The default encoding method for the standard files, and for opened files
12872 for which no WCEM parameter is given in the FORM string matches the
12873 wide character encoding specified for the main program (the default
12874 being brackets encoding if no coding method was specified with -gnatW).
12879 A wide character is represented using
12880 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12881 10646-1/Am.2. Depending on the character value, the representation
12882 is a one, two, three, or four byte sequence:
12885 16#000000#-16#00007f#: 2#0xxxxxxx#
12886 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx#
12887 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12888 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
12892 where the @var{xxx} bits correspond to the left-padded bits of the
12893 21-bit character value. Note that all lower half ASCII characters
12894 are represented as ASCII bytes and all upper half characters and
12895 other wide characters are represented as sequences of upper-half
12898 @item Brackets Coding
12899 In this encoding, a wide wide character is represented by the following eight
12900 character sequence if is in wide character range
12906 and by the following ten character sequence if not
12909 [ " a b c d e f " ]
12913 where @code{a}, @code{b}, @code{c}, @code{d}, @code{e}, and @code{f}
12914 are the four or six hexadecimal
12915 characters (using uppercase letters) of the wide wide character code. For
12916 example, @code{["01A345"]} is used to represent the wide wide character
12917 with code @code{16#01A345#}.
12919 This scheme is compatible with use of the full Wide_Wide_Character set.
12920 On input, brackets coding can also be used for upper half characters,
12921 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12922 is only used for wide characters with a code greater than @code{16#FF#}.
12927 If is also possible to use the other Wide_Character encoding methods,
12928 such as Shift-JIS, but the other schemes cannot support the full range
12929 of wide wide characters.
12930 An attempt to output a character that cannot
12931 be represented using the encoding scheme for the file causes
12932 Constraint_Error to be raised. An invalid wide character sequence on
12933 input also causes Constraint_Error to be raised.
12936 * Wide_Wide_Text_IO Stream Pointer Positioning::
12937 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
12940 @node Wide_Wide_Text_IO Stream Pointer Positioning
12941 @subsection Stream Pointer Positioning
12944 @code{Ada.Wide_Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12945 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12948 If @code{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the
12949 normal lower ASCII set (i.e.@: a character in the range:
12951 @smallexample @c ada
12952 Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
12956 then although the logical position of the file pointer is unchanged by
12957 the @code{Look_Ahead} call, the stream is physically positioned past the
12958 wide character sequence. Again this is to avoid the need for buffering
12959 or backup, and all @code{Wide_Wide_Text_IO} routines check the internal
12960 indication that this situation has occurred so that this is not visible
12961 to a normal program using @code{Wide_Wide_Text_IO}. However, this discrepancy
12962 can be observed if the wide text file shares a stream with another file.
12964 @node Wide_Wide_Text_IO Reading and Writing Non-Regular Files
12965 @subsection Reading and Writing Non-Regular Files
12968 As in the case of Text_IO, when a non-regular file is read, it is
12969 assumed that the file contains no page marks (any form characters are
12970 treated as data characters), and @code{End_Of_Page} always returns
12971 @code{False}. Similarly, the end of file indication is not sticky, so
12972 it is possible to read beyond an end of file.
12978 A stream file is a sequence of bytes, where individual elements are
12979 written to the file as described in the Ada Reference Manual. The type
12980 @code{Stream_Element} is simply a byte. There are two ways to read or
12981 write a stream file.
12985 The operations @code{Read} and @code{Write} directly read or write a
12986 sequence of stream elements with no control information.
12989 The stream attributes applied to a stream file transfer data in the
12990 manner described for stream attributes.
12993 @node Text Translation
12994 @section Text Translation
12997 @samp{Text_Translation=@var{xxx}} may be used as the Form parameter
12998 passed to Text_IO.Create and Text_IO.Open:
12999 @samp{Text_Translation=@var{Yes}} is the default, which means to
13000 translate LF to/from CR/LF on Windows systems.
13001 @samp{Text_Translation=@var{No}} disables this translation; i.e. it
13002 uses binary mode. For output files, @samp{Text_Translation=@var{No}}
13003 may be used to create Unix-style files on
13004 Windows. @samp{Text_Translation=@var{xxx}} has no effect on Unix
13008 @section Shared Files
13011 Section A.14 of the Ada Reference Manual allows implementations to
13012 provide a wide variety of behavior if an attempt is made to access the
13013 same external file with two or more internal files.
13015 To provide a full range of functionality, while at the same time
13016 minimizing the problems of portability caused by this implementation
13017 dependence, GNAT handles file sharing as follows:
13021 In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
13022 to open two or more files with the same full name is considered an error
13023 and is not supported. The exception @code{Use_Error} will be
13024 raised. Note that a file that is not explicitly closed by the program
13025 remains open until the program terminates.
13028 If the form parameter @samp{shared=no} appears in the form string, the
13029 file can be opened or created with its own separate stream identifier,
13030 regardless of whether other files sharing the same external file are
13031 opened. The exact effect depends on how the C stream routines handle
13032 multiple accesses to the same external files using separate streams.
13035 If the form parameter @samp{shared=yes} appears in the form string for
13036 each of two or more files opened using the same full name, the same
13037 stream is shared between these files, and the semantics are as described
13038 in Ada Reference Manual, Section A.14.
13042 When a program that opens multiple files with the same name is ported
13043 from another Ada compiler to GNAT, the effect will be that
13044 @code{Use_Error} is raised.
13046 The documentation of the original compiler and the documentation of the
13047 program should then be examined to determine if file sharing was
13048 expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
13049 and @code{Create} calls as required.
13051 When a program is ported from GNAT to some other Ada compiler, no
13052 special attention is required unless the @samp{shared=@var{xxx}} form
13053 parameter is used in the program. In this case, you must examine the
13054 documentation of the new compiler to see if it supports the required
13055 file sharing semantics, and form strings modified appropriately. Of
13056 course it may be the case that the program cannot be ported if the
13057 target compiler does not support the required functionality. The best
13058 approach in writing portable code is to avoid file sharing (and hence
13059 the use of the @samp{shared=@var{xxx}} parameter in the form string)
13062 One common use of file sharing in Ada 83 is the use of instantiations of
13063 Sequential_IO on the same file with different types, to achieve
13064 heterogeneous input-output. Although this approach will work in GNAT if
13065 @samp{shared=yes} is specified, it is preferable in Ada to use Stream_IO
13066 for this purpose (using the stream attributes)
13068 @node Filenames encoding
13069 @section Filenames encoding
13072 An encoding form parameter can be used to specify the filename
13073 encoding @samp{encoding=@var{xxx}}.
13077 If the form parameter @samp{encoding=utf8} appears in the form string, the
13078 filename must be encoded in UTF-8.
13081 If the form parameter @samp{encoding=8bits} appears in the form
13082 string, the filename must be a standard 8bits string.
13085 In the absence of a @samp{encoding=@var{xxx}} form parameter, the
13086 value UTF-8 is used. This encoding form parameter is only supported on
13087 the Windows platform. On the other Operating Systems the runtime is
13088 supporting UTF-8 natively.
13091 @section Open Modes
13094 @code{Open} and @code{Create} calls result in a call to @code{fopen}
13095 using the mode shown in the following table:
13098 @center @code{Open} and @code{Create} Call Modes
13100 @b{OPEN } @b{CREATE}
13101 Append_File "r+" "w+"
13103 Out_File (Direct_IO) "r+" "w"
13104 Out_File (all other cases) "w" "w"
13105 Inout_File "r+" "w+"
13109 If text file translation is required, then either @samp{b} or @samp{t}
13110 is added to the mode, depending on the setting of Text. Text file
13111 translation refers to the mapping of CR/LF sequences in an external file
13112 to LF characters internally. This mapping only occurs in DOS and
13113 DOS-like systems, and is not relevant to other systems.
13115 A special case occurs with Stream_IO@. As shown in the above table, the
13116 file is initially opened in @samp{r} or @samp{w} mode for the
13117 @code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
13118 subsequently requires switching from reading to writing or vice-versa,
13119 then the file is reopened in @samp{r+} mode to permit the required operation.
13121 @node Operations on C Streams
13122 @section Operations on C Streams
13123 The package @code{Interfaces.C_Streams} provides an Ada program with direct
13124 access to the C library functions for operations on C streams:
13126 @smallexample @c adanocomment
13127 package Interfaces.C_Streams is
13128 -- Note: the reason we do not use the types that are in
13129 -- Interfaces.C is that we want to avoid dragging in the
13130 -- code in this unit if possible.
13131 subtype chars is System.Address;
13132 -- Pointer to null-terminated array of characters
13133 subtype FILEs is System.Address;
13134 -- Corresponds to the C type FILE*
13135 subtype voids is System.Address;
13136 -- Corresponds to the C type void*
13137 subtype int is Integer;
13138 subtype long is Long_Integer;
13139 -- Note: the above types are subtypes deliberately, and it
13140 -- is part of this spec that the above correspondences are
13141 -- guaranteed. This means that it is legitimate to, for
13142 -- example, use Integer instead of int. We provide these
13143 -- synonyms for clarity, but in some cases it may be
13144 -- convenient to use the underlying types (for example to
13145 -- avoid an unnecessary dependency of a spec on the spec
13147 type size_t is mod 2 ** Standard'Address_Size;
13148 NULL_Stream : constant FILEs;
13149 -- Value returned (NULL in C) to indicate an
13150 -- fdopen/fopen/tmpfile error
13151 ----------------------------------
13152 -- Constants Defined in stdio.h --
13153 ----------------------------------
13154 EOF : constant int;
13155 -- Used by a number of routines to indicate error or
13157 IOFBF : constant int;
13158 IOLBF : constant int;
13159 IONBF : constant int;
13160 -- Used to indicate buffering mode for setvbuf call
13161 SEEK_CUR : constant int;
13162 SEEK_END : constant int;
13163 SEEK_SET : constant int;
13164 -- Used to indicate origin for fseek call
13165 function stdin return FILEs;
13166 function stdout return FILEs;
13167 function stderr return FILEs;
13168 -- Streams associated with standard files
13169 --------------------------
13170 -- Standard C functions --
13171 --------------------------
13172 -- The functions selected below are ones that are
13173 -- available in DOS, OS/2, UNIX and Xenix (but not
13174 -- necessarily in ANSI C). These are very thin interfaces
13175 -- which copy exactly the C headers. For more
13176 -- documentation on these functions, see the Microsoft C
13177 -- "Run-Time Library Reference" (Microsoft Press, 1990,
13178 -- ISBN 1-55615-225-6), which includes useful information
13179 -- on system compatibility.
13180 procedure clearerr (stream : FILEs);
13181 function fclose (stream : FILEs) return int;
13182 function fdopen (handle : int; mode : chars) return FILEs;
13183 function feof (stream : FILEs) return int;
13184 function ferror (stream : FILEs) return int;
13185 function fflush (stream : FILEs) return int;
13186 function fgetc (stream : FILEs) return int;
13187 function fgets (strng : chars; n : int; stream : FILEs)
13189 function fileno (stream : FILEs) return int;
13190 function fopen (filename : chars; Mode : chars)
13192 -- Note: to maintain target independence, use
13193 -- text_translation_required, a boolean variable defined in
13194 -- a-sysdep.c to deal with the target dependent text
13195 -- translation requirement. If this variable is set,
13196 -- then b/t should be appended to the standard mode
13197 -- argument to set the text translation mode off or on
13199 function fputc (C : int; stream : FILEs) return int;
13200 function fputs (Strng : chars; Stream : FILEs) return int;
13217 function ftell (stream : FILEs) return long;
13224 function isatty (handle : int) return int;
13225 procedure mktemp (template : chars);
13226 -- The return value (which is just a pointer to template)
13228 procedure rewind (stream : FILEs);
13229 function rmtmp return int;
13237 function tmpfile return FILEs;
13238 function ungetc (c : int; stream : FILEs) return int;
13239 function unlink (filename : chars) return int;
13240 ---------------------
13241 -- Extra functions --
13242 ---------------------
13243 -- These functions supply slightly thicker bindings than
13244 -- those above. They are derived from functions in the
13245 -- C Run-Time Library, but may do a bit more work than
13246 -- just directly calling one of the Library functions.
13247 function is_regular_file (handle : int) return int;
13248 -- Tests if given handle is for a regular file (result 1)
13249 -- or for a non-regular file (pipe or device, result 0).
13250 ---------------------------------
13251 -- Control of Text/Binary Mode --
13252 ---------------------------------
13253 -- If text_translation_required is true, then the following
13254 -- functions may be used to dynamically switch a file from
13255 -- binary to text mode or vice versa. These functions have
13256 -- no effect if text_translation_required is false (i.e.@: in
13257 -- normal UNIX mode). Use fileno to get a stream handle.
13258 procedure set_binary_mode (handle : int);
13259 procedure set_text_mode (handle : int);
13260 ----------------------------
13261 -- Full Path Name support --
13262 ----------------------------
13263 procedure full_name (nam : chars; buffer : chars);
13264 -- Given a NUL terminated string representing a file
13265 -- name, returns in buffer a NUL terminated string
13266 -- representing the full path name for the file name.
13267 -- On systems where it is relevant the drive is also
13268 -- part of the full path name. It is the responsibility
13269 -- of the caller to pass an actual parameter for buffer
13270 -- that is big enough for any full path name. Use
13271 -- max_path_len given below as the size of buffer.
13272 max_path_len : integer;
13273 -- Maximum length of an allowable full path name on the
13274 -- system, including a terminating NUL character.
13275 end Interfaces.C_Streams;
13278 @node Interfacing to C Streams
13279 @section Interfacing to C Streams
13282 The packages in this section permit interfacing Ada files to C Stream
13285 @smallexample @c ada
13286 with Interfaces.C_Streams;
13287 package Ada.Sequential_IO.C_Streams is
13288 function C_Stream (F : File_Type)
13289 return Interfaces.C_Streams.FILEs;
13291 (File : in out File_Type;
13292 Mode : in File_Mode;
13293 C_Stream : in Interfaces.C_Streams.FILEs;
13294 Form : in String := "");
13295 end Ada.Sequential_IO.C_Streams;
13297 with Interfaces.C_Streams;
13298 package Ada.Direct_IO.C_Streams is
13299 function C_Stream (F : File_Type)
13300 return Interfaces.C_Streams.FILEs;
13302 (File : in out File_Type;
13303 Mode : in File_Mode;
13304 C_Stream : in Interfaces.C_Streams.FILEs;
13305 Form : in String := "");
13306 end Ada.Direct_IO.C_Streams;
13308 with Interfaces.C_Streams;
13309 package Ada.Text_IO.C_Streams is
13310 function C_Stream (F : File_Type)
13311 return Interfaces.C_Streams.FILEs;
13313 (File : in out File_Type;
13314 Mode : in File_Mode;
13315 C_Stream : in Interfaces.C_Streams.FILEs;
13316 Form : in String := "");
13317 end Ada.Text_IO.C_Streams;
13319 with Interfaces.C_Streams;
13320 package Ada.Wide_Text_IO.C_Streams is
13321 function C_Stream (F : File_Type)
13322 return Interfaces.C_Streams.FILEs;
13324 (File : in out File_Type;
13325 Mode : in File_Mode;
13326 C_Stream : in Interfaces.C_Streams.FILEs;
13327 Form : in String := "");
13328 end Ada.Wide_Text_IO.C_Streams;
13330 with Interfaces.C_Streams;
13331 package Ada.Wide_Wide_Text_IO.C_Streams is
13332 function C_Stream (F : File_Type)
13333 return Interfaces.C_Streams.FILEs;
13335 (File : in out File_Type;
13336 Mode : in File_Mode;
13337 C_Stream : in Interfaces.C_Streams.FILEs;
13338 Form : in String := "");
13339 end Ada.Wide_Wide_Text_IO.C_Streams;
13341 with Interfaces.C_Streams;
13342 package Ada.Stream_IO.C_Streams is
13343 function C_Stream (F : File_Type)
13344 return Interfaces.C_Streams.FILEs;
13346 (File : in out File_Type;
13347 Mode : in File_Mode;
13348 C_Stream : in Interfaces.C_Streams.FILEs;
13349 Form : in String := "");
13350 end Ada.Stream_IO.C_Streams;
13354 In each of these six packages, the @code{C_Stream} function obtains the
13355 @code{FILE} pointer from a currently opened Ada file. It is then
13356 possible to use the @code{Interfaces.C_Streams} package to operate on
13357 this stream, or the stream can be passed to a C program which can
13358 operate on it directly. Of course the program is responsible for
13359 ensuring that only appropriate sequences of operations are executed.
13361 One particular use of relevance to an Ada program is that the
13362 @code{setvbuf} function can be used to control the buffering of the
13363 stream used by an Ada file. In the absence of such a call the standard
13364 default buffering is used.
13366 The @code{Open} procedures in these packages open a file giving an
13367 existing C Stream instead of a file name. Typically this stream is
13368 imported from a C program, allowing an Ada file to operate on an
13371 @node The GNAT Library
13372 @chapter The GNAT Library
13375 The GNAT library contains a number of general and special purpose packages.
13376 It represents functionality that the GNAT developers have found useful, and
13377 which is made available to GNAT users. The packages described here are fully
13378 supported, and upwards compatibility will be maintained in future releases,
13379 so you can use these facilities with the confidence that the same functionality
13380 will be available in future releases.
13382 The chapter here simply gives a brief summary of the facilities available.
13383 The full documentation is found in the spec file for the package. The full
13384 sources of these library packages, including both spec and body, are provided
13385 with all GNAT releases. For example, to find out the full specifications of
13386 the SPITBOL pattern matching capability, including a full tutorial and
13387 extensive examples, look in the @file{g-spipat.ads} file in the library.
13389 For each entry here, the package name (as it would appear in a @code{with}
13390 clause) is given, followed by the name of the corresponding spec file in
13391 parentheses. The packages are children in four hierarchies, @code{Ada},
13392 @code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
13393 GNAT-specific hierarchy.
13395 Note that an application program should only use packages in one of these
13396 four hierarchies if the package is defined in the Ada Reference Manual,
13397 or is listed in this section of the GNAT Programmers Reference Manual.
13398 All other units should be considered internal implementation units and
13399 should not be directly @code{with}'ed by application code. The use of
13400 a @code{with} statement that references one of these internal implementation
13401 units makes an application potentially dependent on changes in versions
13402 of GNAT, and will generate a warning message.
13405 * Ada.Characters.Latin_9 (a-chlat9.ads)::
13406 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
13407 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
13408 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
13409 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
13410 * Ada.Command_Line.Environment (a-colien.ads)::
13411 * Ada.Command_Line.Remove (a-colire.ads)::
13412 * Ada.Command_Line.Response_File (a-clrefi.ads)::
13413 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
13414 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
13415 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
13416 * Ada.Exceptions.Traceback (a-exctra.ads)::
13417 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
13418 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
13419 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
13420 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
13421 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
13422 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
13423 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
13424 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
13425 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
13426 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
13427 * GNAT.Altivec (g-altive.ads)::
13428 * GNAT.Altivec.Conversions (g-altcon.ads)::
13429 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
13430 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
13431 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
13432 * GNAT.Array_Split (g-arrspl.ads)::
13433 * GNAT.AWK (g-awk.ads)::
13434 * GNAT.Bounded_Buffers (g-boubuf.ads)::
13435 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
13436 * GNAT.Bubble_Sort (g-bubsor.ads)::
13437 * GNAT.Bubble_Sort_A (g-busora.ads)::
13438 * GNAT.Bubble_Sort_G (g-busorg.ads)::
13439 * GNAT.Byte_Order_Mark (g-byorma.ads)::
13440 * GNAT.Byte_Swapping (g-bytswa.ads)::
13441 * GNAT.Calendar (g-calend.ads)::
13442 * GNAT.Calendar.Time_IO (g-catiio.ads)::
13443 * GNAT.Case_Util (g-casuti.ads)::
13444 * GNAT.CGI (g-cgi.ads)::
13445 * GNAT.CGI.Cookie (g-cgicoo.ads)::
13446 * GNAT.CGI.Debug (g-cgideb.ads)::
13447 * GNAT.Command_Line (g-comlin.ads)::
13448 * GNAT.Compiler_Version (g-comver.ads)::
13449 * GNAT.Ctrl_C (g-ctrl_c.ads)::
13450 * GNAT.CRC32 (g-crc32.ads)::
13451 * GNAT.Current_Exception (g-curexc.ads)::
13452 * GNAT.Debug_Pools (g-debpoo.ads)::
13453 * GNAT.Debug_Utilities (g-debuti.ads)::
13454 * GNAT.Decode_String (g-decstr.ads)::
13455 * GNAT.Decode_UTF8_String (g-deutst.ads)::
13456 * GNAT.Directory_Operations (g-dirope.ads)::
13457 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
13458 * GNAT.Dynamic_HTables (g-dynhta.ads)::
13459 * GNAT.Dynamic_Tables (g-dyntab.ads)::
13460 * GNAT.Encode_String (g-encstr.ads)::
13461 * GNAT.Encode_UTF8_String (g-enutst.ads)::
13462 * GNAT.Exception_Actions (g-excact.ads)::
13463 * GNAT.Exception_Traces (g-exctra.ads)::
13464 * GNAT.Exceptions (g-except.ads)::
13465 * GNAT.Expect (g-expect.ads)::
13466 * GNAT.Float_Control (g-flocon.ads)::
13467 * GNAT.Heap_Sort (g-heasor.ads)::
13468 * GNAT.Heap_Sort_A (g-hesora.ads)::
13469 * GNAT.Heap_Sort_G (g-hesorg.ads)::
13470 * GNAT.HTable (g-htable.ads)::
13471 * GNAT.IO (g-io.ads)::
13472 * GNAT.IO_Aux (g-io_aux.ads)::
13473 * GNAT.Lock_Files (g-locfil.ads)::
13474 * GNAT.MD5 (g-md5.ads)::
13475 * GNAT.Memory_Dump (g-memdum.ads)::
13476 * GNAT.Most_Recent_Exception (g-moreex.ads)::
13477 * GNAT.OS_Lib (g-os_lib.ads)::
13478 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
13479 * GNAT.Random_Numbers (g-rannum.ads)::
13480 * GNAT.Regexp (g-regexp.ads)::
13481 * GNAT.Registry (g-regist.ads)::
13482 * GNAT.Regpat (g-regpat.ads)::
13483 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
13484 * GNAT.Semaphores (g-semaph.ads)::
13485 * GNAT.Serial_Communications (g-sercom.ads)::
13486 * GNAT.SHA1 (g-sha1.ads)::
13487 * GNAT.Signals (g-signal.ads)::
13488 * GNAT.Sockets (g-socket.ads)::
13489 * GNAT.Source_Info (g-souinf.ads)::
13490 * GNAT.Spelling_Checker (g-speche.ads)::
13491 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
13492 * GNAT.Spitbol.Patterns (g-spipat.ads)::
13493 * GNAT.Spitbol (g-spitbo.ads)::
13494 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
13495 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
13496 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
13497 * GNAT.Strings (g-string.ads)::
13498 * GNAT.String_Split (g-strspl.ads)::
13499 * GNAT.Table (g-table.ads)::
13500 * GNAT.Task_Lock (g-tasloc.ads)::
13501 * GNAT.Threads (g-thread.ads)::
13502 * GNAT.Time_Stamp (g-timsta.ads)::
13503 * GNAT.Traceback (g-traceb.ads)::
13504 * GNAT.Traceback.Symbolic (g-trasym.ads)::
13505 * GNAT.UTF_32 (g-utf_32.ads)::
13506 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
13507 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
13508 * GNAT.Wide_String_Split (g-wistsp.ads)::
13509 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
13510 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
13511 * Interfaces.C.Extensions (i-cexten.ads)::
13512 * Interfaces.C.Streams (i-cstrea.ads)::
13513 * Interfaces.CPP (i-cpp.ads)::
13514 * Interfaces.Packed_Decimal (i-pacdec.ads)::
13515 * Interfaces.VxWorks (i-vxwork.ads)::
13516 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
13517 * System.Address_Image (s-addima.ads)::
13518 * System.Assertions (s-assert.ads)::
13519 * System.Memory (s-memory.ads)::
13520 * System.Partition_Interface (s-parint.ads)::
13521 * System.Pool_Global (s-pooglo.ads)::
13522 * System.Pool_Local (s-pooloc.ads)::
13523 * System.Restrictions (s-restri.ads)::
13524 * System.Rident (s-rident.ads)::
13525 * System.Task_Info (s-tasinf.ads)::
13526 * System.Wch_Cnv (s-wchcnv.ads)::
13527 * System.Wch_Con (s-wchcon.ads)::
13530 @node Ada.Characters.Latin_9 (a-chlat9.ads)
13531 @section @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13532 @cindex @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13533 @cindex Latin_9 constants for Character
13536 This child of @code{Ada.Characters}
13537 provides a set of definitions corresponding to those in the
13538 RM-defined package @code{Ada.Characters.Latin_1} but with the
13539 few modifications required for @code{Latin-9}
13540 The provision of such a package
13541 is specifically authorized by the Ada Reference Manual
13544 @node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
13545 @section @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13546 @cindex @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13547 @cindex Latin_1 constants for Wide_Character
13550 This child of @code{Ada.Characters}
13551 provides a set of definitions corresponding to those in the
13552 RM-defined package @code{Ada.Characters.Latin_1} but with the
13553 types of the constants being @code{Wide_Character}
13554 instead of @code{Character}. The provision of such a package
13555 is specifically authorized by the Ada Reference Manual
13558 @node Ada.Characters.Wide_Latin_9 (a-cwila9.ads)
13559 @section @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13560 @cindex @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13561 @cindex Latin_9 constants for Wide_Character
13564 This child of @code{Ada.Characters}
13565 provides a set of definitions corresponding to those in the
13566 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13567 types of the constants being @code{Wide_Character}
13568 instead of @code{Character}. The provision of such a package
13569 is specifically authorized by the Ada Reference Manual
13572 @node Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)
13573 @section @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13574 @cindex @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13575 @cindex Latin_1 constants for Wide_Wide_Character
13578 This child of @code{Ada.Characters}
13579 provides a set of definitions corresponding to those in the
13580 RM-defined package @code{Ada.Characters.Latin_1} but with the
13581 types of the constants being @code{Wide_Wide_Character}
13582 instead of @code{Character}. The provision of such a package
13583 is specifically authorized by the Ada Reference Manual
13586 @node Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)
13587 @section @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13588 @cindex @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13589 @cindex Latin_9 constants for Wide_Wide_Character
13592 This child of @code{Ada.Characters}
13593 provides a set of definitions corresponding to those in the
13594 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13595 types of the constants being @code{Wide_Wide_Character}
13596 instead of @code{Character}. The provision of such a package
13597 is specifically authorized by the Ada Reference Manual
13600 @node Ada.Command_Line.Environment (a-colien.ads)
13601 @section @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13602 @cindex @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13603 @cindex Environment entries
13606 This child of @code{Ada.Command_Line}
13607 provides a mechanism for obtaining environment values on systems
13608 where this concept makes sense.
13610 @node Ada.Command_Line.Remove (a-colire.ads)
13611 @section @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13612 @cindex @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13613 @cindex Removing command line arguments
13614 @cindex Command line, argument removal
13617 This child of @code{Ada.Command_Line}
13618 provides a mechanism for logically removing
13619 arguments from the argument list. Once removed, an argument is not visible
13620 to further calls on the subprograms in @code{Ada.Command_Line} will not
13621 see the removed argument.
13623 @node Ada.Command_Line.Response_File (a-clrefi.ads)
13624 @section @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13625 @cindex @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13626 @cindex Response file for command line
13627 @cindex Command line, response file
13628 @cindex Command line, handling long command lines
13631 This child of @code{Ada.Command_Line} provides a mechanism facilities for
13632 getting command line arguments from a text file, called a "response file".
13633 Using a response file allow passing a set of arguments to an executable longer
13634 than the maximum allowed by the system on the command line.
13636 @node Ada.Direct_IO.C_Streams (a-diocst.ads)
13637 @section @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13638 @cindex @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13639 @cindex C Streams, Interfacing with Direct_IO
13642 This package provides subprograms that allow interfacing between
13643 C streams and @code{Direct_IO}. The stream identifier can be
13644 extracted from a file opened on the Ada side, and an Ada file
13645 can be constructed from a stream opened on the C side.
13647 @node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
13648 @section @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13649 @cindex @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13650 @cindex Null_Occurrence, testing for
13653 This child subprogram provides a way of testing for the null
13654 exception occurrence (@code{Null_Occurrence}) without raising
13657 @node Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)
13658 @section @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13659 @cindex @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13660 @cindex Null_Occurrence, testing for
13663 This child subprogram is used for handling otherwise unhandled
13664 exceptions (hence the name last chance), and perform clean ups before
13665 terminating the program. Note that this subprogram never returns.
13667 @node Ada.Exceptions.Traceback (a-exctra.ads)
13668 @section @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13669 @cindex @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13670 @cindex Traceback for Exception Occurrence
13673 This child package provides the subprogram (@code{Tracebacks}) to
13674 give a traceback array of addresses based on an exception
13677 @node Ada.Sequential_IO.C_Streams (a-siocst.ads)
13678 @section @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13679 @cindex @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13680 @cindex C Streams, Interfacing with Sequential_IO
13683 This package provides subprograms that allow interfacing between
13684 C streams and @code{Sequential_IO}. The stream identifier can be
13685 extracted from a file opened on the Ada side, and an Ada file
13686 can be constructed from a stream opened on the C side.
13688 @node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
13689 @section @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13690 @cindex @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13691 @cindex C Streams, Interfacing with Stream_IO
13694 This package provides subprograms that allow interfacing between
13695 C streams and @code{Stream_IO}. The stream identifier can be
13696 extracted from a file opened on the Ada side, and an Ada file
13697 can be constructed from a stream opened on the C side.
13699 @node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
13700 @section @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13701 @cindex @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13702 @cindex @code{Unbounded_String}, IO support
13703 @cindex @code{Text_IO}, extensions for unbounded strings
13706 This package provides subprograms for Text_IO for unbounded
13707 strings, avoiding the necessity for an intermediate operation
13708 with ordinary strings.
13710 @node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
13711 @section @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13712 @cindex @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13713 @cindex @code{Unbounded_Wide_String}, IO support
13714 @cindex @code{Text_IO}, extensions for unbounded wide strings
13717 This package provides subprograms for Text_IO for unbounded
13718 wide strings, avoiding the necessity for an intermediate operation
13719 with ordinary wide strings.
13721 @node Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)
13722 @section @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13723 @cindex @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13724 @cindex @code{Unbounded_Wide_Wide_String}, IO support
13725 @cindex @code{Text_IO}, extensions for unbounded wide wide strings
13728 This package provides subprograms for Text_IO for unbounded
13729 wide wide strings, avoiding the necessity for an intermediate operation
13730 with ordinary wide wide strings.
13732 @node Ada.Text_IO.C_Streams (a-tiocst.ads)
13733 @section @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13734 @cindex @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13735 @cindex C Streams, Interfacing with @code{Text_IO}
13738 This package provides subprograms that allow interfacing between
13739 C streams and @code{Text_IO}. The stream identifier can be
13740 extracted from a file opened on the Ada side, and an Ada file
13741 can be constructed from a stream opened on the C side.
13743 @node Ada.Wide_Characters.Unicode (a-wichun.ads)
13744 @section @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13745 @cindex @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13746 @cindex Unicode categorization, Wide_Character
13749 This package provides subprograms that allow categorization of
13750 Wide_Character values according to Unicode categories.
13752 @node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
13753 @section @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13754 @cindex @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13755 @cindex C Streams, Interfacing with @code{Wide_Text_IO}
13758 This package provides subprograms that allow interfacing between
13759 C streams and @code{Wide_Text_IO}. The stream identifier can be
13760 extracted from a file opened on the Ada side, and an Ada file
13761 can be constructed from a stream opened on the C side.
13763 @node Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)
13764 @section @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13765 @cindex @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13766 @cindex Unicode categorization, Wide_Wide_Character
13769 This package provides subprograms that allow categorization of
13770 Wide_Wide_Character values according to Unicode categories.
13772 @node Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)
13773 @section @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13774 @cindex @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13775 @cindex C Streams, Interfacing with @code{Wide_Wide_Text_IO}
13778 This package provides subprograms that allow interfacing between
13779 C streams and @code{Wide_Wide_Text_IO}. The stream identifier can be
13780 extracted from a file opened on the Ada side, and an Ada file
13781 can be constructed from a stream opened on the C side.
13783 @node GNAT.Altivec (g-altive.ads)
13784 @section @code{GNAT.Altivec} (@file{g-altive.ads})
13785 @cindex @code{GNAT.Altivec} (@file{g-altive.ads})
13789 This is the root package of the GNAT AltiVec binding. It provides
13790 definitions of constants and types common to all the versions of the
13793 @node GNAT.Altivec.Conversions (g-altcon.ads)
13794 @section @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13795 @cindex @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13799 This package provides the Vector/View conversion routines.
13801 @node GNAT.Altivec.Vector_Operations (g-alveop.ads)
13802 @section @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13803 @cindex @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13807 This package exposes the Ada interface to the AltiVec operations on
13808 vector objects. A soft emulation is included by default in the GNAT
13809 library. The hard binding is provided as a separate package. This unit
13810 is common to both bindings.
13812 @node GNAT.Altivec.Vector_Types (g-alvety.ads)
13813 @section @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13814 @cindex @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13818 This package exposes the various vector types part of the Ada binding
13819 to AltiVec facilities.
13821 @node GNAT.Altivec.Vector_Views (g-alvevi.ads)
13822 @section @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13823 @cindex @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13827 This package provides public 'View' data types from/to which private
13828 vector representations can be converted via
13829 GNAT.Altivec.Conversions. This allows convenient access to individual
13830 vector elements and provides a simple way to initialize vector
13833 @node GNAT.Array_Split (g-arrspl.ads)
13834 @section @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13835 @cindex @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13836 @cindex Array splitter
13839 Useful array-manipulation routines: given a set of separators, split
13840 an array wherever the separators appear, and provide direct access
13841 to the resulting slices.
13843 @node GNAT.AWK (g-awk.ads)
13844 @section @code{GNAT.AWK} (@file{g-awk.ads})
13845 @cindex @code{GNAT.AWK} (@file{g-awk.ads})
13850 Provides AWK-like parsing functions, with an easy interface for parsing one
13851 or more files containing formatted data. The file is viewed as a database
13852 where each record is a line and a field is a data element in this line.
13854 @node GNAT.Bounded_Buffers (g-boubuf.ads)
13855 @section @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13856 @cindex @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13858 @cindex Bounded Buffers
13861 Provides a concurrent generic bounded buffer abstraction. Instances are
13862 useful directly or as parts of the implementations of other abstractions,
13865 @node GNAT.Bounded_Mailboxes (g-boumai.ads)
13866 @section @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13867 @cindex @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13872 Provides a thread-safe asynchronous intertask mailbox communication facility.
13874 @node GNAT.Bubble_Sort (g-bubsor.ads)
13875 @section @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13876 @cindex @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13878 @cindex Bubble sort
13881 Provides a general implementation of bubble sort usable for sorting arbitrary
13882 data items. Exchange and comparison procedures are provided by passing
13883 access-to-procedure values.
13885 @node GNAT.Bubble_Sort_A (g-busora.ads)
13886 @section @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13887 @cindex @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13889 @cindex Bubble sort
13892 Provides a general implementation of bubble sort usable for sorting arbitrary
13893 data items. Move and comparison procedures are provided by passing
13894 access-to-procedure values. This is an older version, retained for
13895 compatibility. Usually @code{GNAT.Bubble_Sort} will be preferable.
13897 @node GNAT.Bubble_Sort_G (g-busorg.ads)
13898 @section @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13899 @cindex @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13901 @cindex Bubble sort
13904 Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
13905 are provided as generic parameters, this improves efficiency, especially
13906 if the procedures can be inlined, at the expense of duplicating code for
13907 multiple instantiations.
13909 @node GNAT.Byte_Order_Mark (g-byorma.ads)
13910 @section @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13911 @cindex @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13912 @cindex UTF-8 representation
13913 @cindex Wide characte representations
13916 Provides a routine which given a string, reads the start of the string to
13917 see whether it is one of the standard byte order marks (BOM's) which signal
13918 the encoding of the string. The routine includes detection of special XML
13919 sequences for various UCS input formats.
13921 @node GNAT.Byte_Swapping (g-bytswa.ads)
13922 @section @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
13923 @cindex @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
13924 @cindex Byte swapping
13928 General routines for swapping the bytes in 2-, 4-, and 8-byte quantities.
13929 Machine-specific implementations are available in some cases.
13931 @node GNAT.Calendar (g-calend.ads)
13932 @section @code{GNAT.Calendar} (@file{g-calend.ads})
13933 @cindex @code{GNAT.Calendar} (@file{g-calend.ads})
13934 @cindex @code{Calendar}
13937 Extends the facilities provided by @code{Ada.Calendar} to include handling
13938 of days of the week, an extended @code{Split} and @code{Time_Of} capability.
13939 Also provides conversion of @code{Ada.Calendar.Time} values to and from the
13940 C @code{timeval} format.
13942 @node GNAT.Calendar.Time_IO (g-catiio.ads)
13943 @section @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
13944 @cindex @code{Calendar}
13946 @cindex @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
13948 @node GNAT.CRC32 (g-crc32.ads)
13949 @section @code{GNAT.CRC32} (@file{g-crc32.ads})
13950 @cindex @code{GNAT.CRC32} (@file{g-crc32.ads})
13952 @cindex Cyclic Redundancy Check
13955 This package implements the CRC-32 algorithm. For a full description
13956 of this algorithm see
13957 ``Computation of Cyclic Redundancy Checks via Table Look-Up'',
13958 @cite{Communications of the ACM}, Vol.@: 31 No.@: 8, pp.@: 1008-1013,
13959 Aug.@: 1988. Sarwate, D.V@.
13961 @node GNAT.Case_Util (g-casuti.ads)
13962 @section @code{GNAT.Case_Util} (@file{g-casuti.ads})
13963 @cindex @code{GNAT.Case_Util} (@file{g-casuti.ads})
13964 @cindex Casing utilities
13965 @cindex Character handling (@code{GNAT.Case_Util})
13968 A set of simple routines for handling upper and lower casing of strings
13969 without the overhead of the full casing tables
13970 in @code{Ada.Characters.Handling}.
13972 @node GNAT.CGI (g-cgi.ads)
13973 @section @code{GNAT.CGI} (@file{g-cgi.ads})
13974 @cindex @code{GNAT.CGI} (@file{g-cgi.ads})
13975 @cindex CGI (Common Gateway Interface)
13978 This is a package for interfacing a GNAT program with a Web server via the
13979 Common Gateway Interface (CGI)@. Basically this package parses the CGI
13980 parameters, which are a set of key/value pairs sent by the Web server. It
13981 builds a table whose index is the key and provides some services to deal
13984 @node GNAT.CGI.Cookie (g-cgicoo.ads)
13985 @section @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
13986 @cindex @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
13987 @cindex CGI (Common Gateway Interface) cookie support
13988 @cindex Cookie support in CGI
13991 This is a package to interface a GNAT program with a Web server via the
13992 Common Gateway Interface (CGI). It exports services to deal with Web
13993 cookies (piece of information kept in the Web client software).
13995 @node GNAT.CGI.Debug (g-cgideb.ads)
13996 @section @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
13997 @cindex @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
13998 @cindex CGI (Common Gateway Interface) debugging
14001 This is a package to help debugging CGI (Common Gateway Interface)
14002 programs written in Ada.
14004 @node GNAT.Command_Line (g-comlin.ads)
14005 @section @code{GNAT.Command_Line} (@file{g-comlin.ads})
14006 @cindex @code{GNAT.Command_Line} (@file{g-comlin.ads})
14007 @cindex Command line
14010 Provides a high level interface to @code{Ada.Command_Line} facilities,
14011 including the ability to scan for named switches with optional parameters
14012 and expand file names using wild card notations.
14014 @node GNAT.Compiler_Version (g-comver.ads)
14015 @section @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14016 @cindex @code{GNAT.Compiler_Version} (@file{g-comver.ads})
14017 @cindex Compiler Version
14018 @cindex Version, of compiler
14021 Provides a routine for obtaining the version of the compiler used to
14022 compile the program. More accurately this is the version of the binder
14023 used to bind the program (this will normally be the same as the version
14024 of the compiler if a consistent tool set is used to compile all units
14027 @node GNAT.Ctrl_C (g-ctrl_c.ads)
14028 @section @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14029 @cindex @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
14033 Provides a simple interface to handle Ctrl-C keyboard events.
14035 @node GNAT.Current_Exception (g-curexc.ads)
14036 @section @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14037 @cindex @code{GNAT.Current_Exception} (@file{g-curexc.ads})
14038 @cindex Current exception
14039 @cindex Exception retrieval
14042 Provides access to information on the current exception that has been raised
14043 without the need for using the Ada 95 / Ada 2005 exception choice parameter
14044 specification syntax.
14045 This is particularly useful in simulating typical facilities for
14046 obtaining information about exceptions provided by Ada 83 compilers.
14048 @node GNAT.Debug_Pools (g-debpoo.ads)
14049 @section @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14050 @cindex @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
14052 @cindex Debug pools
14053 @cindex Memory corruption debugging
14056 Provide a debugging storage pools that helps tracking memory corruption
14057 problems. @xref{The GNAT Debug Pool Facility,,, gnat_ugn,
14058 @value{EDITION} User's Guide}.
14060 @node GNAT.Debug_Utilities (g-debuti.ads)
14061 @section @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14062 @cindex @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
14066 Provides a few useful utilities for debugging purposes, including conversion
14067 to and from string images of address values. Supports both C and Ada formats
14068 for hexadecimal literals.
14070 @node GNAT.Decode_String (g-decstr.ads)
14071 @section @code{GNAT.Decode_String} (@file{g-decstr.ads})
14072 @cindex @code{GNAT.Decode_String} (@file{g-decstr.ads})
14073 @cindex Decoding strings
14074 @cindex String decoding
14075 @cindex Wide character encoding
14080 A generic package providing routines for decoding wide character and wide wide
14081 character strings encoded as sequences of 8-bit characters using a specified
14082 encoding method. Includes validation routines, and also routines for stepping
14083 to next or previous encoded character in an encoded string.
14084 Useful in conjunction with Unicode character coding. Note there is a
14085 preinstantiation for UTF-8. See next entry.
14087 @node GNAT.Decode_UTF8_String (g-deutst.ads)
14088 @section @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14089 @cindex @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
14090 @cindex Decoding strings
14091 @cindex Decoding UTF-8 strings
14092 @cindex UTF-8 string decoding
14093 @cindex Wide character decoding
14098 A preinstantiation of GNAT.Decode_Strings for UTF-8 encoding.
14100 @node GNAT.Directory_Operations (g-dirope.ads)
14101 @section @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14102 @cindex @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
14103 @cindex Directory operations
14106 Provides a set of routines for manipulating directories, including changing
14107 the current directory, making new directories, and scanning the files in a
14110 @node GNAT.Directory_Operations.Iteration (g-diopit.ads)
14111 @section @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14112 @cindex @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
14113 @cindex Directory operations iteration
14116 A child unit of GNAT.Directory_Operations providing additional operations
14117 for iterating through directories.
14119 @node GNAT.Dynamic_HTables (g-dynhta.ads)
14120 @section @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14121 @cindex @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
14122 @cindex Hash tables
14125 A generic implementation of hash tables that can be used to hash arbitrary
14126 data. Provided in two forms, a simple form with built in hash functions,
14127 and a more complex form in which the hash function is supplied.
14130 This package provides a facility similar to that of @code{GNAT.HTable},
14131 except that this package declares a type that can be used to define
14132 dynamic instances of the hash table, while an instantiation of
14133 @code{GNAT.HTable} creates a single instance of the hash table.
14135 @node GNAT.Dynamic_Tables (g-dyntab.ads)
14136 @section @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14137 @cindex @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
14138 @cindex Table implementation
14139 @cindex Arrays, extendable
14142 A generic package providing a single dimension array abstraction where the
14143 length of the array can be dynamically modified.
14146 This package provides a facility similar to that of @code{GNAT.Table},
14147 except that this package declares a type that can be used to define
14148 dynamic instances of the table, while an instantiation of
14149 @code{GNAT.Table} creates a single instance of the table type.
14151 @node GNAT.Encode_String (g-encstr.ads)
14152 @section @code{GNAT.Encode_String} (@file{g-encstr.ads})
14153 @cindex @code{GNAT.Encode_String} (@file{g-encstr.ads})
14154 @cindex Encoding strings
14155 @cindex String encoding
14156 @cindex Wide character encoding
14161 A generic package providing routines for encoding wide character and wide
14162 wide character strings as sequences of 8-bit characters using a specified
14163 encoding method. Useful in conjunction with Unicode character coding.
14164 Note there is a preinstantiation for UTF-8. See next entry.
14166 @node GNAT.Encode_UTF8_String (g-enutst.ads)
14167 @section @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14168 @cindex @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14169 @cindex Encoding strings
14170 @cindex Encoding UTF-8 strings
14171 @cindex UTF-8 string encoding
14172 @cindex Wide character encoding
14177 A preinstantiation of GNAT.Encode_Strings for UTF-8 encoding.
14179 @node GNAT.Exception_Actions (g-excact.ads)
14180 @section @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14181 @cindex @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14182 @cindex Exception actions
14185 Provides callbacks when an exception is raised. Callbacks can be registered
14186 for specific exceptions, or when any exception is raised. This
14187 can be used for instance to force a core dump to ease debugging.
14189 @node GNAT.Exception_Traces (g-exctra.ads)
14190 @section @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14191 @cindex @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14192 @cindex Exception traces
14196 Provides an interface allowing to control automatic output upon exception
14199 @node GNAT.Exceptions (g-except.ads)
14200 @section @code{GNAT.Exceptions} (@file{g-expect.ads})
14201 @cindex @code{GNAT.Exceptions} (@file{g-expect.ads})
14202 @cindex Exceptions, Pure
14203 @cindex Pure packages, exceptions
14206 Normally it is not possible to raise an exception with
14207 a message from a subprogram in a pure package, since the
14208 necessary types and subprograms are in @code{Ada.Exceptions}
14209 which is not a pure unit. @code{GNAT.Exceptions} provides a
14210 facility for getting around this limitation for a few
14211 predefined exceptions, and for example allow raising
14212 @code{Constraint_Error} with a message from a pure subprogram.
14214 @node GNAT.Expect (g-expect.ads)
14215 @section @code{GNAT.Expect} (@file{g-expect.ads})
14216 @cindex @code{GNAT.Expect} (@file{g-expect.ads})
14219 Provides a set of subprograms similar to what is available
14220 with the standard Tcl Expect tool.
14221 It allows you to easily spawn and communicate with an external process.
14222 You can send commands or inputs to the process, and compare the output
14223 with some expected regular expression. Currently @code{GNAT.Expect}
14224 is implemented on all native GNAT ports except for OpenVMS@.
14225 It is not implemented for cross ports, and in particular is not
14226 implemented for VxWorks or LynxOS@.
14228 @node GNAT.Float_Control (g-flocon.ads)
14229 @section @code{GNAT.Float_Control} (@file{g-flocon.ads})
14230 @cindex @code{GNAT.Float_Control} (@file{g-flocon.ads})
14231 @cindex Floating-Point Processor
14234 Provides an interface for resetting the floating-point processor into the
14235 mode required for correct semantic operation in Ada. Some third party
14236 library calls may cause this mode to be modified, and the Reset procedure
14237 in this package can be used to reestablish the required mode.
14239 @node GNAT.Heap_Sort (g-heasor.ads)
14240 @section @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14241 @cindex @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14245 Provides a general implementation of heap sort usable for sorting arbitrary
14246 data items. Exchange and comparison procedures are provided by passing
14247 access-to-procedure values. The algorithm used is a modified heap sort
14248 that performs approximately N*log(N) comparisons in the worst case.
14250 @node GNAT.Heap_Sort_A (g-hesora.ads)
14251 @section @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14252 @cindex @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14256 Provides a general implementation of heap sort usable for sorting arbitrary
14257 data items. Move and comparison procedures are provided by passing
14258 access-to-procedure values. The algorithm used is a modified heap sort
14259 that performs approximately N*log(N) comparisons in the worst case.
14260 This differs from @code{GNAT.Heap_Sort} in having a less convenient
14261 interface, but may be slightly more efficient.
14263 @node GNAT.Heap_Sort_G (g-hesorg.ads)
14264 @section @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14265 @cindex @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14269 Similar to @code{Heap_Sort_A} except that the move and sorting procedures
14270 are provided as generic parameters, this improves efficiency, especially
14271 if the procedures can be inlined, at the expense of duplicating code for
14272 multiple instantiations.
14274 @node GNAT.HTable (g-htable.ads)
14275 @section @code{GNAT.HTable} (@file{g-htable.ads})
14276 @cindex @code{GNAT.HTable} (@file{g-htable.ads})
14277 @cindex Hash tables
14280 A generic implementation of hash tables that can be used to hash arbitrary
14281 data. Provides two approaches, one a simple static approach, and the other
14282 allowing arbitrary dynamic hash tables.
14284 @node GNAT.IO (g-io.ads)
14285 @section @code{GNAT.IO} (@file{g-io.ads})
14286 @cindex @code{GNAT.IO} (@file{g-io.ads})
14288 @cindex Input/Output facilities
14291 A simple preelaborable input-output package that provides a subset of
14292 simple Text_IO functions for reading characters and strings from
14293 Standard_Input, and writing characters, strings and integers to either
14294 Standard_Output or Standard_Error.
14296 @node GNAT.IO_Aux (g-io_aux.ads)
14297 @section @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14298 @cindex @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14300 @cindex Input/Output facilities
14302 Provides some auxiliary functions for use with Text_IO, including a test
14303 for whether a file exists, and functions for reading a line of text.
14305 @node GNAT.Lock_Files (g-locfil.ads)
14306 @section @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14307 @cindex @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14308 @cindex File locking
14309 @cindex Locking using files
14312 Provides a general interface for using files as locks. Can be used for
14313 providing program level synchronization.
14315 @node GNAT.MD5 (g-md5.ads)
14316 @section @code{GNAT.MD5} (@file{g-md5.ads})
14317 @cindex @code{GNAT.MD5} (@file{g-md5.ads})
14318 @cindex Message Digest MD5
14321 Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
14323 @node GNAT.Memory_Dump (g-memdum.ads)
14324 @section @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14325 @cindex @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14326 @cindex Dump Memory
14329 Provides a convenient routine for dumping raw memory to either the
14330 standard output or standard error files. Uses GNAT.IO for actual
14333 @node GNAT.Most_Recent_Exception (g-moreex.ads)
14334 @section @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14335 @cindex @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14336 @cindex Exception, obtaining most recent
14339 Provides access to the most recently raised exception. Can be used for
14340 various logging purposes, including duplicating functionality of some
14341 Ada 83 implementation dependent extensions.
14343 @node GNAT.OS_Lib (g-os_lib.ads)
14344 @section @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14345 @cindex @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14346 @cindex Operating System interface
14347 @cindex Spawn capability
14350 Provides a range of target independent operating system interface functions,
14351 including time/date management, file operations, subprocess management,
14352 including a portable spawn procedure, and access to environment variables
14353 and error return codes.
14355 @node GNAT.Perfect_Hash_Generators (g-pehage.ads)
14356 @section @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14357 @cindex @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14358 @cindex Hash functions
14361 Provides a generator of static minimal perfect hash functions. No
14362 collisions occur and each item can be retrieved from the table in one
14363 probe (perfect property). The hash table size corresponds to the exact
14364 size of the key set and no larger (minimal property). The key set has to
14365 be know in advance (static property). The hash functions are also order
14366 preserving. If w2 is inserted after w1 in the generator, their
14367 hashcode are in the same order. These hashing functions are very
14368 convenient for use with realtime applications.
14370 @node GNAT.Random_Numbers (g-rannum.ads)
14371 @section @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14372 @cindex @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14373 @cindex Random number generation
14376 Provides random number capabilities which extend those available in the
14377 standard Ada library and are more convenient to use.
14379 @node GNAT.Regexp (g-regexp.ads)
14380 @section @code{GNAT.Regexp} (@file{g-regexp.ads})
14381 @cindex @code{GNAT.Regexp} (@file{g-regexp.ads})
14382 @cindex Regular expressions
14383 @cindex Pattern matching
14386 A simple implementation of regular expressions, using a subset of regular
14387 expression syntax copied from familiar Unix style utilities. This is the
14388 simples of the three pattern matching packages provided, and is particularly
14389 suitable for ``file globbing'' applications.
14391 @node GNAT.Registry (g-regist.ads)
14392 @section @code{GNAT.Registry} (@file{g-regist.ads})
14393 @cindex @code{GNAT.Registry} (@file{g-regist.ads})
14394 @cindex Windows Registry
14397 This is a high level binding to the Windows registry. It is possible to
14398 do simple things like reading a key value, creating a new key. For full
14399 registry API, but at a lower level of abstraction, refer to the Win32.Winreg
14400 package provided with the Win32Ada binding
14402 @node GNAT.Regpat (g-regpat.ads)
14403 @section @code{GNAT.Regpat} (@file{g-regpat.ads})
14404 @cindex @code{GNAT.Regpat} (@file{g-regpat.ads})
14405 @cindex Regular expressions
14406 @cindex Pattern matching
14409 A complete implementation of Unix-style regular expression matching, copied
14410 from the original V7 style regular expression library written in C by
14411 Henry Spencer (and binary compatible with this C library).
14413 @node GNAT.Secondary_Stack_Info (g-sestin.ads)
14414 @section @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14415 @cindex @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14416 @cindex Secondary Stack Info
14419 Provide the capability to query the high water mark of the current task's
14422 @node GNAT.Semaphores (g-semaph.ads)
14423 @section @code{GNAT.Semaphores} (@file{g-semaph.ads})
14424 @cindex @code{GNAT.Semaphores} (@file{g-semaph.ads})
14428 Provides classic counting and binary semaphores using protected types.
14430 @node GNAT.Serial_Communications (g-sercom.ads)
14431 @section @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14432 @cindex @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14433 @cindex Serial_Communications
14436 Provides a simple interface to send and receive data over a serial
14437 port. This is only supported on GNU/Linux and Windows.
14439 @node GNAT.SHA1 (g-sha1.ads)
14440 @section @code{GNAT.SHA1} (@file{g-sha1.ads})
14441 @cindex @code{GNAT.SHA1} (@file{g-sha1.ads})
14442 @cindex Secure Hash Algorithm SHA-1
14445 Implements the SHA-1 Secure Hash Algorithm as described in RFC 3174.
14447 @node GNAT.Signals (g-signal.ads)
14448 @section @code{GNAT.Signals} (@file{g-signal.ads})
14449 @cindex @code{GNAT.Signals} (@file{g-signal.ads})
14453 Provides the ability to manipulate the blocked status of signals on supported
14456 @node GNAT.Sockets (g-socket.ads)
14457 @section @code{GNAT.Sockets} (@file{g-socket.ads})
14458 @cindex @code{GNAT.Sockets} (@file{g-socket.ads})
14462 A high level and portable interface to develop sockets based applications.
14463 This package is based on the sockets thin binding found in
14464 @code{GNAT.Sockets.Thin}. Currently @code{GNAT.Sockets} is implemented
14465 on all native GNAT ports except for OpenVMS@. It is not implemented
14466 for the LynxOS@ cross port.
14468 @node GNAT.Source_Info (g-souinf.ads)
14469 @section @code{GNAT.Source_Info} (@file{g-souinf.ads})
14470 @cindex @code{GNAT.Source_Info} (@file{g-souinf.ads})
14471 @cindex Source Information
14474 Provides subprograms that give access to source code information known at
14475 compile time, such as the current file name and line number.
14477 @node GNAT.Spelling_Checker (g-speche.ads)
14478 @section @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14479 @cindex @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14480 @cindex Spell checking
14483 Provides a function for determining whether one string is a plausible
14484 near misspelling of another string.
14486 @node GNAT.Spelling_Checker_Generic (g-spchge.ads)
14487 @section @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14488 @cindex @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14489 @cindex Spell checking
14492 Provides a generic function that can be instantiated with a string type for
14493 determining whether one string is a plausible near misspelling of another
14496 @node GNAT.Spitbol.Patterns (g-spipat.ads)
14497 @section @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14498 @cindex @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14499 @cindex SPITBOL pattern matching
14500 @cindex Pattern matching
14503 A complete implementation of SNOBOL4 style pattern matching. This is the
14504 most elaborate of the pattern matching packages provided. It fully duplicates
14505 the SNOBOL4 dynamic pattern construction and matching capabilities, using the
14506 efficient algorithm developed by Robert Dewar for the SPITBOL system.
14508 @node GNAT.Spitbol (g-spitbo.ads)
14509 @section @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14510 @cindex @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14511 @cindex SPITBOL interface
14514 The top level package of the collection of SPITBOL-style functionality, this
14515 package provides basic SNOBOL4 string manipulation functions, such as
14516 Pad, Reverse, Trim, Substr capability, as well as a generic table function
14517 useful for constructing arbitrary mappings from strings in the style of
14518 the SNOBOL4 TABLE function.
14520 @node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
14521 @section @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14522 @cindex @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14523 @cindex Sets of strings
14524 @cindex SPITBOL Tables
14527 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14528 for type @code{Standard.Boolean}, giving an implementation of sets of
14531 @node GNAT.Spitbol.Table_Integer (g-sptain.ads)
14532 @section @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14533 @cindex @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14534 @cindex Integer maps
14536 @cindex SPITBOL Tables
14539 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14540 for type @code{Standard.Integer}, giving an implementation of maps
14541 from string to integer values.
14543 @node GNAT.Spitbol.Table_VString (g-sptavs.ads)
14544 @section @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14545 @cindex @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14546 @cindex String maps
14548 @cindex SPITBOL Tables
14551 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table} for
14552 a variable length string type, giving an implementation of general
14553 maps from strings to strings.
14555 @node GNAT.Strings (g-string.ads)
14556 @section @code{GNAT.Strings} (@file{g-string.ads})
14557 @cindex @code{GNAT.Strings} (@file{g-string.ads})
14560 Common String access types and related subprograms. Basically it
14561 defines a string access and an array of string access types.
14563 @node GNAT.String_Split (g-strspl.ads)
14564 @section @code{GNAT.String_Split} (@file{g-strspl.ads})
14565 @cindex @code{GNAT.String_Split} (@file{g-strspl.ads})
14566 @cindex String splitter
14569 Useful string manipulation routines: given a set of separators, split
14570 a string wherever the separators appear, and provide direct access
14571 to the resulting slices. This package is instantiated from
14572 @code{GNAT.Array_Split}.
14574 @node GNAT.Table (g-table.ads)
14575 @section @code{GNAT.Table} (@file{g-table.ads})
14576 @cindex @code{GNAT.Table} (@file{g-table.ads})
14577 @cindex Table implementation
14578 @cindex Arrays, extendable
14581 A generic package providing a single dimension array abstraction where the
14582 length of the array can be dynamically modified.
14585 This package provides a facility similar to that of @code{GNAT.Dynamic_Tables},
14586 except that this package declares a single instance of the table type,
14587 while an instantiation of @code{GNAT.Dynamic_Tables} creates a type that can be
14588 used to define dynamic instances of the table.
14590 @node GNAT.Task_Lock (g-tasloc.ads)
14591 @section @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14592 @cindex @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14593 @cindex Task synchronization
14594 @cindex Task locking
14598 A very simple facility for locking and unlocking sections of code using a
14599 single global task lock. Appropriate for use in situations where contention
14600 between tasks is very rarely expected.
14602 @node GNAT.Time_Stamp (g-timsta.ads)
14603 @section @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14604 @cindex @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14606 @cindex Current time
14609 Provides a simple function that returns a string YYYY-MM-DD HH:MM:SS.SS that
14610 represents the current date and time in ISO 8601 format. This is a very simple
14611 routine with minimal code and there are no dependencies on any other unit.
14613 @node GNAT.Threads (g-thread.ads)
14614 @section @code{GNAT.Threads} (@file{g-thread.ads})
14615 @cindex @code{GNAT.Threads} (@file{g-thread.ads})
14616 @cindex Foreign threads
14617 @cindex Threads, foreign
14620 Provides facilities for dealing with foreign threads which need to be known
14621 by the GNAT run-time system. Consult the documentation of this package for
14622 further details if your program has threads that are created by a non-Ada
14623 environment which then accesses Ada code.
14625 @node GNAT.Traceback (g-traceb.ads)
14626 @section @code{GNAT.Traceback} (@file{g-traceb.ads})
14627 @cindex @code{GNAT.Traceback} (@file{g-traceb.ads})
14628 @cindex Trace back facilities
14631 Provides a facility for obtaining non-symbolic traceback information, useful
14632 in various debugging situations.
14634 @node GNAT.Traceback.Symbolic (g-trasym.ads)
14635 @section @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14636 @cindex @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14637 @cindex Trace back facilities
14639 @node GNAT.UTF_32 (g-utf_32.ads)
14640 @section @code{GNAT.UTF_32} (@file{g-table.ads})
14641 @cindex @code{GNAT.UTF_32} (@file{g-table.ads})
14642 @cindex Wide character codes
14645 This is a package intended to be used in conjunction with the
14646 @code{Wide_Character} type in Ada 95 and the
14647 @code{Wide_Wide_Character} type in Ada 2005 (available
14648 in @code{GNAT} in Ada 2005 mode). This package contains
14649 Unicode categorization routines, as well as lexical
14650 categorization routines corresponding to the Ada 2005
14651 lexical rules for identifiers and strings, and also a
14652 lower case to upper case fold routine corresponding to
14653 the Ada 2005 rules for identifier equivalence.
14655 @node GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)
14656 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14657 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14658 @cindex Spell checking
14661 Provides a function for determining whether one wide wide string is a plausible
14662 near misspelling of another wide wide string, where the strings are represented
14663 using the UTF_32_String type defined in System.Wch_Cnv.
14665 @node GNAT.Wide_Spelling_Checker (g-wispch.ads)
14666 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14667 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14668 @cindex Spell checking
14671 Provides a function for determining whether one wide string is a plausible
14672 near misspelling of another wide string.
14674 @node GNAT.Wide_String_Split (g-wistsp.ads)
14675 @section @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14676 @cindex @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14677 @cindex Wide_String splitter
14680 Useful wide string manipulation routines: given a set of separators, split
14681 a wide string wherever the separators appear, and provide direct access
14682 to the resulting slices. This package is instantiated from
14683 @code{GNAT.Array_Split}.
14685 @node GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)
14686 @section @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14687 @cindex @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14688 @cindex Spell checking
14691 Provides a function for determining whether one wide wide string is a plausible
14692 near misspelling of another wide wide string.
14694 @node GNAT.Wide_Wide_String_Split (g-zistsp.ads)
14695 @section @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14696 @cindex @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14697 @cindex Wide_Wide_String splitter
14700 Useful wide wide string manipulation routines: given a set of separators, split
14701 a wide wide string wherever the separators appear, and provide direct access
14702 to the resulting slices. This package is instantiated from
14703 @code{GNAT.Array_Split}.
14705 @node Interfaces.C.Extensions (i-cexten.ads)
14706 @section @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14707 @cindex @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14710 This package contains additional C-related definitions, intended
14711 for use with either manually or automatically generated bindings
14714 @node Interfaces.C.Streams (i-cstrea.ads)
14715 @section @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14716 @cindex @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14717 @cindex C streams, interfacing
14720 This package is a binding for the most commonly used operations
14723 @node Interfaces.CPP (i-cpp.ads)
14724 @section @code{Interfaces.CPP} (@file{i-cpp.ads})
14725 @cindex @code{Interfaces.CPP} (@file{i-cpp.ads})
14726 @cindex C++ interfacing
14727 @cindex Interfacing, to C++
14730 This package provides facilities for use in interfacing to C++. It
14731 is primarily intended to be used in connection with automated tools
14732 for the generation of C++ interfaces.
14734 @node Interfaces.Packed_Decimal (i-pacdec.ads)
14735 @section @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14736 @cindex @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14737 @cindex IBM Packed Format
14738 @cindex Packed Decimal
14741 This package provides a set of routines for conversions to and
14742 from a packed decimal format compatible with that used on IBM
14745 @node Interfaces.VxWorks (i-vxwork.ads)
14746 @section @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14747 @cindex @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14748 @cindex Interfacing to VxWorks
14749 @cindex VxWorks, interfacing
14752 This package provides a limited binding to the VxWorks API.
14753 In particular, it interfaces with the
14754 VxWorks hardware interrupt facilities.
14756 @node Interfaces.VxWorks.IO (i-vxwoio.ads)
14757 @section @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14758 @cindex @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14759 @cindex Interfacing to VxWorks' I/O
14760 @cindex VxWorks, I/O interfacing
14761 @cindex VxWorks, Get_Immediate
14762 @cindex Get_Immediate, VxWorks
14765 This package provides a binding to the ioctl (IO/Control)
14766 function of VxWorks, defining a set of option values and
14767 function codes. A particular use of this package is
14768 to enable the use of Get_Immediate under VxWorks.
14770 @node System.Address_Image (s-addima.ads)
14771 @section @code{System.Address_Image} (@file{s-addima.ads})
14772 @cindex @code{System.Address_Image} (@file{s-addima.ads})
14773 @cindex Address image
14774 @cindex Image, of an address
14777 This function provides a useful debugging
14778 function that gives an (implementation dependent)
14779 string which identifies an address.
14781 @node System.Assertions (s-assert.ads)
14782 @section @code{System.Assertions} (@file{s-assert.ads})
14783 @cindex @code{System.Assertions} (@file{s-assert.ads})
14785 @cindex Assert_Failure, exception
14788 This package provides the declaration of the exception raised
14789 by an run-time assertion failure, as well as the routine that
14790 is used internally to raise this assertion.
14792 @node System.Memory (s-memory.ads)
14793 @section @code{System.Memory} (@file{s-memory.ads})
14794 @cindex @code{System.Memory} (@file{s-memory.ads})
14795 @cindex Memory allocation
14798 This package provides the interface to the low level routines used
14799 by the generated code for allocation and freeing storage for the
14800 default storage pool (analogous to the C routines malloc and free.
14801 It also provides a reallocation interface analogous to the C routine
14802 realloc. The body of this unit may be modified to provide alternative
14803 allocation mechanisms for the default pool, and in addition, direct
14804 calls to this unit may be made for low level allocation uses (for
14805 example see the body of @code{GNAT.Tables}).
14807 @node System.Partition_Interface (s-parint.ads)
14808 @section @code{System.Partition_Interface} (@file{s-parint.ads})
14809 @cindex @code{System.Partition_Interface} (@file{s-parint.ads})
14810 @cindex Partition interfacing functions
14813 This package provides facilities for partition interfacing. It
14814 is used primarily in a distribution context when using Annex E
14817 @node System.Pool_Global (s-pooglo.ads)
14818 @section @code{System.Pool_Global} (@file{s-pooglo.ads})
14819 @cindex @code{System.Pool_Global} (@file{s-pooglo.ads})
14820 @cindex Storage pool, global
14821 @cindex Global storage pool
14824 This package provides a storage pool that is equivalent to the default
14825 storage pool used for access types for which no pool is specifically
14826 declared. It uses malloc/free to allocate/free and does not attempt to
14827 do any automatic reclamation.
14829 @node System.Pool_Local (s-pooloc.ads)
14830 @section @code{System.Pool_Local} (@file{s-pooloc.ads})
14831 @cindex @code{System.Pool_Local} (@file{s-pooloc.ads})
14832 @cindex Storage pool, local
14833 @cindex Local storage pool
14836 This package provides a storage pool that is intended for use with locally
14837 defined access types. It uses malloc/free for allocate/free, and maintains
14838 a list of allocated blocks, so that all storage allocated for the pool can
14839 be freed automatically when the pool is finalized.
14841 @node System.Restrictions (s-restri.ads)
14842 @section @code{System.Restrictions} (@file{s-restri.ads})
14843 @cindex @code{System.Restrictions} (@file{s-restri.ads})
14844 @cindex Run-time restrictions access
14847 This package provides facilities for accessing at run time
14848 the status of restrictions specified at compile time for
14849 the partition. Information is available both with regard
14850 to actual restrictions specified, and with regard to
14851 compiler determined information on which restrictions
14852 are violated by one or more packages in the partition.
14854 @node System.Rident (s-rident.ads)
14855 @section @code{System.Rident} (@file{s-rident.ads})
14856 @cindex @code{System.Rident} (@file{s-rident.ads})
14857 @cindex Restrictions definitions
14860 This package provides definitions of the restrictions
14861 identifiers supported by GNAT, and also the format of
14862 the restrictions provided in package System.Restrictions.
14863 It is not normally necessary to @code{with} this generic package
14864 since the necessary instantiation is included in
14865 package System.Restrictions.
14867 @node System.Task_Info (s-tasinf.ads)
14868 @section @code{System.Task_Info} (@file{s-tasinf.ads})
14869 @cindex @code{System.Task_Info} (@file{s-tasinf.ads})
14870 @cindex Task_Info pragma
14873 This package provides target dependent functionality that is used
14874 to support the @code{Task_Info} pragma
14876 @node System.Wch_Cnv (s-wchcnv.ads)
14877 @section @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14878 @cindex @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14879 @cindex Wide Character, Representation
14880 @cindex Wide String, Conversion
14881 @cindex Representation of wide characters
14884 This package provides routines for converting between
14885 wide and wide wide characters and a representation as a value of type
14886 @code{Standard.String}, using a specified wide character
14887 encoding method. It uses definitions in
14888 package @code{System.Wch_Con}.
14890 @node System.Wch_Con (s-wchcon.ads)
14891 @section @code{System.Wch_Con} (@file{s-wchcon.ads})
14892 @cindex @code{System.Wch_Con} (@file{s-wchcon.ads})
14895 This package provides definitions and descriptions of
14896 the various methods used for encoding wide characters
14897 in ordinary strings. These definitions are used by
14898 the package @code{System.Wch_Cnv}.
14900 @node Interfacing to Other Languages
14901 @chapter Interfacing to Other Languages
14903 The facilities in annex B of the Ada Reference Manual are fully
14904 implemented in GNAT, and in addition, a full interface to C++ is
14908 * Interfacing to C::
14909 * Interfacing to C++::
14910 * Interfacing to COBOL::
14911 * Interfacing to Fortran::
14912 * Interfacing to non-GNAT Ada code::
14915 @node Interfacing to C
14916 @section Interfacing to C
14919 Interfacing to C with GNAT can use one of two approaches:
14923 The types in the package @code{Interfaces.C} may be used.
14925 Standard Ada types may be used directly. This may be less portable to
14926 other compilers, but will work on all GNAT compilers, which guarantee
14927 correspondence between the C and Ada types.
14931 Pragma @code{Convention C} may be applied to Ada types, but mostly has no
14932 effect, since this is the default. The following table shows the
14933 correspondence between Ada scalar types and the corresponding C types.
14938 @item Short_Integer
14940 @item Short_Short_Integer
14944 @item Long_Long_Integer
14952 @item Long_Long_Float
14953 This is the longest floating-point type supported by the hardware.
14957 Additionally, there are the following general correspondences between Ada
14961 Ada enumeration types map to C enumeration types directly if pragma
14962 @code{Convention C} is specified, which causes them to have int
14963 length. Without pragma @code{Convention C}, Ada enumeration types map to
14964 8, 16, or 32 bits (i.e.@: C types @code{signed char}, @code{short},
14965 @code{int}, respectively) depending on the number of values passed.
14966 This is the only case in which pragma @code{Convention C} affects the
14967 representation of an Ada type.
14970 Ada access types map to C pointers, except for the case of pointers to
14971 unconstrained types in Ada, which have no direct C equivalent.
14974 Ada arrays map directly to C arrays.
14977 Ada records map directly to C structures.
14980 Packed Ada records map to C structures where all members are bit fields
14981 of the length corresponding to the @code{@var{type}'Size} value in Ada.
14984 @node Interfacing to C++
14985 @section Interfacing to C++
14988 The interface to C++ makes use of the following pragmas, which are
14989 primarily intended to be constructed automatically using a binding generator
14990 tool, although it is possible to construct them by hand. No suitable binding
14991 generator tool is supplied with GNAT though.
14993 Using these pragmas it is possible to achieve complete
14994 inter-operability between Ada tagged types and C++ class definitions.
14995 See @ref{Implementation Defined Pragmas}, for more details.
14998 @item pragma CPP_Class ([Entity =>] @var{LOCAL_NAME})
14999 The argument denotes an entity in the current declarative region that is
15000 declared as a tagged or untagged record type. It indicates that the type
15001 corresponds to an externally declared C++ class type, and is to be laid
15002 out the same way that C++ would lay out the type.
15004 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
15005 for backward compatibility but its functionality is available
15006 using pragma @code{Import} with @code{Convention} = @code{CPP}.
15008 @item pragma CPP_Constructor ([Entity =>] @var{LOCAL_NAME})
15009 This pragma identifies an imported function (imported in the usual way
15010 with pragma @code{Import}) as corresponding to a C++ constructor.
15013 @node Interfacing to COBOL
15014 @section Interfacing to COBOL
15017 Interfacing to COBOL is achieved as described in section B.4 of
15018 the Ada Reference Manual.
15020 @node Interfacing to Fortran
15021 @section Interfacing to Fortran
15024 Interfacing to Fortran is achieved as described in section B.5 of the
15025 Ada Reference Manual. The pragma @code{Convention Fortran}, applied to a
15026 multi-dimensional array causes the array to be stored in column-major
15027 order as required for convenient interface to Fortran.
15029 @node Interfacing to non-GNAT Ada code
15030 @section Interfacing to non-GNAT Ada code
15032 It is possible to specify the convention @code{Ada} in a pragma
15033 @code{Import} or pragma @code{Export}. However this refers to
15034 the calling conventions used by GNAT, which may or may not be
15035 similar enough to those used by some other Ada 83 / Ada 95 / Ada 2005
15036 compiler to allow interoperation.
15038 If arguments types are kept simple, and if the foreign compiler generally
15039 follows system calling conventions, then it may be possible to integrate
15040 files compiled by other Ada compilers, provided that the elaboration
15041 issues are adequately addressed (for example by eliminating the
15042 need for any load time elaboration).
15044 In particular, GNAT running on VMS is designed to
15045 be highly compatible with the DEC Ada 83 compiler, so this is one
15046 case in which it is possible to import foreign units of this type,
15047 provided that the data items passed are restricted to simple scalar
15048 values or simple record types without variants, or simple array
15049 types with fixed bounds.
15051 @node Specialized Needs Annexes
15052 @chapter Specialized Needs Annexes
15055 Ada 95 and Ada 2005 define a number of Specialized Needs Annexes, which are not
15056 required in all implementations. However, as described in this chapter,
15057 GNAT implements all of these annexes:
15060 @item Systems Programming (Annex C)
15061 The Systems Programming Annex is fully implemented.
15063 @item Real-Time Systems (Annex D)
15064 The Real-Time Systems Annex is fully implemented.
15066 @item Distributed Systems (Annex E)
15067 Stub generation is fully implemented in the GNAT compiler. In addition,
15068 a complete compatible PCS is available as part of the GLADE system,
15069 a separate product. When the two
15070 products are used in conjunction, this annex is fully implemented.
15072 @item Information Systems (Annex F)
15073 The Information Systems annex is fully implemented.
15075 @item Numerics (Annex G)
15076 The Numerics Annex is fully implemented.
15078 @item Safety and Security / High-Integrity Systems (Annex H)
15079 The Safety and Security Annex (termed the High-Integrity Systems Annex
15080 in Ada 2005) is fully implemented.
15083 @node Implementation of Specific Ada Features
15084 @chapter Implementation of Specific Ada Features
15087 This chapter describes the GNAT implementation of several Ada language
15091 * Machine Code Insertions::
15092 * GNAT Implementation of Tasking::
15093 * GNAT Implementation of Shared Passive Packages::
15094 * Code Generation for Array Aggregates::
15095 * The Size of Discriminated Records with Default Discriminants::
15096 * Strict Conformance to the Ada Reference Manual::
15099 @node Machine Code Insertions
15100 @section Machine Code Insertions
15101 @cindex Machine Code insertions
15104 Package @code{Machine_Code} provides machine code support as described
15105 in the Ada Reference Manual in two separate forms:
15108 Machine code statements, consisting of qualified expressions that
15109 fit the requirements of RM section 13.8.
15111 An intrinsic callable procedure, providing an alternative mechanism of
15112 including machine instructions in a subprogram.
15116 The two features are similar, and both are closely related to the mechanism
15117 provided by the asm instruction in the GNU C compiler. Full understanding
15118 and use of the facilities in this package requires understanding the asm
15119 instruction, see @ref{Extended Asm,, Assembler Instructions with C Expression
15120 Operands, gcc, Using the GNU Compiler Collection (GCC)}.
15122 Calls to the function @code{Asm} and the procedure @code{Asm} have identical
15123 semantic restrictions and effects as described below. Both are provided so
15124 that the procedure call can be used as a statement, and the function call
15125 can be used to form a code_statement.
15127 The first example given in the GCC documentation is the C @code{asm}
15130 asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
15134 The equivalent can be written for GNAT as:
15136 @smallexample @c ada
15137 Asm ("fsinx %1 %0",
15138 My_Float'Asm_Output ("=f", result),
15139 My_Float'Asm_Input ("f", angle));
15143 The first argument to @code{Asm} is the assembler template, and is
15144 identical to what is used in GNU C@. This string must be a static
15145 expression. The second argument is the output operand list. It is
15146 either a single @code{Asm_Output} attribute reference, or a list of such
15147 references enclosed in parentheses (technically an array aggregate of
15150 The @code{Asm_Output} attribute denotes a function that takes two
15151 parameters. The first is a string, the second is the name of a variable
15152 of the type designated by the attribute prefix. The first (string)
15153 argument is required to be a static expression and designates the
15154 constraint for the parameter (e.g.@: what kind of register is
15155 required). The second argument is the variable to be updated with the
15156 result. The possible values for constraint are the same as those used in
15157 the RTL, and are dependent on the configuration file used to build the
15158 GCC back end. If there are no output operands, then this argument may
15159 either be omitted, or explicitly given as @code{No_Output_Operands}.
15161 The second argument of @code{@var{my_float}'Asm_Output} functions as
15162 though it were an @code{out} parameter, which is a little curious, but
15163 all names have the form of expressions, so there is no syntactic
15164 irregularity, even though normally functions would not be permitted
15165 @code{out} parameters. The third argument is the list of input
15166 operands. It is either a single @code{Asm_Input} attribute reference, or
15167 a list of such references enclosed in parentheses (technically an array
15168 aggregate of such references).
15170 The @code{Asm_Input} attribute denotes a function that takes two
15171 parameters. The first is a string, the second is an expression of the
15172 type designated by the prefix. The first (string) argument is required
15173 to be a static expression, and is the constraint for the parameter,
15174 (e.g.@: what kind of register is required). The second argument is the
15175 value to be used as the input argument. The possible values for the
15176 constant are the same as those used in the RTL, and are dependent on
15177 the configuration file used to built the GCC back end.
15179 If there are no input operands, this argument may either be omitted, or
15180 explicitly given as @code{No_Input_Operands}. The fourth argument, not
15181 present in the above example, is a list of register names, called the
15182 @dfn{clobber} argument. This argument, if given, must be a static string
15183 expression, and is a space or comma separated list of names of registers
15184 that must be considered destroyed as a result of the @code{Asm} call. If
15185 this argument is the null string (the default value), then the code
15186 generator assumes that no additional registers are destroyed.
15188 The fifth argument, not present in the above example, called the
15189 @dfn{volatile} argument, is by default @code{False}. It can be set to
15190 the literal value @code{True} to indicate to the code generator that all
15191 optimizations with respect to the instruction specified should be
15192 suppressed, and that in particular, for an instruction that has outputs,
15193 the instruction will still be generated, even if none of the outputs are
15194 used. @xref{Extended Asm,, Assembler Instructions with C Expression Operands,
15195 gcc, Using the GNU Compiler Collection (GCC)}, for the full description.
15196 Generally it is strongly advisable to use Volatile for any ASM statement
15197 that is missing either input or output operands, or when two or more ASM
15198 statements appear in sequence, to avoid unwanted optimizations. A warning
15199 is generated if this advice is not followed.
15201 The @code{Asm} subprograms may be used in two ways. First the procedure
15202 forms can be used anywhere a procedure call would be valid, and
15203 correspond to what the RM calls ``intrinsic'' routines. Such calls can
15204 be used to intersperse machine instructions with other Ada statements.
15205 Second, the function forms, which return a dummy value of the limited
15206 private type @code{Asm_Insn}, can be used in code statements, and indeed
15207 this is the only context where such calls are allowed. Code statements
15208 appear as aggregates of the form:
15210 @smallexample @c ada
15211 Asm_Insn'(Asm (@dots{}));
15212 Asm_Insn'(Asm_Volatile (@dots{}));
15216 In accordance with RM rules, such code statements are allowed only
15217 within subprograms whose entire body consists of such statements. It is
15218 not permissible to intermix such statements with other Ada statements.
15220 Typically the form using intrinsic procedure calls is more convenient
15221 and more flexible. The code statement form is provided to meet the RM
15222 suggestion that such a facility should be made available. The following
15223 is the exact syntax of the call to @code{Asm}. As usual, if named notation
15224 is used, the arguments may be given in arbitrary order, following the
15225 normal rules for use of positional and named arguments)
15229 [Template =>] static_string_EXPRESSION
15230 [,[Outputs =>] OUTPUT_OPERAND_LIST ]
15231 [,[Inputs =>] INPUT_OPERAND_LIST ]
15232 [,[Clobber =>] static_string_EXPRESSION ]
15233 [,[Volatile =>] static_boolean_EXPRESSION] )
15235 OUTPUT_OPERAND_LIST ::=
15236 [PREFIX.]No_Output_Operands
15237 | OUTPUT_OPERAND_ATTRIBUTE
15238 | (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
15240 OUTPUT_OPERAND_ATTRIBUTE ::=
15241 SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
15243 INPUT_OPERAND_LIST ::=
15244 [PREFIX.]No_Input_Operands
15245 | INPUT_OPERAND_ATTRIBUTE
15246 | (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
15248 INPUT_OPERAND_ATTRIBUTE ::=
15249 SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
15253 The identifiers @code{No_Input_Operands} and @code{No_Output_Operands}
15254 are declared in the package @code{Machine_Code} and must be referenced
15255 according to normal visibility rules. In particular if there is no
15256 @code{use} clause for this package, then appropriate package name
15257 qualification is required.
15259 @node GNAT Implementation of Tasking
15260 @section GNAT Implementation of Tasking
15263 This chapter outlines the basic GNAT approach to tasking (in particular,
15264 a multi-layered library for portability) and discusses issues related
15265 to compliance with the Real-Time Systems Annex.
15268 * Mapping Ada Tasks onto the Underlying Kernel Threads::
15269 * Ensuring Compliance with the Real-Time Annex::
15272 @node Mapping Ada Tasks onto the Underlying Kernel Threads
15273 @subsection Mapping Ada Tasks onto the Underlying Kernel Threads
15276 GNAT's run-time support comprises two layers:
15279 @item GNARL (GNAT Run-time Layer)
15280 @item GNULL (GNAT Low-level Library)
15284 In GNAT, Ada's tasking services rely on a platform and OS independent
15285 layer known as GNARL@. This code is responsible for implementing the
15286 correct semantics of Ada's task creation, rendezvous, protected
15289 GNARL decomposes Ada's tasking semantics into simpler lower level
15290 operations such as create a thread, set the priority of a thread,
15291 yield, create a lock, lock/unlock, etc. The spec for these low-level
15292 operations constitutes GNULLI, the GNULL Interface. This interface is
15293 directly inspired from the POSIX real-time API@.
15295 If the underlying executive or OS implements the POSIX standard
15296 faithfully, the GNULL Interface maps as is to the services offered by
15297 the underlying kernel. Otherwise, some target dependent glue code maps
15298 the services offered by the underlying kernel to the semantics expected
15301 Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
15302 key point is that each Ada task is mapped on a thread in the underlying
15303 kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
15305 In addition Ada task priorities map onto the underlying thread priorities.
15306 Mapping Ada tasks onto the underlying kernel threads has several advantages:
15310 The underlying scheduler is used to schedule the Ada tasks. This
15311 makes Ada tasks as efficient as kernel threads from a scheduling
15315 Interaction with code written in C containing threads is eased
15316 since at the lowest level Ada tasks and C threads map onto the same
15317 underlying kernel concept.
15320 When an Ada task is blocked during I/O the remaining Ada tasks are
15324 On multiprocessor systems Ada tasks can execute in parallel.
15328 Some threads libraries offer a mechanism to fork a new process, with the
15329 child process duplicating the threads from the parent.
15331 support this functionality when the parent contains more than one task.
15332 @cindex Forking a new process
15334 @node Ensuring Compliance with the Real-Time Annex
15335 @subsection Ensuring Compliance with the Real-Time Annex
15336 @cindex Real-Time Systems Annex compliance
15339 Although mapping Ada tasks onto
15340 the underlying threads has significant advantages, it does create some
15341 complications when it comes to respecting the scheduling semantics
15342 specified in the real-time annex (Annex D).
15344 For instance the Annex D requirement for the @code{FIFO_Within_Priorities}
15345 scheduling policy states:
15348 @emph{When the active priority of a ready task that is not running
15349 changes, or the setting of its base priority takes effect, the
15350 task is removed from the ready queue for its old active priority
15351 and is added at the tail of the ready queue for its new active
15352 priority, except in the case where the active priority is lowered
15353 due to the loss of inherited priority, in which case the task is
15354 added at the head of the ready queue for its new active priority.}
15358 While most kernels do put tasks at the end of the priority queue when
15359 a task changes its priority, (which respects the main
15360 FIFO_Within_Priorities requirement), almost none keep a thread at the
15361 beginning of its priority queue when its priority drops from the loss
15362 of inherited priority.
15364 As a result most vendors have provided incomplete Annex D implementations.
15366 The GNAT run-time, has a nice cooperative solution to this problem
15367 which ensures that accurate FIFO_Within_Priorities semantics are
15370 The principle is as follows. When an Ada task T is about to start
15371 running, it checks whether some other Ada task R with the same
15372 priority as T has been suspended due to the loss of priority
15373 inheritance. If this is the case, T yields and is placed at the end of
15374 its priority queue. When R arrives at the front of the queue it
15377 Note that this simple scheme preserves the relative order of the tasks
15378 that were ready to execute in the priority queue where R has been
15381 @node GNAT Implementation of Shared Passive Packages
15382 @section GNAT Implementation of Shared Passive Packages
15383 @cindex Shared passive packages
15386 GNAT fully implements the pragma @code{Shared_Passive} for
15387 @cindex pragma @code{Shared_Passive}
15388 the purpose of designating shared passive packages.
15389 This allows the use of passive partitions in the
15390 context described in the Ada Reference Manual; i.e., for communication
15391 between separate partitions of a distributed application using the
15392 features in Annex E.
15394 @cindex Distribution Systems Annex
15396 However, the implementation approach used by GNAT provides for more
15397 extensive usage as follows:
15400 @item Communication between separate programs
15402 This allows separate programs to access the data in passive
15403 partitions, using protected objects for synchronization where
15404 needed. The only requirement is that the two programs have a
15405 common shared file system. It is even possible for programs
15406 running on different machines with different architectures
15407 (e.g.@: different endianness) to communicate via the data in
15408 a passive partition.
15410 @item Persistence between program runs
15412 The data in a passive package can persist from one run of a
15413 program to another, so that a later program sees the final
15414 values stored by a previous run of the same program.
15419 The implementation approach used is to store the data in files. A
15420 separate stream file is created for each object in the package, and
15421 an access to an object causes the corresponding file to be read or
15424 The environment variable @code{SHARED_MEMORY_DIRECTORY} should be
15425 @cindex @code{SHARED_MEMORY_DIRECTORY} environment variable
15426 set to the directory to be used for these files.
15427 The files in this directory
15428 have names that correspond to their fully qualified names. For
15429 example, if we have the package
15431 @smallexample @c ada
15433 pragma Shared_Passive (X);
15440 and the environment variable is set to @code{/stemp/}, then the files created
15441 will have the names:
15449 These files are created when a value is initially written to the object, and
15450 the files are retained until manually deleted. This provides the persistence
15451 semantics. If no file exists, it means that no partition has assigned a value
15452 to the variable; in this case the initial value declared in the package
15453 will be used. This model ensures that there are no issues in synchronizing
15454 the elaboration process, since elaboration of passive packages elaborates the
15455 initial values, but does not create the files.
15457 The files are written using normal @code{Stream_IO} access.
15458 If you want to be able
15459 to communicate between programs or partitions running on different
15460 architectures, then you should use the XDR versions of the stream attribute
15461 routines, since these are architecture independent.
15463 If active synchronization is required for access to the variables in the
15464 shared passive package, then as described in the Ada Reference Manual, the
15465 package may contain protected objects used for this purpose. In this case
15466 a lock file (whose name is @file{___lock} (three underscores)
15467 is created in the shared memory directory.
15468 @cindex @file{___lock} file (for shared passive packages)
15469 This is used to provide the required locking
15470 semantics for proper protected object synchronization.
15472 As of January 2003, GNAT supports shared passive packages on all platforms
15473 except for OpenVMS.
15475 @node Code Generation for Array Aggregates
15476 @section Code Generation for Array Aggregates
15479 * Static constant aggregates with static bounds::
15480 * Constant aggregates with unconstrained nominal types::
15481 * Aggregates with static bounds::
15482 * Aggregates with non-static bounds::
15483 * Aggregates in assignment statements::
15487 Aggregates have a rich syntax and allow the user to specify the values of
15488 complex data structures by means of a single construct. As a result, the
15489 code generated for aggregates can be quite complex and involve loops, case
15490 statements and multiple assignments. In the simplest cases, however, the
15491 compiler will recognize aggregates whose components and constraints are
15492 fully static, and in those cases the compiler will generate little or no
15493 executable code. The following is an outline of the code that GNAT generates
15494 for various aggregate constructs. For further details, you will find it
15495 useful to examine the output produced by the -gnatG flag to see the expanded
15496 source that is input to the code generator. You may also want to examine
15497 the assembly code generated at various levels of optimization.
15499 The code generated for aggregates depends on the context, the component values,
15500 and the type. In the context of an object declaration the code generated is
15501 generally simpler than in the case of an assignment. As a general rule, static
15502 component values and static subtypes also lead to simpler code.
15504 @node Static constant aggregates with static bounds
15505 @subsection Static constant aggregates with static bounds
15508 For the declarations:
15509 @smallexample @c ada
15510 type One_Dim is array (1..10) of integer;
15511 ar0 : constant One_Dim := (1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
15515 GNAT generates no executable code: the constant ar0 is placed in static memory.
15516 The same is true for constant aggregates with named associations:
15518 @smallexample @c ada
15519 Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1 => 1, 5 .. 10 => 0);
15520 Cr3 : constant One_Dim := (others => 7777);
15524 The same is true for multidimensional constant arrays such as:
15526 @smallexample @c ada
15527 type two_dim is array (1..3, 1..3) of integer;
15528 Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
15532 The same is true for arrays of one-dimensional arrays: the following are
15535 @smallexample @c ada
15536 type ar1b is array (1..3) of boolean;
15537 type ar_ar is array (1..3) of ar1b;
15538 None : constant ar1b := (others => false); -- fully static
15539 None2 : constant ar_ar := (1..3 => None); -- fully static
15543 However, for multidimensional aggregates with named associations, GNAT will
15544 generate assignments and loops, even if all associations are static. The
15545 following two declarations generate a loop for the first dimension, and
15546 individual component assignments for the second dimension:
15548 @smallexample @c ada
15549 Zero1: constant two_dim := (1..3 => (1..3 => 0));
15550 Zero2: constant two_dim := (others => (others => 0));
15553 @node Constant aggregates with unconstrained nominal types
15554 @subsection Constant aggregates with unconstrained nominal types
15557 In such cases the aggregate itself establishes the subtype, so that
15558 associations with @code{others} cannot be used. GNAT determines the
15559 bounds for the actual subtype of the aggregate, and allocates the
15560 aggregate statically as well. No code is generated for the following:
15562 @smallexample @c ada
15563 type One_Unc is array (natural range <>) of integer;
15564 Cr_Unc : constant One_Unc := (12,24,36);
15567 @node Aggregates with static bounds
15568 @subsection Aggregates with static bounds
15571 In all previous examples the aggregate was the initial (and immutable) value
15572 of a constant. If the aggregate initializes a variable, then code is generated
15573 for it as a combination of individual assignments and loops over the target
15574 object. The declarations
15576 @smallexample @c ada
15577 Cr_Var1 : One_Dim := (2, 5, 7, 11, 0, 0, 0, 0, 0, 0);
15578 Cr_Var2 : One_Dim := (others > -1);
15582 generate the equivalent of
15584 @smallexample @c ada
15590 for I in Cr_Var2'range loop
15595 @node Aggregates with non-static bounds
15596 @subsection Aggregates with non-static bounds
15599 If the bounds of the aggregate are not statically compatible with the bounds
15600 of the nominal subtype of the target, then constraint checks have to be
15601 generated on the bounds. For a multidimensional array, constraint checks may
15602 have to be applied to sub-arrays individually, if they do not have statically
15603 compatible subtypes.
15605 @node Aggregates in assignment statements
15606 @subsection Aggregates in assignment statements
15609 In general, aggregate assignment requires the construction of a temporary,
15610 and a copy from the temporary to the target of the assignment. This is because
15611 it is not always possible to convert the assignment into a series of individual
15612 component assignments. For example, consider the simple case:
15614 @smallexample @c ada
15619 This cannot be converted into:
15621 @smallexample @c ada
15627 So the aggregate has to be built first in a separate location, and then
15628 copied into the target. GNAT recognizes simple cases where this intermediate
15629 step is not required, and the assignments can be performed in place, directly
15630 into the target. The following sufficient criteria are applied:
15634 The bounds of the aggregate are static, and the associations are static.
15636 The components of the aggregate are static constants, names of
15637 simple variables that are not renamings, or expressions not involving
15638 indexed components whose operands obey these rules.
15642 If any of these conditions are violated, the aggregate will be built in
15643 a temporary (created either by the front-end or the code generator) and then
15644 that temporary will be copied onto the target.
15647 @node The Size of Discriminated Records with Default Discriminants
15648 @section The Size of Discriminated Records with Default Discriminants
15651 If a discriminated type @code{T} has discriminants with default values, it is
15652 possible to declare an object of this type without providing an explicit
15655 @smallexample @c ada
15657 type Size is range 1..100;
15659 type Rec (D : Size := 15) is record
15660 Name : String (1..D);
15668 Such an object is said to be @emph{unconstrained}.
15669 The discriminant of the object
15670 can be modified by a full assignment to the object, as long as it preserves the
15671 relation between the value of the discriminant, and the value of the components
15674 @smallexample @c ada
15676 Word := (3, "yes");
15678 Word := (5, "maybe");
15680 Word := (5, "no"); -- raises Constraint_Error
15685 In order to support this behavior efficiently, an unconstrained object is
15686 given the maximum size that any value of the type requires. In the case
15687 above, @code{Word} has storage for the discriminant and for
15688 a @code{String} of length 100.
15689 It is important to note that unconstrained objects do not require dynamic
15690 allocation. It would be an improper implementation to place on the heap those
15691 components whose size depends on discriminants. (This improper implementation
15692 was used by some Ada83 compilers, where the @code{Name} component above
15694 been stored as a pointer to a dynamic string). Following the principle that
15695 dynamic storage management should never be introduced implicitly,
15696 an Ada compiler should reserve the full size for an unconstrained declared
15697 object, and place it on the stack.
15699 This maximum size approach
15700 has been a source of surprise to some users, who expect the default
15701 values of the discriminants to determine the size reserved for an
15702 unconstrained object: ``If the default is 15, why should the object occupy
15704 The answer, of course, is that the discriminant may be later modified,
15705 and its full range of values must be taken into account. This is why the
15710 type Rec (D : Positive := 15) is record
15711 Name : String (1..D);
15719 is flagged by the compiler with a warning:
15720 an attempt to create @code{Too_Large} will raise @code{Storage_Error},
15721 because the required size includes @code{Positive'Last}
15722 bytes. As the first example indicates, the proper approach is to declare an
15723 index type of ``reasonable'' range so that unconstrained objects are not too
15726 One final wrinkle: if the object is declared to be @code{aliased}, or if it is
15727 created in the heap by means of an allocator, then it is @emph{not}
15729 it is constrained by the default values of the discriminants, and those values
15730 cannot be modified by full assignment. This is because in the presence of
15731 aliasing all views of the object (which may be manipulated by different tasks,
15732 say) must be consistent, so it is imperative that the object, once created,
15735 @node Strict Conformance to the Ada Reference Manual
15736 @section Strict Conformance to the Ada Reference Manual
15739 The dynamic semantics defined by the Ada Reference Manual impose a set of
15740 run-time checks to be generated. By default, the GNAT compiler will insert many
15741 run-time checks into the compiled code, including most of those required by the
15742 Ada Reference Manual. However, there are three checks that are not enabled
15743 in the default mode for efficiency reasons: arithmetic overflow checking for
15744 integer operations (including division by zero), checks for access before
15745 elaboration on subprogram calls, and stack overflow checking (most operating
15746 systems do not perform this check by default).
15748 Strict conformance to the Ada Reference Manual can be achieved by adding
15749 three compiler options for overflow checking for integer operations
15750 (@option{-gnato}), dynamic checks for access-before-elaboration on subprogram
15751 calls and generic instantiations (@option{-gnatE}), and stack overflow
15752 checking (@option{-fstack-check}).
15754 Note that the result of a floating point arithmetic operation in overflow and
15755 invalid situations, when the @code{Machine_Overflows} attribute of the result
15756 type is @code{False}, is to generate IEEE NaN and infinite values. This is the
15757 case for machines compliant with the IEEE floating-point standard, but on
15758 machines that are not fully compliant with this standard, such as Alpha, the
15759 @option{-mieee} compiler flag must be used for achieving IEEE confirming
15760 behavior (although at the cost of a significant performance penalty), so
15761 infinite and and NaN values are properly generated.
15764 @node Project File Reference
15765 @chapter Project File Reference
15768 This chapter describes the syntax and semantics of project files.
15769 Project files specify the options to be used when building a system.
15770 Project files can specify global settings for all tools,
15771 as well as tool-specific settings.
15772 @xref{Examples of Project Files,,, gnat_ugn, @value{EDITION} User's Guide},
15773 for examples of use.
15777 * Lexical Elements::
15779 * Empty declarations::
15780 * Typed string declarations::
15784 * Project Attributes::
15785 * Attribute References::
15786 * External Values::
15787 * Case Construction::
15789 * Package Renamings::
15791 * Project Extensions::
15792 * Project File Elaboration::
15795 @node Reserved Words
15796 @section Reserved Words
15799 All Ada reserved words are reserved in project files, and cannot be used
15800 as variable names or project names. In addition, the following are
15801 also reserved in project files:
15804 @item @code{extends}
15806 @item @code{external}
15808 @item @code{project}
15812 @node Lexical Elements
15813 @section Lexical Elements
15816 Rules for identifiers are the same as in Ada. Identifiers
15817 are case-insensitive. Strings are case sensitive, except where noted.
15818 Comments have the same form as in Ada.
15828 simple_name @{. simple_name@}
15832 @section Declarations
15835 Declarations introduce new entities that denote types, variables, attributes,
15836 and packages. Some declarations can only appear immediately within a project
15837 declaration. Others can appear within a project or within a package.
15841 declarative_item ::=
15842 simple_declarative_item |
15843 typed_string_declaration |
15844 package_declaration
15846 simple_declarative_item ::=
15847 variable_declaration |
15848 typed_variable_declaration |
15849 attribute_declaration |
15850 case_construction |
15854 @node Empty declarations
15855 @section Empty declarations
15858 empty_declaration ::=
15862 An empty declaration is allowed anywhere a declaration is allowed.
15865 @node Typed string declarations
15866 @section Typed string declarations
15869 Typed strings are sequences of string literals. Typed strings are the only
15870 named types in project files. They are used in case constructions, where they
15871 provide support for conditional attribute definitions.
15875 typed_string_declaration ::=
15876 @b{type} <typed_string_>_simple_name @b{is}
15877 ( string_literal @{, string_literal@} );
15881 A typed string declaration can only appear immediately within a project
15884 All the string literals in a typed string declaration must be distinct.
15890 Variables denote values, and appear as constituents of expressions.
15893 typed_variable_declaration ::=
15894 <typed_variable_>simple_name : <typed_string_>name := string_expression ;
15896 variable_declaration ::=
15897 <variable_>simple_name := expression;
15901 The elaboration of a variable declaration introduces the variable and
15902 assigns to it the value of the expression. The name of the variable is
15903 available after the assignment symbol.
15906 A typed_variable can only be declare once.
15909 a non-typed variable can be declared multiple times.
15912 Before the completion of its first declaration, the value of variable
15913 is the null string.
15916 @section Expressions
15919 An expression is a formula that defines a computation or retrieval of a value.
15920 In a project file the value of an expression is either a string or a list
15921 of strings. A string value in an expression is either a literal, the current
15922 value of a variable, an external value, an attribute reference, or a
15923 concatenation operation.
15936 attribute_reference
15942 ( <string_>expression @{ , <string_>expression @} )
15945 @subsection Concatenation
15947 The following concatenation functions are defined:
15949 @smallexample @c ada
15950 function "&" (X : String; Y : String) return String;
15951 function "&" (X : String_List; Y : String) return String_List;
15952 function "&" (X : String_List; Y : String_List) return String_List;
15956 @section Attributes
15959 An attribute declaration defines a property of a project or package. This
15960 property can later be queried by means of an attribute reference.
15961 Attribute values are strings or string lists.
15963 Some attributes are associative arrays. These attributes are mappings whose
15964 domain is a set of strings. These attributes are declared one association
15965 at a time, by specifying a point in the domain and the corresponding image
15966 of the attribute. They may also be declared as a full associative array,
15967 getting the same associations as the corresponding attribute in an imported
15968 or extended project.
15970 Attributes that are not associative arrays are called simple attributes.
15974 attribute_declaration ::=
15975 full_associative_array_declaration |
15976 @b{for} attribute_designator @b{use} expression ;
15978 full_associative_array_declaration ::=
15979 @b{for} <associative_array_attribute_>simple_name @b{use}
15980 <project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
15982 attribute_designator ::=
15983 <simple_attribute_>simple_name |
15984 <associative_array_attribute_>simple_name ( string_literal )
15988 Some attributes are project-specific, and can only appear immediately within
15989 a project declaration. Others are package-specific, and can only appear within
15990 the proper package.
15992 The expression in an attribute definition must be a string or a string_list.
15993 The string literal appearing in the attribute_designator of an associative
15994 array attribute is case-insensitive.
15996 @node Project Attributes
15997 @section Project Attributes
16000 The following attributes apply to a project. All of them are simple
16005 Expression must be a path name. The attribute defines the
16006 directory in which the object files created by the build are to be placed. If
16007 not specified, object files are placed in the project directory.
16010 Expression must be a path name. The attribute defines the
16011 directory in which the executables created by the build are to be placed.
16012 If not specified, executables are placed in the object directory.
16015 Expression must be a list of path names. The attribute
16016 defines the directories in which the source files for the project are to be
16017 found. If not specified, source files are found in the project directory.
16018 If a string in the list ends with "/**", then the directory that precedes
16019 "/**" and all of its subdirectories (recursively) are included in the list
16020 of source directories.
16022 @item Excluded_Source_Dirs
16023 Expression must be a list of strings. Each entry designates a directory that
16024 is not to be included in the list of source directories of the project.
16025 This is normally used when there are strings ending with "/**" in the value
16026 of attribute Source_Dirs.
16029 Expression must be a list of file names. The attribute
16030 defines the individual files, in the project directory, which are to be used
16031 as sources for the project. File names are path_names that contain no directory
16032 information. If the project has no sources the attribute must be declared
16033 explicitly with an empty list.
16035 @item Excluded_Source_Files (Locally_Removed_Files)
16036 Expression must be a list of strings that are legal file names.
16037 Each file name must designate a source that would normally be a source file
16038 in the source directories of the project or, if the project file is an
16039 extending project file, inherited by the current project file. It cannot
16040 designate an immediate source that is not inherited. Each of the source files
16041 in the list are not considered to be sources of the project file: they are not
16042 inherited. Attribute Locally_Removed_Files is obsolescent, attribute
16043 Excluded_Source_Files is preferred.
16045 @item Source_List_File
16046 Expression must a single path name. The attribute
16047 defines a text file that contains a list of source file names to be used
16048 as sources for the project
16051 Expression must be a path name. The attribute defines the
16052 directory in which a library is to be built. The directory must exist, must
16053 be distinct from the project's object directory, and must be writable.
16056 Expression must be a string that is a legal file name,
16057 without extension. The attribute defines a string that is used to generate
16058 the name of the library to be built by the project.
16061 Argument must be a string value that must be one of the
16062 following @code{"static"}, @code{"dynamic"} or @code{"relocatable"}. This
16063 string is case-insensitive. If this attribute is not specified, the library is
16064 a static library. Otherwise, the library may be dynamic or relocatable. This
16065 distinction is operating-system dependent.
16067 @item Library_Version
16068 Expression must be a string value whose interpretation
16069 is platform dependent. On UNIX, it is used only for dynamic/relocatable
16070 libraries as the internal name of the library (the @code{"soname"}). If the
16071 library file name (built from the @code{Library_Name}) is different from the
16072 @code{Library_Version}, then the library file will be a symbolic link to the
16073 actual file whose name will be @code{Library_Version}.
16075 @item Library_Interface
16076 Expression must be a string list. Each element of the string list
16077 must designate a unit of the project.
16078 If this attribute is present in a Library Project File, then the project
16079 file is a Stand-alone Library_Project_File.
16081 @item Library_Auto_Init
16082 Expression must be a single string "true" or "false", case-insensitive.
16083 If this attribute is present in a Stand-alone Library Project File,
16084 it indicates if initialization is automatic when the dynamic library
16087 @item Library_Options
16088 Expression must be a string list. Indicates additional switches that
16089 are to be used when building a shared library.
16092 Expression must be a single string. Designates an alternative to "gcc"
16093 for building shared libraries.
16095 @item Library_Src_Dir
16096 Expression must be a path name. The attribute defines the
16097 directory in which the sources of the interfaces of a Stand-alone Library will
16098 be copied. The directory must exist, must be distinct from the project's
16099 object directory and source directories of all projects in the project tree,
16100 and must be writable.
16102 @item Library_Src_Dir
16103 Expression must be a path name. The attribute defines the
16104 directory in which the ALI files of a Library will
16105 be copied. The directory must exist, must be distinct from the project's
16106 object directory and source directories of all projects in the project tree,
16107 and must be writable.
16109 @item Library_Symbol_File
16110 Expression must be a single string. Its value is the single file name of a
16111 symbol file to be created when building a stand-alone library when the
16112 symbol policy is either "compliant", "controlled" or "restricted",
16113 on platforms that support symbol control, such as VMS. When symbol policy
16114 is "direct", then a file with this name must exist in the object directory.
16116 @item Library_Reference_Symbol_File
16117 Expression must be a single string. Its value is the path name of a
16118 reference symbol file that is read when the symbol policy is either
16119 "compliant" or "controlled", on platforms that support symbol control,
16120 such as VMS, when building a stand-alone library. The path may be an absolute
16121 path or a path relative to the project directory.
16123 @item Library_Symbol_Policy
16124 Expression must be a single string. Its case-insensitive value can only be
16125 "autonomous", "default", "compliant", "controlled", "restricted" or "direct".
16127 This attribute is not taken into account on all platforms. It controls the
16128 policy for exported symbols and, on some platforms (like VMS) that have the
16129 notions of major and minor IDs built in the library files, it controls
16130 the setting of these IDs.
16132 "autonomous" or "default": exported symbols are not controlled.
16134 "compliant": if attribute Library_Reference_Symbol_File is not defined, then
16135 it is equivalent to policy "autonomous". If there are exported symbols in
16136 the reference symbol file that are not in the object files of the interfaces,
16137 the major ID of the library is increased. If there are symbols in the
16138 object files of the interfaces that are not in the reference symbol file,
16139 these symbols are put at the end of the list in the newly created symbol file
16140 and the minor ID is increased.
16142 "controlled": the attribute Library_Reference_Symbol_File must be defined.
16143 The library will fail to build if the exported symbols in the object files of
16144 the interfaces do not match exactly the symbol in the symbol file.
16146 "restricted": The attribute Library_Symbol_File must be defined. The library
16147 will fail to build if there are symbols in the symbol file that are not in
16148 the exported symbols of the object files of the interfaces. Additional symbols
16149 in the object files are not added to the symbol file.
16151 "direct": The attribute Library_Symbol_File must be defined and must designate
16152 an existing file in the object directory. This symbol file is passed directly
16153 to the underlying linker without any symbol processing.
16156 Expression must be a list of strings that are legal file names.
16157 These file names designate existing compilation units in the source directory
16158 that are legal main subprograms.
16160 When a project file is elaborated, as part of the execution of a gnatmake
16161 command, one or several executables are built and placed in the Exec_Dir.
16162 If the gnatmake command does not include explicit file names, the executables
16163 that are built correspond to the files specified by this attribute.
16165 @item Externally_Built
16166 Expression must be a single string. Its value must be either "true" of "false",
16167 case-insensitive. The default is "false". When the value of this attribute is
16168 "true", no attempt is made to compile the sources or to build the library,
16169 when the project is a library project.
16171 @item Main_Language
16172 This is a simple attribute. Its value is a string that specifies the
16173 language of the main program.
16176 Expression must be a string list. Each string designates
16177 a programming language that is known to GNAT. The strings are case-insensitive.
16181 @node Attribute References
16182 @section Attribute References
16185 Attribute references are used to retrieve the value of previously defined
16186 attribute for a package or project.
16189 attribute_reference ::=
16190 attribute_prefix ' <simple_attribute_>simple_name [ ( string_literal ) ]
16192 attribute_prefix ::=
16194 <project_simple_name | package_identifier |
16195 <project_>simple_name . package_identifier
16199 If an attribute has not been specified for a given package or project, its
16200 value is the null string or the empty list.
16202 @node External Values
16203 @section External Values
16206 An external value is an expression whose value is obtained from the command
16207 that invoked the processing of the current project file (typically a
16213 @b{external} ( string_literal [, string_literal] )
16217 The first string_literal is the string to be used on the command line or
16218 in the environment to specify the external value. The second string_literal,
16219 if present, is the default to use if there is no specification for this
16220 external value either on the command line or in the environment.
16222 @node Case Construction
16223 @section Case Construction
16226 A case construction supports attribute and variable declarations that depend
16227 on the value of a previously declared variable.
16231 case_construction ::=
16232 @b{case} <typed_variable_>name @b{is}
16237 @b{when} discrete_choice_list =>
16238 @{case_construction |
16239 attribute_declaration |
16240 variable_declaration |
16241 empty_declaration@}
16243 discrete_choice_list ::=
16244 string_literal @{| string_literal@} |
16249 Inside a case construction, variable declarations must be for variables that
16250 have already been declared before the case construction.
16252 All choices in a choice list must be distinct. The choice lists of two
16253 distinct alternatives must be disjoint. Unlike Ada, the choice lists of all
16254 alternatives do not need to include all values of the type. An @code{others}
16255 choice must appear last in the list of alternatives.
16261 A package provides a grouping of variable declarations and attribute
16262 declarations to be used when invoking various GNAT tools. The name of
16263 the package indicates the tool(s) to which it applies.
16267 package_declaration ::=
16268 package_spec | package_renaming
16271 @b{package} package_identifier @b{is}
16272 @{simple_declarative_item@}
16273 @b{end} package_identifier ;
16275 package_identifier ::=
16276 @code{Naming} | @code{Builder} | @code{Compiler} | @code{Binder} |
16277 @code{Linker} | @code{Finder} | @code{Cross_Reference} |
16278 @code{gnatls} | @code{IDE} | @code{Pretty_Printer}
16281 @subsection Package Naming
16284 The attributes of a @code{Naming} package specifies the naming conventions
16285 that apply to the source files in a project. When invoking other GNAT tools,
16286 they will use the sources in the source directories that satisfy these
16287 naming conventions.
16289 The following attributes apply to a @code{Naming} package:
16293 This is a simple attribute whose value is a string. Legal values of this
16294 string are @code{"lowercase"}, @code{"uppercase"} or @code{"mixedcase"}.
16295 These strings are themselves case insensitive.
16298 If @code{Casing} is not specified, then the default is @code{"lowercase"}.
16300 @item Dot_Replacement
16301 This is a simple attribute whose string value satisfies the following
16305 @item It must not be empty
16306 @item It cannot start or end with an alphanumeric character
16307 @item It cannot be a single underscore
16308 @item It cannot start with an underscore followed by an alphanumeric
16309 @item It cannot contain a dot @code{'.'} if longer than one character
16313 If @code{Dot_Replacement} is not specified, then the default is @code{"-"}.
16316 This is an associative array attribute, defined on language names,
16317 whose image is a string that must satisfy the following
16321 @item It must not be empty
16322 @item It cannot start with an alphanumeric character
16323 @item It cannot start with an underscore followed by an alphanumeric character
16327 For Ada, the attribute denotes the suffix used in file names that contain
16328 library unit declarations, that is to say units that are package and
16329 subprogram declarations. If @code{Spec_Suffix ("Ada")} is not
16330 specified, then the default is @code{".ads"}.
16332 For C and C++, the attribute denotes the suffix used in file names that
16333 contain prototypes.
16336 This is an associative array attribute defined on language names,
16337 whose image is a string that must satisfy the following
16341 @item It must not be empty
16342 @item It cannot start with an alphanumeric character
16343 @item It cannot start with an underscore followed by an alphanumeric character
16344 @item It cannot be a suffix of @code{Spec_Suffix}
16348 For Ada, the attribute denotes the suffix used in file names that contain
16349 library bodies, that is to say units that are package and subprogram bodies.
16350 If @code{Body_Suffix ("Ada")} is not specified, then the default is
16353 For C and C++, the attribute denotes the suffix used in file names that contain
16356 @item Separate_Suffix
16357 This is a simple attribute whose value satisfies the same conditions as
16358 @code{Body_Suffix}.
16360 This attribute is specific to Ada. It denotes the suffix used in file names
16361 that contain separate bodies. If it is not specified, then it defaults to same
16362 value as @code{Body_Suffix ("Ada")}.
16365 This is an associative array attribute, specific to Ada, defined over
16366 compilation unit names. The image is a string that is the name of the file
16367 that contains that library unit. The file name is case sensitive if the
16368 conventions of the host operating system require it.
16371 This is an associative array attribute, specific to Ada, defined over
16372 compilation unit names. The image is a string that is the name of the file
16373 that contains the library unit body for the named unit. The file name is case
16374 sensitive if the conventions of the host operating system require it.
16376 @item Specification_Exceptions
16377 This is an associative array attribute defined on language names,
16378 whose value is a list of strings.
16380 This attribute is not significant for Ada.
16382 For C and C++, each string in the list denotes the name of a file that
16383 contains prototypes, but whose suffix is not necessarily the
16384 @code{Spec_Suffix} for the language.
16386 @item Implementation_Exceptions
16387 This is an associative array attribute defined on language names,
16388 whose value is a list of strings.
16390 This attribute is not significant for Ada.
16392 For C and C++, each string in the list denotes the name of a file that
16393 contains source code, but whose suffix is not necessarily the
16394 @code{Body_Suffix} for the language.
16397 The following attributes of package @code{Naming} are obsolescent. They are
16398 kept as synonyms of other attributes for compatibility with previous versions
16399 of the Project Manager.
16402 @item Specification_Suffix
16403 This is a synonym of @code{Spec_Suffix}.
16405 @item Implementation_Suffix
16406 This is a synonym of @code{Body_Suffix}.
16408 @item Specification
16409 This is a synonym of @code{Spec}.
16411 @item Implementation
16412 This is a synonym of @code{Body}.
16415 @subsection package Compiler
16418 The attributes of the @code{Compiler} package specify the compilation options
16419 to be used by the underlying compiler.
16422 @item Default_Switches
16423 This is an associative array attribute. Its
16424 domain is a set of language names. Its range is a string list that
16425 specifies the compilation options to be used when compiling a component
16426 written in that language, for which no file-specific switches have been
16430 This is an associative array attribute. Its domain is
16431 a set of file names. Its range is a string list that specifies the
16432 compilation options to be used when compiling the named file. If a file
16433 is not specified in the Switches attribute, it is compiled with the
16434 options specified by Default_Switches of its language, if defined.
16436 @item Local_Configuration_Pragmas.
16437 This is a simple attribute, whose
16438 value is a path name that designates a file containing configuration pragmas
16439 to be used for all invocations of the compiler for immediate sources of the
16443 @subsection package Builder
16446 The attributes of package @code{Builder} specify the compilation, binding, and
16447 linking options to be used when building an executable for a project. The
16448 following attributes apply to package @code{Builder}:
16451 @item Default_Switches
16452 This is an associative array attribute. Its
16453 domain is a set of language names. Its range is a string list that
16454 specifies options to be used when building a main
16455 written in that language, for which no file-specific switches have been
16459 This is an associative array attribute. Its domain is
16460 a set of file names. Its range is a string list that specifies
16461 options to be used when building the named main file. If a main file
16462 is not specified in the Switches attribute, it is built with the
16463 options specified by Default_Switches of its language, if defined.
16465 @item Global_Configuration_Pragmas
16466 This is a simple attribute, whose
16467 value is a path name that designates a file that contains configuration pragmas
16468 to be used in every build of an executable. If both local and global
16469 configuration pragmas are specified, a compilation makes use of both sets.
16473 This is an associative array attribute. Its domain is
16474 a set of main source file names. Its range is a simple string that specifies
16475 the executable file name to be used when linking the specified main source.
16476 If a main source is not specified in the Executable attribute, the executable
16477 file name is deducted from the main source file name.
16478 This attribute has no effect if its value is the empty string.
16480 @item Executable_Suffix
16481 This is a simple attribute whose value is the suffix to be added to
16482 the executables that don't have an attribute Executable specified.
16485 @subsection package Gnatls
16488 The attributes of package @code{Gnatls} specify the tool options to be used
16489 when invoking the library browser @command{gnatls}.
16490 The following attributes apply to package @code{Gnatls}:
16494 This is a single attribute with a string list value. Each nonempty string
16495 in the list is an option when invoking @code{gnatls}.
16498 @subsection package Binder
16501 The attributes of package @code{Binder} specify the options to be used
16502 when invoking the binder in the construction of an executable.
16503 The following attributes apply to package @code{Binder}:
16506 @item Default_Switches
16507 This is an associative array attribute. Its
16508 domain is a set of language names. Its range is a string list that
16509 specifies options to be used when binding a main
16510 written in that language, for which no file-specific switches have been
16514 This is an associative array attribute. Its domain is
16515 a set of file names. Its range is a string list that specifies
16516 options to be used when binding the named main file. If a main file
16517 is not specified in the Switches attribute, it is bound with the
16518 options specified by Default_Switches of its language, if defined.
16521 @subsection package Linker
16524 The attributes of package @code{Linker} specify the options to be used when
16525 invoking the linker in the construction of an executable.
16526 The following attributes apply to package @code{Linker}:
16529 @item Default_Switches
16530 This is an associative array attribute. Its
16531 domain is a set of language names. Its range is a string list that
16532 specifies options to be used when linking a main
16533 written in that language, for which no file-specific switches have been
16537 This is an associative array attribute. Its domain is
16538 a set of file names. Its range is a string list that specifies
16539 options to be used when linking the named main file. If a main file
16540 is not specified in the Switches attribute, it is linked with the
16541 options specified by Default_Switches of its language, if defined.
16543 @item Linker_Options
16544 This is a string list attribute. Its value specifies additional options that
16545 be given to the linker when linking an executable. This attribute is not
16546 used in the main project, only in projects imported directly or indirectly.
16550 @subsection package Cross_Reference
16553 The attributes of package @code{Cross_Reference} specify the tool options
16555 when invoking the library tool @command{gnatxref}.
16556 The following attributes apply to package @code{Cross_Reference}:
16559 @item Default_Switches
16560 This is an associative array attribute. Its
16561 domain is a set of language names. Its range is a string list that
16562 specifies options to be used when calling @command{gnatxref} on a source
16563 written in that language, for which no file-specific switches have been
16567 This is an associative array attribute. Its domain is
16568 a set of file names. Its range is a string list that specifies
16569 options to be used when calling @command{gnatxref} on the named main source.
16570 If a source is not specified in the Switches attribute, @command{gnatxref} will
16571 be called with the options specified by Default_Switches of its language,
16575 @subsection package Finder
16578 The attributes of package @code{Finder} specify the tool options to be used
16579 when invoking the search tool @command{gnatfind}.
16580 The following attributes apply to package @code{Finder}:
16583 @item Default_Switches
16584 This is an associative array attribute. Its
16585 domain is a set of language names. Its range is a string list that
16586 specifies options to be used when calling @command{gnatfind} on a source
16587 written in that language, for which no file-specific switches have been
16591 This is an associative array attribute. Its domain is
16592 a set of file names. Its range is a string list that specifies
16593 options to be used when calling @command{gnatfind} on the named main source.
16594 If a source is not specified in the Switches attribute, @command{gnatfind} will
16595 be called with the options specified by Default_Switches of its language,
16599 @subsection package Pretty_Printer
16602 The attributes of package @code{Pretty_Printer}
16603 specify the tool options to be used
16604 when invoking the formatting tool @command{gnatpp}.
16605 The following attributes apply to package @code{Pretty_Printer}:
16608 @item Default_switches
16609 This is an associative array attribute. Its
16610 domain is a set of language names. Its range is a string list that
16611 specifies options to be used when calling @command{gnatpp} on a source
16612 written in that language, for which no file-specific switches have been
16616 This is an associative array attribute. Its domain is
16617 a set of file names. Its range is a string list that specifies
16618 options to be used when calling @command{gnatpp} on the named main source.
16619 If a source is not specified in the Switches attribute, @command{gnatpp} will
16620 be called with the options specified by Default_Switches of its language,
16624 @subsection package gnatstub
16627 The attributes of package @code{gnatstub}
16628 specify the tool options to be used
16629 when invoking the tool @command{gnatstub}.
16630 The following attributes apply to package @code{gnatstub}:
16633 @item Default_switches
16634 This is an associative array attribute. Its
16635 domain is a set of language names. Its range is a string list that
16636 specifies options to be used when calling @command{gnatstub} on a source
16637 written in that language, for which no file-specific switches have been
16641 This is an associative array attribute. Its domain is
16642 a set of file names. Its range is a string list that specifies
16643 options to be used when calling @command{gnatstub} on the named main source.
16644 If a source is not specified in the Switches attribute, @command{gnatpp} will
16645 be called with the options specified by Default_Switches of its language,
16649 @subsection package Eliminate
16652 The attributes of package @code{Eliminate}
16653 specify the tool options to be used
16654 when invoking the tool @command{gnatelim}.
16655 The following attributes apply to package @code{Eliminate}:
16658 @item Default_switches
16659 This is an associative array attribute. Its
16660 domain is a set of language names. Its range is a string list that
16661 specifies options to be used when calling @command{gnatelim} on a source
16662 written in that language, for which no file-specific switches have been
16666 This is an associative array attribute. Its domain is
16667 a set of file names. Its range is a string list that specifies
16668 options to be used when calling @command{gnatelim} on the named main source.
16669 If a source is not specified in the Switches attribute, @command{gnatelim} will
16670 be called with the options specified by Default_Switches of its language,
16674 @subsection package Metrics
16677 The attributes of package @code{Metrics}
16678 specify the tool options to be used
16679 when invoking the tool @command{gnatmetric}.
16680 The following attributes apply to package @code{Metrics}:
16683 @item Default_switches
16684 This is an associative array attribute. Its
16685 domain is a set of language names. Its range is a string list that
16686 specifies options to be used when calling @command{gnatmetric} on a source
16687 written in that language, for which no file-specific switches have been
16691 This is an associative array attribute. Its domain is
16692 a set of file names. Its range is a string list that specifies
16693 options to be used when calling @command{gnatmetric} on the named main source.
16694 If a source is not specified in the Switches attribute, @command{gnatmetric}
16695 will be called with the options specified by Default_Switches of its language,
16699 @subsection package IDE
16702 The attributes of package @code{IDE} specify the options to be used when using
16703 an Integrated Development Environment such as @command{GPS}.
16707 This is a simple attribute. Its value is a string that designates the remote
16708 host in a cross-compilation environment, to be used for remote compilation and
16709 debugging. This field should not be specified when running on the local
16713 This is a simple attribute. Its value is a string that specifies the
16714 name of IP address of the embedded target in a cross-compilation environment,
16715 on which the program should execute.
16717 @item Communication_Protocol
16718 This is a simple string attribute. Its value is the name of the protocol
16719 to use to communicate with the target in a cross-compilation environment,
16720 e.g.@: @code{"wtx"} or @code{"vxworks"}.
16722 @item Compiler_Command
16723 This is an associative array attribute, whose domain is a language name. Its
16724 value is string that denotes the command to be used to invoke the compiler.
16725 The value of @code{Compiler_Command ("Ada")} is expected to be compatible with
16726 gnatmake, in particular in the handling of switches.
16728 @item Debugger_Command
16729 This is simple attribute, Its value is a string that specifies the name of
16730 the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
16732 @item Default_Switches
16733 This is an associative array attribute. Its indexes are the name of the
16734 external tools that the GNAT Programming System (GPS) is supporting. Its
16735 value is a list of switches to use when invoking that tool.
16738 This is a simple attribute. Its value is a string that specifies the name
16739 of the @command{gnatls} utility to be used to retrieve information about the
16740 predefined path; e.g., @code{"gnatls"}, @code{"powerpc-wrs-vxworks-gnatls"}.
16743 This is a simple attribute. Its value is a string used to specify the
16744 Version Control System (VCS) to be used for this project, e.g.@: CVS, RCS
16745 ClearCase or Perforce.
16747 @item VCS_File_Check
16748 This is a simple attribute. Its value is a string that specifies the
16749 command used by the VCS to check the validity of a file, either
16750 when the user explicitly asks for a check, or as a sanity check before
16751 doing the check-in.
16753 @item VCS_Log_Check
16754 This is a simple attribute. Its value is a string that specifies
16755 the command used by the VCS to check the validity of a log file.
16757 @item VCS_Repository_Root
16758 The VCS repository root path. This is used to create tags or branches
16759 of the repository. For subversion the value should be the @code{URL}
16760 as specified to check-out the working copy of the repository.
16762 @item VCS_Patch_Root
16763 The local root directory to use for building patch file. All patch chunks
16764 will be relative to this path. The root project directory is used if
16765 this value is not defined.
16769 @node Package Renamings
16770 @section Package Renamings
16773 A package can be defined by a renaming declaration. The new package renames
16774 a package declared in a different project file, and has the same attributes
16775 as the package it renames.
16778 package_renaming ::==
16779 @b{package} package_identifier @b{renames}
16780 <project_>simple_name.package_identifier ;
16784 The package_identifier of the renamed package must be the same as the
16785 package_identifier. The project whose name is the prefix of the renamed
16786 package must contain a package declaration with this name. This project
16787 must appear in the context_clause of the enclosing project declaration,
16788 or be the parent project of the enclosing child project.
16794 A project file specifies a set of rules for constructing a software system.
16795 A project file can be self-contained, or depend on other project files.
16796 Dependencies are expressed through a context clause that names other projects.
16802 context_clause project_declaration
16804 project_declaration ::=
16805 simple_project_declaration | project_extension
16807 simple_project_declaration ::=
16808 @b{project} <project_>simple_name @b{is}
16809 @{declarative_item@}
16810 @b{end} <project_>simple_name;
16816 [@b{limited}] @b{with} path_name @{ , path_name @} ;
16823 A path name denotes a project file. A path name can be absolute or relative.
16824 An absolute path name includes a sequence of directories, in the syntax of
16825 the host operating system, that identifies uniquely the project file in the
16826 file system. A relative path name identifies the project file, relative
16827 to the directory that contains the current project, or relative to a
16828 directory listed in the environment variable ADA_PROJECT_PATH.
16829 Path names are case sensitive if file names in the host operating system
16830 are case sensitive.
16832 The syntax of the environment variable ADA_PROJECT_PATH is a list of
16833 directory names separated by colons (semicolons on Windows).
16835 A given project name can appear only once in a context_clause.
16837 It is illegal for a project imported by a context clause to refer, directly
16838 or indirectly, to the project in which this context clause appears (the
16839 dependency graph cannot contain cycles), except when one of the with_clause
16840 in the cycle is a @code{limited with}.
16842 @node Project Extensions
16843 @section Project Extensions
16846 A project extension introduces a new project, which inherits the declarations
16847 of another project.
16851 project_extension ::=
16852 @b{project} <project_>simple_name @b{extends} path_name @b{is}
16853 @{declarative_item@}
16854 @b{end} <project_>simple_name;
16858 The project extension declares a child project. The child project inherits
16859 all the declarations and all the files of the parent project, These inherited
16860 declaration can be overridden in the child project, by means of suitable
16863 @node Project File Elaboration
16864 @section Project File Elaboration
16867 A project file is processed as part of the invocation of a gnat tool that
16868 uses the project option. Elaboration of the process file consists in the
16869 sequential elaboration of all its declarations. The computed values of
16870 attributes and variables in the project are then used to establish the
16871 environment in which the gnat tool will execute.
16873 @node Obsolescent Features
16874 @chapter Obsolescent Features
16877 This chapter describes features that are provided by GNAT, but are
16878 considered obsolescent since there are preferred ways of achieving
16879 the same effect. These features are provided solely for historical
16880 compatibility purposes.
16883 * pragma No_Run_Time::
16884 * pragma Ravenscar::
16885 * pragma Restricted_Run_Time::
16888 @node pragma No_Run_Time
16889 @section pragma No_Run_Time
16891 The pragma @code{No_Run_Time} is used to achieve an affect similar
16892 to the use of the "Zero Foot Print" configurable run time, but without
16893 requiring a specially configured run time. The result of using this
16894 pragma, which must be used for all units in a partition, is to restrict
16895 the use of any language features requiring run-time support code. The
16896 preferred usage is to use an appropriately configured run-time that
16897 includes just those features that are to be made accessible.
16899 @node pragma Ravenscar
16900 @section pragma Ravenscar
16902 The pragma @code{Ravenscar} has exactly the same effect as pragma
16903 @code{Profile (Ravenscar)}. The latter usage is preferred since it
16904 is part of the new Ada 2005 standard.
16906 @node pragma Restricted_Run_Time
16907 @section pragma Restricted_Run_Time
16909 The pragma @code{Restricted_Run_Time} has exactly the same effect as
16910 pragma @code{Profile (Restricted)}. The latter usage is
16911 preferred since the Ada 2005 pragma @code{Profile} is intended for
16912 this kind of implementation dependent addition.
16915 @c GNU Free Documentation License
16917 @node Index,,GNU Free Documentation License, Top