1 \input texinfo @c -*-texinfo-*-
5 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
7 @c GNAT DOCUMENTATION o
11 @c Copyright (C) 1995-2008, Free Software Foundation o
14 @c GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). o
16 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
18 @setfilename gnat_rm.info
21 @set DEFAULTLANGUAGEVERSION Ada 2005
22 @set NONDEFAULTLANGUAGEVERSION Ada 95
24 @settitle GNAT Reference Manual
26 @setchapternewpage odd
29 @include gcc-common.texi
31 @dircategory GNU Ada tools
33 * GNAT Reference Manual: (gnat_rm). Reference Manual for GNU Ada tools.
37 Copyright @copyright{} 1995-2008, Free Software Foundation, Inc.
39 Permission is granted to copy, distribute and/or modify this document
40 under the terms of the GNU Free Documentation License, Version 1.2
41 or any later version published by the Free Software Foundation;
42 with the Invariant Sections being ``GNU Free Documentation License'',
43 with the Front-Cover Texts being ``GNAT Reference Manual'', and with
44 no Back-Cover Texts. A copy of the license is included in the section
45 entitled ``GNU Free Documentation License''.
49 @title GNAT Reference Manual
50 @subtitle GNAT, The GNU Ada Compiler
54 @vskip 0pt plus 1filll
61 @node Top, About This Guide, (dir), (dir)
62 @top GNAT Reference Manual
68 GNAT, The GNU Ada Compiler@*
69 GCC version @value{version-GCC}@*
76 * Implementation Defined Pragmas::
77 * Implementation Defined Attributes::
78 * Implementation Advice::
79 * Implementation Defined Characteristics::
80 * Intrinsic Subprograms::
81 * Representation Clauses and Pragmas::
82 * Standard Library Routines::
83 * The Implementation of Standard I/O::
85 * Interfacing to Other Languages::
86 * Specialized Needs Annexes::
87 * Implementation of Specific Ada Features::
88 * Project File Reference::
89 * Obsolescent Features::
90 * GNU Free Documentation License::
93 --- The Detailed Node Listing ---
97 * What This Reference Manual Contains::
98 * Related Information::
100 Implementation Defined Pragmas
102 * Pragma Abort_Defer::
110 * Pragma C_Pass_By_Copy::
112 * Pragma Check_Name::
113 * Pragma Check_Policy::
115 * Pragma Common_Object::
116 * Pragma Compile_Time_Error::
117 * Pragma Compile_Time_Warning::
118 * Pragma Complete_Representation::
119 * Pragma Complex_Representation::
120 * Pragma Component_Alignment::
121 * Pragma Convention_Identifier::
123 * Pragma CPP_Constructor::
124 * Pragma CPP_Virtual::
125 * Pragma CPP_Vtable::
127 * Pragma Debug_Policy::
128 * Pragma Detect_Blocking::
129 * Pragma Elaboration_Checks::
131 * Pragma Export_Exception::
132 * Pragma Export_Function::
133 * Pragma Export_Object::
134 * Pragma Export_Procedure::
135 * Pragma Export_Value::
136 * Pragma Export_Valued_Procedure::
137 * Pragma Extend_System::
139 * Pragma External_Name_Casing::
141 * Pragma Favor_Top_Level::
142 * Pragma Finalize_Storage_Only::
143 * Pragma Float_Representation::
145 * Pragma Implemented_By_Entry::
146 * Pragma Implicit_Packing::
147 * Pragma Import_Exception::
148 * Pragma Import_Function::
149 * Pragma Import_Object::
150 * Pragma Import_Procedure::
151 * Pragma Import_Valued_Procedure::
152 * Pragma Initialize_Scalars::
153 * Pragma Inline_Always::
154 * Pragma Inline_Generic::
156 * Pragma Interface_Name::
157 * Pragma Interrupt_Handler::
158 * Pragma Interrupt_State::
159 * Pragma Keep_Names::
162 * Pragma Linker_Alias::
163 * Pragma Linker_Constructor::
164 * Pragma Linker_Destructor::
165 * Pragma Linker_Section::
166 * Pragma Long_Float::
167 * Pragma Machine_Attribute::
169 * Pragma Main_Storage::
172 * Pragma No_Strict_Aliasing ::
173 * Pragma Normalize_Scalars::
174 * Pragma Obsolescent::
175 * Pragma Optimize_Alignment::
177 * Pragma Persistent_BSS::
179 * Pragma Postcondition::
180 * Pragma Precondition::
181 * Pragma Profile (Ravenscar)::
182 * Pragma Profile (Restricted)::
183 * Pragma Psect_Object::
184 * Pragma Pure_Function::
185 * Pragma Restriction_Warnings::
187 * Pragma Source_File_Name::
188 * Pragma Source_File_Name_Project::
189 * Pragma Source_Reference::
190 * Pragma Stream_Convert::
191 * Pragma Style_Checks::
194 * Pragma Suppress_All::
195 * Pragma Suppress_Exception_Locations::
196 * Pragma Suppress_Initialization::
199 * Pragma Task_Storage::
200 * Pragma Time_Slice::
202 * Pragma Unchecked_Union::
203 * Pragma Unimplemented_Unit::
204 * Pragma Universal_Aliasing ::
205 * Pragma Universal_Data::
206 * Pragma Unmodified::
207 * Pragma Unreferenced::
208 * Pragma Unreferenced_Objects::
209 * Pragma Unreserve_All_Interrupts::
210 * Pragma Unsuppress::
211 * Pragma Use_VADS_Size::
212 * Pragma Validity_Checks::
215 * Pragma Weak_External::
216 * Pragma Wide_Character_Encoding::
218 Implementation Defined Attributes
228 * Default_Bit_Order::
238 * Has_Access_Values::
239 * Has_Discriminants::
246 * Max_Interrupt_Priority::
248 * Maximum_Alignment::
253 * Passed_By_Reference::
266 * Unconstrained_Array::
267 * Universal_Literal_String::
268 * Unrestricted_Access::
274 The Implementation of Standard I/O
276 * Standard I/O Packages::
282 * Wide_Wide_Text_IO::
285 * Filenames encoding::
287 * Operations on C Streams::
288 * Interfacing to C Streams::
292 * Ada.Characters.Latin_9 (a-chlat9.ads)::
293 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
294 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
295 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
296 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
297 * Ada.Command_Line.Environment (a-colien.ads)::
298 * Ada.Command_Line.Remove (a-colire.ads)::
299 * Ada.Command_Line.Response_File (a-clrefi.ads)::
300 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
301 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
302 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
303 * Ada.Exceptions.Traceback (a-exctra.ads)::
304 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
305 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
306 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
307 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
308 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
309 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
310 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
311 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
312 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
313 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
314 * GNAT.Altivec (g-altive.ads)::
315 * GNAT.Altivec.Conversions (g-altcon.ads)::
316 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
317 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
318 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
319 * GNAT.Array_Split (g-arrspl.ads)::
320 * GNAT.AWK (g-awk.ads)::
321 * GNAT.Bounded_Buffers (g-boubuf.ads)::
322 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
323 * GNAT.Bubble_Sort (g-bubsor.ads)::
324 * GNAT.Bubble_Sort_A (g-busora.ads)::
325 * GNAT.Bubble_Sort_G (g-busorg.ads)::
326 * GNAT.Byte_Order_Mark (g-byorma.ads)::
327 * GNAT.Byte_Swapping (g-bytswa.ads)::
328 * GNAT.Calendar (g-calend.ads)::
329 * GNAT.Calendar.Time_IO (g-catiio.ads)::
330 * GNAT.Case_Util (g-casuti.ads)::
331 * GNAT.CGI (g-cgi.ads)::
332 * GNAT.CGI.Cookie (g-cgicoo.ads)::
333 * GNAT.CGI.Debug (g-cgideb.ads)::
334 * GNAT.Command_Line (g-comlin.ads)::
335 * GNAT.Compiler_Version (g-comver.ads)::
336 * GNAT.Ctrl_C (g-ctrl_c.ads)::
337 * GNAT.CRC32 (g-crc32.ads)::
338 * GNAT.Current_Exception (g-curexc.ads)::
339 * GNAT.Debug_Pools (g-debpoo.ads)::
340 * GNAT.Debug_Utilities (g-debuti.ads)::
341 * GNAT.Decode_String (g-decstr.ads)::
342 * GNAT.Decode_UTF8_String (g-deutst.ads)::
343 * GNAT.Directory_Operations (g-dirope.ads)::
344 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
345 * GNAT.Dynamic_HTables (g-dynhta.ads)::
346 * GNAT.Dynamic_Tables (g-dyntab.ads)::
347 * GNAT.Encode_String (g-encstr.ads)::
348 * GNAT.Encode_UTF8_String (g-enutst.ads)::
349 * GNAT.Exception_Actions (g-excact.ads)::
350 * GNAT.Exception_Traces (g-exctra.ads)::
351 * GNAT.Exceptions (g-except.ads)::
352 * GNAT.Expect (g-expect.ads)::
353 * GNAT.Float_Control (g-flocon.ads)::
354 * GNAT.Heap_Sort (g-heasor.ads)::
355 * GNAT.Heap_Sort_A (g-hesora.ads)::
356 * GNAT.Heap_Sort_G (g-hesorg.ads)::
357 * GNAT.HTable (g-htable.ads)::
358 * GNAT.IO (g-io.ads)::
359 * GNAT.IO_Aux (g-io_aux.ads)::
360 * GNAT.Lock_Files (g-locfil.ads)::
361 * GNAT.MD5 (g-md5.ads)::
362 * GNAT.Memory_Dump (g-memdum.ads)::
363 * GNAT.Most_Recent_Exception (g-moreex.ads)::
364 * GNAT.OS_Lib (g-os_lib.ads)::
365 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
366 * GNAT.Random_Numbers (g-rannum.ads)::
367 * GNAT.Regexp (g-regexp.ads)::
368 * GNAT.Registry (g-regist.ads)::
369 * GNAT.Regpat (g-regpat.ads)::
370 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
371 * GNAT.Semaphores (g-semaph.ads)::
372 * GNAT.Serial_Communications (g-sercom.ads)::
373 * GNAT.SHA1 (g-sha1.ads)::
374 * GNAT.Signals (g-signal.ads)::
375 * GNAT.Sockets (g-socket.ads)::
376 * GNAT.Source_Info (g-souinf.ads)::
377 * GNAT.Spelling_Checker (g-speche.ads)::
378 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
379 * GNAT.Spitbol.Patterns (g-spipat.ads)::
380 * GNAT.Spitbol (g-spitbo.ads)::
381 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
382 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
383 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
384 * GNAT.Strings (g-string.ads)::
385 * GNAT.String_Split (g-strspl.ads)::
386 * GNAT.Table (g-table.ads)::
387 * GNAT.Task_Lock (g-tasloc.ads)::
388 * GNAT.Threads (g-thread.ads)::
389 * GNAT.Time_Stamp (g-timsta.ads)::
390 * GNAT.Traceback (g-traceb.ads)::
391 * GNAT.Traceback.Symbolic (g-trasym.ads)::
392 * GNAT.UTF_32 (g-utf_32.ads)::
393 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
394 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
395 * GNAT.Wide_String_Split (g-wistsp.ads)::
396 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
397 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
398 * Interfaces.C.Extensions (i-cexten.ads)::
399 * Interfaces.C.Streams (i-cstrea.ads)::
400 * Interfaces.CPP (i-cpp.ads)::
401 * Interfaces.Packed_Decimal (i-pacdec.ads)::
402 * Interfaces.VxWorks (i-vxwork.ads)::
403 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
404 * System.Address_Image (s-addima.ads)::
405 * System.Assertions (s-assert.ads)::
406 * System.Memory (s-memory.ads)::
407 * System.Partition_Interface (s-parint.ads)::
408 * System.Pool_Global (s-pooglo.ads)::
409 * System.Pool_Local (s-pooloc.ads)::
410 * System.Restrictions (s-restri.ads)::
411 * System.Rident (s-rident.ads)::
412 * System.Task_Info (s-tasinf.ads)::
413 * System.Wch_Cnv (s-wchcnv.ads)::
414 * System.Wch_Con (s-wchcon.ads)::
418 * Text_IO Stream Pointer Positioning::
419 * Text_IO Reading and Writing Non-Regular Files::
421 * Treating Text_IO Files as Streams::
422 * Text_IO Extensions::
423 * Text_IO Facilities for Unbounded Strings::
427 * Wide_Text_IO Stream Pointer Positioning::
428 * Wide_Text_IO Reading and Writing Non-Regular Files::
432 * Wide_Wide_Text_IO Stream Pointer Positioning::
433 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
435 Interfacing to Other Languages
438 * Interfacing to C++::
439 * Interfacing to COBOL::
440 * Interfacing to Fortran::
441 * Interfacing to non-GNAT Ada code::
443 Specialized Needs Annexes
445 Implementation of Specific Ada Features
446 * Machine Code Insertions::
447 * GNAT Implementation of Tasking::
448 * GNAT Implementation of Shared Passive Packages::
449 * Code Generation for Array Aggregates::
450 * The Size of Discriminated Records with Default Discriminants::
451 * Strict Conformance to the Ada Reference Manual::
453 Project File Reference
457 GNU Free Documentation License
464 @node About This Guide
465 @unnumbered About This Guide
468 This manual contains useful information in writing programs using the
469 @value{EDITION} compiler. It includes information on implementation dependent
470 characteristics of @value{EDITION}, including all the information required by
471 Annex M of the Ada language standard.
473 @value{EDITION} implements Ada 95 and Ada 2005, and it may also be invoked in
474 Ada 83 compatibility mode.
475 By default, @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION},
476 but you can override with a compiler switch
477 to explicitly specify the language version.
478 (Please refer to @ref{Compiling Different Versions of Ada,,, gnat_ugn,
479 @value{EDITION} User's Guide}, for details on these switches.)
480 Throughout this manual, references to ``Ada'' without a year suffix
481 apply to both the Ada 95 and Ada 2005 versions of the language.
483 Ada is designed to be highly portable.
484 In general, a program will have the same effect even when compiled by
485 different compilers on different platforms.
486 However, since Ada is designed to be used in a
487 wide variety of applications, it also contains a number of system
488 dependent features to be used in interfacing to the external world.
489 @cindex Implementation-dependent features
492 Note: Any program that makes use of implementation-dependent features
493 may be non-portable. You should follow good programming practice and
494 isolate and clearly document any sections of your program that make use
495 of these features in a non-portable manner.
498 For ease of exposition, ``GNAT Pro'' will be referred to simply as
499 ``GNAT'' in the remainder of this document.
503 * What This Reference Manual Contains::
505 * Related Information::
508 @node What This Reference Manual Contains
509 @unnumberedsec What This Reference Manual Contains
512 This reference manual contains the following chapters:
516 @ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
517 pragmas, which can be used to extend and enhance the functionality of the
521 @ref{Implementation Defined Attributes}, lists GNAT
522 implementation-dependent attributes which can be used to extend and
523 enhance the functionality of the compiler.
526 @ref{Implementation Advice}, provides information on generally
527 desirable behavior which are not requirements that all compilers must
528 follow since it cannot be provided on all systems, or which may be
529 undesirable on some systems.
532 @ref{Implementation Defined Characteristics}, provides a guide to
533 minimizing implementation dependent features.
536 @ref{Intrinsic Subprograms}, describes the intrinsic subprograms
537 implemented by GNAT, and how they can be imported into user
538 application programs.
541 @ref{Representation Clauses and Pragmas}, describes in detail the
542 way that GNAT represents data, and in particular the exact set
543 of representation clauses and pragmas that is accepted.
546 @ref{Standard Library Routines}, provides a listing of packages and a
547 brief description of the functionality that is provided by Ada's
548 extensive set of standard library routines as implemented by GNAT@.
551 @ref{The Implementation of Standard I/O}, details how the GNAT
552 implementation of the input-output facilities.
555 @ref{The GNAT Library}, is a catalog of packages that complement
556 the Ada predefined library.
559 @ref{Interfacing to Other Languages}, describes how programs
560 written in Ada using GNAT can be interfaced to other programming
563 @ref{Specialized Needs Annexes}, describes the GNAT implementation of all
564 of the specialized needs annexes.
567 @ref{Implementation of Specific Ada Features}, discusses issues related
568 to GNAT's implementation of machine code insertions, tasking, and several
572 @ref{Project File Reference}, presents the syntax and semantics
576 @ref{Obsolescent Features} documents implementation dependent features,
577 including pragmas and attributes, which are considered obsolescent, since
578 there are other preferred ways of achieving the same results. These
579 obsolescent forms are retained for backwards compatibility.
583 @cindex Ada 95 Language Reference Manual
584 @cindex Ada 2005 Language Reference Manual
586 This reference manual assumes a basic familiarity with the Ada 95 language, as
587 described in the International Standard ANSI/ISO/IEC-8652:1995,
589 It does not require knowledge of the new features introduced by Ada 2005,
590 (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1
592 Both reference manuals are included in the GNAT documentation
596 @unnumberedsec Conventions
597 @cindex Conventions, typographical
598 @cindex Typographical conventions
601 Following are examples of the typographical and graphic conventions used
606 @code{Functions}, @code{utility program names}, @code{standard names},
613 @file{File names}, @samp{button names}, and @samp{field names}.
616 @code{Variables}, @env{environment variables}, and @var{metasyntactic
623 [optional information or parameters]
626 Examples are described by text
628 and then shown this way.
633 Commands that are entered by the user are preceded in this manual by the
634 characters @samp{$ } (dollar sign followed by space). If your system uses this
635 sequence as a prompt, then the commands will appear exactly as you see them
636 in the manual. If your system uses some other prompt, then the command will
637 appear with the @samp{$} replaced by whatever prompt character you are using.
639 @node Related Information
640 @unnumberedsec Related Information
642 See the following documents for further information on GNAT:
646 @xref{Top, @value{EDITION} User's Guide, About This Guide, gnat_ugn,
647 @value{EDITION} User's Guide}, which provides information on how to use the
648 GNAT compiler system.
651 @cite{Ada 95 Reference Manual}, which contains all reference
652 material for the Ada 95 programming language.
655 @cite{Ada 95 Annotated Reference Manual}, which is an annotated version
656 of the Ada 95 standard. The annotations describe
657 detailed aspects of the design decision, and in particular contain useful
658 sections on Ada 83 compatibility.
661 @cite{Ada 2005 Reference Manual}, which contains all reference
662 material for the Ada 2005 programming language.
665 @cite{Ada 2005 Annotated Reference Manual}, which is an annotated version
666 of the Ada 2005 standard. The annotations describe
667 detailed aspects of the design decision, and in particular contain useful
668 sections on Ada 83 and Ada 95 compatibility.
671 @cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
672 which contains specific information on compatibility between GNAT and
676 @cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
677 describes in detail the pragmas and attributes provided by the DEC Ada 83
682 @node Implementation Defined Pragmas
683 @chapter Implementation Defined Pragmas
686 Ada defines a set of pragmas that can be used to supply additional
687 information to the compiler. These language defined pragmas are
688 implemented in GNAT and work as described in the Ada Reference
691 In addition, Ada allows implementations to define additional pragmas
692 whose meaning is defined by the implementation. GNAT provides a number
693 of these implementation-defined pragmas, which can be used to extend
694 and enhance the functionality of the compiler. This section of the GNAT
695 Reference Manual describes these additional pragmas.
697 Note that any program using these pragmas might not be portable to other
698 compilers (although GNAT implements this set of pragmas on all
699 platforms). Therefore if portability to other compilers is an important
700 consideration, the use of these pragmas should be minimized.
703 * Pragma Abort_Defer::
711 * Pragma C_Pass_By_Copy::
713 * Pragma Check_Name::
714 * Pragma Check_Policy::
716 * Pragma Common_Object::
717 * Pragma Compile_Time_Error::
718 * Pragma Compile_Time_Warning::
719 * Pragma Complete_Representation::
720 * Pragma Complex_Representation::
721 * Pragma Component_Alignment::
722 * Pragma Convention_Identifier::
724 * Pragma CPP_Constructor::
725 * Pragma CPP_Virtual::
726 * Pragma CPP_Vtable::
728 * Pragma Debug_Policy::
729 * Pragma Detect_Blocking::
730 * Pragma Elaboration_Checks::
732 * Pragma Export_Exception::
733 * Pragma Export_Function::
734 * Pragma Export_Object::
735 * Pragma Export_Procedure::
736 * Pragma Export_Value::
737 * Pragma Export_Valued_Procedure::
738 * Pragma Extend_System::
740 * Pragma External_Name_Casing::
742 * Pragma Favor_Top_Level::
743 * Pragma Finalize_Storage_Only::
744 * Pragma Float_Representation::
746 * Pragma Implemented_By_Entry::
747 * Pragma Implicit_Packing::
748 * Pragma Import_Exception::
749 * Pragma Import_Function::
750 * Pragma Import_Object::
751 * Pragma Import_Procedure::
752 * Pragma Import_Valued_Procedure::
753 * Pragma Initialize_Scalars::
754 * Pragma Inline_Always::
755 * Pragma Inline_Generic::
757 * Pragma Interface_Name::
758 * Pragma Interrupt_Handler::
759 * Pragma Interrupt_State::
760 * Pragma Keep_Names::
763 * Pragma Linker_Alias::
764 * Pragma Linker_Constructor::
765 * Pragma Linker_Destructor::
766 * Pragma Linker_Section::
767 * Pragma Long_Float::
768 * Pragma Machine_Attribute::
770 * Pragma Main_Storage::
773 * Pragma No_Strict_Aliasing::
774 * Pragma Normalize_Scalars::
775 * Pragma Obsolescent::
776 * Pragma Optimize_Alignment::
778 * Pragma Persistent_BSS::
780 * Pragma Postcondition::
781 * Pragma Precondition::
782 * Pragma Profile (Ravenscar)::
783 * Pragma Profile (Restricted)::
784 * Pragma Psect_Object::
785 * Pragma Pure_Function::
786 * Pragma Restriction_Warnings::
788 * Pragma Source_File_Name::
789 * Pragma Source_File_Name_Project::
790 * Pragma Source_Reference::
791 * Pragma Stream_Convert::
792 * Pragma Style_Checks::
795 * Pragma Suppress_All::
796 * Pragma Suppress_Exception_Locations::
797 * Pragma Suppress_Initialization::
800 * Pragma Task_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 Ast_Entry
1004 @unnumberedsec Pragma Ast_Entry
1009 @smallexample @c ada
1010 pragma AST_Entry (entry_IDENTIFIER);
1014 This pragma is implemented only in the OpenVMS implementation of GNAT@. The
1015 argument is the simple name of a single entry; at most one @code{AST_Entry}
1016 pragma is allowed for any given entry. This pragma must be used in
1017 conjunction with the @code{AST_Entry} attribute, and is only allowed after
1018 the entry declaration and in the same task type specification or single task
1019 as the entry to which it applies. This pragma specifies that the given entry
1020 may be used to handle an OpenVMS asynchronous system trap (@code{AST})
1021 resulting from an OpenVMS system service call. The pragma does not affect
1022 normal use of the entry. For further details on this pragma, see the
1023 DEC Ada Language Reference Manual, section 9.12a.
1025 @node Pragma C_Pass_By_Copy
1026 @unnumberedsec Pragma C_Pass_By_Copy
1027 @cindex Passing by copy
1028 @findex C_Pass_By_Copy
1031 @smallexample @c ada
1032 pragma C_Pass_By_Copy
1033 ([Max_Size =>] static_integer_EXPRESSION);
1037 Normally the default mechanism for passing C convention records to C
1038 convention subprograms is to pass them by reference, as suggested by RM
1039 B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
1040 this default, by requiring that record formal parameters be passed by
1041 copy if all of the following conditions are met:
1045 The size of the record type does not exceed the value specified for
1048 The record type has @code{Convention C}.
1050 The formal parameter has this record type, and the subprogram has a
1051 foreign (non-Ada) convention.
1055 If these conditions are met the argument is passed by copy, i.e.@: in a
1056 manner consistent with what C expects if the corresponding formal in the
1057 C prototype is a struct (rather than a pointer to a struct).
1059 You can also pass records by copy by specifying the convention
1060 @code{C_Pass_By_Copy} for the record type, or by using the extended
1061 @code{Import} and @code{Export} pragmas, which allow specification of
1062 passing mechanisms on a parameter by parameter basis.
1065 @unnumberedsec Pragma Check
1067 @cindex Named assertions
1071 @smallexample @c ada
1073 [Name =>] Identifier,
1074 [Check =>] Boolean_EXPRESSION
1075 [, [Message =>] string_EXPRESSION] );
1079 This pragma is similar to the predefined pragma @code{Assert} except that an
1080 extra identifier argument is present. In conjunction with pragma
1081 @code{Check_Policy}, this can be used to define groups of assertions that can
1082 be independently controlled. The identifier @code{Assertion} is special, it
1083 refers to the normal set of pragma @code{Assert} statements. The identifiers
1084 @code{Precondition} and @code{Postcondition} correspond to the pragmas of these
1085 names, so these three names would normally not be used directly in a pragma
1088 Checks introduced by this pragma are normally deactivated by default. They can
1089 be activated either by the command line option @option{-gnata}, which turns on
1090 all checks, or individually controlled using pragma @code{Check_Policy}.
1092 @node Pragma Check_Name
1093 @unnumberedsec Pragma Check_Name
1094 @cindex Defining check names
1095 @cindex Check names, defining
1099 @smallexample @c ada
1100 pragma Check_Name (check_name_IDENTIFIER);
1104 This is a configuration pragma that defines a new implementation
1105 defined check name (unless IDENTIFIER matches one of the predefined
1106 check names, in which case the pragma has no effect). Check names
1107 are global to a partition, so if two or more configuration pragmas
1108 are present in a partition mentioning the same name, only one new
1109 check name is introduced.
1111 An implementation defined check name introduced with this pragma may
1112 be used in only three contexts: @code{pragma Suppress},
1113 @code{pragma Unsuppress},
1114 and as the prefix of a @code{Check_Name'Enabled} attribute reference. For
1115 any of these three cases, the check name must be visible. A check
1116 name is visible if it is in the configuration pragmas applying to
1117 the current unit, or if it appears at the start of any unit that
1118 is part of the dependency set of the current unit (e.g., units that
1119 are mentioned in @code{with} clauses).
1121 @node Pragma Check_Policy
1122 @unnumberedsec Pragma Check_Policy
1123 @cindex Controlling assertions
1124 @cindex Assertions, control
1125 @cindex Check pragma control
1126 @cindex Named assertions
1130 @smallexample @c ada
1131 pragma Check_Policy ([Name =>] Identifier, POLICY_IDENTIFIER);
1133 POLICY_IDENTIFIER ::= On | Off | Check | Ignore
1137 This pragma is similar to the predefined pragma @code{Assertion_Policy},
1138 except that it controls sets of named assertions introduced using the
1139 @code{Check} pragmas. It can be used as a configuration pragma or (unlike
1140 @code{Assertion_Policy}) can be used within a declarative part, in which case
1141 it controls the status to the end of the corresponding construct (in a manner
1142 identical to pragma @code{Suppress)}.
1144 The identifier given as the first argument corresponds to a name used in
1145 associated @code{Check} pragmas. For example, if the pragma:
1147 @smallexample @c ada
1148 pragma Check_Policy (Critical_Error, Off);
1152 is given, then subsequent @code{Check} pragmas whose first argument is also
1153 @code{Critical_Error} will be disabled. The special identifier @code{Assertion}
1154 controls the behavior of normal @code{Assert} pragmas (thus a pragma
1155 @code{Check_Policy} with this identifier is similar to the normal
1156 @code{Assertion_Policy} pragma except that it can appear within a
1159 The special identifiers @code{Precondition} and @code{Postcondition} control
1160 the status of preconditions and postconditions. If a @code{Precondition} pragma
1161 is encountered, it is ignored if turned off by a @code{Check_Policy} specifying
1162 that @code{Precondition} checks are @code{Off} or @code{Ignored}. Similarly use
1163 of the name @code{Postcondition} controls whether @code{Postcondition} pragmas
1166 The check policy is @code{Off} to turn off corresponding checks, and @code{On}
1167 to turn on corresponding checks. The default for a set of checks for which no
1168 @code{Check_Policy} is given is @code{Off} unless the compiler switch
1169 @option{-gnata} is given, which turns on all checks by default.
1171 The check policy settings @code{Check} and @code{Ignore} are also recognized
1172 as synonyms for @code{On} and @code{Off}. These synonyms are provided for
1173 compatibility with the standard @code{Assertion_Policy} pragma.
1175 @node Pragma Comment
1176 @unnumberedsec Pragma Comment
1181 @smallexample @c ada
1182 pragma Comment (static_string_EXPRESSION);
1186 This is almost identical in effect to pragma @code{Ident}. It allows the
1187 placement of a comment into the object file and hence into the
1188 executable file if the operating system permits such usage. The
1189 difference is that @code{Comment}, unlike @code{Ident}, has
1190 no limitations on placement of the pragma (it can be placed
1191 anywhere in the main source unit), and if more than one pragma
1192 is used, all comments are retained.
1194 @node Pragma Common_Object
1195 @unnumberedsec Pragma Common_Object
1196 @findex Common_Object
1200 @smallexample @c ada
1201 pragma Common_Object (
1202 [Internal =>] LOCAL_NAME
1203 [, [External =>] EXTERNAL_SYMBOL]
1204 [, [Size =>] EXTERNAL_SYMBOL] );
1208 | static_string_EXPRESSION
1212 This pragma enables the shared use of variables stored in overlaid
1213 linker areas corresponding to the use of @code{COMMON}
1214 in Fortran. The single
1215 object @var{LOCAL_NAME} is assigned to the area designated by
1216 the @var{External} argument.
1217 You may define a record to correspond to a series
1218 of fields. The @var{Size} argument
1219 is syntax checked in GNAT, but otherwise ignored.
1221 @code{Common_Object} is not supported on all platforms. If no
1222 support is available, then the code generator will issue a message
1223 indicating that the necessary attribute for implementation of this
1224 pragma is not available.
1226 @node Pragma Compile_Time_Error
1227 @unnumberedsec Pragma Compile_Time_Error
1228 @findex Compile_Time_Error
1232 @smallexample @c ada
1233 pragma Compile_Time_Error
1234 (boolean_EXPRESSION, static_string_EXPRESSION);
1238 This pragma can be used to generate additional compile time
1240 is particularly useful in generics, where errors can be issued for
1241 specific problematic instantiations. The first parameter is a boolean
1242 expression. The pragma is effective only if the value of this expression
1243 is known at compile time, and has the value True. The set of expressions
1244 whose values are known at compile time includes all static boolean
1245 expressions, and also other values which the compiler can determine
1246 at compile time (e.g., the size of a record type set by an explicit
1247 size representation clause, or the value of a variable which was
1248 initialized to a constant and is known not to have been modified).
1249 If these conditions are met, an error message is generated using
1250 the value given as the second argument. This string value may contain
1251 embedded ASCII.LF characters to break the message into multiple lines.
1253 @node Pragma Compile_Time_Warning
1254 @unnumberedsec Pragma Compile_Time_Warning
1255 @findex Compile_Time_Warning
1259 @smallexample @c ada
1260 pragma Compile_Time_Warning
1261 (boolean_EXPRESSION, static_string_EXPRESSION);
1265 Same as pragma Compile_Time_Error, except a warning is issued instead
1266 of an error message. Note that if this pragma is used in a package that
1267 is with'ed by a client, the client will get the warning even though it
1268 is issued by a with'ed package (normally warnings in with'ed units are
1269 suppressed, but this is a special exception to that rule).
1271 One typical use is within a generic where compile time known characteristics
1272 of formal parameters are tested, and warnings given appropriately. Another use
1273 with a first parameter of True is to warn a client about use of a package,
1274 for example that it is not fully implemented.
1276 @node Pragma Complete_Representation
1277 @unnumberedsec Pragma Complete_Representation
1278 @findex Complete_Representation
1282 @smallexample @c ada
1283 pragma Complete_Representation;
1287 This pragma must appear immediately within a record representation
1288 clause. Typical placements are before the first component clause
1289 or after the last component clause. The effect is to give an error
1290 message if any component is missing a component clause. This pragma
1291 may be used to ensure that a record representation clause is
1292 complete, and that this invariant is maintained if fields are
1293 added to the record in the future.
1295 @node Pragma Complex_Representation
1296 @unnumberedsec Pragma Complex_Representation
1297 @findex Complex_Representation
1301 @smallexample @c ada
1302 pragma Complex_Representation
1303 ([Entity =>] LOCAL_NAME);
1307 The @var{Entity} argument must be the name of a record type which has
1308 two fields of the same floating-point type. The effect of this pragma is
1309 to force gcc to use the special internal complex representation form for
1310 this record, which may be more efficient. Note that this may result in
1311 the code for this type not conforming to standard ABI (application
1312 binary interface) requirements for the handling of record types. For
1313 example, in some environments, there is a requirement for passing
1314 records by pointer, and the use of this pragma may result in passing
1315 this type in floating-point registers.
1317 @node Pragma Component_Alignment
1318 @unnumberedsec Pragma Component_Alignment
1319 @cindex Alignments of components
1320 @findex Component_Alignment
1324 @smallexample @c ada
1325 pragma Component_Alignment (
1326 [Form =>] ALIGNMENT_CHOICE
1327 [, [Name =>] type_LOCAL_NAME]);
1329 ALIGNMENT_CHOICE ::=
1337 Specifies the alignment of components in array or record types.
1338 The meaning of the @var{Form} argument is as follows:
1341 @findex Component_Size
1342 @item Component_Size
1343 Aligns scalar components and subcomponents of the array or record type
1344 on boundaries appropriate to their inherent size (naturally
1345 aligned). For example, 1-byte components are aligned on byte boundaries,
1346 2-byte integer components are aligned on 2-byte boundaries, 4-byte
1347 integer components are aligned on 4-byte boundaries and so on. These
1348 alignment rules correspond to the normal rules for C compilers on all
1349 machines except the VAX@.
1351 @findex Component_Size_4
1352 @item Component_Size_4
1353 Naturally aligns components with a size of four or fewer
1354 bytes. Components that are larger than 4 bytes are placed on the next
1357 @findex Storage_Unit
1359 Specifies that array or record components are byte aligned, i.e.@:
1360 aligned on boundaries determined by the value of the constant
1361 @code{System.Storage_Unit}.
1365 Specifies that array or record components are aligned on default
1366 boundaries, appropriate to the underlying hardware or operating system or
1367 both. For OpenVMS VAX systems, the @code{Default} choice is the same as
1368 the @code{Storage_Unit} choice (byte alignment). For all other systems,
1369 the @code{Default} choice is the same as @code{Component_Size} (natural
1374 If the @code{Name} parameter is present, @var{type_LOCAL_NAME} must
1375 refer to a local record or array type, and the specified alignment
1376 choice applies to the specified type. The use of
1377 @code{Component_Alignment} together with a pragma @code{Pack} causes the
1378 @code{Component_Alignment} pragma to be ignored. The use of
1379 @code{Component_Alignment} together with a record representation clause
1380 is only effective for fields not specified by the representation clause.
1382 If the @code{Name} parameter is absent, the pragma can be used as either
1383 a configuration pragma, in which case it applies to one or more units in
1384 accordance with the normal rules for configuration pragmas, or it can be
1385 used within a declarative part, in which case it applies to types that
1386 are declared within this declarative part, or within any nested scope
1387 within this declarative part. In either case it specifies the alignment
1388 to be applied to any record or array type which has otherwise standard
1391 If the alignment for a record or array type is not specified (using
1392 pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
1393 clause), the GNAT uses the default alignment as described previously.
1395 @node Pragma Convention_Identifier
1396 @unnumberedsec Pragma Convention_Identifier
1397 @findex Convention_Identifier
1398 @cindex Conventions, synonyms
1402 @smallexample @c ada
1403 pragma Convention_Identifier (
1404 [Name =>] IDENTIFIER,
1405 [Convention =>] convention_IDENTIFIER);
1409 This pragma provides a mechanism for supplying synonyms for existing
1410 convention identifiers. The @code{Name} identifier can subsequently
1411 be used as a synonym for the given convention in other pragmas (including
1412 for example pragma @code{Import} or another @code{Convention_Identifier}
1413 pragma). As an example of the use of this, suppose you had legacy code
1414 which used Fortran77 as the identifier for Fortran. Then the pragma:
1416 @smallexample @c ada
1417 pragma Convention_Identifier (Fortran77, Fortran);
1421 would allow the use of the convention identifier @code{Fortran77} in
1422 subsequent code, avoiding the need to modify the sources. As another
1423 example, you could use this to parametrize convention requirements
1424 according to systems. Suppose you needed to use @code{Stdcall} on
1425 windows systems, and @code{C} on some other system, then you could
1426 define a convention identifier @code{Library} and use a single
1427 @code{Convention_Identifier} pragma to specify which convention
1428 would be used system-wide.
1430 @node Pragma CPP_Class
1431 @unnumberedsec Pragma CPP_Class
1433 @cindex Interfacing with C++
1437 @smallexample @c ada
1438 pragma CPP_Class ([Entity =>] LOCAL_NAME);
1442 The argument denotes an entity in the current declarative region that is
1443 declared as a tagged record type. It indicates that the type corresponds
1444 to an externally declared C++ class type, and is to be laid out the same
1445 way that C++ would lay out the type.
1447 Types for which @code{CPP_Class} is specified do not have assignment or
1448 equality operators defined (such operations can be imported or declared
1449 as subprograms as required). Initialization is allowed only by constructor
1450 functions (see pragma @code{CPP_Constructor}). Such types are implicitly
1451 limited if not explicitly declared as limited or derived from a limited
1452 type, and a warning is issued in that case.
1454 Pragma @code{CPP_Class} is intended primarily for automatic generation
1455 using an automatic binding generator tool.
1456 See @ref{Interfacing to C++} for related information.
1458 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
1459 for backward compatibility but its functionality is available
1460 using pragma @code{Import} with @code{Convention} = @code{CPP}.
1462 @node Pragma CPP_Constructor
1463 @unnumberedsec Pragma CPP_Constructor
1464 @cindex Interfacing with C++
1465 @findex CPP_Constructor
1469 @smallexample @c ada
1470 pragma CPP_Constructor ([Entity =>] LOCAL_NAME
1471 [, [External_Name =>] static_string_EXPRESSION ]
1472 [, [Link_Name =>] static_string_EXPRESSION ]);
1476 This pragma identifies an imported function (imported in the usual way
1477 with pragma @code{Import}) as corresponding to a C++ constructor. If
1478 @code{External_Name} and @code{Link_Name} are not specified then the
1479 @code{Entity} argument is a name that must have been previously mentioned
1480 in a pragma @code{Import} with @code{Convention} = @code{CPP}. Such name
1481 must be of one of the following forms:
1485 @code{function @var{Fname} return @var{T}'Class}
1488 @code{function @var{Fname} (@dots{}) return @var{T}'Class}
1492 where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.
1494 The first form is the default constructor, used when an object of type
1495 @var{T} is created on the Ada side with no explicit constructor. Other
1496 constructors (including the copy constructor, which is simply a special
1497 case of the second form in which the one and only argument is of type
1498 @var{T}), can only appear in two contexts:
1502 On the right side of an initialization of an object of type @var{T}.
1504 In an extension aggregate for an object of a type derived from @var{T}.
1508 Although the constructor is described as a function that returns a value
1509 on the Ada side, it is typically a procedure with an extra implicit
1510 argument (the object being initialized) at the implementation
1511 level. GNAT issues the appropriate call, whatever it is, to get the
1512 object properly initialized.
1514 In the case of derived objects, you may use one of two possible forms
1515 for declaring and creating an object:
1518 @item @code{New_Object : Derived_T}
1519 @item @code{New_Object : Derived_T := (@var{constructor-call with} @dots{})}
1523 In the first case the default constructor is called and extension fields
1524 if any are initialized according to the default initialization
1525 expressions in the Ada declaration. In the second case, the given
1526 constructor is called and the extension aggregate indicates the explicit
1527 values of the extension fields.
1529 If no constructors are imported, it is impossible to create any objects
1530 on the Ada side. If no default constructor is imported, only the
1531 initialization forms using an explicit call to a constructor are
1534 Pragma @code{CPP_Constructor} is intended primarily for automatic generation
1535 using an automatic binding generator tool.
1536 See @ref{Interfacing to C++} for more related information.
1538 @node Pragma CPP_Virtual
1539 @unnumberedsec Pragma CPP_Virtual
1540 @cindex Interfacing to C++
1543 This pragma is now obsolete has has no effect because GNAT generates
1544 the same object layout than the G++ compiler.
1546 See @ref{Interfacing to C++} for related information.
1548 @node Pragma CPP_Vtable
1549 @unnumberedsec Pragma CPP_Vtable
1550 @cindex Interfacing with C++
1553 This pragma is now obsolete has has no effect because GNAT generates
1554 the same object layout than the G++ compiler.
1556 See @ref{Interfacing to C++} for related information.
1559 @unnumberedsec Pragma Debug
1564 @smallexample @c ada
1565 pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON);
1567 PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
1569 | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
1573 The procedure call argument has the syntactic form of an expression, meeting
1574 the syntactic requirements for pragmas.
1576 If debug pragmas are not enabled or if the condition is present and evaluates
1577 to False, this pragma has no effect. If debug pragmas are enabled, the
1578 semantics of the pragma is exactly equivalent to the procedure call statement
1579 corresponding to the argument with a terminating semicolon. Pragmas are
1580 permitted in sequences of declarations, so you can use pragma @code{Debug} to
1581 intersperse calls to debug procedures in the middle of declarations. Debug
1582 pragmas can be enabled either by use of the command line switch @option{-gnata}
1583 or by use of the configuration pragma @code{Debug_Policy}.
1585 @node Pragma Debug_Policy
1586 @unnumberedsec Pragma Debug_Policy
1587 @findex Debug_Policy
1591 @smallexample @c ada
1592 pragma Debug_Policy (CHECK | IGNORE);
1596 If the argument is @code{CHECK}, then pragma @code{DEBUG} is enabled.
1597 If the argument is @code{IGNORE}, then pragma @code{DEBUG} is ignored.
1598 This pragma overrides the effect of the @option{-gnata} switch on the
1601 @node Pragma Detect_Blocking
1602 @unnumberedsec Pragma Detect_Blocking
1603 @findex Detect_Blocking
1607 @smallexample @c ada
1608 pragma Detect_Blocking;
1612 This is a configuration pragma that forces the detection of potentially
1613 blocking operations within a protected operation, and to raise Program_Error
1616 @node Pragma Elaboration_Checks
1617 @unnumberedsec Pragma Elaboration_Checks
1618 @cindex Elaboration control
1619 @findex Elaboration_Checks
1623 @smallexample @c ada
1624 pragma Elaboration_Checks (Dynamic | Static);
1628 This is a configuration pragma that provides control over the
1629 elaboration model used by the compilation affected by the
1630 pragma. If the parameter is @code{Dynamic},
1631 then the dynamic elaboration
1632 model described in the Ada Reference Manual is used, as though
1633 the @option{-gnatE} switch had been specified on the command
1634 line. If the parameter is @code{Static}, then the default GNAT static
1635 model is used. This configuration pragma overrides the setting
1636 of the command line. For full details on the elaboration models
1637 used by the GNAT compiler, see @ref{Elaboration Order Handling in GNAT,,,
1638 gnat_ugn, @value{EDITION} User's Guide}.
1640 @node Pragma Eliminate
1641 @unnumberedsec Pragma Eliminate
1642 @cindex Elimination of unused subprograms
1647 @smallexample @c ada
1649 [Unit_Name =>] IDENTIFIER |
1650 SELECTED_COMPONENT);
1653 [Unit_Name =>] IDENTIFIER |
1655 [Entity =>] IDENTIFIER |
1656 SELECTED_COMPONENT |
1658 [,OVERLOADING_RESOLUTION]);
1660 OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
1663 PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
1666 PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES
1668 FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
1669 Result_Type => result_SUBTYPE_NAME]
1671 PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
1672 SUBTYPE_NAME ::= STRING_VALUE
1674 SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
1675 SOURCE_TRACE ::= STRING_VALUE
1677 STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
1681 This pragma indicates that the given entity is not used outside the
1682 compilation unit it is defined in. The entity must be an explicitly declared
1683 subprogram; this includes generic subprogram instances and
1684 subprograms declared in generic package instances.
1686 If the entity to be eliminated is a library level subprogram, then
1687 the first form of pragma @code{Eliminate} is used with only a single argument.
1688 In this form, the @code{Unit_Name} argument specifies the name of the
1689 library level unit to be eliminated.
1691 In all other cases, both @code{Unit_Name} and @code{Entity} arguments
1692 are required. If item is an entity of a library package, then the first
1693 argument specifies the unit name, and the second argument specifies
1694 the particular entity. If the second argument is in string form, it must
1695 correspond to the internal manner in which GNAT stores entity names (see
1696 compilation unit Namet in the compiler sources for details).
1698 The remaining parameters (OVERLOADING_RESOLUTION) are optionally used
1699 to distinguish between overloaded subprograms. If a pragma does not contain
1700 the OVERLOADING_RESOLUTION parameter(s), it is applied to all the overloaded
1701 subprograms denoted by the first two parameters.
1703 Use PARAMETER_AND_RESULT_TYPE_PROFILE to specify the profile of the subprogram
1704 to be eliminated in a manner similar to that used for the extended
1705 @code{Import} and @code{Export} pragmas, except that the subtype names are
1706 always given as strings. At the moment, this form of distinguishing
1707 overloaded subprograms is implemented only partially, so we do not recommend
1708 using it for practical subprogram elimination.
1710 Note that in case of a parameterless procedure its profile is represented
1711 as @code{Parameter_Types => ("")}
1713 Alternatively, the @code{Source_Location} parameter is used to specify
1714 which overloaded alternative is to be eliminated by pointing to the
1715 location of the DEFINING_PROGRAM_UNIT_NAME of this subprogram in the
1716 source text. The string literal (or concatenation of string literals)
1717 given as SOURCE_TRACE must have the following format:
1719 @smallexample @c ada
1720 SOURCE_TRACE ::= SOURCE_LOCATION@{LBRACKET SOURCE_LOCATION RBRACKET@}
1725 SOURCE_LOCATION ::= FILE_NAME:LINE_NUMBER
1726 FILE_NAME ::= STRING_LITERAL
1727 LINE_NUMBER ::= DIGIT @{DIGIT@}
1730 SOURCE_TRACE should be the short name of the source file (with no directory
1731 information), and LINE_NUMBER is supposed to point to the line where the
1732 defining name of the subprogram is located.
1734 For the subprograms that are not a part of generic instantiations, only one
1735 SOURCE_LOCATION is used. If a subprogram is declared in a package
1736 instantiation, SOURCE_TRACE contains two SOURCE_LOCATIONs, the first one is
1737 the location of the (DEFINING_PROGRAM_UNIT_NAME of the) instantiation, and the
1738 second one denotes the declaration of the corresponding subprogram in the
1739 generic package. This approach is recursively used to create SOURCE_LOCATIONs
1740 in case of nested instantiations.
1742 The effect of the pragma is to allow the compiler to eliminate
1743 the code or data associated with the named entity. Any reference to
1744 an eliminated entity outside the compilation unit it is defined in,
1745 causes a compile time or link time error.
1747 The intention of pragma @code{Eliminate} is to allow a program to be compiled
1748 in a system independent manner, with unused entities eliminated, without
1749 the requirement of modifying the source text. Normally the required set
1750 of @code{Eliminate} pragmas is constructed automatically using the gnatelim
1751 tool. Elimination of unused entities local to a compilation unit is
1752 automatic, without requiring the use of pragma @code{Eliminate}.
1754 Note that the reason this pragma takes string literals where names might
1755 be expected is that a pragma @code{Eliminate} can appear in a context where the
1756 relevant names are not visible.
1758 Note that any change in the source files that includes removing, splitting of
1759 adding lines may make the set of Eliminate pragmas using SOURCE_LOCATION
1762 It is legal to use pragma Eliminate where the referenced entity is a
1763 dispatching operation, but it is not clear what this would mean, since
1764 in general the call does not know which entity is actually being called.
1765 Consequently, a pragma Eliminate for a dispatching operation is ignored.
1767 @node Pragma Export_Exception
1768 @unnumberedsec Pragma Export_Exception
1770 @findex Export_Exception
1774 @smallexample @c ada
1775 pragma Export_Exception (
1776 [Internal =>] LOCAL_NAME
1777 [, [External =>] EXTERNAL_SYMBOL]
1778 [, [Form =>] Ada | VMS]
1779 [, [Code =>] static_integer_EXPRESSION]);
1783 | static_string_EXPRESSION
1787 This pragma is implemented only in the OpenVMS implementation of GNAT@. It
1788 causes the specified exception to be propagated outside of the Ada program,
1789 so that it can be handled by programs written in other OpenVMS languages.
1790 This pragma establishes an external name for an Ada exception and makes the
1791 name available to the OpenVMS Linker as a global symbol. For further details
1792 on this pragma, see the
1793 DEC Ada Language Reference Manual, section 13.9a3.2.
1795 @node Pragma Export_Function
1796 @unnumberedsec Pragma Export_Function
1797 @cindex Argument passing mechanisms
1798 @findex Export_Function
1803 @smallexample @c ada
1804 pragma Export_Function (
1805 [Internal =>] LOCAL_NAME
1806 [, [External =>] EXTERNAL_SYMBOL]
1807 [, [Parameter_Types =>] PARAMETER_TYPES]
1808 [, [Result_Type =>] result_SUBTYPE_MARK]
1809 [, [Mechanism =>] MECHANISM]
1810 [, [Result_Mechanism =>] MECHANISM_NAME]);
1814 | static_string_EXPRESSION
1819 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1823 | subtype_Name ' Access
1827 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1829 MECHANISM_ASSOCIATION ::=
1830 [formal_parameter_NAME =>] MECHANISM_NAME
1835 | Descriptor [([Class =>] CLASS_NAME)]
1837 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1841 Use this pragma to make a function externally callable and optionally
1842 provide information on mechanisms to be used for passing parameter and
1843 result values. We recommend, for the purposes of improving portability,
1844 this pragma always be used in conjunction with a separate pragma
1845 @code{Export}, which must precede the pragma @code{Export_Function}.
1846 GNAT does not require a separate pragma @code{Export}, but if none is
1847 present, @code{Convention Ada} is assumed, which is usually
1848 not what is wanted, so it is usually appropriate to use this
1849 pragma in conjunction with a @code{Export} or @code{Convention}
1850 pragma that specifies the desired foreign convention.
1851 Pragma @code{Export_Function}
1852 (and @code{Export}, if present) must appear in the same declarative
1853 region as the function to which they apply.
1855 @var{internal_name} must uniquely designate the function to which the
1856 pragma applies. If more than one function name exists of this name in
1857 the declarative part you must use the @code{Parameter_Types} and
1858 @code{Result_Type} parameters is mandatory to achieve the required
1859 unique designation. @var{subtype_mark}s in these parameters must
1860 exactly match the subtypes in the corresponding function specification,
1861 using positional notation to match parameters with subtype marks.
1862 The form with an @code{'Access} attribute can be used to match an
1863 anonymous access parameter.
1866 @cindex Passing by descriptor
1867 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
1869 @cindex Suppressing external name
1870 Special treatment is given if the EXTERNAL is an explicit null
1871 string or a static string expressions that evaluates to the null
1872 string. In this case, no external name is generated. This form
1873 still allows the specification of parameter mechanisms.
1875 @node Pragma Export_Object
1876 @unnumberedsec Pragma Export_Object
1877 @findex Export_Object
1881 @smallexample @c ada
1882 pragma Export_Object
1883 [Internal =>] LOCAL_NAME
1884 [, [External =>] EXTERNAL_SYMBOL]
1885 [, [Size =>] EXTERNAL_SYMBOL]
1889 | static_string_EXPRESSION
1893 This pragma designates an object as exported, and apart from the
1894 extended rules for external symbols, is identical in effect to the use of
1895 the normal @code{Export} pragma applied to an object. You may use a
1896 separate Export pragma (and you probably should from the point of view
1897 of portability), but it is not required. @var{Size} is syntax checked,
1898 but otherwise ignored by GNAT@.
1900 @node Pragma Export_Procedure
1901 @unnumberedsec Pragma Export_Procedure
1902 @findex Export_Procedure
1906 @smallexample @c ada
1907 pragma Export_Procedure (
1908 [Internal =>] LOCAL_NAME
1909 [, [External =>] EXTERNAL_SYMBOL]
1910 [, [Parameter_Types =>] PARAMETER_TYPES]
1911 [, [Mechanism =>] MECHANISM]);
1915 | static_string_EXPRESSION
1920 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1924 | subtype_Name ' Access
1928 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1930 MECHANISM_ASSOCIATION ::=
1931 [formal_parameter_NAME =>] MECHANISM_NAME
1936 | Descriptor [([Class =>] CLASS_NAME)]
1938 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
1942 This pragma is identical to @code{Export_Function} except that it
1943 applies to a procedure rather than a function and the parameters
1944 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
1945 GNAT does not require a separate pragma @code{Export}, but if none is
1946 present, @code{Convention Ada} is assumed, which is usually
1947 not what is wanted, so it is usually appropriate to use this
1948 pragma in conjunction with a @code{Export} or @code{Convention}
1949 pragma that specifies the desired foreign convention.
1952 @cindex Passing by descriptor
1953 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
1955 @cindex Suppressing external name
1956 Special treatment is given if the EXTERNAL is an explicit null
1957 string or a static string expressions that evaluates to the null
1958 string. In this case, no external name is generated. This form
1959 still allows the specification of parameter mechanisms.
1961 @node Pragma Export_Value
1962 @unnumberedsec Pragma Export_Value
1963 @findex Export_Value
1967 @smallexample @c ada
1968 pragma Export_Value (
1969 [Value =>] static_integer_EXPRESSION,
1970 [Link_Name =>] static_string_EXPRESSION);
1974 This pragma serves to export a static integer value for external use.
1975 The first argument specifies the value to be exported. The Link_Name
1976 argument specifies the symbolic name to be associated with the integer
1977 value. This pragma is useful for defining a named static value in Ada
1978 that can be referenced in assembly language units to be linked with
1979 the application. This pragma is currently supported only for the
1980 AAMP target and is ignored for other targets.
1982 @node Pragma Export_Valued_Procedure
1983 @unnumberedsec Pragma Export_Valued_Procedure
1984 @findex Export_Valued_Procedure
1988 @smallexample @c ada
1989 pragma Export_Valued_Procedure (
1990 [Internal =>] LOCAL_NAME
1991 [, [External =>] EXTERNAL_SYMBOL]
1992 [, [Parameter_Types =>] PARAMETER_TYPES]
1993 [, [Mechanism =>] MECHANISM]);
1997 | static_string_EXPRESSION
2002 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2006 | subtype_Name ' Access
2010 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2012 MECHANISM_ASSOCIATION ::=
2013 [formal_parameter_NAME =>] MECHANISM_NAME
2018 | Descriptor [([Class =>] CLASS_NAME)]
2020 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a
2024 This pragma is identical to @code{Export_Procedure} except that the
2025 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2026 mode @code{OUT}, and externally the subprogram is treated as a function
2027 with this parameter as the result of the function. GNAT provides for
2028 this capability to allow the use of @code{OUT} and @code{IN OUT}
2029 parameters in interfacing to external functions (which are not permitted
2031 GNAT does not require a separate pragma @code{Export}, but if none is
2032 present, @code{Convention Ada} is assumed, which is almost certainly
2033 not what is wanted since the whole point of this pragma is to interface
2034 with foreign language functions, so it is usually appropriate to use this
2035 pragma in conjunction with a @code{Export} or @code{Convention}
2036 pragma that specifies the desired foreign convention.
2039 @cindex Passing by descriptor
2040 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2042 @cindex Suppressing external name
2043 Special treatment is given if the EXTERNAL is an explicit null
2044 string or a static string expressions that evaluates to the null
2045 string. In this case, no external name is generated. This form
2046 still allows the specification of parameter mechanisms.
2048 @node Pragma Extend_System
2049 @unnumberedsec Pragma Extend_System
2050 @cindex @code{system}, extending
2052 @findex Extend_System
2056 @smallexample @c ada
2057 pragma Extend_System ([Name =>] IDENTIFIER);
2061 This pragma is used to provide backwards compatibility with other
2062 implementations that extend the facilities of package @code{System}. In
2063 GNAT, @code{System} contains only the definitions that are present in
2064 the Ada RM@. However, other implementations, notably the DEC Ada 83
2065 implementation, provide many extensions to package @code{System}.
2067 For each such implementation accommodated by this pragma, GNAT provides a
2068 package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
2069 implementation, which provides the required additional definitions. You
2070 can use this package in two ways. You can @code{with} it in the normal
2071 way and access entities either by selection or using a @code{use}
2072 clause. In this case no special processing is required.
2074 However, if existing code contains references such as
2075 @code{System.@var{xxx}} where @var{xxx} is an entity in the extended
2076 definitions provided in package @code{System}, you may use this pragma
2077 to extend visibility in @code{System} in a non-standard way that
2078 provides greater compatibility with the existing code. Pragma
2079 @code{Extend_System} is a configuration pragma whose single argument is
2080 the name of the package containing the extended definition
2081 (e.g.@: @code{Aux_DEC} for the DEC Ada case). A unit compiled under
2082 control of this pragma will be processed using special visibility
2083 processing that looks in package @code{System.Aux_@var{xxx}} where
2084 @code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
2085 package @code{System}, but not found in package @code{System}.
2087 You can use this pragma either to access a predefined @code{System}
2088 extension supplied with the compiler, for example @code{Aux_DEC} or
2089 you can construct your own extension unit following the above
2090 definition. Note that such a package is a child of @code{System}
2091 and thus is considered part of the implementation. To compile
2092 it you will have to use the appropriate switch for compiling
2093 system units. @xref{Top, @value{EDITION} User's Guide, About This
2094 Guide,, gnat_ugn, @value{EDITION} User's Guide}, for details.
2096 @node Pragma External
2097 @unnumberedsec Pragma External
2102 @smallexample @c ada
2104 [ Convention =>] convention_IDENTIFIER,
2105 [ Entity =>] LOCAL_NAME
2106 [, [External_Name =>] static_string_EXPRESSION ]
2107 [, [Link_Name =>] static_string_EXPRESSION ]);
2111 This pragma is identical in syntax and semantics to pragma
2112 @code{Export} as defined in the Ada Reference Manual. It is
2113 provided for compatibility with some Ada 83 compilers that
2114 used this pragma for exactly the same purposes as pragma
2115 @code{Export} before the latter was standardized.
2117 @node Pragma External_Name_Casing
2118 @unnumberedsec Pragma External_Name_Casing
2119 @cindex Dec Ada 83 casing compatibility
2120 @cindex External Names, casing
2121 @cindex Casing of External names
2122 @findex External_Name_Casing
2126 @smallexample @c ada
2127 pragma External_Name_Casing (
2128 Uppercase | Lowercase
2129 [, Uppercase | Lowercase | As_Is]);
2133 This pragma provides control over the casing of external names associated
2134 with Import and Export pragmas. There are two cases to consider:
2137 @item Implicit external names
2138 Implicit external names are derived from identifiers. The most common case
2139 arises when a standard Ada Import or Export pragma is used with only two
2142 @smallexample @c ada
2143 pragma Import (C, C_Routine);
2147 Since Ada is a case-insensitive language, the spelling of the identifier in
2148 the Ada source program does not provide any information on the desired
2149 casing of the external name, and so a convention is needed. In GNAT the
2150 default treatment is that such names are converted to all lower case
2151 letters. This corresponds to the normal C style in many environments.
2152 The first argument of pragma @code{External_Name_Casing} can be used to
2153 control this treatment. If @code{Uppercase} is specified, then the name
2154 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2155 then the normal default of all lower case letters will be used.
2157 This same implicit treatment is also used in the case of extended DEC Ada 83
2158 compatible Import and Export pragmas where an external name is explicitly
2159 specified using an identifier rather than a string.
2161 @item Explicit external names
2162 Explicit external names are given as string literals. The most common case
2163 arises when a standard Ada Import or Export pragma is used with three
2166 @smallexample @c ada
2167 pragma Import (C, C_Routine, "C_routine");
2171 In this case, the string literal normally provides the exact casing required
2172 for the external name. The second argument of pragma
2173 @code{External_Name_Casing} may be used to modify this behavior.
2174 If @code{Uppercase} is specified, then the name
2175 will be forced to all uppercase letters. If @code{Lowercase} is specified,
2176 then the name will be forced to all lowercase letters. A specification of
2177 @code{As_Is} provides the normal default behavior in which the casing is
2178 taken from the string provided.
2182 This pragma may appear anywhere that a pragma is valid. In particular, it
2183 can be used as a configuration pragma in the @file{gnat.adc} file, in which
2184 case it applies to all subsequent compilations, or it can be used as a program
2185 unit pragma, in which case it only applies to the current unit, or it can
2186 be used more locally to control individual Import/Export pragmas.
2188 It is primarily intended for use with OpenVMS systems, where many
2189 compilers convert all symbols to upper case by default. For interfacing to
2190 such compilers (e.g.@: the DEC C compiler), it may be convenient to use
2193 @smallexample @c ada
2194 pragma External_Name_Casing (Uppercase, Uppercase);
2198 to enforce the upper casing of all external symbols.
2200 @node Pragma Fast_Math
2201 @unnumberedsec Pragma Fast_Math
2206 @smallexample @c ada
2211 This is a configuration pragma which activates a mode in which speed is
2212 considered more important for floating-point operations than absolutely
2213 accurate adherence to the requirements of the standard. Currently the
2214 following operations are affected:
2217 @item Complex Multiplication
2218 The normal simple formula for complex multiplication can result in intermediate
2219 overflows for numbers near the end of the range. The Ada standard requires that
2220 this situation be detected and corrected by scaling, but in Fast_Math mode such
2221 cases will simply result in overflow. Note that to take advantage of this you
2222 must instantiate your own version of @code{Ada.Numerics.Generic_Complex_Types}
2223 under control of the pragma, rather than use the preinstantiated versions.
2226 @node Pragma Favor_Top_Level
2227 @unnumberedsec Pragma Favor_Top_Level
2228 @findex Favor_Top_Level
2232 @smallexample @c ada
2233 pragma Favor_Top_Level (type_NAME);
2237 The named type must be an access-to-subprogram type. This pragma is an
2238 efficiency hint to the compiler, regarding the use of 'Access or
2239 'Unrestricted_Access on nested (non-library-level) subprograms. The
2240 pragma means that nested subprograms are not used with this type, or
2241 are rare, so that the generated code should be efficient in the
2242 top-level case. When this pragma is used, dynamically generated
2243 trampolines may be used on some targets for nested subprograms.
2244 See also the No_Implicit_Dynamic_Code restriction.
2246 @node Pragma Finalize_Storage_Only
2247 @unnumberedsec Pragma Finalize_Storage_Only
2248 @findex Finalize_Storage_Only
2252 @smallexample @c ada
2253 pragma Finalize_Storage_Only (first_subtype_LOCAL_NAME);
2257 This pragma allows the compiler not to emit a Finalize call for objects
2258 defined at the library level. This is mostly useful for types where
2259 finalization is only used to deal with storage reclamation since in most
2260 environments it is not necessary to reclaim memory just before terminating
2261 execution, hence the name.
2263 @node Pragma Float_Representation
2264 @unnumberedsec Pragma Float_Representation
2266 @findex Float_Representation
2270 @smallexample @c ada
2271 pragma Float_Representation (FLOAT_REP[, float_type_LOCAL_NAME]);
2273 FLOAT_REP ::= VAX_Float | IEEE_Float
2277 In the one argument form, this pragma is a configuration pragma which
2278 allows control over the internal representation chosen for the predefined
2279 floating point types declared in the packages @code{Standard} and
2280 @code{System}. On all systems other than OpenVMS, the argument must
2281 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2282 argument may be @code{VAX_Float} to specify the use of the VAX float
2283 format for the floating-point types in Standard. This requires that
2284 the standard runtime libraries be recompiled. @xref{The GNAT Run-Time
2285 Library Builder gnatlbr,,, gnat_ugn, @value{EDITION} User's Guide
2286 OpenVMS}, for a description of the @code{GNAT LIBRARY} command.
2288 The two argument form specifies the representation to be used for
2289 the specified floating-point type. On all systems other than OpenVMS,
2291 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
2292 argument may be @code{VAX_Float} to specify the use of the VAX float
2297 For digits values up to 6, F float format will be used.
2299 For digits values from 7 to 9, G float format will be used.
2301 For digits values from 10 to 15, F float format will be used.
2303 Digits values above 15 are not allowed.
2307 @unnumberedsec Pragma Ident
2312 @smallexample @c ada
2313 pragma Ident (static_string_EXPRESSION);
2317 This pragma provides a string identification in the generated object file,
2318 if the system supports the concept of this kind of identification string.
2319 This pragma is allowed only in the outermost declarative part or
2320 declarative items of a compilation unit. If more than one @code{Ident}
2321 pragma is given, only the last one processed is effective.
2323 On OpenVMS systems, the effect of the pragma is identical to the effect of
2324 the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
2325 maximum allowed length is 31 characters, so if it is important to
2326 maintain compatibility with this compiler, you should obey this length
2329 @node Pragma Implemented_By_Entry
2330 @unnumberedsec Pragma Implemented_By_Entry
2331 @findex Implemented_By_Entry
2335 @smallexample @c ada
2336 pragma Implemented_By_Entry (LOCAL_NAME);
2340 This is a representation pragma which applies to protected, synchronized and
2341 task interface primitives. If the pragma is applied to primitive operation Op
2342 of interface Iface, it is illegal to override Op in a type that implements
2343 Iface, with anything other than an entry.
2345 @smallexample @c ada
2346 type Iface is protected interface;
2347 procedure Do_Something (Object : in out Iface) is abstract;
2348 pragma Implemented_By_Entry (Do_Something);
2350 protected type P is new Iface with
2351 procedure Do_Something; -- Illegal
2354 task type T is new Iface with
2355 entry Do_Something; -- Legal
2360 NOTE: The pragma is still in its design stage by the Ada Rapporteur Group. It
2361 is intended to be used in conjunction with dispatching requeue statements as
2362 described in AI05-0030. Should the ARG decide on an official name and syntax,
2363 this pragma will become language-defined rather than GNAT-specific.
2365 @node Pragma Implicit_Packing
2366 @unnumberedsec Pragma Implicit_Packing
2367 @findex Implicit_Packing
2371 @smallexample @c ada
2372 pragma Implicit_Packing;
2376 This is a configuration pragma that requests implicit packing for packed
2377 arrays for which a size clause is given but no explicit pragma Pack or
2378 specification of Component_Size is present. Consider this example:
2380 @smallexample @c ada
2381 type R is array (0 .. 7) of Boolean;
2386 In accordance with the recommendation in the RM (RM 13.3(53)), a Size clause
2387 does not change the layout of a composite object. So the Size clause in the
2388 above example is normally rejected, since the default layout of the array uses
2389 8-bit components, and thus the array requires a minimum of 64 bits.
2391 If this declaration is compiled in a region of code covered by an occurrence
2392 of the configuration pragma Implicit_Packing, then the Size clause in this
2393 and similar examples will cause implicit packing and thus be accepted. For
2394 this implicit packing to occur, the type in question must be an array of small
2395 components whose size is known at compile time, and the Size clause must
2396 specify the exact size that corresponds to the length of the array multiplied
2397 by the size in bits of the component type.
2398 @cindex Array packing
2400 @node Pragma Import_Exception
2401 @unnumberedsec Pragma Import_Exception
2403 @findex Import_Exception
2407 @smallexample @c ada
2408 pragma Import_Exception (
2409 [Internal =>] LOCAL_NAME
2410 [, [External =>] EXTERNAL_SYMBOL]
2411 [, [Form =>] Ada | VMS]
2412 [, [Code =>] static_integer_EXPRESSION]);
2416 | static_string_EXPRESSION
2420 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2421 It allows OpenVMS conditions (for example, from OpenVMS system services or
2422 other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
2423 The pragma specifies that the exception associated with an exception
2424 declaration in an Ada program be defined externally (in non-Ada code).
2425 For further details on this pragma, see the
2426 DEC Ada Language Reference Manual, section 13.9a.3.1.
2428 @node Pragma Import_Function
2429 @unnumberedsec Pragma Import_Function
2430 @findex Import_Function
2434 @smallexample @c ada
2435 pragma Import_Function (
2436 [Internal =>] LOCAL_NAME,
2437 [, [External =>] EXTERNAL_SYMBOL]
2438 [, [Parameter_Types =>] PARAMETER_TYPES]
2439 [, [Result_Type =>] SUBTYPE_MARK]
2440 [, [Mechanism =>] MECHANISM]
2441 [, [Result_Mechanism =>] MECHANISM_NAME]
2442 [, [First_Optional_Parameter =>] IDENTIFIER]);
2446 | static_string_EXPRESSION
2450 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2454 | subtype_Name ' Access
2458 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2460 MECHANISM_ASSOCIATION ::=
2461 [formal_parameter_NAME =>] MECHANISM_NAME
2466 | Descriptor [([Class =>] CLASS_NAME)]
2468 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2472 This pragma is used in conjunction with a pragma @code{Import} to
2473 specify additional information for an imported function. The pragma
2474 @code{Import} (or equivalent pragma @code{Interface}) must precede the
2475 @code{Import_Function} pragma and both must appear in the same
2476 declarative part as the function specification.
2478 The @var{Internal} argument must uniquely designate
2479 the function to which the
2480 pragma applies. If more than one function name exists of this name in
2481 the declarative part you must use the @code{Parameter_Types} and
2482 @var{Result_Type} parameters to achieve the required unique
2483 designation. Subtype marks in these parameters must exactly match the
2484 subtypes in the corresponding function specification, using positional
2485 notation to match parameters with subtype marks.
2486 The form with an @code{'Access} attribute can be used to match an
2487 anonymous access parameter.
2489 You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
2490 parameters to specify passing mechanisms for the
2491 parameters and result. If you specify a single mechanism name, it
2492 applies to all parameters. Otherwise you may specify a mechanism on a
2493 parameter by parameter basis using either positional or named
2494 notation. If the mechanism is not specified, the default mechanism
2498 @cindex Passing by descriptor
2499 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2501 @code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
2502 It specifies that the designated parameter and all following parameters
2503 are optional, meaning that they are not passed at the generated code
2504 level (this is distinct from the notion of optional parameters in Ada
2505 where the parameters are passed anyway with the designated optional
2506 parameters). All optional parameters must be of mode @code{IN} and have
2507 default parameter values that are either known at compile time
2508 expressions, or uses of the @code{'Null_Parameter} attribute.
2510 @node Pragma Import_Object
2511 @unnumberedsec Pragma Import_Object
2512 @findex Import_Object
2516 @smallexample @c ada
2517 pragma Import_Object
2518 [Internal =>] LOCAL_NAME
2519 [, [External =>] EXTERNAL_SYMBOL]
2520 [, [Size =>] EXTERNAL_SYMBOL]);
2524 | static_string_EXPRESSION
2528 This pragma designates an object as imported, and apart from the
2529 extended rules for external symbols, is identical in effect to the use of
2530 the normal @code{Import} pragma applied to an object. Unlike the
2531 subprogram case, you need not use a separate @code{Import} pragma,
2532 although you may do so (and probably should do so from a portability
2533 point of view). @var{size} is syntax checked, but otherwise ignored by
2536 @node Pragma Import_Procedure
2537 @unnumberedsec Pragma Import_Procedure
2538 @findex Import_Procedure
2542 @smallexample @c ada
2543 pragma Import_Procedure (
2544 [Internal =>] LOCAL_NAME
2545 [, [External =>] EXTERNAL_SYMBOL]
2546 [, [Parameter_Types =>] PARAMETER_TYPES]
2547 [, [Mechanism =>] MECHANISM]
2548 [, [First_Optional_Parameter =>] IDENTIFIER]);
2552 | static_string_EXPRESSION
2556 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2560 | subtype_Name ' Access
2564 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2566 MECHANISM_ASSOCIATION ::=
2567 [formal_parameter_NAME =>] MECHANISM_NAME
2572 | Descriptor [([Class =>] CLASS_NAME)]
2574 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2578 This pragma is identical to @code{Import_Function} except that it
2579 applies to a procedure rather than a function and the parameters
2580 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2582 @node Pragma Import_Valued_Procedure
2583 @unnumberedsec Pragma Import_Valued_Procedure
2584 @findex Import_Valued_Procedure
2588 @smallexample @c ada
2589 pragma Import_Valued_Procedure (
2590 [Internal =>] LOCAL_NAME
2591 [, [External =>] EXTERNAL_SYMBOL]
2592 [, [Parameter_Types =>] PARAMETER_TYPES]
2593 [, [Mechanism =>] MECHANISM]
2594 [, [First_Optional_Parameter =>] IDENTIFIER]);
2598 | static_string_EXPRESSION
2602 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2606 | subtype_Name ' Access
2610 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2612 MECHANISM_ASSOCIATION ::=
2613 [formal_parameter_NAME =>] MECHANISM_NAME
2618 | Descriptor [([Class =>] CLASS_NAME)]
2620 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2624 This pragma is identical to @code{Import_Procedure} except that the
2625 first parameter of @var{LOCAL_NAME}, which must be present, must be of
2626 mode @code{OUT}, and externally the subprogram is treated as a function
2627 with this parameter as the result of the function. The purpose of this
2628 capability is to allow the use of @code{OUT} and @code{IN OUT}
2629 parameters in interfacing to external functions (which are not permitted
2630 in Ada functions). You may optionally use the @code{Mechanism}
2631 parameters to specify passing mechanisms for the parameters.
2632 If you specify a single mechanism name, it applies to all parameters.
2633 Otherwise you may specify a mechanism on a parameter by parameter
2634 basis using either positional or named notation. If the mechanism is not
2635 specified, the default mechanism is used.
2637 Note that it is important to use this pragma in conjunction with a separate
2638 pragma Import that specifies the desired convention, since otherwise the
2639 default convention is Ada, which is almost certainly not what is required.
2641 @node Pragma Initialize_Scalars
2642 @unnumberedsec Pragma Initialize_Scalars
2643 @findex Initialize_Scalars
2644 @cindex debugging with Initialize_Scalars
2648 @smallexample @c ada
2649 pragma Initialize_Scalars;
2653 This pragma is similar to @code{Normalize_Scalars} conceptually but has
2654 two important differences. First, there is no requirement for the pragma
2655 to be used uniformly in all units of a partition, in particular, it is fine
2656 to use this just for some or all of the application units of a partition,
2657 without needing to recompile the run-time library.
2659 In the case where some units are compiled with the pragma, and some without,
2660 then a declaration of a variable where the type is defined in package
2661 Standard or is locally declared will always be subject to initialization,
2662 as will any declaration of a scalar variable. For composite variables,
2663 whether the variable is initialized may also depend on whether the package
2664 in which the type of the variable is declared is compiled with the pragma.
2666 The other important difference is that you can control the value used
2667 for initializing scalar objects. At bind time, you can select several
2668 options for initialization. You can
2669 initialize with invalid values (similar to Normalize_Scalars, though for
2670 Initialize_Scalars it is not always possible to determine the invalid
2671 values in complex cases like signed component fields with non-standard
2672 sizes). You can also initialize with high or
2673 low values, or with a specified bit pattern. See the users guide for binder
2674 options for specifying these cases.
2676 This means that you can compile a program, and then without having to
2677 recompile the program, you can run it with different values being used
2678 for initializing otherwise uninitialized values, to test if your program
2679 behavior depends on the choice. Of course the behavior should not change,
2680 and if it does, then most likely you have an erroneous reference to an
2681 uninitialized value.
2683 It is even possible to change the value at execution time eliminating even
2684 the need to rebind with a different switch using an environment variable.
2685 See the GNAT users guide for details.
2687 Note that pragma @code{Initialize_Scalars} is particularly useful in
2688 conjunction with the enhanced validity checking that is now provided
2689 in GNAT, which checks for invalid values under more conditions.
2690 Using this feature (see description of the @option{-gnatV} flag in the
2691 users guide) in conjunction with pragma @code{Initialize_Scalars}
2692 provides a powerful new tool to assist in the detection of problems
2693 caused by uninitialized variables.
2695 Note: the use of @code{Initialize_Scalars} has a fairly extensive
2696 effect on the generated code. This may cause your code to be
2697 substantially larger. It may also cause an increase in the amount
2698 of stack required, so it is probably a good idea to turn on stack
2699 checking (see description of stack checking in the GNAT users guide)
2700 when using this pragma.
2702 @node Pragma Inline_Always
2703 @unnumberedsec Pragma Inline_Always
2704 @findex Inline_Always
2708 @smallexample @c ada
2709 pragma Inline_Always (NAME [, NAME]);
2713 Similar to pragma @code{Inline} except that inlining is not subject to
2714 the use of option @option{-gnatn} and the inlining happens regardless of
2715 whether this option is used.
2717 @node Pragma Inline_Generic
2718 @unnumberedsec Pragma Inline_Generic
2719 @findex Inline_Generic
2723 @smallexample @c ada
2724 pragma Inline_Generic (generic_package_NAME);
2728 This is implemented for compatibility with DEC Ada 83 and is recognized,
2729 but otherwise ignored, by GNAT@. All generic instantiations are inlined
2730 by default when using GNAT@.
2732 @node Pragma Interface
2733 @unnumberedsec Pragma Interface
2738 @smallexample @c ada
2740 [Convention =>] convention_identifier,
2741 [Entity =>] local_NAME
2742 [, [External_Name =>] static_string_expression]
2743 [, [Link_Name =>] static_string_expression]);
2747 This pragma is identical in syntax and semantics to
2748 the standard Ada pragma @code{Import}. It is provided for compatibility
2749 with Ada 83. The definition is upwards compatible both with pragma
2750 @code{Interface} as defined in the Ada 83 Reference Manual, and also
2751 with some extended implementations of this pragma in certain Ada 83
2754 @node Pragma Interface_Name
2755 @unnumberedsec Pragma Interface_Name
2756 @findex Interface_Name
2760 @smallexample @c ada
2761 pragma Interface_Name (
2762 [Entity =>] LOCAL_NAME
2763 [, [External_Name =>] static_string_EXPRESSION]
2764 [, [Link_Name =>] static_string_EXPRESSION]);
2768 This pragma provides an alternative way of specifying the interface name
2769 for an interfaced subprogram, and is provided for compatibility with Ada
2770 83 compilers that use the pragma for this purpose. You must provide at
2771 least one of @var{External_Name} or @var{Link_Name}.
2773 @node Pragma Interrupt_Handler
2774 @unnumberedsec Pragma Interrupt_Handler
2775 @findex Interrupt_Handler
2779 @smallexample @c ada
2780 pragma Interrupt_Handler (procedure_LOCAL_NAME);
2784 This program unit pragma is supported for parameterless protected procedures
2785 as described in Annex C of the Ada Reference Manual. On the AAMP target
2786 the pragma can also be specified for nonprotected parameterless procedures
2787 that are declared at the library level (which includes procedures
2788 declared at the top level of a library package). In the case of AAMP,
2789 when this pragma is applied to a nonprotected procedure, the instruction
2790 @code{IERET} is generated for returns from the procedure, enabling
2791 maskable interrupts, in place of the normal return instruction.
2793 @node Pragma Interrupt_State
2794 @unnumberedsec Pragma Interrupt_State
2795 @findex Interrupt_State
2799 @smallexample @c ada
2800 pragma Interrupt_State (Name => value, State => SYSTEM | RUNTIME | USER);
2804 Normally certain interrupts are reserved to the implementation. Any attempt
2805 to attach an interrupt causes Program_Error to be raised, as described in
2806 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
2807 many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
2808 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
2809 interrupt execution. Additionally, signals such as @code{SIGSEGV},
2810 @code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
2811 Ada exceptions, or used to implement run-time functions such as the
2812 @code{abort} statement and stack overflow checking.
2814 Pragma @code{Interrupt_State} provides a general mechanism for overriding
2815 such uses of interrupts. It subsumes the functionality of pragma
2816 @code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
2817 available on OS/2, Windows or VMS. On all other platforms than VxWorks,
2818 it applies to signals; on VxWorks, it applies to vectored hardware interrupts
2819 and may be used to mark interrupts required by the board support package
2822 Interrupts can be in one of three states:
2826 The interrupt is reserved (no Ada handler can be installed), and the
2827 Ada run-time may not install a handler. As a result you are guaranteed
2828 standard system default action if this interrupt is raised.
2832 The interrupt is reserved (no Ada handler can be installed). The run time
2833 is allowed to install a handler for internal control purposes, but is
2834 not required to do so.
2838 The interrupt is unreserved. The user may install a handler to provide
2843 These states are the allowed values of the @code{State} parameter of the
2844 pragma. The @code{Name} parameter is a value of the type
2845 @code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
2846 @code{Ada.Interrupts.Names}.
2848 This is a configuration pragma, and the binder will check that there
2849 are no inconsistencies between different units in a partition in how a
2850 given interrupt is specified. It may appear anywhere a pragma is legal.
2852 The effect is to move the interrupt to the specified state.
2854 By declaring interrupts to be SYSTEM, you guarantee the standard system
2855 action, such as a core dump.
2857 By declaring interrupts to be USER, you guarantee that you can install
2860 Note that certain signals on many operating systems cannot be caught and
2861 handled by applications. In such cases, the pragma is ignored. See the
2862 operating system documentation, or the value of the array @code{Reserved}
2863 declared in the spec of package @code{System.OS_Interface}.
2865 Overriding the default state of signals used by the Ada runtime may interfere
2866 with an application's runtime behavior in the cases of the synchronous signals,
2867 and in the case of the signal used to implement the @code{abort} statement.
2869 @node Pragma Keep_Names
2870 @unnumberedsec Pragma Keep_Names
2875 @smallexample @c ada
2876 pragma Keep_Names ([On =>] enumeration_first_subtype_LOCAL_NAME);
2880 The @var{LOCAL_NAME} argument
2881 must refer to an enumeration first subtype
2882 in the current declarative part. The effect is to retain the enumeration
2883 literal names for use by @code{Image} and @code{Value} even if a global
2884 @code{Discard_Names} pragma applies. This is useful when you want to
2885 generally suppress enumeration literal names and for example you therefore
2886 use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
2887 want to retain the names for specific enumeration types.
2889 @node Pragma License
2890 @unnumberedsec Pragma License
2892 @cindex License checking
2896 @smallexample @c ada
2897 pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
2901 This pragma is provided to allow automated checking for appropriate license
2902 conditions with respect to the standard and modified GPL@. A pragma
2903 @code{License}, which is a configuration pragma that typically appears at
2904 the start of a source file or in a separate @file{gnat.adc} file, specifies
2905 the licensing conditions of a unit as follows:
2909 This is used for a unit that can be freely used with no license restrictions.
2910 Examples of such units are public domain units, and units from the Ada
2914 This is used for a unit that is licensed under the unmodified GPL, and which
2915 therefore cannot be @code{with}'ed by a restricted unit.
2918 This is used for a unit licensed under the GNAT modified GPL that includes
2919 a special exception paragraph that specifically permits the inclusion of
2920 the unit in programs without requiring the entire program to be released
2924 This is used for a unit that is restricted in that it is not permitted to
2925 depend on units that are licensed under the GPL@. Typical examples are
2926 proprietary code that is to be released under more restrictive license
2927 conditions. Note that restricted units are permitted to @code{with} units
2928 which are licensed under the modified GPL (this is the whole point of the
2934 Normally a unit with no @code{License} pragma is considered to have an
2935 unknown license, and no checking is done. However, standard GNAT headers
2936 are recognized, and license information is derived from them as follows.
2940 A GNAT license header starts with a line containing 78 hyphens. The following
2941 comment text is searched for the appearance of any of the following strings.
2943 If the string ``GNU General Public License'' is found, then the unit is assumed
2944 to have GPL license, unless the string ``As a special exception'' follows, in
2945 which case the license is assumed to be modified GPL@.
2947 If one of the strings
2948 ``This specification is adapted from the Ada Semantic Interface'' or
2949 ``This specification is derived from the Ada Reference Manual'' is found
2950 then the unit is assumed to be unrestricted.
2954 These default actions means that a program with a restricted license pragma
2955 will automatically get warnings if a GPL unit is inappropriately
2956 @code{with}'ed. For example, the program:
2958 @smallexample @c ada
2961 procedure Secret_Stuff is
2967 if compiled with pragma @code{License} (@code{Restricted}) in a
2968 @file{gnat.adc} file will generate the warning:
2973 >>> license of withed unit "Sem_Ch3" is incompatible
2975 2. with GNAT.Sockets;
2976 3. procedure Secret_Stuff is
2980 Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
2981 compiler and is licensed under the
2982 GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
2983 run time, and is therefore licensed under the modified GPL@.
2985 @node Pragma Link_With
2986 @unnumberedsec Pragma Link_With
2991 @smallexample @c ada
2992 pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
2996 This pragma is provided for compatibility with certain Ada 83 compilers.
2997 It has exactly the same effect as pragma @code{Linker_Options} except
2998 that spaces occurring within one of the string expressions are treated
2999 as separators. For example, in the following case:
3001 @smallexample @c ada
3002 pragma Link_With ("-labc -ldef");
3006 results in passing the strings @code{-labc} and @code{-ldef} as two
3007 separate arguments to the linker. In addition pragma Link_With allows
3008 multiple arguments, with the same effect as successive pragmas.
3010 @node Pragma Linker_Alias
3011 @unnumberedsec Pragma Linker_Alias
3012 @findex Linker_Alias
3016 @smallexample @c ada
3017 pragma Linker_Alias (
3018 [Entity =>] LOCAL_NAME,
3019 [Target =>] static_string_EXPRESSION);
3023 @var{LOCAL_NAME} must refer to an object that is declared at the library
3024 level. This pragma establishes the given entity as a linker alias for the
3025 given target. It is equivalent to @code{__attribute__((alias))} in GNU C
3026 and causes @var{LOCAL_NAME} to be emitted as an alias for the symbol
3027 @var{static_string_EXPRESSION} in the object file, that is to say no space
3028 is reserved for @var{LOCAL_NAME} by the assembler and it will be resolved
3029 to the same address as @var{static_string_EXPRESSION} by the linker.
3031 The actual linker name for the target must be used (e.g.@: the fully
3032 encoded name with qualification in Ada, or the mangled name in C++),
3033 or it must be declared using the C convention with @code{pragma Import}
3034 or @code{pragma Export}.
3036 Not all target machines support this pragma. On some of them it is accepted
3037 only if @code{pragma Weak_External} has been applied to @var{LOCAL_NAME}.
3039 @smallexample @c ada
3040 -- Example of the use of pragma Linker_Alias
3044 pragma Export (C, i);
3046 new_name_for_i : Integer;
3047 pragma Linker_Alias (new_name_for_i, "i");
3051 @node Pragma Linker_Constructor
3052 @unnumberedsec Pragma Linker_Constructor
3053 @findex Linker_Constructor
3057 @smallexample @c ada
3058 pragma Linker_Constructor (procedure_LOCAL_NAME);
3062 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3063 is declared at the library level. A procedure to which this pragma is
3064 applied will be treated as an initialization routine by the linker.
3065 It is equivalent to @code{__attribute__((constructor))} in GNU C and
3066 causes @var{procedure_LOCAL_NAME} to be invoked before the entry point
3067 of the executable is called (or immediately after the shared library is
3068 loaded if the procedure is linked in a shared library), in particular
3069 before the Ada run-time environment is set up.
3071 Because of these specific contexts, the set of operations such a procedure
3072 can perform is very limited and the type of objects it can manipulate is
3073 essentially restricted to the elementary types. In particular, it must only
3074 contain code to which pragma Restrictions (No_Elaboration_Code) applies.
3076 This pragma is used by GNAT to implement auto-initialization of shared Stand
3077 Alone Libraries, which provides a related capability without the restrictions
3078 listed above. Where possible, the use of Stand Alone Libraries is preferable
3079 to the use of this pragma.
3081 @node Pragma Linker_Destructor
3082 @unnumberedsec Pragma Linker_Destructor
3083 @findex Linker_Destructor
3087 @smallexample @c ada
3088 pragma Linker_Destructor (procedure_LOCAL_NAME);
3092 @var{procedure_LOCAL_NAME} must refer to a parameterless procedure that
3093 is declared at the library level. A procedure to which this pragma is
3094 applied will be treated as a finalization routine by the linker.
3095 It is equivalent to @code{__attribute__((destructor))} in GNU C and
3096 causes @var{procedure_LOCAL_NAME} to be invoked after the entry point
3097 of the executable has exited (or immediately before the shared library
3098 is unloaded if the procedure is linked in a shared library), in particular
3099 after the Ada run-time environment is shut down.
3101 See @code{pragma Linker_Constructor} for the set of restrictions that apply
3102 because of these specific contexts.
3104 @node Pragma Linker_Section
3105 @unnumberedsec Pragma Linker_Section
3106 @findex Linker_Section
3110 @smallexample @c ada
3111 pragma Linker_Section (
3112 [Entity =>] LOCAL_NAME,
3113 [Section =>] static_string_EXPRESSION);
3117 @var{LOCAL_NAME} must refer to an object that is declared at the library
3118 level. This pragma specifies the name of the linker section for the given
3119 entity. It is equivalent to @code{__attribute__((section))} in GNU C and
3120 causes @var{LOCAL_NAME} to be placed in the @var{static_string_EXPRESSION}
3121 section of the executable (assuming the linker doesn't rename the section).
3123 The compiler normally places library-level objects in standard sections
3124 depending on their type: procedures and functions generally go in the
3125 @code{.text} section, initialized variables in the @code{.data} section
3126 and uninitialized variables in the @code{.bss} section.
3128 Other, special sections may exist on given target machines to map special
3129 hardware, for example I/O ports or flash memory. This pragma is a means to
3130 defer the final layout of the executable to the linker, thus fully working
3131 at the symbolic level with the compiler.
3133 Some file formats do not support arbitrary sections so not all target
3134 machines support this pragma. The use of this pragma may cause a program
3135 execution to be erroneous if it is used to place an entity into an
3136 inappropriate section (e.g.@: a modified variable into the @code{.text}
3137 section). See also @code{pragma Persistent_BSS}.
3139 @smallexample @c ada
3140 -- Example of the use of pragma Linker_Section
3144 pragma Volatile (Port_A);
3145 pragma Linker_Section (Port_A, ".bss.port_a");
3148 pragma Volatile (Port_B);
3149 pragma Linker_Section (Port_B, ".bss.port_b");
3153 @node Pragma Long_Float
3154 @unnumberedsec Pragma Long_Float
3160 @smallexample @c ada
3161 pragma Long_Float (FLOAT_FORMAT);
3163 FLOAT_FORMAT ::= D_Float | G_Float
3167 This pragma is implemented only in the OpenVMS implementation of GNAT@.
3168 It allows control over the internal representation chosen for the predefined
3169 type @code{Long_Float} and for floating point type representations with
3170 @code{digits} specified in the range 7 through 15.
3171 For further details on this pragma, see the
3172 @cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
3173 this pragma, the standard runtime libraries must be recompiled.
3174 @xref{The GNAT Run-Time Library Builder gnatlbr,,, gnat_ugn,
3175 @value{EDITION} User's Guide OpenVMS}, for a description of the
3176 @code{GNAT LIBRARY} command.
3178 @node Pragma Machine_Attribute
3179 @unnumberedsec Pragma Machine_Attribute
3180 @findex Machine_Attribute
3184 @smallexample @c ada
3185 pragma Machine_Attribute (
3186 [Entity =>] LOCAL_NAME,
3187 [Attribute_Name =>] static_string_EXPRESSION
3188 [, [Info =>] static_string_EXPRESSION] );
3192 Machine-dependent attributes can be specified for types and/or
3193 declarations. This pragma is semantically equivalent to
3194 @code{__attribute__((@var{attribute_name}))} (if @var{info} is not
3195 specified) or @code{__attribute__((@var{attribute_name}(@var{info})))}
3196 in GNU C, where @code{@var{attribute_name}} is recognized by the
3197 target macro @code{TARGET_ATTRIBUTE_TABLE} which is defined for each
3198 machine. The optional parameter @var{info} is transformed into an
3199 identifier, which may make this pragma unusable for some attributes
3200 (parameter of some attributes must be a number or a string).
3201 @xref{Target Attributes,, Defining target-specific uses of
3202 @code{__attribute__}, gccint, GNU Compiler Colletion (GCC) Internals},
3203 further information. It is not possible to specify
3204 attributes defined by other languages, only attributes defined by the
3205 machine the code is intended to run on.
3208 @unnumberedsec Pragma Main
3214 @smallexample @c ada
3216 (MAIN_OPTION [, MAIN_OPTION]);
3219 [STACK_SIZE =>] static_integer_EXPRESSION
3220 | [TASK_STACK_SIZE_DEFAULT =>] static_integer_EXPRESSION
3221 | [TIME_SLICING_ENABLED =>] static_boolean_EXPRESSION
3225 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3226 no effect in GNAT, other than being syntax checked.
3228 @node Pragma Main_Storage
3229 @unnumberedsec Pragma Main_Storage
3231 @findex Main_Storage
3235 @smallexample @c ada
3237 (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
3239 MAIN_STORAGE_OPTION ::=
3240 [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
3241 | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
3245 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
3246 no effect in GNAT, other than being syntax checked. Note that the pragma
3247 also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
3249 @node Pragma No_Body
3250 @unnumberedsec Pragma No_Body
3255 @smallexample @c ada
3260 There are a number of cases in which a package spec does not require a body,
3261 and in fact a body is not permitted. GNAT will not permit the spec to be
3262 compiled if there is a body around. The pragma No_Body allows you to provide
3263 a body file, even in a case where no body is allowed. The body file must
3264 contain only comments and a single No_Body pragma. This is recognized by
3265 the compiler as indicating that no body is logically present.
3267 This is particularly useful during maintenance when a package is modified in
3268 such a way that a body needed before is no longer needed. The provision of a
3269 dummy body with a No_Body pragma ensures that there is no interference from
3270 earlier versions of the package body.
3272 @node Pragma No_Return
3273 @unnumberedsec Pragma No_Return
3278 @smallexample @c ada
3279 pragma No_Return (procedure_LOCAL_NAME @{, procedure_LOCAL_NAME@});
3283 Each @var{procedure_LOCAL_NAME} argument must refer to one or more procedure
3284 declarations in the current declarative part. A procedure to which this
3285 pragma is applied may not contain any explicit @code{return} statements.
3286 In addition, if the procedure contains any implicit returns from falling
3287 off the end of a statement sequence, then execution of that implicit
3288 return will cause Program_Error to be raised.
3290 One use of this pragma is to identify procedures whose only purpose is to raise
3291 an exception. Another use of this pragma is to suppress incorrect warnings
3292 about missing returns in functions, where the last statement of a function
3293 statement sequence is a call to such a procedure.
3295 Note that in Ada 2005 mode, this pragma is part of the language, and is
3296 identical in effect to the pragma as implemented in Ada 95 mode.
3298 @node Pragma No_Strict_Aliasing
3299 @unnumberedsec Pragma No_Strict_Aliasing
3300 @findex No_Strict_Aliasing
3304 @smallexample @c ada
3305 pragma No_Strict_Aliasing [([Entity =>] type_LOCAL_NAME)];
3309 @var{type_LOCAL_NAME} must refer to an access type
3310 declaration in the current declarative part. The effect is to inhibit
3311 strict aliasing optimization for the given type. The form with no
3312 arguments is a configuration pragma which applies to all access types
3313 declared in units to which the pragma applies. For a detailed
3314 description of the strict aliasing optimization, and the situations
3315 in which it must be suppressed, see @ref{Optimization and Strict
3316 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
3318 @node Pragma Normalize_Scalars
3319 @unnumberedsec Pragma Normalize_Scalars
3320 @findex Normalize_Scalars
3324 @smallexample @c ada
3325 pragma Normalize_Scalars;
3329 This is a language defined pragma which is fully implemented in GNAT@. The
3330 effect is to cause all scalar objects that are not otherwise initialized
3331 to be initialized. The initial values are implementation dependent and
3335 @item Standard.Character
3337 Objects whose root type is Standard.Character are initialized to
3338 Character'Last unless the subtype range excludes NUL (in which case
3339 NUL is used). This choice will always generate an invalid value if
3342 @item Standard.Wide_Character
3344 Objects whose root type is Standard.Wide_Character are initialized to
3345 Wide_Character'Last unless the subtype range excludes NUL (in which case
3346 NUL is used). This choice will always generate an invalid value if
3349 @item Standard.Wide_Wide_Character
3351 Objects whose root type is Standard.Wide_Wide_Character are initialized to
3352 the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in
3353 which case NUL is used). This choice will always generate an invalid value if
3358 Objects of an integer type are treated differently depending on whether
3359 negative values are present in the subtype. If no negative values are
3360 present, then all one bits is used as the initial value except in the
3361 special case where zero is excluded from the subtype, in which case
3362 all zero bits are used. This choice will always generate an invalid
3363 value if one exists.
3365 For subtypes with negative values present, the largest negative number
3366 is used, except in the unusual case where this largest negative number
3367 is in the subtype, and the largest positive number is not, in which case
3368 the largest positive value is used. This choice will always generate
3369 an invalid value if one exists.
3371 @item Floating-Point Types
3372 Objects of all floating-point types are initialized to all 1-bits. For
3373 standard IEEE format, this corresponds to a NaN (not a number) which is
3374 indeed an invalid value.
3376 @item Fixed-Point Types
3377 Objects of all fixed-point types are treated as described above for integers,
3378 with the rules applying to the underlying integer value used to represent
3379 the fixed-point value.
3382 Objects of a modular type are initialized to all one bits, except in
3383 the special case where zero is excluded from the subtype, in which
3384 case all zero bits are used. This choice will always generate an
3385 invalid value if one exists.
3387 @item Enumeration types
3388 Objects of an enumeration type are initialized to all one-bits, i.e.@: to
3389 the value @code{2 ** typ'Size - 1} unless the subtype excludes the literal
3390 whose Pos value is zero, in which case a code of zero is used. This choice
3391 will always generate an invalid value if one exists.
3395 @node Pragma Obsolescent
3396 @unnumberedsec Pragma Obsolescent
3401 @smallexample @c ada
3403 (Entity => NAME [, static_string_EXPRESSION [,Ada_05]]);
3407 This pragma can occur immediately following a declaration of an entity,
3408 including the case of a record component, and usually the Entity name
3409 must match the name of the entity declared by this declaration.
3410 Alternatively, the pragma can immediately follow an
3411 enumeration type declaration, where the entity argument names one of the
3412 enumeration literals.
3414 This pragma is used to indicate that the named entity
3415 is considered obsolescent and should not be used. Typically this is
3416 used when an API must be modified by eventually removing or modifying
3417 existing subprograms or other entities. The pragma can be used at an
3418 intermediate stage when the entity is still present, but will be
3421 The effect of this pragma is to output a warning message on
3422 a call to a program thus marked that the
3423 subprogram is obsolescent if the appropriate warning option in the
3424 compiler is activated. If the string parameter is present, then a second
3425 warning message is given containing this text.
3426 In addition, a call to such a program is considered a violation of
3427 pragma Restrictions (No_Obsolescent_Features).
3429 This pragma can also be used as a program unit pragma for a package,
3430 in which case the entity name is the name of the package, and the
3431 pragma indicates that the entire package is considered
3432 obsolescent. In this case a client @code{with}'ing such a package
3433 violates the restriction, and the @code{with} statement is
3434 flagged with warnings if the warning option is set.
3436 If the optional third parameter is present (which must be exactly
3437 the identifier Ada_05, no other argument is allowed), then the
3438 indication of obsolescence applies only when compiling in Ada 2005
3439 mode. This is primarily intended for dealing with the situations
3440 in the predefined library where subprograms or packages
3441 have become defined as obsolescent in Ada 2005
3442 (e.g.@: in Ada.Characters.Handling), but may be used anywhere.
3444 The following examples show typical uses of this pragma:
3446 @smallexample @c ada
3449 (Entity => p, "use pp instead of p");
3455 (Entity => q2, "use q2new instead");
3457 type R is new integer;
3459 (Entity => R, "use RR in Ada 2005", Ada_05);
3464 pragma Obsolescent (Entity => F2);
3468 type E is (a, bc, 'd', quack);
3469 pragma Obsolescent (Entity => bc)
3470 pragma Obsolescent (Entity => 'd')
3473 (a, b : character) return character;
3474 pragma Obsolescent (Entity => "+");
3479 In an earlier version of GNAT, the Entity parameter was not required,
3480 and this form is still accepted for compatibility purposes. If the
3481 Entity parameter is omitted, then the pragma applies to the declaration
3482 immediately preceding the pragma (this form cannot be used for the
3483 enumeration literal case).
3485 @node Pragma Optimize_Alignment
3486 @unnumberedsec Pragma Optimize_Alignment
3487 @findex Optimize_Alignment
3488 @cindex Alignment, default settings
3492 @smallexample @c ada
3493 pragma Optimize_Alignment (TIME | SPACE | OFF);
3497 This is a configuration pragma which affects the choice of default alignments
3498 for types where no alignment is explicitly specified. There is a time/space
3499 trade-off in the selection of these values. Large alignments result in more
3500 efficient code, at the expense of larger data space, since sizes have to be
3501 increased to match these alignments. Smaller alignments save space, but the
3502 access code is slower. The normal choice of default alignments (which is what
3503 you get if you do not use this pragma, or if you use an argument of OFF),
3504 tries to balance these two requirements.
3506 Specifying SPACE causes smaller default alignments to be chosen in two cases.
3507 First any packed record is given an alignment of 1. Second, if a size is given
3508 for the type, then the alignment is chosen to avoid increasing this size. For
3511 @smallexample @c ada
3521 In the default mode, this type gets an alignment of 4, so that access to the
3522 Integer field X are efficient. But this means that objects of the type end up
3523 with a size of 8 bytes. This is a valid choice, since sizes of objects are
3524 allowed to be bigger than the size of the type, but it can waste space if for
3525 example fields of type R appear in an enclosing record. If the above type is
3526 compiled in @code{Optimize_Alignment (Space)} mode, the alignment is set to 1.
3528 Specifying TIME causes larger default alignments to be chosen in the case of
3529 small types with sizes that are not a power of 2. For example, consider:
3531 @smallexample @c ada
3543 The default alignment for this record is normally 1, but if this type is
3544 compiled in @code{Optimize_Alignment (Time)} mode, then the alignment is set
3545 to 4, which wastes space for objects of the type, since they are now 4 bytes
3546 long, but results in more efficient access when the whole record is referenced.
3548 As noted above, this is a configuration pragma, and there is a requirement
3549 that all units in a partition be compiled with a consistent setting of the
3550 optimization setting. This would normally be achieved by use of a configuration
3551 pragma file containing the appropriate setting. The exception to this rule is
3552 that units with an explicit configuration pragma in the same file as the source
3553 unit are excluded from the consistency check, as are all predefined units. The
3554 latter are compiled by default in pragma Optimize_Alignment (Off) mode if no
3555 pragma appears at the start of the file.
3557 @node Pragma Passive
3558 @unnumberedsec Pragma Passive
3563 @smallexample @c ada
3564 pragma Passive [(Semaphore | No)];
3568 Syntax checked, but otherwise ignored by GNAT@. This is recognized for
3569 compatibility with DEC Ada 83 implementations, where it is used within a
3570 task definition to request that a task be made passive. If the argument
3571 @code{Semaphore} is present, or the argument is omitted, then DEC Ada 83
3572 treats the pragma as an assertion that the containing task is passive
3573 and that optimization of context switch with this task is permitted and
3574 desired. If the argument @code{No} is present, the task must not be
3575 optimized. GNAT does not attempt to optimize any tasks in this manner
3576 (since protected objects are available in place of passive tasks).
3578 @node Pragma Persistent_BSS
3579 @unnumberedsec Pragma Persistent_BSS
3580 @findex Persistent_BSS
3584 @smallexample @c ada
3585 pragma Persistent_BSS [(LOCAL_NAME)]
3589 This pragma allows selected objects to be placed in the @code{.persistent_bss}
3590 section. On some targets the linker and loader provide for special
3591 treatment of this section, allowing a program to be reloaded without
3592 affecting the contents of this data (hence the name persistent).
3594 There are two forms of usage. If an argument is given, it must be the
3595 local name of a library level object, with no explicit initialization
3596 and whose type is potentially persistent. If no argument is given, then
3597 the pragma is a configuration pragma, and applies to all library level
3598 objects with no explicit initialization of potentially persistent types.
3600 A potentially persistent type is a scalar type, or a non-tagged,
3601 non-discriminated record, all of whose components have no explicit
3602 initialization and are themselves of a potentially persistent type,
3603 or an array, all of whose constraints are static, and whose component
3604 type is potentially persistent.
3606 If this pragma is used on a target where this feature is not supported,
3607 then the pragma will be ignored. See also @code{pragma Linker_Section}.
3609 @node Pragma Polling
3610 @unnumberedsec Pragma Polling
3615 @smallexample @c ada
3616 pragma Polling (ON | OFF);
3620 This pragma controls the generation of polling code. This is normally off.
3621 If @code{pragma Polling (ON)} is used then periodic calls are generated to
3622 the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
3623 runtime library, and can be found in file @file{a-excpol.adb}.
3625 Pragma @code{Polling} can appear as a configuration pragma (for example it
3626 can be placed in the @file{gnat.adc} file) to enable polling globally, or it
3627 can be used in the statement or declaration sequence to control polling
3630 A call to the polling routine is generated at the start of every loop and
3631 at the start of every subprogram call. This guarantees that the @code{Poll}
3632 routine is called frequently, and places an upper bound (determined by
3633 the complexity of the code) on the period between two @code{Poll} calls.
3635 The primary purpose of the polling interface is to enable asynchronous
3636 aborts on targets that cannot otherwise support it (for example Windows
3637 NT), but it may be used for any other purpose requiring periodic polling.
3638 The standard version is null, and can be replaced by a user program. This
3639 will require re-compilation of the @code{Ada.Exceptions} package that can
3640 be found in files @file{a-except.ads} and @file{a-except.adb}.
3642 A standard alternative unit (in file @file{4wexcpol.adb} in the standard GNAT
3643 distribution) is used to enable the asynchronous abort capability on
3644 targets that do not normally support the capability. The version of
3645 @code{Poll} in this file makes a call to the appropriate runtime routine
3646 to test for an abort condition.
3648 Note that polling can also be enabled by use of the @option{-gnatP} switch.
3649 @xref{Switches for gcc,,, gnat_ugn, @value{EDITION} User's Guide}, for
3652 @node Pragma Postcondition
3653 @unnumberedsec Pragma Postcondition
3654 @cindex Postconditions
3655 @cindex Checks, postconditions
3656 @findex Postconditions
3660 @smallexample @c ada
3661 pragma Postcondition (
3662 [Check =>] Boolean_Expression
3663 [,[Message =>] String_Expression]);
3667 The @code{Postcondition} pragma allows specification of automatic
3668 postcondition checks for subprograms. These checks are similar to
3669 assertions, but are automatically inserted just prior to the return
3670 statements of the subprogram with which they are associated.
3671 Furthermore, the boolean expression which is the condition which
3672 must be true may contain references to function'Result in the case
3673 of a function to refer to the returned value.
3675 @code{Postcondition} pragmas may appear either immediate following the
3676 (separate) declaration of a subprogram, or at the start of the
3677 declarations of a subprogram body. Only other pragmas may intervene
3678 (that is appear between the subprogram declaration and its
3679 postconditions, or appear before the postcondition in the
3680 declaration sequence in a subprogram body). In the case of a
3681 postcondition appearing after a subprogram declaration, the
3682 formal arguments of the subprogram are visible, and can be
3683 referenced in the postcondition expressions.
3685 The postconditions are collected and automatically tested just
3686 before any return (implicit or explicit) in the subprogram body.
3687 A postcondition is only recognized if postconditions are active
3688 at the time the pragma is encountered. The compiler switch @option{gnata}
3689 turns on all postconditions by default, and pragma @code{Check_Policy}
3690 with an identifier of @code{Postcondition} can also be used to
3691 control whether postconditions are active.
3693 The general approach is that postconditions are placed in the spec
3694 if they represent functional aspects which make sense to the client.
3695 For example we might have:
3697 @smallexample @c ada
3698 function Direction return Integer;
3699 pragma Postcondition
3700 (Direction'Result = +1
3702 Direction'Result = -1);
3706 which serves to document that the result must be +1 or -1, and
3707 will test that this is the case at run time if postcondition
3710 Postconditions within the subprogram body can be used to
3711 check that some internal aspect of the implementation,
3712 not visible to the client, is operating as expected.
3713 For instance if a square root routine keeps an internal
3714 counter of the number of times it is called, then we
3715 might have the following postcondition:
3717 @smallexample @c ada
3718 Sqrt_Calls : Natural := 0;
3720 function Sqrt (Arg : Float) return Float is
3721 pragma Postcondition
3722 (Sqrt_Calls = Sqrt_Calls'Old + 1);
3728 As this example, shows, the use of the @code{Old} attribute
3729 is often useful in postconditions to refer to the state on
3730 entry to the subprogram.
3732 Note that postconditions are only checked on normal returns
3733 from the subprogram. If an abnormal return results from
3734 raising an exception, then the postconditions are not checked.
3736 If a postcondition fails, then the exception
3737 @code{System.Assertions.Assert_Failure} is raised. If
3738 a message argument was supplied, then the given string
3739 will be used as the exception message. If no message
3740 argument was supplied, then the default message has
3741 the form "Postcondition failed at file:line". The
3742 exception is raised in the context of the subprogram
3743 body, so it is possible to catch postcondition failures
3744 within the subprogram body itself.
3746 Within a package spec, normal visibility rules
3747 in Ada would prevent forward references within a
3748 postcondition pragma to functions defined later in
3749 the same package. This would introduce undesirable
3750 ordering constraints. To avoid this problem, all
3751 postcondition pragmas are analyzed at the end of
3752 the package spec, allowing forward references.
3754 The following example shows that this even allows
3755 mutually recursive postconditions as in:
3757 @smallexample @c ada
3758 package Parity_Functions is
3759 function Odd (X : Natural) return Boolean;
3760 pragma Postcondition
3764 (x /= 0 and then Even (X - 1))));
3766 function Even (X : Natural) return Boolean;
3767 pragma Postcondition
3771 (x /= 1 and then Odd (X - 1))));
3773 end Parity_Functions;
3777 There are no restrictions on the complexity or form of
3778 conditions used within @code{Postcondition} pragmas.
3779 The following example shows that it is even possible
3780 to verify performance behavior.
3782 @smallexample @c ada
3785 Performance : constant Float;
3786 -- Performance constant set by implementation
3787 -- to match target architecture behavior.
3789 procedure Treesort (Arg : String);
3790 -- Sorts characters of argument using N*logN sort
3791 pragma Postcondition
3792 (Float (Clock - Clock'Old) <=
3793 Float (Arg'Length) *
3794 log (Float (Arg'Length)) *
3799 @node Pragma Precondition
3800 @unnumberedsec Pragma Precondition
3801 @cindex Preconditions
3802 @cindex Checks, preconditions
3803 @findex Preconditions
3807 @smallexample @c ada
3808 pragma Precondition (
3809 [Check =>] Boolean_Expression
3810 [,[Message =>] String_Expression]);
3814 The @code{Precondition} pragma is similar to @code{Postcondition}
3815 except that the corresponding checks take place immediately upon
3816 entry to the subprogram, and if a precondition fails, the exception
3817 is raised in the context of the caller, and the attribute 'Result
3818 cannot be used within the precondition expression.
3820 Otherwise, the placement and visibility rules are identical to those
3821 described for postconditions. The following is an example of use
3822 within a package spec:
3824 @smallexample @c ada
3825 package Math_Functions is
3827 function Sqrt (Arg : Float) return Float;
3828 pragma Precondition (Arg >= 0.0)
3833 @code{Postcondition} pragmas may appear either immediate following the
3834 (separate) declaration of a subprogram, or at the start of the
3835 declarations of a subprogram body. Only other pragmas may intervene
3836 (that is appear between the subprogram declaration and its
3837 postconditions, or appear before the postcondition in the
3838 declaration sequence in a subprogram body).
3840 @node Pragma Profile (Ravenscar)
3841 @unnumberedsec Pragma Profile (Ravenscar)
3846 @smallexample @c ada
3847 pragma Profile (Ravenscar);
3851 A configuration pragma that establishes the following set of configuration
3855 @item Task_Dispatching_Policy (FIFO_Within_Priorities)
3856 [RM D.2.2] Tasks are dispatched following a preemptive
3857 priority-ordered scheduling policy.
3859 @item Locking_Policy (Ceiling_Locking)
3860 [RM D.3] While tasks and interrupts execute a protected action, they inherit
3861 the ceiling priority of the corresponding protected object.
3863 @c @item Detect_Blocking
3864 @c This pragma forces the detection of potentially blocking operations within a
3865 @c protected operation, and to raise Program_Error if that happens.
3869 plus the following set of restrictions:
3872 @item Max_Entry_Queue_Length = 1
3873 Defines the maximum number of calls that are queued on a (protected) entry.
3874 Note that this restrictions is checked at run time. Violation of this
3875 restriction results in the raising of Program_Error exception at the point of
3876 the call. For the Profile (Ravenscar) the value of Max_Entry_Queue_Length is
3877 always 1 and hence no task can be queued on a protected entry.
3879 @item Max_Protected_Entries = 1
3880 [RM D.7] Specifies the maximum number of entries per protected type. The
3881 bounds of every entry family of a protected unit shall be static, or shall be
3882 defined by a discriminant of a subtype whose corresponding bound is static.
3883 For the Profile (Ravenscar) the value of Max_Protected_Entries is always 1.
3885 @item Max_Task_Entries = 0
3886 [RM D.7] Specifies the maximum number of entries
3887 per task. The bounds of every entry family
3888 of a task unit shall be static, or shall be
3889 defined by a discriminant of a subtype whose
3890 corresponding bound is static. A value of zero
3891 indicates that no rendezvous are possible. For
3892 the Profile (Ravenscar), the value of Max_Task_Entries is always
3895 @item No_Abort_Statements
3896 [RM D.7] There are no abort_statements, and there are
3897 no calls to Task_Identification.Abort_Task.
3899 @item No_Asynchronous_Control
3900 [RM D.7] There are no semantic dependences on the package
3901 Asynchronous_Task_Control.
3904 There are no semantic dependencies on the package Ada.Calendar.
3906 @item No_Dynamic_Attachment
3907 There is no call to any of the operations defined in package Ada.Interrupts
3908 (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler,
3909 Detach_Handler, and Reference).
3911 @item No_Dynamic_Priorities
3912 [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
3914 @item No_Implicit_Heap_Allocations
3915 [RM D.7] No constructs are allowed to cause implicit heap allocation.
3917 @item No_Local_Protected_Objects
3918 Protected objects and access types that designate
3919 such objects shall be declared only at library level.
3921 @item No_Protected_Type_Allocators
3922 There are no allocators for protected types or
3923 types containing protected subcomponents.
3925 @item No_Relative_Delay
3926 There are no delay_relative statements.
3928 @item No_Requeue_Statements
3929 Requeue statements are not allowed.
3931 @item No_Select_Statements
3932 There are no select_statements.
3934 @item No_Task_Allocators
3935 [RM D.7] There are no allocators for task types
3936 or types containing task subcomponents.
3938 @item No_Task_Attributes_Package
3939 There are no semantic dependencies on the Ada.Task_Attributes package.
3941 @item No_Task_Hierarchy
3942 [RM D.7] All (non-environment) tasks depend
3943 directly on the environment task of the partition.
3945 @item No_Task_Termination
3946 Tasks which terminate are erroneous.
3948 @item Simple_Barriers
3949 Entry barrier condition expressions shall be either static
3950 boolean expressions or boolean objects which are declared in
3951 the protected type which contains the entry.
3955 This set of configuration pragmas and restrictions correspond to the
3956 definition of the ``Ravenscar Profile'' for limited tasking, devised and
3957 published by the @cite{International Real-Time Ada Workshop}, 1997,
3958 and whose most recent description is available at
3959 @url{http://www-users.cs.york.ac.uk/~burns/ravenscar.ps}.
3961 The original definition of the profile was revised at subsequent IRTAW
3962 meetings. It has been included in the ISO
3963 @cite{Guide for the Use of the Ada Programming Language in High
3964 Integrity Systems}, and has been approved by ISO/IEC/SC22/WG9 for inclusion in
3965 the next revision of the standard. The formal definition given by
3966 the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and
3967 AI-305) available at
3968 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00249.TXT} and
3969 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00305.TXT}
3972 The above set is a superset of the restrictions provided by pragma
3973 @code{Profile (Restricted)}, it includes six additional restrictions
3974 (@code{Simple_Barriers}, @code{No_Select_Statements},
3975 @code{No_Calendar}, @code{No_Implicit_Heap_Allocations},
3976 @code{No_Relative_Delay} and @code{No_Task_Termination}). This means
3977 that pragma @code{Profile (Ravenscar)}, like the pragma
3978 @code{Profile (Restricted)},
3979 automatically causes the use of a simplified,
3980 more efficient version of the tasking run-time system.
3982 @node Pragma Profile (Restricted)
3983 @unnumberedsec Pragma Profile (Restricted)
3984 @findex Restricted Run Time
3988 @smallexample @c ada
3989 pragma Profile (Restricted);
3993 A configuration pragma that establishes the following set of restrictions:
3996 @item No_Abort_Statements
3997 @item No_Entry_Queue
3998 @item No_Task_Hierarchy
3999 @item No_Task_Allocators
4000 @item No_Dynamic_Priorities
4001 @item No_Terminate_Alternatives
4002 @item No_Dynamic_Attachment
4003 @item No_Protected_Type_Allocators
4004 @item No_Local_Protected_Objects
4005 @item No_Requeue_Statements
4006 @item No_Task_Attributes_Package
4007 @item Max_Asynchronous_Select_Nesting = 0
4008 @item Max_Task_Entries = 0
4009 @item Max_Protected_Entries = 1
4010 @item Max_Select_Alternatives = 0
4014 This set of restrictions causes the automatic selection of a simplified
4015 version of the run time that provides improved performance for the
4016 limited set of tasking functionality permitted by this set of restrictions.
4018 @node Pragma Psect_Object
4019 @unnumberedsec Pragma Psect_Object
4020 @findex Psect_Object
4024 @smallexample @c ada
4025 pragma Psect_Object (
4026 [Internal =>] LOCAL_NAME,
4027 [, [External =>] EXTERNAL_SYMBOL]
4028 [, [Size =>] EXTERNAL_SYMBOL]);
4032 | static_string_EXPRESSION
4036 This pragma is identical in effect to pragma @code{Common_Object}.
4038 @node Pragma Pure_Function
4039 @unnumberedsec Pragma Pure_Function
4040 @findex Pure_Function
4044 @smallexample @c ada
4045 pragma Pure_Function ([Entity =>] function_LOCAL_NAME);
4049 This pragma appears in the same declarative part as a function
4050 declaration (or a set of function declarations if more than one
4051 overloaded declaration exists, in which case the pragma applies
4052 to all entities). It specifies that the function @code{Entity} is
4053 to be considered pure for the purposes of code generation. This means
4054 that the compiler can assume that there are no side effects, and
4055 in particular that two calls with identical arguments produce the
4056 same result. It also means that the function can be used in an
4059 Note that, quite deliberately, there are no static checks to try
4060 to ensure that this promise is met, so @code{Pure_Function} can be used
4061 with functions that are conceptually pure, even if they do modify
4062 global variables. For example, a square root function that is
4063 instrumented to count the number of times it is called is still
4064 conceptually pure, and can still be optimized, even though it
4065 modifies a global variable (the count). Memo functions are another
4066 example (where a table of previous calls is kept and consulted to
4067 avoid re-computation).
4070 Note: Most functions in a @code{Pure} package are automatically pure, and
4071 there is no need to use pragma @code{Pure_Function} for such functions. One
4072 exception is any function that has at least one formal of type
4073 @code{System.Address} or a type derived from it. Such functions are not
4074 considered pure by default, since the compiler assumes that the
4075 @code{Address} parameter may be functioning as a pointer and that the
4076 referenced data may change even if the address value does not.
4077 Similarly, imported functions are not considered to be pure by default,
4078 since there is no way of checking that they are in fact pure. The use
4079 of pragma @code{Pure_Function} for such a function will override these default
4080 assumption, and cause the compiler to treat a designated subprogram as pure
4083 Note: If pragma @code{Pure_Function} is applied to a renamed function, it
4084 applies to the underlying renamed function. This can be used to
4085 disambiguate cases of overloading where some but not all functions
4086 in a set of overloaded functions are to be designated as pure.
4088 If pragma @code{Pure_Function} is applied to a library level function, the
4089 function is also considered pure from an optimization point of view, but the
4090 unit is not a Pure unit in the categorization sense. So for example, a function
4091 thus marked is free to @code{with} non-pure units.
4093 @node Pragma Restriction_Warnings
4094 @unnumberedsec Pragma Restriction_Warnings
4095 @findex Restriction_Warnings
4099 @smallexample @c ada
4100 pragma Restriction_Warnings
4101 (restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
4105 This pragma allows a series of restriction identifiers to be
4106 specified (the list of allowed identifiers is the same as for
4107 pragma @code{Restrictions}). For each of these identifiers
4108 the compiler checks for violations of the restriction, but
4109 generates a warning message rather than an error message
4110 if the restriction is violated.
4113 @unnumberedsec Pragma Shared
4117 This pragma is provided for compatibility with Ada 83. The syntax and
4118 semantics are identical to pragma Atomic.
4120 @node Pragma Source_File_Name
4121 @unnumberedsec Pragma Source_File_Name
4122 @findex Source_File_Name
4126 @smallexample @c ada
4127 pragma Source_File_Name (
4128 [Unit_Name =>] unit_NAME,
4129 Spec_File_Name => STRING_LITERAL);
4131 pragma Source_File_Name (
4132 [Unit_Name =>] unit_NAME,
4133 Body_File_Name => STRING_LITERAL);
4137 Use this to override the normal naming convention. It is a configuration
4138 pragma, and so has the usual applicability of configuration pragmas
4139 (i.e.@: it applies to either an entire partition, or to all units in a
4140 compilation, or to a single unit, depending on how it is used.
4141 @var{unit_name} is mapped to @var{file_name_literal}. The identifier for
4142 the second argument is required, and indicates whether this is the file
4143 name for the spec or for the body.
4145 Another form of the @code{Source_File_Name} pragma allows
4146 the specification of patterns defining alternative file naming schemes
4147 to apply to all files.
4149 @smallexample @c ada
4150 pragma Source_File_Name
4151 (Spec_File_Name => STRING_LITERAL
4152 [,Casing => CASING_SPEC]
4153 [,Dot_Replacement => STRING_LITERAL]);
4155 pragma Source_File_Name
4156 (Body_File_Name => STRING_LITERAL
4157 [,Casing => CASING_SPEC]
4158 [,Dot_Replacement => STRING_LITERAL]);
4160 pragma Source_File_Name
4161 (Subunit_File_Name => STRING_LITERAL
4162 [,Casing => CASING_SPEC]
4163 [,Dot_Replacement => STRING_LITERAL]);
4165 CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
4169 The first argument is a pattern that contains a single asterisk indicating
4170 the point at which the unit name is to be inserted in the pattern string
4171 to form the file name. The second argument is optional. If present it
4172 specifies the casing of the unit name in the resulting file name string.
4173 The default is lower case. Finally the third argument allows for systematic
4174 replacement of any dots in the unit name by the specified string literal.
4176 A pragma Source_File_Name cannot appear after a
4177 @ref{Pragma Source_File_Name_Project}.
4179 For more details on the use of the @code{Source_File_Name} pragma,
4180 @xref{Using Other File Names,,, gnat_ugn, @value{EDITION} User's Guide},
4181 and @ref{Alternative File Naming Schemes,,, gnat_ugn, @value{EDITION}
4184 @node Pragma Source_File_Name_Project
4185 @unnumberedsec Pragma Source_File_Name_Project
4186 @findex Source_File_Name_Project
4189 This pragma has the same syntax and semantics as pragma Source_File_Name.
4190 It is only allowed as a stand alone configuration pragma.
4191 It cannot appear after a @ref{Pragma Source_File_Name}, and
4192 most importantly, once pragma Source_File_Name_Project appears,
4193 no further Source_File_Name pragmas are allowed.
4195 The intention is that Source_File_Name_Project pragmas are always
4196 generated by the Project Manager in a manner consistent with the naming
4197 specified in a project file, and when naming is controlled in this manner,
4198 it is not permissible to attempt to modify this naming scheme using
4199 Source_File_Name pragmas (which would not be known to the project manager).
4201 @node Pragma Source_Reference
4202 @unnumberedsec Pragma Source_Reference
4203 @findex Source_Reference
4207 @smallexample @c ada
4208 pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
4212 This pragma must appear as the first line of a source file.
4213 @var{integer_literal} is the logical line number of the line following
4214 the pragma line (for use in error messages and debugging
4215 information). @var{string_literal} is a static string constant that
4216 specifies the file name to be used in error messages and debugging
4217 information. This is most notably used for the output of @code{gnatchop}
4218 with the @option{-r} switch, to make sure that the original unchopped
4219 source file is the one referred to.
4221 The second argument must be a string literal, it cannot be a static
4222 string expression other than a string literal. This is because its value
4223 is needed for error messages issued by all phases of the compiler.
4225 @node Pragma Stream_Convert
4226 @unnumberedsec Pragma Stream_Convert
4227 @findex Stream_Convert
4231 @smallexample @c ada
4232 pragma Stream_Convert (
4233 [Entity =>] type_LOCAL_NAME,
4234 [Read =>] function_NAME,
4235 [Write =>] function_NAME);
4239 This pragma provides an efficient way of providing stream functions for
4240 types defined in packages. Not only is it simpler to use than declaring
4241 the necessary functions with attribute representation clauses, but more
4242 significantly, it allows the declaration to made in such a way that the
4243 stream packages are not loaded unless they are needed. The use of
4244 the Stream_Convert pragma adds no overhead at all, unless the stream
4245 attributes are actually used on the designated type.
4247 The first argument specifies the type for which stream functions are
4248 provided. The second parameter provides a function used to read values
4249 of this type. It must name a function whose argument type may be any
4250 subtype, and whose returned type must be the type given as the first
4251 argument to the pragma.
4253 The meaning of the @var{Read}
4254 parameter is that if a stream attribute directly
4255 or indirectly specifies reading of the type given as the first parameter,
4256 then a value of the type given as the argument to the Read function is
4257 read from the stream, and then the Read function is used to convert this
4258 to the required target type.
4260 Similarly the @var{Write} parameter specifies how to treat write attributes
4261 that directly or indirectly apply to the type given as the first parameter.
4262 It must have an input parameter of the type specified by the first parameter,
4263 and the return type must be the same as the input type of the Read function.
4264 The effect is to first call the Write function to convert to the given stream
4265 type, and then write the result type to the stream.
4267 The Read and Write functions must not be overloaded subprograms. If necessary
4268 renamings can be supplied to meet this requirement.
4269 The usage of this attribute is best illustrated by a simple example, taken
4270 from the GNAT implementation of package Ada.Strings.Unbounded:
4272 @smallexample @c ada
4273 function To_Unbounded (S : String)
4274 return Unbounded_String
4275 renames To_Unbounded_String;
4277 pragma Stream_Convert
4278 (Unbounded_String, To_Unbounded, To_String);
4282 The specifications of the referenced functions, as given in the Ada
4283 Reference Manual are:
4285 @smallexample @c ada
4286 function To_Unbounded_String (Source : String)
4287 return Unbounded_String;
4289 function To_String (Source : Unbounded_String)
4294 The effect is that if the value of an unbounded string is written to a
4295 stream, then the representation of the item in the stream is in the same
4296 format used for @code{Standard.String}, and this same representation is
4297 expected when a value of this type is read from the stream.
4299 @node Pragma Style_Checks
4300 @unnumberedsec Pragma Style_Checks
4301 @findex Style_Checks
4305 @smallexample @c ada
4306 pragma Style_Checks (string_LITERAL | ALL_CHECKS |
4307 On | Off [, LOCAL_NAME]);
4311 This pragma is used in conjunction with compiler switches to control the
4312 built in style checking provided by GNAT@. The compiler switches, if set,
4313 provide an initial setting for the switches, and this pragma may be used
4314 to modify these settings, or the settings may be provided entirely by
4315 the use of the pragma. This pragma can be used anywhere that a pragma
4316 is legal, including use as a configuration pragma (including use in
4317 the @file{gnat.adc} file).
4319 The form with a string literal specifies which style options are to be
4320 activated. These are additive, so they apply in addition to any previously
4321 set style check options. The codes for the options are the same as those
4322 used in the @option{-gnaty} switch to @command{gcc} or @command{gnatmake}.
4323 For example the following two methods can be used to enable
4328 @smallexample @c ada
4329 pragma Style_Checks ("l");
4334 gcc -c -gnatyl @dots{}
4339 The form ALL_CHECKS activates all standard checks (its use is equivalent
4340 to the use of the @code{gnaty} switch with no options. @xref{Top,
4341 @value{EDITION} User's Guide, About This Guide, gnat_ugn,
4342 @value{EDITION} User's Guide}, for details.
4344 The forms with @code{Off} and @code{On}
4345 can be used to temporarily disable style checks
4346 as shown in the following example:
4348 @smallexample @c ada
4352 pragma Style_Checks ("k"); -- requires keywords in lower case
4353 pragma Style_Checks (Off); -- turn off style checks
4354 NULL; -- this will not generate an error message
4355 pragma Style_Checks (On); -- turn style checks back on
4356 NULL; -- this will generate an error message
4360 Finally the two argument form is allowed only if the first argument is
4361 @code{On} or @code{Off}. The effect is to turn of semantic style checks
4362 for the specified entity, as shown in the following example:
4364 @smallexample @c ada
4368 pragma Style_Checks ("r"); -- require consistency of identifier casing
4370 Rf1 : Integer := ARG; -- incorrect, wrong case
4371 pragma Style_Checks (Off, Arg);
4372 Rf2 : Integer := ARG; -- OK, no error
4375 @node Pragma Subtitle
4376 @unnumberedsec Pragma Subtitle
4381 @smallexample @c ada
4382 pragma Subtitle ([Subtitle =>] STRING_LITERAL);
4386 This pragma is recognized for compatibility with other Ada compilers
4387 but is ignored by GNAT@.
4389 @node Pragma Suppress
4390 @unnumberedsec Pragma Suppress
4395 @smallexample @c ada
4396 pragma Suppress (Identifier [, [On =>] Name]);
4400 This is a standard pragma, and supports all the check names required in
4401 the RM. It is included here because GNAT recognizes one additional check
4402 name: @code{Alignment_Check} which can be used to suppress alignment checks
4403 on addresses used in address clauses. Such checks can also be suppressed
4404 by suppressing range checks, but the specific use of @code{Alignment_Check}
4405 allows suppression of alignment checks without suppressing other range checks.
4407 @node Pragma Suppress_All
4408 @unnumberedsec Pragma Suppress_All
4409 @findex Suppress_All
4413 @smallexample @c ada
4414 pragma Suppress_All;
4418 This pragma can only appear immediately following a compilation
4419 unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
4420 which it follows. This pragma is implemented for compatibility with DEC
4421 Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
4422 configuration pragma is the preferred usage in GNAT@.
4424 @node Pragma Suppress_Exception_Locations
4425 @unnumberedsec Pragma Suppress_Exception_Locations
4426 @findex Suppress_Exception_Locations
4430 @smallexample @c ada
4431 pragma Suppress_Exception_Locations;
4435 In normal mode, a raise statement for an exception by default generates
4436 an exception message giving the file name and line number for the location
4437 of the raise. This is useful for debugging and logging purposes, but this
4438 entails extra space for the strings for the messages. The configuration
4439 pragma @code{Suppress_Exception_Locations} can be used to suppress the
4440 generation of these strings, with the result that space is saved, but the
4441 exception message for such raises is null. This configuration pragma may
4442 appear in a global configuration pragma file, or in a specific unit as
4443 usual. It is not required that this pragma be used consistently within
4444 a partition, so it is fine to have some units within a partition compiled
4445 with this pragma and others compiled in normal mode without it.
4447 @node Pragma Suppress_Initialization
4448 @unnumberedsec Pragma Suppress_Initialization
4449 @findex Suppress_Initialization
4450 @cindex Suppressing initialization
4451 @cindex Initialization, suppression of
4455 @smallexample @c ada
4456 pragma Suppress_Initialization ([Entity =>] type_Name);
4460 This pragma suppresses any implicit or explicit initialization
4461 associated with the given type name for all variables of this type.
4463 @node Pragma Task_Info
4464 @unnumberedsec Pragma Task_Info
4469 @smallexample @c ada
4470 pragma Task_Info (EXPRESSION);
4474 This pragma appears within a task definition (like pragma
4475 @code{Priority}) and applies to the task in which it appears. The
4476 argument must be of type @code{System.Task_Info.Task_Info_Type}.
4477 The @code{Task_Info} pragma provides system dependent control over
4478 aspects of tasking implementation, for example, the ability to map
4479 tasks to specific processors. For details on the facilities available
4480 for the version of GNAT that you are using, see the documentation
4481 in the spec of package System.Task_Info in the runtime
4484 @node Pragma Task_Name
4485 @unnumberedsec Pragma Task_Name
4490 @smallexample @c ada
4491 pragma Task_Name (string_EXPRESSION);
4495 This pragma appears within a task definition (like pragma
4496 @code{Priority}) and applies to the task in which it appears. The
4497 argument must be of type String, and provides a name to be used for
4498 the task instance when the task is created. Note that this expression
4499 is not required to be static, and in particular, it can contain
4500 references to task discriminants. This facility can be used to
4501 provide different names for different tasks as they are created,
4502 as illustrated in the example below.
4504 The task name is recorded internally in the run-time structures
4505 and is accessible to tools like the debugger. In addition the
4506 routine @code{Ada.Task_Identification.Image} will return this
4507 string, with a unique task address appended.
4509 @smallexample @c ada
4510 -- Example of the use of pragma Task_Name
4512 with Ada.Task_Identification;
4513 use Ada.Task_Identification;
4514 with Text_IO; use Text_IO;
4517 type Astring is access String;
4519 task type Task_Typ (Name : access String) is
4520 pragma Task_Name (Name.all);
4523 task body Task_Typ is
4524 Nam : constant String := Image (Current_Task);
4526 Put_Line ("-->" & Nam (1 .. 14) & "<--");
4529 type Ptr_Task is access Task_Typ;
4530 Task_Var : Ptr_Task;
4534 new Task_Typ (new String'("This is task 1"));
4536 new Task_Typ (new String'("This is task 2"));
4540 @node Pragma Task_Storage
4541 @unnumberedsec Pragma Task_Storage
4542 @findex Task_Storage
4545 @smallexample @c ada
4546 pragma Task_Storage (
4547 [Task_Type =>] LOCAL_NAME,
4548 [Top_Guard =>] static_integer_EXPRESSION);
4552 This pragma specifies the length of the guard area for tasks. The guard
4553 area is an additional storage area allocated to a task. A value of zero
4554 means that either no guard area is created or a minimal guard area is
4555 created, depending on the target. This pragma can appear anywhere a
4556 @code{Storage_Size} attribute definition clause is allowed for a task
4559 @node Pragma Time_Slice
4560 @unnumberedsec Pragma Time_Slice
4565 @smallexample @c ada
4566 pragma Time_Slice (static_duration_EXPRESSION);
4570 For implementations of GNAT on operating systems where it is possible
4571 to supply a time slice value, this pragma may be used for this purpose.
4572 It is ignored if it is used in a system that does not allow this control,
4573 or if it appears in other than the main program unit.
4575 Note that the effect of this pragma is identical to the effect of the
4576 DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
4579 @unnumberedsec Pragma Title
4584 @smallexample @c ada
4585 pragma Title (TITLING_OPTION [, TITLING OPTION]);
4588 [Title =>] STRING_LITERAL,
4589 | [Subtitle =>] STRING_LITERAL
4593 Syntax checked but otherwise ignored by GNAT@. This is a listing control
4594 pragma used in DEC Ada 83 implementations to provide a title and/or
4595 subtitle for the program listing. The program listing generated by GNAT
4596 does not have titles or subtitles.
4598 Unlike other pragmas, the full flexibility of named notation is allowed
4599 for this pragma, i.e.@: the parameters may be given in any order if named
4600 notation is used, and named and positional notation can be mixed
4601 following the normal rules for procedure calls in Ada.
4603 @node Pragma Unchecked_Union
4604 @unnumberedsec Pragma Unchecked_Union
4606 @findex Unchecked_Union
4610 @smallexample @c ada
4611 pragma Unchecked_Union (first_subtype_LOCAL_NAME);
4615 This pragma is used to specify a representation of a record type that is
4616 equivalent to a C union. It was introduced as a GNAT implementation defined
4617 pragma in the GNAT Ada 95 mode. Ada 2005 includes an extended version of this
4618 pragma, making it language defined, and GNAT fully implements this extended
4619 version in all language modes (Ada 83, Ada 95, and Ada 2005). For full
4620 details, consult the Ada 2005 Reference Manual, section B.3.3.
4622 @node Pragma Unimplemented_Unit
4623 @unnumberedsec Pragma Unimplemented_Unit
4624 @findex Unimplemented_Unit
4628 @smallexample @c ada
4629 pragma Unimplemented_Unit;
4633 If this pragma occurs in a unit that is processed by the compiler, GNAT
4634 aborts with the message @samp{@var{xxx} not implemented}, where
4635 @var{xxx} is the name of the current compilation unit. This pragma is
4636 intended to allow the compiler to handle unimplemented library units in
4639 The abort only happens if code is being generated. Thus you can use
4640 specs of unimplemented packages in syntax or semantic checking mode.
4642 @node Pragma Universal_Aliasing
4643 @unnumberedsec Pragma Universal_Aliasing
4644 @findex Universal_Aliasing
4648 @smallexample @c ada
4649 pragma Universal_Aliasing [([Entity =>] type_LOCAL_NAME)];
4653 @var{type_LOCAL_NAME} must refer to a type declaration in the current
4654 declarative part. The effect is to inhibit strict type-based aliasing
4655 optimization for the given type. In other words, the effect is as though
4656 access types designating this type were subject to pragma No_Strict_Aliasing.
4657 For a detailed description of the strict aliasing optimization, and the
4658 situations in which it must be suppressed, @xref{Optimization and Strict
4659 Aliasing,,, gnat_ugn, @value{EDITION} User's Guide}.
4661 @node Pragma Universal_Data
4662 @unnumberedsec Pragma Universal_Data
4663 @findex Universal_Data
4667 @smallexample @c ada
4668 pragma Universal_Data [(library_unit_Name)];
4672 This pragma is supported only for the AAMP target and is ignored for
4673 other targets. The pragma specifies that all library-level objects
4674 (Counter 0 data) associated with the library unit are to be accessed
4675 and updated using universal addressing (24-bit addresses for AAMP5)
4676 rather than the default of 16-bit Data Environment (DENV) addressing.
4677 Use of this pragma will generally result in less efficient code for
4678 references to global data associated with the library unit, but
4679 allows such data to be located anywhere in memory. This pragma is
4680 a library unit pragma, but can also be used as a configuration pragma
4681 (including use in the @file{gnat.adc} file). The functionality
4682 of this pragma is also available by applying the -univ switch on the
4683 compilations of units where universal addressing of the data is desired.
4685 @node Pragma Unmodified
4686 @unnumberedsec Pragma Unmodified
4688 @cindex Warnings, unmodified
4692 @smallexample @c ada
4693 pragma Unmodified (LOCAL_NAME @{, LOCAL_NAME@});
4697 This pragma signals that the assignable entities (variables,
4698 @code{out} parameters, @code{in out} parameters) whose names are listed are
4699 deliberately not assigned in the current source unit. This
4700 suppresses warnings about the
4701 entities being referenced but not assigned, and in addition a warning will be
4702 generated if one of these entities is in fact assigned in the
4703 same unit as the pragma (or in the corresponding body, or one
4706 This is particularly useful for clearly signaling that a particular
4707 parameter is not modified, even though the spec suggests that it might
4710 @node Pragma Unreferenced
4711 @unnumberedsec Pragma Unreferenced
4712 @findex Unreferenced
4713 @cindex Warnings, unreferenced
4717 @smallexample @c ada
4718 pragma Unreferenced (LOCAL_NAME @{, LOCAL_NAME@});
4719 pragma Unreferenced (library_unit_NAME @{, library_unit_NAME@});
4723 This pragma signals that the entities whose names are listed are
4724 deliberately not referenced in the current source unit. This
4725 suppresses warnings about the
4726 entities being unreferenced, and in addition a warning will be
4727 generated if one of these entities is in fact referenced in the
4728 same unit as the pragma (or in the corresponding body, or one
4731 This is particularly useful for clearly signaling that a particular
4732 parameter is not referenced in some particular subprogram implementation
4733 and that this is deliberate. It can also be useful in the case of
4734 objects declared only for their initialization or finalization side
4737 If @code{LOCAL_NAME} identifies more than one matching homonym in the
4738 current scope, then the entity most recently declared is the one to which
4739 the pragma applies. Note that in the case of accept formals, the pragma
4740 Unreferenced may appear immediately after the keyword @code{do} which
4741 allows the indication of whether or not accept formals are referenced
4742 or not to be given individually for each accept statement.
4744 The left hand side of an assignment does not count as a reference for the
4745 purpose of this pragma. Thus it is fine to assign to an entity for which
4746 pragma Unreferenced is given.
4748 Note that if a warning is desired for all calls to a given subprogram,
4749 regardless of whether they occur in the same unit as the subprogram
4750 declaration, then this pragma should not be used (calls from another
4751 unit would not be flagged); pragma Obsolescent can be used instead
4752 for this purpose, see @xref{Pragma Obsolescent}.
4754 The second form of pragma @code{Unreferenced} is used within a context
4755 clause. In this case the arguments must be unit names of units previously
4756 mentioned in @code{with} clauses (similar to the usage of pragma
4757 @code{Elaborate_All}. The effect is to suppress warnings about unreferenced
4758 units and unreferenced entities within these units.
4760 @node Pragma Unreferenced_Objects
4761 @unnumberedsec Pragma Unreferenced_Objects
4762 @findex Unreferenced_Objects
4763 @cindex Warnings, unreferenced
4767 @smallexample @c ada
4768 pragma Unreferenced_Objects (local_subtype_NAME @{, local_subtype_NAME@});
4772 This pragma signals that for the types or subtypes whose names are
4773 listed, objects which are declared with one of these types or subtypes may
4774 not be referenced, and if no references appear, no warnings are given.
4776 This is particularly useful for objects which are declared solely for their
4777 initialization and finalization effect. Such variables are sometimes referred
4778 to as RAII variables (Resource Acquisition Is Initialization). Using this
4779 pragma on the relevant type (most typically a limited controlled type), the
4780 compiler will automatically suppress unwanted warnings about these variables
4781 not being referenced.
4783 @node Pragma Unreserve_All_Interrupts
4784 @unnumberedsec Pragma Unreserve_All_Interrupts
4785 @findex Unreserve_All_Interrupts
4789 @smallexample @c ada
4790 pragma Unreserve_All_Interrupts;
4794 Normally certain interrupts are reserved to the implementation. Any attempt
4795 to attach an interrupt causes Program_Error to be raised, as described in
4796 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
4797 many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
4798 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
4799 interrupt execution.
4801 If the pragma @code{Unreserve_All_Interrupts} appears anywhere in any unit in
4802 a program, then all such interrupts are unreserved. This allows the
4803 program to handle these interrupts, but disables their standard
4804 functions. For example, if this pragma is used, then pressing
4805 @kbd{Ctrl-C} will not automatically interrupt execution. However,
4806 a program can then handle the @code{SIGINT} interrupt as it chooses.
4808 For a full list of the interrupts handled in a specific implementation,
4809 see the source code for the spec of @code{Ada.Interrupts.Names} in
4810 file @file{a-intnam.ads}. This is a target dependent file that contains the
4811 list of interrupts recognized for a given target. The documentation in
4812 this file also specifies what interrupts are affected by the use of
4813 the @code{Unreserve_All_Interrupts} pragma.
4815 For a more general facility for controlling what interrupts can be
4816 handled, see pragma @code{Interrupt_State}, which subsumes the functionality
4817 of the @code{Unreserve_All_Interrupts} pragma.
4819 @node Pragma Unsuppress
4820 @unnumberedsec Pragma Unsuppress
4825 @smallexample @c ada
4826 pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
4830 This pragma undoes the effect of a previous pragma @code{Suppress}. If
4831 there is no corresponding pragma @code{Suppress} in effect, it has no
4832 effect. The range of the effect is the same as for pragma
4833 @code{Suppress}. The meaning of the arguments is identical to that used
4834 in pragma @code{Suppress}.
4836 One important application is to ensure that checks are on in cases where
4837 code depends on the checks for its correct functioning, so that the code
4838 will compile correctly even if the compiler switches are set to suppress
4841 @node Pragma Use_VADS_Size
4842 @unnumberedsec Pragma Use_VADS_Size
4843 @cindex @code{Size}, VADS compatibility
4844 @findex Use_VADS_Size
4848 @smallexample @c ada
4849 pragma Use_VADS_Size;
4853 This is a configuration pragma. In a unit to which it applies, any use
4854 of the 'Size attribute is automatically interpreted as a use of the
4855 'VADS_Size attribute. Note that this may result in incorrect semantic
4856 processing of valid Ada 95 or Ada 2005 programs. This is intended to aid in
4857 the handling of existing code which depends on the interpretation of Size
4858 as implemented in the VADS compiler. See description of the VADS_Size
4859 attribute for further details.
4861 @node Pragma Validity_Checks
4862 @unnumberedsec Pragma Validity_Checks
4863 @findex Validity_Checks
4867 @smallexample @c ada
4868 pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
4872 This pragma is used in conjunction with compiler switches to control the
4873 built-in validity checking provided by GNAT@. The compiler switches, if set
4874 provide an initial setting for the switches, and this pragma may be used
4875 to modify these settings, or the settings may be provided entirely by
4876 the use of the pragma. This pragma can be used anywhere that a pragma
4877 is legal, including use as a configuration pragma (including use in
4878 the @file{gnat.adc} file).
4880 The form with a string literal specifies which validity options are to be
4881 activated. The validity checks are first set to include only the default
4882 reference manual settings, and then a string of letters in the string
4883 specifies the exact set of options required. The form of this string
4884 is exactly as described for the @option{-gnatVx} compiler switch (see the
4885 GNAT users guide for details). For example the following two methods
4886 can be used to enable validity checking for mode @code{in} and
4887 @code{in out} subprogram parameters:
4891 @smallexample @c ada
4892 pragma Validity_Checks ("im");
4897 gcc -c -gnatVim @dots{}
4902 The form ALL_CHECKS activates all standard checks (its use is equivalent
4903 to the use of the @code{gnatva} switch.
4905 The forms with @code{Off} and @code{On}
4906 can be used to temporarily disable validity checks
4907 as shown in the following example:
4909 @smallexample @c ada
4913 pragma Validity_Checks ("c"); -- validity checks for copies
4914 pragma Validity_Checks (Off); -- turn off validity checks
4915 A := B; -- B will not be validity checked
4916 pragma Validity_Checks (On); -- turn validity checks back on
4917 A := C; -- C will be validity checked
4920 @node Pragma Volatile
4921 @unnumberedsec Pragma Volatile
4926 @smallexample @c ada
4927 pragma Volatile (LOCAL_NAME);
4931 This pragma is defined by the Ada Reference Manual, and the GNAT
4932 implementation is fully conformant with this definition. The reason it
4933 is mentioned in this section is that a pragma of the same name was supplied
4934 in some Ada 83 compilers, including DEC Ada 83. The Ada 95 / Ada 2005
4935 implementation of pragma Volatile is upwards compatible with the
4936 implementation in DEC Ada 83.
4938 @node Pragma Warnings
4939 @unnumberedsec Pragma Warnings
4944 @smallexample @c ada
4945 pragma Warnings (On | Off);
4946 pragma Warnings (On | Off, LOCAL_NAME);
4947 pragma Warnings (static_string_EXPRESSION);
4948 pragma Warnings (On | Off, static_string_EXPRESSION);
4952 Normally warnings are enabled, with the output being controlled by
4953 the command line switch. Warnings (@code{Off}) turns off generation of
4954 warnings until a Warnings (@code{On}) is encountered or the end of the
4955 current unit. If generation of warnings is turned off using this
4956 pragma, then no warning messages are output, regardless of the
4957 setting of the command line switches.
4959 The form with a single argument may be used as a configuration pragma.
4961 If the @var{LOCAL_NAME} parameter is present, warnings are suppressed for
4962 the specified entity. This suppression is effective from the point where
4963 it occurs till the end of the extended scope of the variable (similar to
4964 the scope of @code{Suppress}).
4966 The form with a single static_string_EXPRESSION argument provides more precise
4967 control over which warnings are active. The string is a list of letters
4968 specifying which warnings are to be activated and which deactivated. The
4969 code for these letters is the same as the string used in the command
4970 line switch controlling warnings. The following is a brief summary. For
4971 full details see @ref{Warning Message Control,,, gnat_ugn, @value{EDITION}
4975 a turn on all optional warnings (except d h l .o)
4976 A turn off all optional warnings
4977 .a* turn on warnings for failing assertions
4978 .A turn off warnings for failing assertions
4979 b turn on warnings for bad fixed value (not multiple of small)
4980 B* turn off warnings for bad fixed value (not multiple of small)
4981 c turn on warnings for constant conditional
4982 C* turn off warnings for constant conditional
4983 .c turn on warnings for unrepped components
4984 .C* turn off warnings for unrepped components
4985 d turn on warnings for implicit dereference
4986 D* turn off warnings for implicit dereference
4987 e treat all warnings as errors
4988 f turn on warnings for unreferenced formal
4989 F* turn off warnings for unreferenced formal
4990 g* turn on warnings for unrecognized pragma
4991 G turn off warnings for unrecognized pragma
4992 h turn on warnings for hiding variable
4993 H* turn off warnings for hiding variable
4994 i* turn on warnings for implementation unit
4995 I turn off warnings for implementation unit
4996 j turn on warnings for obsolescent (annex J) feature
4997 J* turn off warnings for obsolescent (annex J) feature
4998 k turn on warnings on constant variable
4999 K* turn off warnings on constant variable
5000 l turn on warnings for missing elaboration pragma
5001 L* turn off warnings for missing elaboration pragma
5002 m turn on warnings for variable assigned but not read
5003 M* turn off warnings for variable assigned but not read
5004 n* normal warning mode (cancels -gnatws/-gnatwe)
5005 o* turn on warnings for address clause overlay
5006 O turn off warnings for address clause overlay
5007 .o turn on warnings for out parameters assigned but not read
5008 .O* turn off warnings for out parameters assigned but not read
5009 p turn on warnings for ineffective pragma Inline in frontend
5010 P* turn off warnings for ineffective pragma Inline in frontend
5011 q* turn on warnings for questionable missing parentheses
5012 Q turn off warnings for questionable missing parentheses
5013 r turn on warnings for redundant construct
5014 R* turn off warnings for redundant construct
5015 .r turn on warnings for object renaming function
5016 .R* turn off warnings for object renaming function
5017 s suppress all warnings
5018 t turn on warnings for tracking deleted code
5019 T* turn off warnings for tracking deleted code
5020 u turn on warnings for unused entity
5021 U* turn off warnings for unused entity
5022 v* turn on warnings for unassigned variable
5023 V turn off warnings for unassigned variable
5024 w* turn on warnings for wrong low bound assumption
5025 W turn off warnings for wrong low bound assumption
5026 x* turn on warnings for export/import
5027 X turn off warnings for export/import
5028 .x turn on warnings for non-local exceptions
5029 .X* turn off warnings for non-local exceptions
5030 y* turn on warnings for Ada 2005 incompatibility
5031 Y turn off warnings for Ada 2005 incompatibility
5032 z* turn on convention/size/align warnings for unchecked conversion
5033 Z turn off convention/size/align warnings for unchecked conversion
5034 * indicates default in above list
5038 The specified warnings will be in effect until the end of the program
5039 or another pragma Warnings is encountered. The effect of the pragma is
5040 cumulative. Initially the set of warnings is the standard default set
5041 as possibly modified by compiler switches. Then each pragma Warning
5042 modifies this set of warnings as specified. This form of the pragma may
5043 also be used as a configuration pragma.
5045 The fourth form, with an On|Off parameter and a string, is used to
5046 control individual messages, based on their text. The string argument
5047 is a pattern that is used to match against the text of individual
5048 warning messages (not including the initial "warnings: " tag).
5050 The pattern may contain asterisks which match zero or more characters in
5051 the message. For example, you can use
5052 @code{pragma Warnings (Off, "*bits of*unused")} to suppress the warning
5053 message @code{warning: 960 bits of "a" unused}. No other regular
5054 expression notations are permitted. All characters other than asterisk in
5055 these three specific cases are treated as literal characters in the match.
5057 There are two ways to use this pragma. The OFF form can be used as a
5058 configuration pragma. The effect is to suppress all warnings (if any)
5059 that match the pattern string throughout the compilation.
5061 The second usage is to suppress a warning locally, and in this case, two
5062 pragmas must appear in sequence:
5064 @smallexample @c ada
5065 pragma Warnings (Off, Pattern);
5066 @dots{} code where given warning is to be suppressed
5067 pragma Warnings (On, Pattern);
5071 In this usage, the pattern string must match in the Off and On pragmas,
5072 and at least one matching warning must be suppressed.
5074 @node Pragma Weak_External
5075 @unnumberedsec Pragma Weak_External
5076 @findex Weak_External
5080 @smallexample @c ada
5081 pragma Weak_External ([Entity =>] LOCAL_NAME);
5085 @var{LOCAL_NAME} must refer to an object that is declared at the library
5086 level. This pragma specifies that the given entity should be marked as a
5087 weak symbol for the linker. It is equivalent to @code{__attribute__((weak))}
5088 in GNU C and causes @var{LOCAL_NAME} to be emitted as a weak symbol instead
5089 of a regular symbol, that is to say a symbol that does not have to be
5090 resolved by the linker if used in conjunction with a pragma Import.
5092 When a weak symbol is not resolved by the linker, its address is set to
5093 zero. This is useful in writing interfaces to external modules that may
5094 or may not be linked in the final executable, for example depending on
5095 configuration settings.
5097 If a program references at run time an entity to which this pragma has been
5098 applied, and the corresponding symbol was not resolved at link time, then
5099 the execution of the program is erroneous. It is not erroneous to take the
5100 Address of such an entity, for example to guard potential references,
5101 as shown in the example below.
5103 Some file formats do not support weak symbols so not all target machines
5104 support this pragma.
5106 @smallexample @c ada
5107 -- Example of the use of pragma Weak_External
5109 package External_Module is
5111 pragma Import (C, key);
5112 pragma Weak_External (key);
5113 function Present return boolean;
5114 end External_Module;
5116 with System; use System;
5117 package body External_Module is
5118 function Present return boolean is
5120 return key'Address /= System.Null_Address;
5122 end External_Module;
5125 @node Pragma Wide_Character_Encoding
5126 @unnumberedsec Pragma Wide_Character_Encoding
5127 @findex Wide_Character_Encoding
5131 @smallexample @c ada
5132 pragma Wide_Character_Encoding (IDENTIFIER | CHARACTER_LITERAL);
5136 This pragma specifies the wide character encoding to be used in program
5137 source text appearing subsequently. It is a configuration pragma, but may
5138 also be used at any point that a pragma is allowed, and it is permissible
5139 to have more than one such pragma in a file, allowing multiple encodings
5140 to appear within the same file.
5142 The argument can be an identifier or a character literal. In the identifier
5143 case, it is one of @code{HEX}, @code{UPPER}, @code{SHIFT_JIS},
5144 @code{EUC}, @code{UTF8}, or @code{BRACKETS}. In the character literal
5145 case it is correspondingly one of the characters @samp{h}, @samp{u},
5146 @samp{s}, @samp{e}, @samp{8}, or @samp{b}.
5148 Note that when the pragma is used within a file, it affects only the
5149 encoding within that file, and does not affect withed units, specs,
5152 @node Implementation Defined Attributes
5153 @chapter Implementation Defined Attributes
5154 Ada defines (throughout the Ada reference manual,
5155 summarized in Annex K),
5156 a set of attributes that provide useful additional functionality in all
5157 areas of the language. These language defined attributes are implemented
5158 in GNAT and work as described in the Ada Reference Manual.
5160 In addition, Ada allows implementations to define additional
5161 attributes whose meaning is defined by the implementation. GNAT provides
5162 a number of these implementation-dependent attributes which can be used
5163 to extend and enhance the functionality of the compiler. This section of
5164 the GNAT reference manual describes these additional attributes.
5166 Note that any program using these attributes may not be portable to
5167 other compilers (although GNAT implements this set of attributes on all
5168 platforms). Therefore if portability to other compilers is an important
5169 consideration, you should minimize the use of these attributes.
5180 * Default_Bit_Order::
5190 * Has_Access_Values::
5191 * Has_Discriminants::
5198 * Max_Interrupt_Priority::
5200 * Maximum_Alignment::
5205 * Passed_By_Reference::
5218 * Unconstrained_Array::
5219 * Universal_Literal_String::
5220 * Unrestricted_Access::
5228 @unnumberedsec Abort_Signal
5229 @findex Abort_Signal
5231 @code{Standard'Abort_Signal} (@code{Standard} is the only allowed
5232 prefix) provides the entity for the special exception used to signal
5233 task abort or asynchronous transfer of control. Normally this attribute
5234 should only be used in the tasking runtime (it is highly peculiar, and
5235 completely outside the normal semantics of Ada, for a user program to
5236 intercept the abort exception).
5239 @unnumberedsec Address_Size
5240 @cindex Size of @code{Address}
5241 @findex Address_Size
5243 @code{Standard'Address_Size} (@code{Standard} is the only allowed
5244 prefix) is a static constant giving the number of bits in an
5245 @code{Address}. It is the same value as System.Address'Size,
5246 but has the advantage of being static, while a direct
5247 reference to System.Address'Size is non-static because Address
5251 @unnumberedsec Asm_Input
5254 The @code{Asm_Input} attribute denotes a function that takes two
5255 parameters. The first is a string, the second is an expression of the
5256 type designated by the prefix. The first (string) argument is required
5257 to be a static expression, and is the constraint for the parameter,
5258 (e.g.@: what kind of register is required). The second argument is the
5259 value to be used as the input argument. The possible values for the
5260 constant are the same as those used in the RTL, and are dependent on
5261 the configuration file used to built the GCC back end.
5262 @ref{Machine Code Insertions}
5265 @unnumberedsec Asm_Output
5268 The @code{Asm_Output} attribute denotes a function that takes two
5269 parameters. The first is a string, the second is the name of a variable
5270 of the type designated by the attribute prefix. The first (string)
5271 argument is required to be a static expression and designates the
5272 constraint for the parameter (e.g.@: what kind of register is
5273 required). The second argument is the variable to be updated with the
5274 result. The possible values for constraint are the same as those used in
5275 the RTL, and are dependent on the configuration file used to build the
5276 GCC back end. If there are no output operands, then this argument may
5277 either be omitted, or explicitly given as @code{No_Output_Operands}.
5278 @ref{Machine Code Insertions}
5281 @unnumberedsec AST_Entry
5285 This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
5286 the name of an entry, it yields a value of the predefined type AST_Handler
5287 (declared in the predefined package System, as extended by the use of
5288 pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
5289 be called when an AST occurs. For further details, refer to the @cite{DEC Ada
5290 Language Reference Manual}, section 9.12a.
5295 @code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
5296 offset within the storage unit (byte) that contains the first bit of
5297 storage allocated for the object. The value of this attribute is of the
5298 type @code{Universal_Integer}, and is always a non-negative number not
5299 exceeding the value of @code{System.Storage_Unit}.
5301 For an object that is a variable or a constant allocated in a register,
5302 the value is zero. (The use of this attribute does not force the
5303 allocation of a variable to memory).
5305 For an object that is a formal parameter, this attribute applies
5306 to either the matching actual parameter or to a copy of the
5307 matching actual parameter.
5309 For an access object the value is zero. Note that
5310 @code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
5311 designated object. Similarly for a record component
5312 @code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
5313 @code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
5314 are subject to index checks.
5316 This attribute is designed to be compatible with the DEC Ada 83 definition
5317 and implementation of the @code{Bit} attribute.
5320 @unnumberedsec Bit_Position
5321 @findex Bit_Position
5323 @code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
5324 of the fields of the record type, yields the bit
5325 offset within the record contains the first bit of
5326 storage allocated for the object. The value of this attribute is of the
5327 type @code{Universal_Integer}. The value depends only on the field
5328 @var{C} and is independent of the alignment of
5329 the containing record @var{R}.
5332 @unnumberedsec Code_Address
5333 @findex Code_Address
5334 @cindex Subprogram address
5335 @cindex Address of subprogram code
5338 attribute may be applied to subprograms in Ada 95 and Ada 2005, but the
5339 intended effect seems to be to provide
5340 an address value which can be used to call the subprogram by means of
5341 an address clause as in the following example:
5343 @smallexample @c ada
5344 procedure K is @dots{}
5347 for L'Address use K'Address;
5348 pragma Import (Ada, L);
5352 A call to @code{L} is then expected to result in a call to @code{K}@.
5353 In Ada 83, where there were no access-to-subprogram values, this was
5354 a common work-around for getting the effect of an indirect call.
5355 GNAT implements the above use of @code{Address} and the technique
5356 illustrated by the example code works correctly.
5358 However, for some purposes, it is useful to have the address of the start
5359 of the generated code for the subprogram. On some architectures, this is
5360 not necessarily the same as the @code{Address} value described above.
5361 For example, the @code{Address} value may reference a subprogram
5362 descriptor rather than the subprogram itself.
5364 The @code{'Code_Address} attribute, which can only be applied to
5365 subprogram entities, always returns the address of the start of the
5366 generated code of the specified subprogram, which may or may not be
5367 the same value as is returned by the corresponding @code{'Address}
5370 @node Default_Bit_Order
5371 @unnumberedsec Default_Bit_Order
5373 @cindex Little endian
5374 @findex Default_Bit_Order
5376 @code{Standard'Default_Bit_Order} (@code{Standard} is the only
5377 permissible prefix), provides the value @code{System.Default_Bit_Order}
5378 as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
5379 @code{Low_Order_First}). This is used to construct the definition of
5380 @code{Default_Bit_Order} in package @code{System}.
5383 @unnumberedsec Elaborated
5386 The prefix of the @code{'Elaborated} attribute must be a unit name. The
5387 value is a Boolean which indicates whether or not the given unit has been
5388 elaborated. This attribute is primarily intended for internal use by the
5389 generated code for dynamic elaboration checking, but it can also be used
5390 in user programs. The value will always be True once elaboration of all
5391 units has been completed. An exception is for units which need no
5392 elaboration, the value is always False for such units.
5395 @unnumberedsec Elab_Body
5398 This attribute can only be applied to a program unit name. It returns
5399 the entity for the corresponding elaboration procedure for elaborating
5400 the body of the referenced unit. This is used in the main generated
5401 elaboration procedure by the binder and is not normally used in any
5402 other context. However, there may be specialized situations in which it
5403 is useful to be able to call this elaboration procedure from Ada code,
5404 e.g.@: if it is necessary to do selective re-elaboration to fix some
5408 @unnumberedsec Elab_Spec
5411 This attribute can only be applied to a program unit name. It returns
5412 the entity for the corresponding elaboration procedure for elaborating
5413 the spec of the referenced unit. This is used in the main
5414 generated elaboration procedure by the binder and is not normally used
5415 in any other context. However, there may be specialized situations in
5416 which it is useful to be able to call this elaboration procedure from
5417 Ada code, e.g.@: if it is necessary to do selective re-elaboration to fix
5422 @cindex Ada 83 attributes
5425 The @code{Emax} attribute is provided for compatibility with Ada 83. See
5426 the Ada 83 reference manual for an exact description of the semantics of
5430 @unnumberedsec Enabled
5433 The @code{Enabled} attribute allows an application program to check at compile
5434 time to see if the designated check is currently enabled. The prefix is a
5435 simple identifier, referencing any predefined check name (other than
5436 @code{All_Checks}) or a check name introduced by pragma Check_Name. If
5437 no argument is given for the attribute, the check is for the general state
5438 of the check, if an argument is given, then it is an entity name, and the
5439 check indicates whether an @code{Suppress} or @code{Unsuppress} has been
5440 given naming the entity (if not, then the argument is ignored).
5442 Note that instantiations inherit the check status at the point of the
5443 instantiation, so a useful idiom is to have a library package that
5444 introduces a check name with @code{pragma Check_Name}, and then contains
5445 generic packages or subprograms which use the @code{Enabled} attribute
5446 to see if the check is enabled. A user of this package can then issue
5447 a @code{pragma Suppress} or @code{pragma Unsuppress} before instantiating
5448 the package or subprogram, controlling whether the check will be present.
5451 @unnumberedsec Enum_Rep
5452 @cindex Representation of enums
5455 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5456 function with the following spec:
5458 @smallexample @c ada
5459 function @var{S}'Enum_Rep (Arg : @var{S}'Base)
5460 return @i{Universal_Integer};
5464 It is also allowable to apply @code{Enum_Rep} directly to an object of an
5465 enumeration type or to a non-overloaded enumeration
5466 literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
5467 @code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
5468 enumeration literal or object.
5470 The function returns the representation value for the given enumeration
5471 value. This will be equal to value of the @code{Pos} attribute in the
5472 absence of an enumeration representation clause. This is a static
5473 attribute (i.e.@: the result is static if the argument is static).
5475 @code{@var{S}'Enum_Rep} can also be used with integer types and objects,
5476 in which case it simply returns the integer value. The reason for this
5477 is to allow it to be used for @code{(<>)} discrete formal arguments in
5478 a generic unit that can be instantiated with either enumeration types
5479 or integer types. Note that if @code{Enum_Rep} is used on a modular
5480 type whose upper bound exceeds the upper bound of the largest signed
5481 integer type, and the argument is a variable, so that the universal
5482 integer calculation is done at run time, then the call to @code{Enum_Rep}
5483 may raise @code{Constraint_Error}.
5486 @unnumberedsec Enum_Val
5487 @cindex Representation of enums
5490 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
5491 function with the following spec:
5493 @smallexample @c ada
5494 function @var{S}'Enum_Rep (Arg : @i{Universal_Integer)
5495 return @var{S}'Base};
5499 The function returns the enumeration value whose representation matches the
5500 argument, or raises Constraint_Error if no enumeration literal of the type
5501 has the matching value.
5502 This will be equal to value of the @code{Val} attribute in the
5503 absence of an enumeration representation clause. This is a static
5504 attribute (i.e.@: the result is static if the argument is static).
5507 @unnumberedsec Epsilon
5508 @cindex Ada 83 attributes
5511 The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
5512 the Ada 83 reference manual for an exact description of the semantics of
5516 @unnumberedsec Fixed_Value
5519 For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
5520 function with the following specification:
5522 @smallexample @c ada
5523 function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
5528 The value returned is the fixed-point value @var{V} such that
5530 @smallexample @c ada
5531 @var{V} = Arg * @var{S}'Small
5535 The effect is thus similar to first converting the argument to the
5536 integer type used to represent @var{S}, and then doing an unchecked
5537 conversion to the fixed-point type. The difference is
5538 that there are full range checks, to ensure that the result is in range.
5539 This attribute is primarily intended for use in implementation of the
5540 input-output functions for fixed-point values.
5542 @node Has_Access_Values
5543 @unnumberedsec Has_Access_Values
5544 @cindex Access values, testing for
5545 @findex Has_Access_Values
5547 The prefix of the @code{Has_Access_Values} attribute is a type. The result
5548 is a Boolean value which is True if the is an access type, or is a composite
5549 type with a component (at any nesting depth) that is an access type, and is
5551 The intended use of this attribute is in conjunction with generic
5552 definitions. If the attribute is applied to a generic private type, it
5553 indicates whether or not the corresponding actual type has access values.
5555 @node Has_Discriminants
5556 @unnumberedsec Has_Discriminants
5557 @cindex Discriminants, testing for
5558 @findex Has_Discriminants
5560 The prefix of the @code{Has_Discriminants} attribute is a type. The result
5561 is a Boolean value which is True if the type has discriminants, and False
5562 otherwise. The intended use of this attribute is in conjunction with generic
5563 definitions. If the attribute is applied to a generic private type, it
5564 indicates whether or not the corresponding actual type has discriminants.
5570 The @code{Img} attribute differs from @code{Image} in that it may be
5571 applied to objects as well as types, in which case it gives the
5572 @code{Image} for the subtype of the object. This is convenient for
5575 @smallexample @c ada
5576 Put_Line ("X = " & X'Img);
5580 has the same meaning as the more verbose:
5582 @smallexample @c ada
5583 Put_Line ("X = " & @var{T}'Image (X));
5587 where @var{T} is the (sub)type of the object @code{X}.
5590 @unnumberedsec Integer_Value
5591 @findex Integer_Value
5593 For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
5594 function with the following spec:
5596 @smallexample @c ada
5597 function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
5602 The value returned is the integer value @var{V}, such that
5604 @smallexample @c ada
5605 Arg = @var{V} * @var{T}'Small
5609 where @var{T} is the type of @code{Arg}.
5610 The effect is thus similar to first doing an unchecked conversion from
5611 the fixed-point type to its corresponding implementation type, and then
5612 converting the result to the target integer type. The difference is
5613 that there are full range checks, to ensure that the result is in range.
5614 This attribute is primarily intended for use in implementation of the
5615 standard input-output functions for fixed-point values.
5618 @unnumberedsec Invalid_Value
5619 @findex Invalid_Value
5621 For every scalar type S, S'Invalid_Value returns an undefined value of the
5622 type. If possible this value is an invalid representation for the type. The
5623 value returned is identical to the value used to initialize an otherwise
5624 uninitialized value of the type if pragma Initialize_Scalars is used,
5625 including the ability to modify the value with the binder -Sxx flag and
5626 relevant environment variables at run time.
5629 @unnumberedsec Large
5630 @cindex Ada 83 attributes
5633 The @code{Large} attribute is provided for compatibility with Ada 83. See
5634 the Ada 83 reference manual for an exact description of the semantics of
5638 @unnumberedsec Machine_Size
5639 @findex Machine_Size
5641 This attribute is identical to the @code{Object_Size} attribute. It is
5642 provided for compatibility with the DEC Ada 83 attribute of this name.
5645 @unnumberedsec Mantissa
5646 @cindex Ada 83 attributes
5649 The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
5650 the Ada 83 reference manual for an exact description of the semantics of
5653 @node Max_Interrupt_Priority
5654 @unnumberedsec Max_Interrupt_Priority
5655 @cindex Interrupt priority, maximum
5656 @findex Max_Interrupt_Priority
5658 @code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
5659 permissible prefix), provides the same value as
5660 @code{System.Max_Interrupt_Priority}.
5663 @unnumberedsec Max_Priority
5664 @cindex Priority, maximum
5665 @findex Max_Priority
5667 @code{Standard'Max_Priority} (@code{Standard} is the only permissible
5668 prefix) provides the same value as @code{System.Max_Priority}.
5670 @node Maximum_Alignment
5671 @unnumberedsec Maximum_Alignment
5672 @cindex Alignment, maximum
5673 @findex Maximum_Alignment
5675 @code{Standard'Maximum_Alignment} (@code{Standard} is the only
5676 permissible prefix) provides the maximum useful alignment value for the
5677 target. This is a static value that can be used to specify the alignment
5678 for an object, guaranteeing that it is properly aligned in all
5681 @node Mechanism_Code
5682 @unnumberedsec Mechanism_Code
5683 @cindex Return values, passing mechanism
5684 @cindex Parameters, passing mechanism
5685 @findex Mechanism_Code
5687 @code{@var{function}'Mechanism_Code} yields an integer code for the
5688 mechanism used for the result of function, and
5689 @code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
5690 used for formal parameter number @var{n} (a static integer value with 1
5691 meaning the first parameter) of @var{subprogram}. The code returned is:
5699 by descriptor (default descriptor class)
5701 by descriptor (UBS: unaligned bit string)
5703 by descriptor (UBSB: aligned bit string with arbitrary bounds)
5705 by descriptor (UBA: unaligned bit array)
5707 by descriptor (S: string, also scalar access type parameter)
5709 by descriptor (SB: string with arbitrary bounds)
5711 by descriptor (A: contiguous array)
5713 by descriptor (NCA: non-contiguous array)
5717 Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
5720 @node Null_Parameter
5721 @unnumberedsec Null_Parameter
5722 @cindex Zero address, passing
5723 @findex Null_Parameter
5725 A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
5726 type or subtype @var{T} allocated at machine address zero. The attribute
5727 is allowed only as the default expression of a formal parameter, or as
5728 an actual expression of a subprogram call. In either case, the
5729 subprogram must be imported.
5731 The identity of the object is represented by the address zero in the
5732 argument list, independent of the passing mechanism (explicit or
5735 This capability is needed to specify that a zero address should be
5736 passed for a record or other composite object passed by reference.
5737 There is no way of indicating this without the @code{Null_Parameter}
5741 @unnumberedsec Object_Size
5742 @cindex Size, used for objects
5745 The size of an object is not necessarily the same as the size of the type
5746 of an object. This is because by default object sizes are increased to be
5747 a multiple of the alignment of the object. For example,
5748 @code{Natural'Size} is
5749 31, but by default objects of type @code{Natural} will have a size of 32 bits.
5750 Similarly, a record containing an integer and a character:
5752 @smallexample @c ada
5760 will have a size of 40 (that is @code{Rec'Size} will be 40. The
5761 alignment will be 4, because of the
5762 integer field, and so the default size of record objects for this type
5763 will be 64 (8 bytes).
5767 @cindex Capturing Old values
5768 @cindex Postconditions
5770 The attribute Prefix'Old can be used within a
5771 subprogram to refer to the value of the prefix on entry. So for
5772 example if you have an argument of a record type X called Arg1,
5773 you can refer to Arg1.Field'Old which yields the value of
5774 Arg1.Field on entry. The implementation simply involves generating
5775 an object declaration which captures the value on entry. Any
5776 prefix is allowed except one of a limited type (since limited
5777 types cannot be copied to capture their values) or a local variable
5778 (since it does not exist at subprogram entry time).
5780 The following example shows the use of 'Old to implement
5781 a test of a postcondition:
5783 @smallexample @c ada
5794 package body Old_Pkg is
5795 Count : Natural := 0;
5799 ... code manipulating the value of Count
5801 pragma Assert (Count = Count'Old + 1);
5807 Note that it is allowed to apply 'Old to a constant entity, but this will
5808 result in a warning, since the old and new values will always be the same.
5810 @node Passed_By_Reference
5811 @unnumberedsec Passed_By_Reference
5812 @cindex Parameters, when passed by reference
5813 @findex Passed_By_Reference
5815 @code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
5816 a value of type @code{Boolean} value that is @code{True} if the type is
5817 normally passed by reference and @code{False} if the type is normally
5818 passed by copy in calls. For scalar types, the result is always @code{False}
5819 and is static. For non-scalar types, the result is non-static.
5822 @unnumberedsec Pool_Address
5823 @cindex Parameters, when passed by reference
5824 @findex Pool_Address
5826 @code{@var{X}'Pool_Address} for any object @var{X} returns the address
5827 of X within its storage pool. This is the same as
5828 @code{@var{X}'Address}, except that for an unconstrained array whose
5829 bounds are allocated just before the first component,
5830 @code{@var{X}'Pool_Address} returns the address of those bounds,
5831 whereas @code{@var{X}'Address} returns the address of the first
5834 Here, we are interpreting ``storage pool'' broadly to mean ``wherever
5835 the object is allocated'', which could be a user-defined storage pool,
5836 the global heap, on the stack, or in a static memory area. For an
5837 object created by @code{new}, @code{@var{Ptr.all}'Pool_Address} is
5838 what is passed to @code{Allocate} and returned from @code{Deallocate}.
5841 @unnumberedsec Range_Length
5842 @findex Range_Length
5844 @code{@var{type}'Range_Length} for any discrete type @var{type} yields
5845 the number of values represented by the subtype (zero for a null
5846 range). The result is static for static subtypes. @code{Range_Length}
5847 applied to the index subtype of a one dimensional array always gives the
5848 same result as @code{Range} applied to the array itself.
5851 @unnumberedsec Safe_Emax
5852 @cindex Ada 83 attributes
5855 The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
5856 the Ada 83 reference manual for an exact description of the semantics of
5860 @unnumberedsec Safe_Large
5861 @cindex Ada 83 attributes
5864 The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
5865 the Ada 83 reference manual for an exact description of the semantics of
5869 @unnumberedsec Small
5870 @cindex Ada 83 attributes
5873 The @code{Small} attribute is defined in Ada 95 (and Ada 2005) only for
5875 GNAT also allows this attribute to be applied to floating-point types
5876 for compatibility with Ada 83. See
5877 the Ada 83 reference manual for an exact description of the semantics of
5878 this attribute when applied to floating-point types.
5881 @unnumberedsec Storage_Unit
5882 @findex Storage_Unit
5884 @code{Standard'Storage_Unit} (@code{Standard} is the only permissible
5885 prefix) provides the same value as @code{System.Storage_Unit}.
5888 @unnumberedsec Stub_Type
5891 The GNAT implementation of remote access-to-classwide types is
5892 organized as described in AARM section E.4 (20.t): a value of an RACW type
5893 (designating a remote object) is represented as a normal access
5894 value, pointing to a "stub" object which in turn contains the
5895 necessary information to contact the designated remote object. A
5896 call on any dispatching operation of such a stub object does the
5897 remote call, if necessary, using the information in the stub object
5898 to locate the target partition, etc.
5900 For a prefix @code{T} that denotes a remote access-to-classwide type,
5901 @code{T'Stub_Type} denotes the type of the corresponding stub objects.
5903 By construction, the layout of @code{T'Stub_Type} is identical to that of
5904 type @code{RACW_Stub_Type} declared in the internal implementation-defined
5905 unit @code{System.Partition_Interface}. Use of this attribute will create
5906 an implicit dependency on this unit.
5909 @unnumberedsec Target_Name
5912 @code{Standard'Target_Name} (@code{Standard} is the only permissible
5913 prefix) provides a static string value that identifies the target
5914 for the current compilation. For GCC implementations, this is the
5915 standard gcc target name without the terminating slash (for
5916 example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
5922 @code{Standard'Tick} (@code{Standard} is the only permissible prefix)
5923 provides the same value as @code{System.Tick},
5926 @unnumberedsec To_Address
5929 The @code{System'To_Address}
5930 (@code{System} is the only permissible prefix)
5931 denotes a function identical to
5932 @code{System.Storage_Elements.To_Address} except that
5933 it is a static attribute. This means that if its argument is
5934 a static expression, then the result of the attribute is a
5935 static expression. The result is that such an expression can be
5936 used in contexts (e.g.@: preelaborable packages) which require a
5937 static expression and where the function call could not be used
5938 (since the function call is always non-static, even if its
5939 argument is static).
5942 @unnumberedsec Type_Class
5945 @code{@var{type}'Type_Class} for any type or subtype @var{type} yields
5946 the value of the type class for the full type of @var{type}. If
5947 @var{type} is a generic formal type, the value is the value for the
5948 corresponding actual subtype. The value of this attribute is of type
5949 @code{System.Aux_DEC.Type_Class}, which has the following definition:
5951 @smallexample @c ada
5953 (Type_Class_Enumeration,
5955 Type_Class_Fixed_Point,
5956 Type_Class_Floating_Point,
5961 Type_Class_Address);
5965 Protected types yield the value @code{Type_Class_Task}, which thus
5966 applies to all concurrent types. This attribute is designed to
5967 be compatible with the DEC Ada 83 attribute of the same name.
5970 @unnumberedsec UET_Address
5973 The @code{UET_Address} attribute can only be used for a prefix which
5974 denotes a library package. It yields the address of the unit exception
5975 table when zero cost exception handling is used. This attribute is
5976 intended only for use within the GNAT implementation. See the unit
5977 @code{Ada.Exceptions} in files @file{a-except.ads} and @file{a-except.adb}
5978 for details on how this attribute is used in the implementation.
5980 @node Unconstrained_Array
5981 @unnumberedsec Unconstrained_Array
5982 @findex Unconstrained_Array
5984 The @code{Unconstrained_Array} attribute can be used with a prefix that
5985 denotes any type or subtype. It is a static attribute that yields
5986 @code{True} if the prefix designates an unconstrained array,
5987 and @code{False} otherwise. In a generic instance, the result is
5988 still static, and yields the result of applying this test to the
5991 @node Universal_Literal_String
5992 @unnumberedsec Universal_Literal_String
5993 @cindex Named numbers, representation of
5994 @findex Universal_Literal_String
5996 The prefix of @code{Universal_Literal_String} must be a named
5997 number. The static result is the string consisting of the characters of
5998 the number as defined in the original source. This allows the user
5999 program to access the actual text of named numbers without intermediate
6000 conversions and without the need to enclose the strings in quotes (which
6001 would preclude their use as numbers). This is used internally for the
6002 construction of values of the floating-point attributes from the file
6003 @file{ttypef.ads}, but may also be used by user programs.
6005 For example, the following program prints the first 50 digits of pi:
6007 @smallexample @c ada
6008 with Text_IO; use Text_IO;
6012 Put (Ada.Numerics.Pi'Universal_Literal_String);
6016 @node Unrestricted_Access
6017 @unnumberedsec Unrestricted_Access
6018 @cindex @code{Access}, unrestricted
6019 @findex Unrestricted_Access
6021 The @code{Unrestricted_Access} attribute is similar to @code{Access}
6022 except that all accessibility and aliased view checks are omitted. This
6023 is a user-beware attribute. It is similar to
6024 @code{Address}, for which it is a desirable replacement where the value
6025 desired is an access type. In other words, its effect is identical to
6026 first applying the @code{Address} attribute and then doing an unchecked
6027 conversion to a desired access type. In GNAT, but not necessarily in
6028 other implementations, the use of static chains for inner level
6029 subprograms means that @code{Unrestricted_Access} applied to a
6030 subprogram yields a value that can be called as long as the subprogram
6031 is in scope (normal Ada accessibility rules restrict this usage).
6033 It is possible to use @code{Unrestricted_Access} for any type, but care
6034 must be exercised if it is used to create pointers to unconstrained
6035 objects. In this case, the resulting pointer has the same scope as the
6036 context of the attribute, and may not be returned to some enclosing
6037 scope. For instance, a function cannot use @code{Unrestricted_Access}
6038 to create a unconstrained pointer and then return that value to the
6042 @unnumberedsec VADS_Size
6043 @cindex @code{Size}, VADS compatibility
6046 The @code{'VADS_Size} attribute is intended to make it easier to port
6047 legacy code which relies on the semantics of @code{'Size} as implemented
6048 by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
6049 same semantic interpretation. In particular, @code{'VADS_Size} applied
6050 to a predefined or other primitive type with no Size clause yields the
6051 Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
6052 typical machines). In addition @code{'VADS_Size} applied to an object
6053 gives the result that would be obtained by applying the attribute to
6054 the corresponding type.
6057 @unnumberedsec Value_Size
6058 @cindex @code{Size}, setting for not-first subtype
6060 @code{@var{type}'Value_Size} is the number of bits required to represent
6061 a value of the given subtype. It is the same as @code{@var{type}'Size},
6062 but, unlike @code{Size}, may be set for non-first subtypes.
6065 @unnumberedsec Wchar_T_Size
6066 @findex Wchar_T_Size
6067 @code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
6068 prefix) provides the size in bits of the C @code{wchar_t} type
6069 primarily for constructing the definition of this type in
6070 package @code{Interfaces.C}.
6073 @unnumberedsec Word_Size
6075 @code{Standard'Word_Size} (@code{Standard} is the only permissible
6076 prefix) provides the value @code{System.Word_Size}.
6078 @c ------------------------
6079 @node Implementation Advice
6080 @chapter Implementation Advice
6082 The main text of the Ada Reference Manual describes the required
6083 behavior of all Ada compilers, and the GNAT compiler conforms to
6086 In addition, there are sections throughout the Ada Reference Manual headed
6087 by the phrase ``Implementation advice''. These sections are not normative,
6088 i.e., they do not specify requirements that all compilers must
6089 follow. Rather they provide advice on generally desirable behavior. You
6090 may wonder why they are not requirements. The most typical answer is
6091 that they describe behavior that seems generally desirable, but cannot
6092 be provided on all systems, or which may be undesirable on some systems.
6094 As far as practical, GNAT follows the implementation advice sections in
6095 the Ada Reference Manual. This chapter contains a table giving the
6096 reference manual section number, paragraph number and several keywords
6097 for each advice. Each entry consists of the text of the advice followed
6098 by the GNAT interpretation of this advice. Most often, this simply says
6099 ``followed'', which means that GNAT follows the advice. However, in a
6100 number of cases, GNAT deliberately deviates from this advice, in which
6101 case the text describes what GNAT does and why.
6103 @cindex Error detection
6104 @unnumberedsec 1.1.3(20): Error Detection
6107 If an implementation detects the use of an unsupported Specialized Needs
6108 Annex feature at run time, it should raise @code{Program_Error} if
6111 Not relevant. All specialized needs annex features are either supported,
6112 or diagnosed at compile time.
6115 @unnumberedsec 1.1.3(31): Child Units
6118 If an implementation wishes to provide implementation-defined
6119 extensions to the functionality of a language-defined library unit, it
6120 should normally do so by adding children to the library unit.
6124 @cindex Bounded errors
6125 @unnumberedsec 1.1.5(12): Bounded Errors
6128 If an implementation detects a bounded error or erroneous
6129 execution, it should raise @code{Program_Error}.
6131 Followed in all cases in which the implementation detects a bounded
6132 error or erroneous execution. Not all such situations are detected at
6136 @unnumberedsec 2.8(16): Pragmas
6139 Normally, implementation-defined pragmas should have no semantic effect
6140 for error-free programs; that is, if the implementation-defined pragmas
6141 are removed from a working program, the program should still be legal,
6142 and should still have the same semantics.
6144 The following implementation defined pragmas are exceptions to this
6156 @item CPP_Constructor
6160 @item Interface_Name
6162 @item Machine_Attribute
6164 @item Unimplemented_Unit
6166 @item Unchecked_Union
6171 In each of the above cases, it is essential to the purpose of the pragma
6172 that this advice not be followed. For details see the separate section
6173 on implementation defined pragmas.
6175 @unnumberedsec 2.8(17-19): Pragmas
6178 Normally, an implementation should not define pragmas that can
6179 make an illegal program legal, except as follows:
6183 A pragma used to complete a declaration, such as a pragma @code{Import};
6187 A pragma used to configure the environment by adding, removing, or
6188 replacing @code{library_items}.
6190 See response to paragraph 16 of this same section.
6192 @cindex Character Sets
6193 @cindex Alternative Character Sets
6194 @unnumberedsec 3.5.2(5): Alternative Character Sets
6197 If an implementation supports a mode with alternative interpretations
6198 for @code{Character} and @code{Wide_Character}, the set of graphic
6199 characters of @code{Character} should nevertheless remain a proper
6200 subset of the set of graphic characters of @code{Wide_Character}. Any
6201 character set ``localizations'' should be reflected in the results of
6202 the subprograms defined in the language-defined package
6203 @code{Characters.Handling} (see A.3) available in such a mode. In a mode with
6204 an alternative interpretation of @code{Character}, the implementation should
6205 also support a corresponding change in what is a legal
6206 @code{identifier_letter}.
6208 Not all wide character modes follow this advice, in particular the JIS
6209 and IEC modes reflect standard usage in Japan, and in these encoding,
6210 the upper half of the Latin-1 set is not part of the wide-character
6211 subset, since the most significant bit is used for wide character
6212 encoding. However, this only applies to the external forms. Internally
6213 there is no such restriction.
6215 @cindex Integer types
6216 @unnumberedsec 3.5.4(28): Integer Types
6220 An implementation should support @code{Long_Integer} in addition to
6221 @code{Integer} if the target machine supports 32-bit (or longer)
6222 arithmetic. No other named integer subtypes are recommended for package
6223 @code{Standard}. Instead, appropriate named integer subtypes should be
6224 provided in the library package @code{Interfaces} (see B.2).
6226 @code{Long_Integer} is supported. Other standard integer types are supported
6227 so this advice is not fully followed. These types
6228 are supported for convenient interface to C, and so that all hardware
6229 types of the machine are easily available.
6230 @unnumberedsec 3.5.4(29): Integer Types
6234 An implementation for a two's complement machine should support
6235 modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
6236 implementation should support a non-binary modules up to @code{Integer'Last}.
6240 @cindex Enumeration values
6241 @unnumberedsec 3.5.5(8): Enumeration Values
6244 For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
6245 subtype, if the value of the operand does not correspond to the internal
6246 code for any enumeration literal of its type (perhaps due to an
6247 un-initialized variable), then the implementation should raise
6248 @code{Program_Error}. This is particularly important for enumeration
6249 types with noncontiguous internal codes specified by an
6250 enumeration_representation_clause.
6255 @unnumberedsec 3.5.7(17): Float Types
6258 An implementation should support @code{Long_Float} in addition to
6259 @code{Float} if the target machine supports 11 or more digits of
6260 precision. No other named floating point subtypes are recommended for
6261 package @code{Standard}. Instead, appropriate named floating point subtypes
6262 should be provided in the library package @code{Interfaces} (see B.2).
6264 @code{Short_Float} and @code{Long_Long_Float} are also provided. The
6265 former provides improved compatibility with other implementations
6266 supporting this type. The latter corresponds to the highest precision
6267 floating-point type supported by the hardware. On most machines, this
6268 will be the same as @code{Long_Float}, but on some machines, it will
6269 correspond to the IEEE extended form. The notable case is all ia32
6270 (x86) implementations, where @code{Long_Long_Float} corresponds to
6271 the 80-bit extended precision format supported in hardware on this
6272 processor. Note that the 128-bit format on SPARC is not supported,
6273 since this is a software rather than a hardware format.
6275 @cindex Multidimensional arrays
6276 @cindex Arrays, multidimensional
6277 @unnumberedsec 3.6.2(11): Multidimensional Arrays
6280 An implementation should normally represent multidimensional arrays in
6281 row-major order, consistent with the notation used for multidimensional
6282 array aggregates (see 4.3.3). However, if a pragma @code{Convention}
6283 (@code{Fortran}, @dots{}) applies to a multidimensional array type, then
6284 column-major order should be used instead (see B.5, ``Interfacing with
6289 @findex Duration'Small
6290 @unnumberedsec 9.6(30-31): Duration'Small
6293 Whenever possible in an implementation, the value of @code{Duration'Small}
6294 should be no greater than 100 microseconds.
6296 Followed. (@code{Duration'Small} = 10**(@minus{}9)).
6300 The time base for @code{delay_relative_statements} should be monotonic;
6301 it need not be the same time base as used for @code{Calendar.Clock}.
6305 @unnumberedsec 10.2.1(12): Consistent Representation
6308 In an implementation, a type declared in a pre-elaborated package should
6309 have the same representation in every elaboration of a given version of
6310 the package, whether the elaborations occur in distinct executions of
6311 the same program, or in executions of distinct programs or partitions
6312 that include the given version.
6314 Followed, except in the case of tagged types. Tagged types involve
6315 implicit pointers to a local copy of a dispatch table, and these pointers
6316 have representations which thus depend on a particular elaboration of the
6317 package. It is not easy to see how it would be possible to follow this
6318 advice without severely impacting efficiency of execution.
6320 @cindex Exception information
6321 @unnumberedsec 11.4.1(19): Exception Information
6324 @code{Exception_Message} by default and @code{Exception_Information}
6325 should produce information useful for
6326 debugging. @code{Exception_Message} should be short, about one
6327 line. @code{Exception_Information} can be long. @code{Exception_Message}
6328 should not include the
6329 @code{Exception_Name}. @code{Exception_Information} should include both
6330 the @code{Exception_Name} and the @code{Exception_Message}.
6332 Followed. For each exception that doesn't have a specified
6333 @code{Exception_Message}, the compiler generates one containing the location
6334 of the raise statement. This location has the form ``file:line'', where
6335 file is the short file name (without path information) and line is the line
6336 number in the file. Note that in the case of the Zero Cost Exception
6337 mechanism, these messages become redundant with the Exception_Information that
6338 contains a full backtrace of the calling sequence, so they are disabled.
6339 To disable explicitly the generation of the source location message, use the
6340 Pragma @code{Discard_Names}.
6342 @cindex Suppression of checks
6343 @cindex Checks, suppression of
6344 @unnumberedsec 11.5(28): Suppression of Checks
6347 The implementation should minimize the code executed for checks that
6348 have been suppressed.
6352 @cindex Representation clauses
6353 @unnumberedsec 13.1 (21-24): Representation Clauses
6356 The recommended level of support for all representation items is
6357 qualified as follows:
6361 An implementation need not support representation items containing
6362 non-static expressions, except that an implementation should support a
6363 representation item for a given entity if each non-static expression in
6364 the representation item is a name that statically denotes a constant
6365 declared before the entity.
6367 Followed. In fact, GNAT goes beyond the recommended level of support
6368 by allowing nonstatic expressions in some representation clauses even
6369 without the need to declare constants initialized with the values of
6373 @smallexample @c ada
6376 for Y'Address use X'Address;>>
6382 An implementation need not support a specification for the @code{Size}
6383 for a given composite subtype, nor the size or storage place for an
6384 object (including a component) of a given composite subtype, unless the
6385 constraints on the subtype and its composite subcomponents (if any) are
6386 all static constraints.
6388 Followed. Size Clauses are not permitted on non-static components, as
6393 An aliased component, or a component whose type is by-reference, should
6394 always be allocated at an addressable location.
6398 @cindex Packed types
6399 @unnumberedsec 13.2(6-8): Packed Types
6402 If a type is packed, then the implementation should try to minimize
6403 storage allocated to objects of the type, possibly at the expense of
6404 speed of accessing components, subject to reasonable complexity in
6405 addressing calculations.
6409 The recommended level of support pragma @code{Pack} is:
6411 For a packed record type, the components should be packed as tightly as
6412 possible subject to the Sizes of the component subtypes, and subject to
6413 any @code{record_representation_clause} that applies to the type; the
6414 implementation may, but need not, reorder components or cross aligned
6415 word boundaries to improve the packing. A component whose @code{Size} is
6416 greater than the word size may be allocated an integral number of words.
6418 Followed. Tight packing of arrays is supported for all component sizes
6419 up to 64-bits. If the array component size is 1 (that is to say, if
6420 the component is a boolean type or an enumeration type with two values)
6421 then values of the type are implicitly initialized to zero. This
6422 happens both for objects of the packed type, and for objects that have a
6423 subcomponent of the packed type.
6427 An implementation should support Address clauses for imported
6431 @cindex @code{Address} clauses
6432 @unnumberedsec 13.3(14-19): Address Clauses
6436 For an array @var{X}, @code{@var{X}'Address} should point at the first
6437 component of the array, and not at the array bounds.
6443 The recommended level of support for the @code{Address} attribute is:
6445 @code{@var{X}'Address} should produce a useful result if @var{X} is an
6446 object that is aliased or of a by-reference type, or is an entity whose
6447 @code{Address} has been specified.
6449 Followed. A valid address will be produced even if none of those
6450 conditions have been met. If necessary, the object is forced into
6451 memory to ensure the address is valid.
6455 An implementation should support @code{Address} clauses for imported
6462 Objects (including subcomponents) that are aliased or of a by-reference
6463 type should be allocated on storage element boundaries.
6469 If the @code{Address} of an object is specified, or it is imported or exported,
6470 then the implementation should not perform optimizations based on
6471 assumptions of no aliases.
6475 @cindex @code{Alignment} clauses
6476 @unnumberedsec 13.3(29-35): Alignment Clauses
6479 The recommended level of support for the @code{Alignment} attribute for
6482 An implementation should support specified Alignments that are factors
6483 and multiples of the number of storage elements per word, subject to the
6490 An implementation need not support specified @code{Alignment}s for
6491 combinations of @code{Size}s and @code{Alignment}s that cannot be easily
6492 loaded and stored by available machine instructions.
6498 An implementation need not support specified @code{Alignment}s that are
6499 greater than the maximum @code{Alignment} the implementation ever returns by
6506 The recommended level of support for the @code{Alignment} attribute for
6509 Same as above, for subtypes, but in addition:
6515 For stand-alone library-level objects of statically constrained
6516 subtypes, the implementation should support all @code{Alignment}s
6517 supported by the target linker. For example, page alignment is likely to
6518 be supported for such objects, but not for subtypes.
6522 @cindex @code{Size} clauses
6523 @unnumberedsec 13.3(42-43): Size Clauses
6526 The recommended level of support for the @code{Size} attribute of
6529 A @code{Size} clause should be supported for an object if the specified
6530 @code{Size} is at least as large as its subtype's @code{Size}, and
6531 corresponds to a size in storage elements that is a multiple of the
6532 object's @code{Alignment} (if the @code{Alignment} is nonzero).
6536 @unnumberedsec 13.3(50-56): Size Clauses
6539 If the @code{Size} of a subtype is specified, and allows for efficient
6540 independent addressability (see 9.10) on the target architecture, then
6541 the @code{Size} of the following objects of the subtype should equal the
6542 @code{Size} of the subtype:
6544 Aliased objects (including components).
6550 @code{Size} clause on a composite subtype should not affect the
6551 internal layout of components.
6553 Followed. But note that this can be overridden by use of the implementation
6554 pragma Implicit_Packing in the case of packed arrays.
6558 The recommended level of support for the @code{Size} attribute of subtypes is:
6562 The @code{Size} (if not specified) of a static discrete or fixed point
6563 subtype should be the number of bits needed to represent each value
6564 belonging to the subtype using an unbiased representation, leaving space
6565 for a sign bit only if the subtype contains negative values. If such a
6566 subtype is a first subtype, then an implementation should support a
6567 specified @code{Size} for it that reflects this representation.
6573 For a subtype implemented with levels of indirection, the @code{Size}
6574 should include the size of the pointers, but not the size of what they
6579 @cindex @code{Component_Size} clauses
6580 @unnumberedsec 13.3(71-73): Component Size Clauses
6583 The recommended level of support for the @code{Component_Size}
6588 An implementation need not support specified @code{Component_Sizes} that are
6589 less than the @code{Size} of the component subtype.
6595 An implementation should support specified @code{Component_Size}s that
6596 are factors and multiples of the word size. For such
6597 @code{Component_Size}s, the array should contain no gaps between
6598 components. For other @code{Component_Size}s (if supported), the array
6599 should contain no gaps between components when packing is also
6600 specified; the implementation should forbid this combination in cases
6601 where it cannot support a no-gaps representation.
6605 @cindex Enumeration representation clauses
6606 @cindex Representation clauses, enumeration
6607 @unnumberedsec 13.4(9-10): Enumeration Representation Clauses
6610 The recommended level of support for enumeration representation clauses
6613 An implementation need not support enumeration representation clauses
6614 for boolean types, but should at minimum support the internal codes in
6615 the range @code{System.Min_Int.System.Max_Int}.
6619 @cindex Record representation clauses
6620 @cindex Representation clauses, records
6621 @unnumberedsec 13.5.1(17-22): Record Representation Clauses
6624 The recommended level of support for
6625 @*@code{record_representation_clauses} is:
6627 An implementation should support storage places that can be extracted
6628 with a load, mask, shift sequence of machine code, and set with a load,
6629 shift, mask, store sequence, given the available machine instructions
6636 A storage place should be supported if its size is equal to the
6637 @code{Size} of the component subtype, and it starts and ends on a
6638 boundary that obeys the @code{Alignment} of the component subtype.
6644 If the default bit ordering applies to the declaration of a given type,
6645 then for a component whose subtype's @code{Size} is less than the word
6646 size, any storage place that does not cross an aligned word boundary
6647 should be supported.
6653 An implementation may reserve a storage place for the tag field of a
6654 tagged type, and disallow other components from overlapping that place.
6656 Followed. The storage place for the tag field is the beginning of the tagged
6657 record, and its size is Address'Size. GNAT will reject an explicit component
6658 clause for the tag field.
6662 An implementation need not support a @code{component_clause} for a
6663 component of an extension part if the storage place is not after the
6664 storage places of all components of the parent type, whether or not
6665 those storage places had been specified.
6667 Followed. The above advice on record representation clauses is followed,
6668 and all mentioned features are implemented.
6670 @cindex Storage place attributes
6671 @unnumberedsec 13.5.2(5): Storage Place Attributes
6674 If a component is represented using some form of pointer (such as an
6675 offset) to the actual data of the component, and this data is contiguous
6676 with the rest of the object, then the storage place attributes should
6677 reflect the place of the actual data, not the pointer. If a component is
6678 allocated discontinuously from the rest of the object, then a warning
6679 should be generated upon reference to one of its storage place
6682 Followed. There are no such components in GNAT@.
6684 @cindex Bit ordering
6685 @unnumberedsec 13.5.3(7-8): Bit Ordering
6688 The recommended level of support for the non-default bit ordering is:
6692 If @code{Word_Size} = @code{Storage_Unit}, then the implementation
6693 should support the non-default bit ordering in addition to the default
6696 Followed. Word size does not equal storage size in this implementation.
6697 Thus non-default bit ordering is not supported.
6699 @cindex @code{Address}, as private type
6700 @unnumberedsec 13.7(37): Address as Private
6703 @code{Address} should be of a private type.
6707 @cindex Operations, on @code{Address}
6708 @cindex @code{Address}, operations of
6709 @unnumberedsec 13.7.1(16): Address Operations
6712 Operations in @code{System} and its children should reflect the target
6713 environment semantics as closely as is reasonable. For example, on most
6714 machines, it makes sense for address arithmetic to ``wrap around''.
6715 Operations that do not make sense should raise @code{Program_Error}.
6717 Followed. Address arithmetic is modular arithmetic that wraps around. No
6718 operation raises @code{Program_Error}, since all operations make sense.
6720 @cindex Unchecked conversion
6721 @unnumberedsec 13.9(14-17): Unchecked Conversion
6724 The @code{Size} of an array object should not include its bounds; hence,
6725 the bounds should not be part of the converted data.
6731 The implementation should not generate unnecessary run-time checks to
6732 ensure that the representation of @var{S} is a representation of the
6733 target type. It should take advantage of the permission to return by
6734 reference when possible. Restrictions on unchecked conversions should be
6735 avoided unless required by the target environment.
6737 Followed. There are no restrictions on unchecked conversion. A warning is
6738 generated if the source and target types do not have the same size since
6739 the semantics in this case may be target dependent.
6743 The recommended level of support for unchecked conversions is:
6747 Unchecked conversions should be supported and should be reversible in
6748 the cases where this clause defines the result. To enable meaningful use
6749 of unchecked conversion, a contiguous representation should be used for
6750 elementary subtypes, for statically constrained array subtypes whose
6751 component subtype is one of the subtypes described in this paragraph,
6752 and for record subtypes without discriminants whose component subtypes
6753 are described in this paragraph.
6757 @cindex Heap usage, implicit
6758 @unnumberedsec 13.11(23-25): Implicit Heap Usage
6761 An implementation should document any cases in which it dynamically
6762 allocates heap storage for a purpose other than the evaluation of an
6765 Followed, the only other points at which heap storage is dynamically
6766 allocated are as follows:
6770 At initial elaboration time, to allocate dynamically sized global
6774 To allocate space for a task when a task is created.
6777 To extend the secondary stack dynamically when needed. The secondary
6778 stack is used for returning variable length results.
6783 A default (implementation-provided) storage pool for an
6784 access-to-constant type should not have overhead to support deallocation of
6791 A storage pool for an anonymous access type should be created at the
6792 point of an allocator for the type, and be reclaimed when the designated
6793 object becomes inaccessible.
6797 @cindex Unchecked deallocation
6798 @unnumberedsec 13.11.2(17): Unchecked De-allocation
6801 For a standard storage pool, @code{Free} should actually reclaim the
6806 @cindex Stream oriented attributes
6807 @unnumberedsec 13.13.2(17): Stream Oriented Attributes
6810 If a stream element is the same size as a storage element, then the
6811 normal in-memory representation should be used by @code{Read} and
6812 @code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
6813 should use the smallest number of stream elements needed to represent
6814 all values in the base range of the scalar type.
6817 Followed. By default, GNAT uses the interpretation suggested by AI-195,
6818 which specifies using the size of the first subtype.
6819 However, such an implementation is based on direct binary
6820 representations and is therefore target- and endianness-dependent.
6821 To address this issue, GNAT also supplies an alternate implementation
6822 of the stream attributes @code{Read} and @code{Write},
6823 which uses the target-independent XDR standard representation
6825 @cindex XDR representation
6826 @cindex @code{Read} attribute
6827 @cindex @code{Write} attribute
6828 @cindex Stream oriented attributes
6829 The XDR implementation is provided as an alternative body of the
6830 @code{System.Stream_Attributes} package, in the file
6831 @file{s-strxdr.adb} in the GNAT library.
6832 There is no @file{s-strxdr.ads} file.
6833 In order to install the XDR implementation, do the following:
6835 @item Replace the default implementation of the
6836 @code{System.Stream_Attributes} package with the XDR implementation.
6837 For example on a Unix platform issue the commands:
6839 $ mv s-stratt.adb s-strold.adb
6840 $ mv s-strxdr.adb s-stratt.adb
6844 Rebuild the GNAT run-time library as documented in
6845 @ref{GNAT and Libraries,,, gnat_ugn, @value{EDITION} User's Guide}.
6848 @unnumberedsec A.1(52): Names of Predefined Numeric Types
6851 If an implementation provides additional named predefined integer types,
6852 then the names should end with @samp{Integer} as in
6853 @samp{Long_Integer}. If an implementation provides additional named
6854 predefined floating point types, then the names should end with
6855 @samp{Float} as in @samp{Long_Float}.
6859 @findex Ada.Characters.Handling
6860 @unnumberedsec A.3.2(49): @code{Ada.Characters.Handling}
6863 If an implementation provides a localized definition of @code{Character}
6864 or @code{Wide_Character}, then the effects of the subprograms in
6865 @code{Characters.Handling} should reflect the localizations. See also
6868 Followed. GNAT provides no such localized definitions.
6870 @cindex Bounded-length strings
6871 @unnumberedsec A.4.4(106): Bounded-Length String Handling
6874 Bounded string objects should not be implemented by implicit pointers
6875 and dynamic allocation.
6877 Followed. No implicit pointers or dynamic allocation are used.
6879 @cindex Random number generation
6880 @unnumberedsec A.5.2(46-47): Random Number Generation
6883 Any storage associated with an object of type @code{Generator} should be
6884 reclaimed on exit from the scope of the object.
6890 If the generator period is sufficiently long in relation to the number
6891 of distinct initiator values, then each possible value of
6892 @code{Initiator} passed to @code{Reset} should initiate a sequence of
6893 random numbers that does not, in a practical sense, overlap the sequence
6894 initiated by any other value. If this is not possible, then the mapping
6895 between initiator values and generator states should be a rapidly
6896 varying function of the initiator value.
6898 Followed. The generator period is sufficiently long for the first
6899 condition here to hold true.
6901 @findex Get_Immediate
6902 @unnumberedsec A.10.7(23): @code{Get_Immediate}
6905 The @code{Get_Immediate} procedures should be implemented with
6906 unbuffered input. For a device such as a keyboard, input should be
6907 @dfn{available} if a key has already been typed, whereas for a disk
6908 file, input should always be available except at end of file. For a file
6909 associated with a keyboard-like device, any line-editing features of the
6910 underlying operating system should be disabled during the execution of
6911 @code{Get_Immediate}.
6913 Followed on all targets except VxWorks. For VxWorks, there is no way to
6914 provide this functionality that does not result in the input buffer being
6915 flushed before the @code{Get_Immediate} call. A special unit
6916 @code{Interfaces.Vxworks.IO} is provided that contains routines to enable
6920 @unnumberedsec B.1(39-41): Pragma @code{Export}
6923 If an implementation supports pragma @code{Export} to a given language,
6924 then it should also allow the main subprogram to be written in that
6925 language. It should support some mechanism for invoking the elaboration
6926 of the Ada library units included in the system, and for invoking the
6927 finalization of the environment task. On typical systems, the
6928 recommended mechanism is to provide two subprograms whose link names are
6929 @code{adainit} and @code{adafinal}. @code{adainit} should contain the
6930 elaboration code for library units. @code{adafinal} should contain the
6931 finalization code. These subprograms should have no effect the second
6932 and subsequent time they are called.
6938 Automatic elaboration of pre-elaborated packages should be
6939 provided when pragma @code{Export} is supported.
6941 Followed when the main program is in Ada. If the main program is in a
6942 foreign language, then
6943 @code{adainit} must be called to elaborate pre-elaborated
6948 For each supported convention @var{L} other than @code{Intrinsic}, an
6949 implementation should support @code{Import} and @code{Export} pragmas
6950 for objects of @var{L}-compatible types and for subprograms, and pragma
6951 @code{Convention} for @var{L}-eligible types and for subprograms,
6952 presuming the other language has corresponding features. Pragma
6953 @code{Convention} need not be supported for scalar types.
6957 @cindex Package @code{Interfaces}
6959 @unnumberedsec B.2(12-13): Package @code{Interfaces}
6962 For each implementation-defined convention identifier, there should be a
6963 child package of package Interfaces with the corresponding name. This
6964 package should contain any declarations that would be useful for
6965 interfacing to the language (implementation) represented by the
6966 convention. Any declarations useful for interfacing to any language on
6967 the given hardware architecture should be provided directly in
6970 Followed. An additional package not defined
6971 in the Ada Reference Manual is @code{Interfaces.CPP}, used
6972 for interfacing to C++.
6976 An implementation supporting an interface to C, COBOL, or Fortran should
6977 provide the corresponding package or packages described in the following
6980 Followed. GNAT provides all the packages described in this section.
6982 @cindex C, interfacing with
6983 @unnumberedsec B.3(63-71): Interfacing with C
6986 An implementation should support the following interface correspondences
6993 An Ada procedure corresponds to a void-returning C function.
6999 An Ada function corresponds to a non-void C function.
7005 An Ada @code{in} scalar parameter is passed as a scalar argument to a C
7012 An Ada @code{in} parameter of an access-to-object type with designated
7013 type @var{T} is passed as a @code{@var{t}*} argument to a C function,
7014 where @var{t} is the C type corresponding to the Ada type @var{T}.
7020 An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
7021 parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
7022 argument to a C function, where @var{t} is the C type corresponding to
7023 the Ada type @var{T}. In the case of an elementary @code{out} or
7024 @code{in out} parameter, a pointer to a temporary copy is used to
7025 preserve by-copy semantics.
7031 An Ada parameter of a record type @var{T}, of any mode, is passed as a
7032 @code{@var{t}*} argument to a C function, where @var{t} is the C
7033 structure corresponding to the Ada type @var{T}.
7035 Followed. This convention may be overridden by the use of the C_Pass_By_Copy
7036 pragma, or Convention, or by explicitly specifying the mechanism for a given
7037 call using an extended import or export pragma.
7041 An Ada parameter of an array type with component type @var{T}, of any
7042 mode, is passed as a @code{@var{t}*} argument to a C function, where
7043 @var{t} is the C type corresponding to the Ada type @var{T}.
7049 An Ada parameter of an access-to-subprogram type is passed as a pointer
7050 to a C function whose prototype corresponds to the designated
7051 subprogram's specification.
7055 @cindex COBOL, interfacing with
7056 @unnumberedsec B.4(95-98): Interfacing with COBOL
7059 An Ada implementation should support the following interface
7060 correspondences between Ada and COBOL@.
7066 An Ada access @var{T} parameter is passed as a @samp{BY REFERENCE} data item of
7067 the COBOL type corresponding to @var{T}.
7073 An Ada in scalar parameter is passed as a @samp{BY CONTENT} data item of
7074 the corresponding COBOL type.
7080 Any other Ada parameter is passed as a @samp{BY REFERENCE} data item of the
7081 COBOL type corresponding to the Ada parameter type; for scalars, a local
7082 copy is used if necessary to ensure by-copy semantics.
7086 @cindex Fortran, interfacing with
7087 @unnumberedsec B.5(22-26): Interfacing with Fortran
7090 An Ada implementation should support the following interface
7091 correspondences between Ada and Fortran:
7097 An Ada procedure corresponds to a Fortran subroutine.
7103 An Ada function corresponds to a Fortran function.
7109 An Ada parameter of an elementary, array, or record type @var{T} is
7110 passed as a @var{T} argument to a Fortran procedure, where @var{T} is
7111 the Fortran type corresponding to the Ada type @var{T}, and where the
7112 INTENT attribute of the corresponding dummy argument matches the Ada
7113 formal parameter mode; the Fortran implementation's parameter passing
7114 conventions are used. For elementary types, a local copy is used if
7115 necessary to ensure by-copy semantics.
7121 An Ada parameter of an access-to-subprogram type is passed as a
7122 reference to a Fortran procedure whose interface corresponds to the
7123 designated subprogram's specification.
7127 @cindex Machine operations
7128 @unnumberedsec C.1(3-5): Access to Machine Operations
7131 The machine code or intrinsic support should allow access to all
7132 operations normally available to assembly language programmers for the
7133 target environment, including privileged instructions, if any.
7139 The interfacing pragmas (see Annex B) should support interface to
7140 assembler; the default assembler should be associated with the
7141 convention identifier @code{Assembler}.
7147 If an entity is exported to assembly language, then the implementation
7148 should allocate it at an addressable location, and should ensure that it
7149 is retained by the linking process, even if not otherwise referenced
7150 from the Ada code. The implementation should assume that any call to a
7151 machine code or assembler subprogram is allowed to read or update every
7152 object that is specified as exported.
7156 @unnumberedsec C.1(10-16): Access to Machine Operations
7159 The implementation should ensure that little or no overhead is
7160 associated with calling intrinsic and machine-code subprograms.
7162 Followed for both intrinsics and machine-code subprograms.
7166 It is recommended that intrinsic subprograms be provided for convenient
7167 access to any machine operations that provide special capabilities or
7168 efficiency and that are not otherwise available through the language
7171 Followed. A full set of machine operation intrinsic subprograms is provided.
7175 Atomic read-modify-write operations---e.g.@:, test and set, compare and
7176 swap, decrement and test, enqueue/dequeue.
7178 Followed on any target supporting such operations.
7182 Standard numeric functions---e.g.@:, sin, log.
7184 Followed on any target supporting such operations.
7188 String manipulation operations---e.g.@:, translate and test.
7190 Followed on any target supporting such operations.
7194 Vector operations---e.g.@:, compare vector against thresholds.
7196 Followed on any target supporting such operations.
7200 Direct operations on I/O ports.
7202 Followed on any target supporting such operations.
7204 @cindex Interrupt support
7205 @unnumberedsec C.3(28): Interrupt Support
7208 If the @code{Ceiling_Locking} policy is not in effect, the
7209 implementation should provide means for the application to specify which
7210 interrupts are to be blocked during protected actions, if the underlying
7211 system allows for a finer-grain control of interrupt blocking.
7213 Followed. The underlying system does not allow for finer-grain control
7214 of interrupt blocking.
7216 @cindex Protected procedure handlers
7217 @unnumberedsec C.3.1(20-21): Protected Procedure Handlers
7220 Whenever possible, the implementation should allow interrupt handlers to
7221 be called directly by the hardware.
7225 This is never possible under IRIX, so this is followed by default.
7227 Followed on any target where the underlying operating system permits
7232 Whenever practical, violations of any
7233 implementation-defined restrictions should be detected before run time.
7235 Followed. Compile time warnings are given when possible.
7237 @cindex Package @code{Interrupts}
7239 @unnumberedsec C.3.2(25): Package @code{Interrupts}
7243 If implementation-defined forms of interrupt handler procedures are
7244 supported, such as protected procedures with parameters, then for each
7245 such form of a handler, a type analogous to @code{Parameterless_Handler}
7246 should be specified in a child package of @code{Interrupts}, with the
7247 same operations as in the predefined package Interrupts.
7251 @cindex Pre-elaboration requirements
7252 @unnumberedsec C.4(14): Pre-elaboration Requirements
7255 It is recommended that pre-elaborated packages be implemented in such a
7256 way that there should be little or no code executed at run time for the
7257 elaboration of entities not already covered by the Implementation
7260 Followed. Executable code is generated in some cases, e.g.@: loops
7261 to initialize large arrays.
7263 @unnumberedsec C.5(8): Pragma @code{Discard_Names}
7267 If the pragma applies to an entity, then the implementation should
7268 reduce the amount of storage used for storing names associated with that
7273 @cindex Package @code{Task_Attributes}
7274 @findex Task_Attributes
7275 @unnumberedsec C.7.2(30): The Package Task_Attributes
7278 Some implementations are targeted to domains in which memory use at run
7279 time must be completely deterministic. For such implementations, it is
7280 recommended that the storage for task attributes will be pre-allocated
7281 statically and not from the heap. This can be accomplished by either
7282 placing restrictions on the number and the size of the task's
7283 attributes, or by using the pre-allocated storage for the first @var{N}
7284 attribute objects, and the heap for the others. In the latter case,
7285 @var{N} should be documented.
7287 Not followed. This implementation is not targeted to such a domain.
7289 @cindex Locking Policies
7290 @unnumberedsec D.3(17): Locking Policies
7294 The implementation should use names that end with @samp{_Locking} for
7295 locking policies defined by the implementation.
7297 Followed. A single implementation-defined locking policy is defined,
7298 whose name (@code{Inheritance_Locking}) follows this suggestion.
7300 @cindex Entry queuing policies
7301 @unnumberedsec D.4(16): Entry Queuing Policies
7304 Names that end with @samp{_Queuing} should be used
7305 for all implementation-defined queuing policies.
7307 Followed. No such implementation-defined queuing policies exist.
7309 @cindex Preemptive abort
7310 @unnumberedsec D.6(9-10): Preemptive Abort
7313 Even though the @code{abort_statement} is included in the list of
7314 potentially blocking operations (see 9.5.1), it is recommended that this
7315 statement be implemented in a way that never requires the task executing
7316 the @code{abort_statement} to block.
7322 On a multi-processor, the delay associated with aborting a task on
7323 another processor should be bounded; the implementation should use
7324 periodic polling, if necessary, to achieve this.
7328 @cindex Tasking restrictions
7329 @unnumberedsec D.7(21): Tasking Restrictions
7332 When feasible, the implementation should take advantage of the specified
7333 restrictions to produce a more efficient implementation.
7335 GNAT currently takes advantage of these restrictions by providing an optimized
7336 run time when the Ravenscar profile and the GNAT restricted run time set
7337 of restrictions are specified. See pragma @code{Profile (Ravenscar)} and
7338 pragma @code{Profile (Restricted)} for more details.
7340 @cindex Time, monotonic
7341 @unnumberedsec D.8(47-49): Monotonic Time
7344 When appropriate, implementations should provide configuration
7345 mechanisms to change the value of @code{Tick}.
7347 Such configuration mechanisms are not appropriate to this implementation
7348 and are thus not supported.
7352 It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
7353 be implemented as transformations of the same time base.
7359 It is recommended that the @dfn{best} time base which exists in
7360 the underlying system be available to the application through
7361 @code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
7365 @cindex Partition communication subsystem
7367 @unnumberedsec E.5(28-29): Partition Communication Subsystem
7370 Whenever possible, the PCS on the called partition should allow for
7371 multiple tasks to call the RPC-receiver with different messages and
7372 should allow them to block until the corresponding subprogram body
7375 Followed by GLADE, a separately supplied PCS that can be used with
7380 The @code{Write} operation on a stream of type @code{Params_Stream_Type}
7381 should raise @code{Storage_Error} if it runs out of space trying to
7382 write the @code{Item} into the stream.
7384 Followed by GLADE, a separately supplied PCS that can be used with
7387 @cindex COBOL support
7388 @unnumberedsec F(7): COBOL Support
7391 If COBOL (respectively, C) is widely supported in the target
7392 environment, implementations supporting the Information Systems Annex
7393 should provide the child package @code{Interfaces.COBOL} (respectively,
7394 @code{Interfaces.C}) specified in Annex B and should support a
7395 @code{convention_identifier} of COBOL (respectively, C) in the interfacing
7396 pragmas (see Annex B), thus allowing Ada programs to interface with
7397 programs written in that language.
7401 @cindex Decimal radix support
7402 @unnumberedsec F.1(2): Decimal Radix Support
7405 Packed decimal should be used as the internal representation for objects
7406 of subtype @var{S} when @var{S}'Machine_Radix = 10.
7408 Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
7412 @unnumberedsec G: Numerics
7415 If Fortran (respectively, C) is widely supported in the target
7416 environment, implementations supporting the Numerics Annex
7417 should provide the child package @code{Interfaces.Fortran} (respectively,
7418 @code{Interfaces.C}) specified in Annex B and should support a
7419 @code{convention_identifier} of Fortran (respectively, C) in the interfacing
7420 pragmas (see Annex B), thus allowing Ada programs to interface with
7421 programs written in that language.
7425 @cindex Complex types
7426 @unnumberedsec G.1.1(56-58): Complex Types
7429 Because the usual mathematical meaning of multiplication of a complex
7430 operand and a real operand is that of the scaling of both components of
7431 the former by the latter, an implementation should not perform this
7432 operation by first promoting the real operand to complex type and then
7433 performing a full complex multiplication. In systems that, in the
7434 future, support an Ada binding to IEC 559:1989, the latter technique
7435 will not generate the required result when one of the components of the
7436 complex operand is infinite. (Explicit multiplication of the infinite
7437 component by the zero component obtained during promotion yields a NaN
7438 that propagates into the final result.) Analogous advice applies in the
7439 case of multiplication of a complex operand and a pure-imaginary
7440 operand, and in the case of division of a complex operand by a real or
7441 pure-imaginary operand.
7447 Similarly, because the usual mathematical meaning of addition of a
7448 complex operand and a real operand is that the imaginary operand remains
7449 unchanged, an implementation should not perform this operation by first
7450 promoting the real operand to complex type and then performing a full
7451 complex addition. In implementations in which the @code{Signed_Zeros}
7452 attribute of the component type is @code{True} (and which therefore
7453 conform to IEC 559:1989 in regard to the handling of the sign of zero in
7454 predefined arithmetic operations), the latter technique will not
7455 generate the required result when the imaginary component of the complex
7456 operand is a negatively signed zero. (Explicit addition of the negative
7457 zero to the zero obtained during promotion yields a positive zero.)
7458 Analogous advice applies in the case of addition of a complex operand
7459 and a pure-imaginary operand, and in the case of subtraction of a
7460 complex operand and a real or pure-imaginary operand.
7466 Implementations in which @code{Real'Signed_Zeros} is @code{True} should
7467 attempt to provide a rational treatment of the signs of zero results and
7468 result components. As one example, the result of the @code{Argument}
7469 function should have the sign of the imaginary component of the
7470 parameter @code{X} when the point represented by that parameter lies on
7471 the positive real axis; as another, the sign of the imaginary component
7472 of the @code{Compose_From_Polar} function should be the same as
7473 (respectively, the opposite of) that of the @code{Argument} parameter when that
7474 parameter has a value of zero and the @code{Modulus} parameter has a
7475 nonnegative (respectively, negative) value.
7479 @cindex Complex elementary functions
7480 @unnumberedsec G.1.2(49): Complex Elementary Functions
7483 Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
7484 @code{True} should attempt to provide a rational treatment of the signs
7485 of zero results and result components. For example, many of the complex
7486 elementary functions have components that are odd functions of one of
7487 the parameter components; in these cases, the result component should
7488 have the sign of the parameter component at the origin. Other complex
7489 elementary functions have zero components whose sign is opposite that of
7490 a parameter component at the origin, or is always positive or always
7495 @cindex Accuracy requirements
7496 @unnumberedsec G.2.4(19): Accuracy Requirements
7499 The versions of the forward trigonometric functions without a
7500 @code{Cycle} parameter should not be implemented by calling the
7501 corresponding version with a @code{Cycle} parameter of
7502 @code{2.0*Numerics.Pi}, since this will not provide the required
7503 accuracy in some portions of the domain. For the same reason, the
7504 version of @code{Log} without a @code{Base} parameter should not be
7505 implemented by calling the corresponding version with a @code{Base}
7506 parameter of @code{Numerics.e}.
7510 @cindex Complex arithmetic accuracy
7511 @cindex Accuracy, complex arithmetic
7512 @unnumberedsec G.2.6(15): Complex Arithmetic Accuracy
7516 The version of the @code{Compose_From_Polar} function without a
7517 @code{Cycle} parameter should not be implemented by calling the
7518 corresponding version with a @code{Cycle} parameter of
7519 @code{2.0*Numerics.Pi}, since this will not provide the required
7520 accuracy in some portions of the domain.
7524 @c -----------------------------------------
7525 @node Implementation Defined Characteristics
7526 @chapter Implementation Defined Characteristics
7529 In addition to the implementation dependent pragmas and attributes, and
7530 the implementation advice, there are a number of other Ada features
7531 that are potentially implementation dependent. These are mentioned
7532 throughout the Ada Reference Manual, and are summarized in annex M@.
7534 A requirement for conforming Ada compilers is that they provide
7535 documentation describing how the implementation deals with each of these
7536 issues. In this chapter, you will find each point in annex M listed
7537 followed by a description in italic font of how GNAT
7541 implementation on IRIX 5.3 operating system or greater
7543 handles the implementation dependence.
7545 You can use this chapter as a guide to minimizing implementation
7546 dependent features in your programs if portability to other compilers
7547 and other operating systems is an important consideration. The numbers
7548 in each section below correspond to the paragraph number in the Ada
7554 @strong{2}. Whether or not each recommendation given in Implementation
7555 Advice is followed. See 1.1.2(37).
7558 @xref{Implementation Advice}.
7563 @strong{3}. Capacity limitations of the implementation. See 1.1.3(3).
7566 The complexity of programs that can be processed is limited only by the
7567 total amount of available virtual memory, and disk space for the
7568 generated object files.
7573 @strong{4}. Variations from the standard that are impractical to avoid
7574 given the implementation's execution environment. See 1.1.3(6).
7577 There are no variations from the standard.
7582 @strong{5}. Which @code{code_statement}s cause external
7583 interactions. See 1.1.3(10).
7586 Any @code{code_statement} can potentially cause external interactions.
7591 @strong{6}. The coded representation for the text of an Ada
7592 program. See 2.1(4).
7595 See separate section on source representation.
7600 @strong{7}. The control functions allowed in comments. See 2.1(14).
7603 See separate section on source representation.
7608 @strong{8}. The representation for an end of line. See 2.2(2).
7611 See separate section on source representation.
7616 @strong{9}. Maximum supported line length and lexical element
7617 length. See 2.2(15).
7620 The maximum line length is 255 characters and the maximum length of a
7621 lexical element is also 255 characters.
7626 @strong{10}. Implementation defined pragmas. See 2.8(14).
7630 @xref{Implementation Defined Pragmas}.
7635 @strong{11}. Effect of pragma @code{Optimize}. See 2.8(27).
7638 Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
7639 parameter, checks that the optimization flag is set, and aborts if it is
7645 @strong{12}. The sequence of characters of the value returned by
7646 @code{@var{S}'Image} when some of the graphic characters of
7647 @code{@var{S}'Wide_Image} are not defined in @code{Character}. See
7651 The sequence of characters is as defined by the wide character encoding
7652 method used for the source. See section on source representation for
7658 @strong{13}. The predefined integer types declared in
7659 @code{Standard}. See 3.5.4(25).
7663 @item Short_Short_Integer
7666 (Short) 16 bit signed
7670 64 bit signed (Alpha OpenVMS only)
7671 32 bit signed (all other targets)
7672 @item Long_Long_Integer
7679 @strong{14}. Any nonstandard integer types and the operators defined
7680 for them. See 3.5.4(26).
7683 There are no nonstandard integer types.
7688 @strong{15}. Any nonstandard real types and the operators defined for
7692 There are no nonstandard real types.
7697 @strong{16}. What combinations of requested decimal precision and range
7698 are supported for floating point types. See 3.5.7(7).
7701 The precision and range is as defined by the IEEE standard.
7706 @strong{17}. The predefined floating point types declared in
7707 @code{Standard}. See 3.5.7(16).
7714 (Short) 32 bit IEEE short
7717 @item Long_Long_Float
7718 64 bit IEEE long (80 bit IEEE long on x86 processors)
7724 @strong{18}. The small of an ordinary fixed point type. See 3.5.9(8).
7727 @code{Fine_Delta} is 2**(@minus{}63)
7732 @strong{19}. What combinations of small, range, and digits are
7733 supported for fixed point types. See 3.5.9(10).
7736 Any combinations are permitted that do not result in a small less than
7737 @code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
7738 If the mantissa is larger than 53 bits on machines where Long_Long_Float
7739 is 64 bits (true of all architectures except ia32), then the output from
7740 Text_IO is accurate to only 53 bits, rather than the full mantissa. This
7741 is because floating-point conversions are used to convert fixed point.
7746 @strong{20}. The result of @code{Tags.Expanded_Name} for types declared
7747 within an unnamed @code{block_statement}. See 3.9(10).
7750 Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
7751 decimal integer are allocated.
7756 @strong{21}. Implementation-defined attributes. See 4.1.4(12).
7759 @xref{Implementation Defined Attributes}.
7764 @strong{22}. Any implementation-defined time types. See 9.6(6).
7767 There are no implementation-defined time types.
7772 @strong{23}. The time base associated with relative delays.
7775 See 9.6(20). The time base used is that provided by the C library
7776 function @code{gettimeofday}.
7781 @strong{24}. The time base of the type @code{Calendar.Time}. See
7785 The time base used is that provided by the C library function
7786 @code{gettimeofday}.
7791 @strong{25}. The time zone used for package @code{Calendar}
7792 operations. See 9.6(24).
7795 The time zone used by package @code{Calendar} is the current system time zone
7796 setting for local time, as accessed by the C library function
7802 @strong{26}. Any limit on @code{delay_until_statements} of
7803 @code{select_statements}. See 9.6(29).
7806 There are no such limits.
7811 @strong{27}. Whether or not two non-overlapping parts of a composite
7812 object are independently addressable, in the case where packing, record
7813 layout, or @code{Component_Size} is specified for the object. See
7817 Separate components are independently addressable if they do not share
7818 overlapping storage units.
7823 @strong{28}. The representation for a compilation. See 10.1(2).
7826 A compilation is represented by a sequence of files presented to the
7827 compiler in a single invocation of the @command{gcc} command.
7832 @strong{29}. Any restrictions on compilations that contain multiple
7833 compilation_units. See 10.1(4).
7836 No single file can contain more than one compilation unit, but any
7837 sequence of files can be presented to the compiler as a single
7843 @strong{30}. The mechanisms for creating an environment and for adding
7844 and replacing compilation units. See 10.1.4(3).
7847 See separate section on compilation model.
7852 @strong{31}. The manner of explicitly assigning library units to a
7853 partition. See 10.2(2).
7856 If a unit contains an Ada main program, then the Ada units for the partition
7857 are determined by recursive application of the rules in the Ada Reference
7858 Manual section 10.2(2-6). In other words, the Ada units will be those that
7859 are needed by the main program, and then this definition of need is applied
7860 recursively to those units, and the partition contains the transitive
7861 closure determined by this relationship. In short, all the necessary units
7862 are included, with no need to explicitly specify the list. If additional
7863 units are required, e.g.@: by foreign language units, then all units must be
7864 mentioned in the context clause of one of the needed Ada units.
7866 If the partition contains no main program, or if the main program is in
7867 a language other than Ada, then GNAT
7868 provides the binder options @option{-z} and @option{-n} respectively, and in
7869 this case a list of units can be explicitly supplied to the binder for
7870 inclusion in the partition (all units needed by these units will also
7871 be included automatically). For full details on the use of these
7872 options, refer to @ref{The GNAT Make Program gnatmake,,, gnat_ugn,
7873 @value{EDITION} User's Guide}.
7878 @strong{32}. The implementation-defined means, if any, of specifying
7879 which compilation units are needed by a given compilation unit. See
7883 The units needed by a given compilation unit are as defined in
7884 the Ada Reference Manual section 10.2(2-6). There are no
7885 implementation-defined pragmas or other implementation-defined
7886 means for specifying needed units.
7891 @strong{33}. The manner of designating the main subprogram of a
7892 partition. See 10.2(7).
7895 The main program is designated by providing the name of the
7896 corresponding @file{ALI} file as the input parameter to the binder.
7901 @strong{34}. The order of elaboration of @code{library_items}. See
7905 The first constraint on ordering is that it meets the requirements of
7906 Chapter 10 of the Ada Reference Manual. This still leaves some
7907 implementation dependent choices, which are resolved by first
7908 elaborating bodies as early as possible (i.e., in preference to specs
7909 where there is a choice), and second by evaluating the immediate with
7910 clauses of a unit to determine the probably best choice, and
7911 third by elaborating in alphabetical order of unit names
7912 where a choice still remains.
7917 @strong{35}. Parameter passing and function return for the main
7918 subprogram. See 10.2(21).
7921 The main program has no parameters. It may be a procedure, or a function
7922 returning an integer type. In the latter case, the returned integer
7923 value is the return code of the program (overriding any value that
7924 may have been set by a call to @code{Ada.Command_Line.Set_Exit_Status}).
7929 @strong{36}. The mechanisms for building and running partitions. See
7933 GNAT itself supports programs with only a single partition. The GNATDIST
7934 tool provided with the GLADE package (which also includes an implementation
7935 of the PCS) provides a completely flexible method for building and running
7936 programs consisting of multiple partitions. See the separate GLADE manual
7942 @strong{37}. The details of program execution, including program
7943 termination. See 10.2(25).
7946 See separate section on compilation model.
7951 @strong{38}. The semantics of any non-active partitions supported by the
7952 implementation. See 10.2(28).
7955 Passive partitions are supported on targets where shared memory is
7956 provided by the operating system. See the GLADE reference manual for
7962 @strong{39}. The information returned by @code{Exception_Message}. See
7966 Exception message returns the null string unless a specific message has
7967 been passed by the program.
7972 @strong{40}. The result of @code{Exceptions.Exception_Name} for types
7973 declared within an unnamed @code{block_statement}. See 11.4.1(12).
7976 Blocks have implementation defined names of the form @code{B@var{nnn}}
7977 where @var{nnn} is an integer.
7982 @strong{41}. The information returned by
7983 @code{Exception_Information}. See 11.4.1(13).
7986 @code{Exception_Information} returns a string in the following format:
7989 @emph{Exception_Name:} nnnnn
7990 @emph{Message:} mmmmm
7992 @emph{Call stack traceback locations:}
7993 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
8001 @code{nnnn} is the fully qualified name of the exception in all upper
8002 case letters. This line is always present.
8005 @code{mmmm} is the message (this line present only if message is non-null)
8008 @code{ppp} is the Process Id value as a decimal integer (this line is
8009 present only if the Process Id is nonzero). Currently we are
8010 not making use of this field.
8013 The Call stack traceback locations line and the following values
8014 are present only if at least one traceback location was recorded.
8015 The values are given in C style format, with lower case letters
8016 for a-f, and only as many digits present as are necessary.
8020 The line terminator sequence at the end of each line, including
8021 the last line is a single @code{LF} character (@code{16#0A#}).
8026 @strong{42}. Implementation-defined check names. See 11.5(27).
8029 The implementation defined check name Alignment_Check controls checking of
8030 address clause values for proper alignment (that is, the address supplied
8031 must be consistent with the alignment of the type).
8033 In addition, a user program can add implementation-defined check names
8034 by means of the pragma Check_Name.
8039 @strong{43}. The interpretation of each aspect of representation. See
8043 See separate section on data representations.
8048 @strong{44}. Any restrictions placed upon representation items. See
8052 See separate section on data representations.
8057 @strong{45}. The meaning of @code{Size} for indefinite subtypes. See
8061 Size for an indefinite subtype is the maximum possible size, except that
8062 for the case of a subprogram parameter, the size of the parameter object
8068 @strong{46}. The default external representation for a type tag. See
8072 The default external representation for a type tag is the fully expanded
8073 name of the type in upper case letters.
8078 @strong{47}. What determines whether a compilation unit is the same in
8079 two different partitions. See 13.3(76).
8082 A compilation unit is the same in two different partitions if and only
8083 if it derives from the same source file.
8088 @strong{48}. Implementation-defined components. See 13.5.1(15).
8091 The only implementation defined component is the tag for a tagged type,
8092 which contains a pointer to the dispatching table.
8097 @strong{49}. If @code{Word_Size} = @code{Storage_Unit}, the default bit
8098 ordering. See 13.5.3(5).
8101 @code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
8102 implementation, so no non-default bit ordering is supported. The default
8103 bit ordering corresponds to the natural endianness of the target architecture.
8108 @strong{50}. The contents of the visible part of package @code{System}
8109 and its language-defined children. See 13.7(2).
8112 See the definition of these packages in files @file{system.ads} and
8113 @file{s-stoele.ads}.
8118 @strong{51}. The contents of the visible part of package
8119 @code{System.Machine_Code}, and the meaning of
8120 @code{code_statements}. See 13.8(7).
8123 See the definition and documentation in file @file{s-maccod.ads}.
8128 @strong{52}. The effect of unchecked conversion. See 13.9(11).
8131 Unchecked conversion between types of the same size
8132 results in an uninterpreted transmission of the bits from one type
8133 to the other. If the types are of unequal sizes, then in the case of
8134 discrete types, a shorter source is first zero or sign extended as
8135 necessary, and a shorter target is simply truncated on the left.
8136 For all non-discrete types, the source is first copied if necessary
8137 to ensure that the alignment requirements of the target are met, then
8138 a pointer is constructed to the source value, and the result is obtained
8139 by dereferencing this pointer after converting it to be a pointer to the
8140 target type. Unchecked conversions where the target subtype is an
8141 unconstrained array are not permitted. If the target alignment is
8142 greater than the source alignment, then a copy of the result is
8143 made with appropriate alignment
8148 @strong{53}. The manner of choosing a storage pool for an access type
8149 when @code{Storage_Pool} is not specified for the type. See 13.11(17).
8152 There are 3 different standard pools used by the compiler when
8153 @code{Storage_Pool} is not specified depending whether the type is local
8154 to a subprogram or defined at the library level and whether
8155 @code{Storage_Size}is specified or not. See documentation in the runtime
8156 library units @code{System.Pool_Global}, @code{System.Pool_Size} and
8157 @code{System.Pool_Local} in files @file{s-poosiz.ads},
8158 @file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
8164 @strong{54}. Whether or not the implementation provides user-accessible
8165 names for the standard pool type(s). See 13.11(17).
8169 See documentation in the sources of the run time mentioned in paragraph
8170 @strong{53} . All these pools are accessible by means of @code{with}'ing
8176 @strong{55}. The meaning of @code{Storage_Size}. See 13.11(18).
8179 @code{Storage_Size} is measured in storage units, and refers to the
8180 total space available for an access type collection, or to the primary
8181 stack space for a task.
8186 @strong{56}. Implementation-defined aspects of storage pools. See
8190 See documentation in the sources of the run time mentioned in paragraph
8191 @strong{53} for details on GNAT-defined aspects of storage pools.
8196 @strong{57}. The set of restrictions allowed in a pragma
8197 @code{Restrictions}. See 13.12(7).
8200 All RM defined Restriction identifiers are implemented. The following
8201 additional restriction identifiers are provided. There are two separate
8202 lists of implementation dependent restriction identifiers. The first
8203 set requires consistency throughout a partition (in other words, if the
8204 restriction identifier is used for any compilation unit in the partition,
8205 then all compilation units in the partition must obey the restriction.
8209 @item Simple_Barriers
8210 @findex Simple_Barriers
8211 This restriction ensures at compile time that barriers in entry declarations
8212 for protected types are restricted to either static boolean expressions or
8213 references to simple boolean variables defined in the private part of the
8214 protected type. No other form of entry barriers is permitted. This is one
8215 of the restrictions of the Ravenscar profile for limited tasking (see also
8216 pragma @code{Profile (Ravenscar)}).
8218 @item Max_Entry_Queue_Length => Expr
8219 @findex Max_Entry_Queue_Length
8220 This restriction is a declaration that any protected entry compiled in
8221 the scope of the restriction has at most the specified number of
8222 tasks waiting on the entry
8223 at any one time, and so no queue is required. This restriction is not
8224 checked at compile time. A program execution is erroneous if an attempt
8225 is made to queue more than the specified number of tasks on such an entry.
8229 This restriction ensures at compile time that there is no implicit or
8230 explicit dependence on the package @code{Ada.Calendar}.
8232 @item No_Default_Initialization
8233 @findex No_Default_Initialization
8235 This restriction prohibits any instance of default initialization of variables.
8236 The binder implements a consistency rule which prevents any unit compiled
8237 without the restriction from with'ing a unit with the restriction (this allows
8238 the generation of initialization procedures to be skipped, since you can be
8239 sure that no call is ever generated to an initialization procedure in a unit
8240 with the restriction active). If used in conjunction with Initialize_Scalars or
8241 Normalize_Scalars, the effect is to prohibit all cases of variables declared
8242 without a specific initializer (including the case of OUT scalar parameters).
8244 @item No_Direct_Boolean_Operators
8245 @findex No_Direct_Boolean_Operators
8246 This restriction ensures that no logical (and/or/xor) or comparison
8247 operators are used on operands of type Boolean (or any type derived
8248 from Boolean). This is intended for use in safety critical programs
8249 where the certification protocol requires the use of short-circuit
8250 (and then, or else) forms for all composite boolean operations.
8252 @item No_Dispatching_Calls
8253 @findex No_Dispatching_Calls
8254 This restriction ensures at compile time that the code generated by the
8255 compiler involves no dispatching calls. The use of this restriction allows the
8256 safe use of record extensions, classwide membership tests and other classwide
8257 features not involving implicit dispatching. This restriction ensures that
8258 the code contains no indirect calls through a dispatching mechanism. Note that
8259 this includes internally-generated calls created by the compiler, for example
8260 in the implementation of class-wide objects assignments. The
8261 membership test is allowed in the presence of this restriction, because its
8262 implementation requires no dispatching.
8263 This restriction is comparable to the official Ada restriction
8264 @code{No_Dispatch} except that it is a bit less restrictive in that it allows
8265 all classwide constructs that do not imply dispatching.
8266 The following example indicates constructs that violate this restriction.
8270 type T is tagged record
8273 procedure P (X : T);
8275 type DT is new T with record
8276 More_Data : Natural;
8278 procedure Q (X : DT);
8282 procedure Example is
8283 procedure Test (O : T'Class) is
8284 N : Natural := O'Size;-- Error: Dispatching call
8285 C : T'Class := O; -- Error: implicit Dispatching Call
8287 if O in DT'Class then -- OK : Membership test
8288 Q (DT (O)); -- OK : Type conversion plus direct call
8290 P (O); -- Error: Dispatching call
8296 P (Obj); -- OK : Direct call
8297 P (T (Obj)); -- OK : Type conversion plus direct call
8298 P (T'Class (Obj)); -- Error: Dispatching call
8300 Test (Obj); -- OK : Type conversion
8302 if Obj in T'Class then -- OK : Membership test
8308 @item No_Dynamic_Attachment
8309 @findex No_Dynamic_Attachment
8310 This restriction ensures that there is no call to any of the operations
8311 defined in package Ada.Interrupts.
8313 @item No_Enumeration_Maps
8314 @findex No_Enumeration_Maps
8315 This restriction ensures at compile time that no operations requiring
8316 enumeration maps are used (that is Image and Value attributes applied
8317 to enumeration types).
8319 @item No_Entry_Calls_In_Elaboration_Code
8320 @findex No_Entry_Calls_In_Elaboration_Code
8321 This restriction ensures at compile time that no task or protected entry
8322 calls are made during elaboration code. As a result of the use of this
8323 restriction, the compiler can assume that no code past an accept statement
8324 in a task can be executed at elaboration time.
8326 @item No_Exception_Handlers
8327 @findex No_Exception_Handlers
8328 This restriction ensures at compile time that there are no explicit
8329 exception handlers. It also indicates that no exception propagation will
8330 be provided. In this mode, exceptions may be raised but will result in
8331 an immediate call to the last chance handler, a routine that the user
8332 must define with the following profile:
8334 procedure Last_Chance_Handler
8335 (Source_Location : System.Address; Line : Integer);
8336 pragma Export (C, Last_Chance_Handler,
8337 "__gnat_last_chance_handler");
8339 The parameter is a C null-terminated string representing a message to be
8340 associated with the exception (typically the source location of the raise
8341 statement generated by the compiler). The Line parameter when nonzero
8342 represents the line number in the source program where the raise occurs.
8344 @item No_Exception_Propagation
8345 @findex No_Exception_Propagation
8346 This restriction guarantees that exceptions are never propagated to an outer
8347 subprogram scope). The only case in which an exception may be raised is when
8348 the handler is statically in the same subprogram, so that the effect of a raise
8349 is essentially like a goto statement. Any other raise statement (implicit or
8350 explicit) will be considered unhandled. Exception handlers are allowed, but may
8351 not contain an exception occurrence identifier (exception choice). In addition
8352 use of the package GNAT.Current_Exception is not permitted, and reraise
8353 statements (raise with no operand) are not permitted.
8355 @item No_Exception_Registration
8356 @findex No_Exception_Registration
8357 This restriction ensures at compile time that no stream operations for
8358 types Exception_Id or Exception_Occurrence are used. This also makes it
8359 impossible to pass exceptions to or from a partition with this restriction
8360 in a distributed environment. If this exception is active, then the generated
8361 code is simplified by omitting the otherwise-required global registration
8362 of exceptions when they are declared.
8364 @item No_Implicit_Conditionals
8365 @findex No_Implicit_Conditionals
8366 This restriction ensures that the generated code does not contain any
8367 implicit conditionals, either by modifying the generated code where possible,
8368 or by rejecting any construct that would otherwise generate an implicit
8369 conditional. Note that this check does not include run time constraint
8370 checks, which on some targets may generate implicit conditionals as
8371 well. To control the latter, constraint checks can be suppressed in the
8372 normal manner. Constructs generating implicit conditionals include comparisons
8373 of composite objects and the Max/Min attributes.
8375 @item No_Implicit_Dynamic_Code
8376 @findex No_Implicit_Dynamic_Code
8378 This restriction prevents the compiler from building ``trampolines''.
8379 This is a structure that is built on the stack and contains dynamic
8380 code to be executed at run time. On some targets, a trampoline is
8381 built for the following features: @code{Access},
8382 @code{Unrestricted_Access}, or @code{Address} of a nested subprogram;
8383 nested task bodies; primitive operations of nested tagged types.
8384 Trampolines do not work on machines that prevent execution of stack
8385 data. For example, on windows systems, enabling DEP (data execution
8386 protection) will cause trampolines to raise an exception.
8387 Trampolines are also quite slow at run time.
8389 On many targets, trampolines have been largely eliminated. Look at the
8390 version of system.ads for your target --- if it has
8391 Always_Compatible_Rep equal to False, then trampolines are largely
8392 eliminated. In particular, a trampoline is built for the following
8393 features: @code{Address} of a nested subprogram;
8394 @code{Access} or @code{Unrestricted_Access} of a nested subprogram,
8395 but only if pragma Favor_Top_Level applies, or the access type has a
8396 foreign-language convention; primitive operations of nested tagged
8399 @item No_Implicit_Loops
8400 @findex No_Implicit_Loops
8401 This restriction ensures that the generated code does not contain any
8402 implicit @code{for} loops, either by modifying
8403 the generated code where possible,
8404 or by rejecting any construct that would otherwise generate an implicit
8405 @code{for} loop. If this restriction is active, it is possible to build
8406 large array aggregates with all static components without generating an
8407 intermediate temporary, and without generating a loop to initialize individual
8408 components. Otherwise, a loop is created for arrays larger than about 5000
8411 @item No_Initialize_Scalars
8412 @findex No_Initialize_Scalars
8413 This restriction ensures that no unit in the partition is compiled with
8414 pragma Initialize_Scalars. This allows the generation of more efficient
8415 code, and in particular eliminates dummy null initialization routines that
8416 are otherwise generated for some record and array types.
8418 @item No_Local_Protected_Objects
8419 @findex No_Local_Protected_Objects
8420 This restriction ensures at compile time that protected objects are
8421 only declared at the library level.
8423 @item No_Protected_Type_Allocators
8424 @findex No_Protected_Type_Allocators
8425 This restriction ensures at compile time that there are no allocator
8426 expressions that attempt to allocate protected objects.
8428 @item No_Secondary_Stack
8429 @findex No_Secondary_Stack
8430 This restriction ensures at compile time that the generated code does not
8431 contain any reference to the secondary stack. The secondary stack is used
8432 to implement functions returning unconstrained objects (arrays or records)
8435 @item No_Select_Statements
8436 @findex No_Select_Statements
8437 This restriction ensures at compile time no select statements of any kind
8438 are permitted, that is the keyword @code{select} may not appear.
8439 This is one of the restrictions of the Ravenscar
8440 profile for limited tasking (see also pragma @code{Profile (Ravenscar)}).
8442 @item No_Standard_Storage_Pools
8443 @findex No_Standard_Storage_Pools
8444 This restriction ensures at compile time that no access types
8445 use the standard default storage pool. Any access type declared must
8446 have an explicit Storage_Pool attribute defined specifying a
8447 user-defined storage pool.
8451 This restriction ensures at compile/bind time that there are no
8452 stream objects created (and therefore no actual stream operations).
8453 This restriction does not forbid dependences on the package
8454 @code{Ada.Streams}. So it is permissible to with
8455 @code{Ada.Streams} (or another package that does so itself)
8456 as long as no actual stream objects are created.
8458 @item No_Task_Attributes_Package
8459 @findex No_Task_Attributes_Package
8460 This restriction ensures at compile time that there are no implicit or
8461 explicit dependencies on the package @code{Ada.Task_Attributes}.
8463 @item No_Task_Termination
8464 @findex No_Task_Termination
8465 This restriction ensures at compile time that no terminate alternatives
8466 appear in any task body.
8470 This restriction prevents the declaration of tasks or task types throughout
8471 the partition. It is similar in effect to the use of @code{Max_Tasks => 0}
8472 except that violations are caught at compile time and cause an error message
8473 to be output either by the compiler or binder.
8475 @item Static_Priorities
8476 @findex Static_Priorities
8477 This restriction ensures at compile time that all priority expressions
8478 are static, and that there are no dependencies on the package
8479 @code{Ada.Dynamic_Priorities}.
8481 @item Static_Storage_Size
8482 @findex Static_Storage_Size
8483 This restriction ensures at compile time that any expression appearing
8484 in a Storage_Size pragma or attribute definition clause is static.
8489 The second set of implementation dependent restriction identifiers
8490 does not require partition-wide consistency.
8491 The restriction may be enforced for a single
8492 compilation unit without any effect on any of the
8493 other compilation units in the partition.
8497 @item No_Elaboration_Code
8498 @findex No_Elaboration_Code
8499 This restriction ensures at compile time that no elaboration code is
8500 generated. Note that this is not the same condition as is enforced
8501 by pragma @code{Preelaborate}. There are cases in which pragma
8502 @code{Preelaborate} still permits code to be generated (e.g.@: code
8503 to initialize a large array to all zeroes), and there are cases of units
8504 which do not meet the requirements for pragma @code{Preelaborate},
8505 but for which no elaboration code is generated. Generally, it is
8506 the case that preelaborable units will meet the restrictions, with
8507 the exception of large aggregates initialized with an others_clause,
8508 and exception declarations (which generate calls to a run-time
8509 registry procedure). This restriction is enforced on
8510 a unit by unit basis, it need not be obeyed consistently
8511 throughout a partition.
8513 In the case of aggregates with others, if the aggregate has a dynamic
8514 size, there is no way to eliminate the elaboration code (such dynamic
8515 bounds would be incompatible with @code{Preelaborate} in any case). If
8516 the bounds are static, then use of this restriction actually modifies
8517 the code choice of the compiler to avoid generating a loop, and instead
8518 generate the aggregate statically if possible, no matter how many times
8519 the data for the others clause must be repeatedly generated.
8521 It is not possible to precisely document
8522 the constructs which are compatible with this restriction, since,
8523 unlike most other restrictions, this is not a restriction on the
8524 source code, but a restriction on the generated object code. For
8525 example, if the source contains a declaration:
8528 Val : constant Integer := X;
8532 where X is not a static constant, it may be possible, depending
8533 on complex optimization circuitry, for the compiler to figure
8534 out the value of X at compile time, in which case this initialization
8535 can be done by the loader, and requires no initialization code. It
8536 is not possible to document the precise conditions under which the
8537 optimizer can figure this out.
8539 Note that this the implementation of this restriction requires full
8540 code generation. If it is used in conjunction with "semantics only"
8541 checking, then some cases of violations may be missed.
8543 @item No_Entry_Queue
8544 @findex No_Entry_Queue
8545 This restriction is a declaration that any protected entry compiled in
8546 the scope of the restriction has at most one task waiting on the entry
8547 at any one time, and so no queue is required. This restriction is not
8548 checked at compile time. A program execution is erroneous if an attempt
8549 is made to queue a second task on such an entry.
8551 @item No_Implementation_Attributes
8552 @findex No_Implementation_Attributes
8553 This restriction checks at compile time that no GNAT-defined attributes
8554 are present. With this restriction, the only attributes that can be used
8555 are those defined in the Ada Reference Manual.
8557 @item No_Implementation_Pragmas
8558 @findex No_Implementation_Pragmas
8559 This restriction checks at compile time that no GNAT-defined pragmas
8560 are present. With this restriction, the only pragmas that can be used
8561 are those defined in the Ada Reference Manual.
8563 @item No_Implementation_Restrictions
8564 @findex No_Implementation_Restrictions
8565 This restriction checks at compile time that no GNAT-defined restriction
8566 identifiers (other than @code{No_Implementation_Restrictions} itself)
8567 are present. With this restriction, the only other restriction identifiers
8568 that can be used are those defined in the Ada Reference Manual.
8570 @item No_Wide_Characters
8571 @findex No_Wide_Characters
8572 This restriction ensures at compile time that no uses of the types
8573 @code{Wide_Character} or @code{Wide_String} or corresponding wide
8575 appear, and that no wide or wide wide string or character literals
8576 appear in the program (that is literals representing characters not in
8577 type @code{Character}.
8584 @strong{58}. The consequences of violating limitations on
8585 @code{Restrictions} pragmas. See 13.12(9).
8588 Restrictions that can be checked at compile time result in illegalities
8589 if violated. Currently there are no other consequences of violating
8595 @strong{59}. The representation used by the @code{Read} and
8596 @code{Write} attributes of elementary types in terms of stream
8597 elements. See 13.13.2(9).
8600 The representation is the in-memory representation of the base type of
8601 the type, using the number of bits corresponding to the
8602 @code{@var{type}'Size} value, and the natural ordering of the machine.
8607 @strong{60}. The names and characteristics of the numeric subtypes
8608 declared in the visible part of package @code{Standard}. See A.1(3).
8611 See items describing the integer and floating-point types supported.
8616 @strong{61}. The accuracy actually achieved by the elementary
8617 functions. See A.5.1(1).
8620 The elementary functions correspond to the functions available in the C
8621 library. Only fast math mode is implemented.
8626 @strong{62}. The sign of a zero result from some of the operators or
8627 functions in @code{Numerics.Generic_Elementary_Functions}, when
8628 @code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
8631 The sign of zeroes follows the requirements of the IEEE 754 standard on
8637 @strong{63}. The value of
8638 @code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
8641 Maximum image width is 649, see library file @file{a-numran.ads}.
8646 @strong{64}. The value of
8647 @code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
8650 Maximum image width is 80, see library file @file{a-nudira.ads}.
8655 @strong{65}. The algorithms for random number generation. See
8659 The algorithm is documented in the source files @file{a-numran.ads} and
8660 @file{a-numran.adb}.
8665 @strong{66}. The string representation of a random number generator's
8666 state. See A.5.2(38).
8669 See the documentation contained in the file @file{a-numran.adb}.
8674 @strong{67}. The minimum time interval between calls to the
8675 time-dependent Reset procedure that are guaranteed to initiate different
8676 random number sequences. See A.5.2(45).
8679 The minimum period between reset calls to guarantee distinct series of
8680 random numbers is one microsecond.
8685 @strong{68}. The values of the @code{Model_Mantissa},
8686 @code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
8687 @code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
8688 Annex is not supported. See A.5.3(72).
8691 See the source file @file{ttypef.ads} for the values of all numeric
8697 @strong{69}. Any implementation-defined characteristics of the
8698 input-output packages. See A.7(14).
8701 There are no special implementation defined characteristics for these
8707 @strong{70}. The value of @code{Buffer_Size} in @code{Storage_IO}. See
8711 All type representations are contiguous, and the @code{Buffer_Size} is
8712 the value of @code{@var{type}'Size} rounded up to the next storage unit
8718 @strong{71}. External files for standard input, standard output, and
8719 standard error See A.10(5).
8722 These files are mapped onto the files provided by the C streams
8723 libraries. See source file @file{i-cstrea.ads} for further details.
8728 @strong{72}. The accuracy of the value produced by @code{Put}. See
8732 If more digits are requested in the output than are represented by the
8733 precision of the value, zeroes are output in the corresponding least
8734 significant digit positions.
8739 @strong{73}. The meaning of @code{Argument_Count}, @code{Argument}, and
8740 @code{Command_Name}. See A.15(1).
8743 These are mapped onto the @code{argv} and @code{argc} parameters of the
8744 main program in the natural manner.
8749 @strong{74}. Implementation-defined convention names. See B.1(11).
8752 The following convention names are supported
8760 Synonym for Assembler
8762 Synonym for Assembler
8765 @item C_Pass_By_Copy
8766 Allowed only for record types, like C, but also notes that record
8767 is to be passed by copy rather than reference.
8770 @item C_Plus_Plus (or CPP)
8773 Treated the same as C
8775 Treated the same as C
8779 For support of pragma @code{Import} with convention Intrinsic, see
8780 separate section on Intrinsic Subprograms.
8782 Stdcall (used for Windows implementations only). This convention correspond
8783 to the WINAPI (previously called Pascal convention) C/C++ convention under
8784 Windows. A function with this convention cleans the stack before exit.
8790 Stubbed is a special convention used to indicate that the body of the
8791 subprogram will be entirely ignored. Any call to the subprogram
8792 is converted into a raise of the @code{Program_Error} exception. If a
8793 pragma @code{Import} specifies convention @code{stubbed} then no body need
8794 be present at all. This convention is useful during development for the
8795 inclusion of subprograms whose body has not yet been written.
8799 In addition, all otherwise unrecognized convention names are also
8800 treated as being synonymous with convention C@. In all implementations
8801 except for VMS, use of such other names results in a warning. In VMS
8802 implementations, these names are accepted silently.
8807 @strong{75}. The meaning of link names. See B.1(36).
8810 Link names are the actual names used by the linker.
8815 @strong{76}. The manner of choosing link names when neither the link
8816 name nor the address of an imported or exported entity is specified. See
8820 The default linker name is that which would be assigned by the relevant
8821 external language, interpreting the Ada name as being in all lower case
8827 @strong{77}. The effect of pragma @code{Linker_Options}. See B.1(37).
8830 The string passed to @code{Linker_Options} is presented uninterpreted as
8831 an argument to the link command, unless it contains ASCII.NUL characters.
8832 NUL characters if they appear act as argument separators, so for example
8834 @smallexample @c ada
8835 pragma Linker_Options ("-labc" & ASCII.NUL & "-ldef");
8839 causes two separate arguments @code{-labc} and @code{-ldef} to be passed to the
8840 linker. The order of linker options is preserved for a given unit. The final
8841 list of options passed to the linker is in reverse order of the elaboration
8842 order. For example, linker options for a body always appear before the options
8843 from the corresponding package spec.
8848 @strong{78}. The contents of the visible part of package
8849 @code{Interfaces} and its language-defined descendants. See B.2(1).
8852 See files with prefix @file{i-} in the distributed library.
8857 @strong{79}. Implementation-defined children of package
8858 @code{Interfaces}. The contents of the visible part of package
8859 @code{Interfaces}. See B.2(11).
8862 See files with prefix @file{i-} in the distributed library.
8867 @strong{80}. The types @code{Floating}, @code{Long_Floating},
8868 @code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
8869 @code{COBOL_Character}; and the initialization of the variables
8870 @code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
8871 @code{Interfaces.COBOL}. See B.4(50).
8878 (Floating) Long_Float
8883 @item Decimal_Element
8885 @item COBOL_Character
8890 For initialization, see the file @file{i-cobol.ads} in the distributed library.
8895 @strong{81}. Support for access to machine instructions. See C.1(1).
8898 See documentation in file @file{s-maccod.ads} in the distributed library.
8903 @strong{82}. Implementation-defined aspects of access to machine
8904 operations. See C.1(9).
8907 See documentation in file @file{s-maccod.ads} in the distributed library.
8912 @strong{83}. Implementation-defined aspects of interrupts. See C.3(2).
8915 Interrupts are mapped to signals or conditions as appropriate. See
8917 @code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
8918 on the interrupts supported on a particular target.
8923 @strong{84}. Implementation-defined aspects of pre-elaboration. See
8927 GNAT does not permit a partition to be restarted without reloading,
8928 except under control of the debugger.
8933 @strong{85}. The semantics of pragma @code{Discard_Names}. See C.5(7).
8936 Pragma @code{Discard_Names} causes names of enumeration literals to
8937 be suppressed. In the presence of this pragma, the Image attribute
8938 provides the image of the Pos of the literal, and Value accepts
8944 @strong{86}. The result of the @code{Task_Identification.Image}
8945 attribute. See C.7.1(7).
8948 The result of this attribute is a string that identifies
8949 the object or component that denotes a given task. If a variable @code{Var}
8950 has a task type, the image for this task will have the form @code{Var_@var{XXXXXXXX}},
8952 is the hexadecimal representation of the virtual address of the corresponding
8953 task control block. If the variable is an array of tasks, the image of each
8954 task will have the form of an indexed component indicating the position of a
8955 given task in the array, e.g.@: @code{Group(5)_@var{XXXXXXX}}. If the task is a
8956 component of a record, the image of the task will have the form of a selected
8957 component. These rules are fully recursive, so that the image of a task that
8958 is a subcomponent of a composite object corresponds to the expression that
8959 designates this task.
8961 If a task is created by an allocator, its image depends on the context. If the
8962 allocator is part of an object declaration, the rules described above are used
8963 to construct its image, and this image is not affected by subsequent
8964 assignments. If the allocator appears within an expression, the image
8965 includes only the name of the task type.
8967 If the configuration pragma Discard_Names is present, or if the restriction
8968 No_Implicit_Heap_Allocation is in effect, the image reduces to
8969 the numeric suffix, that is to say the hexadecimal representation of the
8970 virtual address of the control block of the task.
8974 @strong{87}. The value of @code{Current_Task} when in a protected entry
8975 or interrupt handler. See C.7.1(17).
8978 Protected entries or interrupt handlers can be executed by any
8979 convenient thread, so the value of @code{Current_Task} is undefined.
8984 @strong{88}. The effect of calling @code{Current_Task} from an entry
8985 body or interrupt handler. See C.7.1(19).
8988 The effect of calling @code{Current_Task} from an entry body or
8989 interrupt handler is to return the identification of the task currently
8995 @strong{89}. Implementation-defined aspects of
8996 @code{Task_Attributes}. See C.7.2(19).
8999 There are no implementation-defined aspects of @code{Task_Attributes}.
9004 @strong{90}. Values of all @code{Metrics}. See D(2).
9007 The metrics information for GNAT depends on the performance of the
9008 underlying operating system. The sources of the run-time for tasking
9009 implementation, together with the output from @option{-gnatG} can be
9010 used to determine the exact sequence of operating systems calls made
9011 to implement various tasking constructs. Together with appropriate
9012 information on the performance of the underlying operating system,
9013 on the exact target in use, this information can be used to determine
9014 the required metrics.
9019 @strong{91}. The declarations of @code{Any_Priority} and
9020 @code{Priority}. See D.1(11).
9023 See declarations in file @file{system.ads}.
9028 @strong{92}. Implementation-defined execution resources. See D.1(15).
9031 There are no implementation-defined execution resources.
9036 @strong{93}. Whether, on a multiprocessor, a task that is waiting for
9037 access to a protected object keeps its processor busy. See D.2.1(3).
9040 On a multi-processor, a task that is waiting for access to a protected
9041 object does not keep its processor busy.
9046 @strong{94}. The affect of implementation defined execution resources
9047 on task dispatching. See D.2.1(9).
9052 Tasks map to IRIX threads, and the dispatching policy is as defined by
9053 the IRIX implementation of threads.
9055 Tasks map to threads in the threads package used by GNAT@. Where possible
9056 and appropriate, these threads correspond to native threads of the
9057 underlying operating system.
9062 @strong{95}. Implementation-defined @code{policy_identifiers} allowed
9063 in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
9066 There are no implementation-defined policy-identifiers allowed in this
9072 @strong{96}. Implementation-defined aspects of priority inversion. See
9076 Execution of a task cannot be preempted by the implementation processing
9077 of delay expirations for lower priority tasks.
9082 @strong{97}. Implementation defined task dispatching. See D.2.2(18).
9087 Tasks map to IRIX threads, and the dispatching policy is as defined by
9088 the IRIX implementation of threads.
9090 The policy is the same as that of the underlying threads implementation.
9095 @strong{98}. Implementation-defined @code{policy_identifiers} allowed
9096 in a pragma @code{Locking_Policy}. See D.3(4).
9099 The only implementation defined policy permitted in GNAT is
9100 @code{Inheritance_Locking}. On targets that support this policy, locking
9101 is implemented by inheritance, i.e.@: the task owning the lock operates
9102 at a priority equal to the highest priority of any task currently
9103 requesting the lock.
9108 @strong{99}. Default ceiling priorities. See D.3(10).
9111 The ceiling priority of protected objects of the type
9112 @code{System.Interrupt_Priority'Last} as described in the Ada
9113 Reference Manual D.3(10),
9118 @strong{100}. The ceiling of any protected object used internally by
9119 the implementation. See D.3(16).
9122 The ceiling priority of internal protected objects is
9123 @code{System.Priority'Last}.
9128 @strong{101}. Implementation-defined queuing policies. See D.4(1).
9131 There are no implementation-defined queuing policies.
9136 @strong{102}. On a multiprocessor, any conditions that cause the
9137 completion of an aborted construct to be delayed later than what is
9138 specified for a single processor. See D.6(3).
9141 The semantics for abort on a multi-processor is the same as on a single
9142 processor, there are no further delays.
9147 @strong{103}. Any operations that implicitly require heap storage
9148 allocation. See D.7(8).
9151 The only operation that implicitly requires heap storage allocation is
9157 @strong{104}. Implementation-defined aspects of pragma
9158 @code{Restrictions}. See D.7(20).
9161 There are no such implementation-defined aspects.
9166 @strong{105}. Implementation-defined aspects of package
9167 @code{Real_Time}. See D.8(17).
9170 There are no implementation defined aspects of package @code{Real_Time}.
9175 @strong{106}. Implementation-defined aspects of
9176 @code{delay_statements}. See D.9(8).
9179 Any difference greater than one microsecond will cause the task to be
9180 delayed (see D.9(7)).
9185 @strong{107}. The upper bound on the duration of interrupt blocking
9186 caused by the implementation. See D.12(5).
9189 The upper bound is determined by the underlying operating system. In
9190 no cases is it more than 10 milliseconds.
9195 @strong{108}. The means for creating and executing distributed
9199 The GLADE package provides a utility GNATDIST for creating and executing
9200 distributed programs. See the GLADE reference manual for further details.
9205 @strong{109}. Any events that can result in a partition becoming
9206 inaccessible. See E.1(7).
9209 See the GLADE reference manual for full details on such events.
9214 @strong{110}. The scheduling policies, treatment of priorities, and
9215 management of shared resources between partitions in certain cases. See
9219 See the GLADE reference manual for full details on these aspects of
9220 multi-partition execution.
9225 @strong{111}. Events that cause the version of a compilation unit to
9229 Editing the source file of a compilation unit, or the source files of
9230 any units on which it is dependent in a significant way cause the version
9231 to change. No other actions cause the version number to change. All changes
9232 are significant except those which affect only layout, capitalization or
9238 @strong{112}. Whether the execution of the remote subprogram is
9239 immediately aborted as a result of cancellation. See E.4(13).
9242 See the GLADE reference manual for details on the effect of abort in
9243 a distributed application.
9248 @strong{113}. Implementation-defined aspects of the PCS@. See E.5(25).
9251 See the GLADE reference manual for a full description of all implementation
9252 defined aspects of the PCS@.
9257 @strong{114}. Implementation-defined interfaces in the PCS@. See
9261 See the GLADE reference manual for a full description of all
9262 implementation defined interfaces.
9267 @strong{115}. The values of named numbers in the package
9268 @code{Decimal}. See F.2(7).
9280 @item Max_Decimal_Digits
9287 @strong{116}. The value of @code{Max_Picture_Length} in the package
9288 @code{Text_IO.Editing}. See F.3.3(16).
9296 @strong{117}. The value of @code{Max_Picture_Length} in the package
9297 @code{Wide_Text_IO.Editing}. See F.3.4(5).
9305 @strong{118}. The accuracy actually achieved by the complex elementary
9306 functions and by other complex arithmetic operations. See G.1(1).
9309 Standard library functions are used for the complex arithmetic
9310 operations. Only fast math mode is currently supported.
9315 @strong{119}. The sign of a zero result (or a component thereof) from
9316 any operator or function in @code{Numerics.Generic_Complex_Types}, when
9317 @code{Real'Signed_Zeros} is True. See G.1.1(53).
9320 The signs of zero values are as recommended by the relevant
9321 implementation advice.
9326 @strong{120}. The sign of a zero result (or a component thereof) from
9327 any operator or function in
9328 @code{Numerics.Generic_Complex_Elementary_Functions}, when
9329 @code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
9332 The signs of zero values are as recommended by the relevant
9333 implementation advice.
9338 @strong{121}. Whether the strict mode or the relaxed mode is the
9339 default. See G.2(2).
9342 The strict mode is the default. There is no separate relaxed mode. GNAT
9343 provides a highly efficient implementation of strict mode.
9348 @strong{122}. The result interval in certain cases of fixed-to-float
9349 conversion. See G.2.1(10).
9352 For cases where the result interval is implementation dependent, the
9353 accuracy is that provided by performing all operations in 64-bit IEEE
9354 floating-point format.
9359 @strong{123}. The result of a floating point arithmetic operation in
9360 overflow situations, when the @code{Machine_Overflows} attribute of the
9361 result type is @code{False}. See G.2.1(13).
9364 Infinite and NaN values are produced as dictated by the IEEE
9365 floating-point standard.
9367 Note that on machines that are not fully compliant with the IEEE
9368 floating-point standard, such as Alpha, the @option{-mieee} compiler flag
9369 must be used for achieving IEEE confirming behavior (although at the cost
9370 of a significant performance penalty), so infinite and NaN values are
9376 @strong{124}. The result interval for division (or exponentiation by a
9377 negative exponent), when the floating point hardware implements division
9378 as multiplication by a reciprocal. See G.2.1(16).
9381 Not relevant, division is IEEE exact.
9386 @strong{125}. The definition of close result set, which determines the
9387 accuracy of certain fixed point multiplications and divisions. See
9391 Operations in the close result set are performed using IEEE long format
9392 floating-point arithmetic. The input operands are converted to
9393 floating-point, the operation is done in floating-point, and the result
9394 is converted to the target type.
9399 @strong{126}. Conditions on a @code{universal_real} operand of a fixed
9400 point multiplication or division for which the result shall be in the
9401 perfect result set. See G.2.3(22).
9404 The result is only defined to be in the perfect result set if the result
9405 can be computed by a single scaling operation involving a scale factor
9406 representable in 64-bits.
9411 @strong{127}. The result of a fixed point arithmetic operation in
9412 overflow situations, when the @code{Machine_Overflows} attribute of the
9413 result type is @code{False}. See G.2.3(27).
9416 Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
9422 @strong{128}. The result of an elementary function reference in
9423 overflow situations, when the @code{Machine_Overflows} attribute of the
9424 result type is @code{False}. See G.2.4(4).
9427 IEEE infinite and Nan values are produced as appropriate.
9432 @strong{129}. The value of the angle threshold, within which certain
9433 elementary functions, complex arithmetic operations, and complex
9434 elementary functions yield results conforming to a maximum relative
9435 error bound. See G.2.4(10).
9438 Information on this subject is not yet available.
9443 @strong{130}. The accuracy of certain elementary functions for
9444 parameters beyond the angle threshold. See G.2.4(10).
9447 Information on this subject is not yet available.
9452 @strong{131}. The result of a complex arithmetic operation or complex
9453 elementary function reference in overflow situations, when the
9454 @code{Machine_Overflows} attribute of the corresponding real type is
9455 @code{False}. See G.2.6(5).
9458 IEEE infinite and Nan values are produced as appropriate.
9463 @strong{132}. The accuracy of certain complex arithmetic operations and
9464 certain complex elementary functions for parameters (or components
9465 thereof) beyond the angle threshold. See G.2.6(8).
9468 Information on those subjects is not yet available.
9473 @strong{133}. Information regarding bounded errors and erroneous
9474 execution. See H.2(1).
9477 Information on this subject is not yet available.
9482 @strong{134}. Implementation-defined aspects of pragma
9483 @code{Inspection_Point}. See H.3.2(8).
9486 Pragma @code{Inspection_Point} ensures that the variable is live and can
9487 be examined by the debugger at the inspection point.
9492 @strong{135}. Implementation-defined aspects of pragma
9493 @code{Restrictions}. See H.4(25).
9496 There are no implementation-defined aspects of pragma @code{Restrictions}. The
9497 use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
9498 generated code. Checks must suppressed by use of pragma @code{Suppress}.
9503 @strong{136}. Any restrictions on pragma @code{Restrictions}. See
9507 There are no restrictions on pragma @code{Restrictions}.
9509 @node Intrinsic Subprograms
9510 @chapter Intrinsic Subprograms
9511 @cindex Intrinsic Subprograms
9514 * Intrinsic Operators::
9515 * Enclosing_Entity::
9516 * Exception_Information::
9517 * Exception_Message::
9525 * Shift_Right_Arithmetic::
9530 GNAT allows a user application program to write the declaration:
9532 @smallexample @c ada
9533 pragma Import (Intrinsic, name);
9537 providing that the name corresponds to one of the implemented intrinsic
9538 subprograms in GNAT, and that the parameter profile of the referenced
9539 subprogram meets the requirements. This chapter describes the set of
9540 implemented intrinsic subprograms, and the requirements on parameter profiles.
9541 Note that no body is supplied; as with other uses of pragma Import, the
9542 body is supplied elsewhere (in this case by the compiler itself). Note
9543 that any use of this feature is potentially non-portable, since the
9544 Ada standard does not require Ada compilers to implement this feature.
9546 @node Intrinsic Operators
9547 @section Intrinsic Operators
9548 @cindex Intrinsic operator
9551 All the predefined numeric operators in package Standard
9552 in @code{pragma Import (Intrinsic,..)}
9553 declarations. In the binary operator case, the operands must have the same
9554 size. The operand or operands must also be appropriate for
9555 the operator. For example, for addition, the operands must
9556 both be floating-point or both be fixed-point, and the
9557 right operand for @code{"**"} must have a root type of
9558 @code{Standard.Integer'Base}.
9559 You can use an intrinsic operator declaration as in the following example:
9561 @smallexample @c ada
9562 type Int1 is new Integer;
9563 type Int2 is new Integer;
9565 function "+" (X1 : Int1; X2 : Int2) return Int1;
9566 function "+" (X1 : Int1; X2 : Int2) return Int2;
9567 pragma Import (Intrinsic, "+");
9571 This declaration would permit ``mixed mode'' arithmetic on items
9572 of the differing types @code{Int1} and @code{Int2}.
9573 It is also possible to specify such operators for private types, if the
9574 full views are appropriate arithmetic types.
9576 @node Enclosing_Entity
9577 @section Enclosing_Entity
9578 @cindex Enclosing_Entity
9580 This intrinsic subprogram is used in the implementation of the
9581 library routine @code{GNAT.Source_Info}. The only useful use of the
9582 intrinsic import in this case is the one in this unit, so an
9583 application program should simply call the function
9584 @code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
9585 the current subprogram, package, task, entry, or protected subprogram.
9587 @node Exception_Information
9588 @section Exception_Information
9589 @cindex Exception_Information'
9591 This intrinsic subprogram is used in the implementation of the
9592 library routine @code{GNAT.Current_Exception}. The only useful
9593 use of the intrinsic import in this case is the one in this unit,
9594 so an application program should simply call the function
9595 @code{GNAT.Current_Exception.Exception_Information} to obtain
9596 the exception information associated with the current exception.
9598 @node Exception_Message
9599 @section Exception_Message
9600 @cindex Exception_Message
9602 This intrinsic subprogram is used in the implementation of the
9603 library routine @code{GNAT.Current_Exception}. The only useful
9604 use of the intrinsic import in this case is the one in this unit,
9605 so an application program should simply call the function
9606 @code{GNAT.Current_Exception.Exception_Message} to obtain
9607 the message associated with the current exception.
9609 @node Exception_Name
9610 @section Exception_Name
9611 @cindex Exception_Name
9613 This intrinsic subprogram is used in the implementation of the
9614 library routine @code{GNAT.Current_Exception}. The only useful
9615 use of the intrinsic import in this case is the one in this unit,
9616 so an application program should simply call the function
9617 @code{GNAT.Current_Exception.Exception_Name} to obtain
9618 the name of the current exception.
9624 This intrinsic subprogram is used in the implementation of the
9625 library routine @code{GNAT.Source_Info}. The only useful use of the
9626 intrinsic import in this case is the one in this unit, so an
9627 application program should simply call the function
9628 @code{GNAT.Source_Info.File} to obtain the name of the current
9635 This intrinsic subprogram is used in the implementation of the
9636 library routine @code{GNAT.Source_Info}. The only useful use of the
9637 intrinsic import in this case is the one in this unit, so an
9638 application program should simply call the function
9639 @code{GNAT.Source_Info.Line} to obtain the number of the current
9643 @section Rotate_Left
9646 In standard Ada, the @code{Rotate_Left} function is available only
9647 for the predefined modular types in package @code{Interfaces}. However, in
9648 GNAT it is possible to define a Rotate_Left function for a user
9649 defined modular type or any signed integer type as in this example:
9651 @smallexample @c ada
9653 (Value : My_Modular_Type;
9655 return My_Modular_Type;
9659 The requirements are that the profile be exactly as in the example
9660 above. The only modifications allowed are in the formal parameter
9661 names, and in the type of @code{Value} and the return type, which
9662 must be the same, and must be either a signed integer type, or
9663 a modular integer type with a binary modulus, and the size must
9664 be 8. 16, 32 or 64 bits.
9667 @section Rotate_Right
9668 @cindex Rotate_Right
9670 A @code{Rotate_Right} function can be defined for any user defined
9671 binary modular integer type, or signed integer type, as described
9672 above for @code{Rotate_Left}.
9678 A @code{Shift_Left} function can be defined for any user defined
9679 binary modular integer type, or signed integer type, as described
9680 above for @code{Rotate_Left}.
9683 @section Shift_Right
9686 A @code{Shift_Right} function can be defined for any user defined
9687 binary modular integer type, or signed integer type, as described
9688 above for @code{Rotate_Left}.
9690 @node Shift_Right_Arithmetic
9691 @section Shift_Right_Arithmetic
9692 @cindex Shift_Right_Arithmetic
9694 A @code{Shift_Right_Arithmetic} function can be defined for any user
9695 defined binary modular integer type, or signed integer type, as described
9696 above for @code{Rotate_Left}.
9698 @node Source_Location
9699 @section Source_Location
9700 @cindex Source_Location
9702 This intrinsic subprogram is used in the implementation of the
9703 library routine @code{GNAT.Source_Info}. The only useful use of the
9704 intrinsic import in this case is the one in this unit, so an
9705 application program should simply call the function
9706 @code{GNAT.Source_Info.Source_Location} to obtain the current
9707 source file location.
9709 @node Representation Clauses and Pragmas
9710 @chapter Representation Clauses and Pragmas
9711 @cindex Representation Clauses
9714 * Alignment Clauses::
9716 * Storage_Size Clauses::
9717 * Size of Variant Record Objects::
9718 * Biased Representation ::
9719 * Value_Size and Object_Size Clauses::
9720 * Component_Size Clauses::
9721 * Bit_Order Clauses::
9722 * Effect of Bit_Order on Byte Ordering::
9723 * Pragma Pack for Arrays::
9724 * Pragma Pack for Records::
9725 * Record Representation Clauses::
9726 * Enumeration Clauses::
9728 * Effect of Convention on Representation::
9729 * Determining the Representations chosen by GNAT::
9733 @cindex Representation Clause
9734 @cindex Representation Pragma
9735 @cindex Pragma, representation
9736 This section describes the representation clauses accepted by GNAT, and
9737 their effect on the representation of corresponding data objects.
9739 GNAT fully implements Annex C (Systems Programming). This means that all
9740 the implementation advice sections in chapter 13 are fully implemented.
9741 However, these sections only require a minimal level of support for
9742 representation clauses. GNAT provides much more extensive capabilities,
9743 and this section describes the additional capabilities provided.
9745 @node Alignment Clauses
9746 @section Alignment Clauses
9747 @cindex Alignment Clause
9750 GNAT requires that all alignment clauses specify a power of 2, and all
9751 default alignments are always a power of 2. The default alignment
9752 values are as follows:
9755 @item @emph{Primitive Types}.
9756 For primitive types, the alignment is the minimum of the actual size of
9757 objects of the type divided by @code{Storage_Unit},
9758 and the maximum alignment supported by the target.
9759 (This maximum alignment is given by the GNAT-specific attribute
9760 @code{Standard'Maximum_Alignment}; see @ref{Maximum_Alignment}.)
9761 @cindex @code{Maximum_Alignment} attribute
9762 For example, for type @code{Long_Float}, the object size is 8 bytes, and the
9763 default alignment will be 8 on any target that supports alignments
9764 this large, but on some targets, the maximum alignment may be smaller
9765 than 8, in which case objects of type @code{Long_Float} will be maximally
9768 @item @emph{Arrays}.
9769 For arrays, the alignment is equal to the alignment of the component type
9770 for the normal case where no packing or component size is given. If the
9771 array is packed, and the packing is effective (see separate section on
9772 packed arrays), then the alignment will be one for long packed arrays,
9773 or arrays whose length is not known at compile time. For short packed
9774 arrays, which are handled internally as modular types, the alignment
9775 will be as described for primitive types, e.g.@: a packed array of length
9776 31 bits will have an object size of four bytes, and an alignment of 4.
9778 @item @emph{Records}.
9779 For the normal non-packed case, the alignment of a record is equal to
9780 the maximum alignment of any of its components. For tagged records, this
9781 includes the implicit access type used for the tag. If a pragma @code{Pack}
9782 is used and all components are packable (see separate section on pragma
9783 @code{Pack}), then the resulting alignment is 1, unless the layout of the
9784 record makes it profitable to increase it.
9786 A special case is when:
9789 the size of the record is given explicitly, or a
9790 full record representation clause is given, and
9792 the size of the record is 2, 4, or 8 bytes.
9795 In this case, an alignment is chosen to match the
9796 size of the record. For example, if we have:
9798 @smallexample @c ada
9799 type Small is record
9802 for Small'Size use 16;
9806 then the default alignment of the record type @code{Small} is 2, not 1. This
9807 leads to more efficient code when the record is treated as a unit, and also
9808 allows the type to specified as @code{Atomic} on architectures requiring
9814 An alignment clause may specify a larger alignment than the default value
9815 up to some maximum value dependent on the target (obtainable by using the
9816 attribute reference @code{Standard'Maximum_Alignment}). It may also specify
9817 a smaller alignment than the default value for enumeration, integer and
9818 fixed point types, as well as for record types, for example
9820 @smallexample @c ada
9825 for V'alignment use 1;
9829 @cindex Alignment, default
9830 The default alignment for the type @code{V} is 4, as a result of the
9831 Integer field in the record, but it is permissible, as shown, to
9832 override the default alignment of the record with a smaller value.
9835 @section Size Clauses
9839 The default size for a type @code{T} is obtainable through the
9840 language-defined attribute @code{T'Size} and also through the
9841 equivalent GNAT-defined attribute @code{T'Value_Size}.
9842 For objects of type @code{T}, GNAT will generally increase the type size
9843 so that the object size (obtainable through the GNAT-defined attribute
9844 @code{T'Object_Size})
9845 is a multiple of @code{T'Alignment * Storage_Unit}.
9848 @smallexample @c ada
9849 type Smallint is range 1 .. 6;
9858 In this example, @code{Smallint'Size} = @code{Smallint'Value_Size} = 3,
9859 as specified by the RM rules,
9860 but objects of this type will have a size of 8
9861 (@code{Smallint'Object_Size} = 8),
9862 since objects by default occupy an integral number
9863 of storage units. On some targets, notably older
9864 versions of the Digital Alpha, the size of stand
9865 alone objects of this type may be 32, reflecting
9866 the inability of the hardware to do byte load/stores.
9868 Similarly, the size of type @code{Rec} is 40 bits
9869 (@code{Rec'Size} = @code{Rec'Value_Size} = 40), but
9870 the alignment is 4, so objects of this type will have
9871 their size increased to 64 bits so that it is a multiple
9872 of the alignment (in bits). This decision is
9873 in accordance with the specific Implementation Advice in RM 13.3(43):
9876 A @code{Size} clause should be supported for an object if the specified
9877 @code{Size} is at least as large as its subtype's @code{Size}, and corresponds
9878 to a size in storage elements that is a multiple of the object's
9879 @code{Alignment} (if the @code{Alignment} is nonzero).
9883 An explicit size clause may be used to override the default size by
9884 increasing it. For example, if we have:
9886 @smallexample @c ada
9887 type My_Boolean is new Boolean;
9888 for My_Boolean'Size use 32;
9892 then values of this type will always be 32 bits long. In the case of
9893 discrete types, the size can be increased up to 64 bits, with the effect
9894 that the entire specified field is used to hold the value, sign- or
9895 zero-extended as appropriate. If more than 64 bits is specified, then
9896 padding space is allocated after the value, and a warning is issued that
9897 there are unused bits.
9899 Similarly the size of records and arrays may be increased, and the effect
9900 is to add padding bits after the value. This also causes a warning message
9903 The largest Size value permitted in GNAT is 2**31@minus{}1. Since this is a
9904 Size in bits, this corresponds to an object of size 256 megabytes (minus
9905 one). This limitation is true on all targets. The reason for this
9906 limitation is that it improves the quality of the code in many cases
9907 if it is known that a Size value can be accommodated in an object of
9910 @node Storage_Size Clauses
9911 @section Storage_Size Clauses
9912 @cindex Storage_Size Clause
9915 For tasks, the @code{Storage_Size} clause specifies the amount of space
9916 to be allocated for the task stack. This cannot be extended, and if the
9917 stack is exhausted, then @code{Storage_Error} will be raised (if stack
9918 checking is enabled). Use a @code{Storage_Size} attribute definition clause,
9919 or a @code{Storage_Size} pragma in the task definition to set the
9920 appropriate required size. A useful technique is to include in every
9921 task definition a pragma of the form:
9923 @smallexample @c ada
9924 pragma Storage_Size (Default_Stack_Size);
9928 Then @code{Default_Stack_Size} can be defined in a global package, and
9929 modified as required. Any tasks requiring stack sizes different from the
9930 default can have an appropriate alternative reference in the pragma.
9932 You can also use the @option{-d} binder switch to modify the default stack
9935 For access types, the @code{Storage_Size} clause specifies the maximum
9936 space available for allocation of objects of the type. If this space is
9937 exceeded then @code{Storage_Error} will be raised by an allocation attempt.
9938 In the case where the access type is declared local to a subprogram, the
9939 use of a @code{Storage_Size} clause triggers automatic use of a special
9940 predefined storage pool (@code{System.Pool_Size}) that ensures that all
9941 space for the pool is automatically reclaimed on exit from the scope in
9942 which the type is declared.
9944 A special case recognized by the compiler is the specification of a
9945 @code{Storage_Size} of zero for an access type. This means that no
9946 items can be allocated from the pool, and this is recognized at compile
9947 time, and all the overhead normally associated with maintaining a fixed
9948 size storage pool is eliminated. Consider the following example:
9950 @smallexample @c ada
9952 type R is array (Natural) of Character;
9953 type P is access all R;
9954 for P'Storage_Size use 0;
9955 -- Above access type intended only for interfacing purposes
9959 procedure g (m : P);
9960 pragma Import (C, g);
9971 As indicated in this example, these dummy storage pools are often useful in
9972 connection with interfacing where no object will ever be allocated. If you
9973 compile the above example, you get the warning:
9976 p.adb:16:09: warning: allocation from empty storage pool
9977 p.adb:16:09: warning: Storage_Error will be raised at run time
9981 Of course in practice, there will not be any explicit allocators in the
9982 case of such an access declaration.
9984 @node Size of Variant Record Objects
9985 @section Size of Variant Record Objects
9986 @cindex Size, variant record objects
9987 @cindex Variant record objects, size
9990 In the case of variant record objects, there is a question whether Size gives
9991 information about a particular variant, or the maximum size required
9992 for any variant. Consider the following program
9994 @smallexample @c ada
9995 with Text_IO; use Text_IO;
9997 type R1 (A : Boolean := False) is record
9999 when True => X : Character;
10000 when False => null;
10008 Put_Line (Integer'Image (V1'Size));
10009 Put_Line (Integer'Image (V2'Size));
10014 Here we are dealing with a variant record, where the True variant
10015 requires 16 bits, and the False variant requires 8 bits.
10016 In the above example, both V1 and V2 contain the False variant,
10017 which is only 8 bits long. However, the result of running the
10026 The reason for the difference here is that the discriminant value of
10027 V1 is fixed, and will always be False. It is not possible to assign
10028 a True variant value to V1, therefore 8 bits is sufficient. On the
10029 other hand, in the case of V2, the initial discriminant value is
10030 False (from the default), but it is possible to assign a True
10031 variant value to V2, therefore 16 bits must be allocated for V2
10032 in the general case, even fewer bits may be needed at any particular
10033 point during the program execution.
10035 As can be seen from the output of this program, the @code{'Size}
10036 attribute applied to such an object in GNAT gives the actual allocated
10037 size of the variable, which is the largest size of any of the variants.
10038 The Ada Reference Manual is not completely clear on what choice should
10039 be made here, but the GNAT behavior seems most consistent with the
10040 language in the RM@.
10042 In some cases, it may be desirable to obtain the size of the current
10043 variant, rather than the size of the largest variant. This can be
10044 achieved in GNAT by making use of the fact that in the case of a
10045 subprogram parameter, GNAT does indeed return the size of the current
10046 variant (because a subprogram has no way of knowing how much space
10047 is actually allocated for the actual).
10049 Consider the following modified version of the above program:
10051 @smallexample @c ada
10052 with Text_IO; use Text_IO;
10054 type R1 (A : Boolean := False) is record
10056 when True => X : Character;
10057 when False => null;
10063 function Size (V : R1) return Integer is
10069 Put_Line (Integer'Image (V2'Size));
10070 Put_Line (Integer'IMage (Size (V2)));
10072 Put_Line (Integer'Image (V2'Size));
10073 Put_Line (Integer'IMage (Size (V2)));
10078 The output from this program is
10088 Here we see that while the @code{'Size} attribute always returns
10089 the maximum size, regardless of the current variant value, the
10090 @code{Size} function does indeed return the size of the current
10093 @node Biased Representation
10094 @section Biased Representation
10095 @cindex Size for biased representation
10096 @cindex Biased representation
10099 In the case of scalars with a range starting at other than zero, it is
10100 possible in some cases to specify a size smaller than the default minimum
10101 value, and in such cases, GNAT uses an unsigned biased representation,
10102 in which zero is used to represent the lower bound, and successive values
10103 represent successive values of the type.
10105 For example, suppose we have the declaration:
10107 @smallexample @c ada
10108 type Small is range -7 .. -4;
10109 for Small'Size use 2;
10113 Although the default size of type @code{Small} is 4, the @code{Size}
10114 clause is accepted by GNAT and results in the following representation
10118 -7 is represented as 2#00#
10119 -6 is represented as 2#01#
10120 -5 is represented as 2#10#
10121 -4 is represented as 2#11#
10125 Biased representation is only used if the specified @code{Size} clause
10126 cannot be accepted in any other manner. These reduced sizes that force
10127 biased representation can be used for all discrete types except for
10128 enumeration types for which a representation clause is given.
10130 @node Value_Size and Object_Size Clauses
10131 @section Value_Size and Object_Size Clauses
10133 @findex Object_Size
10134 @cindex Size, of objects
10137 In Ada 95 and Ada 2005, @code{T'Size} for a type @code{T} is the minimum
10138 number of bits required to hold values of type @code{T}.
10139 Although this interpretation was allowed in Ada 83, it was not required,
10140 and this requirement in practice can cause some significant difficulties.
10141 For example, in most Ada 83 compilers, @code{Natural'Size} was 32.
10142 However, in Ada 95 and Ada 2005,
10143 @code{Natural'Size} is
10144 typically 31. This means that code may change in behavior when moving
10145 from Ada 83 to Ada 95 or Ada 2005. For example, consider:
10147 @smallexample @c ada
10148 type Rec is record;
10154 at 0 range 0 .. Natural'Size - 1;
10155 at 0 range Natural'Size .. 2 * Natural'Size - 1;
10160 In the above code, since the typical size of @code{Natural} objects
10161 is 32 bits and @code{Natural'Size} is 31, the above code can cause
10162 unexpected inefficient packing in Ada 95 and Ada 2005, and in general
10163 there are cases where the fact that the object size can exceed the
10164 size of the type causes surprises.
10166 To help get around this problem GNAT provides two implementation
10167 defined attributes, @code{Value_Size} and @code{Object_Size}. When
10168 applied to a type, these attributes yield the size of the type
10169 (corresponding to the RM defined size attribute), and the size of
10170 objects of the type respectively.
10172 The @code{Object_Size} is used for determining the default size of
10173 objects and components. This size value can be referred to using the
10174 @code{Object_Size} attribute. The phrase ``is used'' here means that it is
10175 the basis of the determination of the size. The backend is free to
10176 pad this up if necessary for efficiency, e.g.@: an 8-bit stand-alone
10177 character might be stored in 32 bits on a machine with no efficient
10178 byte access instructions such as the Alpha.
10180 The default rules for the value of @code{Object_Size} for
10181 discrete types are as follows:
10185 The @code{Object_Size} for base subtypes reflect the natural hardware
10186 size in bits (run the compiler with @option{-gnatS} to find those values
10187 for numeric types). Enumeration types and fixed-point base subtypes have
10188 8, 16, 32 or 64 bits for this size, depending on the range of values
10192 The @code{Object_Size} of a subtype is the same as the
10193 @code{Object_Size} of
10194 the type from which it is obtained.
10197 The @code{Object_Size} of a derived base type is copied from the parent
10198 base type, and the @code{Object_Size} of a derived first subtype is copied
10199 from the parent first subtype.
10203 The @code{Value_Size} attribute
10204 is the (minimum) number of bits required to store a value
10206 This value is used to determine how tightly to pack
10207 records or arrays with components of this type, and also affects
10208 the semantics of unchecked conversion (unchecked conversions where
10209 the @code{Value_Size} values differ generate a warning, and are potentially
10212 The default rules for the value of @code{Value_Size} are as follows:
10216 The @code{Value_Size} for a base subtype is the minimum number of bits
10217 required to store all values of the type (including the sign bit
10218 only if negative values are possible).
10221 If a subtype statically matches the first subtype of a given type, then it has
10222 by default the same @code{Value_Size} as the first subtype. This is a
10223 consequence of RM 13.1(14) (``if two subtypes statically match,
10224 then their subtype-specific aspects are the same''.)
10227 All other subtypes have a @code{Value_Size} corresponding to the minimum
10228 number of bits required to store all values of the subtype. For
10229 dynamic bounds, it is assumed that the value can range down or up
10230 to the corresponding bound of the ancestor
10234 The RM defined attribute @code{Size} corresponds to the
10235 @code{Value_Size} attribute.
10237 The @code{Size} attribute may be defined for a first-named subtype. This sets
10238 the @code{Value_Size} of
10239 the first-named subtype to the given value, and the
10240 @code{Object_Size} of this first-named subtype to the given value padded up
10241 to an appropriate boundary. It is a consequence of the default rules
10242 above that this @code{Object_Size} will apply to all further subtypes. On the
10243 other hand, @code{Value_Size} is affected only for the first subtype, any
10244 dynamic subtypes obtained from it directly, and any statically matching
10245 subtypes. The @code{Value_Size} of any other static subtypes is not affected.
10247 @code{Value_Size} and
10248 @code{Object_Size} may be explicitly set for any subtype using
10249 an attribute definition clause. Note that the use of these attributes
10250 can cause the RM 13.1(14) rule to be violated. If two access types
10251 reference aliased objects whose subtypes have differing @code{Object_Size}
10252 values as a result of explicit attribute definition clauses, then it
10253 is erroneous to convert from one access subtype to the other.
10255 At the implementation level, Esize stores the Object_Size and the
10256 RM_Size field stores the @code{Value_Size} (and hence the value of the
10257 @code{Size} attribute,
10258 which, as noted above, is equivalent to @code{Value_Size}).
10260 To get a feel for the difference, consider the following examples (note
10261 that in each case the base is @code{Short_Short_Integer} with a size of 8):
10264 Object_Size Value_Size
10266 type x1 is range 0 .. 5; 8 3
10268 type x2 is range 0 .. 5;
10269 for x2'size use 12; 16 12
10271 subtype x3 is x2 range 0 .. 3; 16 2
10273 subtype x4 is x2'base range 0 .. 10; 8 4
10275 subtype x5 is x2 range 0 .. dynamic; 16 3*
10277 subtype x6 is x2'base range 0 .. dynamic; 8 3*
10282 Note: the entries marked ``3*'' are not actually specified by the Ada
10283 Reference Manual, but it seems in the spirit of the RM rules to allocate
10284 the minimum number of bits (here 3, given the range for @code{x2})
10285 known to be large enough to hold the given range of values.
10287 So far, so good, but GNAT has to obey the RM rules, so the question is
10288 under what conditions must the RM @code{Size} be used.
10289 The following is a list
10290 of the occasions on which the RM @code{Size} must be used:
10294 Component size for packed arrays or records
10297 Value of the attribute @code{Size} for a type
10300 Warning about sizes not matching for unchecked conversion
10304 For record types, the @code{Object_Size} is always a multiple of the
10305 alignment of the type (this is true for all types). In some cases the
10306 @code{Value_Size} can be smaller. Consider:
10316 On a typical 32-bit architecture, the X component will be four bytes, and
10317 require four-byte alignment, and the Y component will be one byte. In this
10318 case @code{R'Value_Size} will be 40 (bits) since this is the minimum size
10319 required to store a value of this type, and for example, it is permissible
10320 to have a component of type R in an outer record whose component size is
10321 specified to be 48 bits. However, @code{R'Object_Size} will be 64 (bits),
10322 since it must be rounded up so that this value is a multiple of the
10323 alignment (4 bytes = 32 bits).
10326 For all other types, the @code{Object_Size}
10327 and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
10328 Only @code{Size} may be specified for such types.
10330 @node Component_Size Clauses
10331 @section Component_Size Clauses
10332 @cindex Component_Size Clause
10335 Normally, the value specified in a component size clause must be consistent
10336 with the subtype of the array component with regard to size and alignment.
10337 In other words, the value specified must be at least equal to the size
10338 of this subtype, and must be a multiple of the alignment value.
10340 In addition, component size clauses are allowed which cause the array
10341 to be packed, by specifying a smaller value. A first case is for
10342 component size values in the range 1 through 63. The value specified
10343 must not be smaller than the Size of the subtype. GNAT will accurately
10344 honor all packing requests in this range. For example, if we have:
10346 @smallexample @c ada
10347 type r is array (1 .. 8) of Natural;
10348 for r'Component_Size use 31;
10352 then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
10353 Of course access to the components of such an array is considerably
10354 less efficient than if the natural component size of 32 is used.
10355 A second case is when the subtype of the component is a record type
10356 padded because of its default alignment. For example, if we have:
10358 @smallexample @c ada
10365 type a is array (1 .. 8) of r;
10366 for a'Component_Size use 72;
10370 then the resulting array has a length of 72 bytes, instead of 96 bytes
10371 if the alignment of the record (4) was obeyed.
10373 Note that there is no point in giving both a component size clause
10374 and a pragma Pack for the same array type. if such duplicate
10375 clauses are given, the pragma Pack will be ignored.
10377 @node Bit_Order Clauses
10378 @section Bit_Order Clauses
10379 @cindex Bit_Order Clause
10380 @cindex bit ordering
10381 @cindex ordering, of bits
10384 For record subtypes, GNAT permits the specification of the @code{Bit_Order}
10385 attribute. The specification may either correspond to the default bit
10386 order for the target, in which case the specification has no effect and
10387 places no additional restrictions, or it may be for the non-standard
10388 setting (that is the opposite of the default).
10390 In the case where the non-standard value is specified, the effect is
10391 to renumber bits within each byte, but the ordering of bytes is not
10392 affected. There are certain
10393 restrictions placed on component clauses as follows:
10397 @item Components fitting within a single storage unit.
10399 These are unrestricted, and the effect is merely to renumber bits. For
10400 example if we are on a little-endian machine with @code{Low_Order_First}
10401 being the default, then the following two declarations have exactly
10404 @smallexample @c ada
10407 B : Integer range 1 .. 120;
10411 A at 0 range 0 .. 0;
10412 B at 0 range 1 .. 7;
10417 B : Integer range 1 .. 120;
10420 for R2'Bit_Order use High_Order_First;
10423 A at 0 range 7 .. 7;
10424 B at 0 range 0 .. 6;
10429 The useful application here is to write the second declaration with the
10430 @code{Bit_Order} attribute definition clause, and know that it will be treated
10431 the same, regardless of whether the target is little-endian or big-endian.
10433 @item Components occupying an integral number of bytes.
10435 These are components that exactly fit in two or more bytes. Such component
10436 declarations are allowed, but have no effect, since it is important to realize
10437 that the @code{Bit_Order} specification does not affect the ordering of bytes.
10438 In particular, the following attempt at getting an endian-independent integer
10441 @smallexample @c ada
10446 for R2'Bit_Order use High_Order_First;
10449 A at 0 range 0 .. 31;
10454 This declaration will result in a little-endian integer on a
10455 little-endian machine, and a big-endian integer on a big-endian machine.
10456 If byte flipping is required for interoperability between big- and
10457 little-endian machines, this must be explicitly programmed. This capability
10458 is not provided by @code{Bit_Order}.
10460 @item Components that are positioned across byte boundaries
10462 but do not occupy an integral number of bytes. Given that bytes are not
10463 reordered, such fields would occupy a non-contiguous sequence of bits
10464 in memory, requiring non-trivial code to reassemble. They are for this
10465 reason not permitted, and any component clause specifying such a layout
10466 will be flagged as illegal by GNAT@.
10471 Since the misconception that Bit_Order automatically deals with all
10472 endian-related incompatibilities is a common one, the specification of
10473 a component field that is an integral number of bytes will always
10474 generate a warning. This warning may be suppressed using @code{pragma
10475 Warnings (Off)} if desired. The following section contains additional
10476 details regarding the issue of byte ordering.
10478 @node Effect of Bit_Order on Byte Ordering
10479 @section Effect of Bit_Order on Byte Ordering
10480 @cindex byte ordering
10481 @cindex ordering, of bytes
10484 In this section we will review the effect of the @code{Bit_Order} attribute
10485 definition clause on byte ordering. Briefly, it has no effect at all, but
10486 a detailed example will be helpful. Before giving this
10487 example, let us review the precise
10488 definition of the effect of defining @code{Bit_Order}. The effect of a
10489 non-standard bit order is described in section 15.5.3 of the Ada
10493 2 A bit ordering is a method of interpreting the meaning of
10494 the storage place attributes.
10498 To understand the precise definition of storage place attributes in
10499 this context, we visit section 13.5.1 of the manual:
10502 13 A record_representation_clause (without the mod_clause)
10503 specifies the layout. The storage place attributes (see 13.5.2)
10504 are taken from the values of the position, first_bit, and last_bit
10505 expressions after normalizing those values so that first_bit is
10506 less than Storage_Unit.
10510 The critical point here is that storage places are taken from
10511 the values after normalization, not before. So the @code{Bit_Order}
10512 interpretation applies to normalized values. The interpretation
10513 is described in the later part of the 15.5.3 paragraph:
10516 2 A bit ordering is a method of interpreting the meaning of
10517 the storage place attributes. High_Order_First (known in the
10518 vernacular as ``big endian'') means that the first bit of a
10519 storage element (bit 0) is the most significant bit (interpreting
10520 the sequence of bits that represent a component as an unsigned
10521 integer value). Low_Order_First (known in the vernacular as
10522 ``little endian'') means the opposite: the first bit is the
10527 Note that the numbering is with respect to the bits of a storage
10528 unit. In other words, the specification affects only the numbering
10529 of bits within a single storage unit.
10531 We can make the effect clearer by giving an example.
10533 Suppose that we have an external device which presents two bytes, the first
10534 byte presented, which is the first (low addressed byte) of the two byte
10535 record is called Master, and the second byte is called Slave.
10537 The left most (most significant bit is called Control for each byte, and
10538 the remaining 7 bits are called V1, V2, @dots{} V7, where V7 is the rightmost
10539 (least significant) bit.
10541 On a big-endian machine, we can write the following representation clause
10543 @smallexample @c ada
10544 type Data is record
10545 Master_Control : Bit;
10553 Slave_Control : Bit;
10563 for Data use record
10564 Master_Control at 0 range 0 .. 0;
10565 Master_V1 at 0 range 1 .. 1;
10566 Master_V2 at 0 range 2 .. 2;
10567 Master_V3 at 0 range 3 .. 3;
10568 Master_V4 at 0 range 4 .. 4;
10569 Master_V5 at 0 range 5 .. 5;
10570 Master_V6 at 0 range 6 .. 6;
10571 Master_V7 at 0 range 7 .. 7;
10572 Slave_Control at 1 range 0 .. 0;
10573 Slave_V1 at 1 range 1 .. 1;
10574 Slave_V2 at 1 range 2 .. 2;
10575 Slave_V3 at 1 range 3 .. 3;
10576 Slave_V4 at 1 range 4 .. 4;
10577 Slave_V5 at 1 range 5 .. 5;
10578 Slave_V6 at 1 range 6 .. 6;
10579 Slave_V7 at 1 range 7 .. 7;
10584 Now if we move this to a little endian machine, then the bit ordering within
10585 the byte is backwards, so we have to rewrite the record rep clause as:
10587 @smallexample @c ada
10588 for Data use record
10589 Master_Control at 0 range 7 .. 7;
10590 Master_V1 at 0 range 6 .. 6;
10591 Master_V2 at 0 range 5 .. 5;
10592 Master_V3 at 0 range 4 .. 4;
10593 Master_V4 at 0 range 3 .. 3;
10594 Master_V5 at 0 range 2 .. 2;
10595 Master_V6 at 0 range 1 .. 1;
10596 Master_V7 at 0 range 0 .. 0;
10597 Slave_Control at 1 range 7 .. 7;
10598 Slave_V1 at 1 range 6 .. 6;
10599 Slave_V2 at 1 range 5 .. 5;
10600 Slave_V3 at 1 range 4 .. 4;
10601 Slave_V4 at 1 range 3 .. 3;
10602 Slave_V5 at 1 range 2 .. 2;
10603 Slave_V6 at 1 range 1 .. 1;
10604 Slave_V7 at 1 range 0 .. 0;
10609 It is a nuisance to have to rewrite the clause, especially if
10610 the code has to be maintained on both machines. However,
10611 this is a case that we can handle with the
10612 @code{Bit_Order} attribute if it is implemented.
10613 Note that the implementation is not required on byte addressed
10614 machines, but it is indeed implemented in GNAT.
10615 This means that we can simply use the
10616 first record clause, together with the declaration
10618 @smallexample @c ada
10619 for Data'Bit_Order use High_Order_First;
10623 and the effect is what is desired, namely the layout is exactly the same,
10624 independent of whether the code is compiled on a big-endian or little-endian
10627 The important point to understand is that byte ordering is not affected.
10628 A @code{Bit_Order} attribute definition never affects which byte a field
10629 ends up in, only where it ends up in that byte.
10630 To make this clear, let us rewrite the record rep clause of the previous
10633 @smallexample @c ada
10634 for Data'Bit_Order use High_Order_First;
10635 for Data use record
10636 Master_Control at 0 range 0 .. 0;
10637 Master_V1 at 0 range 1 .. 1;
10638 Master_V2 at 0 range 2 .. 2;
10639 Master_V3 at 0 range 3 .. 3;
10640 Master_V4 at 0 range 4 .. 4;
10641 Master_V5 at 0 range 5 .. 5;
10642 Master_V6 at 0 range 6 .. 6;
10643 Master_V7 at 0 range 7 .. 7;
10644 Slave_Control at 0 range 8 .. 8;
10645 Slave_V1 at 0 range 9 .. 9;
10646 Slave_V2 at 0 range 10 .. 10;
10647 Slave_V3 at 0 range 11 .. 11;
10648 Slave_V4 at 0 range 12 .. 12;
10649 Slave_V5 at 0 range 13 .. 13;
10650 Slave_V6 at 0 range 14 .. 14;
10651 Slave_V7 at 0 range 15 .. 15;
10656 This is exactly equivalent to saying (a repeat of the first example):
10658 @smallexample @c ada
10659 for Data'Bit_Order use High_Order_First;
10660 for Data use record
10661 Master_Control at 0 range 0 .. 0;
10662 Master_V1 at 0 range 1 .. 1;
10663 Master_V2 at 0 range 2 .. 2;
10664 Master_V3 at 0 range 3 .. 3;
10665 Master_V4 at 0 range 4 .. 4;
10666 Master_V5 at 0 range 5 .. 5;
10667 Master_V6 at 0 range 6 .. 6;
10668 Master_V7 at 0 range 7 .. 7;
10669 Slave_Control at 1 range 0 .. 0;
10670 Slave_V1 at 1 range 1 .. 1;
10671 Slave_V2 at 1 range 2 .. 2;
10672 Slave_V3 at 1 range 3 .. 3;
10673 Slave_V4 at 1 range 4 .. 4;
10674 Slave_V5 at 1 range 5 .. 5;
10675 Slave_V6 at 1 range 6 .. 6;
10676 Slave_V7 at 1 range 7 .. 7;
10681 Why are they equivalent? Well take a specific field, the @code{Slave_V2}
10682 field. The storage place attributes are obtained by normalizing the
10683 values given so that the @code{First_Bit} value is less than 8. After
10684 normalizing the values (0,10,10) we get (1,2,2) which is exactly what
10685 we specified in the other case.
10687 Now one might expect that the @code{Bit_Order} attribute might affect
10688 bit numbering within the entire record component (two bytes in this
10689 case, thus affecting which byte fields end up in), but that is not
10690 the way this feature is defined, it only affects numbering of bits,
10691 not which byte they end up in.
10693 Consequently it never makes sense to specify a starting bit number
10694 greater than 7 (for a byte addressable field) if an attribute
10695 definition for @code{Bit_Order} has been given, and indeed it
10696 may be actively confusing to specify such a value, so the compiler
10697 generates a warning for such usage.
10699 If you do need to control byte ordering then appropriate conditional
10700 values must be used. If in our example, the slave byte came first on
10701 some machines we might write:
10703 @smallexample @c ada
10704 Master_Byte_First constant Boolean := @dots{};
10706 Master_Byte : constant Natural :=
10707 1 - Boolean'Pos (Master_Byte_First);
10708 Slave_Byte : constant Natural :=
10709 Boolean'Pos (Master_Byte_First);
10711 for Data'Bit_Order use High_Order_First;
10712 for Data use record
10713 Master_Control at Master_Byte range 0 .. 0;
10714 Master_V1 at Master_Byte range 1 .. 1;
10715 Master_V2 at Master_Byte range 2 .. 2;
10716 Master_V3 at Master_Byte range 3 .. 3;
10717 Master_V4 at Master_Byte range 4 .. 4;
10718 Master_V5 at Master_Byte range 5 .. 5;
10719 Master_V6 at Master_Byte range 6 .. 6;
10720 Master_V7 at Master_Byte range 7 .. 7;
10721 Slave_Control at Slave_Byte range 0 .. 0;
10722 Slave_V1 at Slave_Byte range 1 .. 1;
10723 Slave_V2 at Slave_Byte range 2 .. 2;
10724 Slave_V3 at Slave_Byte range 3 .. 3;
10725 Slave_V4 at Slave_Byte range 4 .. 4;
10726 Slave_V5 at Slave_Byte range 5 .. 5;
10727 Slave_V6 at Slave_Byte range 6 .. 6;
10728 Slave_V7 at Slave_Byte range 7 .. 7;
10733 Now to switch between machines, all that is necessary is
10734 to set the boolean constant @code{Master_Byte_First} in
10735 an appropriate manner.
10737 @node Pragma Pack for Arrays
10738 @section Pragma Pack for Arrays
10739 @cindex Pragma Pack (for arrays)
10742 Pragma @code{Pack} applied to an array has no effect unless the component type
10743 is packable. For a component type to be packable, it must be one of the
10750 Any type whose size is specified with a size clause
10752 Any packed array type with a static size
10754 Any record type padded because of its default alignment
10758 For all these cases, if the component subtype size is in the range
10759 1 through 63, then the effect of the pragma @code{Pack} is exactly as though a
10760 component size were specified giving the component subtype size.
10761 For example if we have:
10763 @smallexample @c ada
10764 type r is range 0 .. 17;
10766 type ar is array (1 .. 8) of r;
10771 Then the component size of @code{ar} will be set to 5 (i.e.@: to @code{r'size},
10772 and the size of the array @code{ar} will be exactly 40 bits.
10774 Note that in some cases this rather fierce approach to packing can produce
10775 unexpected effects. For example, in Ada 95 and Ada 2005,
10776 subtype @code{Natural} typically has a size of 31, meaning that if you
10777 pack an array of @code{Natural}, you get 31-bit
10778 close packing, which saves a few bits, but results in far less efficient
10779 access. Since many other Ada compilers will ignore such a packing request,
10780 GNAT will generate a warning on some uses of pragma @code{Pack} that it guesses
10781 might not be what is intended. You can easily remove this warning by
10782 using an explicit @code{Component_Size} setting instead, which never generates
10783 a warning, since the intention of the programmer is clear in this case.
10785 GNAT treats packed arrays in one of two ways. If the size of the array is
10786 known at compile time and is less than 64 bits, then internally the array
10787 is represented as a single modular type, of exactly the appropriate number
10788 of bits. If the length is greater than 63 bits, or is not known at compile
10789 time, then the packed array is represented as an array of bytes, and the
10790 length is always a multiple of 8 bits.
10792 Note that to represent a packed array as a modular type, the alignment must
10793 be suitable for the modular type involved. For example, on typical machines
10794 a 32-bit packed array will be represented by a 32-bit modular integer with
10795 an alignment of four bytes. If you explicitly override the default alignment
10796 with an alignment clause that is too small, the modular representation
10797 cannot be used. For example, consider the following set of declarations:
10799 @smallexample @c ada
10800 type R is range 1 .. 3;
10801 type S is array (1 .. 31) of R;
10802 for S'Component_Size use 2;
10804 for S'Alignment use 1;
10808 If the alignment clause were not present, then a 62-bit modular
10809 representation would be chosen (typically with an alignment of 4 or 8
10810 bytes depending on the target). But the default alignment is overridden
10811 with the explicit alignment clause. This means that the modular
10812 representation cannot be used, and instead the array of bytes
10813 representation must be used, meaning that the length must be a multiple
10814 of 8. Thus the above set of declarations will result in a diagnostic
10815 rejecting the size clause and noting that the minimum size allowed is 64.
10817 @cindex Pragma Pack (for type Natural)
10818 @cindex Pragma Pack warning
10820 One special case that is worth noting occurs when the base type of the
10821 component size is 8/16/32 and the subtype is one bit less. Notably this
10822 occurs with subtype @code{Natural}. Consider:
10824 @smallexample @c ada
10825 type Arr is array (1 .. 32) of Natural;
10830 In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
10831 since typically @code{Natural'Size} is 32 in Ada 83, and in any case most
10832 Ada 83 compilers did not attempt 31 bit packing.
10834 In Ada 95 and Ada 2005, @code{Natural'Size} is required to be 31. Furthermore,
10835 GNAT really does pack 31-bit subtype to 31 bits. This may result in a
10836 substantial unintended performance penalty when porting legacy Ada 83 code.
10837 To help prevent this, GNAT generates a warning in such cases. If you really
10838 want 31 bit packing in a case like this, you can set the component size
10841 @smallexample @c ada
10842 type Arr is array (1 .. 32) of Natural;
10843 for Arr'Component_Size use 31;
10847 Here 31-bit packing is achieved as required, and no warning is generated,
10848 since in this case the programmer intention is clear.
10850 @node Pragma Pack for Records
10851 @section Pragma Pack for Records
10852 @cindex Pragma Pack (for records)
10855 Pragma @code{Pack} applied to a record will pack the components to reduce
10856 wasted space from alignment gaps and by reducing the amount of space
10857 taken by components. We distinguish between @emph{packable} components and
10858 @emph{non-packable} components.
10859 Components of the following types are considered packable:
10862 All primitive types are packable.
10865 Small packed arrays, whose size does not exceed 64 bits, and where the
10866 size is statically known at compile time, are represented internally
10867 as modular integers, and so they are also packable.
10872 All packable components occupy the exact number of bits corresponding to
10873 their @code{Size} value, and are packed with no padding bits, i.e.@: they
10874 can start on an arbitrary bit boundary.
10876 All other types are non-packable, they occupy an integral number of
10878 are placed at a boundary corresponding to their alignment requirements.
10880 For example, consider the record
10882 @smallexample @c ada
10883 type Rb1 is array (1 .. 13) of Boolean;
10886 type Rb2 is array (1 .. 65) of Boolean;
10901 The representation for the record x2 is as follows:
10903 @smallexample @c ada
10904 for x2'Size use 224;
10906 l1 at 0 range 0 .. 0;
10907 l2 at 0 range 1 .. 64;
10908 l3 at 12 range 0 .. 31;
10909 l4 at 16 range 0 .. 0;
10910 l5 at 16 range 1 .. 13;
10911 l6 at 18 range 0 .. 71;
10916 Studying this example, we see that the packable fields @code{l1}
10918 of length equal to their sizes, and placed at specific bit boundaries (and
10919 not byte boundaries) to
10920 eliminate padding. But @code{l3} is of a non-packable float type, so
10921 it is on the next appropriate alignment boundary.
10923 The next two fields are fully packable, so @code{l4} and @code{l5} are
10924 minimally packed with no gaps. However, type @code{Rb2} is a packed
10925 array that is longer than 64 bits, so it is itself non-packable. Thus
10926 the @code{l6} field is aligned to the next byte boundary, and takes an
10927 integral number of bytes, i.e.@: 72 bits.
10929 @node Record Representation Clauses
10930 @section Record Representation Clauses
10931 @cindex Record Representation Clause
10934 Record representation clauses may be given for all record types, including
10935 types obtained by record extension. Component clauses are allowed for any
10936 static component. The restrictions on component clauses depend on the type
10939 @cindex Component Clause
10940 For all components of an elementary type, the only restriction on component
10941 clauses is that the size must be at least the 'Size value of the type
10942 (actually the Value_Size). There are no restrictions due to alignment,
10943 and such components may freely cross storage boundaries.
10945 Packed arrays with a size up to and including 64 bits are represented
10946 internally using a modular type with the appropriate number of bits, and
10947 thus the same lack of restriction applies. For example, if you declare:
10949 @smallexample @c ada
10950 type R is array (1 .. 49) of Boolean;
10956 then a component clause for a component of type R may start on any
10957 specified bit boundary, and may specify a value of 49 bits or greater.
10959 For packed bit arrays that are longer than 64 bits, there are two
10960 cases. If the component size is a power of 2 (1,2,4,8,16,32 bits),
10961 including the important case of single bits or boolean values, then
10962 there are no limitations on placement of such components, and they
10963 may start and end at arbitrary bit boundaries.
10965 If the component size is not a power of 2 (e.g.@: 3 or 5), then
10966 an array of this type longer than 64 bits must always be placed on
10967 on a storage unit (byte) boundary and occupy an integral number
10968 of storage units (bytes). Any component clause that does not
10969 meet this requirement will be rejected.
10971 Any aliased component, or component of an aliased type, must
10972 have its normal alignment and size. A component clause that
10973 does not meet this requirement will be rejected.
10975 The tag field of a tagged type always occupies an address sized field at
10976 the start of the record. No component clause may attempt to overlay this
10977 tag. When a tagged type appears as a component, the tag field must have
10980 In the case of a record extension T1, of a type T, no component clause applied
10981 to the type T1 can specify a storage location that would overlap the first
10982 T'Size bytes of the record.
10984 For all other component types, including non-bit-packed arrays,
10985 the component can be placed at an arbitrary bit boundary,
10986 so for example, the following is permitted:
10988 @smallexample @c ada
10989 type R is array (1 .. 10) of Boolean;
10998 G at 0 range 0 .. 0;
10999 H at 0 range 1 .. 1;
11000 L at 0 range 2 .. 81;
11001 R at 0 range 82 .. 161;
11006 Note: the above rules apply to recent releases of GNAT 5.
11007 In GNAT 3, there are more severe restrictions on larger components.
11008 For non-primitive types, including packed arrays with a size greater than
11009 64 bits, component clauses must respect the alignment requirement of the
11010 type, in particular, always starting on a byte boundary, and the length
11011 must be a multiple of the storage unit.
11013 @node Enumeration Clauses
11014 @section Enumeration Clauses
11016 The only restriction on enumeration clauses is that the range of values
11017 must be representable. For the signed case, if one or more of the
11018 representation values are negative, all values must be in the range:
11020 @smallexample @c ada
11021 System.Min_Int .. System.Max_Int
11025 For the unsigned case, where all values are nonnegative, the values must
11028 @smallexample @c ada
11029 0 .. System.Max_Binary_Modulus;
11033 A @emph{confirming} representation clause is one in which the values range
11034 from 0 in sequence, i.e.@: a clause that confirms the default representation
11035 for an enumeration type.
11036 Such a confirming representation
11037 is permitted by these rules, and is specially recognized by the compiler so
11038 that no extra overhead results from the use of such a clause.
11040 If an array has an index type which is an enumeration type to which an
11041 enumeration clause has been applied, then the array is stored in a compact
11042 manner. Consider the declarations:
11044 @smallexample @c ada
11045 type r is (A, B, C);
11046 for r use (A => 1, B => 5, C => 10);
11047 type t is array (r) of Character;
11051 The array type t corresponds to a vector with exactly three elements and
11052 has a default size equal to @code{3*Character'Size}. This ensures efficient
11053 use of space, but means that accesses to elements of the array will incur
11054 the overhead of converting representation values to the corresponding
11055 positional values, (i.e.@: the value delivered by the @code{Pos} attribute).
11057 @node Address Clauses
11058 @section Address Clauses
11059 @cindex Address Clause
11061 The reference manual allows a general restriction on representation clauses,
11062 as found in RM 13.1(22):
11065 An implementation need not support representation
11066 items containing nonstatic expressions, except that
11067 an implementation should support a representation item
11068 for a given entity if each nonstatic expression in the
11069 representation item is a name that statically denotes
11070 a constant declared before the entity.
11074 In practice this is applicable only to address clauses, since this is the
11075 only case in which a non-static expression is permitted by the syntax. As
11076 the AARM notes in sections 13.1 (22.a-22.h):
11079 22.a Reason: This is to avoid the following sort of thing:
11081 22.b X : Integer := F(@dots{});
11082 Y : Address := G(@dots{});
11083 for X'Address use Y;
11085 22.c In the above, we have to evaluate the
11086 initialization expression for X before we
11087 know where to put the result. This seems
11088 like an unreasonable implementation burden.
11090 22.d The above code should instead be written
11093 22.e Y : constant Address := G(@dots{});
11094 X : Integer := F(@dots{});
11095 for X'Address use Y;
11097 22.f This allows the expression ``Y'' to be safely
11098 evaluated before X is created.
11100 22.g The constant could be a formal parameter of mode in.
11102 22.h An implementation can support other nonstatic
11103 expressions if it wants to. Expressions of type
11104 Address are hardly ever static, but their value
11105 might be known at compile time anyway in many
11110 GNAT does indeed permit many additional cases of non-static expressions. In
11111 particular, if the type involved is elementary there are no restrictions
11112 (since in this case, holding a temporary copy of the initialization value,
11113 if one is present, is inexpensive). In addition, if there is no implicit or
11114 explicit initialization, then there are no restrictions. GNAT will reject
11115 only the case where all three of these conditions hold:
11120 The type of the item is non-elementary (e.g.@: a record or array).
11123 There is explicit or implicit initialization required for the object.
11124 Note that access values are always implicitly initialized, and also
11125 in GNAT, certain bit-packed arrays (those having a dynamic length or
11126 a length greater than 64) will also be implicitly initialized to zero.
11129 The address value is non-static. Here GNAT is more permissive than the
11130 RM, and allows the address value to be the address of a previously declared
11131 stand-alone variable, as long as it does not itself have an address clause.
11133 @smallexample @c ada
11134 Anchor : Some_Initialized_Type;
11135 Overlay : Some_Initialized_Type;
11136 for Overlay'Address use Anchor'Address;
11140 However, the prefix of the address clause cannot be an array component, or
11141 a component of a discriminated record.
11146 As noted above in section 22.h, address values are typically non-static. In
11147 particular the To_Address function, even if applied to a literal value, is
11148 a non-static function call. To avoid this minor annoyance, GNAT provides
11149 the implementation defined attribute 'To_Address. The following two
11150 expressions have identical values:
11154 @smallexample @c ada
11155 To_Address (16#1234_0000#)
11156 System'To_Address (16#1234_0000#);
11160 except that the second form is considered to be a static expression, and
11161 thus when used as an address clause value is always permitted.
11164 Additionally, GNAT treats as static an address clause that is an
11165 unchecked_conversion of a static integer value. This simplifies the porting
11166 of legacy code, and provides a portable equivalent to the GNAT attribute
11169 Another issue with address clauses is the interaction with alignment
11170 requirements. When an address clause is given for an object, the address
11171 value must be consistent with the alignment of the object (which is usually
11172 the same as the alignment of the type of the object). If an address clause
11173 is given that specifies an inappropriately aligned address value, then the
11174 program execution is erroneous.
11176 Since this source of erroneous behavior can have unfortunate effects, GNAT
11177 checks (at compile time if possible, generating a warning, or at execution
11178 time with a run-time check) that the alignment is appropriate. If the
11179 run-time check fails, then @code{Program_Error} is raised. This run-time
11180 check is suppressed if range checks are suppressed, or if the special GNAT
11181 check Alignment_Check is suppressed, or if
11182 @code{pragma Restrictions (No_Elaboration_Code)} is in effect.
11184 Finally, GNAT does not permit overlaying of objects of controlled types or
11185 composite types containing a controlled component. In most cases, the compiler
11186 can detect an attempt at such overlays and will generate a warning at compile
11187 time and a Program_Error exception at run time.
11190 An address clause cannot be given for an exported object. More
11191 understandably the real restriction is that objects with an address
11192 clause cannot be exported. This is because such variables are not
11193 defined by the Ada program, so there is no external object to export.
11196 It is permissible to give an address clause and a pragma Import for the
11197 same object. In this case, the variable is not really defined by the
11198 Ada program, so there is no external symbol to be linked. The link name
11199 and the external name are ignored in this case. The reason that we allow this
11200 combination is that it provides a useful idiom to avoid unwanted
11201 initializations on objects with address clauses.
11203 When an address clause is given for an object that has implicit or
11204 explicit initialization, then by default initialization takes place. This
11205 means that the effect of the object declaration is to overwrite the
11206 memory at the specified address. This is almost always not what the
11207 programmer wants, so GNAT will output a warning:
11217 for Ext'Address use System'To_Address (16#1234_1234#);
11219 >>> warning: implicit initialization of "Ext" may
11220 modify overlaid storage
11221 >>> warning: use pragma Import for "Ext" to suppress
11222 initialization (RM B(24))
11228 As indicated by the warning message, the solution is to use a (dummy) pragma
11229 Import to suppress this initialization. The pragma tell the compiler that the
11230 object is declared and initialized elsewhere. The following package compiles
11231 without warnings (and the initialization is suppressed):
11233 @smallexample @c ada
11241 for Ext'Address use System'To_Address (16#1234_1234#);
11242 pragma Import (Ada, Ext);
11247 A final issue with address clauses involves their use for overlaying
11248 variables, as in the following example:
11249 @cindex Overlaying of objects
11251 @smallexample @c ada
11254 for B'Address use A'Address;
11258 or alternatively, using the form recommended by the RM:
11260 @smallexample @c ada
11262 Addr : constant Address := A'Address;
11264 for B'Address use Addr;
11268 In both of these cases, @code{A}
11269 and @code{B} become aliased to one another via the
11270 address clause. This use of address clauses to overlay
11271 variables, achieving an effect similar to unchecked
11272 conversion was erroneous in Ada 83, but in Ada 95 and Ada 2005
11273 the effect is implementation defined. Furthermore, the
11274 Ada RM specifically recommends that in a situation
11275 like this, @code{B} should be subject to the following
11276 implementation advice (RM 13.3(19)):
11279 19 If the Address of an object is specified, or it is imported
11280 or exported, then the implementation should not perform
11281 optimizations based on assumptions of no aliases.
11285 GNAT follows this recommendation, and goes further by also applying
11286 this recommendation to the overlaid variable (@code{A}
11287 in the above example) in this case. This means that the overlay
11288 works "as expected", in that a modification to one of the variables
11289 will affect the value of the other.
11291 @node Effect of Convention on Representation
11292 @section Effect of Convention on Representation
11293 @cindex Convention, effect on representation
11296 Normally the specification of a foreign language convention for a type or
11297 an object has no effect on the chosen representation. In particular, the
11298 representation chosen for data in GNAT generally meets the standard system
11299 conventions, and for example records are laid out in a manner that is
11300 consistent with C@. This means that specifying convention C (for example)
11303 There are four exceptions to this general rule:
11307 @item Convention Fortran and array subtypes
11308 If pragma Convention Fortran is specified for an array subtype, then in
11309 accordance with the implementation advice in section 3.6.2(11) of the
11310 Ada Reference Manual, the array will be stored in a Fortran-compatible
11311 column-major manner, instead of the normal default row-major order.
11313 @item Convention C and enumeration types
11314 GNAT normally stores enumeration types in 8, 16, or 32 bits as required
11315 to accommodate all values of the type. For example, for the enumeration
11318 @smallexample @c ada
11319 type Color is (Red, Green, Blue);
11323 8 bits is sufficient to store all values of the type, so by default, objects
11324 of type @code{Color} will be represented using 8 bits. However, normal C
11325 convention is to use 32 bits for all enum values in C, since enum values
11326 are essentially of type int. If pragma @code{Convention C} is specified for an
11327 Ada enumeration type, then the size is modified as necessary (usually to
11328 32 bits) to be consistent with the C convention for enum values.
11330 Note that this treatment applies only to types. If Convention C is given for
11331 an enumeration object, where the enumeration type is not Convention C, then
11332 Object_Size bits are allocated. For example, for a normal enumeration type,
11333 with less than 256 elements, only 8 bits will be allocated for the object.
11334 Since this may be a surprise in terms of what C expects, GNAT will issue a
11335 warning in this situation. The warning can be suppressed by giving an explicit
11336 size clause specifying the desired size.
11338 @item Convention C/Fortran and Boolean types
11339 In C, the usual convention for boolean values, that is values used for
11340 conditions, is that zero represents false, and nonzero values represent
11341 true. In Ada, the normal convention is that two specific values, typically
11342 0/1, are used to represent false/true respectively.
11344 Fortran has a similar convention for @code{LOGICAL} values (any nonzero
11345 value represents true).
11347 To accommodate the Fortran and C conventions, if a pragma Convention specifies
11348 C or Fortran convention for a derived Boolean, as in the following example:
11350 @smallexample @c ada
11351 type C_Switch is new Boolean;
11352 pragma Convention (C, C_Switch);
11356 then the GNAT generated code will treat any nonzero value as true. For truth
11357 values generated by GNAT, the conventional value 1 will be used for True, but
11358 when one of these values is read, any nonzero value is treated as True.
11360 @item Access types on OpenVMS
11361 For 64-bit OpenVMS systems, access types (other than those for unconstrained
11362 arrays) are 64-bits long. An exception to this rule is for the case of
11363 C-convention access types where there is no explicit size clause present (or
11364 inherited for derived types). In this case, GNAT chooses to make these
11365 pointers 32-bits, which provides an easier path for migration of 32-bit legacy
11366 code. size clause specifying 64-bits must be used to obtain a 64-bit pointer.
11370 @node Determining the Representations chosen by GNAT
11371 @section Determining the Representations chosen by GNAT
11372 @cindex Representation, determination of
11373 @cindex @option{-gnatR} switch
11376 Although the descriptions in this section are intended to be complete, it is
11377 often easier to simply experiment to see what GNAT accepts and what the
11378 effect is on the layout of types and objects.
11380 As required by the Ada RM, if a representation clause is not accepted, then
11381 it must be rejected as illegal by the compiler. However, when a
11382 representation clause or pragma is accepted, there can still be questions
11383 of what the compiler actually does. For example, if a partial record
11384 representation clause specifies the location of some components and not
11385 others, then where are the non-specified components placed? Or if pragma
11386 @code{Pack} is used on a record, then exactly where are the resulting
11387 fields placed? The section on pragma @code{Pack} in this chapter can be
11388 used to answer the second question, but it is often easier to just see
11389 what the compiler does.
11391 For this purpose, GNAT provides the option @option{-gnatR}. If you compile
11392 with this option, then the compiler will output information on the actual
11393 representations chosen, in a format similar to source representation
11394 clauses. For example, if we compile the package:
11396 @smallexample @c ada
11398 type r (x : boolean) is tagged record
11400 when True => S : String (1 .. 100);
11401 when False => null;
11405 type r2 is new r (false) with record
11410 y2 at 16 range 0 .. 31;
11417 type x1 is array (1 .. 10) of x;
11418 for x1'component_size use 11;
11420 type ia is access integer;
11422 type Rb1 is array (1 .. 13) of Boolean;
11425 type Rb2 is array (1 .. 65) of Boolean;
11441 using the switch @option{-gnatR} we obtain the following output:
11444 Representation information for unit q
11445 -------------------------------------
11448 for r'Alignment use 4;
11450 x at 4 range 0 .. 7;
11451 _tag at 0 range 0 .. 31;
11452 s at 5 range 0 .. 799;
11455 for r2'Size use 160;
11456 for r2'Alignment use 4;
11458 x at 4 range 0 .. 7;
11459 _tag at 0 range 0 .. 31;
11460 _parent at 0 range 0 .. 63;
11461 y2 at 16 range 0 .. 31;
11465 for x'Alignment use 1;
11467 y at 0 range 0 .. 7;
11470 for x1'Size use 112;
11471 for x1'Alignment use 1;
11472 for x1'Component_Size use 11;
11474 for rb1'Size use 13;
11475 for rb1'Alignment use 2;
11476 for rb1'Component_Size use 1;
11478 for rb2'Size use 72;
11479 for rb2'Alignment use 1;
11480 for rb2'Component_Size use 1;
11482 for x2'Size use 224;
11483 for x2'Alignment use 4;
11485 l1 at 0 range 0 .. 0;
11486 l2 at 0 range 1 .. 64;
11487 l3 at 12 range 0 .. 31;
11488 l4 at 16 range 0 .. 0;
11489 l5 at 16 range 1 .. 13;
11490 l6 at 18 range 0 .. 71;
11495 The Size values are actually the Object_Size, i.e.@: the default size that
11496 will be allocated for objects of the type.
11497 The ?? size for type r indicates that we have a variant record, and the
11498 actual size of objects will depend on the discriminant value.
11500 The Alignment values show the actual alignment chosen by the compiler
11501 for each record or array type.
11503 The record representation clause for type r shows where all fields
11504 are placed, including the compiler generated tag field (whose location
11505 cannot be controlled by the programmer).
11507 The record representation clause for the type extension r2 shows all the
11508 fields present, including the parent field, which is a copy of the fields
11509 of the parent type of r2, i.e.@: r1.
11511 The component size and size clauses for types rb1 and rb2 show
11512 the exact effect of pragma @code{Pack} on these arrays, and the record
11513 representation clause for type x2 shows how pragma @code{Pack} affects
11516 In some cases, it may be useful to cut and paste the representation clauses
11517 generated by the compiler into the original source to fix and guarantee
11518 the actual representation to be used.
11520 @node Standard Library Routines
11521 @chapter Standard Library Routines
11524 The Ada Reference Manual contains in Annex A a full description of an
11525 extensive set of standard library routines that can be used in any Ada
11526 program, and which must be provided by all Ada compilers. They are
11527 analogous to the standard C library used by C programs.
11529 GNAT implements all of the facilities described in annex A, and for most
11530 purposes the description in the Ada Reference Manual, or appropriate Ada
11531 text book, will be sufficient for making use of these facilities.
11533 In the case of the input-output facilities,
11534 @xref{The Implementation of Standard I/O},
11535 gives details on exactly how GNAT interfaces to the
11536 file system. For the remaining packages, the Ada Reference Manual
11537 should be sufficient. The following is a list of the packages included,
11538 together with a brief description of the functionality that is provided.
11540 For completeness, references are included to other predefined library
11541 routines defined in other sections of the Ada Reference Manual (these are
11542 cross-indexed from Annex A).
11546 This is a parent package for all the standard library packages. It is
11547 usually included implicitly in your program, and itself contains no
11548 useful data or routines.
11550 @item Ada.Calendar (9.6)
11551 @code{Calendar} provides time of day access, and routines for
11552 manipulating times and durations.
11554 @item Ada.Characters (A.3.1)
11555 This is a dummy parent package that contains no useful entities
11557 @item Ada.Characters.Handling (A.3.2)
11558 This package provides some basic character handling capabilities,
11559 including classification functions for classes of characters (e.g.@: test
11560 for letters, or digits).
11562 @item Ada.Characters.Latin_1 (A.3.3)
11563 This package includes a complete set of definitions of the characters
11564 that appear in type CHARACTER@. It is useful for writing programs that
11565 will run in international environments. For example, if you want an
11566 upper case E with an acute accent in a string, it is often better to use
11567 the definition of @code{UC_E_Acute} in this package. Then your program
11568 will print in an understandable manner even if your environment does not
11569 support these extended characters.
11571 @item Ada.Command_Line (A.15)
11572 This package provides access to the command line parameters and the name
11573 of the current program (analogous to the use of @code{argc} and @code{argv}
11574 in C), and also allows the exit status for the program to be set in a
11575 system-independent manner.
11577 @item Ada.Decimal (F.2)
11578 This package provides constants describing the range of decimal numbers
11579 implemented, and also a decimal divide routine (analogous to the COBOL
11580 verb DIVIDE @dots{} GIVING @dots{} REMAINDER @dots{})
11582 @item Ada.Direct_IO (A.8.4)
11583 This package provides input-output using a model of a set of records of
11584 fixed-length, containing an arbitrary definite Ada type, indexed by an
11585 integer record number.
11587 @item Ada.Dynamic_Priorities (D.5)
11588 This package allows the priorities of a task to be adjusted dynamically
11589 as the task is running.
11591 @item Ada.Exceptions (11.4.1)
11592 This package provides additional information on exceptions, and also
11593 contains facilities for treating exceptions as data objects, and raising
11594 exceptions with associated messages.
11596 @item Ada.Finalization (7.6)
11597 This package contains the declarations and subprograms to support the
11598 use of controlled types, providing for automatic initialization and
11599 finalization (analogous to the constructors and destructors of C++)
11601 @item Ada.Interrupts (C.3.2)
11602 This package provides facilities for interfacing to interrupts, which
11603 includes the set of signals or conditions that can be raised and
11604 recognized as interrupts.
11606 @item Ada.Interrupts.Names (C.3.2)
11607 This package provides the set of interrupt names (actually signal
11608 or condition names) that can be handled by GNAT@.
11610 @item Ada.IO_Exceptions (A.13)
11611 This package defines the set of exceptions that can be raised by use of
11612 the standard IO packages.
11615 This package contains some standard constants and exceptions used
11616 throughout the numerics packages. Note that the constants pi and e are
11617 defined here, and it is better to use these definitions than rolling
11620 @item Ada.Numerics.Complex_Elementary_Functions
11621 Provides the implementation of standard elementary functions (such as
11622 log and trigonometric functions) operating on complex numbers using the
11623 standard @code{Float} and the @code{Complex} and @code{Imaginary} types
11624 created by the package @code{Numerics.Complex_Types}.
11626 @item Ada.Numerics.Complex_Types
11627 This is a predefined instantiation of
11628 @code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
11629 build the type @code{Complex} and @code{Imaginary}.
11631 @item Ada.Numerics.Discrete_Random
11632 This package provides a random number generator suitable for generating
11633 random integer values from a specified range.
11635 @item Ada.Numerics.Float_Random
11636 This package provides a random number generator suitable for generating
11637 uniformly distributed floating point values.
11639 @item Ada.Numerics.Generic_Complex_Elementary_Functions
11640 This is a generic version of the package that provides the
11641 implementation of standard elementary functions (such as log and
11642 trigonometric functions) for an arbitrary complex type.
11644 The following predefined instantiations of this package are provided:
11648 @code{Ada.Numerics.Short_Complex_Elementary_Functions}
11650 @code{Ada.Numerics.Complex_Elementary_Functions}
11652 @code{Ada.Numerics.
11653 Long_Complex_Elementary_Functions}
11656 @item Ada.Numerics.Generic_Complex_Types
11657 This is a generic package that allows the creation of complex types,
11658 with associated complex arithmetic operations.
11660 The following predefined instantiations of this package exist
11663 @code{Ada.Numerics.Short_Complex_Complex_Types}
11665 @code{Ada.Numerics.Complex_Complex_Types}
11667 @code{Ada.Numerics.Long_Complex_Complex_Types}
11670 @item Ada.Numerics.Generic_Elementary_Functions
11671 This is a generic package that provides the implementation of standard
11672 elementary functions (such as log an trigonometric functions) for an
11673 arbitrary float type.
11675 The following predefined instantiations of this package exist
11679 @code{Ada.Numerics.Short_Elementary_Functions}
11681 @code{Ada.Numerics.Elementary_Functions}
11683 @code{Ada.Numerics.Long_Elementary_Functions}
11686 @item Ada.Real_Time (D.8)
11687 This package provides facilities similar to those of @code{Calendar}, but
11688 operating with a finer clock suitable for real time control. Note that
11689 annex D requires that there be no backward clock jumps, and GNAT generally
11690 guarantees this behavior, but of course if the external clock on which
11691 the GNAT runtime depends is deliberately reset by some external event,
11692 then such a backward jump may occur.
11694 @item Ada.Sequential_IO (A.8.1)
11695 This package provides input-output facilities for sequential files,
11696 which can contain a sequence of values of a single type, which can be
11697 any Ada type, including indefinite (unconstrained) types.
11699 @item Ada.Storage_IO (A.9)
11700 This package provides a facility for mapping arbitrary Ada types to and
11701 from a storage buffer. It is primarily intended for the creation of new
11704 @item Ada.Streams (13.13.1)
11705 This is a generic package that provides the basic support for the
11706 concept of streams as used by the stream attributes (@code{Input},
11707 @code{Output}, @code{Read} and @code{Write}).
11709 @item Ada.Streams.Stream_IO (A.12.1)
11710 This package is a specialization of the type @code{Streams} defined in
11711 package @code{Streams} together with a set of operations providing
11712 Stream_IO capability. The Stream_IO model permits both random and
11713 sequential access to a file which can contain an arbitrary set of values
11714 of one or more Ada types.
11716 @item Ada.Strings (A.4.1)
11717 This package provides some basic constants used by the string handling
11720 @item Ada.Strings.Bounded (A.4.4)
11721 This package provides facilities for handling variable length
11722 strings. The bounded model requires a maximum length. It is thus
11723 somewhat more limited than the unbounded model, but avoids the use of
11724 dynamic allocation or finalization.
11726 @item Ada.Strings.Fixed (A.4.3)
11727 This package provides facilities for handling fixed length strings.
11729 @item Ada.Strings.Maps (A.4.2)
11730 This package provides facilities for handling character mappings and
11731 arbitrarily defined subsets of characters. For instance it is useful in
11732 defining specialized translation tables.
11734 @item Ada.Strings.Maps.Constants (A.4.6)
11735 This package provides a standard set of predefined mappings and
11736 predefined character sets. For example, the standard upper to lower case
11737 conversion table is found in this package. Note that upper to lower case
11738 conversion is non-trivial if you want to take the entire set of
11739 characters, including extended characters like E with an acute accent,
11740 into account. You should use the mappings in this package (rather than
11741 adding 32 yourself) to do case mappings.
11743 @item Ada.Strings.Unbounded (A.4.5)
11744 This package provides facilities for handling variable length
11745 strings. The unbounded model allows arbitrary length strings, but
11746 requires the use of dynamic allocation and finalization.
11748 @item Ada.Strings.Wide_Bounded (A.4.7)
11749 @itemx Ada.Strings.Wide_Fixed (A.4.7)
11750 @itemx Ada.Strings.Wide_Maps (A.4.7)
11751 @itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
11752 @itemx Ada.Strings.Wide_Unbounded (A.4.7)
11753 These packages provide analogous capabilities to the corresponding
11754 packages without @samp{Wide_} in the name, but operate with the types
11755 @code{Wide_String} and @code{Wide_Character} instead of @code{String}
11756 and @code{Character}.
11758 @item Ada.Strings.Wide_Wide_Bounded (A.4.7)
11759 @itemx Ada.Strings.Wide_Wide_Fixed (A.4.7)
11760 @itemx Ada.Strings.Wide_Wide_Maps (A.4.7)
11761 @itemx Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
11762 @itemx Ada.Strings.Wide_Wide_Unbounded (A.4.7)
11763 These packages provide analogous capabilities to the corresponding
11764 packages without @samp{Wide_} in the name, but operate with the types
11765 @code{Wide_Wide_String} and @code{Wide_Wide_Character} instead
11766 of @code{String} and @code{Character}.
11768 @item Ada.Synchronous_Task_Control (D.10)
11769 This package provides some standard facilities for controlling task
11770 communication in a synchronous manner.
11773 This package contains definitions for manipulation of the tags of tagged
11776 @item Ada.Task_Attributes
11777 This package provides the capability of associating arbitrary
11778 task-specific data with separate tasks.
11781 This package provides basic text input-output capabilities for
11782 character, string and numeric data. The subpackages of this
11783 package are listed next.
11785 @item Ada.Text_IO.Decimal_IO
11786 Provides input-output facilities for decimal fixed-point types
11788 @item Ada.Text_IO.Enumeration_IO
11789 Provides input-output facilities for enumeration types.
11791 @item Ada.Text_IO.Fixed_IO
11792 Provides input-output facilities for ordinary fixed-point types.
11794 @item Ada.Text_IO.Float_IO
11795 Provides input-output facilities for float types. The following
11796 predefined instantiations of this generic package are available:
11800 @code{Short_Float_Text_IO}
11802 @code{Float_Text_IO}
11804 @code{Long_Float_Text_IO}
11807 @item Ada.Text_IO.Integer_IO
11808 Provides input-output facilities for integer types. The following
11809 predefined instantiations of this generic package are available:
11812 @item Short_Short_Integer
11813 @code{Ada.Short_Short_Integer_Text_IO}
11814 @item Short_Integer
11815 @code{Ada.Short_Integer_Text_IO}
11817 @code{Ada.Integer_Text_IO}
11819 @code{Ada.Long_Integer_Text_IO}
11820 @item Long_Long_Integer
11821 @code{Ada.Long_Long_Integer_Text_IO}
11824 @item Ada.Text_IO.Modular_IO
11825 Provides input-output facilities for modular (unsigned) types
11827 @item Ada.Text_IO.Complex_IO (G.1.3)
11828 This package provides basic text input-output capabilities for complex
11831 @item Ada.Text_IO.Editing (F.3.3)
11832 This package contains routines for edited output, analogous to the use
11833 of pictures in COBOL@. The picture formats used by this package are a
11834 close copy of the facility in COBOL@.
11836 @item Ada.Text_IO.Text_Streams (A.12.2)
11837 This package provides a facility that allows Text_IO files to be treated
11838 as streams, so that the stream attributes can be used for writing
11839 arbitrary data, including binary data, to Text_IO files.
11841 @item Ada.Unchecked_Conversion (13.9)
11842 This generic package allows arbitrary conversion from one type to
11843 another of the same size, providing for breaking the type safety in
11844 special circumstances.
11846 If the types have the same Size (more accurately the same Value_Size),
11847 then the effect is simply to transfer the bits from the source to the
11848 target type without any modification. This usage is well defined, and
11849 for simple types whose representation is typically the same across
11850 all implementations, gives a portable method of performing such
11853 If the types do not have the same size, then the result is implementation
11854 defined, and thus may be non-portable. The following describes how GNAT
11855 handles such unchecked conversion cases.
11857 If the types are of different sizes, and are both discrete types, then
11858 the effect is of a normal type conversion without any constraint checking.
11859 In particular if the result type has a larger size, the result will be
11860 zero or sign extended. If the result type has a smaller size, the result
11861 will be truncated by ignoring high order bits.
11863 If the types are of different sizes, and are not both discrete types,
11864 then the conversion works as though pointers were created to the source
11865 and target, and the pointer value is converted. The effect is that bits
11866 are copied from successive low order storage units and bits of the source
11867 up to the length of the target type.
11869 A warning is issued if the lengths differ, since the effect in this
11870 case is implementation dependent, and the above behavior may not match
11871 that of some other compiler.
11873 A pointer to one type may be converted to a pointer to another type using
11874 unchecked conversion. The only case in which the effect is undefined is
11875 when one or both pointers are pointers to unconstrained array types. In
11876 this case, the bounds information may get incorrectly transferred, and in
11877 particular, GNAT uses double size pointers for such types, and it is
11878 meaningless to convert between such pointer types. GNAT will issue a
11879 warning if the alignment of the target designated type is more strict
11880 than the alignment of the source designated type (since the result may
11881 be unaligned in this case).
11883 A pointer other than a pointer to an unconstrained array type may be
11884 converted to and from System.Address. Such usage is common in Ada 83
11885 programs, but note that Ada.Address_To_Access_Conversions is the
11886 preferred method of performing such conversions in Ada 95 and Ada 2005.
11888 unchecked conversion nor Ada.Address_To_Access_Conversions should be
11889 used in conjunction with pointers to unconstrained objects, since
11890 the bounds information cannot be handled correctly in this case.
11892 @item Ada.Unchecked_Deallocation (13.11.2)
11893 This generic package allows explicit freeing of storage previously
11894 allocated by use of an allocator.
11896 @item Ada.Wide_Text_IO (A.11)
11897 This package is similar to @code{Ada.Text_IO}, except that the external
11898 file supports wide character representations, and the internal types are
11899 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
11900 and @code{String}. It contains generic subpackages listed next.
11902 @item Ada.Wide_Text_IO.Decimal_IO
11903 Provides input-output facilities for decimal fixed-point types
11905 @item Ada.Wide_Text_IO.Enumeration_IO
11906 Provides input-output facilities for enumeration types.
11908 @item Ada.Wide_Text_IO.Fixed_IO
11909 Provides input-output facilities for ordinary fixed-point types.
11911 @item Ada.Wide_Text_IO.Float_IO
11912 Provides input-output facilities for float types. The following
11913 predefined instantiations of this generic package are available:
11917 @code{Short_Float_Wide_Text_IO}
11919 @code{Float_Wide_Text_IO}
11921 @code{Long_Float_Wide_Text_IO}
11924 @item Ada.Wide_Text_IO.Integer_IO
11925 Provides input-output facilities for integer types. The following
11926 predefined instantiations of this generic package are available:
11929 @item Short_Short_Integer
11930 @code{Ada.Short_Short_Integer_Wide_Text_IO}
11931 @item Short_Integer
11932 @code{Ada.Short_Integer_Wide_Text_IO}
11934 @code{Ada.Integer_Wide_Text_IO}
11936 @code{Ada.Long_Integer_Wide_Text_IO}
11937 @item Long_Long_Integer
11938 @code{Ada.Long_Long_Integer_Wide_Text_IO}
11941 @item Ada.Wide_Text_IO.Modular_IO
11942 Provides input-output facilities for modular (unsigned) types
11944 @item Ada.Wide_Text_IO.Complex_IO (G.1.3)
11945 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
11946 external file supports wide character representations.
11948 @item Ada.Wide_Text_IO.Editing (F.3.4)
11949 This package is similar to @code{Ada.Text_IO.Editing}, except that the
11950 types are @code{Wide_Character} and @code{Wide_String} instead of
11951 @code{Character} and @code{String}.
11953 @item Ada.Wide_Text_IO.Streams (A.12.3)
11954 This package is similar to @code{Ada.Text_IO.Streams}, except that the
11955 types are @code{Wide_Character} and @code{Wide_String} instead of
11956 @code{Character} and @code{String}.
11958 @item Ada.Wide_Wide_Text_IO (A.11)
11959 This package is similar to @code{Ada.Text_IO}, except that the external
11960 file supports wide character representations, and the internal types are
11961 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
11962 and @code{String}. It contains generic subpackages listed next.
11964 @item Ada.Wide_Wide_Text_IO.Decimal_IO
11965 Provides input-output facilities for decimal fixed-point types
11967 @item Ada.Wide_Wide_Text_IO.Enumeration_IO
11968 Provides input-output facilities for enumeration types.
11970 @item Ada.Wide_Wide_Text_IO.Fixed_IO
11971 Provides input-output facilities for ordinary fixed-point types.
11973 @item Ada.Wide_Wide_Text_IO.Float_IO
11974 Provides input-output facilities for float types. The following
11975 predefined instantiations of this generic package are available:
11979 @code{Short_Float_Wide_Wide_Text_IO}
11981 @code{Float_Wide_Wide_Text_IO}
11983 @code{Long_Float_Wide_Wide_Text_IO}
11986 @item Ada.Wide_Wide_Text_IO.Integer_IO
11987 Provides input-output facilities for integer types. The following
11988 predefined instantiations of this generic package are available:
11991 @item Short_Short_Integer
11992 @code{Ada.Short_Short_Integer_Wide_Wide_Text_IO}
11993 @item Short_Integer
11994 @code{Ada.Short_Integer_Wide_Wide_Text_IO}
11996 @code{Ada.Integer_Wide_Wide_Text_IO}
11998 @code{Ada.Long_Integer_Wide_Wide_Text_IO}
11999 @item Long_Long_Integer
12000 @code{Ada.Long_Long_Integer_Wide_Wide_Text_IO}
12003 @item Ada.Wide_Wide_Text_IO.Modular_IO
12004 Provides input-output facilities for modular (unsigned) types
12006 @item Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
12007 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
12008 external file supports wide character representations.
12010 @item Ada.Wide_Wide_Text_IO.Editing (F.3.4)
12011 This package is similar to @code{Ada.Text_IO.Editing}, except that the
12012 types are @code{Wide_Character} and @code{Wide_String} instead of
12013 @code{Character} and @code{String}.
12015 @item Ada.Wide_Wide_Text_IO.Streams (A.12.3)
12016 This package is similar to @code{Ada.Text_IO.Streams}, except that the
12017 types are @code{Wide_Character} and @code{Wide_String} instead of
12018 @code{Character} and @code{String}.
12023 @node The Implementation of Standard I/O
12024 @chapter The Implementation of Standard I/O
12027 GNAT implements all the required input-output facilities described in
12028 A.6 through A.14. These sections of the Ada Reference Manual describe the
12029 required behavior of these packages from the Ada point of view, and if
12030 you are writing a portable Ada program that does not need to know the
12031 exact manner in which Ada maps to the outside world when it comes to
12032 reading or writing external files, then you do not need to read this
12033 chapter. As long as your files are all regular files (not pipes or
12034 devices), and as long as you write and read the files only from Ada, the
12035 description in the Ada Reference Manual is sufficient.
12037 However, if you want to do input-output to pipes or other devices, such
12038 as the keyboard or screen, or if the files you are dealing with are
12039 either generated by some other language, or to be read by some other
12040 language, then you need to know more about the details of how the GNAT
12041 implementation of these input-output facilities behaves.
12043 In this chapter we give a detailed description of exactly how GNAT
12044 interfaces to the file system. As always, the sources of the system are
12045 available to you for answering questions at an even more detailed level,
12046 but for most purposes the information in this chapter will suffice.
12048 Another reason that you may need to know more about how input-output is
12049 implemented arises when you have a program written in mixed languages
12050 where, for example, files are shared between the C and Ada sections of
12051 the same program. GNAT provides some additional facilities, in the form
12052 of additional child library packages, that facilitate this sharing, and
12053 these additional facilities are also described in this chapter.
12056 * Standard I/O Packages::
12062 * Wide_Wide_Text_IO::
12065 * Filenames encoding::
12067 * Operations on C Streams::
12068 * Interfacing to C Streams::
12071 @node Standard I/O Packages
12072 @section Standard I/O Packages
12075 The Standard I/O packages described in Annex A for
12081 Ada.Text_IO.Complex_IO
12083 Ada.Text_IO.Text_Streams
12087 Ada.Wide_Text_IO.Complex_IO
12089 Ada.Wide_Text_IO.Text_Streams
12091 Ada.Wide_Wide_Text_IO
12093 Ada.Wide_Wide_Text_IO.Complex_IO
12095 Ada.Wide_Wide_Text_IO.Text_Streams
12105 are implemented using the C
12106 library streams facility; where
12110 All files are opened using @code{fopen}.
12112 All input/output operations use @code{fread}/@code{fwrite}.
12116 There is no internal buffering of any kind at the Ada library level. The only
12117 buffering is that provided at the system level in the implementation of the
12118 library routines that support streams. This facilitates shared use of these
12119 streams by mixed language programs. Note though that system level buffering is
12120 explicitly enabled at elaboration of the standard I/O packages and that can
12121 have an impact on mixed language programs, in particular those using I/O before
12122 calling the Ada elaboration routine (e.g.@: adainit). It is recommended to call
12123 the Ada elaboration routine before performing any I/O or when impractical,
12124 flush the common I/O streams and in particular Standard_Output before
12125 elaborating the Ada code.
12128 @section FORM Strings
12131 The format of a FORM string in GNAT is:
12134 "keyword=value,keyword=value,@dots{},keyword=value"
12138 where letters may be in upper or lower case, and there are no spaces
12139 between values. The order of the entries is not important. Currently
12140 there are two keywords defined.
12144 WCEM=[n|h|u|s|e|8|b]
12148 The use of these parameters is described later in this section.
12154 Direct_IO can only be instantiated for definite types. This is a
12155 restriction of the Ada language, which means that the records are fixed
12156 length (the length being determined by @code{@var{type}'Size}, rounded
12157 up to the next storage unit boundary if necessary).
12159 The records of a Direct_IO file are simply written to the file in index
12160 sequence, with the first record starting at offset zero, and subsequent
12161 records following. There is no control information of any kind. For
12162 example, if 32-bit integers are being written, each record takes
12163 4-bytes, so the record at index @var{K} starts at offset
12164 (@var{K}@minus{}1)*4.
12166 There is no limit on the size of Direct_IO files, they are expanded as
12167 necessary to accommodate whatever records are written to the file.
12169 @node Sequential_IO
12170 @section Sequential_IO
12173 Sequential_IO may be instantiated with either a definite (constrained)
12174 or indefinite (unconstrained) type.
12176 For the definite type case, the elements written to the file are simply
12177 the memory images of the data values with no control information of any
12178 kind. The resulting file should be read using the same type, no validity
12179 checking is performed on input.
12181 For the indefinite type case, the elements written consist of two
12182 parts. First is the size of the data item, written as the memory image
12183 of a @code{Interfaces.C.size_t} value, followed by the memory image of
12184 the data value. The resulting file can only be read using the same
12185 (unconstrained) type. Normal assignment checks are performed on these
12186 read operations, and if these checks fail, @code{Data_Error} is
12187 raised. In particular, in the array case, the lengths must match, and in
12188 the variant record case, if the variable for a particular read operation
12189 is constrained, the discriminants must match.
12191 Note that it is not possible to use Sequential_IO to write variable
12192 length array items, and then read the data back into different length
12193 arrays. For example, the following will raise @code{Data_Error}:
12195 @smallexample @c ada
12196 package IO is new Sequential_IO (String);
12201 IO.Write (F, "hello!")
12202 IO.Reset (F, Mode=>In_File);
12209 On some Ada implementations, this will print @code{hell}, but the program is
12210 clearly incorrect, since there is only one element in the file, and that
12211 element is the string @code{hello!}.
12213 In Ada 95 and Ada 2005, this kind of behavior can be legitimately achieved
12214 using Stream_IO, and this is the preferred mechanism. In particular, the
12215 above program fragment rewritten to use Stream_IO will work correctly.
12221 Text_IO files consist of a stream of characters containing the following
12222 special control characters:
12225 LF (line feed, 16#0A#) Line Mark
12226 FF (form feed, 16#0C#) Page Mark
12230 A canonical Text_IO file is defined as one in which the following
12231 conditions are met:
12235 The character @code{LF} is used only as a line mark, i.e.@: to mark the end
12239 The character @code{FF} is used only as a page mark, i.e.@: to mark the
12240 end of a page and consequently can appear only immediately following a
12241 @code{LF} (line mark) character.
12244 The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
12245 (line mark, page mark). In the former case, the page mark is implicitly
12246 assumed to be present.
12250 A file written using Text_IO will be in canonical form provided that no
12251 explicit @code{LF} or @code{FF} characters are written using @code{Put}
12252 or @code{Put_Line}. There will be no @code{FF} character at the end of
12253 the file unless an explicit @code{New_Page} operation was performed
12254 before closing the file.
12256 A canonical Text_IO file that is a regular file (i.e., not a device or a
12257 pipe) can be read using any of the routines in Text_IO@. The
12258 semantics in this case will be exactly as defined in the Ada Reference
12259 Manual, and all the routines in Text_IO are fully implemented.
12261 A text file that does not meet the requirements for a canonical Text_IO
12262 file has one of the following:
12266 The file contains @code{FF} characters not immediately following a
12267 @code{LF} character.
12270 The file contains @code{LF} or @code{FF} characters written by
12271 @code{Put} or @code{Put_Line}, which are not logically considered to be
12272 line marks or page marks.
12275 The file ends in a character other than @code{LF} or @code{FF},
12276 i.e.@: there is no explicit line mark or page mark at the end of the file.
12280 Text_IO can be used to read such non-standard text files but subprograms
12281 to do with line or page numbers do not have defined meanings. In
12282 particular, a @code{FF} character that does not follow a @code{LF}
12283 character may or may not be treated as a page mark from the point of
12284 view of page and line numbering. Every @code{LF} character is considered
12285 to end a line, and there is an implied @code{LF} character at the end of
12289 * Text_IO Stream Pointer Positioning::
12290 * Text_IO Reading and Writing Non-Regular Files::
12292 * Treating Text_IO Files as Streams::
12293 * Text_IO Extensions::
12294 * Text_IO Facilities for Unbounded Strings::
12297 @node Text_IO Stream Pointer Positioning
12298 @subsection Stream Pointer Positioning
12301 @code{Ada.Text_IO} has a definition of current position for a file that
12302 is being read. No internal buffering occurs in Text_IO, and usually the
12303 physical position in the stream used to implement the file corresponds
12304 to this logical position defined by Text_IO@. There are two exceptions:
12308 After a call to @code{End_Of_Page} that returns @code{True}, the stream
12309 is positioned past the @code{LF} (line mark) that precedes the page
12310 mark. Text_IO maintains an internal flag so that subsequent read
12311 operations properly handle the logical position which is unchanged by
12312 the @code{End_Of_Page} call.
12315 After a call to @code{End_Of_File} that returns @code{True}, if the
12316 Text_IO file was positioned before the line mark at the end of file
12317 before the call, then the logical position is unchanged, but the stream
12318 is physically positioned right at the end of file (past the line mark,
12319 and past a possible page mark following the line mark. Again Text_IO
12320 maintains internal flags so that subsequent read operations properly
12321 handle the logical position.
12325 These discrepancies have no effect on the observable behavior of
12326 Text_IO, but if a single Ada stream is shared between a C program and
12327 Ada program, or shared (using @samp{shared=yes} in the form string)
12328 between two Ada files, then the difference may be observable in some
12331 @node Text_IO Reading and Writing Non-Regular Files
12332 @subsection Reading and Writing Non-Regular Files
12335 A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
12336 can be used for reading and writing. Writing is not affected and the
12337 sequence of characters output is identical to the normal file case, but
12338 for reading, the behavior of Text_IO is modified to avoid undesirable
12339 look-ahead as follows:
12341 An input file that is not a regular file is considered to have no page
12342 marks. Any @code{Ascii.FF} characters (the character normally used for a
12343 page mark) appearing in the file are considered to be data
12344 characters. In particular:
12348 @code{Get_Line} and @code{Skip_Line} do not test for a page mark
12349 following a line mark. If a page mark appears, it will be treated as a
12353 This avoids the need to wait for an extra character to be typed or
12354 entered from the pipe to complete one of these operations.
12357 @code{End_Of_Page} always returns @code{False}
12360 @code{End_Of_File} will return @code{False} if there is a page mark at
12361 the end of the file.
12365 Output to non-regular files is the same as for regular files. Page marks
12366 may be written to non-regular files using @code{New_Page}, but as noted
12367 above they will not be treated as page marks on input if the output is
12368 piped to another Ada program.
12370 Another important discrepancy when reading non-regular files is that the end
12371 of file indication is not ``sticky''. If an end of file is entered, e.g.@: by
12372 pressing the @key{EOT} key,
12374 is signaled once (i.e.@: the test @code{End_Of_File}
12375 will yield @code{True}, or a read will
12376 raise @code{End_Error}), but then reading can resume
12377 to read data past that end of
12378 file indication, until another end of file indication is entered.
12380 @node Get_Immediate
12381 @subsection Get_Immediate
12382 @cindex Get_Immediate
12385 Get_Immediate returns the next character (including control characters)
12386 from the input file. In particular, Get_Immediate will return LF or FF
12387 characters used as line marks or page marks. Such operations leave the
12388 file positioned past the control character, and it is thus not treated
12389 as having its normal function. This means that page, line and column
12390 counts after this kind of Get_Immediate call are set as though the mark
12391 did not occur. In the case where a Get_Immediate leaves the file
12392 positioned between the line mark and page mark (which is not normally
12393 possible), it is undefined whether the FF character will be treated as a
12396 @node Treating Text_IO Files as Streams
12397 @subsection Treating Text_IO Files as Streams
12398 @cindex Stream files
12401 The package @code{Text_IO.Streams} allows a Text_IO file to be treated
12402 as a stream. Data written to a Text_IO file in this stream mode is
12403 binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
12404 16#0C# (@code{FF}), the resulting file may have non-standard
12405 format. Similarly if read operations are used to read from a Text_IO
12406 file treated as a stream, then @code{LF} and @code{FF} characters may be
12407 skipped and the effect is similar to that described above for
12408 @code{Get_Immediate}.
12410 @node Text_IO Extensions
12411 @subsection Text_IO Extensions
12412 @cindex Text_IO extensions
12415 A package GNAT.IO_Aux in the GNAT library provides some useful extensions
12416 to the standard @code{Text_IO} package:
12419 @item function File_Exists (Name : String) return Boolean;
12420 Determines if a file of the given name exists.
12422 @item function Get_Line return String;
12423 Reads a string from the standard input file. The value returned is exactly
12424 the length of the line that was read.
12426 @item function Get_Line (File : Ada.Text_IO.File_Type) return String;
12427 Similar, except that the parameter File specifies the file from which
12428 the string is to be read.
12432 @node Text_IO Facilities for Unbounded Strings
12433 @subsection Text_IO Facilities for Unbounded Strings
12434 @cindex Text_IO for unbounded strings
12435 @cindex Unbounded_String, Text_IO operations
12438 The package @code{Ada.Strings.Unbounded.Text_IO}
12439 in library files @code{a-suteio.ads/adb} contains some GNAT-specific
12440 subprograms useful for Text_IO operations on unbounded strings:
12444 @item function Get_Line (File : File_Type) return Unbounded_String;
12445 Reads a line from the specified file
12446 and returns the result as an unbounded string.
12448 @item procedure Put (File : File_Type; U : Unbounded_String);
12449 Writes the value of the given unbounded string to the specified file
12450 Similar to the effect of
12451 @code{Put (To_String (U))} except that an extra copy is avoided.
12453 @item procedure Put_Line (File : File_Type; U : Unbounded_String);
12454 Writes the value of the given unbounded string to the specified file,
12455 followed by a @code{New_Line}.
12456 Similar to the effect of @code{Put_Line (To_String (U))} except
12457 that an extra copy is avoided.
12461 In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
12462 and is optional. If the parameter is omitted, then the standard input or
12463 output file is referenced as appropriate.
12465 The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
12466 files @file{a-swuwti.ads} and @file{a-swuwti.adb} provides similar extended
12467 @code{Wide_Text_IO} functionality for unbounded wide strings.
12469 The package @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library
12470 files @file{a-szuzti.ads} and @file{a-szuzti.adb} provides similar extended
12471 @code{Wide_Wide_Text_IO} functionality for unbounded wide wide strings.
12474 @section Wide_Text_IO
12477 @code{Wide_Text_IO} is similar in most respects to Text_IO, except that
12478 both input and output files may contain special sequences that represent
12479 wide character values. The encoding scheme for a given file may be
12480 specified using a FORM parameter:
12487 as part of the FORM string (WCEM = wide character encoding method),
12488 where @var{x} is one of the following characters
12494 Upper half encoding
12506 The encoding methods match those that
12507 can be used in a source
12508 program, but there is no requirement that the encoding method used for
12509 the source program be the same as the encoding method used for files,
12510 and different files may use different encoding methods.
12512 The default encoding method for the standard files, and for opened files
12513 for which no WCEM parameter is given in the FORM string matches the
12514 wide character encoding specified for the main program (the default
12515 being brackets encoding if no coding method was specified with -gnatW).
12519 In this encoding, a wide character is represented by a five character
12527 where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
12528 characters (using upper case letters) of the wide character code. For
12529 example, ESC A345 is used to represent the wide character with code
12530 16#A345#. This scheme is compatible with use of the full
12531 @code{Wide_Character} set.
12533 @item Upper Half Coding
12534 The wide character with encoding 16#abcd#, where the upper bit is on
12535 (i.e.@: a is in the range 8-F) is represented as two bytes 16#ab# and
12536 16#cd#. The second byte may never be a format control character, but is
12537 not required to be in the upper half. This method can be also used for
12538 shift-JIS or EUC where the internal coding matches the external coding.
12540 @item Shift JIS Coding
12541 A wide character is represented by a two character sequence 16#ab# and
12542 16#cd#, with the restrictions described for upper half encoding as
12543 described above. The internal character code is the corresponding JIS
12544 character according to the standard algorithm for Shift-JIS
12545 conversion. Only characters defined in the JIS code set table can be
12546 used with this encoding method.
12549 A wide character is represented by a two character sequence 16#ab# and
12550 16#cd#, with both characters being in the upper half. The internal
12551 character code is the corresponding JIS character according to the EUC
12552 encoding algorithm. Only characters defined in the JIS code set table
12553 can be used with this encoding method.
12556 A wide character is represented using
12557 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12558 10646-1/Am.2. Depending on the character value, the representation
12559 is a one, two, or three byte sequence:
12562 16#0000#-16#007f#: 2#0xxxxxxx#
12563 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
12564 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12568 where the @var{xxx} bits correspond to the left-padded bits of the
12569 16-bit character value. Note that all lower half ASCII characters
12570 are represented as ASCII bytes and all upper half characters and
12571 other wide characters are represented as sequences of upper-half
12572 (The full UTF-8 scheme allows for encoding 31-bit characters as
12573 6-byte sequences, but in this implementation, all UTF-8 sequences
12574 of four or more bytes length will raise a Constraint_Error, as
12575 will all invalid UTF-8 sequences.)
12577 @item Brackets Coding
12578 In this encoding, a wide character is represented by the following eight
12579 character sequence:
12586 where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
12587 characters (using uppercase letters) of the wide character code. For
12588 example, @code{["A345"]} is used to represent the wide character with code
12590 This scheme is compatible with use of the full Wide_Character set.
12591 On input, brackets coding can also be used for upper half characters,
12592 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12593 is only used for wide characters with a code greater than @code{16#FF#}.
12595 Note that brackets coding is not normally used in the context of
12596 Wide_Text_IO or Wide_Wide_Text_IO, since it is really just designed as
12597 a portable way of encoding source files. In the context of Wide_Text_IO
12598 or Wide_Wide_Text_IO, it can only be used if the file does not contain
12599 any instance of the left bracket character other than to encode wide
12600 character values using the brackets encoding method. In practice it is
12601 expected that some standard wide character encoding method such
12602 as UTF-8 will be used for text input output.
12604 If brackets notation is used, then any occurrence of a left bracket
12605 in the input file which is not the start of a valid wide character
12606 sequence will cause Constraint_Error to be raised. It is possible to
12607 encode a left bracket as ["5B"] and Wide_Text_IO and Wide_Wide_Text_IO
12608 input will interpret this as a left bracket.
12610 However, when a left bracket is output, it will be output as a left bracket
12611 and not as ["5B"]. We make this decision because for normal use of
12612 Wide_Text_IO for outputting messages, it is unpleasant to clobber left
12613 brackets. For example, if we write:
12616 Put_Line ("Start of output [first run]");
12620 we really do not want to have the left bracket in this message clobbered so
12621 that the output reads:
12624 Start of output ["5B"]first run]
12628 In practice brackets encoding is reasonably useful for normal Put_Line use
12629 since we won't get confused between left brackets and wide character
12630 sequences in the output. But for input, or when files are written out
12631 and read back in, it really makes better sense to use one of the standard
12632 encoding methods such as UTF-8.
12637 For the coding schemes other than UTF-8, Hex, or Brackets encoding,
12638 not all wide character
12639 values can be represented. An attempt to output a character that cannot
12640 be represented using the encoding scheme for the file causes
12641 Constraint_Error to be raised. An invalid wide character sequence on
12642 input also causes Constraint_Error to be raised.
12645 * Wide_Text_IO Stream Pointer Positioning::
12646 * Wide_Text_IO Reading and Writing Non-Regular Files::
12649 @node Wide_Text_IO Stream Pointer Positioning
12650 @subsection Stream Pointer Positioning
12653 @code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12654 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12657 If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
12658 normal lower ASCII set (i.e.@: a character in the range:
12660 @smallexample @c ada
12661 Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
12665 then although the logical position of the file pointer is unchanged by
12666 the @code{Look_Ahead} call, the stream is physically positioned past the
12667 wide character sequence. Again this is to avoid the need for buffering
12668 or backup, and all @code{Wide_Text_IO} routines check the internal
12669 indication that this situation has occurred so that this is not visible
12670 to a normal program using @code{Wide_Text_IO}. However, this discrepancy
12671 can be observed if the wide text file shares a stream with another file.
12673 @node Wide_Text_IO Reading and Writing Non-Regular Files
12674 @subsection Reading and Writing Non-Regular Files
12677 As in the case of Text_IO, when a non-regular file is read, it is
12678 assumed that the file contains no page marks (any form characters are
12679 treated as data characters), and @code{End_Of_Page} always returns
12680 @code{False}. Similarly, the end of file indication is not sticky, so
12681 it is possible to read beyond an end of file.
12683 @node Wide_Wide_Text_IO
12684 @section Wide_Wide_Text_IO
12687 @code{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that
12688 both input and output files may contain special sequences that represent
12689 wide wide character values. The encoding scheme for a given file may be
12690 specified using a FORM parameter:
12697 as part of the FORM string (WCEM = wide character encoding method),
12698 where @var{x} is one of the following characters
12704 Upper half encoding
12716 The encoding methods match those that
12717 can be used in a source
12718 program, but there is no requirement that the encoding method used for
12719 the source program be the same as the encoding method used for files,
12720 and different files may use different encoding methods.
12722 The default encoding method for the standard files, and for opened files
12723 for which no WCEM parameter is given in the FORM string matches the
12724 wide character encoding specified for the main program (the default
12725 being brackets encoding if no coding method was specified with -gnatW).
12730 A wide character is represented using
12731 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
12732 10646-1/Am.2. Depending on the character value, the representation
12733 is a one, two, three, or four byte sequence:
12736 16#000000#-16#00007f#: 2#0xxxxxxx#
12737 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx#
12738 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
12739 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
12743 where the @var{xxx} bits correspond to the left-padded bits of the
12744 21-bit character value. Note that all lower half ASCII characters
12745 are represented as ASCII bytes and all upper half characters and
12746 other wide characters are represented as sequences of upper-half
12749 @item Brackets Coding
12750 In this encoding, a wide wide character is represented by the following eight
12751 character sequence if is in wide character range
12757 and by the following ten character sequence if not
12760 [ " a b c d e f " ]
12764 where @code{a}, @code{b}, @code{c}, @code{d}, @code{e}, and @code{f}
12765 are the four or six hexadecimal
12766 characters (using uppercase letters) of the wide wide character code. For
12767 example, @code{["01A345"]} is used to represent the wide wide character
12768 with code @code{16#01A345#}.
12770 This scheme is compatible with use of the full Wide_Wide_Character set.
12771 On input, brackets coding can also be used for upper half characters,
12772 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
12773 is only used for wide characters with a code greater than @code{16#FF#}.
12778 If is also possible to use the other Wide_Character encoding methods,
12779 such as Shift-JIS, but the other schemes cannot support the full range
12780 of wide wide characters.
12781 An attempt to output a character that cannot
12782 be represented using the encoding scheme for the file causes
12783 Constraint_Error to be raised. An invalid wide character sequence on
12784 input also causes Constraint_Error to be raised.
12787 * Wide_Wide_Text_IO Stream Pointer Positioning::
12788 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
12791 @node Wide_Wide_Text_IO Stream Pointer Positioning
12792 @subsection Stream Pointer Positioning
12795 @code{Ada.Wide_Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
12796 of stream pointer positioning (@pxref{Text_IO}). There is one additional
12799 If @code{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the
12800 normal lower ASCII set (i.e.@: a character in the range:
12802 @smallexample @c ada
12803 Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
12807 then although the logical position of the file pointer is unchanged by
12808 the @code{Look_Ahead} call, the stream is physically positioned past the
12809 wide character sequence. Again this is to avoid the need for buffering
12810 or backup, and all @code{Wide_Wide_Text_IO} routines check the internal
12811 indication that this situation has occurred so that this is not visible
12812 to a normal program using @code{Wide_Wide_Text_IO}. However, this discrepancy
12813 can be observed if the wide text file shares a stream with another file.
12815 @node Wide_Wide_Text_IO Reading and Writing Non-Regular Files
12816 @subsection Reading and Writing Non-Regular Files
12819 As in the case of Text_IO, when a non-regular file is read, it is
12820 assumed that the file contains no page marks (any form characters are
12821 treated as data characters), and @code{End_Of_Page} always returns
12822 @code{False}. Similarly, the end of file indication is not sticky, so
12823 it is possible to read beyond an end of file.
12829 A stream file is a sequence of bytes, where individual elements are
12830 written to the file as described in the Ada Reference Manual. The type
12831 @code{Stream_Element} is simply a byte. There are two ways to read or
12832 write a stream file.
12836 The operations @code{Read} and @code{Write} directly read or write a
12837 sequence of stream elements with no control information.
12840 The stream attributes applied to a stream file transfer data in the
12841 manner described for stream attributes.
12845 @section Shared Files
12848 Section A.14 of the Ada Reference Manual allows implementations to
12849 provide a wide variety of behavior if an attempt is made to access the
12850 same external file with two or more internal files.
12852 To provide a full range of functionality, while at the same time
12853 minimizing the problems of portability caused by this implementation
12854 dependence, GNAT handles file sharing as follows:
12858 In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
12859 to open two or more files with the same full name is considered an error
12860 and is not supported. The exception @code{Use_Error} will be
12861 raised. Note that a file that is not explicitly closed by the program
12862 remains open until the program terminates.
12865 If the form parameter @samp{shared=no} appears in the form string, the
12866 file can be opened or created with its own separate stream identifier,
12867 regardless of whether other files sharing the same external file are
12868 opened. The exact effect depends on how the C stream routines handle
12869 multiple accesses to the same external files using separate streams.
12872 If the form parameter @samp{shared=yes} appears in the form string for
12873 each of two or more files opened using the same full name, the same
12874 stream is shared between these files, and the semantics are as described
12875 in Ada Reference Manual, Section A.14.
12879 When a program that opens multiple files with the same name is ported
12880 from another Ada compiler to GNAT, the effect will be that
12881 @code{Use_Error} is raised.
12883 The documentation of the original compiler and the documentation of the
12884 program should then be examined to determine if file sharing was
12885 expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
12886 and @code{Create} calls as required.
12888 When a program is ported from GNAT to some other Ada compiler, no
12889 special attention is required unless the @samp{shared=@var{xxx}} form
12890 parameter is used in the program. In this case, you must examine the
12891 documentation of the new compiler to see if it supports the required
12892 file sharing semantics, and form strings modified appropriately. Of
12893 course it may be the case that the program cannot be ported if the
12894 target compiler does not support the required functionality. The best
12895 approach in writing portable code is to avoid file sharing (and hence
12896 the use of the @samp{shared=@var{xxx}} parameter in the form string)
12899 One common use of file sharing in Ada 83 is the use of instantiations of
12900 Sequential_IO on the same file with different types, to achieve
12901 heterogeneous input-output. Although this approach will work in GNAT if
12902 @samp{shared=yes} is specified, it is preferable in Ada to use Stream_IO
12903 for this purpose (using the stream attributes)
12905 @node Filenames encoding
12906 @section Filenames encoding
12909 An encoding form parameter can be used to specify the filename
12910 encoding @samp{encoding=@var{xxx}}.
12914 If the form parameter @samp{encoding=utf8} appears in the form string, the
12915 filename must be encoded in UTF-8.
12918 If the form parameter @samp{encoding=8bits} appears in the form
12919 string, the filename must be a standard 8bits string.
12922 In the absence of a @samp{encoding=@var{xxx}} form parameter, the
12923 value UTF-8 is used. This encoding form parameter is only supported on
12924 the Windows platform. On the other Operating Systems the runtime is
12925 supporting UTF-8 natively.
12928 @section Open Modes
12931 @code{Open} and @code{Create} calls result in a call to @code{fopen}
12932 using the mode shown in the following table:
12935 @center @code{Open} and @code{Create} Call Modes
12937 @b{OPEN } @b{CREATE}
12938 Append_File "r+" "w+"
12940 Out_File (Direct_IO) "r+" "w"
12941 Out_File (all other cases) "w" "w"
12942 Inout_File "r+" "w+"
12946 If text file translation is required, then either @samp{b} or @samp{t}
12947 is added to the mode, depending on the setting of Text. Text file
12948 translation refers to the mapping of CR/LF sequences in an external file
12949 to LF characters internally. This mapping only occurs in DOS and
12950 DOS-like systems, and is not relevant to other systems.
12952 A special case occurs with Stream_IO@. As shown in the above table, the
12953 file is initially opened in @samp{r} or @samp{w} mode for the
12954 @code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
12955 subsequently requires switching from reading to writing or vice-versa,
12956 then the file is reopened in @samp{r+} mode to permit the required operation.
12958 @node Operations on C Streams
12959 @section Operations on C Streams
12960 The package @code{Interfaces.C_Streams} provides an Ada program with direct
12961 access to the C library functions for operations on C streams:
12963 @smallexample @c adanocomment
12964 package Interfaces.C_Streams is
12965 -- Note: the reason we do not use the types that are in
12966 -- Interfaces.C is that we want to avoid dragging in the
12967 -- code in this unit if possible.
12968 subtype chars is System.Address;
12969 -- Pointer to null-terminated array of characters
12970 subtype FILEs is System.Address;
12971 -- Corresponds to the C type FILE*
12972 subtype voids is System.Address;
12973 -- Corresponds to the C type void*
12974 subtype int is Integer;
12975 subtype long is Long_Integer;
12976 -- Note: the above types are subtypes deliberately, and it
12977 -- is part of this spec that the above correspondences are
12978 -- guaranteed. This means that it is legitimate to, for
12979 -- example, use Integer instead of int. We provide these
12980 -- synonyms for clarity, but in some cases it may be
12981 -- convenient to use the underlying types (for example to
12982 -- avoid an unnecessary dependency of a spec on the spec
12984 type size_t is mod 2 ** Standard'Address_Size;
12985 NULL_Stream : constant FILEs;
12986 -- Value returned (NULL in C) to indicate an
12987 -- fdopen/fopen/tmpfile error
12988 ----------------------------------
12989 -- Constants Defined in stdio.h --
12990 ----------------------------------
12991 EOF : constant int;
12992 -- Used by a number of routines to indicate error or
12994 IOFBF : constant int;
12995 IOLBF : constant int;
12996 IONBF : constant int;
12997 -- Used to indicate buffering mode for setvbuf call
12998 SEEK_CUR : constant int;
12999 SEEK_END : constant int;
13000 SEEK_SET : constant int;
13001 -- Used to indicate origin for fseek call
13002 function stdin return FILEs;
13003 function stdout return FILEs;
13004 function stderr return FILEs;
13005 -- Streams associated with standard files
13006 --------------------------
13007 -- Standard C functions --
13008 --------------------------
13009 -- The functions selected below are ones that are
13010 -- available in DOS, OS/2, UNIX and Xenix (but not
13011 -- necessarily in ANSI C). These are very thin interfaces
13012 -- which copy exactly the C headers. For more
13013 -- documentation on these functions, see the Microsoft C
13014 -- "Run-Time Library Reference" (Microsoft Press, 1990,
13015 -- ISBN 1-55615-225-6), which includes useful information
13016 -- on system compatibility.
13017 procedure clearerr (stream : FILEs);
13018 function fclose (stream : FILEs) return int;
13019 function fdopen (handle : int; mode : chars) return FILEs;
13020 function feof (stream : FILEs) return int;
13021 function ferror (stream : FILEs) return int;
13022 function fflush (stream : FILEs) return int;
13023 function fgetc (stream : FILEs) return int;
13024 function fgets (strng : chars; n : int; stream : FILEs)
13026 function fileno (stream : FILEs) return int;
13027 function fopen (filename : chars; Mode : chars)
13029 -- Note: to maintain target independence, use
13030 -- text_translation_required, a boolean variable defined in
13031 -- a-sysdep.c to deal with the target dependent text
13032 -- translation requirement. If this variable is set,
13033 -- then b/t should be appended to the standard mode
13034 -- argument to set the text translation mode off or on
13036 function fputc (C : int; stream : FILEs) return int;
13037 function fputs (Strng : chars; Stream : FILEs) return int;
13054 function ftell (stream : FILEs) return long;
13061 function isatty (handle : int) return int;
13062 procedure mktemp (template : chars);
13063 -- The return value (which is just a pointer to template)
13065 procedure rewind (stream : FILEs);
13066 function rmtmp return int;
13074 function tmpfile return FILEs;
13075 function ungetc (c : int; stream : FILEs) return int;
13076 function unlink (filename : chars) return int;
13077 ---------------------
13078 -- Extra functions --
13079 ---------------------
13080 -- These functions supply slightly thicker bindings than
13081 -- those above. They are derived from functions in the
13082 -- C Run-Time Library, but may do a bit more work than
13083 -- just directly calling one of the Library functions.
13084 function is_regular_file (handle : int) return int;
13085 -- Tests if given handle is for a regular file (result 1)
13086 -- or for a non-regular file (pipe or device, result 0).
13087 ---------------------------------
13088 -- Control of Text/Binary Mode --
13089 ---------------------------------
13090 -- If text_translation_required is true, then the following
13091 -- functions may be used to dynamically switch a file from
13092 -- binary to text mode or vice versa. These functions have
13093 -- no effect if text_translation_required is false (i.e.@: in
13094 -- normal UNIX mode). Use fileno to get a stream handle.
13095 procedure set_binary_mode (handle : int);
13096 procedure set_text_mode (handle : int);
13097 ----------------------------
13098 -- Full Path Name support --
13099 ----------------------------
13100 procedure full_name (nam : chars; buffer : chars);
13101 -- Given a NUL terminated string representing a file
13102 -- name, returns in buffer a NUL terminated string
13103 -- representing the full path name for the file name.
13104 -- On systems where it is relevant the drive is also
13105 -- part of the full path name. It is the responsibility
13106 -- of the caller to pass an actual parameter for buffer
13107 -- that is big enough for any full path name. Use
13108 -- max_path_len given below as the size of buffer.
13109 max_path_len : integer;
13110 -- Maximum length of an allowable full path name on the
13111 -- system, including a terminating NUL character.
13112 end Interfaces.C_Streams;
13115 @node Interfacing to C Streams
13116 @section Interfacing to C Streams
13119 The packages in this section permit interfacing Ada files to C Stream
13122 @smallexample @c ada
13123 with Interfaces.C_Streams;
13124 package Ada.Sequential_IO.C_Streams is
13125 function C_Stream (F : File_Type)
13126 return Interfaces.C_Streams.FILEs;
13128 (File : in out File_Type;
13129 Mode : in File_Mode;
13130 C_Stream : in Interfaces.C_Streams.FILEs;
13131 Form : in String := "");
13132 end Ada.Sequential_IO.C_Streams;
13134 with Interfaces.C_Streams;
13135 package Ada.Direct_IO.C_Streams is
13136 function C_Stream (F : File_Type)
13137 return Interfaces.C_Streams.FILEs;
13139 (File : in out File_Type;
13140 Mode : in File_Mode;
13141 C_Stream : in Interfaces.C_Streams.FILEs;
13142 Form : in String := "");
13143 end Ada.Direct_IO.C_Streams;
13145 with Interfaces.C_Streams;
13146 package Ada.Text_IO.C_Streams is
13147 function C_Stream (F : File_Type)
13148 return Interfaces.C_Streams.FILEs;
13150 (File : in out File_Type;
13151 Mode : in File_Mode;
13152 C_Stream : in Interfaces.C_Streams.FILEs;
13153 Form : in String := "");
13154 end Ada.Text_IO.C_Streams;
13156 with Interfaces.C_Streams;
13157 package Ada.Wide_Text_IO.C_Streams is
13158 function C_Stream (F : File_Type)
13159 return Interfaces.C_Streams.FILEs;
13161 (File : in out File_Type;
13162 Mode : in File_Mode;
13163 C_Stream : in Interfaces.C_Streams.FILEs;
13164 Form : in String := "");
13165 end Ada.Wide_Text_IO.C_Streams;
13167 with Interfaces.C_Streams;
13168 package Ada.Wide_Wide_Text_IO.C_Streams is
13169 function C_Stream (F : File_Type)
13170 return Interfaces.C_Streams.FILEs;
13172 (File : in out File_Type;
13173 Mode : in File_Mode;
13174 C_Stream : in Interfaces.C_Streams.FILEs;
13175 Form : in String := "");
13176 end Ada.Wide_Wide_Text_IO.C_Streams;
13178 with Interfaces.C_Streams;
13179 package Ada.Stream_IO.C_Streams is
13180 function C_Stream (F : File_Type)
13181 return Interfaces.C_Streams.FILEs;
13183 (File : in out File_Type;
13184 Mode : in File_Mode;
13185 C_Stream : in Interfaces.C_Streams.FILEs;
13186 Form : in String := "");
13187 end Ada.Stream_IO.C_Streams;
13191 In each of these six packages, the @code{C_Stream} function obtains the
13192 @code{FILE} pointer from a currently opened Ada file. It is then
13193 possible to use the @code{Interfaces.C_Streams} package to operate on
13194 this stream, or the stream can be passed to a C program which can
13195 operate on it directly. Of course the program is responsible for
13196 ensuring that only appropriate sequences of operations are executed.
13198 One particular use of relevance to an Ada program is that the
13199 @code{setvbuf} function can be used to control the buffering of the
13200 stream used by an Ada file. In the absence of such a call the standard
13201 default buffering is used.
13203 The @code{Open} procedures in these packages open a file giving an
13204 existing C Stream instead of a file name. Typically this stream is
13205 imported from a C program, allowing an Ada file to operate on an
13208 @node The GNAT Library
13209 @chapter The GNAT Library
13212 The GNAT library contains a number of general and special purpose packages.
13213 It represents functionality that the GNAT developers have found useful, and
13214 which is made available to GNAT users. The packages described here are fully
13215 supported, and upwards compatibility will be maintained in future releases,
13216 so you can use these facilities with the confidence that the same functionality
13217 will be available in future releases.
13219 The chapter here simply gives a brief summary of the facilities available.
13220 The full documentation is found in the spec file for the package. The full
13221 sources of these library packages, including both spec and body, are provided
13222 with all GNAT releases. For example, to find out the full specifications of
13223 the SPITBOL pattern matching capability, including a full tutorial and
13224 extensive examples, look in the @file{g-spipat.ads} file in the library.
13226 For each entry here, the package name (as it would appear in a @code{with}
13227 clause) is given, followed by the name of the corresponding spec file in
13228 parentheses. The packages are children in four hierarchies, @code{Ada},
13229 @code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
13230 GNAT-specific hierarchy.
13232 Note that an application program should only use packages in one of these
13233 four hierarchies if the package is defined in the Ada Reference Manual,
13234 or is listed in this section of the GNAT Programmers Reference Manual.
13235 All other units should be considered internal implementation units and
13236 should not be directly @code{with}'ed by application code. The use of
13237 a @code{with} statement that references one of these internal implementation
13238 units makes an application potentially dependent on changes in versions
13239 of GNAT, and will generate a warning message.
13242 * Ada.Characters.Latin_9 (a-chlat9.ads)::
13243 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
13244 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
13245 * Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)::
13246 * Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)::
13247 * Ada.Command_Line.Environment (a-colien.ads)::
13248 * Ada.Command_Line.Remove (a-colire.ads)::
13249 * Ada.Command_Line.Response_File (a-clrefi.ads)::
13250 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
13251 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
13252 * Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)::
13253 * Ada.Exceptions.Traceback (a-exctra.ads)::
13254 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
13255 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
13256 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
13257 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
13258 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
13259 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
13260 * Ada.Wide_Characters.Unicode (a-wichun.ads)::
13261 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
13262 * Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)::
13263 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
13264 * GNAT.Altivec (g-altive.ads)::
13265 * GNAT.Altivec.Conversions (g-altcon.ads)::
13266 * GNAT.Altivec.Vector_Operations (g-alveop.ads)::
13267 * GNAT.Altivec.Vector_Types (g-alvety.ads)::
13268 * GNAT.Altivec.Vector_Views (g-alvevi.ads)::
13269 * GNAT.Array_Split (g-arrspl.ads)::
13270 * GNAT.AWK (g-awk.ads)::
13271 * GNAT.Bounded_Buffers (g-boubuf.ads)::
13272 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
13273 * GNAT.Bubble_Sort (g-bubsor.ads)::
13274 * GNAT.Bubble_Sort_A (g-busora.ads)::
13275 * GNAT.Bubble_Sort_G (g-busorg.ads)::
13276 * GNAT.Byte_Order_Mark (g-byorma.ads)::
13277 * GNAT.Byte_Swapping (g-bytswa.ads)::
13278 * GNAT.Calendar (g-calend.ads)::
13279 * GNAT.Calendar.Time_IO (g-catiio.ads)::
13280 * GNAT.Case_Util (g-casuti.ads)::
13281 * GNAT.CGI (g-cgi.ads)::
13282 * GNAT.CGI.Cookie (g-cgicoo.ads)::
13283 * GNAT.CGI.Debug (g-cgideb.ads)::
13284 * GNAT.Command_Line (g-comlin.ads)::
13285 * GNAT.Compiler_Version (g-comver.ads)::
13286 * GNAT.Ctrl_C (g-ctrl_c.ads)::
13287 * GNAT.CRC32 (g-crc32.ads)::
13288 * GNAT.Current_Exception (g-curexc.ads)::
13289 * GNAT.Debug_Pools (g-debpoo.ads)::
13290 * GNAT.Debug_Utilities (g-debuti.ads)::
13291 * GNAT.Decode_String (g-decstr.ads)::
13292 * GNAT.Decode_UTF8_String (g-deutst.ads)::
13293 * GNAT.Directory_Operations (g-dirope.ads)::
13294 * GNAT.Directory_Operations.Iteration (g-diopit.ads)::
13295 * GNAT.Dynamic_HTables (g-dynhta.ads)::
13296 * GNAT.Dynamic_Tables (g-dyntab.ads)::
13297 * GNAT.Encode_String (g-encstr.ads)::
13298 * GNAT.Encode_UTF8_String (g-enutst.ads)::
13299 * GNAT.Exception_Actions (g-excact.ads)::
13300 * GNAT.Exception_Traces (g-exctra.ads)::
13301 * GNAT.Exceptions (g-except.ads)::
13302 * GNAT.Expect (g-expect.ads)::
13303 * GNAT.Float_Control (g-flocon.ads)::
13304 * GNAT.Heap_Sort (g-heasor.ads)::
13305 * GNAT.Heap_Sort_A (g-hesora.ads)::
13306 * GNAT.Heap_Sort_G (g-hesorg.ads)::
13307 * GNAT.HTable (g-htable.ads)::
13308 * GNAT.IO (g-io.ads)::
13309 * GNAT.IO_Aux (g-io_aux.ads)::
13310 * GNAT.Lock_Files (g-locfil.ads)::
13311 * GNAT.MD5 (g-md5.ads)::
13312 * GNAT.Memory_Dump (g-memdum.ads)::
13313 * GNAT.Most_Recent_Exception (g-moreex.ads)::
13314 * GNAT.OS_Lib (g-os_lib.ads)::
13315 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
13316 * GNAT.Random_Numbers (g-rannum.ads)::
13317 * GNAT.Regexp (g-regexp.ads)::
13318 * GNAT.Registry (g-regist.ads)::
13319 * GNAT.Regpat (g-regpat.ads)::
13320 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
13321 * GNAT.Semaphores (g-semaph.ads)::
13322 * GNAT.Serial_Communications (g-sercom.ads)::
13323 * GNAT.SHA1 (g-sha1.ads)::
13324 * GNAT.Signals (g-signal.ads)::
13325 * GNAT.Sockets (g-socket.ads)::
13326 * GNAT.Source_Info (g-souinf.ads)::
13327 * GNAT.Spelling_Checker (g-speche.ads)::
13328 * GNAT.Spelling_Checker_Generic (g-spchge.ads)::
13329 * GNAT.Spitbol.Patterns (g-spipat.ads)::
13330 * GNAT.Spitbol (g-spitbo.ads)::
13331 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
13332 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
13333 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
13334 * GNAT.Strings (g-string.ads)::
13335 * GNAT.String_Split (g-strspl.ads)::
13336 * GNAT.Table (g-table.ads)::
13337 * GNAT.Task_Lock (g-tasloc.ads)::
13338 * GNAT.Threads (g-thread.ads)::
13339 * GNAT.Time_Stamp (g-timsta.ads)::
13340 * GNAT.Traceback (g-traceb.ads)::
13341 * GNAT.Traceback.Symbolic (g-trasym.ads)::
13342 * GNAT.UTF_32 (g-utf_32.ads)::
13343 * GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)::
13344 * GNAT.Wide_Spelling_Checker (g-wispch.ads)::
13345 * GNAT.Wide_String_Split (g-wistsp.ads)::
13346 * GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)::
13347 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
13348 * Interfaces.C.Extensions (i-cexten.ads)::
13349 * Interfaces.C.Streams (i-cstrea.ads)::
13350 * Interfaces.CPP (i-cpp.ads)::
13351 * Interfaces.Packed_Decimal (i-pacdec.ads)::
13352 * Interfaces.VxWorks (i-vxwork.ads)::
13353 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
13354 * System.Address_Image (s-addima.ads)::
13355 * System.Assertions (s-assert.ads)::
13356 * System.Memory (s-memory.ads)::
13357 * System.Partition_Interface (s-parint.ads)::
13358 * System.Pool_Global (s-pooglo.ads)::
13359 * System.Pool_Local (s-pooloc.ads)::
13360 * System.Restrictions (s-restri.ads)::
13361 * System.Rident (s-rident.ads)::
13362 * System.Task_Info (s-tasinf.ads)::
13363 * System.Wch_Cnv (s-wchcnv.ads)::
13364 * System.Wch_Con (s-wchcon.ads)::
13367 @node Ada.Characters.Latin_9 (a-chlat9.ads)
13368 @section @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13369 @cindex @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
13370 @cindex Latin_9 constants for Character
13373 This child of @code{Ada.Characters}
13374 provides a set of definitions corresponding to those in the
13375 RM-defined package @code{Ada.Characters.Latin_1} but with the
13376 few modifications required for @code{Latin-9}
13377 The provision of such a package
13378 is specifically authorized by the Ada Reference Manual
13381 @node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
13382 @section @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13383 @cindex @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
13384 @cindex Latin_1 constants for Wide_Character
13387 This child of @code{Ada.Characters}
13388 provides a set of definitions corresponding to those in the
13389 RM-defined package @code{Ada.Characters.Latin_1} but with the
13390 types of the constants being @code{Wide_Character}
13391 instead of @code{Character}. The provision of such a package
13392 is specifically authorized by the Ada Reference Manual
13395 @node Ada.Characters.Wide_Latin_9 (a-cwila9.ads)
13396 @section @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13397 @cindex @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
13398 @cindex Latin_9 constants for Wide_Character
13401 This child of @code{Ada.Characters}
13402 provides a set of definitions corresponding to those in the
13403 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13404 types of the constants being @code{Wide_Character}
13405 instead of @code{Character}. The provision of such a package
13406 is specifically authorized by the Ada Reference Manual
13409 @node Ada.Characters.Wide_Wide_Latin_1 (a-chzla1.ads)
13410 @section @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13411 @cindex @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-chzla1.ads})
13412 @cindex Latin_1 constants for Wide_Wide_Character
13415 This child of @code{Ada.Characters}
13416 provides a set of definitions corresponding to those in the
13417 RM-defined package @code{Ada.Characters.Latin_1} but with the
13418 types of the constants being @code{Wide_Wide_Character}
13419 instead of @code{Character}. The provision of such a package
13420 is specifically authorized by the Ada Reference Manual
13423 @node Ada.Characters.Wide_Wide_Latin_9 (a-chzla9.ads)
13424 @section @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13425 @cindex @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-chzla9.ads})
13426 @cindex Latin_9 constants for Wide_Wide_Character
13429 This child of @code{Ada.Characters}
13430 provides a set of definitions corresponding to those in the
13431 GNAT defined package @code{Ada.Characters.Latin_9} but with the
13432 types of the constants being @code{Wide_Wide_Character}
13433 instead of @code{Character}. The provision of such a package
13434 is specifically authorized by the Ada Reference Manual
13437 @node Ada.Command_Line.Environment (a-colien.ads)
13438 @section @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13439 @cindex @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
13440 @cindex Environment entries
13443 This child of @code{Ada.Command_Line}
13444 provides a mechanism for obtaining environment values on systems
13445 where this concept makes sense.
13447 @node Ada.Command_Line.Remove (a-colire.ads)
13448 @section @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13449 @cindex @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
13450 @cindex Removing command line arguments
13451 @cindex Command line, argument removal
13454 This child of @code{Ada.Command_Line}
13455 provides a mechanism for logically removing
13456 arguments from the argument list. Once removed, an argument is not visible
13457 to further calls on the subprograms in @code{Ada.Command_Line} will not
13458 see the removed argument.
13460 @node Ada.Command_Line.Response_File (a-clrefi.ads)
13461 @section @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13462 @cindex @code{Ada.Command_Line.Response_File} (@file{a-clrefi.ads})
13463 @cindex Response file for command line
13464 @cindex Command line, response file
13465 @cindex Command line, handling long command lines
13468 This child of @code{Ada.Command_Line} provides a mechanism facilities for
13469 getting command line arguments from a text file, called a "response file".
13470 Using a response file allow passing a set of arguments to an executable longer
13471 than the maximum allowed by the system on the command line.
13473 @node Ada.Direct_IO.C_Streams (a-diocst.ads)
13474 @section @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13475 @cindex @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
13476 @cindex C Streams, Interfacing with Direct_IO
13479 This package provides subprograms that allow interfacing between
13480 C streams and @code{Direct_IO}. The stream identifier can be
13481 extracted from a file opened on the Ada side, and an Ada file
13482 can be constructed from a stream opened on the C side.
13484 @node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
13485 @section @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13486 @cindex @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
13487 @cindex Null_Occurrence, testing for
13490 This child subprogram provides a way of testing for the null
13491 exception occurrence (@code{Null_Occurrence}) without raising
13494 @node Ada.Exceptions.Last_Chance_Handler (a-elchha.ads)
13495 @section @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13496 @cindex @code{Ada.Exceptions.Last_Chance_Handler} (@file{a-elchha.ads})
13497 @cindex Null_Occurrence, testing for
13500 This child subprogram is used for handling otherwise unhandled
13501 exceptions (hence the name last chance), and perform clean ups before
13502 terminating the program. Note that this subprogram never returns.
13504 @node Ada.Exceptions.Traceback (a-exctra.ads)
13505 @section @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13506 @cindex @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
13507 @cindex Traceback for Exception Occurrence
13510 This child package provides the subprogram (@code{Tracebacks}) to
13511 give a traceback array of addresses based on an exception
13514 @node Ada.Sequential_IO.C_Streams (a-siocst.ads)
13515 @section @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13516 @cindex @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
13517 @cindex C Streams, Interfacing with Sequential_IO
13520 This package provides subprograms that allow interfacing between
13521 C streams and @code{Sequential_IO}. The stream identifier can be
13522 extracted from a file opened on the Ada side, and an Ada file
13523 can be constructed from a stream opened on the C side.
13525 @node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
13526 @section @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13527 @cindex @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
13528 @cindex C Streams, Interfacing with Stream_IO
13531 This package provides subprograms that allow interfacing between
13532 C streams and @code{Stream_IO}. The stream identifier can be
13533 extracted from a file opened on the Ada side, and an Ada file
13534 can be constructed from a stream opened on the C side.
13536 @node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
13537 @section @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13538 @cindex @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
13539 @cindex @code{Unbounded_String}, IO support
13540 @cindex @code{Text_IO}, extensions for unbounded strings
13543 This package provides subprograms for Text_IO for unbounded
13544 strings, avoiding the necessity for an intermediate operation
13545 with ordinary strings.
13547 @node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
13548 @section @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13549 @cindex @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
13550 @cindex @code{Unbounded_Wide_String}, IO support
13551 @cindex @code{Text_IO}, extensions for unbounded wide strings
13554 This package provides subprograms for Text_IO for unbounded
13555 wide strings, avoiding the necessity for an intermediate operation
13556 with ordinary wide strings.
13558 @node Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)
13559 @section @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13560 @cindex @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
13561 @cindex @code{Unbounded_Wide_Wide_String}, IO support
13562 @cindex @code{Text_IO}, extensions for unbounded wide wide strings
13565 This package provides subprograms for Text_IO for unbounded
13566 wide wide strings, avoiding the necessity for an intermediate operation
13567 with ordinary wide wide strings.
13569 @node Ada.Text_IO.C_Streams (a-tiocst.ads)
13570 @section @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13571 @cindex @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
13572 @cindex C Streams, Interfacing with @code{Text_IO}
13575 This package provides subprograms that allow interfacing between
13576 C streams and @code{Text_IO}. The stream identifier can be
13577 extracted from a file opened on the Ada side, and an Ada file
13578 can be constructed from a stream opened on the C side.
13580 @node Ada.Wide_Characters.Unicode (a-wichun.ads)
13581 @section @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13582 @cindex @code{Ada.Wide_Characters.Unicode} (@file{a-wichun.ads})
13583 @cindex Unicode categorization, Wide_Character
13586 This package provides subprograms that allow categorization of
13587 Wide_Character values according to Unicode categories.
13589 @node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
13590 @section @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13591 @cindex @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
13592 @cindex C Streams, Interfacing with @code{Wide_Text_IO}
13595 This package provides subprograms that allow interfacing between
13596 C streams and @code{Wide_Text_IO}. The stream identifier can be
13597 extracted from a file opened on the Ada side, and an Ada file
13598 can be constructed from a stream opened on the C side.
13600 @node Ada.Wide_Wide_Characters.Unicode (a-zchuni.ads)
13601 @section @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13602 @cindex @code{Ada.Wide_Wide_Characters.Unicode} (@file{a-zchuni.ads})
13603 @cindex Unicode categorization, Wide_Wide_Character
13606 This package provides subprograms that allow categorization of
13607 Wide_Wide_Character values according to Unicode categories.
13609 @node Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)
13610 @section @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13611 @cindex @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
13612 @cindex C Streams, Interfacing with @code{Wide_Wide_Text_IO}
13615 This package provides subprograms that allow interfacing between
13616 C streams and @code{Wide_Wide_Text_IO}. The stream identifier can be
13617 extracted from a file opened on the Ada side, and an Ada file
13618 can be constructed from a stream opened on the C side.
13620 @node GNAT.Altivec (g-altive.ads)
13621 @section @code{GNAT.Altivec} (@file{g-altive.ads})
13622 @cindex @code{GNAT.Altivec} (@file{g-altive.ads})
13626 This is the root package of the GNAT AltiVec binding. It provides
13627 definitions of constants and types common to all the versions of the
13630 @node GNAT.Altivec.Conversions (g-altcon.ads)
13631 @section @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13632 @cindex @code{GNAT.Altivec.Conversions} (@file{g-altcon.ads})
13636 This package provides the Vector/View conversion routines.
13638 @node GNAT.Altivec.Vector_Operations (g-alveop.ads)
13639 @section @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13640 @cindex @code{GNAT.Altivec.Vector_Operations} (@file{g-alveop.ads})
13644 This package exposes the Ada interface to the AltiVec operations on
13645 vector objects. A soft emulation is included by default in the GNAT
13646 library. The hard binding is provided as a separate package. This unit
13647 is common to both bindings.
13649 @node GNAT.Altivec.Vector_Types (g-alvety.ads)
13650 @section @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13651 @cindex @code{GNAT.Altivec.Vector_Types} (@file{g-alvety.ads})
13655 This package exposes the various vector types part of the Ada binding
13656 to AltiVec facilities.
13658 @node GNAT.Altivec.Vector_Views (g-alvevi.ads)
13659 @section @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13660 @cindex @code{GNAT.Altivec.Vector_Views} (@file{g-alvevi.ads})
13664 This package provides public 'View' data types from/to which private
13665 vector representations can be converted via
13666 GNAT.Altivec.Conversions. This allows convenient access to individual
13667 vector elements and provides a simple way to initialize vector
13670 @node GNAT.Array_Split (g-arrspl.ads)
13671 @section @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13672 @cindex @code{GNAT.Array_Split} (@file{g-arrspl.ads})
13673 @cindex Array splitter
13676 Useful array-manipulation routines: given a set of separators, split
13677 an array wherever the separators appear, and provide direct access
13678 to the resulting slices.
13680 @node GNAT.AWK (g-awk.ads)
13681 @section @code{GNAT.AWK} (@file{g-awk.ads})
13682 @cindex @code{GNAT.AWK} (@file{g-awk.ads})
13687 Provides AWK-like parsing functions, with an easy interface for parsing one
13688 or more files containing formatted data. The file is viewed as a database
13689 where each record is a line and a field is a data element in this line.
13691 @node GNAT.Bounded_Buffers (g-boubuf.ads)
13692 @section @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13693 @cindex @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
13695 @cindex Bounded Buffers
13698 Provides a concurrent generic bounded buffer abstraction. Instances are
13699 useful directly or as parts of the implementations of other abstractions,
13702 @node GNAT.Bounded_Mailboxes (g-boumai.ads)
13703 @section @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13704 @cindex @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
13709 Provides a thread-safe asynchronous intertask mailbox communication facility.
13711 @node GNAT.Bubble_Sort (g-bubsor.ads)
13712 @section @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13713 @cindex @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
13715 @cindex Bubble sort
13718 Provides a general implementation of bubble sort usable for sorting arbitrary
13719 data items. Exchange and comparison procedures are provided by passing
13720 access-to-procedure values.
13722 @node GNAT.Bubble_Sort_A (g-busora.ads)
13723 @section @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13724 @cindex @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
13726 @cindex Bubble sort
13729 Provides a general implementation of bubble sort usable for sorting arbitrary
13730 data items. Move and comparison procedures are provided by passing
13731 access-to-procedure values. This is an older version, retained for
13732 compatibility. Usually @code{GNAT.Bubble_Sort} will be preferable.
13734 @node GNAT.Bubble_Sort_G (g-busorg.ads)
13735 @section @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13736 @cindex @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
13738 @cindex Bubble sort
13741 Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
13742 are provided as generic parameters, this improves efficiency, especially
13743 if the procedures can be inlined, at the expense of duplicating code for
13744 multiple instantiations.
13746 @node GNAT.Byte_Order_Mark (g-byorma.ads)
13747 @section @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13748 @cindex @code{GNAT.Byte_Order_Mark} (@file{g-byorma.ads})
13749 @cindex UTF-8 representation
13750 @cindex Wide characte representations
13753 Provides a routine which given a string, reads the start of the string to
13754 see whether it is one of the standard byte order marks (BOM's) which signal
13755 the encoding of the string. The routine includes detection of special XML
13756 sequences for various UCS input formats.
13758 @node GNAT.Byte_Swapping (g-bytswa.ads)
13759 @section @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
13760 @cindex @code{GNAT.Byte_Swapping} (@file{g-bytswa.ads})
13761 @cindex Byte swapping
13765 General routines for swapping the bytes in 2-, 4-, and 8-byte quantities.
13766 Machine-specific implementations are available in some cases.
13768 @node GNAT.Calendar (g-calend.ads)
13769 @section @code{GNAT.Calendar} (@file{g-calend.ads})
13770 @cindex @code{GNAT.Calendar} (@file{g-calend.ads})
13771 @cindex @code{Calendar}
13774 Extends the facilities provided by @code{Ada.Calendar} to include handling
13775 of days of the week, an extended @code{Split} and @code{Time_Of} capability.
13776 Also provides conversion of @code{Ada.Calendar.Time} values to and from the
13777 C @code{timeval} format.
13779 @node GNAT.Calendar.Time_IO (g-catiio.ads)
13780 @section @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
13781 @cindex @code{Calendar}
13783 @cindex @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
13785 @node GNAT.CRC32 (g-crc32.ads)
13786 @section @code{GNAT.CRC32} (@file{g-crc32.ads})
13787 @cindex @code{GNAT.CRC32} (@file{g-crc32.ads})
13789 @cindex Cyclic Redundancy Check
13792 This package implements the CRC-32 algorithm. For a full description
13793 of this algorithm see
13794 ``Computation of Cyclic Redundancy Checks via Table Look-Up'',
13795 @cite{Communications of the ACM}, Vol.@: 31 No.@: 8, pp.@: 1008-1013,
13796 Aug.@: 1988. Sarwate, D.V@.
13798 @node GNAT.Case_Util (g-casuti.ads)
13799 @section @code{GNAT.Case_Util} (@file{g-casuti.ads})
13800 @cindex @code{GNAT.Case_Util} (@file{g-casuti.ads})
13801 @cindex Casing utilities
13802 @cindex Character handling (@code{GNAT.Case_Util})
13805 A set of simple routines for handling upper and lower casing of strings
13806 without the overhead of the full casing tables
13807 in @code{Ada.Characters.Handling}.
13809 @node GNAT.CGI (g-cgi.ads)
13810 @section @code{GNAT.CGI} (@file{g-cgi.ads})
13811 @cindex @code{GNAT.CGI} (@file{g-cgi.ads})
13812 @cindex CGI (Common Gateway Interface)
13815 This is a package for interfacing a GNAT program with a Web server via the
13816 Common Gateway Interface (CGI)@. Basically this package parses the CGI
13817 parameters, which are a set of key/value pairs sent by the Web server. It
13818 builds a table whose index is the key and provides some services to deal
13821 @node GNAT.CGI.Cookie (g-cgicoo.ads)
13822 @section @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
13823 @cindex @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
13824 @cindex CGI (Common Gateway Interface) cookie support
13825 @cindex Cookie support in CGI
13828 This is a package to interface a GNAT program with a Web server via the
13829 Common Gateway Interface (CGI). It exports services to deal with Web
13830 cookies (piece of information kept in the Web client software).
13832 @node GNAT.CGI.Debug (g-cgideb.ads)
13833 @section @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
13834 @cindex @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
13835 @cindex CGI (Common Gateway Interface) debugging
13838 This is a package to help debugging CGI (Common Gateway Interface)
13839 programs written in Ada.
13841 @node GNAT.Command_Line (g-comlin.ads)
13842 @section @code{GNAT.Command_Line} (@file{g-comlin.ads})
13843 @cindex @code{GNAT.Command_Line} (@file{g-comlin.ads})
13844 @cindex Command line
13847 Provides a high level interface to @code{Ada.Command_Line} facilities,
13848 including the ability to scan for named switches with optional parameters
13849 and expand file names using wild card notations.
13851 @node GNAT.Compiler_Version (g-comver.ads)
13852 @section @code{GNAT.Compiler_Version} (@file{g-comver.ads})
13853 @cindex @code{GNAT.Compiler_Version} (@file{g-comver.ads})
13854 @cindex Compiler Version
13855 @cindex Version, of compiler
13858 Provides a routine for obtaining the version of the compiler used to
13859 compile the program. More accurately this is the version of the binder
13860 used to bind the program (this will normally be the same as the version
13861 of the compiler if a consistent tool set is used to compile all units
13864 @node GNAT.Ctrl_C (g-ctrl_c.ads)
13865 @section @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
13866 @cindex @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
13870 Provides a simple interface to handle Ctrl-C keyboard events.
13872 @node GNAT.Current_Exception (g-curexc.ads)
13873 @section @code{GNAT.Current_Exception} (@file{g-curexc.ads})
13874 @cindex @code{GNAT.Current_Exception} (@file{g-curexc.ads})
13875 @cindex Current exception
13876 @cindex Exception retrieval
13879 Provides access to information on the current exception that has been raised
13880 without the need for using the Ada 95 / Ada 2005 exception choice parameter
13881 specification syntax.
13882 This is particularly useful in simulating typical facilities for
13883 obtaining information about exceptions provided by Ada 83 compilers.
13885 @node GNAT.Debug_Pools (g-debpoo.ads)
13886 @section @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
13887 @cindex @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
13889 @cindex Debug pools
13890 @cindex Memory corruption debugging
13893 Provide a debugging storage pools that helps tracking memory corruption
13894 problems. @xref{The GNAT Debug Pool Facility,,, gnat_ugn,
13895 @value{EDITION} User's Guide}.
13897 @node GNAT.Debug_Utilities (g-debuti.ads)
13898 @section @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
13899 @cindex @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
13903 Provides a few useful utilities for debugging purposes, including conversion
13904 to and from string images of address values. Supports both C and Ada formats
13905 for hexadecimal literals.
13907 @node GNAT.Decode_String (g-decstr.ads)
13908 @section @code{GNAT.Decode_String} (@file{g-decstr.ads})
13909 @cindex @code{GNAT.Decode_String} (@file{g-decstr.ads})
13910 @cindex Decoding strings
13911 @cindex String decoding
13912 @cindex Wide character encoding
13917 A generic package providing routines for decoding wide character and wide wide
13918 character strings encoded as sequences of 8-bit characters using a specified
13919 encoding method. Includes validation routines, and also routines for stepping
13920 to next or previous encoded character in an encoded string.
13921 Useful in conjunction with Unicode character coding. Note there is a
13922 preinstantiation for UTF-8. See next entry.
13924 @node GNAT.Decode_UTF8_String (g-deutst.ads)
13925 @section @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
13926 @cindex @code{GNAT.Decode_UTF8_String} (@file{g-deutst.ads})
13927 @cindex Decoding strings
13928 @cindex Decoding UTF-8 strings
13929 @cindex UTF-8 string decoding
13930 @cindex Wide character decoding
13935 A preinstantiation of GNAT.Decode_Strings for UTF-8 encoding.
13937 @node GNAT.Directory_Operations (g-dirope.ads)
13938 @section @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
13939 @cindex @code{GNAT.Directory_Operations} (@file{g-dirope.ads})
13940 @cindex Directory operations
13943 Provides a set of routines for manipulating directories, including changing
13944 the current directory, making new directories, and scanning the files in a
13947 @node GNAT.Directory_Operations.Iteration (g-diopit.ads)
13948 @section @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
13949 @cindex @code{GNAT.Directory_Operations.Iteration} (@file{g-diopit.ads})
13950 @cindex Directory operations iteration
13953 A child unit of GNAT.Directory_Operations providing additional operations
13954 for iterating through directories.
13956 @node GNAT.Dynamic_HTables (g-dynhta.ads)
13957 @section @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
13958 @cindex @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
13959 @cindex Hash tables
13962 A generic implementation of hash tables that can be used to hash arbitrary
13963 data. Provided in two forms, a simple form with built in hash functions,
13964 and a more complex form in which the hash function is supplied.
13967 This package provides a facility similar to that of @code{GNAT.HTable},
13968 except that this package declares a type that can be used to define
13969 dynamic instances of the hash table, while an instantiation of
13970 @code{GNAT.HTable} creates a single instance of the hash table.
13972 @node GNAT.Dynamic_Tables (g-dyntab.ads)
13973 @section @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
13974 @cindex @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
13975 @cindex Table implementation
13976 @cindex Arrays, extendable
13979 A generic package providing a single dimension array abstraction where the
13980 length of the array can be dynamically modified.
13983 This package provides a facility similar to that of @code{GNAT.Table},
13984 except that this package declares a type that can be used to define
13985 dynamic instances of the table, while an instantiation of
13986 @code{GNAT.Table} creates a single instance of the table type.
13988 @node GNAT.Encode_String (g-encstr.ads)
13989 @section @code{GNAT.Encode_String} (@file{g-encstr.ads})
13990 @cindex @code{GNAT.Encode_String} (@file{g-encstr.ads})
13991 @cindex Encoding strings
13992 @cindex String encoding
13993 @cindex Wide character encoding
13998 A generic package providing routines for encoding wide character and wide
13999 wide character strings as sequences of 8-bit characters using a specified
14000 encoding method. Useful in conjunction with Unicode character coding.
14001 Note there is a preinstantiation for UTF-8. See next entry.
14003 @node GNAT.Encode_UTF8_String (g-enutst.ads)
14004 @section @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14005 @cindex @code{GNAT.Encode_UTF8_String} (@file{g-enutst.ads})
14006 @cindex Encoding strings
14007 @cindex Encoding UTF-8 strings
14008 @cindex UTF-8 string encoding
14009 @cindex Wide character encoding
14014 A preinstantiation of GNAT.Encode_Strings for UTF-8 encoding.
14016 @node GNAT.Exception_Actions (g-excact.ads)
14017 @section @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14018 @cindex @code{GNAT.Exception_Actions} (@file{g-excact.ads})
14019 @cindex Exception actions
14022 Provides callbacks when an exception is raised. Callbacks can be registered
14023 for specific exceptions, or when any exception is raised. This
14024 can be used for instance to force a core dump to ease debugging.
14026 @node GNAT.Exception_Traces (g-exctra.ads)
14027 @section @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14028 @cindex @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
14029 @cindex Exception traces
14033 Provides an interface allowing to control automatic output upon exception
14036 @node GNAT.Exceptions (g-except.ads)
14037 @section @code{GNAT.Exceptions} (@file{g-expect.ads})
14038 @cindex @code{GNAT.Exceptions} (@file{g-expect.ads})
14039 @cindex Exceptions, Pure
14040 @cindex Pure packages, exceptions
14043 Normally it is not possible to raise an exception with
14044 a message from a subprogram in a pure package, since the
14045 necessary types and subprograms are in @code{Ada.Exceptions}
14046 which is not a pure unit. @code{GNAT.Exceptions} provides a
14047 facility for getting around this limitation for a few
14048 predefined exceptions, and for example allow raising
14049 @code{Constraint_Error} with a message from a pure subprogram.
14051 @node GNAT.Expect (g-expect.ads)
14052 @section @code{GNAT.Expect} (@file{g-expect.ads})
14053 @cindex @code{GNAT.Expect} (@file{g-expect.ads})
14056 Provides a set of subprograms similar to what is available
14057 with the standard Tcl Expect tool.
14058 It allows you to easily spawn and communicate with an external process.
14059 You can send commands or inputs to the process, and compare the output
14060 with some expected regular expression. Currently @code{GNAT.Expect}
14061 is implemented on all native GNAT ports except for OpenVMS@.
14062 It is not implemented for cross ports, and in particular is not
14063 implemented for VxWorks or LynxOS@.
14065 @node GNAT.Float_Control (g-flocon.ads)
14066 @section @code{GNAT.Float_Control} (@file{g-flocon.ads})
14067 @cindex @code{GNAT.Float_Control} (@file{g-flocon.ads})
14068 @cindex Floating-Point Processor
14071 Provides an interface for resetting the floating-point processor into the
14072 mode required for correct semantic operation in Ada. Some third party
14073 library calls may cause this mode to be modified, and the Reset procedure
14074 in this package can be used to reestablish the required mode.
14076 @node GNAT.Heap_Sort (g-heasor.ads)
14077 @section @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14078 @cindex @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
14082 Provides a general implementation of heap sort usable for sorting arbitrary
14083 data items. Exchange and comparison procedures are provided by passing
14084 access-to-procedure values. The algorithm used is a modified heap sort
14085 that performs approximately N*log(N) comparisons in the worst case.
14087 @node GNAT.Heap_Sort_A (g-hesora.ads)
14088 @section @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14089 @cindex @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
14093 Provides a general implementation of heap sort usable for sorting arbitrary
14094 data items. Move and comparison procedures are provided by passing
14095 access-to-procedure values. The algorithm used is a modified heap sort
14096 that performs approximately N*log(N) comparisons in the worst case.
14097 This differs from @code{GNAT.Heap_Sort} in having a less convenient
14098 interface, but may be slightly more efficient.
14100 @node GNAT.Heap_Sort_G (g-hesorg.ads)
14101 @section @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14102 @cindex @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
14106 Similar to @code{Heap_Sort_A} except that the move and sorting procedures
14107 are provided as generic parameters, this improves efficiency, especially
14108 if the procedures can be inlined, at the expense of duplicating code for
14109 multiple instantiations.
14111 @node GNAT.HTable (g-htable.ads)
14112 @section @code{GNAT.HTable} (@file{g-htable.ads})
14113 @cindex @code{GNAT.HTable} (@file{g-htable.ads})
14114 @cindex Hash tables
14117 A generic implementation of hash tables that can be used to hash arbitrary
14118 data. Provides two approaches, one a simple static approach, and the other
14119 allowing arbitrary dynamic hash tables.
14121 @node GNAT.IO (g-io.ads)
14122 @section @code{GNAT.IO} (@file{g-io.ads})
14123 @cindex @code{GNAT.IO} (@file{g-io.ads})
14125 @cindex Input/Output facilities
14128 A simple preelaborable input-output package that provides a subset of
14129 simple Text_IO functions for reading characters and strings from
14130 Standard_Input, and writing characters, strings and integers to either
14131 Standard_Output or Standard_Error.
14133 @node GNAT.IO_Aux (g-io_aux.ads)
14134 @section @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14135 @cindex @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
14137 @cindex Input/Output facilities
14139 Provides some auxiliary functions for use with Text_IO, including a test
14140 for whether a file exists, and functions for reading a line of text.
14142 @node GNAT.Lock_Files (g-locfil.ads)
14143 @section @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14144 @cindex @code{GNAT.Lock_Files} (@file{g-locfil.ads})
14145 @cindex File locking
14146 @cindex Locking using files
14149 Provides a general interface for using files as locks. Can be used for
14150 providing program level synchronization.
14152 @node GNAT.MD5 (g-md5.ads)
14153 @section @code{GNAT.MD5} (@file{g-md5.ads})
14154 @cindex @code{GNAT.MD5} (@file{g-md5.ads})
14155 @cindex Message Digest MD5
14158 Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
14160 @node GNAT.Memory_Dump (g-memdum.ads)
14161 @section @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14162 @cindex @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
14163 @cindex Dump Memory
14166 Provides a convenient routine for dumping raw memory to either the
14167 standard output or standard error files. Uses GNAT.IO for actual
14170 @node GNAT.Most_Recent_Exception (g-moreex.ads)
14171 @section @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14172 @cindex @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
14173 @cindex Exception, obtaining most recent
14176 Provides access to the most recently raised exception. Can be used for
14177 various logging purposes, including duplicating functionality of some
14178 Ada 83 implementation dependent extensions.
14180 @node GNAT.OS_Lib (g-os_lib.ads)
14181 @section @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14182 @cindex @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
14183 @cindex Operating System interface
14184 @cindex Spawn capability
14187 Provides a range of target independent operating system interface functions,
14188 including time/date management, file operations, subprocess management,
14189 including a portable spawn procedure, and access to environment variables
14190 and error return codes.
14192 @node GNAT.Perfect_Hash_Generators (g-pehage.ads)
14193 @section @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14194 @cindex @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
14195 @cindex Hash functions
14198 Provides a generator of static minimal perfect hash functions. No
14199 collisions occur and each item can be retrieved from the table in one
14200 probe (perfect property). The hash table size corresponds to the exact
14201 size of the key set and no larger (minimal property). The key set has to
14202 be know in advance (static property). The hash functions are also order
14203 preserving. If w2 is inserted after w1 in the generator, their
14204 hashcode are in the same order. These hashing functions are very
14205 convenient for use with realtime applications.
14207 @node GNAT.Random_Numbers (g-rannum.ads)
14208 @section @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14209 @cindex @code{GNAT.Random_Numbers} (@file{g-rannum.ads})
14210 @cindex Random number generation
14213 Provides random number capabilities which extend those available in the
14214 standard Ada library and are more convenient to use.
14216 @node GNAT.Regexp (g-regexp.ads)
14217 @section @code{GNAT.Regexp} (@file{g-regexp.ads})
14218 @cindex @code{GNAT.Regexp} (@file{g-regexp.ads})
14219 @cindex Regular expressions
14220 @cindex Pattern matching
14223 A simple implementation of regular expressions, using a subset of regular
14224 expression syntax copied from familiar Unix style utilities. This is the
14225 simples of the three pattern matching packages provided, and is particularly
14226 suitable for ``file globbing'' applications.
14228 @node GNAT.Registry (g-regist.ads)
14229 @section @code{GNAT.Registry} (@file{g-regist.ads})
14230 @cindex @code{GNAT.Registry} (@file{g-regist.ads})
14231 @cindex Windows Registry
14234 This is a high level binding to the Windows registry. It is possible to
14235 do simple things like reading a key value, creating a new key. For full
14236 registry API, but at a lower level of abstraction, refer to the Win32.Winreg
14237 package provided with the Win32Ada binding
14239 @node GNAT.Regpat (g-regpat.ads)
14240 @section @code{GNAT.Regpat} (@file{g-regpat.ads})
14241 @cindex @code{GNAT.Regpat} (@file{g-regpat.ads})
14242 @cindex Regular expressions
14243 @cindex Pattern matching
14246 A complete implementation of Unix-style regular expression matching, copied
14247 from the original V7 style regular expression library written in C by
14248 Henry Spencer (and binary compatible with this C library).
14250 @node GNAT.Secondary_Stack_Info (g-sestin.ads)
14251 @section @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14252 @cindex @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
14253 @cindex Secondary Stack Info
14256 Provide the capability to query the high water mark of the current task's
14259 @node GNAT.Semaphores (g-semaph.ads)
14260 @section @code{GNAT.Semaphores} (@file{g-semaph.ads})
14261 @cindex @code{GNAT.Semaphores} (@file{g-semaph.ads})
14265 Provides classic counting and binary semaphores using protected types.
14267 @node GNAT.Serial_Communications (g-sercom.ads)
14268 @section @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14269 @cindex @code{GNAT.Serial_Communications} (@file{g-sercom.ads})
14270 @cindex Serial_Communications
14273 Provides a simple interface to send and receive data over a serial
14274 port. This is only supported on GNU/Linux and Windows.
14276 @node GNAT.SHA1 (g-sha1.ads)
14277 @section @code{GNAT.SHA1} (@file{g-sha1.ads})
14278 @cindex @code{GNAT.SHA1} (@file{g-sha1.ads})
14279 @cindex Secure Hash Algorithm SHA-1
14282 Implements the SHA-1 Secure Hash Algorithm as described in RFC 3174.
14284 @node GNAT.Signals (g-signal.ads)
14285 @section @code{GNAT.Signals} (@file{g-signal.ads})
14286 @cindex @code{GNAT.Signals} (@file{g-signal.ads})
14290 Provides the ability to manipulate the blocked status of signals on supported
14293 @node GNAT.Sockets (g-socket.ads)
14294 @section @code{GNAT.Sockets} (@file{g-socket.ads})
14295 @cindex @code{GNAT.Sockets} (@file{g-socket.ads})
14299 A high level and portable interface to develop sockets based applications.
14300 This package is based on the sockets thin binding found in
14301 @code{GNAT.Sockets.Thin}. Currently @code{GNAT.Sockets} is implemented
14302 on all native GNAT ports except for OpenVMS@. It is not implemented
14303 for the LynxOS@ cross port.
14305 @node GNAT.Source_Info (g-souinf.ads)
14306 @section @code{GNAT.Source_Info} (@file{g-souinf.ads})
14307 @cindex @code{GNAT.Source_Info} (@file{g-souinf.ads})
14308 @cindex Source Information
14311 Provides subprograms that give access to source code information known at
14312 compile time, such as the current file name and line number.
14314 @node GNAT.Spelling_Checker (g-speche.ads)
14315 @section @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14316 @cindex @code{GNAT.Spelling_Checker} (@file{g-speche.ads})
14317 @cindex Spell checking
14320 Provides a function for determining whether one string is a plausible
14321 near misspelling of another string.
14323 @node GNAT.Spelling_Checker_Generic (g-spchge.ads)
14324 @section @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14325 @cindex @code{GNAT.Spelling_Checker_Generic} (@file{g-spchge.ads})
14326 @cindex Spell checking
14329 Provides a generic function that can be instantiated with a string type for
14330 determining whether one string is a plausible near misspelling of another
14333 @node GNAT.Spitbol.Patterns (g-spipat.ads)
14334 @section @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14335 @cindex @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
14336 @cindex SPITBOL pattern matching
14337 @cindex Pattern matching
14340 A complete implementation of SNOBOL4 style pattern matching. This is the
14341 most elaborate of the pattern matching packages provided. It fully duplicates
14342 the SNOBOL4 dynamic pattern construction and matching capabilities, using the
14343 efficient algorithm developed by Robert Dewar for the SPITBOL system.
14345 @node GNAT.Spitbol (g-spitbo.ads)
14346 @section @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14347 @cindex @code{GNAT.Spitbol} (@file{g-spitbo.ads})
14348 @cindex SPITBOL interface
14351 The top level package of the collection of SPITBOL-style functionality, this
14352 package provides basic SNOBOL4 string manipulation functions, such as
14353 Pad, Reverse, Trim, Substr capability, as well as a generic table function
14354 useful for constructing arbitrary mappings from strings in the style of
14355 the SNOBOL4 TABLE function.
14357 @node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
14358 @section @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14359 @cindex @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
14360 @cindex Sets of strings
14361 @cindex SPITBOL Tables
14364 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14365 for type @code{Standard.Boolean}, giving an implementation of sets of
14368 @node GNAT.Spitbol.Table_Integer (g-sptain.ads)
14369 @section @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14370 @cindex @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
14371 @cindex Integer maps
14373 @cindex SPITBOL Tables
14376 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
14377 for type @code{Standard.Integer}, giving an implementation of maps
14378 from string to integer values.
14380 @node GNAT.Spitbol.Table_VString (g-sptavs.ads)
14381 @section @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14382 @cindex @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
14383 @cindex String maps
14385 @cindex SPITBOL Tables
14388 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table} for
14389 a variable length string type, giving an implementation of general
14390 maps from strings to strings.
14392 @node GNAT.Strings (g-string.ads)
14393 @section @code{GNAT.Strings} (@file{g-string.ads})
14394 @cindex @code{GNAT.Strings} (@file{g-string.ads})
14397 Common String access types and related subprograms. Basically it
14398 defines a string access and an array of string access types.
14400 @node GNAT.String_Split (g-strspl.ads)
14401 @section @code{GNAT.String_Split} (@file{g-strspl.ads})
14402 @cindex @code{GNAT.String_Split} (@file{g-strspl.ads})
14403 @cindex String splitter
14406 Useful string manipulation routines: given a set of separators, split
14407 a string wherever the separators appear, and provide direct access
14408 to the resulting slices. This package is instantiated from
14409 @code{GNAT.Array_Split}.
14411 @node GNAT.Table (g-table.ads)
14412 @section @code{GNAT.Table} (@file{g-table.ads})
14413 @cindex @code{GNAT.Table} (@file{g-table.ads})
14414 @cindex Table implementation
14415 @cindex Arrays, extendable
14418 A generic package providing a single dimension array abstraction where the
14419 length of the array can be dynamically modified.
14422 This package provides a facility similar to that of @code{GNAT.Dynamic_Tables},
14423 except that this package declares a single instance of the table type,
14424 while an instantiation of @code{GNAT.Dynamic_Tables} creates a type that can be
14425 used to define dynamic instances of the table.
14427 @node GNAT.Task_Lock (g-tasloc.ads)
14428 @section @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14429 @cindex @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
14430 @cindex Task synchronization
14431 @cindex Task locking
14435 A very simple facility for locking and unlocking sections of code using a
14436 single global task lock. Appropriate for use in situations where contention
14437 between tasks is very rarely expected.
14439 @node GNAT.Time_Stamp (g-timsta.ads)
14440 @section @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14441 @cindex @code{GNAT.Time_Stamp} (@file{g-timsta.ads})
14443 @cindex Current time
14446 Provides a simple function that returns a string YYYY-MM-DD HH:MM:SS.SS that
14447 represents the current date and time in ISO 8601 format. This is a very simple
14448 routine with minimal code and there are no dependencies on any other unit.
14450 @node GNAT.Threads (g-thread.ads)
14451 @section @code{GNAT.Threads} (@file{g-thread.ads})
14452 @cindex @code{GNAT.Threads} (@file{g-thread.ads})
14453 @cindex Foreign threads
14454 @cindex Threads, foreign
14457 Provides facilities for dealing with foreign threads which need to be known
14458 by the GNAT run-time system. Consult the documentation of this package for
14459 further details if your program has threads that are created by a non-Ada
14460 environment which then accesses Ada code.
14462 @node GNAT.Traceback (g-traceb.ads)
14463 @section @code{GNAT.Traceback} (@file{g-traceb.ads})
14464 @cindex @code{GNAT.Traceback} (@file{g-traceb.ads})
14465 @cindex Trace back facilities
14468 Provides a facility for obtaining non-symbolic traceback information, useful
14469 in various debugging situations.
14471 @node GNAT.Traceback.Symbolic (g-trasym.ads)
14472 @section @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14473 @cindex @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
14474 @cindex Trace back facilities
14476 @node GNAT.UTF_32 (g-utf_32.ads)
14477 @section @code{GNAT.UTF_32} (@file{g-table.ads})
14478 @cindex @code{GNAT.UTF_32} (@file{g-table.ads})
14479 @cindex Wide character codes
14482 This is a package intended to be used in conjunction with the
14483 @code{Wide_Character} type in Ada 95 and the
14484 @code{Wide_Wide_Character} type in Ada 2005 (available
14485 in @code{GNAT} in Ada 2005 mode). This package contains
14486 Unicode categorization routines, as well as lexical
14487 categorization routines corresponding to the Ada 2005
14488 lexical rules for identifiers and strings, and also a
14489 lower case to upper case fold routine corresponding to
14490 the Ada 2005 rules for identifier equivalence.
14492 @node GNAT.UTF_32_Spelling_Checker (g-u3spch.ads)
14493 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14494 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-u3spch.ads})
14495 @cindex Spell checking
14498 Provides a function for determining whether one wide wide string is a plausible
14499 near misspelling of another wide wide string, where the strings are represented
14500 using the UTF_32_String type defined in System.Wch_Cnv.
14502 @node GNAT.Wide_Spelling_Checker (g-wispch.ads)
14503 @section @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14504 @cindex @code{GNAT.Wide_Spelling_Checker} (@file{g-wispch.ads})
14505 @cindex Spell checking
14508 Provides a function for determining whether one wide string is a plausible
14509 near misspelling of another wide string.
14511 @node GNAT.Wide_String_Split (g-wistsp.ads)
14512 @section @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14513 @cindex @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
14514 @cindex Wide_String splitter
14517 Useful wide string manipulation routines: given a set of separators, split
14518 a wide string wherever the separators appear, and provide direct access
14519 to the resulting slices. This package is instantiated from
14520 @code{GNAT.Array_Split}.
14522 @node GNAT.Wide_Wide_Spelling_Checker (g-zspche.ads)
14523 @section @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14524 @cindex @code{GNAT.Wide_Wide_Spelling_Checker} (@file{g-zspche.ads})
14525 @cindex Spell checking
14528 Provides a function for determining whether one wide wide string is a plausible
14529 near misspelling of another wide wide string.
14531 @node GNAT.Wide_Wide_String_Split (g-zistsp.ads)
14532 @section @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14533 @cindex @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
14534 @cindex Wide_Wide_String splitter
14537 Useful wide wide string manipulation routines: given a set of separators, split
14538 a wide wide string wherever the separators appear, and provide direct access
14539 to the resulting slices. This package is instantiated from
14540 @code{GNAT.Array_Split}.
14542 @node Interfaces.C.Extensions (i-cexten.ads)
14543 @section @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14544 @cindex @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
14547 This package contains additional C-related definitions, intended
14548 for use with either manually or automatically generated bindings
14551 @node Interfaces.C.Streams (i-cstrea.ads)
14552 @section @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14553 @cindex @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
14554 @cindex C streams, interfacing
14557 This package is a binding for the most commonly used operations
14560 @node Interfaces.CPP (i-cpp.ads)
14561 @section @code{Interfaces.CPP} (@file{i-cpp.ads})
14562 @cindex @code{Interfaces.CPP} (@file{i-cpp.ads})
14563 @cindex C++ interfacing
14564 @cindex Interfacing, to C++
14567 This package provides facilities for use in interfacing to C++. It
14568 is primarily intended to be used in connection with automated tools
14569 for the generation of C++ interfaces.
14571 @node Interfaces.Packed_Decimal (i-pacdec.ads)
14572 @section @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14573 @cindex @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
14574 @cindex IBM Packed Format
14575 @cindex Packed Decimal
14578 This package provides a set of routines for conversions to and
14579 from a packed decimal format compatible with that used on IBM
14582 @node Interfaces.VxWorks (i-vxwork.ads)
14583 @section @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14584 @cindex @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
14585 @cindex Interfacing to VxWorks
14586 @cindex VxWorks, interfacing
14589 This package provides a limited binding to the VxWorks API.
14590 In particular, it interfaces with the
14591 VxWorks hardware interrupt facilities.
14593 @node Interfaces.VxWorks.IO (i-vxwoio.ads)
14594 @section @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14595 @cindex @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
14596 @cindex Interfacing to VxWorks' I/O
14597 @cindex VxWorks, I/O interfacing
14598 @cindex VxWorks, Get_Immediate
14599 @cindex Get_Immediate, VxWorks
14602 This package provides a binding to the ioctl (IO/Control)
14603 function of VxWorks, defining a set of option values and
14604 function codes. A particular use of this package is
14605 to enable the use of Get_Immediate under VxWorks.
14607 @node System.Address_Image (s-addima.ads)
14608 @section @code{System.Address_Image} (@file{s-addima.ads})
14609 @cindex @code{System.Address_Image} (@file{s-addima.ads})
14610 @cindex Address image
14611 @cindex Image, of an address
14614 This function provides a useful debugging
14615 function that gives an (implementation dependent)
14616 string which identifies an address.
14618 @node System.Assertions (s-assert.ads)
14619 @section @code{System.Assertions} (@file{s-assert.ads})
14620 @cindex @code{System.Assertions} (@file{s-assert.ads})
14622 @cindex Assert_Failure, exception
14625 This package provides the declaration of the exception raised
14626 by an run-time assertion failure, as well as the routine that
14627 is used internally to raise this assertion.
14629 @node System.Memory (s-memory.ads)
14630 @section @code{System.Memory} (@file{s-memory.ads})
14631 @cindex @code{System.Memory} (@file{s-memory.ads})
14632 @cindex Memory allocation
14635 This package provides the interface to the low level routines used
14636 by the generated code for allocation and freeing storage for the
14637 default storage pool (analogous to the C routines malloc and free.
14638 It also provides a reallocation interface analogous to the C routine
14639 realloc. The body of this unit may be modified to provide alternative
14640 allocation mechanisms for the default pool, and in addition, direct
14641 calls to this unit may be made for low level allocation uses (for
14642 example see the body of @code{GNAT.Tables}).
14644 @node System.Partition_Interface (s-parint.ads)
14645 @section @code{System.Partition_Interface} (@file{s-parint.ads})
14646 @cindex @code{System.Partition_Interface} (@file{s-parint.ads})
14647 @cindex Partition interfacing functions
14650 This package provides facilities for partition interfacing. It
14651 is used primarily in a distribution context when using Annex E
14654 @node System.Pool_Global (s-pooglo.ads)
14655 @section @code{System.Pool_Global} (@file{s-pooglo.ads})
14656 @cindex @code{System.Pool_Global} (@file{s-pooglo.ads})
14657 @cindex Storage pool, global
14658 @cindex Global storage pool
14661 This package provides a storage pool that is equivalent to the default
14662 storage pool used for access types for which no pool is specifically
14663 declared. It uses malloc/free to allocate/free and does not attempt to
14664 do any automatic reclamation.
14666 @node System.Pool_Local (s-pooloc.ads)
14667 @section @code{System.Pool_Local} (@file{s-pooloc.ads})
14668 @cindex @code{System.Pool_Local} (@file{s-pooloc.ads})
14669 @cindex Storage pool, local
14670 @cindex Local storage pool
14673 This package provides a storage pool that is intended for use with locally
14674 defined access types. It uses malloc/free for allocate/free, and maintains
14675 a list of allocated blocks, so that all storage allocated for the pool can
14676 be freed automatically when the pool is finalized.
14678 @node System.Restrictions (s-restri.ads)
14679 @section @code{System.Restrictions} (@file{s-restri.ads})
14680 @cindex @code{System.Restrictions} (@file{s-restri.ads})
14681 @cindex Run-time restrictions access
14684 This package provides facilities for accessing at run time
14685 the status of restrictions specified at compile time for
14686 the partition. Information is available both with regard
14687 to actual restrictions specified, and with regard to
14688 compiler determined information on which restrictions
14689 are violated by one or more packages in the partition.
14691 @node System.Rident (s-rident.ads)
14692 @section @code{System.Rident} (@file{s-rident.ads})
14693 @cindex @code{System.Rident} (@file{s-rident.ads})
14694 @cindex Restrictions definitions
14697 This package provides definitions of the restrictions
14698 identifiers supported by GNAT, and also the format of
14699 the restrictions provided in package System.Restrictions.
14700 It is not normally necessary to @code{with} this generic package
14701 since the necessary instantiation is included in
14702 package System.Restrictions.
14704 @node System.Task_Info (s-tasinf.ads)
14705 @section @code{System.Task_Info} (@file{s-tasinf.ads})
14706 @cindex @code{System.Task_Info} (@file{s-tasinf.ads})
14707 @cindex Task_Info pragma
14710 This package provides target dependent functionality that is used
14711 to support the @code{Task_Info} pragma
14713 @node System.Wch_Cnv (s-wchcnv.ads)
14714 @section @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14715 @cindex @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
14716 @cindex Wide Character, Representation
14717 @cindex Wide String, Conversion
14718 @cindex Representation of wide characters
14721 This package provides routines for converting between
14722 wide and wide wide characters and a representation as a value of type
14723 @code{Standard.String}, using a specified wide character
14724 encoding method. It uses definitions in
14725 package @code{System.Wch_Con}.
14727 @node System.Wch_Con (s-wchcon.ads)
14728 @section @code{System.Wch_Con} (@file{s-wchcon.ads})
14729 @cindex @code{System.Wch_Con} (@file{s-wchcon.ads})
14732 This package provides definitions and descriptions of
14733 the various methods used for encoding wide characters
14734 in ordinary strings. These definitions are used by
14735 the package @code{System.Wch_Cnv}.
14737 @node Interfacing to Other Languages
14738 @chapter Interfacing to Other Languages
14740 The facilities in annex B of the Ada Reference Manual are fully
14741 implemented in GNAT, and in addition, a full interface to C++ is
14745 * Interfacing to C::
14746 * Interfacing to C++::
14747 * Interfacing to COBOL::
14748 * Interfacing to Fortran::
14749 * Interfacing to non-GNAT Ada code::
14752 @node Interfacing to C
14753 @section Interfacing to C
14756 Interfacing to C with GNAT can use one of two approaches:
14760 The types in the package @code{Interfaces.C} may be used.
14762 Standard Ada types may be used directly. This may be less portable to
14763 other compilers, but will work on all GNAT compilers, which guarantee
14764 correspondence between the C and Ada types.
14768 Pragma @code{Convention C} may be applied to Ada types, but mostly has no
14769 effect, since this is the default. The following table shows the
14770 correspondence between Ada scalar types and the corresponding C types.
14775 @item Short_Integer
14777 @item Short_Short_Integer
14781 @item Long_Long_Integer
14789 @item Long_Long_Float
14790 This is the longest floating-point type supported by the hardware.
14794 Additionally, there are the following general correspondences between Ada
14798 Ada enumeration types map to C enumeration types directly if pragma
14799 @code{Convention C} is specified, which causes them to have int
14800 length. Without pragma @code{Convention C}, Ada enumeration types map to
14801 8, 16, or 32 bits (i.e.@: C types @code{signed char}, @code{short},
14802 @code{int}, respectively) depending on the number of values passed.
14803 This is the only case in which pragma @code{Convention C} affects the
14804 representation of an Ada type.
14807 Ada access types map to C pointers, except for the case of pointers to
14808 unconstrained types in Ada, which have no direct C equivalent.
14811 Ada arrays map directly to C arrays.
14814 Ada records map directly to C structures.
14817 Packed Ada records map to C structures where all members are bit fields
14818 of the length corresponding to the @code{@var{type}'Size} value in Ada.
14821 @node Interfacing to C++
14822 @section Interfacing to C++
14825 The interface to C++ makes use of the following pragmas, which are
14826 primarily intended to be constructed automatically using a binding generator
14827 tool, although it is possible to construct them by hand. No suitable binding
14828 generator tool is supplied with GNAT though.
14830 Using these pragmas it is possible to achieve complete
14831 inter-operability between Ada tagged types and C++ class definitions.
14832 See @ref{Implementation Defined Pragmas}, for more details.
14835 @item pragma CPP_Class ([Entity =>] @var{LOCAL_NAME})
14836 The argument denotes an entity in the current declarative region that is
14837 declared as a tagged or untagged record type. It indicates that the type
14838 corresponds to an externally declared C++ class type, and is to be laid
14839 out the same way that C++ would lay out the type.
14841 Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
14842 for backward compatibility but its functionality is available
14843 using pragma @code{Import} with @code{Convention} = @code{CPP}.
14845 @item pragma CPP_Constructor ([Entity =>] @var{LOCAL_NAME})
14846 This pragma identifies an imported function (imported in the usual way
14847 with pragma @code{Import}) as corresponding to a C++ constructor.
14850 @node Interfacing to COBOL
14851 @section Interfacing to COBOL
14854 Interfacing to COBOL is achieved as described in section B.4 of
14855 the Ada Reference Manual.
14857 @node Interfacing to Fortran
14858 @section Interfacing to Fortran
14861 Interfacing to Fortran is achieved as described in section B.5 of the
14862 Ada Reference Manual. The pragma @code{Convention Fortran}, applied to a
14863 multi-dimensional array causes the array to be stored in column-major
14864 order as required for convenient interface to Fortran.
14866 @node Interfacing to non-GNAT Ada code
14867 @section Interfacing to non-GNAT Ada code
14869 It is possible to specify the convention @code{Ada} in a pragma
14870 @code{Import} or pragma @code{Export}. However this refers to
14871 the calling conventions used by GNAT, which may or may not be
14872 similar enough to those used by some other Ada 83 / Ada 95 / Ada 2005
14873 compiler to allow interoperation.
14875 If arguments types are kept simple, and if the foreign compiler generally
14876 follows system calling conventions, then it may be possible to integrate
14877 files compiled by other Ada compilers, provided that the elaboration
14878 issues are adequately addressed (for example by eliminating the
14879 need for any load time elaboration).
14881 In particular, GNAT running on VMS is designed to
14882 be highly compatible with the DEC Ada 83 compiler, so this is one
14883 case in which it is possible to import foreign units of this type,
14884 provided that the data items passed are restricted to simple scalar
14885 values or simple record types without variants, or simple array
14886 types with fixed bounds.
14888 @node Specialized Needs Annexes
14889 @chapter Specialized Needs Annexes
14892 Ada 95 and Ada 2005 define a number of Specialized Needs Annexes, which are not
14893 required in all implementations. However, as described in this chapter,
14894 GNAT implements all of these annexes:
14897 @item Systems Programming (Annex C)
14898 The Systems Programming Annex is fully implemented.
14900 @item Real-Time Systems (Annex D)
14901 The Real-Time Systems Annex is fully implemented.
14903 @item Distributed Systems (Annex E)
14904 Stub generation is fully implemented in the GNAT compiler. In addition,
14905 a complete compatible PCS is available as part of the GLADE system,
14906 a separate product. When the two
14907 products are used in conjunction, this annex is fully implemented.
14909 @item Information Systems (Annex F)
14910 The Information Systems annex is fully implemented.
14912 @item Numerics (Annex G)
14913 The Numerics Annex is fully implemented.
14915 @item Safety and Security / High-Integrity Systems (Annex H)
14916 The Safety and Security Annex (termed the High-Integrity Systems Annex
14917 in Ada 2005) is fully implemented.
14920 @node Implementation of Specific Ada Features
14921 @chapter Implementation of Specific Ada Features
14924 This chapter describes the GNAT implementation of several Ada language
14928 * Machine Code Insertions::
14929 * GNAT Implementation of Tasking::
14930 * GNAT Implementation of Shared Passive Packages::
14931 * Code Generation for Array Aggregates::
14932 * The Size of Discriminated Records with Default Discriminants::
14933 * Strict Conformance to the Ada Reference Manual::
14936 @node Machine Code Insertions
14937 @section Machine Code Insertions
14938 @cindex Machine Code insertions
14941 Package @code{Machine_Code} provides machine code support as described
14942 in the Ada Reference Manual in two separate forms:
14945 Machine code statements, consisting of qualified expressions that
14946 fit the requirements of RM section 13.8.
14948 An intrinsic callable procedure, providing an alternative mechanism of
14949 including machine instructions in a subprogram.
14953 The two features are similar, and both are closely related to the mechanism
14954 provided by the asm instruction in the GNU C compiler. Full understanding
14955 and use of the facilities in this package requires understanding the asm
14956 instruction, see @ref{Extended Asm,, Assembler Instructions with C Expression
14957 Operands, gcc, Using the GNU Compiler Collection (GCC)}.
14959 Calls to the function @code{Asm} and the procedure @code{Asm} have identical
14960 semantic restrictions and effects as described below. Both are provided so
14961 that the procedure call can be used as a statement, and the function call
14962 can be used to form a code_statement.
14964 The first example given in the GCC documentation is the C @code{asm}
14967 asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
14971 The equivalent can be written for GNAT as:
14973 @smallexample @c ada
14974 Asm ("fsinx %1 %0",
14975 My_Float'Asm_Output ("=f", result),
14976 My_Float'Asm_Input ("f", angle));
14980 The first argument to @code{Asm} is the assembler template, and is
14981 identical to what is used in GNU C@. This string must be a static
14982 expression. The second argument is the output operand list. It is
14983 either a single @code{Asm_Output} attribute reference, or a list of such
14984 references enclosed in parentheses (technically an array aggregate of
14987 The @code{Asm_Output} attribute denotes a function that takes two
14988 parameters. The first is a string, the second is the name of a variable
14989 of the type designated by the attribute prefix. The first (string)
14990 argument is required to be a static expression and designates the
14991 constraint for the parameter (e.g.@: what kind of register is
14992 required). The second argument is the variable to be updated with the
14993 result. The possible values for constraint are the same as those used in
14994 the RTL, and are dependent on the configuration file used to build the
14995 GCC back end. If there are no output operands, then this argument may
14996 either be omitted, or explicitly given as @code{No_Output_Operands}.
14998 The second argument of @code{@var{my_float}'Asm_Output} functions as
14999 though it were an @code{out} parameter, which is a little curious, but
15000 all names have the form of expressions, so there is no syntactic
15001 irregularity, even though normally functions would not be permitted
15002 @code{out} parameters. The third argument is the list of input
15003 operands. It is either a single @code{Asm_Input} attribute reference, or
15004 a list of such references enclosed in parentheses (technically an array
15005 aggregate of such references).
15007 The @code{Asm_Input} attribute denotes a function that takes two
15008 parameters. The first is a string, the second is an expression of the
15009 type designated by the prefix. The first (string) argument is required
15010 to be a static expression, and is the constraint for the parameter,
15011 (e.g.@: what kind of register is required). The second argument is the
15012 value to be used as the input argument. The possible values for the
15013 constant are the same as those used in the RTL, and are dependent on
15014 the configuration file used to built the GCC back end.
15016 If there are no input operands, this argument may either be omitted, or
15017 explicitly given as @code{No_Input_Operands}. The fourth argument, not
15018 present in the above example, is a list of register names, called the
15019 @dfn{clobber} argument. This argument, if given, must be a static string
15020 expression, and is a space or comma separated list of names of registers
15021 that must be considered destroyed as a result of the @code{Asm} call. If
15022 this argument is the null string (the default value), then the code
15023 generator assumes that no additional registers are destroyed.
15025 The fifth argument, not present in the above example, called the
15026 @dfn{volatile} argument, is by default @code{False}. It can be set to
15027 the literal value @code{True} to indicate to the code generator that all
15028 optimizations with respect to the instruction specified should be
15029 suppressed, and that in particular, for an instruction that has outputs,
15030 the instruction will still be generated, even if none of the outputs are
15031 used. @xref{Extended Asm,, Assembler Instructions with C Expression Operands,
15032 gcc, Using the GNU Compiler Collection (GCC)}, for the full description.
15033 Generally it is strongly advisable to use Volatile for any ASM statement
15034 that is missing either input or output operands, or when two or more ASM
15035 statements appear in sequence, to avoid unwanted optimizations. A warning
15036 is generated if this advice is not followed.
15038 The @code{Asm} subprograms may be used in two ways. First the procedure
15039 forms can be used anywhere a procedure call would be valid, and
15040 correspond to what the RM calls ``intrinsic'' routines. Such calls can
15041 be used to intersperse machine instructions with other Ada statements.
15042 Second, the function forms, which return a dummy value of the limited
15043 private type @code{Asm_Insn}, can be used in code statements, and indeed
15044 this is the only context where such calls are allowed. Code statements
15045 appear as aggregates of the form:
15047 @smallexample @c ada
15048 Asm_Insn'(Asm (@dots{}));
15049 Asm_Insn'(Asm_Volatile (@dots{}));
15053 In accordance with RM rules, such code statements are allowed only
15054 within subprograms whose entire body consists of such statements. It is
15055 not permissible to intermix such statements with other Ada statements.
15057 Typically the form using intrinsic procedure calls is more convenient
15058 and more flexible. The code statement form is provided to meet the RM
15059 suggestion that such a facility should be made available. The following
15060 is the exact syntax of the call to @code{Asm}. As usual, if named notation
15061 is used, the arguments may be given in arbitrary order, following the
15062 normal rules for use of positional and named arguments)
15066 [Template =>] static_string_EXPRESSION
15067 [,[Outputs =>] OUTPUT_OPERAND_LIST ]
15068 [,[Inputs =>] INPUT_OPERAND_LIST ]
15069 [,[Clobber =>] static_string_EXPRESSION ]
15070 [,[Volatile =>] static_boolean_EXPRESSION] )
15072 OUTPUT_OPERAND_LIST ::=
15073 [PREFIX.]No_Output_Operands
15074 | OUTPUT_OPERAND_ATTRIBUTE
15075 | (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
15077 OUTPUT_OPERAND_ATTRIBUTE ::=
15078 SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
15080 INPUT_OPERAND_LIST ::=
15081 [PREFIX.]No_Input_Operands
15082 | INPUT_OPERAND_ATTRIBUTE
15083 | (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
15085 INPUT_OPERAND_ATTRIBUTE ::=
15086 SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
15090 The identifiers @code{No_Input_Operands} and @code{No_Output_Operands}
15091 are declared in the package @code{Machine_Code} and must be referenced
15092 according to normal visibility rules. In particular if there is no
15093 @code{use} clause for this package, then appropriate package name
15094 qualification is required.
15096 @node GNAT Implementation of Tasking
15097 @section GNAT Implementation of Tasking
15100 This chapter outlines the basic GNAT approach to tasking (in particular,
15101 a multi-layered library for portability) and discusses issues related
15102 to compliance with the Real-Time Systems Annex.
15105 * Mapping Ada Tasks onto the Underlying Kernel Threads::
15106 * Ensuring Compliance with the Real-Time Annex::
15109 @node Mapping Ada Tasks onto the Underlying Kernel Threads
15110 @subsection Mapping Ada Tasks onto the Underlying Kernel Threads
15113 GNAT's run-time support comprises two layers:
15116 @item GNARL (GNAT Run-time Layer)
15117 @item GNULL (GNAT Low-level Library)
15121 In GNAT, Ada's tasking services rely on a platform and OS independent
15122 layer known as GNARL@. This code is responsible for implementing the
15123 correct semantics of Ada's task creation, rendezvous, protected
15126 GNARL decomposes Ada's tasking semantics into simpler lower level
15127 operations such as create a thread, set the priority of a thread,
15128 yield, create a lock, lock/unlock, etc. The spec for these low-level
15129 operations constitutes GNULLI, the GNULL Interface. This interface is
15130 directly inspired from the POSIX real-time API@.
15132 If the underlying executive or OS implements the POSIX standard
15133 faithfully, the GNULL Interface maps as is to the services offered by
15134 the underlying kernel. Otherwise, some target dependent glue code maps
15135 the services offered by the underlying kernel to the semantics expected
15138 Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
15139 key point is that each Ada task is mapped on a thread in the underlying
15140 kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
15142 In addition Ada task priorities map onto the underlying thread priorities.
15143 Mapping Ada tasks onto the underlying kernel threads has several advantages:
15147 The underlying scheduler is used to schedule the Ada tasks. This
15148 makes Ada tasks as efficient as kernel threads from a scheduling
15152 Interaction with code written in C containing threads is eased
15153 since at the lowest level Ada tasks and C threads map onto the same
15154 underlying kernel concept.
15157 When an Ada task is blocked during I/O the remaining Ada tasks are
15161 On multiprocessor systems Ada tasks can execute in parallel.
15165 Some threads libraries offer a mechanism to fork a new process, with the
15166 child process duplicating the threads from the parent.
15168 support this functionality when the parent contains more than one task.
15169 @cindex Forking a new process
15171 @node Ensuring Compliance with the Real-Time Annex
15172 @subsection Ensuring Compliance with the Real-Time Annex
15173 @cindex Real-Time Systems Annex compliance
15176 Although mapping Ada tasks onto
15177 the underlying threads has significant advantages, it does create some
15178 complications when it comes to respecting the scheduling semantics
15179 specified in the real-time annex (Annex D).
15181 For instance the Annex D requirement for the @code{FIFO_Within_Priorities}
15182 scheduling policy states:
15185 @emph{When the active priority of a ready task that is not running
15186 changes, or the setting of its base priority takes effect, the
15187 task is removed from the ready queue for its old active priority
15188 and is added at the tail of the ready queue for its new active
15189 priority, except in the case where the active priority is lowered
15190 due to the loss of inherited priority, in which case the task is
15191 added at the head of the ready queue for its new active priority.}
15195 While most kernels do put tasks at the end of the priority queue when
15196 a task changes its priority, (which respects the main
15197 FIFO_Within_Priorities requirement), almost none keep a thread at the
15198 beginning of its priority queue when its priority drops from the loss
15199 of inherited priority.
15201 As a result most vendors have provided incomplete Annex D implementations.
15203 The GNAT run-time, has a nice cooperative solution to this problem
15204 which ensures that accurate FIFO_Within_Priorities semantics are
15207 The principle is as follows. When an Ada task T is about to start
15208 running, it checks whether some other Ada task R with the same
15209 priority as T has been suspended due to the loss of priority
15210 inheritance. If this is the case, T yields and is placed at the end of
15211 its priority queue. When R arrives at the front of the queue it
15214 Note that this simple scheme preserves the relative order of the tasks
15215 that were ready to execute in the priority queue where R has been
15218 @node GNAT Implementation of Shared Passive Packages
15219 @section GNAT Implementation of Shared Passive Packages
15220 @cindex Shared passive packages
15223 GNAT fully implements the pragma @code{Shared_Passive} for
15224 @cindex pragma @code{Shared_Passive}
15225 the purpose of designating shared passive packages.
15226 This allows the use of passive partitions in the
15227 context described in the Ada Reference Manual; i.e., for communication
15228 between separate partitions of a distributed application using the
15229 features in Annex E.
15231 @cindex Distribution Systems Annex
15233 However, the implementation approach used by GNAT provides for more
15234 extensive usage as follows:
15237 @item Communication between separate programs
15239 This allows separate programs to access the data in passive
15240 partitions, using protected objects for synchronization where
15241 needed. The only requirement is that the two programs have a
15242 common shared file system. It is even possible for programs
15243 running on different machines with different architectures
15244 (e.g.@: different endianness) to communicate via the data in
15245 a passive partition.
15247 @item Persistence between program runs
15249 The data in a passive package can persist from one run of a
15250 program to another, so that a later program sees the final
15251 values stored by a previous run of the same program.
15256 The implementation approach used is to store the data in files. A
15257 separate stream file is created for each object in the package, and
15258 an access to an object causes the corresponding file to be read or
15261 The environment variable @code{SHARED_MEMORY_DIRECTORY} should be
15262 @cindex @code{SHARED_MEMORY_DIRECTORY} environment variable
15263 set to the directory to be used for these files.
15264 The files in this directory
15265 have names that correspond to their fully qualified names. For
15266 example, if we have the package
15268 @smallexample @c ada
15270 pragma Shared_Passive (X);
15277 and the environment variable is set to @code{/stemp/}, then the files created
15278 will have the names:
15286 These files are created when a value is initially written to the object, and
15287 the files are retained until manually deleted. This provides the persistence
15288 semantics. If no file exists, it means that no partition has assigned a value
15289 to the variable; in this case the initial value declared in the package
15290 will be used. This model ensures that there are no issues in synchronizing
15291 the elaboration process, since elaboration of passive packages elaborates the
15292 initial values, but does not create the files.
15294 The files are written using normal @code{Stream_IO} access.
15295 If you want to be able
15296 to communicate between programs or partitions running on different
15297 architectures, then you should use the XDR versions of the stream attribute
15298 routines, since these are architecture independent.
15300 If active synchronization is required for access to the variables in the
15301 shared passive package, then as described in the Ada Reference Manual, the
15302 package may contain protected objects used for this purpose. In this case
15303 a lock file (whose name is @file{___lock} (three underscores)
15304 is created in the shared memory directory.
15305 @cindex @file{___lock} file (for shared passive packages)
15306 This is used to provide the required locking
15307 semantics for proper protected object synchronization.
15309 As of January 2003, GNAT supports shared passive packages on all platforms
15310 except for OpenVMS.
15312 @node Code Generation for Array Aggregates
15313 @section Code Generation for Array Aggregates
15316 * Static constant aggregates with static bounds::
15317 * Constant aggregates with unconstrained nominal types::
15318 * Aggregates with static bounds::
15319 * Aggregates with non-static bounds::
15320 * Aggregates in assignment statements::
15324 Aggregates have a rich syntax and allow the user to specify the values of
15325 complex data structures by means of a single construct. As a result, the
15326 code generated for aggregates can be quite complex and involve loops, case
15327 statements and multiple assignments. In the simplest cases, however, the
15328 compiler will recognize aggregates whose components and constraints are
15329 fully static, and in those cases the compiler will generate little or no
15330 executable code. The following is an outline of the code that GNAT generates
15331 for various aggregate constructs. For further details, you will find it
15332 useful to examine the output produced by the -gnatG flag to see the expanded
15333 source that is input to the code generator. You may also want to examine
15334 the assembly code generated at various levels of optimization.
15336 The code generated for aggregates depends on the context, the component values,
15337 and the type. In the context of an object declaration the code generated is
15338 generally simpler than in the case of an assignment. As a general rule, static
15339 component values and static subtypes also lead to simpler code.
15341 @node Static constant aggregates with static bounds
15342 @subsection Static constant aggregates with static bounds
15345 For the declarations:
15346 @smallexample @c ada
15347 type One_Dim is array (1..10) of integer;
15348 ar0 : constant One_Dim := (1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
15352 GNAT generates no executable code: the constant ar0 is placed in static memory.
15353 The same is true for constant aggregates with named associations:
15355 @smallexample @c ada
15356 Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1 => 1, 5 .. 10 => 0);
15357 Cr3 : constant One_Dim := (others => 7777);
15361 The same is true for multidimensional constant arrays such as:
15363 @smallexample @c ada
15364 type two_dim is array (1..3, 1..3) of integer;
15365 Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
15369 The same is true for arrays of one-dimensional arrays: the following are
15372 @smallexample @c ada
15373 type ar1b is array (1..3) of boolean;
15374 type ar_ar is array (1..3) of ar1b;
15375 None : constant ar1b := (others => false); -- fully static
15376 None2 : constant ar_ar := (1..3 => None); -- fully static
15380 However, for multidimensional aggregates with named associations, GNAT will
15381 generate assignments and loops, even if all associations are static. The
15382 following two declarations generate a loop for the first dimension, and
15383 individual component assignments for the second dimension:
15385 @smallexample @c ada
15386 Zero1: constant two_dim := (1..3 => (1..3 => 0));
15387 Zero2: constant two_dim := (others => (others => 0));
15390 @node Constant aggregates with unconstrained nominal types
15391 @subsection Constant aggregates with unconstrained nominal types
15394 In such cases the aggregate itself establishes the subtype, so that
15395 associations with @code{others} cannot be used. GNAT determines the
15396 bounds for the actual subtype of the aggregate, and allocates the
15397 aggregate statically as well. No code is generated for the following:
15399 @smallexample @c ada
15400 type One_Unc is array (natural range <>) of integer;
15401 Cr_Unc : constant One_Unc := (12,24,36);
15404 @node Aggregates with static bounds
15405 @subsection Aggregates with static bounds
15408 In all previous examples the aggregate was the initial (and immutable) value
15409 of a constant. If the aggregate initializes a variable, then code is generated
15410 for it as a combination of individual assignments and loops over the target
15411 object. The declarations
15413 @smallexample @c ada
15414 Cr_Var1 : One_Dim := (2, 5, 7, 11, 0, 0, 0, 0, 0, 0);
15415 Cr_Var2 : One_Dim := (others > -1);
15419 generate the equivalent of
15421 @smallexample @c ada
15427 for I in Cr_Var2'range loop
15432 @node Aggregates with non-static bounds
15433 @subsection Aggregates with non-static bounds
15436 If the bounds of the aggregate are not statically compatible with the bounds
15437 of the nominal subtype of the target, then constraint checks have to be
15438 generated on the bounds. For a multidimensional array, constraint checks may
15439 have to be applied to sub-arrays individually, if they do not have statically
15440 compatible subtypes.
15442 @node Aggregates in assignment statements
15443 @subsection Aggregates in assignment statements
15446 In general, aggregate assignment requires the construction of a temporary,
15447 and a copy from the temporary to the target of the assignment. This is because
15448 it is not always possible to convert the assignment into a series of individual
15449 component assignments. For example, consider the simple case:
15451 @smallexample @c ada
15456 This cannot be converted into:
15458 @smallexample @c ada
15464 So the aggregate has to be built first in a separate location, and then
15465 copied into the target. GNAT recognizes simple cases where this intermediate
15466 step is not required, and the assignments can be performed in place, directly
15467 into the target. The following sufficient criteria are applied:
15471 The bounds of the aggregate are static, and the associations are static.
15473 The components of the aggregate are static constants, names of
15474 simple variables that are not renamings, or expressions not involving
15475 indexed components whose operands obey these rules.
15479 If any of these conditions are violated, the aggregate will be built in
15480 a temporary (created either by the front-end or the code generator) and then
15481 that temporary will be copied onto the target.
15484 @node The Size of Discriminated Records with Default Discriminants
15485 @section The Size of Discriminated Records with Default Discriminants
15488 If a discriminated type @code{T} has discriminants with default values, it is
15489 possible to declare an object of this type without providing an explicit
15492 @smallexample @c ada
15494 type Size is range 1..100;
15496 type Rec (D : Size := 15) is record
15497 Name : String (1..D);
15505 Such an object is said to be @emph{unconstrained}.
15506 The discriminant of the object
15507 can be modified by a full assignment to the object, as long as it preserves the
15508 relation between the value of the discriminant, and the value of the components
15511 @smallexample @c ada
15513 Word := (3, "yes");
15515 Word := (5, "maybe");
15517 Word := (5, "no"); -- raises Constraint_Error
15522 In order to support this behavior efficiently, an unconstrained object is
15523 given the maximum size that any value of the type requires. In the case
15524 above, @code{Word} has storage for the discriminant and for
15525 a @code{String} of length 100.
15526 It is important to note that unconstrained objects do not require dynamic
15527 allocation. It would be an improper implementation to place on the heap those
15528 components whose size depends on discriminants. (This improper implementation
15529 was used by some Ada83 compilers, where the @code{Name} component above
15531 been stored as a pointer to a dynamic string). Following the principle that
15532 dynamic storage management should never be introduced implicitly,
15533 an Ada compiler should reserve the full size for an unconstrained declared
15534 object, and place it on the stack.
15536 This maximum size approach
15537 has been a source of surprise to some users, who expect the default
15538 values of the discriminants to determine the size reserved for an
15539 unconstrained object: ``If the default is 15, why should the object occupy
15541 The answer, of course, is that the discriminant may be later modified,
15542 and its full range of values must be taken into account. This is why the
15547 type Rec (D : Positive := 15) is record
15548 Name : String (1..D);
15556 is flagged by the compiler with a warning:
15557 an attempt to create @code{Too_Large} will raise @code{Storage_Error},
15558 because the required size includes @code{Positive'Last}
15559 bytes. As the first example indicates, the proper approach is to declare an
15560 index type of ``reasonable'' range so that unconstrained objects are not too
15563 One final wrinkle: if the object is declared to be @code{aliased}, or if it is
15564 created in the heap by means of an allocator, then it is @emph{not}
15566 it is constrained by the default values of the discriminants, and those values
15567 cannot be modified by full assignment. This is because in the presence of
15568 aliasing all views of the object (which may be manipulated by different tasks,
15569 say) must be consistent, so it is imperative that the object, once created,
15572 @node Strict Conformance to the Ada Reference Manual
15573 @section Strict Conformance to the Ada Reference Manual
15576 The dynamic semantics defined by the Ada Reference Manual impose a set of
15577 run-time checks to be generated. By default, the GNAT compiler will insert many
15578 run-time checks into the compiled code, including most of those required by the
15579 Ada Reference Manual. However, there are three checks that are not enabled
15580 in the default mode for efficiency reasons: arithmetic overflow checking for
15581 integer operations (including division by zero), checks for access before
15582 elaboration on subprogram calls, and stack overflow checking (most operating
15583 systems do not perform this check by default).
15585 Strict conformance to the Ada Reference Manual can be achieved by adding
15586 three compiler options for overflow checking for integer operations
15587 (@option{-gnato}), dynamic checks for access-before-elaboration on subprogram
15588 calls and generic instantiations (@option{-gnatE}), and stack overflow
15589 checking (@option{-fstack-check}).
15591 Note that the result of a floating point arithmetic operation in overflow and
15592 invalid situations, when the @code{Machine_Overflows} attribute of the result
15593 type is @code{False}, is to generate IEEE NaN and infinite values. This is the
15594 case for machines compliant with the IEEE floating-point standard, but on
15595 machines that are not fully compliant with this standard, such as Alpha, the
15596 @option{-mieee} compiler flag must be used for achieving IEEE confirming
15597 behavior (although at the cost of a significant performance penalty), so
15598 infinite and and NaN values are properly generated.
15601 @node Project File Reference
15602 @chapter Project File Reference
15605 This chapter describes the syntax and semantics of project files.
15606 Project files specify the options to be used when building a system.
15607 Project files can specify global settings for all tools,
15608 as well as tool-specific settings.
15609 @xref{Examples of Project Files,,, gnat_ugn, @value{EDITION} User's Guide},
15610 for examples of use.
15614 * Lexical Elements::
15616 * Empty declarations::
15617 * Typed string declarations::
15621 * Project Attributes::
15622 * Attribute References::
15623 * External Values::
15624 * Case Construction::
15626 * Package Renamings::
15628 * Project Extensions::
15629 * Project File Elaboration::
15632 @node Reserved Words
15633 @section Reserved Words
15636 All Ada reserved words are reserved in project files, and cannot be used
15637 as variable names or project names. In addition, the following are
15638 also reserved in project files:
15641 @item @code{extends}
15643 @item @code{external}
15645 @item @code{project}
15649 @node Lexical Elements
15650 @section Lexical Elements
15653 Rules for identifiers are the same as in Ada. Identifiers
15654 are case-insensitive. Strings are case sensitive, except where noted.
15655 Comments have the same form as in Ada.
15665 simple_name @{. simple_name@}
15669 @section Declarations
15672 Declarations introduce new entities that denote types, variables, attributes,
15673 and packages. Some declarations can only appear immediately within a project
15674 declaration. Others can appear within a project or within a package.
15678 declarative_item ::=
15679 simple_declarative_item |
15680 typed_string_declaration |
15681 package_declaration
15683 simple_declarative_item ::=
15684 variable_declaration |
15685 typed_variable_declaration |
15686 attribute_declaration |
15687 case_construction |
15691 @node Empty declarations
15692 @section Empty declarations
15695 empty_declaration ::=
15699 An empty declaration is allowed anywhere a declaration is allowed.
15702 @node Typed string declarations
15703 @section Typed string declarations
15706 Typed strings are sequences of string literals. Typed strings are the only
15707 named types in project files. They are used in case constructions, where they
15708 provide support for conditional attribute definitions.
15712 typed_string_declaration ::=
15713 @b{type} <typed_string_>_simple_name @b{is}
15714 ( string_literal @{, string_literal@} );
15718 A typed string declaration can only appear immediately within a project
15721 All the string literals in a typed string declaration must be distinct.
15727 Variables denote values, and appear as constituents of expressions.
15730 typed_variable_declaration ::=
15731 <typed_variable_>simple_name : <typed_string_>name := string_expression ;
15733 variable_declaration ::=
15734 <variable_>simple_name := expression;
15738 The elaboration of a variable declaration introduces the variable and
15739 assigns to it the value of the expression. The name of the variable is
15740 available after the assignment symbol.
15743 A typed_variable can only be declare once.
15746 a non-typed variable can be declared multiple times.
15749 Before the completion of its first declaration, the value of variable
15750 is the null string.
15753 @section Expressions
15756 An expression is a formula that defines a computation or retrieval of a value.
15757 In a project file the value of an expression is either a string or a list
15758 of strings. A string value in an expression is either a literal, the current
15759 value of a variable, an external value, an attribute reference, or a
15760 concatenation operation.
15773 attribute_reference
15779 ( <string_>expression @{ , <string_>expression @} )
15782 @subsection Concatenation
15784 The following concatenation functions are defined:
15786 @smallexample @c ada
15787 function "&" (X : String; Y : String) return String;
15788 function "&" (X : String_List; Y : String) return String_List;
15789 function "&" (X : String_List; Y : String_List) return String_List;
15793 @section Attributes
15796 An attribute declaration defines a property of a project or package. This
15797 property can later be queried by means of an attribute reference.
15798 Attribute values are strings or string lists.
15800 Some attributes are associative arrays. These attributes are mappings whose
15801 domain is a set of strings. These attributes are declared one association
15802 at a time, by specifying a point in the domain and the corresponding image
15803 of the attribute. They may also be declared as a full associative array,
15804 getting the same associations as the corresponding attribute in an imported
15805 or extended project.
15807 Attributes that are not associative arrays are called simple attributes.
15811 attribute_declaration ::=
15812 full_associative_array_declaration |
15813 @b{for} attribute_designator @b{use} expression ;
15815 full_associative_array_declaration ::=
15816 @b{for} <associative_array_attribute_>simple_name @b{use}
15817 <project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
15819 attribute_designator ::=
15820 <simple_attribute_>simple_name |
15821 <associative_array_attribute_>simple_name ( string_literal )
15825 Some attributes are project-specific, and can only appear immediately within
15826 a project declaration. Others are package-specific, and can only appear within
15827 the proper package.
15829 The expression in an attribute definition must be a string or a string_list.
15830 The string literal appearing in the attribute_designator of an associative
15831 array attribute is case-insensitive.
15833 @node Project Attributes
15834 @section Project Attributes
15837 The following attributes apply to a project. All of them are simple
15842 Expression must be a path name. The attribute defines the
15843 directory in which the object files created by the build are to be placed. If
15844 not specified, object files are placed in the project directory.
15847 Expression must be a path name. The attribute defines the
15848 directory in which the executables created by the build are to be placed.
15849 If not specified, executables are placed in the object directory.
15852 Expression must be a list of path names. The attribute
15853 defines the directories in which the source files for the project are to be
15854 found. If not specified, source files are found in the project directory.
15855 If a string in the list ends with "/**", then the directory that precedes
15856 "/**" and all of its subdirectories (recursively) are included in the list
15857 of source directories.
15859 @item Excluded_Source_Dirs
15860 Expression must be a list of strings. Each entry designates a directory that
15861 is not to be included in the list of source directories of the project.
15862 This is normally used when there are strings ending with "/**" in the value
15863 of attribute Source_Dirs.
15866 Expression must be a list of file names. The attribute
15867 defines the individual files, in the project directory, which are to be used
15868 as sources for the project. File names are path_names that contain no directory
15869 information. If the project has no sources the attribute must be declared
15870 explicitly with an empty list.
15872 @item Excluded_Source_Files (Locally_Removed_Files)
15873 Expression must be a list of strings that are legal file names.
15874 Each file name must designate a source that would normally be a source file
15875 in the source directories of the project or, if the project file is an
15876 extending project file, inherited by the current project file. It cannot
15877 designate an immediate source that is not inherited. Each of the source files
15878 in the list are not considered to be sources of the project file: they are not
15879 inherited. Attribute Locally_Removed_Files is obsolescent, attribute
15880 Excluded_Source_Files is preferred.
15882 @item Source_List_File
15883 Expression must a single path name. The attribute
15884 defines a text file that contains a list of source file names to be used
15885 as sources for the project
15888 Expression must be a path name. The attribute defines the
15889 directory in which a library is to be built. The directory must exist, must
15890 be distinct from the project's object directory, and must be writable.
15893 Expression must be a string that is a legal file name,
15894 without extension. The attribute defines a string that is used to generate
15895 the name of the library to be built by the project.
15898 Argument must be a string value that must be one of the
15899 following @code{"static"}, @code{"dynamic"} or @code{"relocatable"}. This
15900 string is case-insensitive. If this attribute is not specified, the library is
15901 a static library. Otherwise, the library may be dynamic or relocatable. This
15902 distinction is operating-system dependent.
15904 @item Library_Version
15905 Expression must be a string value whose interpretation
15906 is platform dependent. On UNIX, it is used only for dynamic/relocatable
15907 libraries as the internal name of the library (the @code{"soname"}). If the
15908 library file name (built from the @code{Library_Name}) is different from the
15909 @code{Library_Version}, then the library file will be a symbolic link to the
15910 actual file whose name will be @code{Library_Version}.
15912 @item Library_Interface
15913 Expression must be a string list. Each element of the string list
15914 must designate a unit of the project.
15915 If this attribute is present in a Library Project File, then the project
15916 file is a Stand-alone Library_Project_File.
15918 @item Library_Auto_Init
15919 Expression must be a single string "true" or "false", case-insensitive.
15920 If this attribute is present in a Stand-alone Library Project File,
15921 it indicates if initialization is automatic when the dynamic library
15924 @item Library_Options
15925 Expression must be a string list. Indicates additional switches that
15926 are to be used when building a shared library.
15929 Expression must be a single string. Designates an alternative to "gcc"
15930 for building shared libraries.
15932 @item Library_Src_Dir
15933 Expression must be a path name. The attribute defines the
15934 directory in which the sources of the interfaces of a Stand-alone Library will
15935 be copied. The directory must exist, must be distinct from the project's
15936 object directory and source directories of all projects in the project tree,
15937 and must be writable.
15939 @item Library_Src_Dir
15940 Expression must be a path name. The attribute defines the
15941 directory in which the ALI files of a Library will
15942 be copied. The directory must exist, must be distinct from the project's
15943 object directory and source directories of all projects in the project tree,
15944 and must be writable.
15946 @item Library_Symbol_File
15947 Expression must be a single string. Its value is the single file name of a
15948 symbol file to be created when building a stand-alone library when the
15949 symbol policy is either "compliant", "controlled" or "restricted",
15950 on platforms that support symbol control, such as VMS. When symbol policy
15951 is "direct", then a file with this name must exist in the object directory.
15953 @item Library_Reference_Symbol_File
15954 Expression must be a single string. Its value is the path name of a
15955 reference symbol file that is read when the symbol policy is either
15956 "compliant" or "controlled", on platforms that support symbol control,
15957 such as VMS, when building a stand-alone library. The path may be an absolute
15958 path or a path relative to the project directory.
15960 @item Library_Symbol_Policy
15961 Expression must be a single string. Its case-insensitive value can only be
15962 "autonomous", "default", "compliant", "controlled", "restricted" or "direct".
15964 This attribute is not taken into account on all platforms. It controls the
15965 policy for exported symbols and, on some platforms (like VMS) that have the
15966 notions of major and minor IDs built in the library files, it controls
15967 the setting of these IDs.
15969 "autonomous" or "default": exported symbols are not controlled.
15971 "compliant": if attribute Library_Reference_Symbol_File is not defined, then
15972 it is equivalent to policy "autonomous". If there are exported symbols in
15973 the reference symbol file that are not in the object files of the interfaces,
15974 the major ID of the library is increased. If there are symbols in the
15975 object files of the interfaces that are not in the reference symbol file,
15976 these symbols are put at the end of the list in the newly created symbol file
15977 and the minor ID is increased.
15979 "controlled": the attribute Library_Reference_Symbol_File must be defined.
15980 The library will fail to build if the exported symbols in the object files of
15981 the interfaces do not match exactly the symbol in the symbol file.
15983 "restricted": The attribute Library_Symbol_File must be defined. The library
15984 will fail to build if there are symbols in the symbol file that are not in
15985 the exported symbols of the object files of the interfaces. Additional symbols
15986 in the object files are not added to the symbol file.
15988 "direct": The attribute Library_Symbol_File must be defined and must designate
15989 an existing file in the object directory. This symbol file is passed directly
15990 to the underlying linker without any symbol processing.
15993 Expression must be a list of strings that are legal file names.
15994 These file names designate existing compilation units in the source directory
15995 that are legal main subprograms.
15997 When a project file is elaborated, as part of the execution of a gnatmake
15998 command, one or several executables are built and placed in the Exec_Dir.
15999 If the gnatmake command does not include explicit file names, the executables
16000 that are built correspond to the files specified by this attribute.
16002 @item Externally_Built
16003 Expression must be a single string. Its value must be either "true" of "false",
16004 case-insensitive. The default is "false". When the value of this attribute is
16005 "true", no attempt is made to compile the sources or to build the library,
16006 when the project is a library project.
16008 @item Main_Language
16009 This is a simple attribute. Its value is a string that specifies the
16010 language of the main program.
16013 Expression must be a string list. Each string designates
16014 a programming language that is known to GNAT. The strings are case-insensitive.
16018 @node Attribute References
16019 @section Attribute References
16022 Attribute references are used to retrieve the value of previously defined
16023 attribute for a package or project.
16026 attribute_reference ::=
16027 attribute_prefix ' <simple_attribute_>simple_name [ ( string_literal ) ]
16029 attribute_prefix ::=
16031 <project_simple_name | package_identifier |
16032 <project_>simple_name . package_identifier
16036 If an attribute has not been specified for a given package or project, its
16037 value is the null string or the empty list.
16039 @node External Values
16040 @section External Values
16043 An external value is an expression whose value is obtained from the command
16044 that invoked the processing of the current project file (typically a
16050 @b{external} ( string_literal [, string_literal] )
16054 The first string_literal is the string to be used on the command line or
16055 in the environment to specify the external value. The second string_literal,
16056 if present, is the default to use if there is no specification for this
16057 external value either on the command line or in the environment.
16059 @node Case Construction
16060 @section Case Construction
16063 A case construction supports attribute and variable declarations that depend
16064 on the value of a previously declared variable.
16068 case_construction ::=
16069 @b{case} <typed_variable_>name @b{is}
16074 @b{when} discrete_choice_list =>
16075 @{case_construction |
16076 attribute_declaration |
16077 variable_declaration |
16078 empty_declaration@}
16080 discrete_choice_list ::=
16081 string_literal @{| string_literal@} |
16086 Inside a case construction, variable declarations must be for variables that
16087 have already been declared before the case construction.
16089 All choices in a choice list must be distinct. The choice lists of two
16090 distinct alternatives must be disjoint. Unlike Ada, the choice lists of all
16091 alternatives do not need to include all values of the type. An @code{others}
16092 choice must appear last in the list of alternatives.
16098 A package provides a grouping of variable declarations and attribute
16099 declarations to be used when invoking various GNAT tools. The name of
16100 the package indicates the tool(s) to which it applies.
16104 package_declaration ::=
16105 package_spec | package_renaming
16108 @b{package} package_identifier @b{is}
16109 @{simple_declarative_item@}
16110 @b{end} package_identifier ;
16112 package_identifier ::=
16113 @code{Naming} | @code{Builder} | @code{Compiler} | @code{Binder} |
16114 @code{Linker} | @code{Finder} | @code{Cross_Reference} |
16115 @code{gnatls} | @code{IDE} | @code{Pretty_Printer}
16118 @subsection Package Naming
16121 The attributes of a @code{Naming} package specifies the naming conventions
16122 that apply to the source files in a project. When invoking other GNAT tools,
16123 they will use the sources in the source directories that satisfy these
16124 naming conventions.
16126 The following attributes apply to a @code{Naming} package:
16130 This is a simple attribute whose value is a string. Legal values of this
16131 string are @code{"lowercase"}, @code{"uppercase"} or @code{"mixedcase"}.
16132 These strings are themselves case insensitive.
16135 If @code{Casing} is not specified, then the default is @code{"lowercase"}.
16137 @item Dot_Replacement
16138 This is a simple attribute whose string value satisfies the following
16142 @item It must not be empty
16143 @item It cannot start or end with an alphanumeric character
16144 @item It cannot be a single underscore
16145 @item It cannot start with an underscore followed by an alphanumeric
16146 @item It cannot contain a dot @code{'.'} if longer than one character
16150 If @code{Dot_Replacement} is not specified, then the default is @code{"-"}.
16153 This is an associative array attribute, defined on language names,
16154 whose image is a string that must satisfy the following
16158 @item It must not be empty
16159 @item It cannot start with an alphanumeric character
16160 @item It cannot start with an underscore followed by an alphanumeric character
16164 For Ada, the attribute denotes the suffix used in file names that contain
16165 library unit declarations, that is to say units that are package and
16166 subprogram declarations. If @code{Spec_Suffix ("Ada")} is not
16167 specified, then the default is @code{".ads"}.
16169 For C and C++, the attribute denotes the suffix used in file names that
16170 contain prototypes.
16173 This is an associative array attribute defined on language names,
16174 whose image is a string that must satisfy the following
16178 @item It must not be empty
16179 @item It cannot start with an alphanumeric character
16180 @item It cannot start with an underscore followed by an alphanumeric character
16181 @item It cannot be a suffix of @code{Spec_Suffix}
16185 For Ada, the attribute denotes the suffix used in file names that contain
16186 library bodies, that is to say units that are package and subprogram bodies.
16187 If @code{Body_Suffix ("Ada")} is not specified, then the default is
16190 For C and C++, the attribute denotes the suffix used in file names that contain
16193 @item Separate_Suffix
16194 This is a simple attribute whose value satisfies the same conditions as
16195 @code{Body_Suffix}.
16197 This attribute is specific to Ada. It denotes the suffix used in file names
16198 that contain separate bodies. If it is not specified, then it defaults to same
16199 value as @code{Body_Suffix ("Ada")}.
16202 This is an associative array attribute, specific to Ada, defined over
16203 compilation unit names. The image is a string that is the name of the file
16204 that contains that library unit. The file name is case sensitive if the
16205 conventions of the host operating system require it.
16208 This is an associative array attribute, specific to Ada, defined over
16209 compilation unit names. The image is a string that is the name of the file
16210 that contains the library unit body for the named unit. The file name is case
16211 sensitive if the conventions of the host operating system require it.
16213 @item Specification_Exceptions
16214 This is an associative array attribute defined on language names,
16215 whose value is a list of strings.
16217 This attribute is not significant for Ada.
16219 For C and C++, each string in the list denotes the name of a file that
16220 contains prototypes, but whose suffix is not necessarily the
16221 @code{Spec_Suffix} for the language.
16223 @item Implementation_Exceptions
16224 This is an associative array attribute defined on language names,
16225 whose value is a list of strings.
16227 This attribute is not significant for Ada.
16229 For C and C++, each string in the list denotes the name of a file that
16230 contains source code, but whose suffix is not necessarily the
16231 @code{Body_Suffix} for the language.
16234 The following attributes of package @code{Naming} are obsolescent. They are
16235 kept as synonyms of other attributes for compatibility with previous versions
16236 of the Project Manager.
16239 @item Specification_Suffix
16240 This is a synonym of @code{Spec_Suffix}.
16242 @item Implementation_Suffix
16243 This is a synonym of @code{Body_Suffix}.
16245 @item Specification
16246 This is a synonym of @code{Spec}.
16248 @item Implementation
16249 This is a synonym of @code{Body}.
16252 @subsection package Compiler
16255 The attributes of the @code{Compiler} package specify the compilation options
16256 to be used by the underlying compiler.
16259 @item Default_Switches
16260 This is an associative array attribute. Its
16261 domain is a set of language names. Its range is a string list that
16262 specifies the compilation options to be used when compiling a component
16263 written in that language, for which no file-specific switches have been
16267 This is an associative array attribute. Its domain is
16268 a set of file names. Its range is a string list that specifies the
16269 compilation options to be used when compiling the named file. If a file
16270 is not specified in the Switches attribute, it is compiled with the
16271 options specified by Default_Switches of its language, if defined.
16273 @item Local_Configuration_Pragmas.
16274 This is a simple attribute, whose
16275 value is a path name that designates a file containing configuration pragmas
16276 to be used for all invocations of the compiler for immediate sources of the
16280 @subsection package Builder
16283 The attributes of package @code{Builder} specify the compilation, binding, and
16284 linking options to be used when building an executable for a project. The
16285 following attributes apply to package @code{Builder}:
16288 @item Default_Switches
16289 This is an associative array attribute. Its
16290 domain is a set of language names. Its range is a string list that
16291 specifies options to be used when building a main
16292 written in that language, for which no file-specific switches have been
16296 This is an associative array attribute. Its domain is
16297 a set of file names. Its range is a string list that specifies
16298 options to be used when building the named main file. If a main file
16299 is not specified in the Switches attribute, it is built with the
16300 options specified by Default_Switches of its language, if defined.
16302 @item Global_Configuration_Pragmas
16303 This is a simple attribute, whose
16304 value is a path name that designates a file that contains configuration pragmas
16305 to be used in every build of an executable. If both local and global
16306 configuration pragmas are specified, a compilation makes use of both sets.
16310 This is an associative array attribute. Its domain is
16311 a set of main source file names. Its range is a simple string that specifies
16312 the executable file name to be used when linking the specified main source.
16313 If a main source is not specified in the Executable attribute, the executable
16314 file name is deducted from the main source file name.
16315 This attribute has no effect if its value is the empty string.
16317 @item Executable_Suffix
16318 This is a simple attribute whose value is the suffix to be added to
16319 the executables that don't have an attribute Executable specified.
16322 @subsection package Gnatls
16325 The attributes of package @code{Gnatls} specify the tool options to be used
16326 when invoking the library browser @command{gnatls}.
16327 The following attributes apply to package @code{Gnatls}:
16331 This is a single attribute with a string list value. Each nonempty string
16332 in the list is an option when invoking @code{gnatls}.
16335 @subsection package Binder
16338 The attributes of package @code{Binder} specify the options to be used
16339 when invoking the binder in the construction of an executable.
16340 The following attributes apply to package @code{Binder}:
16343 @item Default_Switches
16344 This is an associative array attribute. Its
16345 domain is a set of language names. Its range is a string list that
16346 specifies options to be used when binding a main
16347 written in that language, for which no file-specific switches have been
16351 This is an associative array attribute. Its domain is
16352 a set of file names. Its range is a string list that specifies
16353 options to be used when binding the named main file. If a main file
16354 is not specified in the Switches attribute, it is bound with the
16355 options specified by Default_Switches of its language, if defined.
16358 @subsection package Linker
16361 The attributes of package @code{Linker} specify the options to be used when
16362 invoking the linker in the construction of an executable.
16363 The following attributes apply to package @code{Linker}:
16366 @item Default_Switches
16367 This is an associative array attribute. Its
16368 domain is a set of language names. Its range is a string list that
16369 specifies options to be used when linking a main
16370 written in that language, for which no file-specific switches have been
16374 This is an associative array attribute. Its domain is
16375 a set of file names. Its range is a string list that specifies
16376 options to be used when linking the named main file. If a main file
16377 is not specified in the Switches attribute, it is linked with the
16378 options specified by Default_Switches of its language, if defined.
16380 @item Linker_Options
16381 This is a string list attribute. Its value specifies additional options that
16382 be given to the linker when linking an executable. This attribute is not
16383 used in the main project, only in projects imported directly or indirectly.
16387 @subsection package Cross_Reference
16390 The attributes of package @code{Cross_Reference} specify the tool options
16392 when invoking the library tool @command{gnatxref}.
16393 The following attributes apply to package @code{Cross_Reference}:
16396 @item Default_Switches
16397 This is an associative array attribute. Its
16398 domain is a set of language names. Its range is a string list that
16399 specifies options to be used when calling @command{gnatxref} on a source
16400 written in that language, for which no file-specific switches have been
16404 This is an associative array attribute. Its domain is
16405 a set of file names. Its range is a string list that specifies
16406 options to be used when calling @command{gnatxref} on the named main source.
16407 If a source is not specified in the Switches attribute, @command{gnatxref} will
16408 be called with the options specified by Default_Switches of its language,
16412 @subsection package Finder
16415 The attributes of package @code{Finder} specify the tool options to be used
16416 when invoking the search tool @command{gnatfind}.
16417 The following attributes apply to package @code{Finder}:
16420 @item Default_Switches
16421 This is an associative array attribute. Its
16422 domain is a set of language names. Its range is a string list that
16423 specifies options to be used when calling @command{gnatfind} on a source
16424 written in that language, for which no file-specific switches have been
16428 This is an associative array attribute. Its domain is
16429 a set of file names. Its range is a string list that specifies
16430 options to be used when calling @command{gnatfind} on the named main source.
16431 If a source is not specified in the Switches attribute, @command{gnatfind} will
16432 be called with the options specified by Default_Switches of its language,
16436 @subsection package Pretty_Printer
16439 The attributes of package @code{Pretty_Printer}
16440 specify the tool options to be used
16441 when invoking the formatting tool @command{gnatpp}.
16442 The following attributes apply to package @code{Pretty_Printer}:
16445 @item Default_switches
16446 This is an associative array attribute. Its
16447 domain is a set of language names. Its range is a string list that
16448 specifies options to be used when calling @command{gnatpp} on a source
16449 written in that language, for which no file-specific switches have been
16453 This is an associative array attribute. Its domain is
16454 a set of file names. Its range is a string list that specifies
16455 options to be used when calling @command{gnatpp} on the named main source.
16456 If a source is not specified in the Switches attribute, @command{gnatpp} will
16457 be called with the options specified by Default_Switches of its language,
16461 @subsection package gnatstub
16464 The attributes of package @code{gnatstub}
16465 specify the tool options to be used
16466 when invoking the tool @command{gnatstub}.
16467 The following attributes apply to package @code{gnatstub}:
16470 @item Default_switches
16471 This is an associative array attribute. Its
16472 domain is a set of language names. Its range is a string list that
16473 specifies options to be used when calling @command{gnatstub} on a source
16474 written in that language, for which no file-specific switches have been
16478 This is an associative array attribute. Its domain is
16479 a set of file names. Its range is a string list that specifies
16480 options to be used when calling @command{gnatstub} on the named main source.
16481 If a source is not specified in the Switches attribute, @command{gnatpp} will
16482 be called with the options specified by Default_Switches of its language,
16486 @subsection package Eliminate
16489 The attributes of package @code{Eliminate}
16490 specify the tool options to be used
16491 when invoking the tool @command{gnatelim}.
16492 The following attributes apply to package @code{Eliminate}:
16495 @item Default_switches
16496 This is an associative array attribute. Its
16497 domain is a set of language names. Its range is a string list that
16498 specifies options to be used when calling @command{gnatelim} on a source
16499 written in that language, for which no file-specific switches have been
16503 This is an associative array attribute. Its domain is
16504 a set of file names. Its range is a string list that specifies
16505 options to be used when calling @command{gnatelim} on the named main source.
16506 If a source is not specified in the Switches attribute, @command{gnatelim} will
16507 be called with the options specified by Default_Switches of its language,
16511 @subsection package Metrics
16514 The attributes of package @code{Metrics}
16515 specify the tool options to be used
16516 when invoking the tool @command{gnatmetric}.
16517 The following attributes apply to package @code{Metrics}:
16520 @item Default_switches
16521 This is an associative array attribute. Its
16522 domain is a set of language names. Its range is a string list that
16523 specifies options to be used when calling @command{gnatmetric} on a source
16524 written in that language, for which no file-specific switches have been
16528 This is an associative array attribute. Its domain is
16529 a set of file names. Its range is a string list that specifies
16530 options to be used when calling @command{gnatmetric} on the named main source.
16531 If a source is not specified in the Switches attribute, @command{gnatmetric}
16532 will be called with the options specified by Default_Switches of its language,
16536 @subsection package IDE
16539 The attributes of package @code{IDE} specify the options to be used when using
16540 an Integrated Development Environment such as @command{GPS}.
16544 This is a simple attribute. Its value is a string that designates the remote
16545 host in a cross-compilation environment, to be used for remote compilation and
16546 debugging. This field should not be specified when running on the local
16550 This is a simple attribute. Its value is a string that specifies the
16551 name of IP address of the embedded target in a cross-compilation environment,
16552 on which the program should execute.
16554 @item Communication_Protocol
16555 This is a simple string attribute. Its value is the name of the protocol
16556 to use to communicate with the target in a cross-compilation environment,
16557 e.g.@: @code{"wtx"} or @code{"vxworks"}.
16559 @item Compiler_Command
16560 This is an associative array attribute, whose domain is a language name. Its
16561 value is string that denotes the command to be used to invoke the compiler.
16562 The value of @code{Compiler_Command ("Ada")} is expected to be compatible with
16563 gnatmake, in particular in the handling of switches.
16565 @item Debugger_Command
16566 This is simple attribute, Its value is a string that specifies the name of
16567 the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
16569 @item Default_Switches
16570 This is an associative array attribute. Its indexes are the name of the
16571 external tools that the GNAT Programming System (GPS) is supporting. Its
16572 value is a list of switches to use when invoking that tool.
16575 This is a simple attribute. Its value is a string that specifies the name
16576 of the @command{gnatls} utility to be used to retrieve information about the
16577 predefined path; e.g., @code{"gnatls"}, @code{"powerpc-wrs-vxworks-gnatls"}.
16580 This is a simple attribute. Its value is a string used to specify the
16581 Version Control System (VCS) to be used for this project, e.g.@: CVS, RCS
16582 ClearCase or Perforce.
16584 @item VCS_File_Check
16585 This is a simple attribute. Its value is a string that specifies the
16586 command used by the VCS to check the validity of a file, either
16587 when the user explicitly asks for a check, or as a sanity check before
16588 doing the check-in.
16590 @item VCS_Log_Check
16591 This is a simple attribute. Its value is a string that specifies
16592 the command used by the VCS to check the validity of a log file.
16594 @item VCS_Repository_Root
16595 The VCS repository root path. This is used to create tags or branches
16596 of the repository. For subversion the value should be the @code{URL}
16597 as specified to check-out the working copy of the repository.
16599 @item VCS_Patch_Root
16600 The local root directory to use for building patch file. All patch chunks
16601 will be relative to this path. The root project directory is used if
16602 this value is not defined.
16606 @node Package Renamings
16607 @section Package Renamings
16610 A package can be defined by a renaming declaration. The new package renames
16611 a package declared in a different project file, and has the same attributes
16612 as the package it renames.
16615 package_renaming ::==
16616 @b{package} package_identifier @b{renames}
16617 <project_>simple_name.package_identifier ;
16621 The package_identifier of the renamed package must be the same as the
16622 package_identifier. The project whose name is the prefix of the renamed
16623 package must contain a package declaration with this name. This project
16624 must appear in the context_clause of the enclosing project declaration,
16625 or be the parent project of the enclosing child project.
16631 A project file specifies a set of rules for constructing a software system.
16632 A project file can be self-contained, or depend on other project files.
16633 Dependencies are expressed through a context clause that names other projects.
16639 context_clause project_declaration
16641 project_declaration ::=
16642 simple_project_declaration | project_extension
16644 simple_project_declaration ::=
16645 @b{project} <project_>simple_name @b{is}
16646 @{declarative_item@}
16647 @b{end} <project_>simple_name;
16653 [@b{limited}] @b{with} path_name @{ , path_name @} ;
16660 A path name denotes a project file. A path name can be absolute or relative.
16661 An absolute path name includes a sequence of directories, in the syntax of
16662 the host operating system, that identifies uniquely the project file in the
16663 file system. A relative path name identifies the project file, relative
16664 to the directory that contains the current project, or relative to a
16665 directory listed in the environment variable ADA_PROJECT_PATH.
16666 Path names are case sensitive if file names in the host operating system
16667 are case sensitive.
16669 The syntax of the environment variable ADA_PROJECT_PATH is a list of
16670 directory names separated by colons (semicolons on Windows).
16672 A given project name can appear only once in a context_clause.
16674 It is illegal for a project imported by a context clause to refer, directly
16675 or indirectly, to the project in which this context clause appears (the
16676 dependency graph cannot contain cycles), except when one of the with_clause
16677 in the cycle is a @code{limited with}.
16679 @node Project Extensions
16680 @section Project Extensions
16683 A project extension introduces a new project, which inherits the declarations
16684 of another project.
16688 project_extension ::=
16689 @b{project} <project_>simple_name @b{extends} path_name @b{is}
16690 @{declarative_item@}
16691 @b{end} <project_>simple_name;
16695 The project extension declares a child project. The child project inherits
16696 all the declarations and all the files of the parent project, These inherited
16697 declaration can be overridden in the child project, by means of suitable
16700 @node Project File Elaboration
16701 @section Project File Elaboration
16704 A project file is processed as part of the invocation of a gnat tool that
16705 uses the project option. Elaboration of the process file consists in the
16706 sequential elaboration of all its declarations. The computed values of
16707 attributes and variables in the project are then used to establish the
16708 environment in which the gnat tool will execute.
16710 @node Obsolescent Features
16711 @chapter Obsolescent Features
16714 This chapter describes features that are provided by GNAT, but are
16715 considered obsolescent since there are preferred ways of achieving
16716 the same effect. These features are provided solely for historical
16717 compatibility purposes.
16720 * pragma No_Run_Time::
16721 * pragma Ravenscar::
16722 * pragma Restricted_Run_Time::
16725 @node pragma No_Run_Time
16726 @section pragma No_Run_Time
16728 The pragma @code{No_Run_Time} is used to achieve an affect similar
16729 to the use of the "Zero Foot Print" configurable run time, but without
16730 requiring a specially configured run time. The result of using this
16731 pragma, which must be used for all units in a partition, is to restrict
16732 the use of any language features requiring run-time support code. The
16733 preferred usage is to use an appropriately configured run-time that
16734 includes just those features that are to be made accessible.
16736 @node pragma Ravenscar
16737 @section pragma Ravenscar
16739 The pragma @code{Ravenscar} has exactly the same effect as pragma
16740 @code{Profile (Ravenscar)}. The latter usage is preferred since it
16741 is part of the new Ada 2005 standard.
16743 @node pragma Restricted_Run_Time
16744 @section pragma Restricted_Run_Time
16746 The pragma @code{Restricted_Run_Time} has exactly the same effect as
16747 pragma @code{Profile (Restricted)}. The latter usage is
16748 preferred since the Ada 2005 pragma @code{Profile} is intended for
16749 this kind of implementation dependent addition.
16752 @c GNU Free Documentation License
16754 @node Index,,GNU Free Documentation License, Top