1 \input texinfo @c -*-texinfo-*-
5 @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
7 @c GNAT DOCUMENTATION o
11 @c Copyright (C) 1995-2005 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
22 @settitle GNAT Reference Manual
24 @setchapternewpage odd
27 @include gcc-common.texi
29 @dircategory GNU Ada tools
31 * GNAT Reference Manual: (gnat_rm). Reference Manual for GNU Ada tools.
35 Copyright @copyright{} 1995-2004, Free Software Foundation
37 Permission is granted to copy, distribute and/or modify this document
38 under the terms of the GNU Free Documentation License, Version 1.2
39 or any later version published by the Free Software Foundation;
40 with the Invariant Sections being ``GNU Free Documentation License'',
41 with the Front-Cover Texts being ``GNAT Reference Manual'', and with
42 no Back-Cover Texts. A copy of the license is included in the section
43 entitled ``GNU Free Documentation License''.
48 @title GNAT Reference Manual
49 @subtitle GNAT, The GNU Ada 95 Compiler
50 @subtitle GCC version @value{version-GCC}
51 @author Ada Core Technologies, Inc.
54 @vskip 0pt plus 1filll
61 @node Top, About This Guide, (dir), (dir)
62 @top GNAT Reference Manual
68 GNAT, The GNU Ada 95 Compiler@*
69 GCC version @value{version-GCC}@*
72 Ada Core Technologies, Inc.
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::
109 * Pragma C_Pass_By_Copy::
111 * Pragma Common_Object::
112 * Pragma Compile_Time_Warning::
113 * Pragma Complex_Representation::
114 * Pragma Component_Alignment::
115 * Pragma Convention_Identifier::
117 * Pragma CPP_Constructor::
118 * Pragma CPP_Virtual::
119 * Pragma CPP_Vtable::
121 * Pragma Detect_Blocking::
122 * Pragma Elaboration_Checks::
124 * Pragma Export_Exception::
125 * Pragma Export_Function::
126 * Pragma Export_Object::
127 * Pragma Export_Procedure::
128 * Pragma Export_Value::
129 * Pragma Export_Valued_Procedure::
130 * Pragma Extend_System::
132 * Pragma External_Name_Casing::
133 * Pragma Finalize_Storage_Only::
134 * Pragma Float_Representation::
136 * Pragma Import_Exception::
137 * Pragma Import_Function::
138 * Pragma Import_Object::
139 * Pragma Import_Procedure::
140 * Pragma Import_Valued_Procedure::
141 * Pragma Initialize_Scalars::
142 * Pragma Inline_Always::
143 * Pragma Inline_Generic::
145 * Pragma Interface_Name::
146 * Pragma Interrupt_Handler::
147 * Pragma Interrupt_State::
148 * Pragma Keep_Names::
151 * Pragma Linker_Alias::
152 * Pragma Linker_Section::
153 * Pragma Long_Float::
154 * Pragma Machine_Attribute::
155 * Pragma Main_Storage::
157 * Pragma Normalize_Scalars::
158 * Pragma Obsolescent::
160 * Pragma Persistent_BSS::
162 * Pragma Profile (Ravenscar)::
163 * Pragma Profile (Restricted)::
164 * Pragma Propagate_Exceptions::
165 * Pragma Psect_Object::
166 * Pragma Pure_Function::
167 * Pragma Restriction_Warnings::
168 * Pragma Source_File_Name::
169 * Pragma Source_File_Name_Project::
170 * Pragma Source_Reference::
171 * Pragma Stream_Convert::
172 * Pragma Style_Checks::
174 * Pragma Suppress_All::
175 * Pragma Suppress_Exception_Locations::
176 * Pragma Suppress_Initialization::
179 * Pragma Task_Storage::
180 * Pragma Thread_Body::
181 * Pragma Time_Slice::
183 * Pragma Unchecked_Union::
184 * Pragma Unimplemented_Unit::
185 * Pragma Universal_Data::
186 * Pragma Unreferenced::
187 * Pragma Unreserve_All_Interrupts::
188 * Pragma Unsuppress::
189 * Pragma Use_VADS_Size::
190 * Pragma Validity_Checks::
193 * Pragma Weak_External::
195 Implementation Defined Attributes
205 * Default_Bit_Order::
213 * Has_Access_Values::
214 * Has_Discriminants::
220 * Max_Interrupt_Priority::
222 * Maximum_Alignment::
226 * Passed_By_Reference::
237 * Unconstrained_Array::
238 * Universal_Literal_String::
239 * Unrestricted_Access::
245 The Implementation of Standard I/O
247 * Standard I/O Packages::
253 * Wide_Wide_Text_IO::
257 * Operations on C Streams::
258 * Interfacing to C Streams::
262 * Ada.Characters.Latin_9 (a-chlat9.ads)::
263 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
264 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
265 * Ada.Characters.Wide_Wide_Latin_1 (a-czila1.ads)::
266 * Ada.Characters.Wide_Wide_Latin_9 (a-czila9.ads)::
267 * Ada.Command_Line.Remove (a-colire.ads)::
268 * Ada.Command_Line.Environment (a-colien.ads)::
269 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
270 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
271 * Ada.Exceptions.Traceback (a-exctra.ads)::
272 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
273 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
274 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
275 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
276 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
277 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
278 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
279 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
280 * GNAT.Array_Split (g-arrspl.ads)::
281 * GNAT.AWK (g-awk.ads)::
282 * GNAT.Bounded_Buffers (g-boubuf.ads)::
283 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
284 * GNAT.Bubble_Sort (g-bubsor.ads)::
285 * GNAT.Bubble_Sort_A (g-busora.ads)::
286 * GNAT.Bubble_Sort_G (g-busorg.ads)::
287 * GNAT.Calendar (g-calend.ads)::
288 * GNAT.Calendar.Time_IO (g-catiio.ads)::
289 * GNAT.Case_Util (g-casuti.ads)::
290 * GNAT.CGI (g-cgi.ads)::
291 * GNAT.CGI.Cookie (g-cgicoo.ads)::
292 * GNAT.CGI.Debug (g-cgideb.ads)::
293 * GNAT.Command_Line (g-comlin.ads)::
294 * GNAT.Compiler_Version (g-comver.ads)::
295 * GNAT.Ctrl_C (g-ctrl_c.ads)::
296 * GNAT.CRC32 (g-crc32.ads)::
297 * GNAT.Current_Exception (g-curexc.ads)::
298 * GNAT.Debug_Pools (g-debpoo.ads)::
299 * GNAT.Debug_Utilities (g-debuti.ads)::
300 * GNAT.Directory_Operations (g-dirope.ads)::
301 * GNAT.Dynamic_HTables (g-dynhta.ads)::
302 * GNAT.Dynamic_Tables (g-dyntab.ads)::
303 * GNAT.Exception_Actions (g-excact.ads)::
304 * GNAT.Exception_Traces (g-exctra.ads)::
305 * GNAT.Exceptions (g-except.ads)::
306 * GNAT.Expect (g-expect.ads)::
307 * GNAT.Float_Control (g-flocon.ads)::
308 * GNAT.Heap_Sort (g-heasor.ads)::
309 * GNAT.Heap_Sort_A (g-hesora.ads)::
310 * GNAT.Heap_Sort_G (g-hesorg.ads)::
311 * GNAT.HTable (g-htable.ads)::
312 * GNAT.IO (g-io.ads)::
313 * GNAT.IO_Aux (g-io_aux.ads)::
314 * GNAT.Lock_Files (g-locfil.ads)::
315 * GNAT.MD5 (g-md5.ads)::
316 * GNAT.Memory_Dump (g-memdum.ads)::
317 * GNAT.Most_Recent_Exception (g-moreex.ads)::
318 * GNAT.OS_Lib (g-os_lib.ads)::
319 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
320 * GNAT.Regexp (g-regexp.ads)::
321 * GNAT.Registry (g-regist.ads)::
322 * GNAT.Regpat (g-regpat.ads)::
323 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
324 * GNAT.Semaphores (g-semaph.ads)::
325 * GNAT.Signals (g-signal.ads)::
326 * GNAT.Sockets (g-socket.ads)::
327 * GNAT.Source_Info (g-souinf.ads)::
328 * GNAT.Spell_Checker (g-speche.ads)::
329 * GNAT.Spitbol.Patterns (g-spipat.ads)::
330 * GNAT.Spitbol (g-spitbo.ads)::
331 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
332 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
333 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
334 * GNAT.Strings (g-string.ads)::
335 * GNAT.String_Split (g-strspl.ads)::
336 * GNAT.Table (g-table.ads)::
337 * GNAT.Task_Lock (g-tasloc.ads)::
338 * GNAT.Threads (g-thread.ads)::
339 * GNAT.Traceback (g-traceb.ads)::
340 * GNAT.Traceback.Symbolic (g-trasym.ads)::
341 * GNAT.Wide_String_Split (g-wistsp.ads)::
342 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
343 * Interfaces.C.Extensions (i-cexten.ads)::
344 * Interfaces.C.Streams (i-cstrea.ads)::
345 * Interfaces.CPP (i-cpp.ads)::
346 * Interfaces.Os2lib (i-os2lib.ads)::
347 * Interfaces.Os2lib.Errors (i-os2err.ads)::
348 * Interfaces.Os2lib.Synchronization (i-os2syn.ads)::
349 * Interfaces.Os2lib.Threads (i-os2thr.ads)::
350 * Interfaces.Packed_Decimal (i-pacdec.ads)::
351 * Interfaces.VxWorks (i-vxwork.ads)::
352 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
353 * System.Address_Image (s-addima.ads)::
354 * System.Assertions (s-assert.ads)::
355 * System.Memory (s-memory.ads)::
356 * System.Partition_Interface (s-parint.ads)::
357 * System.Restrictions (s-restri.ads)::
358 * System.Rident (s-rident.ads)::
359 * System.Task_Info (s-tasinf.ads)::
360 * System.Wch_Cnv (s-wchcnv.ads)::
361 * System.Wch_Con (s-wchcon.ads)::
365 * Text_IO Stream Pointer Positioning::
366 * Text_IO Reading and Writing Non-Regular Files::
368 * Treating Text_IO Files as Streams::
369 * Text_IO Extensions::
370 * Text_IO Facilities for Unbounded Strings::
374 * Wide_Text_IO Stream Pointer Positioning::
375 * Wide_Text_IO Reading and Writing Non-Regular Files::
379 * Wide_Wide_Text_IO Stream Pointer Positioning::
380 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
382 Interfacing to Other Languages
385 * Interfacing to C++::
386 * Interfacing to COBOL::
387 * Interfacing to Fortran::
388 * Interfacing to non-GNAT Ada code::
390 Specialized Needs Annexes
392 Implementation of Specific Ada Features
393 * Machine Code Insertions::
394 * GNAT Implementation of Tasking::
395 * GNAT Implementation of Shared Passive Packages::
396 * Code Generation for Array Aggregates::
397 * The Size of Discriminated Records with Default Discriminants::
399 Project File Reference
403 GNU Free Documentation License
410 @node About This Guide
411 @unnumbered About This Guide
415 This manual contains useful information in writing programs using the
416 GNAT compiler. It includes information on implementation dependent
417 characteristics of GNAT, including all the information required by Annex
423 This manual contains useful information in writing programs using the
424 GNAT Pro compiler. It includes information on implementation dependent
425 characteristics of GNAT Pro, including all the information required by Annex
429 Ada 95 is designed to be highly portable.
430 In general, a program will have the same effect even when compiled by
431 different compilers on different platforms.
432 However, since Ada 95 is designed to be used in a
433 wide variety of applications, it also contains a number of system
434 dependent features to be used in interfacing to the external world.
435 @cindex Implementation-dependent features
438 Note: Any program that makes use of implementation-dependent features
439 may be non-portable. You should follow good programming practice and
440 isolate and clearly document any sections of your program that make use
441 of these features in a non-portable manner.
444 For ease of exposition, ``GNAT Pro'' will be referred to simply as
445 ``GNAT'' in the remainder of this document.
449 * What This Reference Manual Contains::
451 * Related Information::
454 @node What This Reference Manual Contains
455 @unnumberedsec What This Reference Manual Contains
458 This reference manual contains the following chapters:
462 @ref{Implementation Defined Pragmas}, lists GNAT implementation-dependent
463 pragmas, which can be used to extend and enhance the functionality of the
467 @ref{Implementation Defined Attributes}, lists GNAT
468 implementation-dependent attributes which can be used to extend and
469 enhance the functionality of the compiler.
472 @ref{Implementation Advice}, provides information on generally
473 desirable behavior which are not requirements that all compilers must
474 follow since it cannot be provided on all systems, or which may be
475 undesirable on some systems.
478 @ref{Implementation Defined Characteristics}, provides a guide to
479 minimizing implementation dependent features.
482 @ref{Intrinsic Subprograms}, describes the intrinsic subprograms
483 implemented by GNAT, and how they can be imported into user
484 application programs.
487 @ref{Representation Clauses and Pragmas}, describes in detail the
488 way that GNAT represents data, and in particular the exact set
489 of representation clauses and pragmas that is accepted.
492 @ref{Standard Library Routines}, provides a listing of packages and a
493 brief description of the functionality that is provided by Ada's
494 extensive set of standard library routines as implemented by GNAT@.
497 @ref{The Implementation of Standard I/O}, details how the GNAT
498 implementation of the input-output facilities.
501 @ref{The GNAT Library}, is a catalog of packages that complement
502 the Ada predefined library.
505 @ref{Interfacing to Other Languages}, describes how programs
506 written in Ada using GNAT can be interfaced to other programming
509 @ref{Specialized Needs Annexes}, describes the GNAT implementation of all
510 of the specialized needs annexes.
513 @ref{Implementation of Specific Ada Features}, discusses issues related
514 to GNAT's implementation of machine code insertions, tasking, and several
518 @ref{Project File Reference}, presents the syntax and semantics
522 @ref{Obsolescent Features} documents implementation dependent features,
523 including pragmas and attributes, which are considered obsolescent, since
524 there are other preferred ways of achieving the same results. These
525 obsolescent forms are retained for backwards compatibility.
529 @cindex Ada 95 ISO/ANSI Standard
531 This reference manual assumes that you are familiar with Ada 95
532 language, as described in the International Standard
533 ANSI/ISO/IEC-8652:1995, Jan 1995.
536 @unnumberedsec Conventions
537 @cindex Conventions, typographical
538 @cindex Typographical conventions
541 Following are examples of the typographical and graphic conventions used
546 @code{Functions}, @code{utility program names}, @code{standard names},
553 @file{File Names}, @samp{button names}, and @samp{field names}.
562 [optional information or parameters]
565 Examples are described by text
567 and then shown this way.
572 Commands that are entered by the user are preceded in this manual by the
573 characters @samp{$ } (dollar sign followed by space). If your system uses this
574 sequence as a prompt, then the commands will appear exactly as you see them
575 in the manual. If your system uses some other prompt, then the command will
576 appear with the @samp{$} replaced by whatever prompt character you are using.
578 @node Related Information
579 @unnumberedsec Related Information
581 See the following documents for further information on GNAT:
585 @cite{GNAT User's Guide}, which provides information on how to use
586 the GNAT compiler system.
589 @cite{Ada 95 Reference Manual}, which contains all reference
590 material for the Ada 95 programming language.
593 @cite{Ada 95 Annotated Reference Manual}, which is an annotated version
594 of the standard reference manual cited above. The annotations describe
595 detailed aspects of the design decision, and in particular contain useful
596 sections on Ada 83 compatibility.
599 @cite{DEC Ada, Technical Overview and Comparison on DIGITAL Platforms},
600 which contains specific information on compatibility between GNAT and
604 @cite{DEC Ada, Language Reference Manual, part number AA-PYZAB-TK} which
605 describes in detail the pragmas and attributes provided by the DEC Ada 83
610 @node Implementation Defined Pragmas
611 @chapter Implementation Defined Pragmas
614 Ada 95 defines a set of pragmas that can be used to supply additional
615 information to the compiler. These language defined pragmas are
616 implemented in GNAT and work as described in the Ada 95 Reference
619 In addition, Ada 95 allows implementations to define additional pragmas
620 whose meaning is defined by the implementation. GNAT provides a number
621 of these implementation-dependent pragmas which can be used to extend
622 and enhance the functionality of the compiler. This section of the GNAT
623 Reference Manual describes these additional pragmas.
625 Note that any program using these pragmas may not be portable to other
626 compilers (although GNAT implements this set of pragmas on all
627 platforms). Therefore if portability to other compilers is an important
628 consideration, the use of these pragmas should be minimized.
631 * Pragma Abort_Defer::
638 * Pragma C_Pass_By_Copy::
640 * Pragma Common_Object::
641 * Pragma Compile_Time_Warning::
642 * Pragma Complex_Representation::
643 * Pragma Component_Alignment::
644 * Pragma Convention_Identifier::
646 * Pragma CPP_Constructor::
647 * Pragma CPP_Virtual::
648 * Pragma CPP_Vtable::
650 * Pragma Detect_Blocking::
651 * Pragma Elaboration_Checks::
653 * Pragma Export_Exception::
654 * Pragma Export_Function::
655 * Pragma Export_Object::
656 * Pragma Export_Procedure::
657 * Pragma Export_Value::
658 * Pragma Export_Valued_Procedure::
659 * Pragma Extend_System::
661 * Pragma External_Name_Casing::
662 * Pragma Finalize_Storage_Only::
663 * Pragma Float_Representation::
665 * Pragma Import_Exception::
666 * Pragma Import_Function::
667 * Pragma Import_Object::
668 * Pragma Import_Procedure::
669 * Pragma Import_Valued_Procedure::
670 * Pragma Initialize_Scalars::
671 * Pragma Inline_Always::
672 * Pragma Inline_Generic::
674 * Pragma Interface_Name::
675 * Pragma Interrupt_Handler::
676 * Pragma Interrupt_State::
677 * Pragma Keep_Names::
680 * Pragma Linker_Alias::
681 * Pragma Linker_Section::
682 * Pragma Long_Float::
683 * Pragma Machine_Attribute::
684 * Pragma Main_Storage::
686 * Pragma Normalize_Scalars::
687 * Pragma Obsolescent::
689 * Pragma Persistent_BSS::
691 * Pragma Profile (Ravenscar)::
692 * Pragma Profile (Restricted)::
693 * Pragma Propagate_Exceptions::
694 * Pragma Psect_Object::
695 * Pragma Pure_Function::
696 * Pragma Restriction_Warnings::
697 * Pragma Source_File_Name::
698 * Pragma Source_File_Name_Project::
699 * Pragma Source_Reference::
700 * Pragma Stream_Convert::
701 * Pragma Style_Checks::
703 * Pragma Suppress_All::
704 * Pragma Suppress_Exception_Locations::
705 * Pragma Suppress_Initialization::
708 * Pragma Task_Storage::
709 * Pragma Thread_Body::
710 * Pragma Time_Slice::
712 * Pragma Unchecked_Union::
713 * Pragma Unimplemented_Unit::
714 * Pragma Universal_Data::
715 * Pragma Unreferenced::
716 * Pragma Unreserve_All_Interrupts::
717 * Pragma Unsuppress::
718 * Pragma Use_VADS_Size::
719 * Pragma Validity_Checks::
722 * Pragma Weak_External::
725 @node Pragma Abort_Defer
726 @unnumberedsec Pragma Abort_Defer
728 @cindex Deferring aborts
736 This pragma must appear at the start of the statement sequence of a
737 handled sequence of statements (right after the @code{begin}). It has
738 the effect of deferring aborts for the sequence of statements (but not
739 for the declarations or handlers, if any, associated with this statement
743 @unnumberedsec Pragma Ada_83
752 A configuration pragma that establishes Ada 83 mode for the unit to
753 which it applies, regardless of the mode set by the command line
754 switches. In Ada 83 mode, GNAT attempts to be as compatible with
755 the syntax and semantics of Ada 83, as defined in the original Ada
756 83 Reference Manual as possible. In particular, the new Ada 95
757 keywords are not recognized, optional package bodies are allowed,
758 and generics may name types with unknown discriminants without using
759 the @code{(<>)} notation. In addition, some but not all of the additional
760 restrictions of Ada 83 are enforced.
762 Ada 83 mode is intended for two purposes. Firstly, it allows existing
763 legacy Ada 83 code to be compiled and adapted to GNAT with less effort.
764 Secondly, it aids in keeping code backwards compatible with Ada 83.
765 However, there is no guarantee that code that is processed correctly
766 by GNAT in Ada 83 mode will in fact compile and execute with an Ada
767 83 compiler, since GNAT does not enforce all the additional checks
771 @unnumberedsec Pragma Ada_95
780 A configuration pragma that establishes Ada 95 mode for the unit to which
781 it applies, regardless of the mode set by the command line switches.
782 This mode is set automatically for the @code{Ada} and @code{System}
783 packages and their children, so you need not specify it in these
784 contexts. This pragma is useful when writing a reusable component that
785 itself uses Ada 95 features, but which is intended to be usable from
786 either Ada 83 or Ada 95 programs.
789 @unnumberedsec Pragma Ada_05
798 A configuration pragma that establishes Ada 2005 mode for the unit to which
799 it applies, regardless of the mode set by the command line switches.
800 This mode is set automatically for the @code{Ada} and @code{System}
801 packages and their children, so you need not specify it in these
802 contexts. This pragma is useful when writing a reusable component that
803 itself uses Ada 2005 features, but which is intended to be usable from
804 either Ada 83 or Ada 95 programs.
806 @node Pragma Annotate
807 @unnumberedsec Pragma Annotate
812 pragma Annotate (IDENTIFIER @{, ARG@});
814 ARG ::= NAME | EXPRESSION
818 This pragma is used to annotate programs. @var{identifier} identifies
819 the type of annotation. GNAT verifies this is an identifier, but does
820 not otherwise analyze it. The @var{arg} argument
821 can be either a string literal or an
822 expression. String literals are assumed to be of type
823 @code{Standard.String}. Names of entities are simply analyzed as entity
824 names. All other expressions are analyzed as expressions, and must be
827 The analyzed pragma is retained in the tree, but not otherwise processed
828 by any part of the GNAT compiler. This pragma is intended for use by
829 external tools, including ASIS@.
832 @unnumberedsec Pragma Assert
839 [, static_string_EXPRESSION]);
843 The effect of this pragma depends on whether the corresponding command
844 line switch is set to activate assertions. The pragma expands into code
845 equivalent to the following:
848 if assertions-enabled then
849 if not boolean_EXPRESSION then
850 System.Assertions.Raise_Assert_Failure
857 The string argument, if given, is the message that will be associated
858 with the exception occurrence if the exception is raised. If no second
859 argument is given, the default message is @samp{@var{file}:@var{nnn}},
860 where @var{file} is the name of the source file containing the assert,
861 and @var{nnn} is the line number of the assert. A pragma is not a
862 statement, so if a statement sequence contains nothing but a pragma
863 assert, then a null statement is required in addition, as in:
868 pragma Assert (K > 3, "Bad value for K");
874 Note that, as with the @code{if} statement to which it is equivalent, the
875 type of the expression is either @code{Standard.Boolean}, or any type derived
876 from this standard type.
878 If assertions are disabled (switch @code{-gnata} not used), then there
879 is no effect (and in particular, any side effects from the expression
880 are suppressed). More precisely it is not quite true that the pragma
881 has no effect, since the expression is analyzed, and may cause types
882 to be frozen if they are mentioned here for the first time.
884 If assertions are enabled, then the given expression is tested, and if
885 it is @code{False} then @code{System.Assertions.Raise_Assert_Failure} is called
886 which results in the raising of @code{Assert_Failure} with the given message.
888 If the boolean expression has side effects, these side effects will turn
889 on and off with the setting of the assertions mode, resulting in
890 assertions that have an effect on the program. You should generally
891 avoid side effects in the expression arguments of this pragma. However,
892 the expressions are analyzed for semantic correctness whether or not
893 assertions are enabled, so turning assertions on and off cannot affect
894 the legality of a program.
896 @node Pragma Ast_Entry
897 @unnumberedsec Pragma Ast_Entry
903 pragma AST_Entry (entry_IDENTIFIER);
907 This pragma is implemented only in the OpenVMS implementation of GNAT@. The
908 argument is the simple name of a single entry; at most one @code{AST_Entry}
909 pragma is allowed for any given entry. This pragma must be used in
910 conjunction with the @code{AST_Entry} attribute, and is only allowed after
911 the entry declaration and in the same task type specification or single task
912 as the entry to which it applies. This pragma specifies that the given entry
913 may be used to handle an OpenVMS asynchronous system trap (@code{AST})
914 resulting from an OpenVMS system service call. The pragma does not affect
915 normal use of the entry. For further details on this pragma, see the
916 DEC Ada Language Reference Manual, section 9.12a.
918 @node Pragma C_Pass_By_Copy
919 @unnumberedsec Pragma C_Pass_By_Copy
920 @cindex Passing by copy
921 @findex C_Pass_By_Copy
925 pragma C_Pass_By_Copy
926 ([Max_Size =>] static_integer_EXPRESSION);
930 Normally the default mechanism for passing C convention records to C
931 convention subprograms is to pass them by reference, as suggested by RM
932 B.3(69). Use the configuration pragma @code{C_Pass_By_Copy} to change
933 this default, by requiring that record formal parameters be passed by
934 copy if all of the following conditions are met:
938 The size of the record type does not exceed@*@var{static_integer_expression}.
940 The record type has @code{Convention C}.
942 The formal parameter has this record type, and the subprogram has a
943 foreign (non-Ada) convention.
947 If these conditions are met the argument is passed by copy, i.e.@: in a
948 manner consistent with what C expects if the corresponding formal in the
949 C prototype is a struct (rather than a pointer to a struct).
951 You can also pass records by copy by specifying the convention
952 @code{C_Pass_By_Copy} for the record type, or by using the extended
953 @code{Import} and @code{Export} pragmas, which allow specification of
954 passing mechanisms on a parameter by parameter basis.
957 @unnumberedsec Pragma Comment
963 pragma Comment (static_string_EXPRESSION);
967 This is almost identical in effect to pragma @code{Ident}. It allows the
968 placement of a comment into the object file and hence into the
969 executable file if the operating system permits such usage. The
970 difference is that @code{Comment}, unlike @code{Ident}, has
971 no limitations on placement of the pragma (it can be placed
972 anywhere in the main source unit), and if more than one pragma
973 is used, all comments are retained.
975 @node Pragma Common_Object
976 @unnumberedsec Pragma Common_Object
977 @findex Common_Object
982 pragma Common_Object (
983 [Internal =>] local_NAME,
984 [, [External =>] EXTERNAL_SYMBOL]
985 [, [Size =>] EXTERNAL_SYMBOL] );
989 | static_string_EXPRESSION
993 This pragma enables the shared use of variables stored in overlaid
994 linker areas corresponding to the use of @code{COMMON}
995 in Fortran. The single
996 object @var{local_NAME} is assigned to the area designated by
997 the @var{External} argument.
998 You may define a record to correspond to a series
999 of fields. The @var{size} argument
1000 is syntax checked in GNAT, but otherwise ignored.
1002 @code{Common_Object} is not supported on all platforms. If no
1003 support is available, then the code generator will issue a message
1004 indicating that the necessary attribute for implementation of this
1005 pragma is not available.
1007 @node Pragma Compile_Time_Warning
1008 @unnumberedsec Pragma Compile_Time_Warning
1009 @findex Compile_Time_Warning
1013 @smallexample @c ada
1014 pragma Compile_Time_Warning
1015 (boolean_EXPRESSION, static_string_EXPRESSION);
1019 This pragma can be used to generate additional compile time warnings. It
1020 is particularly useful in generics, where warnings can be issued for
1021 specific problematic instantiations. The first parameter is a boolean
1022 expression. The pragma is effective only if the value of this expression
1023 is known at compile time, and has the value True. The set of expressions
1024 whose values are known at compile time includes all static boolean
1025 expressions, and also other values which the compiler can determine
1026 at compile time (e.g. the size of a record type set by an explicit
1027 size representation clause, or the value of a variable which was
1028 initialized to a constant and is known not to have been modified).
1029 If these conditions are met, a warning message is generated using
1030 the value given as the second argument. This string value may contain
1031 embedded ASCII.LF characters to break the message into multiple lines.
1033 @node Pragma Complex_Representation
1034 @unnumberedsec Pragma Complex_Representation
1035 @findex Complex_Representation
1039 @smallexample @c ada
1040 pragma Complex_Representation
1041 ([Entity =>] local_NAME);
1045 The @var{Entity} argument must be the name of a record type which has
1046 two fields of the same floating-point type. The effect of this pragma is
1047 to force gcc to use the special internal complex representation form for
1048 this record, which may be more efficient. Note that this may result in
1049 the code for this type not conforming to standard ABI (application
1050 binary interface) requirements for the handling of record types. For
1051 example, in some environments, there is a requirement for passing
1052 records by pointer, and the use of this pragma may result in passing
1053 this type in floating-point registers.
1055 @node Pragma Component_Alignment
1056 @unnumberedsec Pragma Component_Alignment
1057 @cindex Alignments of components
1058 @findex Component_Alignment
1062 @smallexample @c ada
1063 pragma Component_Alignment (
1064 [Form =>] ALIGNMENT_CHOICE
1065 [, [Name =>] type_local_NAME]);
1067 ALIGNMENT_CHOICE ::=
1075 Specifies the alignment of components in array or record types.
1076 The meaning of the @var{Form} argument is as follows:
1079 @findex Component_Size
1080 @item Component_Size
1081 Aligns scalar components and subcomponents of the array or record type
1082 on boundaries appropriate to their inherent size (naturally
1083 aligned). For example, 1-byte components are aligned on byte boundaries,
1084 2-byte integer components are aligned on 2-byte boundaries, 4-byte
1085 integer components are aligned on 4-byte boundaries and so on. These
1086 alignment rules correspond to the normal rules for C compilers on all
1087 machines except the VAX@.
1089 @findex Component_Size_4
1090 @item Component_Size_4
1091 Naturally aligns components with a size of four or fewer
1092 bytes. Components that are larger than 4 bytes are placed on the next
1095 @findex Storage_Unit
1097 Specifies that array or record components are byte aligned, i.e.@:
1098 aligned on boundaries determined by the value of the constant
1099 @code{System.Storage_Unit}.
1103 Specifies that array or record components are aligned on default
1104 boundaries, appropriate to the underlying hardware or operating system or
1105 both. For OpenVMS VAX systems, the @code{Default} choice is the same as
1106 the @code{Storage_Unit} choice (byte alignment). For all other systems,
1107 the @code{Default} choice is the same as @code{Component_Size} (natural
1112 If the @code{Name} parameter is present, @var{type_local_NAME} must
1113 refer to a local record or array type, and the specified alignment
1114 choice applies to the specified type. The use of
1115 @code{Component_Alignment} together with a pragma @code{Pack} causes the
1116 @code{Component_Alignment} pragma to be ignored. The use of
1117 @code{Component_Alignment} together with a record representation clause
1118 is only effective for fields not specified by the representation clause.
1120 If the @code{Name} parameter is absent, the pragma can be used as either
1121 a configuration pragma, in which case it applies to one or more units in
1122 accordance with the normal rules for configuration pragmas, or it can be
1123 used within a declarative part, in which case it applies to types that
1124 are declared within this declarative part, or within any nested scope
1125 within this declarative part. In either case it specifies the alignment
1126 to be applied to any record or array type which has otherwise standard
1129 If the alignment for a record or array type is not specified (using
1130 pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
1131 clause), the GNAT uses the default alignment as described previously.
1133 @node Pragma Convention_Identifier
1134 @unnumberedsec Pragma Convention_Identifier
1135 @findex Convention_Identifier
1136 @cindex Conventions, synonyms
1140 @smallexample @c ada
1141 pragma Convention_Identifier (
1142 [Name =>] IDENTIFIER,
1143 [Convention =>] convention_IDENTIFIER);
1147 This pragma provides a mechanism for supplying synonyms for existing
1148 convention identifiers. The @code{Name} identifier can subsequently
1149 be used as a synonym for the given convention in other pragmas (including
1150 for example pragma @code{Import} or another @code{Convention_Identifier}
1151 pragma). As an example of the use of this, suppose you had legacy code
1152 which used Fortran77 as the identifier for Fortran. Then the pragma:
1154 @smallexample @c ada
1155 pragma Convention_Identifier (Fortran77, Fortran);
1159 would allow the use of the convention identifier @code{Fortran77} in
1160 subsequent code, avoiding the need to modify the sources. As another
1161 example, you could use this to parametrize convention requirements
1162 according to systems. Suppose you needed to use @code{Stdcall} on
1163 windows systems, and @code{C} on some other system, then you could
1164 define a convention identifier @code{Library} and use a single
1165 @code{Convention_Identifier} pragma to specify which convention
1166 would be used system-wide.
1168 @node Pragma CPP_Class
1169 @unnumberedsec Pragma CPP_Class
1171 @cindex Interfacing with C++
1175 @smallexample @c ada
1176 pragma CPP_Class ([Entity =>] local_NAME);
1180 The argument denotes an entity in the current declarative region
1181 that is declared as a tagged or untagged record type. It indicates that
1182 the type corresponds to an externally declared C++ class type, and is to
1183 be laid out the same way that C++ would lay out the type.
1185 If (and only if) the type is tagged, at least one component in the
1186 record must be of type @code{Interfaces.CPP.Vtable_Ptr}, corresponding
1187 to the C++ Vtable (or Vtables in the case of multiple inheritance) used
1190 Types for which @code{CPP_Class} is specified do not have assignment or
1191 equality operators defined (such operations can be imported or declared
1192 as subprograms as required). Initialization is allowed only by
1193 constructor functions (see pragma @code{CPP_Constructor}).
1195 Pragma @code{CPP_Class} is intended primarily for automatic generation
1196 using an automatic binding generator tool.
1197 See @ref{Interfacing to C++} for related information.
1199 @node Pragma CPP_Constructor
1200 @unnumberedsec Pragma CPP_Constructor
1201 @cindex Interfacing with C++
1202 @findex CPP_Constructor
1206 @smallexample @c ada
1207 pragma CPP_Constructor ([Entity =>] local_NAME);
1211 This pragma identifies an imported function (imported in the usual way
1212 with pragma @code{Import}) as corresponding to a C++
1213 constructor. The argument is a name that must have been
1214 previously mentioned in a pragma @code{Import}
1215 with @code{Convention} = @code{CPP}, and must be of one of the following
1220 @code{function @var{Fname} return @var{T}'Class}
1223 @code{function @var{Fname} (@dots{}) return @var{T}'Class}
1227 where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.
1229 The first form is the default constructor, used when an object of type
1230 @var{T} is created on the Ada side with no explicit constructor. Other
1231 constructors (including the copy constructor, which is simply a special
1232 case of the second form in which the one and only argument is of type
1233 @var{T}), can only appear in two contexts:
1237 On the right side of an initialization of an object of type @var{T}.
1239 In an extension aggregate for an object of a type derived from @var{T}.
1243 Although the constructor is described as a function that returns a value
1244 on the Ada side, it is typically a procedure with an extra implicit
1245 argument (the object being initialized) at the implementation
1246 level. GNAT issues the appropriate call, whatever it is, to get the
1247 object properly initialized.
1249 In the case of derived objects, you may use one of two possible forms
1250 for declaring and creating an object:
1253 @item @code{New_Object : Derived_T}
1254 @item @code{New_Object : Derived_T := (@var{constructor-call with} @dots{})}
1258 In the first case the default constructor is called and extension fields
1259 if any are initialized according to the default initialization
1260 expressions in the Ada declaration. In the second case, the given
1261 constructor is called and the extension aggregate indicates the explicit
1262 values of the extension fields.
1264 If no constructors are imported, it is impossible to create any objects
1265 on the Ada side. If no default constructor is imported, only the
1266 initialization forms using an explicit call to a constructor are
1269 Pragma @code{CPP_Constructor} is intended primarily for automatic generation
1270 using an automatic binding generator tool.
1271 See @ref{Interfacing to C++} for more related information.
1273 @node Pragma CPP_Virtual
1274 @unnumberedsec Pragma CPP_Virtual
1275 @cindex Interfacing to C++
1280 @smallexample @c ada
1283 [, [Vtable_Ptr =>] vtable_ENTITY,]
1284 [, [Position =>] static_integer_EXPRESSION]);
1288 This pragma serves the same function as pragma @code{Import} in that
1289 case of a virtual function imported from C++. The @var{Entity} argument
1291 primitive subprogram of a tagged type to which pragma @code{CPP_Class}
1292 applies. The @var{Vtable_Ptr} argument specifies
1293 the Vtable_Ptr component which contains the
1294 entry for this virtual function. The @var{Position} argument
1295 is the sequential number
1296 counting virtual functions for this Vtable starting at 1.
1298 The @code{Vtable_Ptr} and @code{Position} arguments may be omitted if
1299 there is one Vtable_Ptr present (single inheritance case) and all
1300 virtual functions are imported. In that case the compiler can deduce both
1303 No @code{External_Name} or @code{Link_Name} arguments are required for a
1304 virtual function, since it is always accessed indirectly via the
1305 appropriate Vtable entry.
1307 Pragma @code{CPP_Virtual} is intended primarily for automatic generation
1308 using an automatic binding generator tool.
1309 See @ref{Interfacing to C++} for related information.
1311 @node Pragma CPP_Vtable
1312 @unnumberedsec Pragma CPP_Vtable
1313 @cindex Interfacing with C++
1318 @smallexample @c ada
1321 [Vtable_Ptr =>] vtable_ENTITY,
1322 [Entry_Count =>] static_integer_EXPRESSION);
1326 Given a record to which the pragma @code{CPP_Class} applies,
1327 this pragma can be specified for each component of type
1328 @code{CPP.Interfaces.Vtable_Ptr}.
1329 @var{Entity} is the tagged type, @var{Vtable_Ptr}
1330 is the record field of type @code{Vtable_Ptr}, and @var{Entry_Count} is
1331 the number of virtual functions on the C++ side. Not all of these
1332 functions need to be imported on the Ada side.
1334 You may omit the @code{CPP_Vtable} pragma if there is only one
1335 @code{Vtable_Ptr} component in the record and all virtual functions are
1336 imported on the Ada side (the default value for the entry count in this
1337 case is simply the total number of virtual functions).
1339 Pragma @code{CPP_Vtable} is intended primarily for automatic generation
1340 using an automatic binding generator tool.
1341 See @ref{Interfacing to C++} for related information.
1344 @unnumberedsec Pragma Debug
1349 @smallexample @c ada
1350 pragma Debug (PROCEDURE_CALL_WITHOUT_SEMICOLON);
1352 PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
1354 | PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
1358 The argument has the syntactic form of an expression, meeting the
1359 syntactic requirements for pragmas.
1361 If assertions are not enabled on the command line, this pragma has no
1362 effect. If asserts are enabled, the semantics of the pragma is exactly
1363 equivalent to the procedure call statement corresponding to the argument
1364 with a terminating semicolon. Pragmas are permitted in sequences of
1365 declarations, so you can use pragma @code{Debug} to intersperse calls to
1366 debug procedures in the middle of declarations.
1368 @node Pragma Detect_Blocking
1369 @unnumberedsec Pragma Detect_Blocking
1370 @findex Detect_Blocking
1374 @smallexample @c ada
1375 pragma Detect_Blocking;
1379 This is a configuration pragma that forces the detection of potentially
1380 blocking operations within a protected operation, and to raise Program_Error
1383 @node Pragma Elaboration_Checks
1384 @unnumberedsec Pragma Elaboration_Checks
1385 @cindex Elaboration control
1386 @findex Elaboration_Checks
1390 @smallexample @c ada
1391 pragma Elaboration_Checks (Dynamic | Static);
1395 This is a configuration pragma that provides control over the
1396 elaboration model used by the compilation affected by the
1397 pragma. If the parameter is @code{Dynamic},
1398 then the dynamic elaboration
1399 model described in the Ada Reference Manual is used, as though
1400 the @code{-gnatE} switch had been specified on the command
1401 line. If the parameter is @code{Static}, then the default GNAT static
1402 model is used. This configuration pragma overrides the setting
1403 of the command line. For full details on the elaboration models
1404 used by the GNAT compiler, see section ``Elaboration Order
1405 Handling in GNAT'' in the @cite{GNAT User's Guide}.
1407 @node Pragma Eliminate
1408 @unnumberedsec Pragma Eliminate
1409 @cindex Elimination of unused subprograms
1414 @smallexample @c ada
1416 [Unit_Name =>] IDENTIFIER |
1417 SELECTED_COMPONENT);
1420 [Unit_Name =>] IDENTIFIER |
1422 [Entity =>] IDENTIFIER |
1423 SELECTED_COMPONENT |
1425 [,OVERLOADING_RESOLUTION]);
1427 OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
1430 PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
1433 PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES
1435 FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
1436 Result_Type => result_SUBTYPE_NAME]
1438 PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
1439 SUBTYPE_NAME ::= STRING_VALUE
1441 SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
1442 SOURCE_TRACE ::= STRING_VALUE
1444 STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
1448 This pragma indicates that the given entity is not used outside the
1449 compilation unit it is defined in. The entity must be an explicitly declared
1450 subprogram; this includes generic subprogram instances and
1451 subprograms declared in generic package instances.
1453 If the entity to be eliminated is a library level subprogram, then
1454 the first form of pragma @code{Eliminate} is used with only a single argument.
1455 In this form, the @code{Unit_Name} argument specifies the name of the
1456 library level unit to be eliminated.
1458 In all other cases, both @code{Unit_Name} and @code{Entity} arguments
1459 are required. If item is an entity of a library package, then the first
1460 argument specifies the unit name, and the second argument specifies
1461 the particular entity. If the second argument is in string form, it must
1462 correspond to the internal manner in which GNAT stores entity names (see
1463 compilation unit Namet in the compiler sources for details).
1465 The remaining parameters (OVERLOADING_RESOLUTION) are optionally used
1466 to distinguish between overloaded subprograms. If a pragma does not contain
1467 the OVERLOADING_RESOLUTION parameter(s), it is applied to all the overloaded
1468 subprograms denoted by the first two parameters.
1470 Use PARAMETER_AND_RESULT_TYPE_PROFILE to specify the profile of the subprogram
1471 to be eliminated in a manner similar to that used for the extended
1472 @code{Import} and @code{Export} pragmas, except that the subtype names are
1473 always given as strings. At the moment, this form of distinguishing
1474 overloaded subprograms is implemented only partially, so we do not recommend
1475 using it for practical subprogram elimination.
1477 Note, that in case of a parameterless procedure its profile is represented
1478 as @code{Parameter_Types => ("")}
1480 Alternatively, the @code{Source_Location} parameter is used to specify
1481 which overloaded alternative is to be eliminated by pointing to the
1482 location of the DEFINING_PROGRAM_UNIT_NAME of this subprogram in the
1483 source text. The string literal (or concatenation of string literals)
1484 given as SOURCE_TRACE must have the following format:
1486 @smallexample @c ada
1487 SOURCE_TRACE ::= SOURCE_LOCATION@{LBRACKET SOURCE_LOCATION RBRACKET@}
1492 SOURCE_LOCATION ::= FILE_NAME:LINE_NUMBER
1493 FILE_NAME ::= STRING_LITERAL
1494 LINE_NUMBER ::= DIGIT @{DIGIT@}
1497 SOURCE_TRACE should be the short name of the source file (with no directory
1498 information), and LINE_NUMBER is supposed to point to the line where the
1499 defining name of the subprogram is located.
1501 For the subprograms that are not a part of generic instantiations, only one
1502 SOURCE_LOCATION is used. If a subprogram is declared in a package
1503 instantiation, SOURCE_TRACE contains two SOURCE_LOCATIONs, the first one is
1504 the location of the (DEFINING_PROGRAM_UNIT_NAME of the) instantiation, and the
1505 second one denotes the declaration of the corresponding subprogram in the
1506 generic package. This approach is recursively used to create SOURCE_LOCATIONs
1507 in case of nested instantiations.
1509 The effect of the pragma is to allow the compiler to eliminate
1510 the code or data associated with the named entity. Any reference to
1511 an eliminated entity outside the compilation unit it is defined in,
1512 causes a compile time or link time error.
1514 The intention of pragma @code{Eliminate} is to allow a program to be compiled
1515 in a system independent manner, with unused entities eliminated, without
1516 the requirement of modifying the source text. Normally the required set
1517 of @code{Eliminate} pragmas is constructed automatically using the gnatelim
1518 tool. Elimination of unused entities local to a compilation unit is
1519 automatic, without requiring the use of pragma @code{Eliminate}.
1521 Note that the reason this pragma takes string literals where names might
1522 be expected is that a pragma @code{Eliminate} can appear in a context where the
1523 relevant names are not visible.
1525 Note that any change in the source files that includes removing, splitting of
1526 adding lines may make the set of Eliminate pragmas using SOURCE_LOCATION
1529 @node Pragma Export_Exception
1530 @unnumberedsec Pragma Export_Exception
1532 @findex Export_Exception
1536 @smallexample @c ada
1537 pragma Export_Exception (
1538 [Internal =>] local_NAME,
1539 [, [External =>] EXTERNAL_SYMBOL,]
1540 [, [Form =>] Ada | VMS]
1541 [, [Code =>] static_integer_EXPRESSION]);
1545 | static_string_EXPRESSION
1549 This pragma is implemented only in the OpenVMS implementation of GNAT@. It
1550 causes the specified exception to be propagated outside of the Ada program,
1551 so that it can be handled by programs written in other OpenVMS languages.
1552 This pragma establishes an external name for an Ada exception and makes the
1553 name available to the OpenVMS Linker as a global symbol. For further details
1554 on this pragma, see the
1555 DEC Ada Language Reference Manual, section 13.9a3.2.
1557 @node Pragma Export_Function
1558 @unnumberedsec Pragma Export_Function
1559 @cindex Argument passing mechanisms
1560 @findex Export_Function
1565 @smallexample @c ada
1566 pragma Export_Function (
1567 [Internal =>] local_NAME,
1568 [, [External =>] EXTERNAL_SYMBOL]
1569 [, [Parameter_Types =>] PARAMETER_TYPES]
1570 [, [Result_Type =>] result_SUBTYPE_MARK]
1571 [, [Mechanism =>] MECHANISM]
1572 [, [Result_Mechanism =>] MECHANISM_NAME]);
1576 | static_string_EXPRESSION
1581 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1585 | subtype_Name ' Access
1589 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1591 MECHANISM_ASSOCIATION ::=
1592 [formal_parameter_NAME =>] MECHANISM_NAME
1600 Use this pragma to make a function externally callable and optionally
1601 provide information on mechanisms to be used for passing parameter and
1602 result values. We recommend, for the purposes of improving portability,
1603 this pragma always be used in conjunction with a separate pragma
1604 @code{Export}, which must precede the pragma @code{Export_Function}.
1605 GNAT does not require a separate pragma @code{Export}, but if none is
1606 present, @code{Convention Ada} is assumed, which is usually
1607 not what is wanted, so it is usually appropriate to use this
1608 pragma in conjunction with a @code{Export} or @code{Convention}
1609 pragma that specifies the desired foreign convention.
1610 Pragma @code{Export_Function}
1611 (and @code{Export}, if present) must appear in the same declarative
1612 region as the function to which they apply.
1614 @var{internal_name} must uniquely designate the function to which the
1615 pragma applies. If more than one function name exists of this name in
1616 the declarative part you must use the @code{Parameter_Types} and
1617 @code{Result_Type} parameters is mandatory to achieve the required
1618 unique designation. @var{subtype_ mark}s in these parameters must
1619 exactly match the subtypes in the corresponding function specification,
1620 using positional notation to match parameters with subtype marks.
1621 The form with an @code{'Access} attribute can be used to match an
1622 anonymous access parameter.
1625 @cindex Passing by descriptor
1626 Note that passing by descriptor is not supported, even on the OpenVMS
1629 @cindex Suppressing external name
1630 Special treatment is given if the EXTERNAL is an explicit null
1631 string or a static string expressions that evaluates to the null
1632 string. In this case, no external name is generated. This form
1633 still allows the specification of parameter mechanisms.
1635 @node Pragma Export_Object
1636 @unnumberedsec Pragma Export_Object
1637 @findex Export_Object
1641 @smallexample @c ada
1642 pragma Export_Object
1643 [Internal =>] local_NAME,
1644 [, [External =>] EXTERNAL_SYMBOL]
1645 [, [Size =>] EXTERNAL_SYMBOL]
1649 | static_string_EXPRESSION
1653 This pragma designates an object as exported, and apart from the
1654 extended rules for external symbols, is identical in effect to the use of
1655 the normal @code{Export} pragma applied to an object. You may use a
1656 separate Export pragma (and you probably should from the point of view
1657 of portability), but it is not required. @var{Size} is syntax checked,
1658 but otherwise ignored by GNAT@.
1660 @node Pragma Export_Procedure
1661 @unnumberedsec Pragma Export_Procedure
1662 @findex Export_Procedure
1666 @smallexample @c ada
1667 pragma Export_Procedure (
1668 [Internal =>] local_NAME
1669 [, [External =>] EXTERNAL_SYMBOL]
1670 [, [Parameter_Types =>] PARAMETER_TYPES]
1671 [, [Mechanism =>] MECHANISM]);
1675 | static_string_EXPRESSION
1680 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1684 | subtype_Name ' Access
1688 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1690 MECHANISM_ASSOCIATION ::=
1691 [formal_parameter_NAME =>] MECHANISM_NAME
1699 This pragma is identical to @code{Export_Function} except that it
1700 applies to a procedure rather than a function and the parameters
1701 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
1702 GNAT does not require a separate pragma @code{Export}, but if none is
1703 present, @code{Convention Ada} is assumed, which is usually
1704 not what is wanted, so it is usually appropriate to use this
1705 pragma in conjunction with a @code{Export} or @code{Convention}
1706 pragma that specifies the desired foreign convention.
1709 @cindex Passing by descriptor
1710 Note that passing by descriptor is not supported, even on the OpenVMS
1713 @cindex Suppressing external name
1714 Special treatment is given if the EXTERNAL is an explicit null
1715 string or a static string expressions that evaluates to the null
1716 string. In this case, no external name is generated. This form
1717 still allows the specification of parameter mechanisms.
1719 @node Pragma Export_Value
1720 @unnumberedsec Pragma Export_Value
1721 @findex Export_Value
1725 @smallexample @c ada
1726 pragma Export_Value (
1727 [Value =>] static_integer_EXPRESSION,
1728 [Link_Name =>] static_string_EXPRESSION);
1732 This pragma serves to export a static integer value for external use.
1733 The first argument specifies the value to be exported. The Link_Name
1734 argument specifies the symbolic name to be associated with the integer
1735 value. This pragma is useful for defining a named static value in Ada
1736 that can be referenced in assembly language units to be linked with
1737 the application. This pragma is currently supported only for the
1738 AAMP target and is ignored for other targets.
1740 @node Pragma Export_Valued_Procedure
1741 @unnumberedsec Pragma Export_Valued_Procedure
1742 @findex Export_Valued_Procedure
1746 @smallexample @c ada
1747 pragma Export_Valued_Procedure (
1748 [Internal =>] local_NAME
1749 [, [External =>] EXTERNAL_SYMBOL]
1750 [, [Parameter_Types =>] PARAMETER_TYPES]
1751 [, [Mechanism =>] MECHANISM]);
1755 | static_string_EXPRESSION
1760 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
1764 | subtype_Name ' Access
1768 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
1770 MECHANISM_ASSOCIATION ::=
1771 [formal_parameter_NAME =>] MECHANISM_NAME
1779 This pragma is identical to @code{Export_Procedure} except that the
1780 first parameter of @var{local_NAME}, which must be present, must be of
1781 mode @code{OUT}, and externally the subprogram is treated as a function
1782 with this parameter as the result of the function. GNAT provides for
1783 this capability to allow the use of @code{OUT} and @code{IN OUT}
1784 parameters in interfacing to external functions (which are not permitted
1786 GNAT does not require a separate pragma @code{Export}, but if none is
1787 present, @code{Convention Ada} is assumed, which is almost certainly
1788 not what is wanted since the whole point of this pragma is to interface
1789 with foreign language functions, so it is usually appropriate to use this
1790 pragma in conjunction with a @code{Export} or @code{Convention}
1791 pragma that specifies the desired foreign convention.
1794 @cindex Passing by descriptor
1795 Note that passing by descriptor is not supported, even on the OpenVMS
1798 @cindex Suppressing external name
1799 Special treatment is given if the EXTERNAL is an explicit null
1800 string or a static string expressions that evaluates to the null
1801 string. In this case, no external name is generated. This form
1802 still allows the specification of parameter mechanisms.
1804 @node Pragma Extend_System
1805 @unnumberedsec Pragma Extend_System
1806 @cindex @code{system}, extending
1808 @findex Extend_System
1812 @smallexample @c ada
1813 pragma Extend_System ([Name =>] IDENTIFIER);
1817 This pragma is used to provide backwards compatibility with other
1818 implementations that extend the facilities of package @code{System}. In
1819 GNAT, @code{System} contains only the definitions that are present in
1820 the Ada 95 RM@. However, other implementations, notably the DEC Ada 83
1821 implementation, provide many extensions to package @code{System}.
1823 For each such implementation accommodated by this pragma, GNAT provides a
1824 package @code{Aux_@var{xxx}}, e.g.@: @code{Aux_DEC} for the DEC Ada 83
1825 implementation, which provides the required additional definitions. You
1826 can use this package in two ways. You can @code{with} it in the normal
1827 way and access entities either by selection or using a @code{use}
1828 clause. In this case no special processing is required.
1830 However, if existing code contains references such as
1831 @code{System.@var{xxx}} where @var{xxx} is an entity in the extended
1832 definitions provided in package @code{System}, you may use this pragma
1833 to extend visibility in @code{System} in a non-standard way that
1834 provides greater compatibility with the existing code. Pragma
1835 @code{Extend_System} is a configuration pragma whose single argument is
1836 the name of the package containing the extended definition
1837 (e.g.@: @code{Aux_DEC} for the DEC Ada case). A unit compiled under
1838 control of this pragma will be processed using special visibility
1839 processing that looks in package @code{System.Aux_@var{xxx}} where
1840 @code{Aux_@var{xxx}} is the pragma argument for any entity referenced in
1841 package @code{System}, but not found in package @code{System}.
1843 You can use this pragma either to access a predefined @code{System}
1844 extension supplied with the compiler, for example @code{Aux_DEC} or
1845 you can construct your own extension unit following the above
1846 definition. Note that such a package is a child of @code{System}
1847 and thus is considered part of the implementation. To compile
1848 it you will have to use the appropriate switch for compiling
1849 system units. See the GNAT User's Guide for details.
1851 @node Pragma External
1852 @unnumberedsec Pragma External
1857 @smallexample @c ada
1859 [ Convention =>] convention_IDENTIFIER,
1860 [ Entity =>] local_NAME
1861 [, [External_Name =>] static_string_EXPRESSION ]
1862 [, [Link_Name =>] static_string_EXPRESSION ]);
1866 This pragma is identical in syntax and semantics to pragma
1867 @code{Export} as defined in the Ada Reference Manual. It is
1868 provided for compatibility with some Ada 83 compilers that
1869 used this pragma for exactly the same purposes as pragma
1870 @code{Export} before the latter was standardized.
1872 @node Pragma External_Name_Casing
1873 @unnumberedsec Pragma External_Name_Casing
1874 @cindex Dec Ada 83 casing compatibility
1875 @cindex External Names, casing
1876 @cindex Casing of External names
1877 @findex External_Name_Casing
1881 @smallexample @c ada
1882 pragma External_Name_Casing (
1883 Uppercase | Lowercase
1884 [, Uppercase | Lowercase | As_Is]);
1888 This pragma provides control over the casing of external names associated
1889 with Import and Export pragmas. There are two cases to consider:
1892 @item Implicit external names
1893 Implicit external names are derived from identifiers. The most common case
1894 arises when a standard Ada 95 Import or Export pragma is used with only two
1897 @smallexample @c ada
1898 pragma Import (C, C_Routine);
1902 Since Ada is a case insensitive language, the spelling of the identifier in
1903 the Ada source program does not provide any information on the desired
1904 casing of the external name, and so a convention is needed. In GNAT the
1905 default treatment is that such names are converted to all lower case
1906 letters. This corresponds to the normal C style in many environments.
1907 The first argument of pragma @code{External_Name_Casing} can be used to
1908 control this treatment. If @code{Uppercase} is specified, then the name
1909 will be forced to all uppercase letters. If @code{Lowercase} is specified,
1910 then the normal default of all lower case letters will be used.
1912 This same implicit treatment is also used in the case of extended DEC Ada 83
1913 compatible Import and Export pragmas where an external name is explicitly
1914 specified using an identifier rather than a string.
1916 @item Explicit external names
1917 Explicit external names are given as string literals. The most common case
1918 arises when a standard Ada 95 Import or Export pragma is used with three
1921 @smallexample @c ada
1922 pragma Import (C, C_Routine, "C_routine");
1926 In this case, the string literal normally provides the exact casing required
1927 for the external name. The second argument of pragma
1928 @code{External_Name_Casing} may be used to modify this behavior.
1929 If @code{Uppercase} is specified, then the name
1930 will be forced to all uppercase letters. If @code{Lowercase} is specified,
1931 then the name will be forced to all lowercase letters. A specification of
1932 @code{As_Is} provides the normal default behavior in which the casing is
1933 taken from the string provided.
1937 This pragma may appear anywhere that a pragma is valid. In particular, it
1938 can be used as a configuration pragma in the @file{gnat.adc} file, in which
1939 case it applies to all subsequent compilations, or it can be used as a program
1940 unit pragma, in which case it only applies to the current unit, or it can
1941 be used more locally to control individual Import/Export pragmas.
1943 It is primarily intended for use with OpenVMS systems, where many
1944 compilers convert all symbols to upper case by default. For interfacing to
1945 such compilers (e.g.@: the DEC C compiler), it may be convenient to use
1948 @smallexample @c ada
1949 pragma External_Name_Casing (Uppercase, Uppercase);
1953 to enforce the upper casing of all external symbols.
1955 @node Pragma Finalize_Storage_Only
1956 @unnumberedsec Pragma Finalize_Storage_Only
1957 @findex Finalize_Storage_Only
1961 @smallexample @c ada
1962 pragma Finalize_Storage_Only (first_subtype_local_NAME);
1966 This pragma allows the compiler not to emit a Finalize call for objects
1967 defined at the library level. This is mostly useful for types where
1968 finalization is only used to deal with storage reclamation since in most
1969 environments it is not necessary to reclaim memory just before terminating
1970 execution, hence the name.
1972 @node Pragma Float_Representation
1973 @unnumberedsec Pragma Float_Representation
1975 @findex Float_Representation
1979 @smallexample @c ada
1980 pragma Float_Representation (FLOAT_REP);
1982 FLOAT_REP ::= VAX_Float | IEEE_Float
1987 allows control over the internal representation chosen for the predefined
1988 floating point types declared in the packages @code{Standard} and
1989 @code{System}. On all systems other than OpenVMS, the argument must
1990 be @code{IEEE_Float} and the pragma has no effect. On OpenVMS, the
1991 argument may be @code{VAX_Float} to specify the use of the VAX float
1992 format for the floating-point types in Standard. This requires that
1993 the standard runtime libraries be recompiled. See the
1994 description of the @code{GNAT LIBRARY} command in the OpenVMS version
1995 of the GNAT Users Guide for details on the use of this command.
1998 @unnumberedsec Pragma Ident
2003 @smallexample @c ada
2004 pragma Ident (static_string_EXPRESSION);
2008 This pragma provides a string identification in the generated object file,
2009 if the system supports the concept of this kind of identification string.
2010 This pragma is allowed only in the outermost declarative part or
2011 declarative items of a compilation unit. If more than one @code{Ident}
2012 pragma is given, only the last one processed is effective.
2014 On OpenVMS systems, the effect of the pragma is identical to the effect of
2015 the DEC Ada 83 pragma of the same name. Note that in DEC Ada 83, the
2016 maximum allowed length is 31 characters, so if it is important to
2017 maintain compatibility with this compiler, you should obey this length
2020 @node Pragma Import_Exception
2021 @unnumberedsec Pragma Import_Exception
2023 @findex Import_Exception
2027 @smallexample @c ada
2028 pragma Import_Exception (
2029 [Internal =>] local_NAME,
2030 [, [External =>] EXTERNAL_SYMBOL,]
2031 [, [Form =>] Ada | VMS]
2032 [, [Code =>] static_integer_EXPRESSION]);
2036 | static_string_EXPRESSION
2040 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2041 It allows OpenVMS conditions (for example, from OpenVMS system services or
2042 other OpenVMS languages) to be propagated to Ada programs as Ada exceptions.
2043 The pragma specifies that the exception associated with an exception
2044 declaration in an Ada program be defined externally (in non-Ada code).
2045 For further details on this pragma, see the
2046 DEC Ada Language Reference Manual, section 13.9a.3.1.
2048 @node Pragma Import_Function
2049 @unnumberedsec Pragma Import_Function
2050 @findex Import_Function
2054 @smallexample @c ada
2055 pragma Import_Function (
2056 [Internal =>] local_NAME,
2057 [, [External =>] EXTERNAL_SYMBOL]
2058 [, [Parameter_Types =>] PARAMETER_TYPES]
2059 [, [Result_Type =>] SUBTYPE_MARK]
2060 [, [Mechanism =>] MECHANISM]
2061 [, [Result_Mechanism =>] MECHANISM_NAME]
2062 [, [First_Optional_Parameter =>] IDENTIFIER]);
2066 | static_string_EXPRESSION
2070 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2074 | subtype_Name ' Access
2078 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2080 MECHANISM_ASSOCIATION ::=
2081 [formal_parameter_NAME =>] MECHANISM_NAME
2086 | Descriptor [([Class =>] CLASS_NAME)]
2088 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2092 This pragma is used in conjunction with a pragma @code{Import} to
2093 specify additional information for an imported function. The pragma
2094 @code{Import} (or equivalent pragma @code{Interface}) must precede the
2095 @code{Import_Function} pragma and both must appear in the same
2096 declarative part as the function specification.
2098 The @var{Internal} argument must uniquely designate
2099 the function to which the
2100 pragma applies. If more than one function name exists of this name in
2101 the declarative part you must use the @code{Parameter_Types} and
2102 @var{Result_Type} parameters to achieve the required unique
2103 designation. Subtype marks in these parameters must exactly match the
2104 subtypes in the corresponding function specification, using positional
2105 notation to match parameters with subtype marks.
2106 The form with an @code{'Access} attribute can be used to match an
2107 anonymous access parameter.
2109 You may optionally use the @var{Mechanism} and @var{Result_Mechanism}
2110 parameters to specify passing mechanisms for the
2111 parameters and result. If you specify a single mechanism name, it
2112 applies to all parameters. Otherwise you may specify a mechanism on a
2113 parameter by parameter basis using either positional or named
2114 notation. If the mechanism is not specified, the default mechanism
2118 @cindex Passing by descriptor
2119 Passing by descriptor is supported only on the OpenVMS ports of GNAT@.
2121 @code{First_Optional_Parameter} applies only to OpenVMS ports of GNAT@.
2122 It specifies that the designated parameter and all following parameters
2123 are optional, meaning that they are not passed at the generated code
2124 level (this is distinct from the notion of optional parameters in Ada
2125 where the parameters are passed anyway with the designated optional
2126 parameters). All optional parameters must be of mode @code{IN} and have
2127 default parameter values that are either known at compile time
2128 expressions, or uses of the @code{'Null_Parameter} attribute.
2130 @node Pragma Import_Object
2131 @unnumberedsec Pragma Import_Object
2132 @findex Import_Object
2136 @smallexample @c ada
2137 pragma Import_Object
2138 [Internal =>] local_NAME,
2139 [, [External =>] EXTERNAL_SYMBOL],
2140 [, [Size =>] EXTERNAL_SYMBOL]);
2144 | static_string_EXPRESSION
2148 This pragma designates an object as imported, and apart from the
2149 extended rules for external symbols, is identical in effect to the use of
2150 the normal @code{Import} pragma applied to an object. Unlike the
2151 subprogram case, you need not use a separate @code{Import} pragma,
2152 although you may do so (and probably should do so from a portability
2153 point of view). @var{size} is syntax checked, but otherwise ignored by
2156 @node Pragma Import_Procedure
2157 @unnumberedsec Pragma Import_Procedure
2158 @findex Import_Procedure
2162 @smallexample @c ada
2163 pragma Import_Procedure (
2164 [Internal =>] local_NAME,
2165 [, [External =>] EXTERNAL_SYMBOL]
2166 [, [Parameter_Types =>] PARAMETER_TYPES]
2167 [, [Mechanism =>] MECHANISM]
2168 [, [First_Optional_Parameter =>] IDENTIFIER]);
2172 | static_string_EXPRESSION
2176 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2180 | subtype_Name ' Access
2184 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2186 MECHANISM_ASSOCIATION ::=
2187 [formal_parameter_NAME =>] MECHANISM_NAME
2192 | Descriptor [([Class =>] CLASS_NAME)]
2194 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2198 This pragma is identical to @code{Import_Function} except that it
2199 applies to a procedure rather than a function and the parameters
2200 @code{Result_Type} and @code{Result_Mechanism} are not permitted.
2202 @node Pragma Import_Valued_Procedure
2203 @unnumberedsec Pragma Import_Valued_Procedure
2204 @findex Import_Valued_Procedure
2208 @smallexample @c ada
2209 pragma Import_Valued_Procedure (
2210 [Internal =>] local_NAME,
2211 [, [External =>] EXTERNAL_SYMBOL]
2212 [, [Parameter_Types =>] PARAMETER_TYPES]
2213 [, [Mechanism =>] MECHANISM]
2214 [, [First_Optional_Parameter =>] IDENTIFIER]);
2218 | static_string_EXPRESSION
2222 | TYPE_DESIGNATOR @{, TYPE_DESIGNATOR@}
2226 | subtype_Name ' Access
2230 | (MECHANISM_ASSOCIATION @{, MECHANISM_ASSOCIATION@})
2232 MECHANISM_ASSOCIATION ::=
2233 [formal_parameter_NAME =>] MECHANISM_NAME
2238 | Descriptor [([Class =>] CLASS_NAME)]
2240 CLASS_NAME ::= ubs | ubsb | uba | s | sb | a | nca
2244 This pragma is identical to @code{Import_Procedure} except that the
2245 first parameter of @var{local_NAME}, which must be present, must be of
2246 mode @code{OUT}, and externally the subprogram is treated as a function
2247 with this parameter as the result of the function. The purpose of this
2248 capability is to allow the use of @code{OUT} and @code{IN OUT}
2249 parameters in interfacing to external functions (which are not permitted
2250 in Ada functions). You may optionally use the @code{Mechanism}
2251 parameters to specify passing mechanisms for the parameters.
2252 If you specify a single mechanism name, it applies to all parameters.
2253 Otherwise you may specify a mechanism on a parameter by parameter
2254 basis using either positional or named notation. If the mechanism is not
2255 specified, the default mechanism is used.
2257 Note that it is important to use this pragma in conjunction with a separate
2258 pragma Import that specifies the desired convention, since otherwise the
2259 default convention is Ada, which is almost certainly not what is required.
2261 @node Pragma Initialize_Scalars
2262 @unnumberedsec Pragma Initialize_Scalars
2263 @findex Initialize_Scalars
2264 @cindex debugging with Initialize_Scalars
2268 @smallexample @c ada
2269 pragma Initialize_Scalars;
2273 This pragma is similar to @code{Normalize_Scalars} conceptually but has
2274 two important differences. First, there is no requirement for the pragma
2275 to be used uniformly in all units of a partition, in particular, it is fine
2276 to use this just for some or all of the application units of a partition,
2277 without needing to recompile the run-time library.
2279 In the case where some units are compiled with the pragma, and some without,
2280 then a declaration of a variable where the type is defined in package
2281 Standard or is locally declared will always be subject to initialization,
2282 as will any declaration of a scalar variable. For composite variables,
2283 whether the variable is initialized may also depend on whether the package
2284 in which the type of the variable is declared is compiled with the pragma.
2286 The other important difference is that you can control the value used
2287 for initializing scalar objects. At bind time, you can select several
2288 options for initialization. You can
2289 initialize with invalid values (similar to Normalize_Scalars, though for
2290 Initialize_Scalars it is not always possible to determine the invalid
2291 values in complex cases like signed component fields with non-standard
2292 sizes). You can also initialize with high or
2293 low values, or with a specified bit pattern. See the users guide for binder
2294 options for specifying these cases.
2296 This means that you can compile a program, and then without having to
2297 recompile the program, you can run it with different values being used
2298 for initializing otherwise uninitialized values, to test if your program
2299 behavior depends on the choice. Of course the behavior should not change,
2300 and if it does, then most likely you have an erroneous reference to an
2301 uninitialized value.
2303 It is even possible to change the value at execution time eliminating even
2304 the need to rebind with a different switch using an environment variable.
2305 See the GNAT users guide for details.
2307 Note that pragma @code{Initialize_Scalars} is particularly useful in
2308 conjunction with the enhanced validity checking that is now provided
2309 in GNAT, which checks for invalid values under more conditions.
2310 Using this feature (see description of the @code{-gnatV} flag in the
2311 users guide) in conjunction with pragma @code{Initialize_Scalars}
2312 provides a powerful new tool to assist in the detection of problems
2313 caused by uninitialized variables.
2315 Note: the use of @code{Initialize_Scalars} has a fairly extensive
2316 effect on the generated code. This may cause your code to be
2317 substantially larger. It may also cause an increase in the amount
2318 of stack required, so it is probably a good idea to turn on stack
2319 checking (see description of stack checking in the GNAT users guide)
2320 when using this pragma.
2322 @node Pragma Inline_Always
2323 @unnumberedsec Pragma Inline_Always
2324 @findex Inline_Always
2328 @smallexample @c ada
2329 pragma Inline_Always (NAME [, NAME]);
2333 Similar to pragma @code{Inline} except that inlining is not subject to
2334 the use of option @code{-gnatn} and the inlining happens regardless of
2335 whether this option is used.
2337 @node Pragma Inline_Generic
2338 @unnumberedsec Pragma Inline_Generic
2339 @findex Inline_Generic
2343 @smallexample @c ada
2344 pragma Inline_Generic (generic_package_NAME);
2348 This is implemented for compatibility with DEC Ada 83 and is recognized,
2349 but otherwise ignored, by GNAT@. All generic instantiations are inlined
2350 by default when using GNAT@.
2352 @node Pragma Interface
2353 @unnumberedsec Pragma Interface
2358 @smallexample @c ada
2360 [Convention =>] convention_identifier,
2361 [Entity =>] local_NAME
2362 [, [External_Name =>] static_string_expression],
2363 [, [Link_Name =>] static_string_expression]);
2367 This pragma is identical in syntax and semantics to
2368 the standard Ada 95 pragma @code{Import}. It is provided for compatibility
2369 with Ada 83. The definition is upwards compatible both with pragma
2370 @code{Interface} as defined in the Ada 83 Reference Manual, and also
2371 with some extended implementations of this pragma in certain Ada 83
2374 @node Pragma Interface_Name
2375 @unnumberedsec Pragma Interface_Name
2376 @findex Interface_Name
2380 @smallexample @c ada
2381 pragma Interface_Name (
2382 [Entity =>] local_NAME
2383 [, [External_Name =>] static_string_EXPRESSION]
2384 [, [Link_Name =>] static_string_EXPRESSION]);
2388 This pragma provides an alternative way of specifying the interface name
2389 for an interfaced subprogram, and is provided for compatibility with Ada
2390 83 compilers that use the pragma for this purpose. You must provide at
2391 least one of @var{External_Name} or @var{Link_Name}.
2393 @node Pragma Interrupt_Handler
2394 @unnumberedsec Pragma Interrupt_Handler
2395 @findex Interrupt_Handler
2399 @smallexample @c ada
2400 pragma Interrupt_Handler (procedure_local_NAME);
2404 This program unit pragma is supported for parameterless protected procedures
2405 as described in Annex C of the Ada Reference Manual. On the AAMP target
2406 the pragma can also be specified for nonprotected parameterless procedures
2407 that are declared at the library level (which includes procedures
2408 declared at the top level of a library package). In the case of AAMP,
2409 when this pragma is applied to a nonprotected procedure, the instruction
2410 @code{IERET} is generated for returns from the procedure, enabling
2411 maskable interrupts, in place of the normal return instruction.
2413 @node Pragma Interrupt_State
2414 @unnumberedsec Pragma Interrupt_State
2415 @findex Interrupt_State
2419 @smallexample @c ada
2420 pragma Interrupt_State (Name => value, State => SYSTEM | RUNTIME | USER);
2424 Normally certain interrupts are reserved to the implementation. Any attempt
2425 to attach an interrupt causes Program_Error to be raised, as described in
2426 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
2427 many systems for an @kbd{Ctrl-C} interrupt. Normally this interrupt is
2428 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
2429 interrupt execution. Additionally, signals such as @code{SIGSEGV},
2430 @code{SIGABRT}, @code{SIGFPE} and @code{SIGILL} are often mapped to specific
2431 Ada exceptions, or used to implement run-time functions such as the
2432 @code{abort} statement and stack overflow checking.
2434 Pragma @code{Interrupt_State} provides a general mechanism for overriding
2435 such uses of interrupts. It subsumes the functionality of pragma
2436 @code{Unreserve_All_Interrupts}. Pragma @code{Interrupt_State} is not
2437 available on OS/2, Windows or VMS. On all other platforms than VxWorks,
2438 it applies to signals; on VxWorks, it applies to vectored hardware interrupts
2439 and may be used to mark interrupts required by the board support package
2442 Interrupts can be in one of three states:
2446 The interrupt is reserved (no Ada handler can be installed), and the
2447 Ada run-time may not install a handler. As a result you are guaranteed
2448 standard system default action if this interrupt is raised.
2452 The interrupt is reserved (no Ada handler can be installed). The run time
2453 is allowed to install a handler for internal control purposes, but is
2454 not required to do so.
2458 The interrupt is unreserved. The user may install a handler to provide
2463 These states are the allowed values of the @code{State} parameter of the
2464 pragma. The @code{Name} parameter is a value of the type
2465 @code{Ada.Interrupts.Interrupt_ID}. Typically, it is a name declared in
2466 @code{Ada.Interrupts.Names}.
2468 This is a configuration pragma, and the binder will check that there
2469 are no inconsistencies between different units in a partition in how a
2470 given interrupt is specified. It may appear anywhere a pragma is legal.
2472 The effect is to move the interrupt to the specified state.
2474 By declaring interrupts to be SYSTEM, you guarantee the standard system
2475 action, such as a core dump.
2477 By declaring interrupts to be USER, you guarantee that you can install
2480 Note that certain signals on many operating systems cannot be caught and
2481 handled by applications. In such cases, the pragma is ignored. See the
2482 operating system documentation, or the value of the array @code{Reserved}
2483 declared in the specification of package @code{System.OS_Interface}.
2485 Overriding the default state of signals used by the Ada runtime may interfere
2486 with an application's runtime behavior in the cases of the synchronous signals,
2487 and in the case of the signal used to implement the @code{abort} statement.
2489 @node Pragma Keep_Names
2490 @unnumberedsec Pragma Keep_Names
2495 @smallexample @c ada
2496 pragma Keep_Names ([On =>] enumeration_first_subtype_local_NAME);
2500 The @var{local_NAME} argument
2501 must refer to an enumeration first subtype
2502 in the current declarative part. The effect is to retain the enumeration
2503 literal names for use by @code{Image} and @code{Value} even if a global
2504 @code{Discard_Names} pragma applies. This is useful when you want to
2505 generally suppress enumeration literal names and for example you therefore
2506 use a @code{Discard_Names} pragma in the @file{gnat.adc} file, but you
2507 want to retain the names for specific enumeration types.
2509 @node Pragma License
2510 @unnumberedsec Pragma License
2512 @cindex License checking
2516 @smallexample @c ada
2517 pragma License (Unrestricted | GPL | Modified_GPL | Restricted);
2521 This pragma is provided to allow automated checking for appropriate license
2522 conditions with respect to the standard and modified GPL@. A pragma
2523 @code{License}, which is a configuration pragma that typically appears at
2524 the start of a source file or in a separate @file{gnat.adc} file, specifies
2525 the licensing conditions of a unit as follows:
2529 This is used for a unit that can be freely used with no license restrictions.
2530 Examples of such units are public domain units, and units from the Ada
2534 This is used for a unit that is licensed under the unmodified GPL, and which
2535 therefore cannot be @code{with}'ed by a restricted unit.
2538 This is used for a unit licensed under the GNAT modified GPL that includes
2539 a special exception paragraph that specifically permits the inclusion of
2540 the unit in programs without requiring the entire program to be released
2541 under the GPL@. This is the license used for the GNAT run-time which ensures
2542 that the run-time can be used freely in any program without GPL concerns.
2545 This is used for a unit that is restricted in that it is not permitted to
2546 depend on units that are licensed under the GPL@. Typical examples are
2547 proprietary code that is to be released under more restrictive license
2548 conditions. Note that restricted units are permitted to @code{with} units
2549 which are licensed under the modified GPL (this is the whole point of the
2555 Normally a unit with no @code{License} pragma is considered to have an
2556 unknown license, and no checking is done. However, standard GNAT headers
2557 are recognized, and license information is derived from them as follows.
2561 A GNAT license header starts with a line containing 78 hyphens. The following
2562 comment text is searched for the appearance of any of the following strings.
2564 If the string ``GNU General Public License'' is found, then the unit is assumed
2565 to have GPL license, unless the string ``As a special exception'' follows, in
2566 which case the license is assumed to be modified GPL@.
2568 If one of the strings
2569 ``This specification is adapted from the Ada Semantic Interface'' or
2570 ``This specification is derived from the Ada Reference Manual'' is found
2571 then the unit is assumed to be unrestricted.
2575 These default actions means that a program with a restricted license pragma
2576 will automatically get warnings if a GPL unit is inappropriately
2577 @code{with}'ed. For example, the program:
2579 @smallexample @c ada
2582 procedure Secret_Stuff is
2588 if compiled with pragma @code{License} (@code{Restricted}) in a
2589 @file{gnat.adc} file will generate the warning:
2594 >>> license of withed unit "Sem_Ch3" is incompatible
2596 2. with GNAT.Sockets;
2597 3. procedure Secret_Stuff is
2601 Here we get a warning on @code{Sem_Ch3} since it is part of the GNAT
2602 compiler and is licensed under the
2603 GPL, but no warning for @code{GNAT.Sockets} which is part of the GNAT
2604 run time, and is therefore licensed under the modified GPL@.
2606 @node Pragma Link_With
2607 @unnumberedsec Pragma Link_With
2612 @smallexample @c ada
2613 pragma Link_With (static_string_EXPRESSION @{,static_string_EXPRESSION@});
2617 This pragma is provided for compatibility with certain Ada 83 compilers.
2618 It has exactly the same effect as pragma @code{Linker_Options} except
2619 that spaces occurring within one of the string expressions are treated
2620 as separators. For example, in the following case:
2622 @smallexample @c ada
2623 pragma Link_With ("-labc -ldef");
2627 results in passing the strings @code{-labc} and @code{-ldef} as two
2628 separate arguments to the linker. In addition pragma Link_With allows
2629 multiple arguments, with the same effect as successive pragmas.
2631 @node Pragma Linker_Alias
2632 @unnumberedsec Pragma Linker_Alias
2633 @findex Linker_Alias
2637 @smallexample @c ada
2638 pragma Linker_Alias (
2639 [Entity =>] local_NAME
2640 [Alias =>] static_string_EXPRESSION);
2644 This pragma establishes a linker alias for the given named entity. For
2645 further details on the exact effect, consult the GCC manual.
2647 @node Pragma Linker_Section
2648 @unnumberedsec Pragma Linker_Section
2649 @findex Linker_Section
2653 @smallexample @c ada
2654 pragma Linker_Section (
2655 [Entity =>] local_NAME
2656 [Section =>] static_string_EXPRESSION);
2660 This pragma specifies the name of the linker section for the given entity.
2661 For further details on the exact effect, consult the GCC manual.
2663 @node Pragma Long_Float
2664 @unnumberedsec Pragma Long_Float
2670 @smallexample @c ada
2671 pragma Long_Float (FLOAT_FORMAT);
2673 FLOAT_FORMAT ::= D_Float | G_Float
2677 This pragma is implemented only in the OpenVMS implementation of GNAT@.
2678 It allows control over the internal representation chosen for the predefined
2679 type @code{Long_Float} and for floating point type representations with
2680 @code{digits} specified in the range 7 through 15.
2681 For further details on this pragma, see the
2682 @cite{DEC Ada Language Reference Manual}, section 3.5.7b. Note that to use
2683 this pragma, the standard runtime libraries must be recompiled. See the
2684 description of the @code{GNAT LIBRARY} command in the OpenVMS version
2685 of the GNAT User's Guide for details on the use of this command.
2687 @node Pragma Machine_Attribute
2688 @unnumberedsec Pragma Machine_Attribute
2689 @findex Machine_Attribute
2693 @smallexample @c ada
2694 pragma Machine_Attribute (
2695 [Attribute_Name =>] string_EXPRESSION,
2696 [Entity =>] local_NAME);
2700 Machine-dependent attributes can be specified for types and/or
2701 declarations. This pragma is semantically equivalent to
2702 @code{__attribute__((@var{string_expression}))} in GNU C,
2703 where @code{@var{string_expression}} is
2704 recognized by the target macro @code{TARGET_ATTRIBUTE_TABLE} which is
2705 defined for each machine. See the GCC manual for further information.
2706 It is not possible to specify attributes defined by other languages,
2707 only attributes defined by the machine the code is intended to run on.
2709 @node Pragma Main_Storage
2710 @unnumberedsec Pragma Main_Storage
2712 @findex Main_Storage
2716 @smallexample @c ada
2718 (MAIN_STORAGE_OPTION [, MAIN_STORAGE_OPTION]);
2720 MAIN_STORAGE_OPTION ::=
2721 [WORKING_STORAGE =>] static_SIMPLE_EXPRESSION
2722 | [TOP_GUARD =>] static_SIMPLE_EXPRESSION
2727 This pragma is provided for compatibility with OpenVMS VAX Systems. It has
2728 no effect in GNAT, other than being syntax checked. Note that the pragma
2729 also has no effect in DEC Ada 83 for OpenVMS Alpha Systems.
2731 @node Pragma No_Return
2732 @unnumberedsec Pragma No_Return
2737 @smallexample @c ada
2738 pragma No_Return (procedure_local_NAME);
2742 @var{procedure_local_NAME} must refer to one or more procedure
2743 declarations in the current declarative part. A procedure to which this
2744 pragma is applied may not contain any explicit @code{return} statements,
2745 and also may not contain any implicit return statements from falling off
2746 the end of a statement sequence. One use of this pragma is to identify
2747 procedures whose only purpose is to raise an exception.
2749 Another use of this pragma is to suppress incorrect warnings about
2750 missing returns in functions, where the last statement of a function
2751 statement sequence is a call to such a procedure.
2753 @node Pragma Normalize_Scalars
2754 @unnumberedsec Pragma Normalize_Scalars
2755 @findex Normalize_Scalars
2759 @smallexample @c ada
2760 pragma Normalize_Scalars;
2764 This is a language defined pragma which is fully implemented in GNAT@. The
2765 effect is to cause all scalar objects that are not otherwise initialized
2766 to be initialized. The initial values are implementation dependent and
2770 @item Standard.Character
2772 Objects whose root type is Standard.Character are initialized to
2773 Character'Last unless the subtype range excludes NUL (in which case
2774 NUL is used). This choice will always generate an invalid value if
2777 @item Standard.Wide_Character
2779 Objects whose root type is Standard.Wide_Character are initialized to
2780 Wide_Character'Last unless the subtype range excludes NUL (in which case
2781 NUL is used). This choice will always generate an invalid value if
2784 @item Standard.Wide_Wide_Character
2786 Objects whose root type is Standard.Wide_Wide_Character are initialized to
2787 the invalid value 16#FFFF_FFFF# unless the subtype range excludes NUL (in
2788 which case NUL is used). This choice will always generate an invalid value if
2793 Objects of an integer type are treated differently depending on whether
2794 negative values are present in the subtype. If no negative values are
2795 present, then all one bits is used as the initial value except in the
2796 special case where zero is excluded from the subtype, in which case
2797 all zero bits are used. This choice will always generate an invalid
2798 value if one exists.
2800 For subtypes with negative values present, the largest negative number
2801 is used, except in the unusual case where this largest negative number
2802 is in the subtype, and the largest positive number is not, in which case
2803 the largest positive value is used. This choice will always generate
2804 an invalid value if one exists.
2806 @item Floating-Point Types
2807 Objects of all floating-point types are initialized to all 1-bits. For
2808 standard IEEE format, this corresponds to a NaN (not a number) which is
2809 indeed an invalid value.
2811 @item Fixed-Point Types
2812 Objects of all fixed-point types are treated as described above for integers,
2813 with the rules applying to the underlying integer value used to represent
2814 the fixed-point value.
2817 Objects of a modular type are initialized to all one bits, except in
2818 the special case where zero is excluded from the subtype, in which
2819 case all zero bits are used. This choice will always generate an
2820 invalid value if one exists.
2822 @item Enumeration types
2823 Objects of an enumeration type are initialized to all one-bits, i.e.@: to
2824 the value @code{2 ** typ'Size - 1} unless the subtype excludes the literal
2825 whose Pos value is zero, in which case a code of zero is used. This choice
2826 will always generate an invalid value if one exists.
2830 @node Pragma Obsolescent
2831 @unnumberedsec Pragma Obsolescent
2836 @smallexample @c ada
2837 pragma Obsolescent [(static_string_EXPRESSION [,Ada_05])];
2841 This pragma must occur immediately following a subprogram
2842 declaration. It indicates that the associated function or procedure
2843 is considered obsolescent and should not be used. Typically this is
2844 used when an API must be modified by eventually removing or modifying
2845 existing subprograms. The pragma can be used at an intermediate stage
2846 when the subprogram is still present, but will be removed later.
2848 The effect of this pragma is to output a warning message that the
2849 subprogram is obsolescent if the appropriate warning option in the
2850 compiler is activated. If a parameter is present, then a second
2851 warning message is given containing this text.
2853 In addition, a call to such a program is considered a violation of
2854 pragma Restrictions (No_Obsolescent_Features).
2856 If the optional second parameter is present (which must be exactly
2857 the identifier Ada_05, no other argument is allowed), then the
2858 indication of obsolescence applies only when compiling in Ada 2005
2859 mode. This is primarily intended for dealing with the situations
2860 in the predefined library where subprograms have become defined
2861 as obsolescent in Ada 2005 (e.g. in Ada.Characters.Handling), but
2862 may be used anywhere.
2864 @node Pragma Passive
2865 @unnumberedsec Pragma Passive
2870 @smallexample @c ada
2871 pragma Passive ([Semaphore | No]);
2875 Syntax checked, but otherwise ignored by GNAT@. This is recognized for
2876 compatibility with DEC Ada 83 implementations, where it is used within a
2877 task definition to request that a task be made passive. If the argument
2878 @code{Semaphore} is present, or the argument is omitted, then DEC Ada 83
2879 treats the pragma as an assertion that the containing task is passive
2880 and that optimization of context switch with this task is permitted and
2881 desired. If the argument @code{No} is present, the task must not be
2882 optimized. GNAT does not attempt to optimize any tasks in this manner
2883 (since protected objects are available in place of passive tasks).
2885 @node Pragma Persistent_BSS
2886 @unnumberedsec Pragma Persistent_BSS
2887 @findex Persistent_BSS
2891 @smallexample @c ada
2892 pragma Persistent_BSS [local_NAME]
2896 This pragma allows selected objects to be placed in the @code{.persistent_bss}
2897 section. On some targets the linker and loader provide for special
2898 treatment of this section, allowing a program to be reloaded without
2899 affecting the contents of this data (hence the name persistent).
2901 There are two forms of usage. If an argument is given, it must be the
2902 local name of a library level object, with no explicit initialization
2903 and whose type is potentially persistent. If no argument is given, then
2904 the pragma is a configuration pragma, and applies to all library level
2905 objects with no explicit initialization of potentially persistent types.
2907 A potentially persistent type is a scalar type, or a non-tagged,
2908 non-discriminated record, all of whose components have no explicit
2909 initialization and are themselves of a potentially persistent type,
2910 or an array, all of whose constraints are static, and whose component
2911 type is potentially persistent.
2913 If this pragma is used on a target where this feature is not supported,
2914 then the pragma will be ignored. See also @code{pragma Linker_Section}.
2916 @node Pragma Polling
2917 @unnumberedsec Pragma Polling
2922 @smallexample @c ada
2923 pragma Polling (ON | OFF);
2927 This pragma controls the generation of polling code. This is normally off.
2928 If @code{pragma Polling (ON)} is used then periodic calls are generated to
2929 the routine @code{Ada.Exceptions.Poll}. This routine is a separate unit in the
2930 runtime library, and can be found in file @file{a-excpol.adb}.
2932 Pragma @code{Polling} can appear as a configuration pragma (for example it
2933 can be placed in the @file{gnat.adc} file) to enable polling globally, or it
2934 can be used in the statement or declaration sequence to control polling
2937 A call to the polling routine is generated at the start of every loop and
2938 at the start of every subprogram call. This guarantees that the @code{Poll}
2939 routine is called frequently, and places an upper bound (determined by
2940 the complexity of the code) on the period between two @code{Poll} calls.
2942 The primary purpose of the polling interface is to enable asynchronous
2943 aborts on targets that cannot otherwise support it (for example Windows
2944 NT), but it may be used for any other purpose requiring periodic polling.
2945 The standard version is null, and can be replaced by a user program. This
2946 will require re-compilation of the @code{Ada.Exceptions} package that can
2947 be found in files @file{a-except.ads} and @file{a-except.adb}.
2949 A standard alternative unit (in file @file{4wexcpol.adb} in the standard GNAT
2950 distribution) is used to enable the asynchronous abort capability on
2951 targets that do not normally support the capability. The version of
2952 @code{Poll} in this file makes a call to the appropriate runtime routine
2953 to test for an abort condition.
2955 Note that polling can also be enabled by use of the @code{-gnatP} switch. See
2956 the @cite{GNAT User's Guide} for details.
2958 @node Pragma Profile (Ravenscar)
2959 @unnumberedsec Pragma Profile (Ravenscar)
2964 @smallexample @c ada
2965 pragma Profile (Ravenscar);
2969 A configuration pragma that establishes the following set of configuration
2973 @item Task_Dispatching_Policy (FIFO_Within_Priorities)
2974 [RM D.2.2] Tasks are dispatched following a preemptive
2975 priority-ordered scheduling policy.
2977 @item Locking_Policy (Ceiling_Locking)
2978 [RM D.3] While tasks and interrupts execute a protected action, they inherit
2979 the ceiling priority of the corresponding protected object.
2981 @c @item Detect_Blocking
2982 @c This pragma forces the detection of potentially blocking operations within a
2983 @c protected operation, and to raise Program_Error if that happens.
2987 plus the following set of restrictions:
2990 @item Max_Entry_Queue_Length = 1
2991 Defines the maximum number of calls that are queued on a (protected) entry.
2992 Note that this restrictions is checked at run time. Violation of this
2993 restriction results in the raising of Program_Error exception at the point of
2994 the call. For the Profile (Ravenscar) the value of Max_Entry_Queue_Length is
2995 always 1 and hence no task can be queued on a protected entry.
2997 @item Max_Protected_Entries = 1
2998 [RM D.7] Specifies the maximum number of entries per protected type. The
2999 bounds of every entry family of a protected unit shall be static, or shall be
3000 defined by a discriminant of a subtype whose corresponding bound is static.
3001 For the Profile (Ravenscar) the value of Max_Protected_Entries is always 1.
3003 @item Max_Task_Entries = 0
3004 [RM D.7] Specifies the maximum number of entries
3005 per task. The bounds of every entry family
3006 of a task unit shall be static, or shall be
3007 defined by a discriminant of a subtype whose
3008 corresponding bound is static. A value of zero
3009 indicates that no rendezvous are possible. For
3010 the Profile (Ravenscar), the value of Max_Task_Entries is always
3013 @item No_Abort_Statements
3014 [RM D.7] There are no abort_statements, and there are
3015 no calls to Task_Identification.Abort_Task.
3017 @item No_Asynchronous_Control
3018 [RM D.7] There are no semantic dependences on the package
3019 Asynchronous_Task_Control.
3022 There are no semantic dependencies on the package Ada.Calendar.
3024 @item No_Dynamic_Attachment
3025 There is no call to any of the operations defined in package Ada.Interrupts
3026 (Is_Reserved, Is_Attached, Current_Handler, Attach_Handler, Exchange_Handler,
3027 Detach_Handler, and Reference).
3029 @item No_Dynamic_Priorities
3030 [RM D.7] There are no semantic dependencies on the package Dynamic_Priorities.
3032 @item No_Implicit_Heap_Allocations
3033 [RM D.7] No constructs are allowed to cause implicit heap allocation.
3035 @item No_Local_Protected_Objects
3036 Protected objects and access types that designate
3037 such objects shall be declared only at library level.
3039 @item No_Protected_Type_Allocators
3040 There are no allocators for protected types or
3041 types containing protected subcomponents.
3043 @item No_Relative_Delay
3044 There are no delay_relative statements.
3046 @item No_Requeue_Statements
3047 Requeue statements are not allowed.
3049 @item No_Select_Statements
3050 There are no select_statements.
3052 @item No_Task_Allocators
3053 [RM D.7] There are no allocators for task types
3054 or types containing task subcomponents.
3056 @item No_Task_Attributes_Package
3057 There are no semantic dependencies on the Ada.Task_Attributes package.
3059 @item No_Task_Hierarchy
3060 [RM D.7] All (non-environment) tasks depend
3061 directly on the environment task of the partition.
3063 @item No_Task_Termination
3064 Tasks which terminate are erroneous.
3066 @item Simple_Barriers
3067 Entry barrier condition expressions shall be either static
3068 boolean expressions or boolean objects which are declared in
3069 the protected type which contains the entry.
3073 This set of configuration pragmas and restrictions correspond to the
3074 definition of the ``Ravenscar Profile'' for limited tasking, devised and
3075 published by the @cite{International Real-Time Ada Workshop}, 1997,
3076 and whose most recent description is available at
3077 @url{ftp://ftp.openravenscar.org/openravenscar/ravenscar00.pdf}.
3079 The original definition of the profile was revised at subsequent IRTAW
3080 meetings. It has been included in the ISO
3081 @cite{Guide for the Use of the Ada Programming Language in High
3082 Integrity Systems}, and has been approved by ISO/IEC/SC22/WG9 for inclusion in
3083 the next revision of the standard. The formal definition given by
3084 the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and
3085 AI-305) available at
3086 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00249.TXT} and
3087 @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00305.TXT}
3090 The above set is a superset of the restrictions provided by pragma
3091 @code{Profile (Restricted)}, it includes six additional restrictions
3092 (@code{Simple_Barriers}, @code{No_Select_Statements},
3093 @code{No_Calendar}, @code{No_Implicit_Heap_Allocations},
3094 @code{No_Relative_Delay} and @code{No_Task_Termination}). This means
3095 that pragma @code{Profile (Ravenscar)}, like the pragma
3096 @code{Profile (Restricted)},
3097 automatically causes the use of a simplified,
3098 more efficient version of the tasking run-time system.
3100 @node Pragma Profile (Restricted)
3101 @unnumberedsec Pragma Profile (Restricted)
3102 @findex Restricted Run Time
3106 @smallexample @c ada
3107 pragma Profile (Restricted);
3111 A configuration pragma that establishes the following set of restrictions:
3114 @item No_Abort_Statements
3115 @item No_Entry_Queue
3116 @item No_Task_Hierarchy
3117 @item No_Task_Allocators
3118 @item No_Dynamic_Priorities
3119 @item No_Terminate_Alternatives
3120 @item No_Dynamic_Attachment
3121 @item No_Protected_Type_Allocators
3122 @item No_Local_Protected_Objects
3123 @item No_Requeue_Statements
3124 @item No_Task_Attributes_Package
3125 @item Max_Asynchronous_Select_Nesting = 0
3126 @item Max_Task_Entries = 0
3127 @item Max_Protected_Entries = 1
3128 @item Max_Select_Alternatives = 0
3132 This set of restrictions causes the automatic selection of a simplified
3133 version of the run time that provides improved performance for the
3134 limited set of tasking functionality permitted by this set of restrictions.
3136 @node Pragma Propagate_Exceptions
3137 @unnumberedsec Pragma Propagate_Exceptions
3138 @findex Propagate_Exceptions
3139 @cindex Zero Cost Exceptions
3143 @smallexample @c ada
3144 pragma Propagate_Exceptions (subprogram_local_NAME);
3148 This pragma indicates that the given entity, which is the name of an
3149 imported foreign-language subprogram may receive an Ada exception,
3150 and that the exception should be propagated. It is relevant only if
3151 zero cost exception handling is in use, and is thus never needed if
3152 the alternative @code{longjmp} / @code{setjmp} implementation of
3153 exceptions is used (although it is harmless to use it in such cases).
3155 The implementation of fast exceptions always properly propagates
3156 exceptions through Ada code, as described in the Ada Reference Manual.
3157 However, this manual is silent about the propagation of exceptions
3158 through foreign code. For example, consider the
3159 situation where @code{P1} calls
3160 @code{P2}, and @code{P2} calls @code{P3}, where
3161 @code{P1} and @code{P3} are in Ada, but @code{P2} is in C@.
3162 @code{P3} raises an Ada exception. The question is whether or not
3163 it will be propagated through @code{P2} and can be handled in
3166 For the @code{longjmp} / @code{setjmp} implementation of exceptions,
3167 the answer is always yes. For some targets on which zero cost exception
3168 handling is implemented, the answer is also always yes. However, there
3169 are some targets, notably in the current version all x86 architecture
3170 targets, in which the answer is that such propagation does not
3171 happen automatically. If such propagation is required on these
3172 targets, it is mandatory to use @code{Propagate_Exceptions} to
3173 name all foreign language routines through which Ada exceptions
3176 @node Pragma Psect_Object
3177 @unnumberedsec Pragma Psect_Object
3178 @findex Psect_Object
3182 @smallexample @c ada
3183 pragma Psect_Object (
3184 [Internal =>] local_NAME,
3185 [, [External =>] EXTERNAL_SYMBOL]
3186 [, [Size =>] EXTERNAL_SYMBOL]);
3190 | static_string_EXPRESSION
3194 This pragma is identical in effect to pragma @code{Common_Object}.
3196 @node Pragma Pure_Function
3197 @unnumberedsec Pragma Pure_Function
3198 @findex Pure_Function
3202 @smallexample @c ada
3203 pragma Pure_Function ([Entity =>] function_local_NAME);
3207 This pragma appears in the same declarative part as a function
3208 declaration (or a set of function declarations if more than one
3209 overloaded declaration exists, in which case the pragma applies
3210 to all entities). It specifies that the function @code{Entity} is
3211 to be considered pure for the purposes of code generation. This means
3212 that the compiler can assume that there are no side effects, and
3213 in particular that two calls with identical arguments produce the
3214 same result. It also means that the function can be used in an
3217 Note that, quite deliberately, there are no static checks to try
3218 to ensure that this promise is met, so @code{Pure_Function} can be used
3219 with functions that are conceptually pure, even if they do modify
3220 global variables. For example, a square root function that is
3221 instrumented to count the number of times it is called is still
3222 conceptually pure, and can still be optimized, even though it
3223 modifies a global variable (the count). Memo functions are another
3224 example (where a table of previous calls is kept and consulted to
3225 avoid re-computation).
3228 Note: Most functions in a @code{Pure} package are automatically pure, and
3229 there is no need to use pragma @code{Pure_Function} for such functions. One
3230 exception is any function that has at least one formal of type
3231 @code{System.Address} or a type derived from it. Such functions are not
3232 considered pure by default, since the compiler assumes that the
3233 @code{Address} parameter may be functioning as a pointer and that the
3234 referenced data may change even if the address value does not.
3235 Similarly, imported functions are not considered to be pure by default,
3236 since there is no way of checking that they are in fact pure. The use
3237 of pragma @code{Pure_Function} for such a function will override these default
3238 assumption, and cause the compiler to treat a designated subprogram as pure
3241 Note: If pragma @code{Pure_Function} is applied to a renamed function, it
3242 applies to the underlying renamed function. This can be used to
3243 disambiguate cases of overloading where some but not all functions
3244 in a set of overloaded functions are to be designated as pure.
3246 @node Pragma Restriction_Warnings
3247 @unnumberedsec Pragma Restriction_Warnings
3248 @findex Restriction_Warnings
3252 @smallexample @c ada
3253 pragma Restriction_Warnings
3254 (restriction_IDENTIFIER @{, restriction_IDENTIFIER@});
3258 This pragma allows a series of restriction identifiers to be
3259 specified (the list of allowed identifiers is the same as for
3260 pragma @code{Restrictions}). For each of these identifiers
3261 the compiler checks for violations of the restriction, but
3262 generates a warning message rather than an error message
3263 if the restriction is violated.
3265 @node Pragma Source_File_Name
3266 @unnumberedsec Pragma Source_File_Name
3267 @findex Source_File_Name
3271 @smallexample @c ada
3272 pragma Source_File_Name (
3273 [Unit_Name =>] unit_NAME,
3274 Spec_File_Name => STRING_LITERAL);
3276 pragma Source_File_Name (
3277 [Unit_Name =>] unit_NAME,
3278 Body_File_Name => STRING_LITERAL);
3282 Use this to override the normal naming convention. It is a configuration
3283 pragma, and so has the usual applicability of configuration pragmas
3284 (i.e.@: it applies to either an entire partition, or to all units in a
3285 compilation, or to a single unit, depending on how it is used.
3286 @var{unit_name} is mapped to @var{file_name_literal}. The identifier for
3287 the second argument is required, and indicates whether this is the file
3288 name for the spec or for the body.
3290 Another form of the @code{Source_File_Name} pragma allows
3291 the specification of patterns defining alternative file naming schemes
3292 to apply to all files.
3294 @smallexample @c ada
3295 pragma Source_File_Name
3296 (Spec_File_Name => STRING_LITERAL
3297 [,Casing => CASING_SPEC]
3298 [,Dot_Replacement => STRING_LITERAL]);
3300 pragma Source_File_Name
3301 (Body_File_Name => STRING_LITERAL
3302 [,Casing => CASING_SPEC]
3303 [,Dot_Replacement => STRING_LITERAL]);
3305 pragma Source_File_Name
3306 (Subunit_File_Name => STRING_LITERAL
3307 [,Casing => CASING_SPEC]
3308 [,Dot_Replacement => STRING_LITERAL]);
3310 CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
3314 The first argument is a pattern that contains a single asterisk indicating
3315 the point at which the unit name is to be inserted in the pattern string
3316 to form the file name. The second argument is optional. If present it
3317 specifies the casing of the unit name in the resulting file name string.
3318 The default is lower case. Finally the third argument allows for systematic
3319 replacement of any dots in the unit name by the specified string literal.
3321 A pragma Source_File_Name cannot appear after a
3322 @ref{Pragma Source_File_Name_Project}.
3324 For more details on the use of the @code{Source_File_Name} pragma,
3325 see the sections ``Using Other File Names'' and
3326 ``Alternative File Naming Schemes'' in the @cite{GNAT User's Guide}.
3328 @node Pragma Source_File_Name_Project
3329 @unnumberedsec Pragma Source_File_Name_Project
3330 @findex Source_File_Name_Project
3333 This pragma has the same syntax and semantics as pragma Source_File_Name.
3334 It is only allowed as a stand alone configuration pragma.
3335 It cannot appear after a @ref{Pragma Source_File_Name}, and
3336 most importantly, once pragma Source_File_Name_Project appears,
3337 no further Source_File_Name pragmas are allowed.
3339 The intention is that Source_File_Name_Project pragmas are always
3340 generated by the Project Manager in a manner consistent with the naming
3341 specified in a project file, and when naming is controlled in this manner,
3342 it is not permissible to attempt to modify this naming scheme using
3343 Source_File_Name pragmas (which would not be known to the project manager).
3345 @node Pragma Source_Reference
3346 @unnumberedsec Pragma Source_Reference
3347 @findex Source_Reference
3351 @smallexample @c ada
3352 pragma Source_Reference (INTEGER_LITERAL, STRING_LITERAL);
3356 This pragma must appear as the first line of a source file.
3357 @var{integer_literal} is the logical line number of the line following
3358 the pragma line (for use in error messages and debugging
3359 information). @var{string_literal} is a static string constant that
3360 specifies the file name to be used in error messages and debugging
3361 information. This is most notably used for the output of @code{gnatchop}
3362 with the @code{-r} switch, to make sure that the original unchopped
3363 source file is the one referred to.
3365 The second argument must be a string literal, it cannot be a static
3366 string expression other than a string literal. This is because its value
3367 is needed for error messages issued by all phases of the compiler.
3369 @node Pragma Stream_Convert
3370 @unnumberedsec Pragma Stream_Convert
3371 @findex Stream_Convert
3375 @smallexample @c ada
3376 pragma Stream_Convert (
3377 [Entity =>] type_local_NAME,
3378 [Read =>] function_NAME,
3379 [Write =>] function_NAME);
3383 This pragma provides an efficient way of providing stream functions for
3384 types defined in packages. Not only is it simpler to use than declaring
3385 the necessary functions with attribute representation clauses, but more
3386 significantly, it allows the declaration to made in such a way that the
3387 stream packages are not loaded unless they are needed. The use of
3388 the Stream_Convert pragma adds no overhead at all, unless the stream
3389 attributes are actually used on the designated type.
3391 The first argument specifies the type for which stream functions are
3392 provided. The second parameter provides a function used to read values
3393 of this type. It must name a function whose argument type may be any
3394 subtype, and whose returned type must be the type given as the first
3395 argument to the pragma.
3397 The meaning of the @var{Read}
3398 parameter is that if a stream attribute directly
3399 or indirectly specifies reading of the type given as the first parameter,
3400 then a value of the type given as the argument to the Read function is
3401 read from the stream, and then the Read function is used to convert this
3402 to the required target type.
3404 Similarly the @var{Write} parameter specifies how to treat write attributes
3405 that directly or indirectly apply to the type given as the first parameter.
3406 It must have an input parameter of the type specified by the first parameter,
3407 and the return type must be the same as the input type of the Read function.
3408 The effect is to first call the Write function to convert to the given stream
3409 type, and then write the result type to the stream.
3411 The Read and Write functions must not be overloaded subprograms. If necessary
3412 renamings can be supplied to meet this requirement.
3413 The usage of this attribute is best illustrated by a simple example, taken
3414 from the GNAT implementation of package Ada.Strings.Unbounded:
3416 @smallexample @c ada
3417 function To_Unbounded (S : String)
3418 return Unbounded_String
3419 renames To_Unbounded_String;
3421 pragma Stream_Convert
3422 (Unbounded_String, To_Unbounded, To_String);
3426 The specifications of the referenced functions, as given in the Ada 95
3427 Reference Manual are:
3429 @smallexample @c ada
3430 function To_Unbounded_String (Source : String)
3431 return Unbounded_String;
3433 function To_String (Source : Unbounded_String)
3438 The effect is that if the value of an unbounded string is written to a
3439 stream, then the representation of the item in the stream is in the same
3440 format used for @code{Standard.String}, and this same representation is
3441 expected when a value of this type is read from the stream.
3443 @node Pragma Style_Checks
3444 @unnumberedsec Pragma Style_Checks
3445 @findex Style_Checks
3449 @smallexample @c ada
3450 pragma Style_Checks (string_LITERAL | ALL_CHECKS |
3451 On | Off [, local_NAME]);
3455 This pragma is used in conjunction with compiler switches to control the
3456 built in style checking provided by GNAT@. The compiler switches, if set,
3457 provide an initial setting for the switches, and this pragma may be used
3458 to modify these settings, or the settings may be provided entirely by
3459 the use of the pragma. This pragma can be used anywhere that a pragma
3460 is legal, including use as a configuration pragma (including use in
3461 the @file{gnat.adc} file).
3463 The form with a string literal specifies which style options are to be
3464 activated. These are additive, so they apply in addition to any previously
3465 set style check options. The codes for the options are the same as those
3466 used in the @code{-gnaty} switch to @code{gcc} or @code{gnatmake}.
3467 For example the following two methods can be used to enable
3472 @smallexample @c ada
3473 pragma Style_Checks ("l");
3478 gcc -c -gnatyl @dots{}
3483 The form ALL_CHECKS activates all standard checks (its use is equivalent
3484 to the use of the @code{gnaty} switch with no options. See GNAT User's
3487 The forms with @code{Off} and @code{On}
3488 can be used to temporarily disable style checks
3489 as shown in the following example:
3491 @smallexample @c ada
3495 pragma Style_Checks ("k"); -- requires keywords in lower case
3496 pragma Style_Checks (Off); -- turn off style checks
3497 NULL; -- this will not generate an error message
3498 pragma Style_Checks (On); -- turn style checks back on
3499 NULL; -- this will generate an error message
3503 Finally the two argument form is allowed only if the first argument is
3504 @code{On} or @code{Off}. The effect is to turn of semantic style checks
3505 for the specified entity, as shown in the following example:
3507 @smallexample @c ada
3511 pragma Style_Checks ("r"); -- require consistency of identifier casing
3513 Rf1 : Integer := ARG; -- incorrect, wrong case
3514 pragma Style_Checks (Off, Arg);
3515 Rf2 : Integer := ARG; -- OK, no error
3518 @node Pragma Subtitle
3519 @unnumberedsec Pragma Subtitle
3524 @smallexample @c ada
3525 pragma Subtitle ([Subtitle =>] STRING_LITERAL);
3529 This pragma is recognized for compatibility with other Ada compilers
3530 but is ignored by GNAT@.
3532 @node Pragma Suppress_All
3533 @unnumberedsec Pragma Suppress_All
3534 @findex Suppress_All
3538 @smallexample @c ada
3539 pragma Suppress_All;
3543 This pragma can only appear immediately following a compilation
3544 unit. The effect is to apply @code{Suppress (All_Checks)} to the unit
3545 which it follows. This pragma is implemented for compatibility with DEC
3546 Ada 83 usage. The use of pragma @code{Suppress (All_Checks)} as a normal
3547 configuration pragma is the preferred usage in GNAT@.
3549 @node Pragma Suppress_Exception_Locations
3550 @unnumberedsec Pragma Suppress_Exception_Locations
3551 @findex Suppress_Exception_Locations
3555 @smallexample @c ada
3556 pragma Suppress_Exception_Locations;
3560 In normal mode, a raise statement for an exception by default generates
3561 an exception message giving the file name and line number for the location
3562 of the raise. This is useful for debugging and logging purposes, but this
3563 entails extra space for the strings for the messages. The configuration
3564 pragma @code{Suppress_Exception_Locations} can be used to suppress the
3565 generation of these strings, with the result that space is saved, but the
3566 exception message for such raises is null. This configuration pragma may
3567 appear in a global configuration pragma file, or in a specific unit as
3568 usual. It is not required that this pragma be used consistently within
3569 a partition, so it is fine to have some units within a partition compiled
3570 with this pragma and others compiled in normal mode without it.
3572 @node Pragma Suppress_Initialization
3573 @unnumberedsec Pragma Suppress_Initialization
3574 @findex Suppress_Initialization
3575 @cindex Suppressing initialization
3576 @cindex Initialization, suppression of
3580 @smallexample @c ada
3581 pragma Suppress_Initialization ([Entity =>] type_Name);
3585 This pragma suppresses any implicit or explicit initialization
3586 associated with the given type name for all variables of this type.
3588 @node Pragma Task_Info
3589 @unnumberedsec Pragma Task_Info
3594 @smallexample @c ada
3595 pragma Task_Info (EXPRESSION);
3599 This pragma appears within a task definition (like pragma
3600 @code{Priority}) and applies to the task in which it appears. The
3601 argument must be of type @code{System.Task_Info.Task_Info_Type}.
3602 The @code{Task_Info} pragma provides system dependent control over
3603 aspects of tasking implementation, for example, the ability to map
3604 tasks to specific processors. For details on the facilities available
3605 for the version of GNAT that you are using, see the documentation
3606 in the specification of package System.Task_Info in the runtime
3609 @node Pragma Task_Name
3610 @unnumberedsec Pragma Task_Name
3615 @smallexample @c ada
3616 pragma Task_Name (string_EXPRESSION);
3620 This pragma appears within a task definition (like pragma
3621 @code{Priority}) and applies to the task in which it appears. The
3622 argument must be of type String, and provides a name to be used for
3623 the task instance when the task is created. Note that this expression
3624 is not required to be static, and in particular, it can contain
3625 references to task discriminants. This facility can be used to
3626 provide different names for different tasks as they are created,
3627 as illustrated in the example below.
3629 The task name is recorded internally in the run-time structures
3630 and is accessible to tools like the debugger. In addition the
3631 routine @code{Ada.Task_Identification.Image} will return this
3632 string, with a unique task address appended.
3634 @smallexample @c ada
3635 -- Example of the use of pragma Task_Name
3637 with Ada.Task_Identification;
3638 use Ada.Task_Identification;
3639 with Text_IO; use Text_IO;
3642 type Astring is access String;
3644 task type Task_Typ (Name : access String) is
3645 pragma Task_Name (Name.all);
3648 task body Task_Typ is
3649 Nam : constant String := Image (Current_Task);
3651 Put_Line ("-->" & Nam (1 .. 14) & "<--");
3654 type Ptr_Task is access Task_Typ;
3655 Task_Var : Ptr_Task;
3659 new Task_Typ (new String'("This is task 1"));
3661 new Task_Typ (new String'("This is task 2"));
3665 @node Pragma Task_Storage
3666 @unnumberedsec Pragma Task_Storage
3667 @findex Task_Storage
3670 @smallexample @c ada
3671 pragma Task_Storage (
3672 [Task_Type =>] local_NAME,
3673 [Top_Guard =>] static_integer_EXPRESSION);
3677 This pragma specifies the length of the guard area for tasks. The guard
3678 area is an additional storage area allocated to a task. A value of zero
3679 means that either no guard area is created or a minimal guard area is
3680 created, depending on the target. This pragma can appear anywhere a
3681 @code{Storage_Size} attribute definition clause is allowed for a task
3684 @node Pragma Thread_Body
3685 @unnumberedsec Pragma Thread_Body
3689 @smallexample @c ada
3690 pragma Thread_Body (
3691 [Entity =>] local_NAME,
3692 [[Secondary_Stack_Size =>] static_integer_EXPRESSION)];
3696 This pragma specifies that the subprogram whose name is given as the
3697 @code{Entity} argument is a thread body, which will be activated
3698 by being called via its Address from foreign code. The purpose is
3699 to allow execution and registration of the foreign thread within the
3700 Ada run-time system.
3702 See the library unit @code{System.Threads} for details on the expansion of
3703 a thread body subprogram, including the calls made to subprograms
3704 within System.Threads to register the task. This unit also lists the
3705 targets and runtime systems for which this pragma is supported.
3707 A thread body subprogram may not be called directly from Ada code, and
3708 it is not permitted to apply the Access (or Unrestricted_Access) attributes
3709 to such a subprogram. The only legitimate way of calling such a subprogram
3710 is to pass its Address to foreign code and then make the call from the
3713 A thread body subprogram may have any parameters, and it may be a function
3714 returning a result. The convention of the thread body subprogram may be
3715 set in the usual manner using @code{pragma Convention}.
3717 The secondary stack size parameter, if given, is used to set the size
3718 of secondary stack for the thread. The secondary stack is allocated as
3719 a local variable of the expanded thread body subprogram, and thus is
3720 allocated out of the main thread stack size. If no secondary stack
3721 size parameter is present, the default size (from the declaration in
3722 @code{System.Secondary_Stack} is used.
3724 @node Pragma Time_Slice
3725 @unnumberedsec Pragma Time_Slice
3730 @smallexample @c ada
3731 pragma Time_Slice (static_duration_EXPRESSION);
3735 For implementations of GNAT on operating systems where it is possible
3736 to supply a time slice value, this pragma may be used for this purpose.
3737 It is ignored if it is used in a system that does not allow this control,
3738 or if it appears in other than the main program unit.
3740 Note that the effect of this pragma is identical to the effect of the
3741 DEC Ada 83 pragma of the same name when operating under OpenVMS systems.
3744 @unnumberedsec Pragma Title
3749 @smallexample @c ada
3750 pragma Title (TITLING_OPTION [, TITLING OPTION]);
3753 [Title =>] STRING_LITERAL,
3754 | [Subtitle =>] STRING_LITERAL
3758 Syntax checked but otherwise ignored by GNAT@. This is a listing control
3759 pragma used in DEC Ada 83 implementations to provide a title and/or
3760 subtitle for the program listing. The program listing generated by GNAT
3761 does not have titles or subtitles.
3763 Unlike other pragmas, the full flexibility of named notation is allowed
3764 for this pragma, i.e.@: the parameters may be given in any order if named
3765 notation is used, and named and positional notation can be mixed
3766 following the normal rules for procedure calls in Ada.
3768 @node Pragma Unchecked_Union
3769 @unnumberedsec Pragma Unchecked_Union
3771 @findex Unchecked_Union
3775 @smallexample @c ada
3776 pragma Unchecked_Union (first_subtype_local_NAME);
3780 This pragma is used to declare that the specified type should be represented
3782 equivalent to a C union type, and is intended only for use in
3783 interfacing with C code that uses union types. In Ada terms, the named
3784 type must obey the following rules:
3788 It is a non-tagged non-limited record type.
3790 It has a single discrete discriminant with a default value.
3792 The component list consists of a single variant part.
3794 Each variant has a component list with a single component.
3796 No nested variants are allowed.
3798 No component has an explicit default value.
3800 No component has a non-static constraint.
3804 In addition, given a type that meets the above requirements, the
3805 following restrictions apply to its use throughout the program:
3809 The discriminant name can be mentioned only in an aggregate.
3811 No subtypes may be created of this type.
3813 The type may not be constrained by giving a discriminant value.
3815 The type cannot be passed as the actual for a generic formal with a
3820 Equality and inequality operations on @code{unchecked_unions} are not
3821 available, since there is no discriminant to compare and the compiler
3822 does not even know how many bits to compare. It is implementation
3823 dependent whether this is detected at compile time as an illegality or
3824 whether it is undetected and considered to be an erroneous construct. In
3825 GNAT, a direct comparison is illegal, but GNAT does not attempt to catch
3826 the composite case (where two composites are compared that contain an
3827 unchecked union component), so such comparisons are simply considered
3830 The layout of the resulting type corresponds exactly to a C union, where
3831 each branch of the union corresponds to a single variant in the Ada
3832 record. The semantics of the Ada program is not changed in any way by
3833 the pragma, i.e.@: provided the above restrictions are followed, and no
3834 erroneous incorrect references to fields or erroneous comparisons occur,
3835 the semantics is exactly as described by the Ada reference manual.
3836 Pragma @code{Suppress (Discriminant_Check)} applies implicitly to the
3837 type and the default convention is C.
3839 @node Pragma Unimplemented_Unit
3840 @unnumberedsec Pragma Unimplemented_Unit
3841 @findex Unimplemented_Unit
3845 @smallexample @c ada
3846 pragma Unimplemented_Unit;
3850 If this pragma occurs in a unit that is processed by the compiler, GNAT
3851 aborts with the message @samp{@var{xxx} not implemented}, where
3852 @var{xxx} is the name of the current compilation unit. This pragma is
3853 intended to allow the compiler to handle unimplemented library units in
3856 The abort only happens if code is being generated. Thus you can use
3857 specs of unimplemented packages in syntax or semantic checking mode.
3859 @node Pragma Universal_Data
3860 @unnumberedsec Pragma Universal_Data
3861 @findex Universal_Data
3865 @smallexample @c ada
3866 pragma Universal_Data [(library_unit_Name)];
3870 This pragma is supported only for the AAMP target and is ignored for
3871 other targets. The pragma specifies that all library-level objects
3872 (Counter 0 data) associated with the library unit are to be accessed
3873 and updated using universal addressing (24-bit addresses for AAMP5)
3874 rather than the default of 16-bit Data Environment (DENV) addressing.
3875 Use of this pragma will generally result in less efficient code for
3876 references to global data associated with the library unit, but
3877 allows such data to be located anywhere in memory. This pragma is
3878 a library unit pragma, but can also be used as a configuration pragma
3879 (including use in the @file{gnat.adc} file). The functionality
3880 of this pragma is also available by applying the -univ switch on the
3881 compilations of units where universal addressing of the data is desired.
3883 @node Pragma Unreferenced
3884 @unnumberedsec Pragma Unreferenced
3885 @findex Unreferenced
3886 @cindex Warnings, unreferenced
3890 @smallexample @c ada
3891 pragma Unreferenced (local_NAME @{, local_NAME@});
3895 This pragma signals that the entities whose names are listed are
3896 deliberately not referenced in the current source unit. This
3897 suppresses warnings about the
3898 entities being unreferenced, and in addition a warning will be
3899 generated if one of these entities is in fact referenced in the
3900 same unit as the pragma (or in the corresponding body, or one
3903 This is particularly useful for clearly signaling that a particular
3904 parameter is not referenced in some particular subprogram implementation
3905 and that this is deliberate. It can also be useful in the case of
3906 objects declared only for their initialization or finalization side
3909 If @code{local_NAME} identifies more than one matching homonym in the
3910 current scope, then the entity most recently declared is the one to which
3913 The left hand side of an assignment does not count as a reference for the
3914 purpose of this pragma. Thus it is fine to assign to an entity for which
3915 pragma Unreferenced is given.
3917 @node Pragma Unreserve_All_Interrupts
3918 @unnumberedsec Pragma Unreserve_All_Interrupts
3919 @findex Unreserve_All_Interrupts
3923 @smallexample @c ada
3924 pragma Unreserve_All_Interrupts;
3928 Normally certain interrupts are reserved to the implementation. Any attempt
3929 to attach an interrupt causes Program_Error to be raised, as described in
3930 RM C.3.2(22). A typical example is the @code{SIGINT} interrupt used in
3931 many systems for a @kbd{Ctrl-C} interrupt. Normally this interrupt is
3932 reserved to the implementation, so that @kbd{Ctrl-C} can be used to
3933 interrupt execution.
3935 If the pragma @code{Unreserve_All_Interrupts} appears anywhere in any unit in
3936 a program, then all such interrupts are unreserved. This allows the
3937 program to handle these interrupts, but disables their standard
3938 functions. For example, if this pragma is used, then pressing
3939 @kbd{Ctrl-C} will not automatically interrupt execution. However,
3940 a program can then handle the @code{SIGINT} interrupt as it chooses.
3942 For a full list of the interrupts handled in a specific implementation,
3943 see the source code for the specification of @code{Ada.Interrupts.Names} in
3944 file @file{a-intnam.ads}. This is a target dependent file that contains the
3945 list of interrupts recognized for a given target. The documentation in
3946 this file also specifies what interrupts are affected by the use of
3947 the @code{Unreserve_All_Interrupts} pragma.
3949 For a more general facility for controlling what interrupts can be
3950 handled, see pragma @code{Interrupt_State}, which subsumes the functionality
3951 of the @code{Unreserve_All_Interrupts} pragma.
3953 @node Pragma Unsuppress
3954 @unnumberedsec Pragma Unsuppress
3959 @smallexample @c ada
3960 pragma Unsuppress (IDENTIFIER [, [On =>] NAME]);
3964 This pragma undoes the effect of a previous pragma @code{Suppress}. If
3965 there is no corresponding pragma @code{Suppress} in effect, it has no
3966 effect. The range of the effect is the same as for pragma
3967 @code{Suppress}. The meaning of the arguments is identical to that used
3968 in pragma @code{Suppress}.
3970 One important application is to ensure that checks are on in cases where
3971 code depends on the checks for its correct functioning, so that the code
3972 will compile correctly even if the compiler switches are set to suppress
3975 @node Pragma Use_VADS_Size
3976 @unnumberedsec Pragma Use_VADS_Size
3977 @cindex @code{Size}, VADS compatibility
3978 @findex Use_VADS_Size
3982 @smallexample @c ada
3983 pragma Use_VADS_Size;
3987 This is a configuration pragma. In a unit to which it applies, any use
3988 of the 'Size attribute is automatically interpreted as a use of the
3989 'VADS_Size attribute. Note that this may result in incorrect semantic
3990 processing of valid Ada 95 programs. This is intended to aid in the
3991 handling of legacy code which depends on the interpretation of Size
3992 as implemented in the VADS compiler. See description of the VADS_Size
3993 attribute for further details.
3995 @node Pragma Validity_Checks
3996 @unnumberedsec Pragma Validity_Checks
3997 @findex Validity_Checks
4001 @smallexample @c ada
4002 pragma Validity_Checks (string_LITERAL | ALL_CHECKS | On | Off);
4006 This pragma is used in conjunction with compiler switches to control the
4007 built-in validity checking provided by GNAT@. The compiler switches, if set
4008 provide an initial setting for the switches, and this pragma may be used
4009 to modify these settings, or the settings may be provided entirely by
4010 the use of the pragma. This pragma can be used anywhere that a pragma
4011 is legal, including use as a configuration pragma (including use in
4012 the @file{gnat.adc} file).
4014 The form with a string literal specifies which validity options are to be
4015 activated. The validity checks are first set to include only the default
4016 reference manual settings, and then a string of letters in the string
4017 specifies the exact set of options required. The form of this string
4018 is exactly as described for the @code{-gnatVx} compiler switch (see the
4019 GNAT users guide for details). For example the following two methods
4020 can be used to enable validity checking for mode @code{in} and
4021 @code{in out} subprogram parameters:
4025 @smallexample @c ada
4026 pragma Validity_Checks ("im");
4031 gcc -c -gnatVim @dots{}
4036 The form ALL_CHECKS activates all standard checks (its use is equivalent
4037 to the use of the @code{gnatva} switch.
4039 The forms with @code{Off} and @code{On}
4040 can be used to temporarily disable validity checks
4041 as shown in the following example:
4043 @smallexample @c ada
4047 pragma Validity_Checks ("c"); -- validity checks for copies
4048 pragma Validity_Checks (Off); -- turn off validity checks
4049 A := B; -- B will not be validity checked
4050 pragma Validity_Checks (On); -- turn validity checks back on
4051 A := C; -- C will be validity checked
4054 @node Pragma Volatile
4055 @unnumberedsec Pragma Volatile
4060 @smallexample @c ada
4061 pragma Volatile (local_NAME);
4065 This pragma is defined by the Ada 95 Reference Manual, and the GNAT
4066 implementation is fully conformant with this definition. The reason it
4067 is mentioned in this section is that a pragma of the same name was supplied
4068 in some Ada 83 compilers, including DEC Ada 83. The Ada 95 implementation
4069 of pragma Volatile is upwards compatible with the implementation in
4072 @node Pragma Warnings
4073 @unnumberedsec Pragma Warnings
4078 @smallexample @c ada
4079 pragma Warnings (On | Off [, local_NAME]);
4083 Normally warnings are enabled, with the output being controlled by
4084 the command line switch. Warnings (@code{Off}) turns off generation of
4085 warnings until a Warnings (@code{On}) is encountered or the end of the
4086 current unit. If generation of warnings is turned off using this
4087 pragma, then no warning messages are output, regardless of the
4088 setting of the command line switches.
4090 The form with a single argument is a configuration pragma.
4092 If the @var{local_NAME} parameter is present, warnings are suppressed for
4093 the specified entity. This suppression is effective from the point where
4094 it occurs till the end of the extended scope of the variable (similar to
4095 the scope of @code{Suppress}).
4097 @node Pragma Weak_External
4098 @unnumberedsec Pragma Weak_External
4099 @findex Weak_External
4103 @smallexample @c ada
4104 pragma Weak_External ([Entity =>] local_NAME);
4108 This pragma specifies that the given entity should be marked as a weak
4109 external (one that does not have to be resolved) for the linker. For
4110 further details, consult the GCC manual.
4112 @node Implementation Defined Attributes
4113 @chapter Implementation Defined Attributes
4114 Ada 95 defines (throughout the Ada 95 reference manual,
4115 summarized in annex K),
4116 a set of attributes that provide useful additional functionality in all
4117 areas of the language. These language defined attributes are implemented
4118 in GNAT and work as described in the Ada 95 Reference Manual.
4120 In addition, Ada 95 allows implementations to define additional
4121 attributes whose meaning is defined by the implementation. GNAT provides
4122 a number of these implementation-dependent attributes which can be used
4123 to extend and enhance the functionality of the compiler. This section of
4124 the GNAT reference manual describes these additional attributes.
4126 Note that any program using these attributes may not be portable to
4127 other compilers (although GNAT implements this set of attributes on all
4128 platforms). Therefore if portability to other compilers is an important
4129 consideration, you should minimize the use of these attributes.
4140 * Default_Bit_Order::
4148 * Has_Access_Values::
4149 * Has_Discriminants::
4155 * Max_Interrupt_Priority::
4157 * Maximum_Alignment::
4161 * Passed_By_Reference::
4172 * Unconstrained_Array::
4173 * Universal_Literal_String::
4174 * Unrestricted_Access::
4182 @unnumberedsec Abort_Signal
4183 @findex Abort_Signal
4185 @code{Standard'Abort_Signal} (@code{Standard} is the only allowed
4186 prefix) provides the entity for the special exception used to signal
4187 task abort or asynchronous transfer of control. Normally this attribute
4188 should only be used in the tasking runtime (it is highly peculiar, and
4189 completely outside the normal semantics of Ada, for a user program to
4190 intercept the abort exception).
4193 @unnumberedsec Address_Size
4194 @cindex Size of @code{Address}
4195 @findex Address_Size
4197 @code{Standard'Address_Size} (@code{Standard} is the only allowed
4198 prefix) is a static constant giving the number of bits in an
4199 @code{Address}. It is the same value as System.Address'Size,
4200 but has the advantage of being static, while a direct
4201 reference to System.Address'Size is non-static because Address
4205 @unnumberedsec Asm_Input
4208 The @code{Asm_Input} attribute denotes a function that takes two
4209 parameters. The first is a string, the second is an expression of the
4210 type designated by the prefix. The first (string) argument is required
4211 to be a static expression, and is the constraint for the parameter,
4212 (e.g.@: what kind of register is required). The second argument is the
4213 value to be used as the input argument. The possible values for the
4214 constant are the same as those used in the RTL, and are dependent on
4215 the configuration file used to built the GCC back end.
4216 @ref{Machine Code Insertions}
4219 @unnumberedsec Asm_Output
4222 The @code{Asm_Output} attribute denotes a function that takes two
4223 parameters. The first is a string, the second is the name of a variable
4224 of the type designated by the attribute prefix. The first (string)
4225 argument is required to be a static expression and designates the
4226 constraint for the parameter (e.g.@: what kind of register is
4227 required). The second argument is the variable to be updated with the
4228 result. The possible values for constraint are the same as those used in
4229 the RTL, and are dependent on the configuration file used to build the
4230 GCC back end. If there are no output operands, then this argument may
4231 either be omitted, or explicitly given as @code{No_Output_Operands}.
4232 @ref{Machine Code Insertions}
4235 @unnumberedsec AST_Entry
4239 This attribute is implemented only in OpenVMS versions of GNAT@. Applied to
4240 the name of an entry, it yields a value of the predefined type AST_Handler
4241 (declared in the predefined package System, as extended by the use of
4242 pragma @code{Extend_System (Aux_DEC)}). This value enables the given entry to
4243 be called when an AST occurs. For further details, refer to the @cite{DEC Ada
4244 Language Reference Manual}, section 9.12a.
4249 @code{@var{obj}'Bit}, where @var{obj} is any object, yields the bit
4250 offset within the storage unit (byte) that contains the first bit of
4251 storage allocated for the object. The value of this attribute is of the
4252 type @code{Universal_Integer}, and is always a non-negative number not
4253 exceeding the value of @code{System.Storage_Unit}.
4255 For an object that is a variable or a constant allocated in a register,
4256 the value is zero. (The use of this attribute does not force the
4257 allocation of a variable to memory).
4259 For an object that is a formal parameter, this attribute applies
4260 to either the matching actual parameter or to a copy of the
4261 matching actual parameter.
4263 For an access object the value is zero. Note that
4264 @code{@var{obj}.all'Bit} is subject to an @code{Access_Check} for the
4265 designated object. Similarly for a record component
4266 @code{@var{X}.@var{C}'Bit} is subject to a discriminant check and
4267 @code{@var{X}(@var{I}).Bit} and @code{@var{X}(@var{I1}..@var{I2})'Bit}
4268 are subject to index checks.
4270 This attribute is designed to be compatible with the DEC Ada 83 definition
4271 and implementation of the @code{Bit} attribute.
4274 @unnumberedsec Bit_Position
4275 @findex Bit_Position
4277 @code{@var{R.C}'Bit}, where @var{R} is a record object and C is one
4278 of the fields of the record type, yields the bit
4279 offset within the record contains the first bit of
4280 storage allocated for the object. The value of this attribute is of the
4281 type @code{Universal_Integer}. The value depends only on the field
4282 @var{C} and is independent of the alignment of
4283 the containing record @var{R}.
4286 @unnumberedsec Code_Address
4287 @findex Code_Address
4288 @cindex Subprogram address
4289 @cindex Address of subprogram code
4292 attribute may be applied to subprograms in Ada 95, but the
4293 intended effect from the Ada 95 reference manual seems to be to provide
4294 an address value which can be used to call the subprogram by means of
4295 an address clause as in the following example:
4297 @smallexample @c ada
4298 procedure K is @dots{}
4301 for L'Address use K'Address;
4302 pragma Import (Ada, L);
4306 A call to @code{L} is then expected to result in a call to @code{K}@.
4307 In Ada 83, where there were no access-to-subprogram values, this was
4308 a common work around for getting the effect of an indirect call.
4309 GNAT implements the above use of @code{Address} and the technique
4310 illustrated by the example code works correctly.
4312 However, for some purposes, it is useful to have the address of the start
4313 of the generated code for the subprogram. On some architectures, this is
4314 not necessarily the same as the @code{Address} value described above.
4315 For example, the @code{Address} value may reference a subprogram
4316 descriptor rather than the subprogram itself.
4318 The @code{'Code_Address} attribute, which can only be applied to
4319 subprogram entities, always returns the address of the start of the
4320 generated code of the specified subprogram, which may or may not be
4321 the same value as is returned by the corresponding @code{'Address}
4324 @node Default_Bit_Order
4325 @unnumberedsec Default_Bit_Order
4327 @cindex Little endian
4328 @findex Default_Bit_Order
4330 @code{Standard'Default_Bit_Order} (@code{Standard} is the only
4331 permissible prefix), provides the value @code{System.Default_Bit_Order}
4332 as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
4333 @code{Low_Order_First}). This is used to construct the definition of
4334 @code{Default_Bit_Order} in package @code{System}.
4337 @unnumberedsec Elaborated
4340 The prefix of the @code{'Elaborated} attribute must be a unit name. The
4341 value is a Boolean which indicates whether or not the given unit has been
4342 elaborated. This attribute is primarily intended for internal use by the
4343 generated code for dynamic elaboration checking, but it can also be used
4344 in user programs. The value will always be True once elaboration of all
4345 units has been completed. An exception is for units which need no
4346 elaboration, the value is always False for such units.
4349 @unnumberedsec Elab_Body
4352 This attribute can only be applied to a program unit name. It returns
4353 the entity for the corresponding elaboration procedure for elaborating
4354 the body of the referenced unit. This is used in the main generated
4355 elaboration procedure by the binder and is not normally used in any
4356 other context. However, there may be specialized situations in which it
4357 is useful to be able to call this elaboration procedure from Ada code,
4358 e.g.@: if it is necessary to do selective re-elaboration to fix some
4362 @unnumberedsec Elab_Spec
4365 This attribute can only be applied to a program unit name. It returns
4366 the entity for the corresponding elaboration procedure for elaborating
4367 the specification of the referenced unit. This is used in the main
4368 generated elaboration procedure by the binder and is not normally used
4369 in any other context. However, there may be specialized situations in
4370 which it is useful to be able to call this elaboration procedure from
4371 Ada code, e.g.@: if it is necessary to do selective re-elaboration to fix
4376 @cindex Ada 83 attributes
4379 The @code{Emax} attribute is provided for compatibility with Ada 83. See
4380 the Ada 83 reference manual for an exact description of the semantics of
4384 @unnumberedsec Enum_Rep
4385 @cindex Representation of enums
4388 For every enumeration subtype @var{S}, @code{@var{S}'Enum_Rep} denotes a
4389 function with the following spec:
4391 @smallexample @c ada
4392 function @var{S}'Enum_Rep (Arg : @var{S}'Base)
4393 return @i{Universal_Integer};
4397 It is also allowable to apply @code{Enum_Rep} directly to an object of an
4398 enumeration type or to a non-overloaded enumeration
4399 literal. In this case @code{@var{S}'Enum_Rep} is equivalent to
4400 @code{@var{typ}'Enum_Rep(@var{S})} where @var{typ} is the type of the
4401 enumeration literal or object.
4403 The function returns the representation value for the given enumeration
4404 value. This will be equal to value of the @code{Pos} attribute in the
4405 absence of an enumeration representation clause. This is a static
4406 attribute (i.e.@: the result is static if the argument is static).
4408 @code{@var{S}'Enum_Rep} can also be used with integer types and objects,
4409 in which case it simply returns the integer value. The reason for this
4410 is to allow it to be used for @code{(<>)} discrete formal arguments in
4411 a generic unit that can be instantiated with either enumeration types
4412 or integer types. Note that if @code{Enum_Rep} is used on a modular
4413 type whose upper bound exceeds the upper bound of the largest signed
4414 integer type, and the argument is a variable, so that the universal
4415 integer calculation is done at run-time, then the call to @code{Enum_Rep}
4416 may raise @code{Constraint_Error}.
4419 @unnumberedsec Epsilon
4420 @cindex Ada 83 attributes
4423 The @code{Epsilon} attribute is provided for compatibility with Ada 83. See
4424 the Ada 83 reference manual for an exact description of the semantics of
4428 @unnumberedsec Fixed_Value
4431 For every fixed-point type @var{S}, @code{@var{S}'Fixed_Value} denotes a
4432 function with the following specification:
4434 @smallexample @c ada
4435 function @var{S}'Fixed_Value (Arg : @i{Universal_Integer})
4440 The value returned is the fixed-point value @var{V} such that
4442 @smallexample @c ada
4443 @var{V} = Arg * @var{S}'Small
4447 The effect is thus similar to first converting the argument to the
4448 integer type used to represent @var{S}, and then doing an unchecked
4449 conversion to the fixed-point type. The difference is
4450 that there are full range checks, to ensure that the result is in range.
4451 This attribute is primarily intended for use in implementation of the
4452 input-output functions for fixed-point values.
4454 @node Has_Access_Values
4455 @unnumberedsec Has_Access_Values
4456 @cindex Access values, testing for
4457 @findex Has_Access_Values
4459 The prefix of the @code{Has_Access_Values} attribute is a type. The result
4460 is a Boolean value which is True if the is an access type, or is a composite
4461 type with a component (at any nesting depth) that is an access type, and is
4463 The intended use of this attribute is in conjunction with generic
4464 definitions. If the attribute is applied to a generic private type, it
4465 indicates whether or not the corresponding actual type has access values.
4467 @node Has_Discriminants
4468 @unnumberedsec Has_Discriminants
4469 @cindex Discriminants, testing for
4470 @findex Has_Discriminants
4472 The prefix of the @code{Has_Discriminants} attribute is a type. The result
4473 is a Boolean value which is True if the type has discriminants, and False
4474 otherwise. The intended use of this attribute is in conjunction with generic
4475 definitions. If the attribute is applied to a generic private type, it
4476 indicates whether or not the corresponding actual type has discriminants.
4482 The @code{Img} attribute differs from @code{Image} in that it may be
4483 applied to objects as well as types, in which case it gives the
4484 @code{Image} for the subtype of the object. This is convenient for
4487 @smallexample @c ada
4488 Put_Line ("X = " & X'Img);
4492 has the same meaning as the more verbose:
4494 @smallexample @c ada
4495 Put_Line ("X = " & @var{T}'Image (X));
4499 where @var{T} is the (sub)type of the object @code{X}.
4502 @unnumberedsec Integer_Value
4503 @findex Integer_Value
4505 For every integer type @var{S}, @code{@var{S}'Integer_Value} denotes a
4506 function with the following spec:
4508 @smallexample @c ada
4509 function @var{S}'Integer_Value (Arg : @i{Universal_Fixed})
4514 The value returned is the integer value @var{V}, such that
4516 @smallexample @c ada
4517 Arg = @var{V} * @var{T}'Small
4521 where @var{T} is the type of @code{Arg}.
4522 The effect is thus similar to first doing an unchecked conversion from
4523 the fixed-point type to its corresponding implementation type, and then
4524 converting the result to the target integer type. The difference is
4525 that there are full range checks, to ensure that the result is in range.
4526 This attribute is primarily intended for use in implementation of the
4527 standard input-output functions for fixed-point values.
4530 @unnumberedsec Large
4531 @cindex Ada 83 attributes
4534 The @code{Large} attribute is provided for compatibility with Ada 83. See
4535 the Ada 83 reference manual for an exact description of the semantics of
4539 @unnumberedsec Machine_Size
4540 @findex Machine_Size
4542 This attribute is identical to the @code{Object_Size} attribute. It is
4543 provided for compatibility with the DEC Ada 83 attribute of this name.
4546 @unnumberedsec Mantissa
4547 @cindex Ada 83 attributes
4550 The @code{Mantissa} attribute is provided for compatibility with Ada 83. See
4551 the Ada 83 reference manual for an exact description of the semantics of
4554 @node Max_Interrupt_Priority
4555 @unnumberedsec Max_Interrupt_Priority
4556 @cindex Interrupt priority, maximum
4557 @findex Max_Interrupt_Priority
4559 @code{Standard'Max_Interrupt_Priority} (@code{Standard} is the only
4560 permissible prefix), provides the same value as
4561 @code{System.Max_Interrupt_Priority}.
4564 @unnumberedsec Max_Priority
4565 @cindex Priority, maximum
4566 @findex Max_Priority
4568 @code{Standard'Max_Priority} (@code{Standard} is the only permissible
4569 prefix) provides the same value as @code{System.Max_Priority}.
4571 @node Maximum_Alignment
4572 @unnumberedsec Maximum_Alignment
4573 @cindex Alignment, maximum
4574 @findex Maximum_Alignment
4576 @code{Standard'Maximum_Alignment} (@code{Standard} is the only
4577 permissible prefix) provides the maximum useful alignment value for the
4578 target. This is a static value that can be used to specify the alignment
4579 for an object, guaranteeing that it is properly aligned in all
4582 @node Mechanism_Code
4583 @unnumberedsec Mechanism_Code
4584 @cindex Return values, passing mechanism
4585 @cindex Parameters, passing mechanism
4586 @findex Mechanism_Code
4588 @code{@var{function}'Mechanism_Code} yields an integer code for the
4589 mechanism used for the result of function, and
4590 @code{@var{subprogram}'Mechanism_Code (@var{n})} yields the mechanism
4591 used for formal parameter number @var{n} (a static integer value with 1
4592 meaning the first parameter) of @var{subprogram}. The code returned is:
4600 by descriptor (default descriptor class)
4602 by descriptor (UBS: unaligned bit string)
4604 by descriptor (UBSB: aligned bit string with arbitrary bounds)
4606 by descriptor (UBA: unaligned bit array)
4608 by descriptor (S: string, also scalar access type parameter)
4610 by descriptor (SB: string with arbitrary bounds)
4612 by descriptor (A: contiguous array)
4614 by descriptor (NCA: non-contiguous array)
4618 Values from 3 through 10 are only relevant to Digital OpenVMS implementations.
4621 @node Null_Parameter
4622 @unnumberedsec Null_Parameter
4623 @cindex Zero address, passing
4624 @findex Null_Parameter
4626 A reference @code{@var{T}'Null_Parameter} denotes an imaginary object of
4627 type or subtype @var{T} allocated at machine address zero. The attribute
4628 is allowed only as the default expression of a formal parameter, or as
4629 an actual expression of a subprogram call. In either case, the
4630 subprogram must be imported.
4632 The identity of the object is represented by the address zero in the
4633 argument list, independent of the passing mechanism (explicit or
4636 This capability is needed to specify that a zero address should be
4637 passed for a record or other composite object passed by reference.
4638 There is no way of indicating this without the @code{Null_Parameter}
4642 @unnumberedsec Object_Size
4643 @cindex Size, used for objects
4646 The size of an object is not necessarily the same as the size of the type
4647 of an object. This is because by default object sizes are increased to be
4648 a multiple of the alignment of the object. For example,
4649 @code{Natural'Size} is
4650 31, but by default objects of type @code{Natural} will have a size of 32 bits.
4651 Similarly, a record containing an integer and a character:
4653 @smallexample @c ada
4661 will have a size of 40 (that is @code{Rec'Size} will be 40. The
4662 alignment will be 4, because of the
4663 integer field, and so the default size of record objects for this type
4664 will be 64 (8 bytes).
4666 The @code{@var{type}'Object_Size} attribute
4667 has been added to GNAT to allow the
4668 default object size of a type to be easily determined. For example,
4669 @code{Natural'Object_Size} is 32, and
4670 @code{Rec'Object_Size} (for the record type in the above example) will be
4671 64. Note also that, unlike the situation with the
4672 @code{Size} attribute as defined in the Ada RM, the
4673 @code{Object_Size} attribute can be specified individually
4674 for different subtypes. For example:
4676 @smallexample @c ada
4677 type R is new Integer;
4678 subtype R1 is R range 1 .. 10;
4679 subtype R2 is R range 1 .. 10;
4680 for R2'Object_Size use 8;
4684 In this example, @code{R'Object_Size} and @code{R1'Object_Size} are both
4685 32 since the default object size for a subtype is the same as the object size
4686 for the parent subtype. This means that objects of type @code{R}
4688 by default be 32 bits (four bytes). But objects of type
4689 @code{R2} will be only
4690 8 bits (one byte), since @code{R2'Object_Size} has been set to 8.
4692 @node Passed_By_Reference
4693 @unnumberedsec Passed_By_Reference
4694 @cindex Parameters, when passed by reference
4695 @findex Passed_By_Reference
4697 @code{@var{type}'Passed_By_Reference} for any subtype @var{type} returns
4698 a value of type @code{Boolean} value that is @code{True} if the type is
4699 normally passed by reference and @code{False} if the type is normally
4700 passed by copy in calls. For scalar types, the result is always @code{False}
4701 and is static. For non-scalar types, the result is non-static.
4704 @unnumberedsec Range_Length
4705 @findex Range_Length
4707 @code{@var{type}'Range_Length} for any discrete type @var{type} yields
4708 the number of values represented by the subtype (zero for a null
4709 range). The result is static for static subtypes. @code{Range_Length}
4710 applied to the index subtype of a one dimensional array always gives the
4711 same result as @code{Range} applied to the array itself.
4714 @unnumberedsec Safe_Emax
4715 @cindex Ada 83 attributes
4718 The @code{Safe_Emax} attribute is provided for compatibility with Ada 83. See
4719 the Ada 83 reference manual for an exact description of the semantics of
4723 @unnumberedsec Safe_Large
4724 @cindex Ada 83 attributes
4727 The @code{Safe_Large} attribute is provided for compatibility with Ada 83. See
4728 the Ada 83 reference manual for an exact description of the semantics of
4732 @unnumberedsec Small
4733 @cindex Ada 83 attributes
4736 The @code{Small} attribute is defined in Ada 95 only for fixed-point types.
4737 GNAT also allows this attribute to be applied to floating-point types
4738 for compatibility with Ada 83. See
4739 the Ada 83 reference manual for an exact description of the semantics of
4740 this attribute when applied to floating-point types.
4743 @unnumberedsec Storage_Unit
4744 @findex Storage_Unit
4746 @code{Standard'Storage_Unit} (@code{Standard} is the only permissible
4747 prefix) provides the same value as @code{System.Storage_Unit}.
4750 @unnumberedsec Target_Name
4753 @code{Standard'Target_Name} (@code{Standard} is the only permissible
4754 prefix) provides a static string value that identifies the target
4755 for the current compilation. For GCC implementations, this is the
4756 standard gcc target name without the terminating slash (for
4757 example, GNAT 5.0 on windows yields "i586-pc-mingw32msv").
4763 @code{Standard'Tick} (@code{Standard} is the only permissible prefix)
4764 provides the same value as @code{System.Tick},
4767 @unnumberedsec To_Address
4770 The @code{System'To_Address}
4771 (@code{System} is the only permissible prefix)
4772 denotes a function identical to
4773 @code{System.Storage_Elements.To_Address} except that
4774 it is a static attribute. This means that if its argument is
4775 a static expression, then the result of the attribute is a
4776 static expression. The result is that such an expression can be
4777 used in contexts (e.g.@: preelaborable packages) which require a
4778 static expression and where the function call could not be used
4779 (since the function call is always non-static, even if its
4780 argument is static).
4783 @unnumberedsec Type_Class
4786 @code{@var{type}'Type_Class} for any type or subtype @var{type} yields
4787 the value of the type class for the full type of @var{type}. If
4788 @var{type} is a generic formal type, the value is the value for the
4789 corresponding actual subtype. The value of this attribute is of type
4790 @code{System.Aux_DEC.Type_Class}, which has the following definition:
4792 @smallexample @c ada
4794 (Type_Class_Enumeration,
4796 Type_Class_Fixed_Point,
4797 Type_Class_Floating_Point,
4802 Type_Class_Address);
4806 Protected types yield the value @code{Type_Class_Task}, which thus
4807 applies to all concurrent types. This attribute is designed to
4808 be compatible with the DEC Ada 83 attribute of the same name.
4811 @unnumberedsec UET_Address
4814 The @code{UET_Address} attribute can only be used for a prefix which
4815 denotes a library package. It yields the address of the unit exception
4816 table when zero cost exception handling is used. This attribute is
4817 intended only for use within the GNAT implementation. See the unit
4818 @code{Ada.Exceptions} in files @file{a-except.ads} and @file{a-except.adb}
4819 for details on how this attribute is used in the implementation.
4821 @node Unconstrained_Array
4822 @unnumberedsec Unconstrained_Array
4823 @findex Unconstrained_Array
4825 The @code{Unconstrained_Array} attribute can be used with a prefix that
4826 denotes any type or subtype. It is a static attribute that yields
4827 @code{True} if the prefix designates an unconstrained array,
4828 and @code{False} otherwise. In a generic instance, the result is
4829 still static, and yields the result of applying this test to the
4832 @node Universal_Literal_String
4833 @unnumberedsec Universal_Literal_String
4834 @cindex Named numbers, representation of
4835 @findex Universal_Literal_String
4837 The prefix of @code{Universal_Literal_String} must be a named
4838 number. The static result is the string consisting of the characters of
4839 the number as defined in the original source. This allows the user
4840 program to access the actual text of named numbers without intermediate
4841 conversions and without the need to enclose the strings in quotes (which
4842 would preclude their use as numbers). This is used internally for the
4843 construction of values of the floating-point attributes from the file
4844 @file{ttypef.ads}, but may also be used by user programs.
4846 @node Unrestricted_Access
4847 @unnumberedsec Unrestricted_Access
4848 @cindex @code{Access}, unrestricted
4849 @findex Unrestricted_Access
4851 The @code{Unrestricted_Access} attribute is similar to @code{Access}
4852 except that all accessibility and aliased view checks are omitted. This
4853 is a user-beware attribute. It is similar to
4854 @code{Address}, for which it is a desirable replacement where the value
4855 desired is an access type. In other words, its effect is identical to
4856 first applying the @code{Address} attribute and then doing an unchecked
4857 conversion to a desired access type. In GNAT, but not necessarily in
4858 other implementations, the use of static chains for inner level
4859 subprograms means that @code{Unrestricted_Access} applied to a
4860 subprogram yields a value that can be called as long as the subprogram
4861 is in scope (normal Ada 95 accessibility rules restrict this usage).
4863 It is possible to use @code{Unrestricted_Access} for any type, but care
4864 must be exercised if it is used to create pointers to unconstrained
4865 objects. In this case, the resulting pointer has the same scope as the
4866 context of the attribute, and may not be returned to some enclosing
4867 scope. For instance, a function cannot use @code{Unrestricted_Access}
4868 to create a unconstrained pointer and then return that value to the
4872 @unnumberedsec VADS_Size
4873 @cindex @code{Size}, VADS compatibility
4876 The @code{'VADS_Size} attribute is intended to make it easier to port
4877 legacy code which relies on the semantics of @code{'Size} as implemented
4878 by the VADS Ada 83 compiler. GNAT makes a best effort at duplicating the
4879 same semantic interpretation. In particular, @code{'VADS_Size} applied
4880 to a predefined or other primitive type with no Size clause yields the
4881 Object_Size (for example, @code{Natural'Size} is 32 rather than 31 on
4882 typical machines). In addition @code{'VADS_Size} applied to an object
4883 gives the result that would be obtained by applying the attribute to
4884 the corresponding type.
4887 @unnumberedsec Value_Size
4888 @cindex @code{Size}, setting for not-first subtype
4890 @code{@var{type}'Value_Size} is the number of bits required to represent
4891 a value of the given subtype. It is the same as @code{@var{type}'Size},
4892 but, unlike @code{Size}, may be set for non-first subtypes.
4895 @unnumberedsec Wchar_T_Size
4896 @findex Wchar_T_Size
4897 @code{Standard'Wchar_T_Size} (@code{Standard} is the only permissible
4898 prefix) provides the size in bits of the C @code{wchar_t} type
4899 primarily for constructing the definition of this type in
4900 package @code{Interfaces.C}.
4903 @unnumberedsec Word_Size
4905 @code{Standard'Word_Size} (@code{Standard} is the only permissible
4906 prefix) provides the value @code{System.Word_Size}.
4908 @c ------------------------
4909 @node Implementation Advice
4910 @chapter Implementation Advice
4912 The main text of the Ada 95 Reference Manual describes the required
4913 behavior of all Ada 95 compilers, and the GNAT compiler conforms to
4916 In addition, there are sections throughout the Ada 95
4917 reference manual headed
4918 by the phrase ``implementation advice''. These sections are not normative,
4919 i.e.@: they do not specify requirements that all compilers must
4920 follow. Rather they provide advice on generally desirable behavior. You
4921 may wonder why they are not requirements. The most typical answer is
4922 that they describe behavior that seems generally desirable, but cannot
4923 be provided on all systems, or which may be undesirable on some systems.
4925 As far as practical, GNAT follows the implementation advice sections in
4926 the Ada 95 Reference Manual. This chapter contains a table giving the
4927 reference manual section number, paragraph number and several keywords
4928 for each advice. Each entry consists of the text of the advice followed
4929 by the GNAT interpretation of this advice. Most often, this simply says
4930 ``followed'', which means that GNAT follows the advice. However, in a
4931 number of cases, GNAT deliberately deviates from this advice, in which
4932 case the text describes what GNAT does and why.
4934 @cindex Error detection
4935 @unnumberedsec 1.1.3(20): Error Detection
4938 If an implementation detects the use of an unsupported Specialized Needs
4939 Annex feature at run time, it should raise @code{Program_Error} if
4942 Not relevant. All specialized needs annex features are either supported,
4943 or diagnosed at compile time.
4946 @unnumberedsec 1.1.3(31): Child Units
4949 If an implementation wishes to provide implementation-defined
4950 extensions to the functionality of a language-defined library unit, it
4951 should normally do so by adding children to the library unit.
4955 @cindex Bounded errors
4956 @unnumberedsec 1.1.5(12): Bounded Errors
4959 If an implementation detects a bounded error or erroneous
4960 execution, it should raise @code{Program_Error}.
4962 Followed in all cases in which the implementation detects a bounded
4963 error or erroneous execution. Not all such situations are detected at
4967 @unnumberedsec 2.8(16): Pragmas
4970 Normally, implementation-defined pragmas should have no semantic effect
4971 for error-free programs; that is, if the implementation-defined pragmas
4972 are removed from a working program, the program should still be legal,
4973 and should still have the same semantics.
4975 The following implementation defined pragmas are exceptions to this
4987 @item CPP_Constructor
4995 @item Interface_Name
4997 @item Machine_Attribute
4999 @item Unimplemented_Unit
5001 @item Unchecked_Union
5006 In each of the above cases, it is essential to the purpose of the pragma
5007 that this advice not be followed. For details see the separate section
5008 on implementation defined pragmas.
5010 @unnumberedsec 2.8(17-19): Pragmas
5013 Normally, an implementation should not define pragmas that can
5014 make an illegal program legal, except as follows:
5018 A pragma used to complete a declaration, such as a pragma @code{Import};
5022 A pragma used to configure the environment by adding, removing, or
5023 replacing @code{library_items}.
5025 See response to paragraph 16 of this same section.
5027 @cindex Character Sets
5028 @cindex Alternative Character Sets
5029 @unnumberedsec 3.5.2(5): Alternative Character Sets
5032 If an implementation supports a mode with alternative interpretations
5033 for @code{Character} and @code{Wide_Character}, the set of graphic
5034 characters of @code{Character} should nevertheless remain a proper
5035 subset of the set of graphic characters of @code{Wide_Character}. Any
5036 character set ``localizations'' should be reflected in the results of
5037 the subprograms defined in the language-defined package
5038 @code{Characters.Handling} (see A.3) available in such a mode. In a mode with
5039 an alternative interpretation of @code{Character}, the implementation should
5040 also support a corresponding change in what is a legal
5041 @code{identifier_letter}.
5043 Not all wide character modes follow this advice, in particular the JIS
5044 and IEC modes reflect standard usage in Japan, and in these encoding,
5045 the upper half of the Latin-1 set is not part of the wide-character
5046 subset, since the most significant bit is used for wide character
5047 encoding. However, this only applies to the external forms. Internally
5048 there is no such restriction.
5050 @cindex Integer types
5051 @unnumberedsec 3.5.4(28): Integer Types
5055 An implementation should support @code{Long_Integer} in addition to
5056 @code{Integer} if the target machine supports 32-bit (or longer)
5057 arithmetic. No other named integer subtypes are recommended for package
5058 @code{Standard}. Instead, appropriate named integer subtypes should be
5059 provided in the library package @code{Interfaces} (see B.2).
5061 @code{Long_Integer} is supported. Other standard integer types are supported
5062 so this advice is not fully followed. These types
5063 are supported for convenient interface to C, and so that all hardware
5064 types of the machine are easily available.
5065 @unnumberedsec 3.5.4(29): Integer Types
5069 An implementation for a two's complement machine should support
5070 modular types with a binary modulus up to @code{System.Max_Int*2+2}. An
5071 implementation should support a non-binary modules up to @code{Integer'Last}.
5075 @cindex Enumeration values
5076 @unnumberedsec 3.5.5(8): Enumeration Values
5079 For the evaluation of a call on @code{@var{S}'Pos} for an enumeration
5080 subtype, if the value of the operand does not correspond to the internal
5081 code for any enumeration literal of its type (perhaps due to an
5082 un-initialized variable), then the implementation should raise
5083 @code{Program_Error}. This is particularly important for enumeration
5084 types with noncontiguous internal codes specified by an
5085 enumeration_representation_clause.
5090 @unnumberedsec 3.5.7(17): Float Types
5093 An implementation should support @code{Long_Float} in addition to
5094 @code{Float} if the target machine supports 11 or more digits of
5095 precision. No other named floating point subtypes are recommended for
5096 package @code{Standard}. Instead, appropriate named floating point subtypes
5097 should be provided in the library package @code{Interfaces} (see B.2).
5099 @code{Short_Float} and @code{Long_Long_Float} are also provided. The
5100 former provides improved compatibility with other implementations
5101 supporting this type. The latter corresponds to the highest precision
5102 floating-point type supported by the hardware. On most machines, this
5103 will be the same as @code{Long_Float}, but on some machines, it will
5104 correspond to the IEEE extended form. The notable case is all ia32
5105 (x86) implementations, where @code{Long_Long_Float} corresponds to
5106 the 80-bit extended precision format supported in hardware on this
5107 processor. Note that the 128-bit format on SPARC is not supported,
5108 since this is a software rather than a hardware format.
5110 @cindex Multidimensional arrays
5111 @cindex Arrays, multidimensional
5112 @unnumberedsec 3.6.2(11): Multidimensional Arrays
5115 An implementation should normally represent multidimensional arrays in
5116 row-major order, consistent with the notation used for multidimensional
5117 array aggregates (see 4.3.3). However, if a pragma @code{Convention}
5118 (@code{Fortran}, @dots{}) applies to a multidimensional array type, then
5119 column-major order should be used instead (see B.5, ``Interfacing with
5124 @findex Duration'Small
5125 @unnumberedsec 9.6(30-31): Duration'Small
5128 Whenever possible in an implementation, the value of @code{Duration'Small}
5129 should be no greater than 100 microseconds.
5131 Followed. (@code{Duration'Small} = 10**(@minus{}9)).
5135 The time base for @code{delay_relative_statements} should be monotonic;
5136 it need not be the same time base as used for @code{Calendar.Clock}.
5140 @unnumberedsec 10.2.1(12): Consistent Representation
5143 In an implementation, a type declared in a pre-elaborated package should
5144 have the same representation in every elaboration of a given version of
5145 the package, whether the elaborations occur in distinct executions of
5146 the same program, or in executions of distinct programs or partitions
5147 that include the given version.
5149 Followed, except in the case of tagged types. Tagged types involve
5150 implicit pointers to a local copy of a dispatch table, and these pointers
5151 have representations which thus depend on a particular elaboration of the
5152 package. It is not easy to see how it would be possible to follow this
5153 advice without severely impacting efficiency of execution.
5155 @cindex Exception information
5156 @unnumberedsec 11.4.1(19): Exception Information
5159 @code{Exception_Message} by default and @code{Exception_Information}
5160 should produce information useful for
5161 debugging. @code{Exception_Message} should be short, about one
5162 line. @code{Exception_Information} can be long. @code{Exception_Message}
5163 should not include the
5164 @code{Exception_Name}. @code{Exception_Information} should include both
5165 the @code{Exception_Name} and the @code{Exception_Message}.
5167 Followed. For each exception that doesn't have a specified
5168 @code{Exception_Message}, the compiler generates one containing the location
5169 of the raise statement. This location has the form ``file:line'', where
5170 file is the short file name (without path information) and line is the line
5171 number in the file. Note that in the case of the Zero Cost Exception
5172 mechanism, these messages become redundant with the Exception_Information that
5173 contains a full backtrace of the calling sequence, so they are disabled.
5174 To disable explicitly the generation of the source location message, use the
5175 Pragma @code{Discard_Names}.
5177 @cindex Suppression of checks
5178 @cindex Checks, suppression of
5179 @unnumberedsec 11.5(28): Suppression of Checks
5182 The implementation should minimize the code executed for checks that
5183 have been suppressed.
5187 @cindex Representation clauses
5188 @unnumberedsec 13.1 (21-24): Representation Clauses
5191 The recommended level of support for all representation items is
5192 qualified as follows:
5196 An implementation need not support representation items containing
5197 non-static expressions, except that an implementation should support a
5198 representation item for a given entity if each non-static expression in
5199 the representation item is a name that statically denotes a constant
5200 declared before the entity.
5202 Followed. In fact, GNAT goes beyond the recommended level of support
5203 by allowing nonstatic expressions in some representation clauses even
5204 without the need to declare constants initialized with the values of
5208 @smallexample @c ada
5211 for Y'Address use X'Address;>>
5217 An implementation need not support a specification for the @code{Size}
5218 for a given composite subtype, nor the size or storage place for an
5219 object (including a component) of a given composite subtype, unless the
5220 constraints on the subtype and its composite subcomponents (if any) are
5221 all static constraints.
5223 Followed. Size Clauses are not permitted on non-static components, as
5228 An aliased component, or a component whose type is by-reference, should
5229 always be allocated at an addressable location.
5233 @cindex Packed types
5234 @unnumberedsec 13.2(6-8): Packed Types
5237 If a type is packed, then the implementation should try to minimize
5238 storage allocated to objects of the type, possibly at the expense of
5239 speed of accessing components, subject to reasonable complexity in
5240 addressing calculations.
5244 The recommended level of support pragma @code{Pack} is:
5246 For a packed record type, the components should be packed as tightly as
5247 possible subject to the Sizes of the component subtypes, and subject to
5248 any @code{record_representation_clause} that applies to the type; the
5249 implementation may, but need not, reorder components or cross aligned
5250 word boundaries to improve the packing. A component whose @code{Size} is
5251 greater than the word size may be allocated an integral number of words.
5253 Followed. Tight packing of arrays is supported for all component sizes
5254 up to 64-bits. If the array component size is 1 (that is to say, if
5255 the component is a boolean type or an enumeration type with two values)
5256 then values of the type are implicitly initialized to zero. This
5257 happens both for objects of the packed type, and for objects that have a
5258 subcomponent of the packed type.
5262 An implementation should support Address clauses for imported
5266 @cindex @code{Address} clauses
5267 @unnumberedsec 13.3(14-19): Address Clauses
5271 For an array @var{X}, @code{@var{X}'Address} should point at the first
5272 component of the array, and not at the array bounds.
5278 The recommended level of support for the @code{Address} attribute is:
5280 @code{@var{X}'Address} should produce a useful result if @var{X} is an
5281 object that is aliased or of a by-reference type, or is an entity whose
5282 @code{Address} has been specified.
5284 Followed. A valid address will be produced even if none of those
5285 conditions have been met. If necessary, the object is forced into
5286 memory to ensure the address is valid.
5290 An implementation should support @code{Address} clauses for imported
5297 Objects (including subcomponents) that are aliased or of a by-reference
5298 type should be allocated on storage element boundaries.
5304 If the @code{Address} of an object is specified, or it is imported or exported,
5305 then the implementation should not perform optimizations based on
5306 assumptions of no aliases.
5310 @cindex @code{Alignment} clauses
5311 @unnumberedsec 13.3(29-35): Alignment Clauses
5314 The recommended level of support for the @code{Alignment} attribute for
5317 An implementation should support specified Alignments that are factors
5318 and multiples of the number of storage elements per word, subject to the
5325 An implementation need not support specified @code{Alignment}s for
5326 combinations of @code{Size}s and @code{Alignment}s that cannot be easily
5327 loaded and stored by available machine instructions.
5333 An implementation need not support specified @code{Alignment}s that are
5334 greater than the maximum @code{Alignment} the implementation ever returns by
5341 The recommended level of support for the @code{Alignment} attribute for
5344 Same as above, for subtypes, but in addition:
5350 For stand-alone library-level objects of statically constrained
5351 subtypes, the implementation should support all @code{Alignment}s
5352 supported by the target linker. For example, page alignment is likely to
5353 be supported for such objects, but not for subtypes.
5357 @cindex @code{Size} clauses
5358 @unnumberedsec 13.3(42-43): Size Clauses
5361 The recommended level of support for the @code{Size} attribute of
5364 A @code{Size} clause should be supported for an object if the specified
5365 @code{Size} is at least as large as its subtype's @code{Size}, and
5366 corresponds to a size in storage elements that is a multiple of the
5367 object's @code{Alignment} (if the @code{Alignment} is nonzero).
5371 @unnumberedsec 13.3(50-56): Size Clauses
5374 If the @code{Size} of a subtype is specified, and allows for efficient
5375 independent addressability (see 9.10) on the target architecture, then
5376 the @code{Size} of the following objects of the subtype should equal the
5377 @code{Size} of the subtype:
5379 Aliased objects (including components).
5385 @code{Size} clause on a composite subtype should not affect the
5386 internal layout of components.
5392 The recommended level of support for the @code{Size} attribute of subtypes is:
5396 The @code{Size} (if not specified) of a static discrete or fixed point
5397 subtype should be the number of bits needed to represent each value
5398 belonging to the subtype using an unbiased representation, leaving space
5399 for a sign bit only if the subtype contains negative values. If such a
5400 subtype is a first subtype, then an implementation should support a
5401 specified @code{Size} for it that reflects this representation.
5407 For a subtype implemented with levels of indirection, the @code{Size}
5408 should include the size of the pointers, but not the size of what they
5413 @cindex @code{Component_Size} clauses
5414 @unnumberedsec 13.3(71-73): Component Size Clauses
5417 The recommended level of support for the @code{Component_Size}
5422 An implementation need not support specified @code{Component_Sizes} that are
5423 less than the @code{Size} of the component subtype.
5429 An implementation should support specified @code{Component_Size}s that
5430 are factors and multiples of the word size. For such
5431 @code{Component_Size}s, the array should contain no gaps between
5432 components. For other @code{Component_Size}s (if supported), the array
5433 should contain no gaps between components when packing is also
5434 specified; the implementation should forbid this combination in cases
5435 where it cannot support a no-gaps representation.
5439 @cindex Enumeration representation clauses
5440 @cindex Representation clauses, enumeration
5441 @unnumberedsec 13.4(9-10): Enumeration Representation Clauses
5444 The recommended level of support for enumeration representation clauses
5447 An implementation need not support enumeration representation clauses
5448 for boolean types, but should at minimum support the internal codes in
5449 the range @code{System.Min_Int.System.Max_Int}.
5453 @cindex Record representation clauses
5454 @cindex Representation clauses, records
5455 @unnumberedsec 13.5.1(17-22): Record Representation Clauses
5458 The recommended level of support for
5459 @*@code{record_representation_clauses} is:
5461 An implementation should support storage places that can be extracted
5462 with a load, mask, shift sequence of machine code, and set with a load,
5463 shift, mask, store sequence, given the available machine instructions
5470 A storage place should be supported if its size is equal to the
5471 @code{Size} of the component subtype, and it starts and ends on a
5472 boundary that obeys the @code{Alignment} of the component subtype.
5478 If the default bit ordering applies to the declaration of a given type,
5479 then for a component whose subtype's @code{Size} is less than the word
5480 size, any storage place that does not cross an aligned word boundary
5481 should be supported.
5487 An implementation may reserve a storage place for the tag field of a
5488 tagged type, and disallow other components from overlapping that place.
5490 Followed. The storage place for the tag field is the beginning of the tagged
5491 record, and its size is Address'Size. GNAT will reject an explicit component
5492 clause for the tag field.
5496 An implementation need not support a @code{component_clause} for a
5497 component of an extension part if the storage place is not after the
5498 storage places of all components of the parent type, whether or not
5499 those storage places had been specified.
5501 Followed. The above advice on record representation clauses is followed,
5502 and all mentioned features are implemented.
5504 @cindex Storage place attributes
5505 @unnumberedsec 13.5.2(5): Storage Place Attributes
5508 If a component is represented using some form of pointer (such as an
5509 offset) to the actual data of the component, and this data is contiguous
5510 with the rest of the object, then the storage place attributes should
5511 reflect the place of the actual data, not the pointer. If a component is
5512 allocated discontinuously from the rest of the object, then a warning
5513 should be generated upon reference to one of its storage place
5516 Followed. There are no such components in GNAT@.
5518 @cindex Bit ordering
5519 @unnumberedsec 13.5.3(7-8): Bit Ordering
5522 The recommended level of support for the non-default bit ordering is:
5526 If @code{Word_Size} = @code{Storage_Unit}, then the implementation
5527 should support the non-default bit ordering in addition to the default
5530 Followed. Word size does not equal storage size in this implementation.
5531 Thus non-default bit ordering is not supported.
5533 @cindex @code{Address}, as private type
5534 @unnumberedsec 13.7(37): Address as Private
5537 @code{Address} should be of a private type.
5541 @cindex Operations, on @code{Address}
5542 @cindex @code{Address}, operations of
5543 @unnumberedsec 13.7.1(16): Address Operations
5546 Operations in @code{System} and its children should reflect the target
5547 environment semantics as closely as is reasonable. For example, on most
5548 machines, it makes sense for address arithmetic to ``wrap around''.
5549 Operations that do not make sense should raise @code{Program_Error}.
5551 Followed. Address arithmetic is modular arithmetic that wraps around. No
5552 operation raises @code{Program_Error}, since all operations make sense.
5554 @cindex Unchecked conversion
5555 @unnumberedsec 13.9(14-17): Unchecked Conversion
5558 The @code{Size} of an array object should not include its bounds; hence,
5559 the bounds should not be part of the converted data.
5565 The implementation should not generate unnecessary run-time checks to
5566 ensure that the representation of @var{S} is a representation of the
5567 target type. It should take advantage of the permission to return by
5568 reference when possible. Restrictions on unchecked conversions should be
5569 avoided unless required by the target environment.
5571 Followed. There are no restrictions on unchecked conversion. A warning is
5572 generated if the source and target types do not have the same size since
5573 the semantics in this case may be target dependent.
5577 The recommended level of support for unchecked conversions is:
5581 Unchecked conversions should be supported and should be reversible in
5582 the cases where this clause defines the result. To enable meaningful use
5583 of unchecked conversion, a contiguous representation should be used for
5584 elementary subtypes, for statically constrained array subtypes whose
5585 component subtype is one of the subtypes described in this paragraph,
5586 and for record subtypes without discriminants whose component subtypes
5587 are described in this paragraph.
5591 @cindex Heap usage, implicit
5592 @unnumberedsec 13.11(23-25): Implicit Heap Usage
5595 An implementation should document any cases in which it dynamically
5596 allocates heap storage for a purpose other than the evaluation of an
5599 Followed, the only other points at which heap storage is dynamically
5600 allocated are as follows:
5604 At initial elaboration time, to allocate dynamically sized global
5608 To allocate space for a task when a task is created.
5611 To extend the secondary stack dynamically when needed. The secondary
5612 stack is used for returning variable length results.
5617 A default (implementation-provided) storage pool for an
5618 access-to-constant type should not have overhead to support deallocation of
5625 A storage pool for an anonymous access type should be created at the
5626 point of an allocator for the type, and be reclaimed when the designated
5627 object becomes inaccessible.
5631 @cindex Unchecked deallocation
5632 @unnumberedsec 13.11.2(17): Unchecked De-allocation
5635 For a standard storage pool, @code{Free} should actually reclaim the
5640 @cindex Stream oriented attributes
5641 @unnumberedsec 13.13.2(17): Stream Oriented Attributes
5644 If a stream element is the same size as a storage element, then the
5645 normal in-memory representation should be used by @code{Read} and
5646 @code{Write} for scalar objects. Otherwise, @code{Read} and @code{Write}
5647 should use the smallest number of stream elements needed to represent
5648 all values in the base range of the scalar type.
5651 Followed. By default, GNAT uses the interpretation suggested by AI-195,
5652 which specifies using the size of the first subtype.
5653 However, such an implementation is based on direct binary
5654 representations and is therefore target- and endianness-dependent.
5655 To address this issue, GNAT also supplies an alternate implementation
5656 of the stream attributes @code{Read} and @code{Write},
5657 which uses the target-independent XDR standard representation
5659 @cindex XDR representation
5660 @cindex @code{Read} attribute
5661 @cindex @code{Write} attribute
5662 @cindex Stream oriented attributes
5663 The XDR implementation is provided as an alternative body of the
5664 @code{System.Stream_Attributes} package, in the file
5665 @file{s-strxdr.adb} in the GNAT library.
5666 There is no @file{s-strxdr.ads} file.
5667 In order to install the XDR implementation, do the following:
5669 @item Replace the default implementation of the
5670 @code{System.Stream_Attributes} package with the XDR implementation.
5671 For example on a Unix platform issue the commands:
5673 $ mv s-stratt.adb s-strold.adb
5674 $ mv s-strxdr.adb s-stratt.adb
5678 Rebuild the GNAT run-time library as documented in the
5679 @cite{GNAT User's Guide}
5682 @unnumberedsec A.1(52): Names of Predefined Numeric Types
5685 If an implementation provides additional named predefined integer types,
5686 then the names should end with @samp{Integer} as in
5687 @samp{Long_Integer}. If an implementation provides additional named
5688 predefined floating point types, then the names should end with
5689 @samp{Float} as in @samp{Long_Float}.
5693 @findex Ada.Characters.Handling
5694 @unnumberedsec A.3.2(49): @code{Ada.Characters.Handling}
5697 If an implementation provides a localized definition of @code{Character}
5698 or @code{Wide_Character}, then the effects of the subprograms in
5699 @code{Characters.Handling} should reflect the localizations. See also
5702 Followed. GNAT provides no such localized definitions.
5704 @cindex Bounded-length strings
5705 @unnumberedsec A.4.4(106): Bounded-Length String Handling
5708 Bounded string objects should not be implemented by implicit pointers
5709 and dynamic allocation.
5711 Followed. No implicit pointers or dynamic allocation are used.
5713 @cindex Random number generation
5714 @unnumberedsec A.5.2(46-47): Random Number Generation
5717 Any storage associated with an object of type @code{Generator} should be
5718 reclaimed on exit from the scope of the object.
5724 If the generator period is sufficiently long in relation to the number
5725 of distinct initiator values, then each possible value of
5726 @code{Initiator} passed to @code{Reset} should initiate a sequence of
5727 random numbers that does not, in a practical sense, overlap the sequence
5728 initiated by any other value. If this is not possible, then the mapping
5729 between initiator values and generator states should be a rapidly
5730 varying function of the initiator value.
5732 Followed. The generator period is sufficiently long for the first
5733 condition here to hold true.
5735 @findex Get_Immediate
5736 @unnumberedsec A.10.7(23): @code{Get_Immediate}
5739 The @code{Get_Immediate} procedures should be implemented with
5740 unbuffered input. For a device such as a keyboard, input should be
5741 @dfn{available} if a key has already been typed, whereas for a disk
5742 file, input should always be available except at end of file. For a file
5743 associated with a keyboard-like device, any line-editing features of the
5744 underlying operating system should be disabled during the execution of
5745 @code{Get_Immediate}.
5747 Followed on all targets except VxWorks. For VxWorks, there is no way to
5748 provide this functionality that does not result in the input buffer being
5749 flushed before the @code{Get_Immediate} call. A special unit
5750 @code{Interfaces.Vxworks.IO} is provided that contains routines to enable
5754 @unnumberedsec B.1(39-41): Pragma @code{Export}
5757 If an implementation supports pragma @code{Export} to a given language,
5758 then it should also allow the main subprogram to be written in that
5759 language. It should support some mechanism for invoking the elaboration
5760 of the Ada library units included in the system, and for invoking the
5761 finalization of the environment task. On typical systems, the
5762 recommended mechanism is to provide two subprograms whose link names are
5763 @code{adainit} and @code{adafinal}. @code{adainit} should contain the
5764 elaboration code for library units. @code{adafinal} should contain the
5765 finalization code. These subprograms should have no effect the second
5766 and subsequent time they are called.
5772 Automatic elaboration of pre-elaborated packages should be
5773 provided when pragma @code{Export} is supported.
5775 Followed when the main program is in Ada. If the main program is in a
5776 foreign language, then
5777 @code{adainit} must be called to elaborate pre-elaborated
5782 For each supported convention @var{L} other than @code{Intrinsic}, an
5783 implementation should support @code{Import} and @code{Export} pragmas
5784 for objects of @var{L}-compatible types and for subprograms, and pragma
5785 @code{Convention} for @var{L}-eligible types and for subprograms,
5786 presuming the other language has corresponding features. Pragma
5787 @code{Convention} need not be supported for scalar types.
5791 @cindex Package @code{Interfaces}
5793 @unnumberedsec B.2(12-13): Package @code{Interfaces}
5796 For each implementation-defined convention identifier, there should be a
5797 child package of package Interfaces with the corresponding name. This
5798 package should contain any declarations that would be useful for
5799 interfacing to the language (implementation) represented by the
5800 convention. Any declarations useful for interfacing to any language on
5801 the given hardware architecture should be provided directly in
5804 Followed. An additional package not defined
5805 in the Ada 95 Reference Manual is @code{Interfaces.CPP}, used
5806 for interfacing to C++.
5810 An implementation supporting an interface to C, COBOL, or Fortran should
5811 provide the corresponding package or packages described in the following
5814 Followed. GNAT provides all the packages described in this section.
5816 @cindex C, interfacing with
5817 @unnumberedsec B.3(63-71): Interfacing with C
5820 An implementation should support the following interface correspondences
5827 An Ada procedure corresponds to a void-returning C function.
5833 An Ada function corresponds to a non-void C function.
5839 An Ada @code{in} scalar parameter is passed as a scalar argument to a C
5846 An Ada @code{in} parameter of an access-to-object type with designated
5847 type @var{T} is passed as a @code{@var{t}*} argument to a C function,
5848 where @var{t} is the C type corresponding to the Ada type @var{T}.
5854 An Ada access @var{T} parameter, or an Ada @code{out} or @code{in out}
5855 parameter of an elementary type @var{T}, is passed as a @code{@var{t}*}
5856 argument to a C function, where @var{t} is the C type corresponding to
5857 the Ada type @var{T}. In the case of an elementary @code{out} or
5858 @code{in out} parameter, a pointer to a temporary copy is used to
5859 preserve by-copy semantics.
5865 An Ada parameter of a record type @var{T}, of any mode, is passed as a
5866 @code{@var{t}*} argument to a C function, where @var{t} is the C
5867 structure corresponding to the Ada type @var{T}.
5869 Followed. This convention may be overridden by the use of the C_Pass_By_Copy
5870 pragma, or Convention, or by explicitly specifying the mechanism for a given
5871 call using an extended import or export pragma.
5875 An Ada parameter of an array type with component type @var{T}, of any
5876 mode, is passed as a @code{@var{t}*} argument to a C function, where
5877 @var{t} is the C type corresponding to the Ada type @var{T}.
5883 An Ada parameter of an access-to-subprogram type is passed as a pointer
5884 to a C function whose prototype corresponds to the designated
5885 subprogram's specification.
5889 @cindex COBOL, interfacing with
5890 @unnumberedsec B.4(95-98): Interfacing with COBOL
5893 An Ada implementation should support the following interface
5894 correspondences between Ada and COBOL@.
5900 An Ada access @var{T} parameter is passed as a @samp{BY REFERENCE} data item of
5901 the COBOL type corresponding to @var{T}.
5907 An Ada in scalar parameter is passed as a @samp{BY CONTENT} data item of
5908 the corresponding COBOL type.
5914 Any other Ada parameter is passed as a @samp{BY REFERENCE} data item of the
5915 COBOL type corresponding to the Ada parameter type; for scalars, a local
5916 copy is used if necessary to ensure by-copy semantics.
5920 @cindex Fortran, interfacing with
5921 @unnumberedsec B.5(22-26): Interfacing with Fortran
5924 An Ada implementation should support the following interface
5925 correspondences between Ada and Fortran:
5931 An Ada procedure corresponds to a Fortran subroutine.
5937 An Ada function corresponds to a Fortran function.
5943 An Ada parameter of an elementary, array, or record type @var{T} is
5944 passed as a @var{T} argument to a Fortran procedure, where @var{T} is
5945 the Fortran type corresponding to the Ada type @var{T}, and where the
5946 INTENT attribute of the corresponding dummy argument matches the Ada
5947 formal parameter mode; the Fortran implementation's parameter passing
5948 conventions are used. For elementary types, a local copy is used if
5949 necessary to ensure by-copy semantics.
5955 An Ada parameter of an access-to-subprogram type is passed as a
5956 reference to a Fortran procedure whose interface corresponds to the
5957 designated subprogram's specification.
5961 @cindex Machine operations
5962 @unnumberedsec C.1(3-5): Access to Machine Operations
5965 The machine code or intrinsic support should allow access to all
5966 operations normally available to assembly language programmers for the
5967 target environment, including privileged instructions, if any.
5973 The interfacing pragmas (see Annex B) should support interface to
5974 assembler; the default assembler should be associated with the
5975 convention identifier @code{Assembler}.
5981 If an entity is exported to assembly language, then the implementation
5982 should allocate it at an addressable location, and should ensure that it
5983 is retained by the linking process, even if not otherwise referenced
5984 from the Ada code. The implementation should assume that any call to a
5985 machine code or assembler subprogram is allowed to read or update every
5986 object that is specified as exported.
5990 @unnumberedsec C.1(10-16): Access to Machine Operations
5993 The implementation should ensure that little or no overhead is
5994 associated with calling intrinsic and machine-code subprograms.
5996 Followed for both intrinsics and machine-code subprograms.
6000 It is recommended that intrinsic subprograms be provided for convenient
6001 access to any machine operations that provide special capabilities or
6002 efficiency and that are not otherwise available through the language
6005 Followed. A full set of machine operation intrinsic subprograms is provided.
6009 Atomic read-modify-write operations---e.g.@:, test and set, compare and
6010 swap, decrement and test, enqueue/dequeue.
6012 Followed on any target supporting such operations.
6016 Standard numeric functions---e.g.@:, sin, log.
6018 Followed on any target supporting such operations.
6022 String manipulation operations---e.g.@:, translate and test.
6024 Followed on any target supporting such operations.
6028 Vector operations---e.g.@:, compare vector against thresholds.
6030 Followed on any target supporting such operations.
6034 Direct operations on I/O ports.
6036 Followed on any target supporting such operations.
6038 @cindex Interrupt support
6039 @unnumberedsec C.3(28): Interrupt Support
6042 If the @code{Ceiling_Locking} policy is not in effect, the
6043 implementation should provide means for the application to specify which
6044 interrupts are to be blocked during protected actions, if the underlying
6045 system allows for a finer-grain control of interrupt blocking.
6047 Followed. The underlying system does not allow for finer-grain control
6048 of interrupt blocking.
6050 @cindex Protected procedure handlers
6051 @unnumberedsec C.3.1(20-21): Protected Procedure Handlers
6054 Whenever possible, the implementation should allow interrupt handlers to
6055 be called directly by the hardware.
6059 This is never possible under IRIX, so this is followed by default.
6061 Followed on any target where the underlying operating system permits
6066 Whenever practical, violations of any
6067 implementation-defined restrictions should be detected before run time.
6069 Followed. Compile time warnings are given when possible.
6071 @cindex Package @code{Interrupts}
6073 @unnumberedsec C.3.2(25): Package @code{Interrupts}
6077 If implementation-defined forms of interrupt handler procedures are
6078 supported, such as protected procedures with parameters, then for each
6079 such form of a handler, a type analogous to @code{Parameterless_Handler}
6080 should be specified in a child package of @code{Interrupts}, with the
6081 same operations as in the predefined package Interrupts.
6085 @cindex Pre-elaboration requirements
6086 @unnumberedsec C.4(14): Pre-elaboration Requirements
6089 It is recommended that pre-elaborated packages be implemented in such a
6090 way that there should be little or no code executed at run time for the
6091 elaboration of entities not already covered by the Implementation
6094 Followed. Executable code is generated in some cases, e.g.@: loops
6095 to initialize large arrays.
6097 @unnumberedsec C.5(8): Pragma @code{Discard_Names}
6101 If the pragma applies to an entity, then the implementation should
6102 reduce the amount of storage used for storing names associated with that
6107 @cindex Package @code{Task_Attributes}
6108 @findex Task_Attributes
6109 @unnumberedsec C.7.2(30): The Package Task_Attributes
6112 Some implementations are targeted to domains in which memory use at run
6113 time must be completely deterministic. For such implementations, it is
6114 recommended that the storage for task attributes will be pre-allocated
6115 statically and not from the heap. This can be accomplished by either
6116 placing restrictions on the number and the size of the task's
6117 attributes, or by using the pre-allocated storage for the first @var{N}
6118 attribute objects, and the heap for the others. In the latter case,
6119 @var{N} should be documented.
6121 Not followed. This implementation is not targeted to such a domain.
6123 @cindex Locking Policies
6124 @unnumberedsec D.3(17): Locking Policies
6128 The implementation should use names that end with @samp{_Locking} for
6129 locking policies defined by the implementation.
6131 Followed. A single implementation-defined locking policy is defined,
6132 whose name (@code{Inheritance_Locking}) follows this suggestion.
6134 @cindex Entry queuing policies
6135 @unnumberedsec D.4(16): Entry Queuing Policies
6138 Names that end with @samp{_Queuing} should be used
6139 for all implementation-defined queuing policies.
6141 Followed. No such implementation-defined queuing policies exist.
6143 @cindex Preemptive abort
6144 @unnumberedsec D.6(9-10): Preemptive Abort
6147 Even though the @code{abort_statement} is included in the list of
6148 potentially blocking operations (see 9.5.1), it is recommended that this
6149 statement be implemented in a way that never requires the task executing
6150 the @code{abort_statement} to block.
6156 On a multi-processor, the delay associated with aborting a task on
6157 another processor should be bounded; the implementation should use
6158 periodic polling, if necessary, to achieve this.
6162 @cindex Tasking restrictions
6163 @unnumberedsec D.7(21): Tasking Restrictions
6166 When feasible, the implementation should take advantage of the specified
6167 restrictions to produce a more efficient implementation.
6169 GNAT currently takes advantage of these restrictions by providing an optimized
6170 run time when the Ravenscar profile and the GNAT restricted run time set
6171 of restrictions are specified. See pragma @code{Profile (Ravenscar)} and
6172 pragma @code{Profile (Restricted)} for more details.
6174 @cindex Time, monotonic
6175 @unnumberedsec D.8(47-49): Monotonic Time
6178 When appropriate, implementations should provide configuration
6179 mechanisms to change the value of @code{Tick}.
6181 Such configuration mechanisms are not appropriate to this implementation
6182 and are thus not supported.
6186 It is recommended that @code{Calendar.Clock} and @code{Real_Time.Clock}
6187 be implemented as transformations of the same time base.
6193 It is recommended that the @dfn{best} time base which exists in
6194 the underlying system be available to the application through
6195 @code{Clock}. @dfn{Best} may mean highest accuracy or largest range.
6199 @cindex Partition communication subsystem
6201 @unnumberedsec E.5(28-29): Partition Communication Subsystem
6204 Whenever possible, the PCS on the called partition should allow for
6205 multiple tasks to call the RPC-receiver with different messages and
6206 should allow them to block until the corresponding subprogram body
6209 Followed by GLADE, a separately supplied PCS that can be used with
6214 The @code{Write} operation on a stream of type @code{Params_Stream_Type}
6215 should raise @code{Storage_Error} if it runs out of space trying to
6216 write the @code{Item} into the stream.
6218 Followed by GLADE, a separately supplied PCS that can be used with
6221 @cindex COBOL support
6222 @unnumberedsec F(7): COBOL Support
6225 If COBOL (respectively, C) is widely supported in the target
6226 environment, implementations supporting the Information Systems Annex
6227 should provide the child package @code{Interfaces.COBOL} (respectively,
6228 @code{Interfaces.C}) specified in Annex B and should support a
6229 @code{convention_identifier} of COBOL (respectively, C) in the interfacing
6230 pragmas (see Annex B), thus allowing Ada programs to interface with
6231 programs written in that language.
6235 @cindex Decimal radix support
6236 @unnumberedsec F.1(2): Decimal Radix Support
6239 Packed decimal should be used as the internal representation for objects
6240 of subtype @var{S} when @var{S}'Machine_Radix = 10.
6242 Not followed. GNAT ignores @var{S}'Machine_Radix and always uses binary
6246 @unnumberedsec G: Numerics
6249 If Fortran (respectively, C) is widely supported in the target
6250 environment, implementations supporting the Numerics Annex
6251 should provide the child package @code{Interfaces.Fortran} (respectively,
6252 @code{Interfaces.C}) specified in Annex B and should support a
6253 @code{convention_identifier} of Fortran (respectively, C) in the interfacing
6254 pragmas (see Annex B), thus allowing Ada programs to interface with
6255 programs written in that language.
6259 @cindex Complex types
6260 @unnumberedsec G.1.1(56-58): Complex Types
6263 Because the usual mathematical meaning of multiplication of a complex
6264 operand and a real operand is that of the scaling of both components of
6265 the former by the latter, an implementation should not perform this
6266 operation by first promoting the real operand to complex type and then
6267 performing a full complex multiplication. In systems that, in the
6268 future, support an Ada binding to IEC 559:1989, the latter technique
6269 will not generate the required result when one of the components of the
6270 complex operand is infinite. (Explicit multiplication of the infinite
6271 component by the zero component obtained during promotion yields a NaN
6272 that propagates into the final result.) Analogous advice applies in the
6273 case of multiplication of a complex operand and a pure-imaginary
6274 operand, and in the case of division of a complex operand by a real or
6275 pure-imaginary operand.
6281 Similarly, because the usual mathematical meaning of addition of a
6282 complex operand and a real operand is that the imaginary operand remains
6283 unchanged, an implementation should not perform this operation by first
6284 promoting the real operand to complex type and then performing a full
6285 complex addition. In implementations in which the @code{Signed_Zeros}
6286 attribute of the component type is @code{True} (and which therefore
6287 conform to IEC 559:1989 in regard to the handling of the sign of zero in
6288 predefined arithmetic operations), the latter technique will not
6289 generate the required result when the imaginary component of the complex
6290 operand is a negatively signed zero. (Explicit addition of the negative
6291 zero to the zero obtained during promotion yields a positive zero.)
6292 Analogous advice applies in the case of addition of a complex operand
6293 and a pure-imaginary operand, and in the case of subtraction of a
6294 complex operand and a real or pure-imaginary operand.
6300 Implementations in which @code{Real'Signed_Zeros} is @code{True} should
6301 attempt to provide a rational treatment of the signs of zero results and
6302 result components. As one example, the result of the @code{Argument}
6303 function should have the sign of the imaginary component of the
6304 parameter @code{X} when the point represented by that parameter lies on
6305 the positive real axis; as another, the sign of the imaginary component
6306 of the @code{Compose_From_Polar} function should be the same as
6307 (respectively, the opposite of) that of the @code{Argument} parameter when that
6308 parameter has a value of zero and the @code{Modulus} parameter has a
6309 nonnegative (respectively, negative) value.
6313 @cindex Complex elementary functions
6314 @unnumberedsec G.1.2(49): Complex Elementary Functions
6317 Implementations in which @code{Complex_Types.Real'Signed_Zeros} is
6318 @code{True} should attempt to provide a rational treatment of the signs
6319 of zero results and result components. For example, many of the complex
6320 elementary functions have components that are odd functions of one of
6321 the parameter components; in these cases, the result component should
6322 have the sign of the parameter component at the origin. Other complex
6323 elementary functions have zero components whose sign is opposite that of
6324 a parameter component at the origin, or is always positive or always
6329 @cindex Accuracy requirements
6330 @unnumberedsec G.2.4(19): Accuracy Requirements
6333 The versions of the forward trigonometric functions without a
6334 @code{Cycle} parameter should not be implemented by calling the
6335 corresponding version with a @code{Cycle} parameter of
6336 @code{2.0*Numerics.Pi}, since this will not provide the required
6337 accuracy in some portions of the domain. For the same reason, the
6338 version of @code{Log} without a @code{Base} parameter should not be
6339 implemented by calling the corresponding version with a @code{Base}
6340 parameter of @code{Numerics.e}.
6344 @cindex Complex arithmetic accuracy
6345 @cindex Accuracy, complex arithmetic
6346 @unnumberedsec G.2.6(15): Complex Arithmetic Accuracy
6350 The version of the @code{Compose_From_Polar} function without a
6351 @code{Cycle} parameter should not be implemented by calling the
6352 corresponding version with a @code{Cycle} parameter of
6353 @code{2.0*Numerics.Pi}, since this will not provide the required
6354 accuracy in some portions of the domain.
6358 @c -----------------------------------------
6359 @node Implementation Defined Characteristics
6360 @chapter Implementation Defined Characteristics
6363 In addition to the implementation dependent pragmas and attributes, and
6364 the implementation advice, there are a number of other features of Ada
6365 95 that are potentially implementation dependent. These are mentioned
6366 throughout the Ada 95 Reference Manual, and are summarized in annex M@.
6368 A requirement for conforming Ada compilers is that they provide
6369 documentation describing how the implementation deals with each of these
6370 issues. In this chapter, you will find each point in annex M listed
6371 followed by a description in italic font of how GNAT
6375 implementation on IRIX 5.3 operating system or greater
6377 handles the implementation dependence.
6379 You can use this chapter as a guide to minimizing implementation
6380 dependent features in your programs if portability to other compilers
6381 and other operating systems is an important consideration. The numbers
6382 in each section below correspond to the paragraph number in the Ada 95
6388 @strong{2}. Whether or not each recommendation given in Implementation
6389 Advice is followed. See 1.1.2(37).
6392 @xref{Implementation Advice}.
6397 @strong{3}. Capacity limitations of the implementation. See 1.1.3(3).
6400 The complexity of programs that can be processed is limited only by the
6401 total amount of available virtual memory, and disk space for the
6402 generated object files.
6407 @strong{4}. Variations from the standard that are impractical to avoid
6408 given the implementation's execution environment. See 1.1.3(6).
6411 There are no variations from the standard.
6416 @strong{5}. Which @code{code_statement}s cause external
6417 interactions. See 1.1.3(10).
6420 Any @code{code_statement} can potentially cause external interactions.
6425 @strong{6}. The coded representation for the text of an Ada
6426 program. See 2.1(4).
6429 See separate section on source representation.
6434 @strong{7}. The control functions allowed in comments. See 2.1(14).
6437 See separate section on source representation.
6442 @strong{8}. The representation for an end of line. See 2.2(2).
6445 See separate section on source representation.
6450 @strong{9}. Maximum supported line length and lexical element
6451 length. See 2.2(15).
6454 The maximum line length is 255 characters an the maximum length of a
6455 lexical element is also 255 characters.
6460 @strong{10}. Implementation defined pragmas. See 2.8(14).
6464 @xref{Implementation Defined Pragmas}.
6469 @strong{11}. Effect of pragma @code{Optimize}. See 2.8(27).
6472 Pragma @code{Optimize}, if given with a @code{Time} or @code{Space}
6473 parameter, checks that the optimization flag is set, and aborts if it is
6479 @strong{12}. The sequence of characters of the value returned by
6480 @code{@var{S}'Image} when some of the graphic characters of
6481 @code{@var{S}'Wide_Image} are not defined in @code{Character}. See
6485 The sequence of characters is as defined by the wide character encoding
6486 method used for the source. See section on source representation for
6492 @strong{13}. The predefined integer types declared in
6493 @code{Standard}. See 3.5.4(25).
6497 @item Short_Short_Integer
6500 (Short) 16 bit signed
6504 64 bit signed (Alpha OpenVMS only)
6505 32 bit signed (all other targets)
6506 @item Long_Long_Integer
6513 @strong{14}. Any nonstandard integer types and the operators defined
6514 for them. See 3.5.4(26).
6517 There are no nonstandard integer types.
6522 @strong{15}. Any nonstandard real types and the operators defined for
6526 There are no nonstandard real types.
6531 @strong{16}. What combinations of requested decimal precision and range
6532 are supported for floating point types. See 3.5.7(7).
6535 The precision and range is as defined by the IEEE standard.
6540 @strong{17}. The predefined floating point types declared in
6541 @code{Standard}. See 3.5.7(16).
6548 (Short) 32 bit IEEE short
6551 @item Long_Long_Float
6552 64 bit IEEE long (80 bit IEEE long on x86 processors)
6558 @strong{18}. The small of an ordinary fixed point type. See 3.5.9(8).
6561 @code{Fine_Delta} is 2**(@minus{}63)
6566 @strong{19}. What combinations of small, range, and digits are
6567 supported for fixed point types. See 3.5.9(10).
6570 Any combinations are permitted that do not result in a small less than
6571 @code{Fine_Delta} and do not result in a mantissa larger than 63 bits.
6572 If the mantissa is larger than 53 bits on machines where Long_Long_Float
6573 is 64 bits (true of all architectures except ia32), then the output from
6574 Text_IO is accurate to only 53 bits, rather than the full mantissa. This
6575 is because floating-point conversions are used to convert fixed point.
6580 @strong{20}. The result of @code{Tags.Expanded_Name} for types declared
6581 within an unnamed @code{block_statement}. See 3.9(10).
6584 Block numbers of the form @code{B@var{nnn}}, where @var{nnn} is a
6585 decimal integer are allocated.
6590 @strong{21}. Implementation-defined attributes. See 4.1.4(12).
6593 @xref{Implementation Defined Attributes}.
6598 @strong{22}. Any implementation-defined time types. See 9.6(6).
6601 There are no implementation-defined time types.
6606 @strong{23}. The time base associated with relative delays.
6609 See 9.6(20). The time base used is that provided by the C library
6610 function @code{gettimeofday}.
6615 @strong{24}. The time base of the type @code{Calendar.Time}. See
6619 The time base used is that provided by the C library function
6620 @code{gettimeofday}.
6625 @strong{25}. The time zone used for package @code{Calendar}
6626 operations. See 9.6(24).
6629 The time zone used by package @code{Calendar} is the current system time zone
6630 setting for local time, as accessed by the C library function
6636 @strong{26}. Any limit on @code{delay_until_statements} of
6637 @code{select_statements}. See 9.6(29).
6640 There are no such limits.
6645 @strong{27}. Whether or not two non overlapping parts of a composite
6646 object are independently addressable, in the case where packing, record
6647 layout, or @code{Component_Size} is specified for the object. See
6651 Separate components are independently addressable if they do not share
6652 overlapping storage units.
6657 @strong{28}. The representation for a compilation. See 10.1(2).
6660 A compilation is represented by a sequence of files presented to the
6661 compiler in a single invocation of the @code{gcc} command.
6666 @strong{29}. Any restrictions on compilations that contain multiple
6667 compilation_units. See 10.1(4).
6670 No single file can contain more than one compilation unit, but any
6671 sequence of files can be presented to the compiler as a single
6677 @strong{30}. The mechanisms for creating an environment and for adding
6678 and replacing compilation units. See 10.1.4(3).
6681 See separate section on compilation model.
6686 @strong{31}. The manner of explicitly assigning library units to a
6687 partition. See 10.2(2).
6690 If a unit contains an Ada main program, then the Ada units for the partition
6691 are determined by recursive application of the rules in the Ada Reference
6692 Manual section 10.2(2-6). In other words, the Ada units will be those that
6693 are needed by the main program, and then this definition of need is applied
6694 recursively to those units, and the partition contains the transitive
6695 closure determined by this relationship. In short, all the necessary units
6696 are included, with no need to explicitly specify the list. If additional
6697 units are required, e.g.@: by foreign language units, then all units must be
6698 mentioned in the context clause of one of the needed Ada units.
6700 If the partition contains no main program, or if the main program is in
6701 a language other than Ada, then GNAT
6702 provides the binder options @code{-z} and @code{-n} respectively, and in
6703 this case a list of units can be explicitly supplied to the binder for
6704 inclusion in the partition (all units needed by these units will also
6705 be included automatically). For full details on the use of these
6706 options, refer to the @cite{GNAT User's Guide} sections on Binding
6712 @strong{32}. The implementation-defined means, if any, of specifying
6713 which compilation units are needed by a given compilation unit. See
6717 The units needed by a given compilation unit are as defined in
6718 the Ada Reference Manual section 10.2(2-6). There are no
6719 implementation-defined pragmas or other implementation-defined
6720 means for specifying needed units.
6725 @strong{33}. The manner of designating the main subprogram of a
6726 partition. See 10.2(7).
6729 The main program is designated by providing the name of the
6730 corresponding @file{ALI} file as the input parameter to the binder.
6735 @strong{34}. The order of elaboration of @code{library_items}. See
6739 The first constraint on ordering is that it meets the requirements of
6740 chapter 10 of the Ada 95 Reference Manual. This still leaves some
6741 implementation dependent choices, which are resolved by first
6742 elaborating bodies as early as possible (i.e.@: in preference to specs
6743 where there is a choice), and second by evaluating the immediate with
6744 clauses of a unit to determine the probably best choice, and
6745 third by elaborating in alphabetical order of unit names
6746 where a choice still remains.
6751 @strong{35}. Parameter passing and function return for the main
6752 subprogram. See 10.2(21).
6755 The main program has no parameters. It may be a procedure, or a function
6756 returning an integer type. In the latter case, the returned integer
6757 value is the return code of the program (overriding any value that
6758 may have been set by a call to @code{Ada.Command_Line.Set_Exit_Status}).
6763 @strong{36}. The mechanisms for building and running partitions. See
6767 GNAT itself supports programs with only a single partition. The GNATDIST
6768 tool provided with the GLADE package (which also includes an implementation
6769 of the PCS) provides a completely flexible method for building and running
6770 programs consisting of multiple partitions. See the separate GLADE manual
6776 @strong{37}. The details of program execution, including program
6777 termination. See 10.2(25).
6780 See separate section on compilation model.
6785 @strong{38}. The semantics of any non-active partitions supported by the
6786 implementation. See 10.2(28).
6789 Passive partitions are supported on targets where shared memory is
6790 provided by the operating system. See the GLADE reference manual for
6796 @strong{39}. The information returned by @code{Exception_Message}. See
6800 Exception message returns the null string unless a specific message has
6801 been passed by the program.
6806 @strong{40}. The result of @code{Exceptions.Exception_Name} for types
6807 declared within an unnamed @code{block_statement}. See 11.4.1(12).
6810 Blocks have implementation defined names of the form @code{B@var{nnn}}
6811 where @var{nnn} is an integer.
6816 @strong{41}. The information returned by
6817 @code{Exception_Information}. See 11.4.1(13).
6820 @code{Exception_Information} returns a string in the following format:
6823 @emph{Exception_Name:} nnnnn
6824 @emph{Message:} mmmmm
6826 @emph{Call stack traceback locations:}
6827 0xhhhh 0xhhhh 0xhhhh ... 0xhhh
6835 @code{nnnn} is the fully qualified name of the exception in all upper
6836 case letters. This line is always present.
6839 @code{mmmm} is the message (this line present only if message is non-null)
6842 @code{ppp} is the Process Id value as a decimal integer (this line is
6843 present only if the Process Id is non-zero). Currently we are
6844 not making use of this field.
6847 The Call stack traceback locations line and the following values
6848 are present only if at least one traceback location was recorded.
6849 The values are given in C style format, with lower case letters
6850 for a-f, and only as many digits present as are necessary.
6854 The line terminator sequence at the end of each line, including
6855 the last line is a single @code{LF} character (@code{16#0A#}).
6860 @strong{42}. Implementation-defined check names. See 11.5(27).
6863 No implementation-defined check names are supported.
6868 @strong{43}. The interpretation of each aspect of representation. See
6872 See separate section on data representations.
6877 @strong{44}. Any restrictions placed upon representation items. See
6881 See separate section on data representations.
6886 @strong{45}. The meaning of @code{Size} for indefinite subtypes. See
6890 Size for an indefinite subtype is the maximum possible size, except that
6891 for the case of a subprogram parameter, the size of the parameter object
6897 @strong{46}. The default external representation for a type tag. See
6901 The default external representation for a type tag is the fully expanded
6902 name of the type in upper case letters.
6907 @strong{47}. What determines whether a compilation unit is the same in
6908 two different partitions. See 13.3(76).
6911 A compilation unit is the same in two different partitions if and only
6912 if it derives from the same source file.
6917 @strong{48}. Implementation-defined components. See 13.5.1(15).
6920 The only implementation defined component is the tag for a tagged type,
6921 which contains a pointer to the dispatching table.
6926 @strong{49}. If @code{Word_Size} = @code{Storage_Unit}, the default bit
6927 ordering. See 13.5.3(5).
6930 @code{Word_Size} (32) is not the same as @code{Storage_Unit} (8) for this
6931 implementation, so no non-default bit ordering is supported. The default
6932 bit ordering corresponds to the natural endianness of the target architecture.
6937 @strong{50}. The contents of the visible part of package @code{System}
6938 and its language-defined children. See 13.7(2).
6941 See the definition of these packages in files @file{system.ads} and
6942 @file{s-stoele.ads}.
6947 @strong{51}. The contents of the visible part of package
6948 @code{System.Machine_Code}, and the meaning of
6949 @code{code_statements}. See 13.8(7).
6952 See the definition and documentation in file @file{s-maccod.ads}.
6957 @strong{52}. The effect of unchecked conversion. See 13.9(11).
6960 Unchecked conversion between types of the same size
6961 and results in an uninterpreted transmission of the bits from one type
6962 to the other. If the types are of unequal sizes, then in the case of
6963 discrete types, a shorter source is first zero or sign extended as
6964 necessary, and a shorter target is simply truncated on the left.
6965 For all non-discrete types, the source is first copied if necessary
6966 to ensure that the alignment requirements of the target are met, then
6967 a pointer is constructed to the source value, and the result is obtained
6968 by dereferencing this pointer after converting it to be a pointer to the
6974 @strong{53}. The manner of choosing a storage pool for an access type
6975 when @code{Storage_Pool} is not specified for the type. See 13.11(17).
6978 There are 3 different standard pools used by the compiler when
6979 @code{Storage_Pool} is not specified depending whether the type is local
6980 to a subprogram or defined at the library level and whether
6981 @code{Storage_Size}is specified or not. See documentation in the runtime
6982 library units @code{System.Pool_Global}, @code{System.Pool_Size} and
6983 @code{System.Pool_Local} in files @file{s-poosiz.ads},
6984 @file{s-pooglo.ads} and @file{s-pooloc.ads} for full details on the
6990 @strong{54}. Whether or not the implementation provides user-accessible
6991 names for the standard pool type(s). See 13.11(17).
6995 See documentation in the sources of the run time mentioned in paragraph
6996 @strong{53} . All these pools are accessible by means of @code{with}'ing
7002 @strong{55}. The meaning of @code{Storage_Size}. See 13.11(18).
7005 @code{Storage_Size} is measured in storage units, and refers to the
7006 total space available for an access type collection, or to the primary
7007 stack space for a task.
7012 @strong{56}. Implementation-defined aspects of storage pools. See
7016 See documentation in the sources of the run time mentioned in paragraph
7017 @strong{53} for details on GNAT-defined aspects of storage pools.
7022 @strong{57}. The set of restrictions allowed in a pragma
7023 @code{Restrictions}. See 13.12(7).
7026 All RM defined Restriction identifiers are implemented. The following
7027 additional restriction identifiers are provided. There are two separate
7028 lists of implementation dependent restriction identifiers. The first
7029 set requires consistency throughout a partition (in other words, if the
7030 restriction identifier is used for any compilation unit in the partition,
7031 then all compilation units in the partition must obey the restriction.
7035 @item Simple_Barriers
7036 @findex Simple_Barriers
7037 This restriction ensures at compile time that barriers in entry declarations
7038 for protected types are restricted to either static boolean expressions or
7039 references to simple boolean variables defined in the private part of the
7040 protected type. No other form of entry barriers is permitted. This is one
7041 of the restrictions of the Ravenscar profile for limited tasking (see also
7042 pragma @code{Profile (Ravenscar)}).
7044 @item Max_Entry_Queue_Length => Expr
7045 @findex Max_Entry_Queue_Length
7046 This restriction is a declaration that any protected entry compiled in
7047 the scope of the restriction has at most the specified number of
7048 tasks waiting on the entry
7049 at any one time, and so no queue is required. This restriction is not
7050 checked at compile time. A program execution is erroneous if an attempt
7051 is made to queue more than the specified number of tasks on such an entry.
7055 This restriction ensures at compile time that there is no implicit or
7056 explicit dependence on the package @code{Ada.Calendar}.
7058 @item No_Direct_Boolean_Operators
7059 @findex No_Direct_Boolean_Operators
7060 This restriction ensures that no logical (and/or/xor) or comparison
7061 operators are used on operands of type Boolean (or any type derived
7062 from Boolean). This is intended for use in safety critical programs
7063 where the certification protocol requires the use of short-circuit
7064 (and then, or else) forms for all composite boolean operations.
7066 @item No_Dynamic_Attachment
7067 @findex No_Dynamic_Attachment
7068 This restriction ensures that there is no call to any of the operations
7069 defined in package Ada.Interrupts.
7071 @item No_Enumeration_Maps
7072 @findex No_Enumeration_Maps
7073 This restriction ensures at compile time that no operations requiring
7074 enumeration maps are used (that is Image and Value attributes applied
7075 to enumeration types).
7077 @item No_Entry_Calls_In_Elaboration_Code
7078 @findex No_Entry_Calls_In_Elaboration_Code
7079 This restriction ensures at compile time that no task or protected entry
7080 calls are made during elaboration code. As a result of the use of this
7081 restriction, the compiler can assume that no code past an accept statement
7082 in a task can be executed at elaboration time.
7084 @item No_Exception_Handlers
7085 @findex No_Exception_Handlers
7086 This restriction ensures at compile time that there are no explicit
7087 exception handlers. It also indicates that no exception propagation will
7088 be provided. In this mode, exceptions may be raised but will result in
7089 an immediate call to the last chance handler, a routine that the user
7090 must define with the following profile:
7092 procedure Last_Chance_Handler
7093 (Source_Location : System.Address; Line : Integer);
7094 pragma Export (C, Last_Chance_Handler,
7095 "__gnat_last_chance_handler");
7097 The parameter is a C null-terminated string representing a message to be
7098 associated with the exception (typically the source location of the raise
7099 statement generated by the compiler). The Line parameter when non-zero
7100 represents the line number in the source program where the raise occurs.
7102 @item No_Exception_Streams
7103 @findex No_Exception_Streams
7104 This restriction ensures at compile time that no stream operations for
7105 types Exception_Id or Exception_Occurrence are used. This also makes it
7106 impossible to pass exceptions to or from a partition with this restriction
7107 in a distributed environment. If this exception is active, then the generated
7108 code is simplified by omitting the otherwise-required global registration
7109 of exceptions when they are declared.
7111 @item No_Implicit_Conditionals
7112 @findex No_Implicit_Conditionals
7113 This restriction ensures that the generated code does not contain any
7114 implicit conditionals, either by modifying the generated code where possible,
7115 or by rejecting any construct that would otherwise generate an implicit
7116 conditional. Note that this check does not include run time constraint
7117 checks, which on some targets may generate implicit conditionals as
7118 well. To control the latter, constraint checks can be suppressed in the
7121 @item No_Implicit_Dynamic_Code
7122 @findex No_Implicit_Dynamic_Code
7123 This restriction prevents the compiler from building ``trampolines''.
7124 This is a structure that is built on the stack and contains dynamic
7125 code to be executed at run time. A trampoline is needed to indirectly
7126 address a nested subprogram (that is a subprogram that is not at the
7127 library level). The restriction prevents the use of any of the
7128 attributes @code{Address}, @code{Access} or @code{Unrestricted_Access}
7129 being applied to a subprogram that is not at the library level.
7131 @item No_Implicit_Loops
7132 @findex No_Implicit_Loops
7133 This restriction ensures that the generated code does not contain any
7134 implicit @code{for} loops, either by modifying
7135 the generated code where possible,
7136 or by rejecting any construct that would otherwise generate an implicit
7139 @item No_Initialize_Scalars
7140 @findex No_Initialize_Scalars
7141 This restriction ensures that no unit in the partition is compiled with
7142 pragma Initialize_Scalars. This allows the generation of more efficient
7143 code, and in particular eliminates dummy null initialization routines that
7144 are otherwise generated for some record and array types.
7146 @item No_Local_Protected_Objects
7147 @findex No_Local_Protected_Objects
7148 This restriction ensures at compile time that protected objects are
7149 only declared at the library level.
7151 @item No_Protected_Type_Allocators
7152 @findex No_Protected_Type_Allocators
7153 This restriction ensures at compile time that there are no allocator
7154 expressions that attempt to allocate protected objects.
7156 @item No_Secondary_Stack
7157 @findex No_Secondary_Stack
7158 This restriction ensures at compile time that the generated code does not
7159 contain any reference to the secondary stack. The secondary stack is used
7160 to implement functions returning unconstrained objects (arrays or records)
7163 @item No_Select_Statements
7164 @findex No_Select_Statements
7165 This restriction ensures at compile time no select statements of any kind
7166 are permitted, that is the keyword @code{select} may not appear.
7167 This is one of the restrictions of the Ravenscar
7168 profile for limited tasking (see also pragma @code{Profile (Ravenscar)}).
7170 @item No_Standard_Storage_Pools
7171 @findex No_Standard_Storage_Pools
7172 This restriction ensures at compile time that no access types
7173 use the standard default storage pool. Any access type declared must
7174 have an explicit Storage_Pool attribute defined specifying a
7175 user-defined storage pool.
7179 This restriction ensures at compile/bind time that there are no
7180 stream objects created (and therefore no actual stream operations).
7181 This restriction does not forbid dependences on the package
7182 @code{Ada.Streams}. So it is permissible to with
7183 @code{Ada.Streams} (or another package that does so itself)
7184 as long as no actual stream objects are created.
7186 @item No_Task_Attributes_Package
7187 @findex No_Task_Attributes_Package
7188 This restriction ensures at compile time that there are no implicit or
7189 explicit dependencies on the package @code{Ada.Task_Attributes}.
7191 @item No_Task_Termination
7192 @findex No_Task_Termination
7193 This restriction ensures at compile time that no terminate alternatives
7194 appear in any task body.
7198 This restriction prevents the declaration of tasks or task types throughout
7199 the partition. It is similar in effect to the use of @code{Max_Tasks => 0}
7200 except that violations are caught at compile time and cause an error message
7201 to be output either by the compiler or binder.
7203 @item No_Wide_Characters
7204 @findex No_Wide_Characters
7205 This restriction ensures at compile time that no uses of the types
7206 @code{Wide_Character} or @code{Wide_String} or corresponding wide
7208 appear, and that no wide or wide wide string or character literals
7209 appear in the program (that is literals representing characters not in
7210 type @code{Character}.
7212 @item Static_Priorities
7213 @findex Static_Priorities
7214 This restriction ensures at compile time that all priority expressions
7215 are static, and that there are no dependencies on the package
7216 @code{Ada.Dynamic_Priorities}.
7218 @item Static_Storage_Size
7219 @findex Static_Storage_Size
7220 This restriction ensures at compile time that any expression appearing
7221 in a Storage_Size pragma or attribute definition clause is static.
7226 The second set of implementation dependent restriction identifiers
7227 does not require partition-wide consistency.
7228 The restriction may be enforced for a single
7229 compilation unit without any effect on any of the
7230 other compilation units in the partition.
7234 @item No_Elaboration_Code
7235 @findex No_Elaboration_Code
7236 This restriction ensures at compile time that no elaboration code is
7237 generated. Note that this is not the same condition as is enforced
7238 by pragma @code{Preelaborate}. There are cases in which pragma
7239 @code{Preelaborate} still permits code to be generated (e.g.@: code
7240 to initialize a large array to all zeroes), and there are cases of units
7241 which do not meet the requirements for pragma @code{Preelaborate},
7242 but for which no elaboration code is generated. Generally, it is
7243 the case that preelaborable units will meet the restrictions, with
7244 the exception of large aggregates initialized with an others_clause,
7245 and exception declarations (which generate calls to a run-time
7246 registry procedure). Note that this restriction is enforced on
7247 a unit by unit basis, it need not be obeyed consistently
7248 throughout a partition.
7250 @item No_Entry_Queue
7251 @findex No_Entry_Queue
7252 This restriction is a declaration that any protected entry compiled in
7253 the scope of the restriction has at most one task waiting on the entry
7254 at any one time, and so no queue is required. This restriction is not
7255 checked at compile time. A program execution is erroneous if an attempt
7256 is made to queue a second task on such an entry.
7258 @item No_Implementation_Attributes
7259 @findex No_Implementation_Attributes
7260 This restriction checks at compile time that no GNAT-defined attributes
7261 are present. With this restriction, the only attributes that can be used
7262 are those defined in the Ada 95 Reference Manual.
7264 @item No_Implementation_Pragmas
7265 @findex No_Implementation_Pragmas
7266 This restriction checks at compile time that no GNAT-defined pragmas
7267 are present. With this restriction, the only pragmas that can be used
7268 are those defined in the Ada 95 Reference Manual.
7270 @item No_Implementation_Restrictions
7271 @findex No_Implementation_Restrictions
7272 This restriction checks at compile time that no GNAT-defined restriction
7273 identifiers (other than @code{No_Implementation_Restrictions} itself)
7274 are present. With this restriction, the only other restriction identifiers
7275 that can be used are those defined in the Ada 95 Reference Manual.
7282 @strong{58}. The consequences of violating limitations on
7283 @code{Restrictions} pragmas. See 13.12(9).
7286 Restrictions that can be checked at compile time result in illegalities
7287 if violated. Currently there are no other consequences of violating
7293 @strong{59}. The representation used by the @code{Read} and
7294 @code{Write} attributes of elementary types in terms of stream
7295 elements. See 13.13.2(9).
7298 The representation is the in-memory representation of the base type of
7299 the type, using the number of bits corresponding to the
7300 @code{@var{type}'Size} value, and the natural ordering of the machine.
7305 @strong{60}. The names and characteristics of the numeric subtypes
7306 declared in the visible part of package @code{Standard}. See A.1(3).
7309 See items describing the integer and floating-point types supported.
7314 @strong{61}. The accuracy actually achieved by the elementary
7315 functions. See A.5.1(1).
7318 The elementary functions correspond to the functions available in the C
7319 library. Only fast math mode is implemented.
7324 @strong{62}. The sign of a zero result from some of the operators or
7325 functions in @code{Numerics.Generic_Elementary_Functions}, when
7326 @code{Float_Type'Signed_Zeros} is @code{True}. See A.5.1(46).
7329 The sign of zeroes follows the requirements of the IEEE 754 standard on
7335 @strong{63}. The value of
7336 @code{Numerics.Float_Random.Max_Image_Width}. See A.5.2(27).
7339 Maximum image width is 649, see library file @file{a-numran.ads}.
7344 @strong{64}. The value of
7345 @code{Numerics.Discrete_Random.Max_Image_Width}. See A.5.2(27).
7348 Maximum image width is 80, see library file @file{a-nudira.ads}.
7353 @strong{65}. The algorithms for random number generation. See
7357 The algorithm is documented in the source files @file{a-numran.ads} and
7358 @file{a-numran.adb}.
7363 @strong{66}. The string representation of a random number generator's
7364 state. See A.5.2(38).
7367 See the documentation contained in the file @file{a-numran.adb}.
7372 @strong{67}. The minimum time interval between calls to the
7373 time-dependent Reset procedure that are guaranteed to initiate different
7374 random number sequences. See A.5.2(45).
7377 The minimum period between reset calls to guarantee distinct series of
7378 random numbers is one microsecond.
7383 @strong{68}. The values of the @code{Model_Mantissa},
7384 @code{Model_Emin}, @code{Model_Epsilon}, @code{Model},
7385 @code{Safe_First}, and @code{Safe_Last} attributes, if the Numerics
7386 Annex is not supported. See A.5.3(72).
7389 See the source file @file{ttypef.ads} for the values of all numeric
7395 @strong{69}. Any implementation-defined characteristics of the
7396 input-output packages. See A.7(14).
7399 There are no special implementation defined characteristics for these
7405 @strong{70}. The value of @code{Buffer_Size} in @code{Storage_IO}. See
7409 All type representations are contiguous, and the @code{Buffer_Size} is
7410 the value of @code{@var{type}'Size} rounded up to the next storage unit
7416 @strong{71}. External files for standard input, standard output, and
7417 standard error See A.10(5).
7420 These files are mapped onto the files provided by the C streams
7421 libraries. See source file @file{i-cstrea.ads} for further details.
7426 @strong{72}. The accuracy of the value produced by @code{Put}. See
7430 If more digits are requested in the output than are represented by the
7431 precision of the value, zeroes are output in the corresponding least
7432 significant digit positions.
7437 @strong{73}. The meaning of @code{Argument_Count}, @code{Argument}, and
7438 @code{Command_Name}. See A.15(1).
7441 These are mapped onto the @code{argv} and @code{argc} parameters of the
7442 main program in the natural manner.
7447 @strong{74}. Implementation-defined convention names. See B.1(11).
7450 The following convention names are supported
7458 Synonym for Assembler
7460 Synonym for Assembler
7463 @item C_Pass_By_Copy
7464 Allowed only for record types, like C, but also notes that record
7465 is to be passed by copy rather than reference.
7471 Treated the same as C
7473 Treated the same as C
7477 For support of pragma @code{Import} with convention Intrinsic, see
7478 separate section on Intrinsic Subprograms.
7480 Stdcall (used for Windows implementations only). This convention correspond
7481 to the WINAPI (previously called Pascal convention) C/C++ convention under
7482 Windows. A function with this convention cleans the stack before exit.
7488 Stubbed is a special convention used to indicate that the body of the
7489 subprogram will be entirely ignored. Any call to the subprogram
7490 is converted into a raise of the @code{Program_Error} exception. If a
7491 pragma @code{Import} specifies convention @code{stubbed} then no body need
7492 be present at all. This convention is useful during development for the
7493 inclusion of subprograms whose body has not yet been written.
7497 In addition, all otherwise unrecognized convention names are also
7498 treated as being synonymous with convention C@. In all implementations
7499 except for VMS, use of such other names results in a warning. In VMS
7500 implementations, these names are accepted silently.
7505 @strong{75}. The meaning of link names. See B.1(36).
7508 Link names are the actual names used by the linker.
7513 @strong{76}. The manner of choosing link names when neither the link
7514 name nor the address of an imported or exported entity is specified. See
7518 The default linker name is that which would be assigned by the relevant
7519 external language, interpreting the Ada name as being in all lower case
7525 @strong{77}. The effect of pragma @code{Linker_Options}. See B.1(37).
7528 The string passed to @code{Linker_Options} is presented uninterpreted as
7529 an argument to the link command, unless it contains Ascii.NUL characters.
7530 NUL characters if they appear act as argument separators, so for example
7532 @smallexample @c ada
7533 pragma Linker_Options ("-labc" & ASCII.Nul & "-ldef");
7537 causes two separate arguments @code{-labc} and @code{-ldef} to be passed to the
7538 linker. The order of linker options is preserved for a given unit. The final
7539 list of options passed to the linker is in reverse order of the elaboration
7540 order. For example, linker options fo a body always appear before the options
7541 from the corresponding package spec.
7546 @strong{78}. The contents of the visible part of package
7547 @code{Interfaces} and its language-defined descendants. See B.2(1).
7550 See files with prefix @file{i-} in the distributed library.
7555 @strong{79}. Implementation-defined children of package
7556 @code{Interfaces}. The contents of the visible part of package
7557 @code{Interfaces}. See B.2(11).
7560 See files with prefix @file{i-} in the distributed library.
7565 @strong{80}. The types @code{Floating}, @code{Long_Floating},
7566 @code{Binary}, @code{Long_Binary}, @code{Decimal_ Element}, and
7567 @code{COBOL_Character}; and the initialization of the variables
7568 @code{Ada_To_COBOL} and @code{COBOL_To_Ada}, in
7569 @code{Interfaces.COBOL}. See B.4(50).
7576 (Floating) Long_Float
7581 @item Decimal_Element
7583 @item COBOL_Character
7588 For initialization, see the file @file{i-cobol.ads} in the distributed library.
7593 @strong{81}. Support for access to machine instructions. See C.1(1).
7596 See documentation in file @file{s-maccod.ads} in the distributed library.
7601 @strong{82}. Implementation-defined aspects of access to machine
7602 operations. See C.1(9).
7605 See documentation in file @file{s-maccod.ads} in the distributed library.
7610 @strong{83}. Implementation-defined aspects of interrupts. See C.3(2).
7613 Interrupts are mapped to signals or conditions as appropriate. See
7615 @code{Ada.Interrupt_Names} in source file @file{a-intnam.ads} for details
7616 on the interrupts supported on a particular target.
7621 @strong{84}. Implementation-defined aspects of pre-elaboration. See
7625 GNAT does not permit a partition to be restarted without reloading,
7626 except under control of the debugger.
7631 @strong{85}. The semantics of pragma @code{Discard_Names}. See C.5(7).
7634 Pragma @code{Discard_Names} causes names of enumeration literals to
7635 be suppressed. In the presence of this pragma, the Image attribute
7636 provides the image of the Pos of the literal, and Value accepts
7642 @strong{86}. The result of the @code{Task_Identification.Image}
7643 attribute. See C.7.1(7).
7646 The result of this attribute is an 8-digit hexadecimal string
7647 representing the virtual address of the task control block.
7652 @strong{87}. The value of @code{Current_Task} when in a protected entry
7653 or interrupt handler. See C.7.1(17).
7656 Protected entries or interrupt handlers can be executed by any
7657 convenient thread, so the value of @code{Current_Task} is undefined.
7662 @strong{88}. The effect of calling @code{Current_Task} from an entry
7663 body or interrupt handler. See C.7.1(19).
7666 The effect of calling @code{Current_Task} from an entry body or
7667 interrupt handler is to return the identification of the task currently
7673 @strong{89}. Implementation-defined aspects of
7674 @code{Task_Attributes}. See C.7.2(19).
7677 There are no implementation-defined aspects of @code{Task_Attributes}.
7682 @strong{90}. Values of all @code{Metrics}. See D(2).
7685 The metrics information for GNAT depends on the performance of the
7686 underlying operating system. The sources of the run-time for tasking
7687 implementation, together with the output from @code{-gnatG} can be
7688 used to determine the exact sequence of operating systems calls made
7689 to implement various tasking constructs. Together with appropriate
7690 information on the performance of the underlying operating system,
7691 on the exact target in use, this information can be used to determine
7692 the required metrics.
7697 @strong{91}. The declarations of @code{Any_Priority} and
7698 @code{Priority}. See D.1(11).
7701 See declarations in file @file{system.ads}.
7706 @strong{92}. Implementation-defined execution resources. See D.1(15).
7709 There are no implementation-defined execution resources.
7714 @strong{93}. Whether, on a multiprocessor, a task that is waiting for
7715 access to a protected object keeps its processor busy. See D.2.1(3).
7718 On a multi-processor, a task that is waiting for access to a protected
7719 object does not keep its processor busy.
7724 @strong{94}. The affect of implementation defined execution resources
7725 on task dispatching. See D.2.1(9).
7730 Tasks map to IRIX threads, and the dispatching policy is as defined by
7731 the IRIX implementation of threads.
7733 Tasks map to threads in the threads package used by GNAT@. Where possible
7734 and appropriate, these threads correspond to native threads of the
7735 underlying operating system.
7740 @strong{95}. Implementation-defined @code{policy_identifiers} allowed
7741 in a pragma @code{Task_Dispatching_Policy}. See D.2.2(3).
7744 There are no implementation-defined policy-identifiers allowed in this
7750 @strong{96}. Implementation-defined aspects of priority inversion. See
7754 Execution of a task cannot be preempted by the implementation processing
7755 of delay expirations for lower priority tasks.
7760 @strong{97}. Implementation defined task dispatching. See D.2.2(18).
7765 Tasks map to IRIX threads, and the dispatching policy is as defied by
7766 the IRIX implementation of threads.
7768 The policy is the same as that of the underlying threads implementation.
7773 @strong{98}. Implementation-defined @code{policy_identifiers} allowed
7774 in a pragma @code{Locking_Policy}. See D.3(4).
7777 The only implementation defined policy permitted in GNAT is
7778 @code{Inheritance_Locking}. On targets that support this policy, locking
7779 is implemented by inheritance, i.e.@: the task owning the lock operates
7780 at a priority equal to the highest priority of any task currently
7781 requesting the lock.
7786 @strong{99}. Default ceiling priorities. See D.3(10).
7789 The ceiling priority of protected objects of the type
7790 @code{System.Interrupt_Priority'Last} as described in the Ada 95
7791 Reference Manual D.3(10),
7796 @strong{100}. The ceiling of any protected object used internally by
7797 the implementation. See D.3(16).
7800 The ceiling priority of internal protected objects is
7801 @code{System.Priority'Last}.
7806 @strong{101}. Implementation-defined queuing policies. See D.4(1).
7809 There are no implementation-defined queueing policies.
7814 @strong{102}. On a multiprocessor, any conditions that cause the
7815 completion of an aborted construct to be delayed later than what is
7816 specified for a single processor. See D.6(3).
7819 The semantics for abort on a multi-processor is the same as on a single
7820 processor, there are no further delays.
7825 @strong{103}. Any operations that implicitly require heap storage
7826 allocation. See D.7(8).
7829 The only operation that implicitly requires heap storage allocation is
7835 @strong{104}. Implementation-defined aspects of pragma
7836 @code{Restrictions}. See D.7(20).
7839 There are no such implementation-defined aspects.
7844 @strong{105}. Implementation-defined aspects of package
7845 @code{Real_Time}. See D.8(17).
7848 There are no implementation defined aspects of package @code{Real_Time}.
7853 @strong{106}. Implementation-defined aspects of
7854 @code{delay_statements}. See D.9(8).
7857 Any difference greater than one microsecond will cause the task to be
7858 delayed (see D.9(7)).
7863 @strong{107}. The upper bound on the duration of interrupt blocking
7864 caused by the implementation. See D.12(5).
7867 The upper bound is determined by the underlying operating system. In
7868 no cases is it more than 10 milliseconds.
7873 @strong{108}. The means for creating and executing distributed
7877 The GLADE package provides a utility GNATDIST for creating and executing
7878 distributed programs. See the GLADE reference manual for further details.
7883 @strong{109}. Any events that can result in a partition becoming
7884 inaccessible. See E.1(7).
7887 See the GLADE reference manual for full details on such events.
7892 @strong{110}. The scheduling policies, treatment of priorities, and
7893 management of shared resources between partitions in certain cases. See
7897 See the GLADE reference manual for full details on these aspects of
7898 multi-partition execution.
7903 @strong{111}. Events that cause the version of a compilation unit to
7907 Editing the source file of a compilation unit, or the source files of
7908 any units on which it is dependent in a significant way cause the version
7909 to change. No other actions cause the version number to change. All changes
7910 are significant except those which affect only layout, capitalization or
7916 @strong{112}. Whether the execution of the remote subprogram is
7917 immediately aborted as a result of cancellation. See E.4(13).
7920 See the GLADE reference manual for details on the effect of abort in
7921 a distributed application.
7926 @strong{113}. Implementation-defined aspects of the PCS@. See E.5(25).
7929 See the GLADE reference manual for a full description of all implementation
7930 defined aspects of the PCS@.
7935 @strong{114}. Implementation-defined interfaces in the PCS@. See
7939 See the GLADE reference manual for a full description of all
7940 implementation defined interfaces.
7945 @strong{115}. The values of named numbers in the package
7946 @code{Decimal}. See F.2(7).
7958 @item Max_Decimal_Digits
7965 @strong{116}. The value of @code{Max_Picture_Length} in the package
7966 @code{Text_IO.Editing}. See F.3.3(16).
7974 @strong{117}. The value of @code{Max_Picture_Length} in the package
7975 @code{Wide_Text_IO.Editing}. See F.3.4(5).
7983 @strong{118}. The accuracy actually achieved by the complex elementary
7984 functions and by other complex arithmetic operations. See G.1(1).
7987 Standard library functions are used for the complex arithmetic
7988 operations. Only fast math mode is currently supported.
7993 @strong{119}. The sign of a zero result (or a component thereof) from
7994 any operator or function in @code{Numerics.Generic_Complex_Types}, when
7995 @code{Real'Signed_Zeros} is True. See G.1.1(53).
7998 The signs of zero values are as recommended by the relevant
7999 implementation advice.
8004 @strong{120}. The sign of a zero result (or a component thereof) from
8005 any operator or function in
8006 @code{Numerics.Generic_Complex_Elementary_Functions}, when
8007 @code{Real'Signed_Zeros} is @code{True}. See G.1.2(45).
8010 The signs of zero values are as recommended by the relevant
8011 implementation advice.
8016 @strong{121}. Whether the strict mode or the relaxed mode is the
8017 default. See G.2(2).
8020 The strict mode is the default. There is no separate relaxed mode. GNAT
8021 provides a highly efficient implementation of strict mode.
8026 @strong{122}. The result interval in certain cases of fixed-to-float
8027 conversion. See G.2.1(10).
8030 For cases where the result interval is implementation dependent, the
8031 accuracy is that provided by performing all operations in 64-bit IEEE
8032 floating-point format.
8037 @strong{123}. The result of a floating point arithmetic operation in
8038 overflow situations, when the @code{Machine_Overflows} attribute of the
8039 result type is @code{False}. See G.2.1(13).
8042 Infinite and Nan values are produced as dictated by the IEEE
8043 floating-point standard.
8048 @strong{124}. The result interval for division (or exponentiation by a
8049 negative exponent), when the floating point hardware implements division
8050 as multiplication by a reciprocal. See G.2.1(16).
8053 Not relevant, division is IEEE exact.
8058 @strong{125}. The definition of close result set, which determines the
8059 accuracy of certain fixed point multiplications and divisions. See
8063 Operations in the close result set are performed using IEEE long format
8064 floating-point arithmetic. The input operands are converted to
8065 floating-point, the operation is done in floating-point, and the result
8066 is converted to the target type.
8071 @strong{126}. Conditions on a @code{universal_real} operand of a fixed
8072 point multiplication or division for which the result shall be in the
8073 perfect result set. See G.2.3(22).
8076 The result is only defined to be in the perfect result set if the result
8077 can be computed by a single scaling operation involving a scale factor
8078 representable in 64-bits.
8083 @strong{127}. The result of a fixed point arithmetic operation in
8084 overflow situations, when the @code{Machine_Overflows} attribute of the
8085 result type is @code{False}. See G.2.3(27).
8088 Not relevant, @code{Machine_Overflows} is @code{True} for fixed-point
8094 @strong{128}. The result of an elementary function reference in
8095 overflow situations, when the @code{Machine_Overflows} attribute of the
8096 result type is @code{False}. See G.2.4(4).
8099 IEEE infinite and Nan values are produced as appropriate.
8104 @strong{129}. The value of the angle threshold, within which certain
8105 elementary functions, complex arithmetic operations, and complex
8106 elementary functions yield results conforming to a maximum relative
8107 error bound. See G.2.4(10).
8110 Information on this subject is not yet available.
8115 @strong{130}. The accuracy of certain elementary functions for
8116 parameters beyond the angle threshold. See G.2.4(10).
8119 Information on this subject is not yet available.
8124 @strong{131}. The result of a complex arithmetic operation or complex
8125 elementary function reference in overflow situations, when the
8126 @code{Machine_Overflows} attribute of the corresponding real type is
8127 @code{False}. See G.2.6(5).
8130 IEEE infinite and Nan values are produced as appropriate.
8135 @strong{132}. The accuracy of certain complex arithmetic operations and
8136 certain complex elementary functions for parameters (or components
8137 thereof) beyond the angle threshold. See G.2.6(8).
8140 Information on those subjects is not yet available.
8145 @strong{133}. Information regarding bounded errors and erroneous
8146 execution. See H.2(1).
8149 Information on this subject is not yet available.
8154 @strong{134}. Implementation-defined aspects of pragma
8155 @code{Inspection_Point}. See H.3.2(8).
8158 Pragma @code{Inspection_Point} ensures that the variable is live and can
8159 be examined by the debugger at the inspection point.
8164 @strong{135}. Implementation-defined aspects of pragma
8165 @code{Restrictions}. See H.4(25).
8168 There are no implementation-defined aspects of pragma @code{Restrictions}. The
8169 use of pragma @code{Restrictions [No_Exceptions]} has no effect on the
8170 generated code. Checks must suppressed by use of pragma @code{Suppress}.
8175 @strong{136}. Any restrictions on pragma @code{Restrictions}. See
8179 There are no restrictions on pragma @code{Restrictions}.
8181 @node Intrinsic Subprograms
8182 @chapter Intrinsic Subprograms
8183 @cindex Intrinsic Subprograms
8186 * Intrinsic Operators::
8187 * Enclosing_Entity::
8188 * Exception_Information::
8189 * Exception_Message::
8197 * Shift_Right_Arithmetic::
8202 GNAT allows a user application program to write the declaration:
8204 @smallexample @c ada
8205 pragma Import (Intrinsic, name);
8209 providing that the name corresponds to one of the implemented intrinsic
8210 subprograms in GNAT, and that the parameter profile of the referenced
8211 subprogram meets the requirements. This chapter describes the set of
8212 implemented intrinsic subprograms, and the requirements on parameter profiles.
8213 Note that no body is supplied; as with other uses of pragma Import, the
8214 body is supplied elsewhere (in this case by the compiler itself). Note
8215 that any use of this feature is potentially non-portable, since the
8216 Ada standard does not require Ada compilers to implement this feature.
8218 @node Intrinsic Operators
8219 @section Intrinsic Operators
8220 @cindex Intrinsic operator
8223 All the predefined numeric operators in package Standard
8224 in @code{pragma Import (Intrinsic,..)}
8225 declarations. In the binary operator case, the operands must have the same
8226 size. The operand or operands must also be appropriate for
8227 the operator. For example, for addition, the operands must
8228 both be floating-point or both be fixed-point, and the
8229 right operand for @code{"**"} must have a root type of
8230 @code{Standard.Integer'Base}.
8231 You can use an intrinsic operator declaration as in the following example:
8233 @smallexample @c ada
8234 type Int1 is new Integer;
8235 type Int2 is new Integer;
8237 function "+" (X1 : Int1; X2 : Int2) return Int1;
8238 function "+" (X1 : Int1; X2 : Int2) return Int2;
8239 pragma Import (Intrinsic, "+");
8243 This declaration would permit ``mixed mode'' arithmetic on items
8244 of the differing types @code{Int1} and @code{Int2}.
8245 It is also possible to specify such operators for private types, if the
8246 full views are appropriate arithmetic types.
8248 @node Enclosing_Entity
8249 @section Enclosing_Entity
8250 @cindex Enclosing_Entity
8252 This intrinsic subprogram is used in the implementation of the
8253 library routine @code{GNAT.Source_Info}. The only useful use of the
8254 intrinsic import in this case is the one in this unit, so an
8255 application program should simply call the function
8256 @code{GNAT.Source_Info.Enclosing_Entity} to obtain the name of
8257 the current subprogram, package, task, entry, or protected subprogram.
8259 @node Exception_Information
8260 @section Exception_Information
8261 @cindex Exception_Information'
8263 This intrinsic subprogram is used in the implementation of the
8264 library routine @code{GNAT.Current_Exception}. The only useful
8265 use of the intrinsic import in this case is the one in this unit,
8266 so an application program should simply call the function
8267 @code{GNAT.Current_Exception.Exception_Information} to obtain
8268 the exception information associated with the current exception.
8270 @node Exception_Message
8271 @section Exception_Message
8272 @cindex Exception_Message
8274 This intrinsic subprogram is used in the implementation of the
8275 library routine @code{GNAT.Current_Exception}. The only useful
8276 use of the intrinsic import in this case is the one in this unit,
8277 so an application program should simply call the function
8278 @code{GNAT.Current_Exception.Exception_Message} to obtain
8279 the message associated with the current exception.
8281 @node Exception_Name
8282 @section Exception_Name
8283 @cindex Exception_Name
8285 This intrinsic subprogram is used in the implementation of the
8286 library routine @code{GNAT.Current_Exception}. The only useful
8287 use of the intrinsic import in this case is the one in this unit,
8288 so an application program should simply call the function
8289 @code{GNAT.Current_Exception.Exception_Name} to obtain
8290 the name of the current exception.
8296 This intrinsic subprogram is used in the implementation of the
8297 library routine @code{GNAT.Source_Info}. The only useful use of the
8298 intrinsic import in this case is the one in this unit, so an
8299 application program should simply call the function
8300 @code{GNAT.Source_Info.File} to obtain the name of the current
8307 This intrinsic subprogram is used in the implementation of the
8308 library routine @code{GNAT.Source_Info}. The only useful use of the
8309 intrinsic import in this case is the one in this unit, so an
8310 application program should simply call the function
8311 @code{GNAT.Source_Info.Line} to obtain the number of the current
8315 @section Rotate_Left
8318 In standard Ada 95, the @code{Rotate_Left} function is available only
8319 for the predefined modular types in package @code{Interfaces}. However, in
8320 GNAT it is possible to define a Rotate_Left function for a user
8321 defined modular type or any signed integer type as in this example:
8323 @smallexample @c ada
8325 (Value : My_Modular_Type;
8327 return My_Modular_Type;
8331 The requirements are that the profile be exactly as in the example
8332 above. The only modifications allowed are in the formal parameter
8333 names, and in the type of @code{Value} and the return type, which
8334 must be the same, and must be either a signed integer type, or
8335 a modular integer type with a binary modulus, and the size must
8336 be 8. 16, 32 or 64 bits.
8339 @section Rotate_Right
8340 @cindex Rotate_Right
8342 A @code{Rotate_Right} function can be defined for any user defined
8343 binary modular integer type, or signed integer type, as described
8344 above for @code{Rotate_Left}.
8350 A @code{Shift_Left} function can be defined for any user defined
8351 binary modular integer type, or signed integer type, as described
8352 above for @code{Rotate_Left}.
8355 @section Shift_Right
8358 A @code{Shift_Right} function can be defined for any user defined
8359 binary modular integer type, or signed integer type, as described
8360 above for @code{Rotate_Left}.
8362 @node Shift_Right_Arithmetic
8363 @section Shift_Right_Arithmetic
8364 @cindex Shift_Right_Arithmetic
8366 A @code{Shift_Right_Arithmetic} function can be defined for any user
8367 defined binary modular integer type, or signed integer type, as described
8368 above for @code{Rotate_Left}.
8370 @node Source_Location
8371 @section Source_Location
8372 @cindex Source_Location
8374 This intrinsic subprogram is used in the implementation of the
8375 library routine @code{GNAT.Source_Info}. The only useful use of the
8376 intrinsic import in this case is the one in this unit, so an
8377 application program should simply call the function
8378 @code{GNAT.Source_Info.Source_Location} to obtain the current
8379 source file location.
8381 @node Representation Clauses and Pragmas
8382 @chapter Representation Clauses and Pragmas
8383 @cindex Representation Clauses
8386 * Alignment Clauses::
8388 * Storage_Size Clauses::
8389 * Size of Variant Record Objects::
8390 * Biased Representation ::
8391 * Value_Size and Object_Size Clauses::
8392 * Component_Size Clauses::
8393 * Bit_Order Clauses::
8394 * Effect of Bit_Order on Byte Ordering::
8395 * Pragma Pack for Arrays::
8396 * Pragma Pack for Records::
8397 * Record Representation Clauses::
8398 * Enumeration Clauses::
8400 * Effect of Convention on Representation::
8401 * Determining the Representations chosen by GNAT::
8405 @cindex Representation Clause
8406 @cindex Representation Pragma
8407 @cindex Pragma, representation
8408 This section describes the representation clauses accepted by GNAT, and
8409 their effect on the representation of corresponding data objects.
8411 GNAT fully implements Annex C (Systems Programming). This means that all
8412 the implementation advice sections in chapter 13 are fully implemented.
8413 However, these sections only require a minimal level of support for
8414 representation clauses. GNAT provides much more extensive capabilities,
8415 and this section describes the additional capabilities provided.
8417 @node Alignment Clauses
8418 @section Alignment Clauses
8419 @cindex Alignment Clause
8422 GNAT requires that all alignment clauses specify a power of 2, and all
8423 default alignments are always a power of 2. The default alignment
8424 values are as follows:
8427 @item @emph{Primitive Types}.
8428 For primitive types, the alignment is the minimum of the actual size of
8429 objects of the type divided by @code{Storage_Unit},
8430 and the maximum alignment supported by the target.
8431 (This maximum alignment is given by the GNAT-specific attribute
8432 @code{Standard'Maximum_Alignment}; see @ref{Maximum_Alignment}.)
8433 @cindex @code{Maximum_Alignment} attribute
8434 For example, for type @code{Long_Float}, the object size is 8 bytes, and the
8435 default alignment will be 8 on any target that supports alignments
8436 this large, but on some targets, the maximum alignment may be smaller
8437 than 8, in which case objects of type @code{Long_Float} will be maximally
8440 @item @emph{Arrays}.
8441 For arrays, the alignment is equal to the alignment of the component type
8442 for the normal case where no packing or component size is given. If the
8443 array is packed, and the packing is effective (see separate section on
8444 packed arrays), then the alignment will be one for long packed arrays,
8445 or arrays whose length is not known at compile time. For short packed
8446 arrays, which are handled internally as modular types, the alignment
8447 will be as described for primitive types, e.g.@: a packed array of length
8448 31 bits will have an object size of four bytes, and an alignment of 4.
8450 @item @emph{Records}.
8451 For the normal non-packed case, the alignment of a record is equal to
8452 the maximum alignment of any of its components. For tagged records, this
8453 includes the implicit access type used for the tag. If a pragma @code{Pack} is
8454 used and all fields are packable (see separate section on pragma @code{Pack}),
8455 then the resulting alignment is 1.
8457 A special case is when:
8460 the size of the record is given explicitly, or a
8461 full record representation clause is given, and
8463 the size of the record is 2, 4, or 8 bytes.
8466 In this case, an alignment is chosen to match the
8467 size of the record. For example, if we have:
8469 @smallexample @c ada
8470 type Small is record
8473 for Small'Size use 16;
8477 then the default alignment of the record type @code{Small} is 2, not 1. This
8478 leads to more efficient code when the record is treated as a unit, and also
8479 allows the type to specified as @code{Atomic} on architectures requiring
8485 An alignment clause may
8486 always specify a larger alignment than the default value, up to some
8487 maximum value dependent on the target (obtainable by using the
8488 attribute reference @code{Standard'Maximum_Alignment}).
8490 it is permissible to specify a smaller alignment than the default value
8491 is for a record with a record representation clause.
8492 In this case, packable fields for which a component clause is
8493 given still result in a default alignment corresponding to the original
8494 type, but this may be overridden, since these components in fact only
8495 require an alignment of one byte. For example, given
8497 @smallexample @c ada
8503 A at 0 range 0 .. 31;
8506 for V'alignment use 1;
8510 @cindex Alignment, default
8511 The default alignment for the type @code{V} is 4, as a result of the
8512 Integer field in the record, but since this field is placed with a
8513 component clause, it is permissible, as shown, to override the default
8514 alignment of the record with a smaller value.
8517 @section Size Clauses
8521 The default size for a type @code{T} is obtainable through the
8522 language-defined attribute @code{T'Size} and also through the
8523 equivalent GNAT-defined attribute @code{T'Value_Size}.
8524 For objects of type @code{T}, GNAT will generally increase the type size
8525 so that the object size (obtainable through the GNAT-defined attribute
8526 @code{T'Object_Size})
8527 is a multiple of @code{T'Alignment * Storage_Unit}.
8530 @smallexample @c ada
8531 type Smallint is range 1 .. 6;
8540 In this example, @code{Smallint'Size} = @code{Smallint'Value_Size} = 3,
8541 as specified by the RM rules,
8542 but objects of this type will have a size of 8
8543 (@code{Smallint'Object_Size} = 8),
8544 since objects by default occupy an integral number
8545 of storage units. On some targets, notably older
8546 versions of the Digital Alpha, the size of stand
8547 alone objects of this type may be 32, reflecting
8548 the inability of the hardware to do byte load/stores.
8550 Similarly, the size of type @code{Rec} is 40 bits
8551 (@code{Rec'Size} = @code{Rec'Value_Size} = 40), but
8552 the alignment is 4, so objects of this type will have
8553 their size increased to 64 bits so that it is a multiple
8554 of the alignment (in bits). This decision is
8555 in accordance with the specific Implementation Advice in RM 13.3(43):
8558 A @code{Size} clause should be supported for an object if the specified
8559 @code{Size} is at least as large as its subtype's @code{Size}, and corresponds
8560 to a size in storage elements that is a multiple of the object's
8561 @code{Alignment} (if the @code{Alignment} is nonzero).
8565 An explicit size clause may be used to override the default size by
8566 increasing it. For example, if we have:
8568 @smallexample @c ada
8569 type My_Boolean is new Boolean;
8570 for My_Boolean'Size use 32;
8574 then values of this type will always be 32 bits long. In the case of
8575 discrete types, the size can be increased up to 64 bits, with the effect
8576 that the entire specified field is used to hold the value, sign- or
8577 zero-extended as appropriate. If more than 64 bits is specified, then
8578 padding space is allocated after the value, and a warning is issued that
8579 there are unused bits.
8581 Similarly the size of records and arrays may be increased, and the effect
8582 is to add padding bits after the value. This also causes a warning message
8585 The largest Size value permitted in GNAT is 2**31@minus{}1. Since this is a
8586 Size in bits, this corresponds to an object of size 256 megabytes (minus
8587 one). This limitation is true on all targets. The reason for this
8588 limitation is that it improves the quality of the code in many cases
8589 if it is known that a Size value can be accommodated in an object of
8592 @node Storage_Size Clauses
8593 @section Storage_Size Clauses
8594 @cindex Storage_Size Clause
8597 For tasks, the @code{Storage_Size} clause specifies the amount of space
8598 to be allocated for the task stack. This cannot be extended, and if the
8599 stack is exhausted, then @code{Storage_Error} will be raised (if stack
8600 checking is enabled). Use a @code{Storage_Size} attribute definition clause,
8601 or a @code{Storage_Size} pragma in the task definition to set the
8602 appropriate required size. A useful technique is to include in every
8603 task definition a pragma of the form:
8605 @smallexample @c ada
8606 pragma Storage_Size (Default_Stack_Size);
8610 Then @code{Default_Stack_Size} can be defined in a global package, and
8611 modified as required. Any tasks requiring stack sizes different from the
8612 default can have an appropriate alternative reference in the pragma.
8614 For access types, the @code{Storage_Size} clause specifies the maximum
8615 space available for allocation of objects of the type. If this space is
8616 exceeded then @code{Storage_Error} will be raised by an allocation attempt.
8617 In the case where the access type is declared local to a subprogram, the
8618 use of a @code{Storage_Size} clause triggers automatic use of a special
8619 predefined storage pool (@code{System.Pool_Size}) that ensures that all
8620 space for the pool is automatically reclaimed on exit from the scope in
8621 which the type is declared.
8623 A special case recognized by the compiler is the specification of a
8624 @code{Storage_Size} of zero for an access type. This means that no
8625 items can be allocated from the pool, and this is recognized at compile
8626 time, and all the overhead normally associated with maintaining a fixed
8627 size storage pool is eliminated. Consider the following example:
8629 @smallexample @c ada
8631 type R is array (Natural) of Character;
8632 type P is access all R;
8633 for P'Storage_Size use 0;
8634 -- Above access type intended only for interfacing purposes
8638 procedure g (m : P);
8639 pragma Import (C, g);
8650 As indicated in this example, these dummy storage pools are often useful in
8651 connection with interfacing where no object will ever be allocated. If you
8652 compile the above example, you get the warning:
8655 p.adb:16:09: warning: allocation from empty storage pool
8656 p.adb:16:09: warning: Storage_Error will be raised at run time
8660 Of course in practice, there will not be any explicit allocators in the
8661 case of such an access declaration.
8663 @node Size of Variant Record Objects
8664 @section Size of Variant Record Objects
8665 @cindex Size, variant record objects
8666 @cindex Variant record objects, size
8669 In the case of variant record objects, there is a question whether Size gives
8670 information about a particular variant, or the maximum size required
8671 for any variant. Consider the following program
8673 @smallexample @c ada
8674 with Text_IO; use Text_IO;
8676 type R1 (A : Boolean := False) is record
8678 when True => X : Character;
8687 Put_Line (Integer'Image (V1'Size));
8688 Put_Line (Integer'Image (V2'Size));
8693 Here we are dealing with a variant record, where the True variant
8694 requires 16 bits, and the False variant requires 8 bits.
8695 In the above example, both V1 and V2 contain the False variant,
8696 which is only 8 bits long. However, the result of running the
8705 The reason for the difference here is that the discriminant value of
8706 V1 is fixed, and will always be False. It is not possible to assign
8707 a True variant value to V1, therefore 8 bits is sufficient. On the
8708 other hand, in the case of V2, the initial discriminant value is
8709 False (from the default), but it is possible to assign a True
8710 variant value to V2, therefore 16 bits must be allocated for V2
8711 in the general case, even fewer bits may be needed at any particular
8712 point during the program execution.
8714 As can be seen from the output of this program, the @code{'Size}
8715 attribute applied to such an object in GNAT gives the actual allocated
8716 size of the variable, which is the largest size of any of the variants.
8717 The Ada Reference Manual is not completely clear on what choice should
8718 be made here, but the GNAT behavior seems most consistent with the
8719 language in the RM@.
8721 In some cases, it may be desirable to obtain the size of the current
8722 variant, rather than the size of the largest variant. This can be
8723 achieved in GNAT by making use of the fact that in the case of a
8724 subprogram parameter, GNAT does indeed return the size of the current
8725 variant (because a subprogram has no way of knowing how much space
8726 is actually allocated for the actual).
8728 Consider the following modified version of the above program:
8730 @smallexample @c ada
8731 with Text_IO; use Text_IO;
8733 type R1 (A : Boolean := False) is record
8735 when True => X : Character;
8742 function Size (V : R1) return Integer is
8748 Put_Line (Integer'Image (V2'Size));
8749 Put_Line (Integer'IMage (Size (V2)));
8751 Put_Line (Integer'Image (V2'Size));
8752 Put_Line (Integer'IMage (Size (V2)));
8757 The output from this program is
8767 Here we see that while the @code{'Size} attribute always returns
8768 the maximum size, regardless of the current variant value, the
8769 @code{Size} function does indeed return the size of the current
8772 @node Biased Representation
8773 @section Biased Representation
8774 @cindex Size for biased representation
8775 @cindex Biased representation
8778 In the case of scalars with a range starting at other than zero, it is
8779 possible in some cases to specify a size smaller than the default minimum
8780 value, and in such cases, GNAT uses an unsigned biased representation,
8781 in which zero is used to represent the lower bound, and successive values
8782 represent successive values of the type.
8784 For example, suppose we have the declaration:
8786 @smallexample @c ada
8787 type Small is range -7 .. -4;
8788 for Small'Size use 2;
8792 Although the default size of type @code{Small} is 4, the @code{Size}
8793 clause is accepted by GNAT and results in the following representation
8797 -7 is represented as 2#00#
8798 -6 is represented as 2#01#
8799 -5 is represented as 2#10#
8800 -4 is represented as 2#11#
8804 Biased representation is only used if the specified @code{Size} clause
8805 cannot be accepted in any other manner. These reduced sizes that force
8806 biased representation can be used for all discrete types except for
8807 enumeration types for which a representation clause is given.
8809 @node Value_Size and Object_Size Clauses
8810 @section Value_Size and Object_Size Clauses
8813 @cindex Size, of objects
8816 In Ada 95, @code{T'Size} for a type @code{T} is the minimum number of bits
8817 required to hold values of type @code{T}. Although this interpretation was
8818 allowed in Ada 83, it was not required, and this requirement in practice
8819 can cause some significant difficulties. For example, in most Ada 83
8820 compilers, @code{Natural'Size} was 32. However, in Ada 95,
8821 @code{Natural'Size} is
8822 typically 31. This means that code may change in behavior when moving
8823 from Ada 83 to Ada 95. For example, consider:
8825 @smallexample @c ada
8832 at 0 range 0 .. Natural'Size - 1;
8833 at 0 range Natural'Size .. 2 * Natural'Size - 1;
8838 In the above code, since the typical size of @code{Natural} objects
8839 is 32 bits and @code{Natural'Size} is 31, the above code can cause
8840 unexpected inefficient packing in Ada 95, and in general there are
8841 cases where the fact that the object size can exceed the
8842 size of the type causes surprises.
8844 To help get around this problem GNAT provides two implementation
8845 defined attributes, @code{Value_Size} and @code{Object_Size}. When
8846 applied to a type, these attributes yield the size of the type
8847 (corresponding to the RM defined size attribute), and the size of
8848 objects of the type respectively.
8850 The @code{Object_Size} is used for determining the default size of
8851 objects and components. This size value can be referred to using the
8852 @code{Object_Size} attribute. The phrase ``is used'' here means that it is
8853 the basis of the determination of the size. The backend is free to
8854 pad this up if necessary for efficiency, e.g.@: an 8-bit stand-alone
8855 character might be stored in 32 bits on a machine with no efficient
8856 byte access instructions such as the Alpha.
8858 The default rules for the value of @code{Object_Size} for
8859 discrete types are as follows:
8863 The @code{Object_Size} for base subtypes reflect the natural hardware
8864 size in bits (run the compiler with @option{-gnatS} to find those values
8865 for numeric types). Enumeration types and fixed-point base subtypes have
8866 8, 16, 32 or 64 bits for this size, depending on the range of values
8870 The @code{Object_Size} of a subtype is the same as the
8871 @code{Object_Size} of
8872 the type from which it is obtained.
8875 The @code{Object_Size} of a derived base type is copied from the parent
8876 base type, and the @code{Object_Size} of a derived first subtype is copied
8877 from the parent first subtype.
8881 The @code{Value_Size} attribute
8882 is the (minimum) number of bits required to store a value
8884 This value is used to determine how tightly to pack
8885 records or arrays with components of this type, and also affects
8886 the semantics of unchecked conversion (unchecked conversions where
8887 the @code{Value_Size} values differ generate a warning, and are potentially
8890 The default rules for the value of @code{Value_Size} are as follows:
8894 The @code{Value_Size} for a base subtype is the minimum number of bits
8895 required to store all values of the type (including the sign bit
8896 only if negative values are possible).
8899 If a subtype statically matches the first subtype of a given type, then it has
8900 by default the same @code{Value_Size} as the first subtype. This is a
8901 consequence of RM 13.1(14) (``if two subtypes statically match,
8902 then their subtype-specific aspects are the same''.)
8905 All other subtypes have a @code{Value_Size} corresponding to the minimum
8906 number of bits required to store all values of the subtype. For
8907 dynamic bounds, it is assumed that the value can range down or up
8908 to the corresponding bound of the ancestor
8912 The RM defined attribute @code{Size} corresponds to the
8913 @code{Value_Size} attribute.
8915 The @code{Size} attribute may be defined for a first-named subtype. This sets
8916 the @code{Value_Size} of
8917 the first-named subtype to the given value, and the
8918 @code{Object_Size} of this first-named subtype to the given value padded up
8919 to an appropriate boundary. It is a consequence of the default rules
8920 above that this @code{Object_Size} will apply to all further subtypes. On the
8921 other hand, @code{Value_Size} is affected only for the first subtype, any
8922 dynamic subtypes obtained from it directly, and any statically matching
8923 subtypes. The @code{Value_Size} of any other static subtypes is not affected.
8925 @code{Value_Size} and
8926 @code{Object_Size} may be explicitly set for any subtype using
8927 an attribute definition clause. Note that the use of these attributes
8928 can cause the RM 13.1(14) rule to be violated. If two access types
8929 reference aliased objects whose subtypes have differing @code{Object_Size}
8930 values as a result of explicit attribute definition clauses, then it
8931 is erroneous to convert from one access subtype to the other.
8933 At the implementation level, Esize stores the Object_Size and the
8934 RM_Size field stores the @code{Value_Size} (and hence the value of the
8935 @code{Size} attribute,
8936 which, as noted above, is equivalent to @code{Value_Size}).
8938 To get a feel for the difference, consider the following examples (note
8939 that in each case the base is @code{Short_Short_Integer} with a size of 8):
8942 Object_Size Value_Size
8944 type x1 is range 0 .. 5; 8 3
8946 type x2 is range 0 .. 5;
8947 for x2'size use 12; 16 12
8949 subtype x3 is x2 range 0 .. 3; 16 2
8951 subtype x4 is x2'base range 0 .. 10; 8 4
8953 subtype x5 is x2 range 0 .. dynamic; 16 3*
8955 subtype x6 is x2'base range 0 .. dynamic; 8 3*
8960 Note: the entries marked ``3*'' are not actually specified by the Ada 95 RM,
8961 but it seems in the spirit of the RM rules to allocate the minimum number
8962 of bits (here 3, given the range for @code{x2})
8963 known to be large enough to hold the given range of values.
8965 So far, so good, but GNAT has to obey the RM rules, so the question is
8966 under what conditions must the RM @code{Size} be used.
8967 The following is a list
8968 of the occasions on which the RM @code{Size} must be used:
8972 Component size for packed arrays or records
8975 Value of the attribute @code{Size} for a type
8978 Warning about sizes not matching for unchecked conversion
8982 For record types, the @code{Object_Size} is always a multiple of the
8983 alignment of the type (this is true for all types). In some cases the
8984 @code{Value_Size} can be smaller. Consider:
8994 On a typical 32-bit architecture, the X component will be four bytes, and
8995 require four-byte alignment, and the Y component will be one byte. In this
8996 case @code{R'Value_Size} will be 40 (bits) since this is the minimum size
8997 required to store a value of this type, and for example, it is permissible
8998 to have a component of type R in an outer record whose component size is
8999 specified to be 48 bits. However, @code{R'Object_Size} will be 64 (bits),
9000 since it must be rounded up so that this value is a multiple of the
9001 alignment (4 bytes = 32 bits).
9004 For all other types, the @code{Object_Size}
9005 and Value_Size are the same (and equivalent to the RM attribute @code{Size}).
9006 Only @code{Size} may be specified for such types.
9008 @node Component_Size Clauses
9009 @section Component_Size Clauses
9010 @cindex Component_Size Clause
9013 Normally, the value specified in a component clause must be consistent
9014 with the subtype of the array component with regard to size and alignment.
9015 In other words, the value specified must be at least equal to the size
9016 of this subtype, and must be a multiple of the alignment value.
9018 In addition, component size clauses are allowed which cause the array
9019 to be packed, by specifying a smaller value. The cases in which this
9020 is allowed are for component size values in the range 1 through 63. The value
9021 specified must not be smaller than the Size of the subtype. GNAT will
9022 accurately honor all packing requests in this range. For example, if
9025 @smallexample @c ada
9026 type r is array (1 .. 8) of Natural;
9027 for r'Component_Size use 31;
9031 then the resulting array has a length of 31 bytes (248 bits = 8 * 31).
9032 Of course access to the components of such an array is considerably
9033 less efficient than if the natural component size of 32 is used.
9035 @node Bit_Order Clauses
9036 @section Bit_Order Clauses
9037 @cindex Bit_Order Clause
9038 @cindex bit ordering
9039 @cindex ordering, of bits
9042 For record subtypes, GNAT permits the specification of the @code{Bit_Order}
9043 attribute. The specification may either correspond to the default bit
9044 order for the target, in which case the specification has no effect and
9045 places no additional restrictions, or it may be for the non-standard
9046 setting (that is the opposite of the default).
9048 In the case where the non-standard value is specified, the effect is
9049 to renumber bits within each byte, but the ordering of bytes is not
9050 affected. There are certain
9051 restrictions placed on component clauses as follows:
9055 @item Components fitting within a single storage unit.
9057 These are unrestricted, and the effect is merely to renumber bits. For
9058 example if we are on a little-endian machine with @code{Low_Order_First}
9059 being the default, then the following two declarations have exactly
9062 @smallexample @c ada
9065 B : Integer range 1 .. 120;
9069 A at 0 range 0 .. 0;
9070 B at 0 range 1 .. 7;
9075 B : Integer range 1 .. 120;
9078 for R2'Bit_Order use High_Order_First;
9081 A at 0 range 7 .. 7;
9082 B at 0 range 0 .. 6;
9087 The useful application here is to write the second declaration with the
9088 @code{Bit_Order} attribute definition clause, and know that it will be treated
9089 the same, regardless of whether the target is little-endian or big-endian.
9091 @item Components occupying an integral number of bytes.
9093 These are components that exactly fit in two or more bytes. Such component
9094 declarations are allowed, but have no effect, since it is important to realize
9095 that the @code{Bit_Order} specification does not affect the ordering of bytes.
9096 In particular, the following attempt at getting an endian-independent integer
9099 @smallexample @c ada
9104 for R2'Bit_Order use High_Order_First;
9107 A at 0 range 0 .. 31;
9112 This declaration will result in a little-endian integer on a
9113 little-endian machine, and a big-endian integer on a big-endian machine.
9114 If byte flipping is required for interoperability between big- and
9115 little-endian machines, this must be explicitly programmed. This capability
9116 is not provided by @code{Bit_Order}.
9118 @item Components that are positioned across byte boundaries
9120 but do not occupy an integral number of bytes. Given that bytes are not
9121 reordered, such fields would occupy a non-contiguous sequence of bits
9122 in memory, requiring non-trivial code to reassemble. They are for this
9123 reason not permitted, and any component clause specifying such a layout
9124 will be flagged as illegal by GNAT@.
9129 Since the misconception that Bit_Order automatically deals with all
9130 endian-related incompatibilities is a common one, the specification of
9131 a component field that is an integral number of bytes will always
9132 generate a warning. This warning may be suppressed using
9133 @code{pragma Suppress} if desired. The following section contains additional
9134 details regarding the issue of byte ordering.
9136 @node Effect of Bit_Order on Byte Ordering
9137 @section Effect of Bit_Order on Byte Ordering
9138 @cindex byte ordering
9139 @cindex ordering, of bytes
9142 In this section we will review the effect of the @code{Bit_Order} attribute
9143 definition clause on byte ordering. Briefly, it has no effect at all, but
9144 a detailed example will be helpful. Before giving this
9145 example, let us review the precise
9146 definition of the effect of defining @code{Bit_Order}. The effect of a
9147 non-standard bit order is described in section 15.5.3 of the Ada
9151 2 A bit ordering is a method of interpreting the meaning of
9152 the storage place attributes.
9156 To understand the precise definition of storage place attributes in
9157 this context, we visit section 13.5.1 of the manual:
9160 13 A record_representation_clause (without the mod_clause)
9161 specifies the layout. The storage place attributes (see 13.5.2)
9162 are taken from the values of the position, first_bit, and last_bit
9163 expressions after normalizing those values so that first_bit is
9164 less than Storage_Unit.
9168 The critical point here is that storage places are taken from
9169 the values after normalization, not before. So the @code{Bit_Order}
9170 interpretation applies to normalized values. The interpretation
9171 is described in the later part of the 15.5.3 paragraph:
9174 2 A bit ordering is a method of interpreting the meaning of
9175 the storage place attributes. High_Order_First (known in the
9176 vernacular as ``big endian'') means that the first bit of a
9177 storage element (bit 0) is the most significant bit (interpreting
9178 the sequence of bits that represent a component as an unsigned
9179 integer value). Low_Order_First (known in the vernacular as
9180 ``little endian'') means the opposite: the first bit is the
9185 Note that the numbering is with respect to the bits of a storage
9186 unit. In other words, the specification affects only the numbering
9187 of bits within a single storage unit.
9189 We can make the effect clearer by giving an example.
9191 Suppose that we have an external device which presents two bytes, the first
9192 byte presented, which is the first (low addressed byte) of the two byte
9193 record is called Master, and the second byte is called Slave.
9195 The left most (most significant bit is called Control for each byte, and
9196 the remaining 7 bits are called V1, V2, @dots{} V7, where V7 is the rightmost
9197 (least significant) bit.
9199 On a big-endian machine, we can write the following representation clause
9201 @smallexample @c ada
9203 Master_Control : Bit;
9211 Slave_Control : Bit;
9222 Master_Control at 0 range 0 .. 0;
9223 Master_V1 at 0 range 1 .. 1;
9224 Master_V2 at 0 range 2 .. 2;
9225 Master_V3 at 0 range 3 .. 3;
9226 Master_V4 at 0 range 4 .. 4;
9227 Master_V5 at 0 range 5 .. 5;
9228 Master_V6 at 0 range 6 .. 6;
9229 Master_V7 at 0 range 7 .. 7;
9230 Slave_Control at 1 range 0 .. 0;
9231 Slave_V1 at 1 range 1 .. 1;
9232 Slave_V2 at 1 range 2 .. 2;
9233 Slave_V3 at 1 range 3 .. 3;
9234 Slave_V4 at 1 range 4 .. 4;
9235 Slave_V5 at 1 range 5 .. 5;
9236 Slave_V6 at 1 range 6 .. 6;
9237 Slave_V7 at 1 range 7 .. 7;
9242 Now if we move this to a little endian machine, then the bit ordering within
9243 the byte is backwards, so we have to rewrite the record rep clause as:
9245 @smallexample @c ada
9247 Master_Control at 0 range 7 .. 7;
9248 Master_V1 at 0 range 6 .. 6;
9249 Master_V2 at 0 range 5 .. 5;
9250 Master_V3 at 0 range 4 .. 4;
9251 Master_V4 at 0 range 3 .. 3;
9252 Master_V5 at 0 range 2 .. 2;
9253 Master_V6 at 0 range 1 .. 1;
9254 Master_V7 at 0 range 0 .. 0;
9255 Slave_Control at 1 range 7 .. 7;
9256 Slave_V1 at 1 range 6 .. 6;
9257 Slave_V2 at 1 range 5 .. 5;
9258 Slave_V3 at 1 range 4 .. 4;
9259 Slave_V4 at 1 range 3 .. 3;
9260 Slave_V5 at 1 range 2 .. 2;
9261 Slave_V6 at 1 range 1 .. 1;
9262 Slave_V7 at 1 range 0 .. 0;
9267 It is a nuisance to have to rewrite the clause, especially if
9268 the code has to be maintained on both machines. However,
9269 this is a case that we can handle with the
9270 @code{Bit_Order} attribute if it is implemented.
9271 Note that the implementation is not required on byte addressed
9272 machines, but it is indeed implemented in GNAT.
9273 This means that we can simply use the
9274 first record clause, together with the declaration
9276 @smallexample @c ada
9277 for Data'Bit_Order use High_Order_First;
9281 and the effect is what is desired, namely the layout is exactly the same,
9282 independent of whether the code is compiled on a big-endian or little-endian
9285 The important point to understand is that byte ordering is not affected.
9286 A @code{Bit_Order} attribute definition never affects which byte a field
9287 ends up in, only where it ends up in that byte.
9288 To make this clear, let us rewrite the record rep clause of the previous
9291 @smallexample @c ada
9292 for Data'Bit_Order use High_Order_First;
9294 Master_Control at 0 range 0 .. 0;
9295 Master_V1 at 0 range 1 .. 1;
9296 Master_V2 at 0 range 2 .. 2;
9297 Master_V3 at 0 range 3 .. 3;
9298 Master_V4 at 0 range 4 .. 4;
9299 Master_V5 at 0 range 5 .. 5;
9300 Master_V6 at 0 range 6 .. 6;
9301 Master_V7 at 0 range 7 .. 7;
9302 Slave_Control at 0 range 8 .. 8;
9303 Slave_V1 at 0 range 9 .. 9;
9304 Slave_V2 at 0 range 10 .. 10;
9305 Slave_V3 at 0 range 11 .. 11;
9306 Slave_V4 at 0 range 12 .. 12;
9307 Slave_V5 at 0 range 13 .. 13;
9308 Slave_V6 at 0 range 14 .. 14;
9309 Slave_V7 at 0 range 15 .. 15;
9314 This is exactly equivalent to saying (a repeat of the first example):
9316 @smallexample @c ada
9317 for Data'Bit_Order use High_Order_First;
9319 Master_Control at 0 range 0 .. 0;
9320 Master_V1 at 0 range 1 .. 1;
9321 Master_V2 at 0 range 2 .. 2;
9322 Master_V3 at 0 range 3 .. 3;
9323 Master_V4 at 0 range 4 .. 4;
9324 Master_V5 at 0 range 5 .. 5;
9325 Master_V6 at 0 range 6 .. 6;
9326 Master_V7 at 0 range 7 .. 7;
9327 Slave_Control at 1 range 0 .. 0;
9328 Slave_V1 at 1 range 1 .. 1;
9329 Slave_V2 at 1 range 2 .. 2;
9330 Slave_V3 at 1 range 3 .. 3;
9331 Slave_V4 at 1 range 4 .. 4;
9332 Slave_V5 at 1 range 5 .. 5;
9333 Slave_V6 at 1 range 6 .. 6;
9334 Slave_V7 at 1 range 7 .. 7;
9339 Why are they equivalent? Well take a specific field, the @code{Slave_V2}
9340 field. The storage place attributes are obtained by normalizing the
9341 values given so that the @code{First_Bit} value is less than 8. After
9342 normalizing the values (0,10,10) we get (1,2,2) which is exactly what
9343 we specified in the other case.
9345 Now one might expect that the @code{Bit_Order} attribute might affect
9346 bit numbering within the entire record component (two bytes in this
9347 case, thus affecting which byte fields end up in), but that is not
9348 the way this feature is defined, it only affects numbering of bits,
9349 not which byte they end up in.
9351 Consequently it never makes sense to specify a starting bit number
9352 greater than 7 (for a byte addressable field) if an attribute
9353 definition for @code{Bit_Order} has been given, and indeed it
9354 may be actively confusing to specify such a value, so the compiler
9355 generates a warning for such usage.
9357 If you do need to control byte ordering then appropriate conditional
9358 values must be used. If in our example, the slave byte came first on
9359 some machines we might write:
9361 @smallexample @c ada
9362 Master_Byte_First constant Boolean := @dots{};
9364 Master_Byte : constant Natural :=
9365 1 - Boolean'Pos (Master_Byte_First);
9366 Slave_Byte : constant Natural :=
9367 Boolean'Pos (Master_Byte_First);
9369 for Data'Bit_Order use High_Order_First;
9371 Master_Control at Master_Byte range 0 .. 0;
9372 Master_V1 at Master_Byte range 1 .. 1;
9373 Master_V2 at Master_Byte range 2 .. 2;
9374 Master_V3 at Master_Byte range 3 .. 3;
9375 Master_V4 at Master_Byte range 4 .. 4;
9376 Master_V5 at Master_Byte range 5 .. 5;
9377 Master_V6 at Master_Byte range 6 .. 6;
9378 Master_V7 at Master_Byte range 7 .. 7;
9379 Slave_Control at Slave_Byte range 0 .. 0;
9380 Slave_V1 at Slave_Byte range 1 .. 1;
9381 Slave_V2 at Slave_Byte range 2 .. 2;
9382 Slave_V3 at Slave_Byte range 3 .. 3;
9383 Slave_V4 at Slave_Byte range 4 .. 4;
9384 Slave_V5 at Slave_Byte range 5 .. 5;
9385 Slave_V6 at Slave_Byte range 6 .. 6;
9386 Slave_V7 at Slave_Byte range 7 .. 7;
9391 Now to switch between machines, all that is necessary is
9392 to set the boolean constant @code{Master_Byte_First} in
9393 an appropriate manner.
9395 @node Pragma Pack for Arrays
9396 @section Pragma Pack for Arrays
9397 @cindex Pragma Pack (for arrays)
9400 Pragma @code{Pack} applied to an array has no effect unless the component type
9401 is packable. For a component type to be packable, it must be one of the
9408 Any type whose size is specified with a size clause
9410 Any packed array type with a static size
9414 For all these cases, if the component subtype size is in the range
9415 1 through 63, then the effect of the pragma @code{Pack} is exactly as though a
9416 component size were specified giving the component subtype size.
9417 For example if we have:
9419 @smallexample @c ada
9420 type r is range 0 .. 17;
9422 type ar is array (1 .. 8) of r;
9427 Then the component size of @code{ar} will be set to 5 (i.e.@: to @code{r'size},
9428 and the size of the array @code{ar} will be exactly 40 bits.
9430 Note that in some cases this rather fierce approach to packing can produce
9431 unexpected effects. For example, in Ada 95, type Natural typically has a
9432 size of 31, meaning that if you pack an array of Natural, you get 31-bit
9433 close packing, which saves a few bits, but results in far less efficient
9434 access. Since many other Ada compilers will ignore such a packing request,
9435 GNAT will generate a warning on some uses of pragma @code{Pack} that it guesses
9436 might not be what is intended. You can easily remove this warning by
9437 using an explicit @code{Component_Size} setting instead, which never generates
9438 a warning, since the intention of the programmer is clear in this case.
9440 GNAT treats packed arrays in one of two ways. If the size of the array is
9441 known at compile time and is less than 64 bits, then internally the array
9442 is represented as a single modular type, of exactly the appropriate number
9443 of bits. If the length is greater than 63 bits, or is not known at compile
9444 time, then the packed array is represented as an array of bytes, and the
9445 length is always a multiple of 8 bits.
9447 Note that to represent a packed array as a modular type, the alignment must
9448 be suitable for the modular type involved. For example, on typical machines
9449 a 32-bit packed array will be represented by a 32-bit modular integer with
9450 an alignment of four bytes. If you explicitly override the default alignment
9451 with an alignment clause that is too small, the modular representation
9452 cannot be used. For example, consider the following set of declarations:
9454 @smallexample @c ada
9455 type R is range 1 .. 3;
9456 type S is array (1 .. 31) of R;
9457 for S'Component_Size use 2;
9459 for S'Alignment use 1;
9463 If the alignment clause were not present, then a 62-bit modular
9464 representation would be chosen (typically with an alignment of 4 or 8
9465 bytes depending on the target). But the default alignment is overridden
9466 with the explicit alignment clause. This means that the modular
9467 representation cannot be used, and instead the array of bytes
9468 representation must be used, meaning that the length must be a multiple
9469 of 8. Thus the above set of declarations will result in a diagnostic
9470 rejecting the size clause and noting that the minimum size allowed is 64.
9472 @cindex Pragma Pack (for type Natural)
9473 @cindex Pragma Pack warning
9475 One special case that is worth noting occurs when the base type of the
9476 component size is 8/16/32 and the subtype is one bit less. Notably this
9477 occurs with subtype @code{Natural}. Consider:
9479 @smallexample @c ada
9480 type Arr is array (1 .. 32) of Natural;
9485 In all commonly used Ada 83 compilers, this pragma Pack would be ignored,
9486 since typically @code{Natural'Size} is 32 in Ada 83, and in any case most
9487 Ada 83 compilers did not attempt 31 bit packing.
9489 In Ada 95, @code{Natural'Size} is required to be 31. Furthermore, GNAT really
9490 does pack 31-bit subtype to 31 bits. This may result in a substantial
9491 unintended performance penalty when porting legacy Ada 83 code. To help
9492 prevent this, GNAT generates a warning in such cases. If you really want 31
9493 bit packing in a case like this, you can set the component size explicitly:
9495 @smallexample @c ada
9496 type Arr is array (1 .. 32) of Natural;
9497 for Arr'Component_Size use 31;
9501 Here 31-bit packing is achieved as required, and no warning is generated,
9502 since in this case the programmer intention is clear.
9504 @node Pragma Pack for Records
9505 @section Pragma Pack for Records
9506 @cindex Pragma Pack (for records)
9509 Pragma @code{Pack} applied to a record will pack the components to reduce
9510 wasted space from alignment gaps and by reducing the amount of space
9511 taken by components. We distinguish between @emph{packable} components and
9512 @emph{non-packable} components.
9513 Components of the following types are considered packable:
9516 All primitive types are packable.
9519 Small packed arrays, whose size does not exceed 64 bits, and where the
9520 size is statically known at compile time, are represented internally
9521 as modular integers, and so they are also packable.
9526 All packable components occupy the exact number of bits corresponding to
9527 their @code{Size} value, and are packed with no padding bits, i.e.@: they
9528 can start on an arbitrary bit boundary.
9530 All other types are non-packable, they occupy an integral number of
9532 are placed at a boundary corresponding to their alignment requirements.
9534 For example, consider the record
9536 @smallexample @c ada
9537 type Rb1 is array (1 .. 13) of Boolean;
9540 type Rb2 is array (1 .. 65) of Boolean;
9555 The representation for the record x2 is as follows:
9557 @smallexample @c ada
9558 for x2'Size use 224;
9560 l1 at 0 range 0 .. 0;
9561 l2 at 0 range 1 .. 64;
9562 l3 at 12 range 0 .. 31;
9563 l4 at 16 range 0 .. 0;
9564 l5 at 16 range 1 .. 13;
9565 l6 at 18 range 0 .. 71;
9570 Studying this example, we see that the packable fields @code{l1}
9572 of length equal to their sizes, and placed at specific bit boundaries (and
9573 not byte boundaries) to
9574 eliminate padding. But @code{l3} is of a non-packable float type, so
9575 it is on the next appropriate alignment boundary.
9577 The next two fields are fully packable, so @code{l4} and @code{l5} are
9578 minimally packed with no gaps. However, type @code{Rb2} is a packed
9579 array that is longer than 64 bits, so it is itself non-packable. Thus
9580 the @code{l6} field is aligned to the next byte boundary, and takes an
9581 integral number of bytes, i.e.@: 72 bits.
9583 @node Record Representation Clauses
9584 @section Record Representation Clauses
9585 @cindex Record Representation Clause
9588 Record representation clauses may be given for all record types, including
9589 types obtained by record extension. Component clauses are allowed for any
9590 static component. The restrictions on component clauses depend on the type
9593 @cindex Component Clause
9594 For all components of an elementary type, the only restriction on component
9595 clauses is that the size must be at least the 'Size value of the type
9596 (actually the Value_Size). There are no restrictions due to alignment,
9597 and such components may freely cross storage boundaries.
9599 Packed arrays with a size up to and including 64 bits are represented
9600 internally using a modular type with the appropriate number of bits, and
9601 thus the same lack of restriction applies. For example, if you declare:
9603 @smallexample @c ada
9604 type R is array (1 .. 49) of Boolean;
9610 then a component clause for a component of type R may start on any
9611 specified bit boundary, and may specify a value of 49 bits or greater.
9613 For packed bit arrays that are longer than 64 bits, there are two
9614 cases. If the component size is a power of 2 (1,2,4,8,16,32 bits),
9615 including the important case of single bits or boolean values, then
9616 there are no limitations on placement of such components, and they
9617 may start and end at arbitrary bit boundaries.
9619 If the component size is not a power of 2 (e.g. 3 or 5), then
9620 an array of this type longer than 64 bits must always be placed on
9621 on a storage unit (byte) boundary and occupy an integral number
9622 of storage units (bytes). Any component clause that does not
9623 meet this requirement will be rejected.
9625 Any aliased component, or component of an aliased type, must
9626 have its normal alignment and size. A component clause that
9627 does not meet this requirement will be rejected.
9629 The tag field of a tagged type always occupies an address sized field at
9630 the start of the record. No component clause may attempt to overlay this
9631 tag. When a tagged type appears as a component, the tag field must have
9634 In the case of a record extension T1, of a type T, no component clause applied
9635 to the type T1 can specify a storage location that would overlap the first
9636 T'Size bytes of the record.
9638 For all other component types, including non-bit-packed arrays,
9639 the component can be placed at an arbitrary bit boundary,
9640 so for example, the following is permitted:
9642 @smallexample @c ada
9643 type R is array (1 .. 10) of Boolean;
9652 G at 0 range 0 .. 0;
9653 H at 0 range 1 .. 1;
9654 L at 0 range 2 .. 81;
9655 R at 0 range 82 .. 161;
9660 Note: the above rules apply to recent releases of GNAT 5.
9661 In GNAT 3, there are more severe restrictions on larger components.
9662 For non-primitive types, including packed arrays with a size greater than
9663 64 bits, component clauses must respect the alignment requirement of the
9664 type, in particular, always starting on a byte boundary, and the length
9665 must be a multiple of the storage unit.
9667 @node Enumeration Clauses
9668 @section Enumeration Clauses
9670 The only restriction on enumeration clauses is that the range of values
9671 must be representable. For the signed case, if one or more of the
9672 representation values are negative, all values must be in the range:
9674 @smallexample @c ada
9675 System.Min_Int .. System.Max_Int
9679 For the unsigned case, where all values are non negative, the values must
9682 @smallexample @c ada
9683 0 .. System.Max_Binary_Modulus;
9687 A @emph{confirming} representation clause is one in which the values range
9688 from 0 in sequence, i.e.@: a clause that confirms the default representation
9689 for an enumeration type.
9690 Such a confirming representation
9691 is permitted by these rules, and is specially recognized by the compiler so
9692 that no extra overhead results from the use of such a clause.
9694 If an array has an index type which is an enumeration type to which an
9695 enumeration clause has been applied, then the array is stored in a compact
9696 manner. Consider the declarations:
9698 @smallexample @c ada
9699 type r is (A, B, C);
9700 for r use (A => 1, B => 5, C => 10);
9701 type t is array (r) of Character;
9705 The array type t corresponds to a vector with exactly three elements and
9706 has a default size equal to @code{3*Character'Size}. This ensures efficient
9707 use of space, but means that accesses to elements of the array will incur
9708 the overhead of converting representation values to the corresponding
9709 positional values, (i.e.@: the value delivered by the @code{Pos} attribute).
9711 @node Address Clauses
9712 @section Address Clauses
9713 @cindex Address Clause
9715 The reference manual allows a general restriction on representation clauses,
9716 as found in RM 13.1(22):
9719 An implementation need not support representation
9720 items containing nonstatic expressions, except that
9721 an implementation should support a representation item
9722 for a given entity if each nonstatic expression in the
9723 representation item is a name that statically denotes
9724 a constant declared before the entity.
9728 In practice this is applicable only to address clauses, since this is the
9729 only case in which a non-static expression is permitted by the syntax. As
9730 the AARM notes in sections 13.1 (22.a-22.h):
9733 22.a Reason: This is to avoid the following sort of thing:
9735 22.b X : Integer := F(@dots{});
9736 Y : Address := G(@dots{});
9737 for X'Address use Y;
9739 22.c In the above, we have to evaluate the
9740 initialization expression for X before we
9741 know where to put the result. This seems
9742 like an unreasonable implementation burden.
9744 22.d The above code should instead be written
9747 22.e Y : constant Address := G(@dots{});
9748 X : Integer := F(@dots{});
9749 for X'Address use Y;
9751 22.f This allows the expression ``Y'' to be safely
9752 evaluated before X is created.
9754 22.g The constant could be a formal parameter of mode in.
9756 22.h An implementation can support other nonstatic
9757 expressions if it wants to. Expressions of type
9758 Address are hardly ever static, but their value
9759 might be known at compile time anyway in many
9764 GNAT does indeed permit many additional cases of non-static expressions. In
9765 particular, if the type involved is elementary there are no restrictions
9766 (since in this case, holding a temporary copy of the initialization value,
9767 if one is present, is inexpensive). In addition, if there is no implicit or
9768 explicit initialization, then there are no restrictions. GNAT will reject
9769 only the case where all three of these conditions hold:
9774 The type of the item is non-elementary (e.g.@: a record or array).
9777 There is explicit or implicit initialization required for the object.
9778 Note that access values are always implicitly initialized, and also
9779 in GNAT, certain bit-packed arrays (those having a dynamic length or
9780 a length greater than 64) will also be implicitly initialized to zero.
9783 The address value is non-static. Here GNAT is more permissive than the
9784 RM, and allows the address value to be the address of a previously declared
9785 stand-alone variable, as long as it does not itself have an address clause.
9787 @smallexample @c ada
9788 Anchor : Some_Initialized_Type;
9789 Overlay : Some_Initialized_Type;
9790 for Overlay'Address use Anchor'Address;
9794 However, the prefix of the address clause cannot be an array component, or
9795 a component of a discriminated record.
9800 As noted above in section 22.h, address values are typically non-static. In
9801 particular the To_Address function, even if applied to a literal value, is
9802 a non-static function call. To avoid this minor annoyance, GNAT provides
9803 the implementation defined attribute 'To_Address. The following two
9804 expressions have identical values:
9808 @smallexample @c ada
9809 To_Address (16#1234_0000#)
9810 System'To_Address (16#1234_0000#);
9814 except that the second form is considered to be a static expression, and
9815 thus when used as an address clause value is always permitted.
9818 Additionally, GNAT treats as static an address clause that is an
9819 unchecked_conversion of a static integer value. This simplifies the porting
9820 of legacy code, and provides a portable equivalent to the GNAT attribute
9823 Another issue with address clauses is the interaction with alignment
9824 requirements. When an address clause is given for an object, the address
9825 value must be consistent with the alignment of the object (which is usually
9826 the same as the alignment of the type of the object). If an address clause
9827 is given that specifies an inappropriately aligned address value, then the
9828 program execution is erroneous.
9830 Since this source of erroneous behavior can have unfortunate effects, GNAT
9831 checks (at compile time if possible, generating a warning, or at execution
9832 time with a run-time check) that the alignment is appropriate. If the
9833 run-time check fails, then @code{Program_Error} is raised. This run-time
9834 check is suppressed if range checks are suppressed, or if
9835 @code{pragma Restrictions (No_Elaboration_Code)} is in effect.
9838 An address clause cannot be given for an exported object. More
9839 understandably the real restriction is that objects with an address
9840 clause cannot be exported. This is because such variables are not
9841 defined by the Ada program, so there is no external object to export.
9844 It is permissible to give an address clause and a pragma Import for the
9845 same object. In this case, the variable is not really defined by the
9846 Ada program, so there is no external symbol to be linked. The link name
9847 and the external name are ignored in this case. The reason that we allow this
9848 combination is that it provides a useful idiom to avoid unwanted
9849 initializations on objects with address clauses.
9851 When an address clause is given for an object that has implicit or
9852 explicit initialization, then by default initialization takes place. This
9853 means that the effect of the object declaration is to overwrite the
9854 memory at the specified address. This is almost always not what the
9855 programmer wants, so GNAT will output a warning:
9865 for Ext'Address use System'To_Address (16#1234_1234#);
9867 >>> warning: implicit initialization of "Ext" may
9868 modify overlaid storage
9869 >>> warning: use pragma Import for "Ext" to suppress
9870 initialization (RM B(24))
9876 As indicated by the warning message, the solution is to use a (dummy) pragma
9877 Import to suppress this initialization. The pragma tell the compiler that the
9878 object is declared and initialized elsewhere. The following package compiles
9879 without warnings (and the initialization is suppressed):
9881 @smallexample @c ada
9889 for Ext'Address use System'To_Address (16#1234_1234#);
9890 pragma Import (Ada, Ext);
9895 A final issue with address clauses involves their use for overlaying
9896 variables, as in the following example:
9897 @cindex Overlaying of objects
9899 @smallexample @c ada
9902 for B'Address use A'Address;
9906 or alternatively, using the form recommended by the RM:
9908 @smallexample @c ada
9910 Addr : constant Address := A'Address;
9912 for B'Address use Addr;
9916 In both of these cases, @code{A}
9917 and @code{B} become aliased to one another via the
9918 address clause. This use of address clauses to overlay
9919 variables, achieving an effect similar to unchecked
9920 conversion was erroneous in Ada 83, but in Ada 95
9921 the effect is implementation defined. Furthermore, the
9922 Ada 95 RM specifically recommends that in a situation
9923 like this, @code{B} should be subject to the following
9924 implementation advice (RM 13.3(19)):
9927 19 If the Address of an object is specified, or it is imported
9928 or exported, then the implementation should not perform
9929 optimizations based on assumptions of no aliases.
9933 GNAT follows this recommendation, and goes further by also applying
9934 this recommendation to the overlaid variable (@code{A}
9935 in the above example) in this case. This means that the overlay
9936 works "as expected", in that a modification to one of the variables
9937 will affect the value of the other.
9939 @node Effect of Convention on Representation
9940 @section Effect of Convention on Representation
9941 @cindex Convention, effect on representation
9944 Normally the specification of a foreign language convention for a type or
9945 an object has no effect on the chosen representation. In particular, the
9946 representation chosen for data in GNAT generally meets the standard system
9947 conventions, and for example records are laid out in a manner that is
9948 consistent with C@. This means that specifying convention C (for example)
9951 There are three exceptions to this general rule:
9955 @item Convention Fortran and array subtypes
9956 If pragma Convention Fortran is specified for an array subtype, then in
9957 accordance with the implementation advice in section 3.6.2(11) of the
9958 Ada Reference Manual, the array will be stored in a Fortran-compatible
9959 column-major manner, instead of the normal default row-major order.
9961 @item Convention C and enumeration types
9962 GNAT normally stores enumeration types in 8, 16, or 32 bits as required
9963 to accommodate all values of the type. For example, for the enumeration
9966 @smallexample @c ada
9967 type Color is (Red, Green, Blue);
9971 8 bits is sufficient to store all values of the type, so by default, objects
9972 of type @code{Color} will be represented using 8 bits. However, normal C
9973 convention is to use 32 bits for all enum values in C, since enum values
9974 are essentially of type int. If pragma @code{Convention C} is specified for an
9975 Ada enumeration type, then the size is modified as necessary (usually to
9976 32 bits) to be consistent with the C convention for enum values.
9978 @item Convention C/Fortran and Boolean types
9979 In C, the usual convention for boolean values, that is values used for
9980 conditions, is that zero represents false, and nonzero values represent
9981 true. In Ada, the normal convention is that two specific values, typically
9982 0/1, are used to represent false/true respectively.
9984 Fortran has a similar convention for @code{LOGICAL} values (any nonzero
9985 value represents true).
9987 To accommodate the Fortran and C conventions, if a pragma Convention specifies
9988 C or Fortran convention for a derived Boolean, as in the following example:
9990 @smallexample @c ada
9991 type C_Switch is new Boolean;
9992 pragma Convention (C, C_Switch);
9996 then the GNAT generated code will treat any nonzero value as true. For truth
9997 values generated by GNAT, the conventional value 1 will be used for True, but
9998 when one of these values is read, any nonzero value is treated as True.
10002 @node Determining the Representations chosen by GNAT
10003 @section Determining the Representations chosen by GNAT
10004 @cindex Representation, determination of
10005 @cindex @code{-gnatR} switch
10008 Although the descriptions in this section are intended to be complete, it is
10009 often easier to simply experiment to see what GNAT accepts and what the
10010 effect is on the layout of types and objects.
10012 As required by the Ada RM, if a representation clause is not accepted, then
10013 it must be rejected as illegal by the compiler. However, when a
10014 representation clause or pragma is accepted, there can still be questions
10015 of what the compiler actually does. For example, if a partial record
10016 representation clause specifies the location of some components and not
10017 others, then where are the non-specified components placed? Or if pragma
10018 @code{Pack} is used on a record, then exactly where are the resulting
10019 fields placed? The section on pragma @code{Pack} in this chapter can be
10020 used to answer the second question, but it is often easier to just see
10021 what the compiler does.
10023 For this purpose, GNAT provides the option @code{-gnatR}. If you compile
10024 with this option, then the compiler will output information on the actual
10025 representations chosen, in a format similar to source representation
10026 clauses. For example, if we compile the package:
10028 @smallexample @c ada
10030 type r (x : boolean) is tagged record
10032 when True => S : String (1 .. 100);
10033 when False => null;
10037 type r2 is new r (false) with record
10042 y2 at 16 range 0 .. 31;
10049 type x1 is array (1 .. 10) of x;
10050 for x1'component_size use 11;
10052 type ia is access integer;
10054 type Rb1 is array (1 .. 13) of Boolean;
10057 type Rb2 is array (1 .. 65) of Boolean;
10073 using the switch @code{-gnatR} we obtain the following output:
10076 Representation information for unit q
10077 -------------------------------------
10080 for r'Alignment use 4;
10082 x at 4 range 0 .. 7;
10083 _tag at 0 range 0 .. 31;
10084 s at 5 range 0 .. 799;
10087 for r2'Size use 160;
10088 for r2'Alignment use 4;
10090 x at 4 range 0 .. 7;
10091 _tag at 0 range 0 .. 31;
10092 _parent at 0 range 0 .. 63;
10093 y2 at 16 range 0 .. 31;
10097 for x'Alignment use 1;
10099 y at 0 range 0 .. 7;
10102 for x1'Size use 112;
10103 for x1'Alignment use 1;
10104 for x1'Component_Size use 11;
10106 for rb1'Size use 13;
10107 for rb1'Alignment use 2;
10108 for rb1'Component_Size use 1;
10110 for rb2'Size use 72;
10111 for rb2'Alignment use 1;
10112 for rb2'Component_Size use 1;
10114 for x2'Size use 224;
10115 for x2'Alignment use 4;
10117 l1 at 0 range 0 .. 0;
10118 l2 at 0 range 1 .. 64;
10119 l3 at 12 range 0 .. 31;
10120 l4 at 16 range 0 .. 0;
10121 l5 at 16 range 1 .. 13;
10122 l6 at 18 range 0 .. 71;
10127 The Size values are actually the Object_Size, i.e.@: the default size that
10128 will be allocated for objects of the type.
10129 The ?? size for type r indicates that we have a variant record, and the
10130 actual size of objects will depend on the discriminant value.
10132 The Alignment values show the actual alignment chosen by the compiler
10133 for each record or array type.
10135 The record representation clause for type r shows where all fields
10136 are placed, including the compiler generated tag field (whose location
10137 cannot be controlled by the programmer).
10139 The record representation clause for the type extension r2 shows all the
10140 fields present, including the parent field, which is a copy of the fields
10141 of the parent type of r2, i.e.@: r1.
10143 The component size and size clauses for types rb1 and rb2 show
10144 the exact effect of pragma @code{Pack} on these arrays, and the record
10145 representation clause for type x2 shows how pragma @code{Pack} affects
10148 In some cases, it may be useful to cut and paste the representation clauses
10149 generated by the compiler into the original source to fix and guarantee
10150 the actual representation to be used.
10152 @node Standard Library Routines
10153 @chapter Standard Library Routines
10156 The Ada 95 Reference Manual contains in Annex A a full description of an
10157 extensive set of standard library routines that can be used in any Ada
10158 program, and which must be provided by all Ada compilers. They are
10159 analogous to the standard C library used by C programs.
10161 GNAT implements all of the facilities described in annex A, and for most
10162 purposes the description in the Ada 95
10163 reference manual, or appropriate Ada
10164 text book, will be sufficient for making use of these facilities.
10166 In the case of the input-output facilities, @xref{The Implementation of
10167 Standard I/O}, gives details on exactly how GNAT interfaces to the
10168 file system. For the remaining packages, the Ada 95 reference manual
10169 should be sufficient. The following is a list of the packages included,
10170 together with a brief description of the functionality that is provided.
10172 For completeness, references are included to other predefined library
10173 routines defined in other sections of the Ada 95 reference manual (these are
10174 cross-indexed from annex A).
10178 This is a parent package for all the standard library packages. It is
10179 usually included implicitly in your program, and itself contains no
10180 useful data or routines.
10182 @item Ada.Calendar (9.6)
10183 @code{Calendar} provides time of day access, and routines for
10184 manipulating times and durations.
10186 @item Ada.Characters (A.3.1)
10187 This is a dummy parent package that contains no useful entities
10189 @item Ada.Characters.Handling (A.3.2)
10190 This package provides some basic character handling capabilities,
10191 including classification functions for classes of characters (e.g.@: test
10192 for letters, or digits).
10194 @item Ada.Characters.Latin_1 (A.3.3)
10195 This package includes a complete set of definitions of the characters
10196 that appear in type CHARACTER@. It is useful for writing programs that
10197 will run in international environments. For example, if you want an
10198 upper case E with an acute accent in a string, it is often better to use
10199 the definition of @code{UC_E_Acute} in this package. Then your program
10200 will print in an understandable manner even if your environment does not
10201 support these extended characters.
10203 @item Ada.Command_Line (A.15)
10204 This package provides access to the command line parameters and the name
10205 of the current program (analogous to the use of @code{argc} and @code{argv}
10206 in C), and also allows the exit status for the program to be set in a
10207 system-independent manner.
10209 @item Ada.Decimal (F.2)
10210 This package provides constants describing the range of decimal numbers
10211 implemented, and also a decimal divide routine (analogous to the COBOL
10212 verb DIVIDE .. GIVING .. REMAINDER ..)
10214 @item Ada.Direct_IO (A.8.4)
10215 This package provides input-output using a model of a set of records of
10216 fixed-length, containing an arbitrary definite Ada type, indexed by an
10217 integer record number.
10219 @item Ada.Dynamic_Priorities (D.5)
10220 This package allows the priorities of a task to be adjusted dynamically
10221 as the task is running.
10223 @item Ada.Exceptions (11.4.1)
10224 This package provides additional information on exceptions, and also
10225 contains facilities for treating exceptions as data objects, and raising
10226 exceptions with associated messages.
10228 @item Ada.Finalization (7.6)
10229 This package contains the declarations and subprograms to support the
10230 use of controlled types, providing for automatic initialization and
10231 finalization (analogous to the constructors and destructors of C++)
10233 @item Ada.Interrupts (C.3.2)
10234 This package provides facilities for interfacing to interrupts, which
10235 includes the set of signals or conditions that can be raised and
10236 recognized as interrupts.
10238 @item Ada.Interrupts.Names (C.3.2)
10239 This package provides the set of interrupt names (actually signal
10240 or condition names) that can be handled by GNAT@.
10242 @item Ada.IO_Exceptions (A.13)
10243 This package defines the set of exceptions that can be raised by use of
10244 the standard IO packages.
10247 This package contains some standard constants and exceptions used
10248 throughout the numerics packages. Note that the constants pi and e are
10249 defined here, and it is better to use these definitions than rolling
10252 @item Ada.Numerics.Complex_Elementary_Functions
10253 Provides the implementation of standard elementary functions (such as
10254 log and trigonometric functions) operating on complex numbers using the
10255 standard @code{Float} and the @code{Complex} and @code{Imaginary} types
10256 created by the package @code{Numerics.Complex_Types}.
10258 @item Ada.Numerics.Complex_Types
10259 This is a predefined instantiation of
10260 @code{Numerics.Generic_Complex_Types} using @code{Standard.Float} to
10261 build the type @code{Complex} and @code{Imaginary}.
10263 @item Ada.Numerics.Discrete_Random
10264 This package provides a random number generator suitable for generating
10265 random integer values from a specified range.
10267 @item Ada.Numerics.Float_Random
10268 This package provides a random number generator suitable for generating
10269 uniformly distributed floating point values.
10271 @item Ada.Numerics.Generic_Complex_Elementary_Functions
10272 This is a generic version of the package that provides the
10273 implementation of standard elementary functions (such as log and
10274 trigonometric functions) for an arbitrary complex type.
10276 The following predefined instantiations of this package are provided:
10280 @code{Ada.Numerics.Short_Complex_Elementary_Functions}
10282 @code{Ada.Numerics.Complex_Elementary_Functions}
10284 @code{Ada.Numerics.
10285 Long_Complex_Elementary_Functions}
10288 @item Ada.Numerics.Generic_Complex_Types
10289 This is a generic package that allows the creation of complex types,
10290 with associated complex arithmetic operations.
10292 The following predefined instantiations of this package exist
10295 @code{Ada.Numerics.Short_Complex_Complex_Types}
10297 @code{Ada.Numerics.Complex_Complex_Types}
10299 @code{Ada.Numerics.Long_Complex_Complex_Types}
10302 @item Ada.Numerics.Generic_Elementary_Functions
10303 This is a generic package that provides the implementation of standard
10304 elementary functions (such as log an trigonometric functions) for an
10305 arbitrary float type.
10307 The following predefined instantiations of this package exist
10311 @code{Ada.Numerics.Short_Elementary_Functions}
10313 @code{Ada.Numerics.Elementary_Functions}
10315 @code{Ada.Numerics.Long_Elementary_Functions}
10318 @item Ada.Real_Time (D.8)
10319 This package provides facilities similar to those of @code{Calendar}, but
10320 operating with a finer clock suitable for real time control. Note that
10321 annex D requires that there be no backward clock jumps, and GNAT generally
10322 guarantees this behavior, but of course if the external clock on which
10323 the GNAT runtime depends is deliberately reset by some external event,
10324 then such a backward jump may occur.
10326 @item Ada.Sequential_IO (A.8.1)
10327 This package provides input-output facilities for sequential files,
10328 which can contain a sequence of values of a single type, which can be
10329 any Ada type, including indefinite (unconstrained) types.
10331 @item Ada.Storage_IO (A.9)
10332 This package provides a facility for mapping arbitrary Ada types to and
10333 from a storage buffer. It is primarily intended for the creation of new
10336 @item Ada.Streams (13.13.1)
10337 This is a generic package that provides the basic support for the
10338 concept of streams as used by the stream attributes (@code{Input},
10339 @code{Output}, @code{Read} and @code{Write}).
10341 @item Ada.Streams.Stream_IO (A.12.1)
10342 This package is a specialization of the type @code{Streams} defined in
10343 package @code{Streams} together with a set of operations providing
10344 Stream_IO capability. The Stream_IO model permits both random and
10345 sequential access to a file which can contain an arbitrary set of values
10346 of one or more Ada types.
10348 @item Ada.Strings (A.4.1)
10349 This package provides some basic constants used by the string handling
10352 @item Ada.Strings.Bounded (A.4.4)
10353 This package provides facilities for handling variable length
10354 strings. The bounded model requires a maximum length. It is thus
10355 somewhat more limited than the unbounded model, but avoids the use of
10356 dynamic allocation or finalization.
10358 @item Ada.Strings.Fixed (A.4.3)
10359 This package provides facilities for handling fixed length strings.
10361 @item Ada.Strings.Maps (A.4.2)
10362 This package provides facilities for handling character mappings and
10363 arbitrarily defined subsets of characters. For instance it is useful in
10364 defining specialized translation tables.
10366 @item Ada.Strings.Maps.Constants (A.4.6)
10367 This package provides a standard set of predefined mappings and
10368 predefined character sets. For example, the standard upper to lower case
10369 conversion table is found in this package. Note that upper to lower case
10370 conversion is non-trivial if you want to take the entire set of
10371 characters, including extended characters like E with an acute accent,
10372 into account. You should use the mappings in this package (rather than
10373 adding 32 yourself) to do case mappings.
10375 @item Ada.Strings.Unbounded (A.4.5)
10376 This package provides facilities for handling variable length
10377 strings. The unbounded model allows arbitrary length strings, but
10378 requires the use of dynamic allocation and finalization.
10380 @item Ada.Strings.Wide_Bounded (A.4.7)
10381 @itemx Ada.Strings.Wide_Fixed (A.4.7)
10382 @itemx Ada.Strings.Wide_Maps (A.4.7)
10383 @itemx Ada.Strings.Wide_Maps.Constants (A.4.7)
10384 @itemx Ada.Strings.Wide_Unbounded (A.4.7)
10385 These packages provide analogous capabilities to the corresponding
10386 packages without @samp{Wide_} in the name, but operate with the types
10387 @code{Wide_String} and @code{Wide_Character} instead of @code{String}
10388 and @code{Character}.
10390 @item Ada.Strings.Wide_Wide_Bounded (A.4.7)
10391 @itemx Ada.Strings.Wide_Wide_Fixed (A.4.7)
10392 @itemx Ada.Strings.Wide_Wide_Maps (A.4.7)
10393 @itemx Ada.Strings.Wide_Wide_Maps.Constants (A.4.7)
10394 @itemx Ada.Strings.Wide_Wide_Unbounded (A.4.7)
10395 These packages provide analogous capabilities to the corresponding
10396 packages without @samp{Wide_} in the name, but operate with the types
10397 @code{Wide_Wide_String} and @code{Wide_Wide_Character} instead
10398 of @code{String} and @code{Character}.
10400 @item Ada.Synchronous_Task_Control (D.10)
10401 This package provides some standard facilities for controlling task
10402 communication in a synchronous manner.
10405 This package contains definitions for manipulation of the tags of tagged
10408 @item Ada.Task_Attributes
10409 This package provides the capability of associating arbitrary
10410 task-specific data with separate tasks.
10413 This package provides basic text input-output capabilities for
10414 character, string and numeric data. The subpackages of this
10415 package are listed next.
10417 @item Ada.Text_IO.Decimal_IO
10418 Provides input-output facilities for decimal fixed-point types
10420 @item Ada.Text_IO.Enumeration_IO
10421 Provides input-output facilities for enumeration types.
10423 @item Ada.Text_IO.Fixed_IO
10424 Provides input-output facilities for ordinary fixed-point types.
10426 @item Ada.Text_IO.Float_IO
10427 Provides input-output facilities for float types. The following
10428 predefined instantiations of this generic package are available:
10432 @code{Short_Float_Text_IO}
10434 @code{Float_Text_IO}
10436 @code{Long_Float_Text_IO}
10439 @item Ada.Text_IO.Integer_IO
10440 Provides input-output facilities for integer types. The following
10441 predefined instantiations of this generic package are available:
10444 @item Short_Short_Integer
10445 @code{Ada.Short_Short_Integer_Text_IO}
10446 @item Short_Integer
10447 @code{Ada.Short_Integer_Text_IO}
10449 @code{Ada.Integer_Text_IO}
10451 @code{Ada.Long_Integer_Text_IO}
10452 @item Long_Long_Integer
10453 @code{Ada.Long_Long_Integer_Text_IO}
10456 @item Ada.Text_IO.Modular_IO
10457 Provides input-output facilities for modular (unsigned) types
10459 @item Ada.Text_IO.Complex_IO (G.1.3)
10460 This package provides basic text input-output capabilities for complex
10463 @item Ada.Text_IO.Editing (F.3.3)
10464 This package contains routines for edited output, analogous to the use
10465 of pictures in COBOL@. The picture formats used by this package are a
10466 close copy of the facility in COBOL@.
10468 @item Ada.Text_IO.Text_Streams (A.12.2)
10469 This package provides a facility that allows Text_IO files to be treated
10470 as streams, so that the stream attributes can be used for writing
10471 arbitrary data, including binary data, to Text_IO files.
10473 @item Ada.Unchecked_Conversion (13.9)
10474 This generic package allows arbitrary conversion from one type to
10475 another of the same size, providing for breaking the type safety in
10476 special circumstances.
10478 If the types have the same Size (more accurately the same Value_Size),
10479 then the effect is simply to transfer the bits from the source to the
10480 target type without any modification. This usage is well defined, and
10481 for simple types whose representation is typically the same across
10482 all implementations, gives a portable method of performing such
10485 If the types do not have the same size, then the result is implementation
10486 defined, and thus may be non-portable. The following describes how GNAT
10487 handles such unchecked conversion cases.
10489 If the types are of different sizes, and are both discrete types, then
10490 the effect is of a normal type conversion without any constraint checking.
10491 In particular if the result type has a larger size, the result will be
10492 zero or sign extended. If the result type has a smaller size, the result
10493 will be truncated by ignoring high order bits.
10495 If the types are of different sizes, and are not both discrete types,
10496 then the conversion works as though pointers were created to the source
10497 and target, and the pointer value is converted. The effect is that bits
10498 are copied from successive low order storage units and bits of the source
10499 up to the length of the target type.
10501 A warning is issued if the lengths differ, since the effect in this
10502 case is implementation dependent, and the above behavior may not match
10503 that of some other compiler.
10505 A pointer to one type may be converted to a pointer to another type using
10506 unchecked conversion. The only case in which the effect is undefined is
10507 when one or both pointers are pointers to unconstrained array types. In
10508 this case, the bounds information may get incorrectly transferred, and in
10509 particular, GNAT uses double size pointers for such types, and it is
10510 meaningless to convert between such pointer types. GNAT will issue a
10511 warning if the alignment of the target designated type is more strict
10512 than the alignment of the source designated type (since the result may
10513 be unaligned in this case).
10515 A pointer other than a pointer to an unconstrained array type may be
10516 converted to and from System.Address. Such usage is common in Ada 83
10517 programs, but note that Ada.Address_To_Access_Conversions is the
10518 preferred method of performing such conversions in Ada 95. Neither
10519 unchecked conversion nor Ada.Address_To_Access_Conversions should be
10520 used in conjunction with pointers to unconstrained objects, since
10521 the bounds information cannot be handled correctly in this case.
10523 @item Ada.Unchecked_Deallocation (13.11.2)
10524 This generic package allows explicit freeing of storage previously
10525 allocated by use of an allocator.
10527 @item Ada.Wide_Text_IO (A.11)
10528 This package is similar to @code{Ada.Text_IO}, except that the external
10529 file supports wide character representations, and the internal types are
10530 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
10531 and @code{String}. It contains generic subpackages listed next.
10533 @item Ada.Wide_Text_IO.Decimal_IO
10534 Provides input-output facilities for decimal fixed-point types
10536 @item Ada.Wide_Text_IO.Enumeration_IO
10537 Provides input-output facilities for enumeration types.
10539 @item Ada.Wide_Text_IO.Fixed_IO
10540 Provides input-output facilities for ordinary fixed-point types.
10542 @item Ada.Wide_Text_IO.Float_IO
10543 Provides input-output facilities for float types. The following
10544 predefined instantiations of this generic package are available:
10548 @code{Short_Float_Wide_Text_IO}
10550 @code{Float_Wide_Text_IO}
10552 @code{Long_Float_Wide_Text_IO}
10555 @item Ada.Wide_Text_IO.Integer_IO
10556 Provides input-output facilities for integer types. The following
10557 predefined instantiations of this generic package are available:
10560 @item Short_Short_Integer
10561 @code{Ada.Short_Short_Integer_Wide_Text_IO}
10562 @item Short_Integer
10563 @code{Ada.Short_Integer_Wide_Text_IO}
10565 @code{Ada.Integer_Wide_Text_IO}
10567 @code{Ada.Long_Integer_Wide_Text_IO}
10568 @item Long_Long_Integer
10569 @code{Ada.Long_Long_Integer_Wide_Text_IO}
10572 @item Ada.Wide_Text_IO.Modular_IO
10573 Provides input-output facilities for modular (unsigned) types
10575 @item Ada.Wide_Text_IO.Complex_IO (G.1.3)
10576 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
10577 external file supports wide character representations.
10579 @item Ada.Wide_Text_IO.Editing (F.3.4)
10580 This package is similar to @code{Ada.Text_IO.Editing}, except that the
10581 types are @code{Wide_Character} and @code{Wide_String} instead of
10582 @code{Character} and @code{String}.
10584 @item Ada.Wide_Text_IO.Streams (A.12.3)
10585 This package is similar to @code{Ada.Text_IO.Streams}, except that the
10586 types are @code{Wide_Character} and @code{Wide_String} instead of
10587 @code{Character} and @code{String}.
10589 @item Ada.Wide_Wide_Text_IO (A.11)
10590 This package is similar to @code{Ada.Text_IO}, except that the external
10591 file supports wide character representations, and the internal types are
10592 @code{Wide_Character} and @code{Wide_String} instead of @code{Character}
10593 and @code{String}. It contains generic subpackages listed next.
10595 @item Ada.Wide_Wide_Text_IO.Decimal_IO
10596 Provides input-output facilities for decimal fixed-point types
10598 @item Ada.Wide_Wide_Text_IO.Enumeration_IO
10599 Provides input-output facilities for enumeration types.
10601 @item Ada.Wide_Wide_Text_IO.Fixed_IO
10602 Provides input-output facilities for ordinary fixed-point types.
10604 @item Ada.Wide_Wide_Text_IO.Float_IO
10605 Provides input-output facilities for float types. The following
10606 predefined instantiations of this generic package are available:
10610 @code{Short_Float_Wide_Wide_Text_IO}
10612 @code{Float_Wide_Wide_Text_IO}
10614 @code{Long_Float_Wide_Wide_Text_IO}
10617 @item Ada.Wide_Wide_Text_IO.Integer_IO
10618 Provides input-output facilities for integer types. The following
10619 predefined instantiations of this generic package are available:
10622 @item Short_Short_Integer
10623 @code{Ada.Short_Short_Integer_Wide_Wide_Text_IO}
10624 @item Short_Integer
10625 @code{Ada.Short_Integer_Wide_Wide_Text_IO}
10627 @code{Ada.Integer_Wide_Wide_Text_IO}
10629 @code{Ada.Long_Integer_Wide_Wide_Text_IO}
10630 @item Long_Long_Integer
10631 @code{Ada.Long_Long_Integer_Wide_Wide_Text_IO}
10634 @item Ada.Wide_Wide_Text_IO.Modular_IO
10635 Provides input-output facilities for modular (unsigned) types
10637 @item Ada.Wide_Wide_Text_IO.Complex_IO (G.1.3)
10638 This package is similar to @code{Ada.Text_IO.Complex_IO}, except that the
10639 external file supports wide character representations.
10641 @item Ada.Wide_Wide_Text_IO.Editing (F.3.4)
10642 This package is similar to @code{Ada.Text_IO.Editing}, except that the
10643 types are @code{Wide_Character} and @code{Wide_String} instead of
10644 @code{Character} and @code{String}.
10646 @item Ada.Wide_Wide_Text_IO.Streams (A.12.3)
10647 This package is similar to @code{Ada.Text_IO.Streams}, except that the
10648 types are @code{Wide_Character} and @code{Wide_String} instead of
10649 @code{Character} and @code{String}.
10654 @node The Implementation of Standard I/O
10655 @chapter The Implementation of Standard I/O
10658 GNAT implements all the required input-output facilities described in
10659 A.6 through A.14. These sections of the Ada 95 reference manual describe the
10660 required behavior of these packages from the Ada point of view, and if
10661 you are writing a portable Ada program that does not need to know the
10662 exact manner in which Ada maps to the outside world when it comes to
10663 reading or writing external files, then you do not need to read this
10664 chapter. As long as your files are all regular files (not pipes or
10665 devices), and as long as you write and read the files only from Ada, the
10666 description in the Ada 95 reference manual is sufficient.
10668 However, if you want to do input-output to pipes or other devices, such
10669 as the keyboard or screen, or if the files you are dealing with are
10670 either generated by some other language, or to be read by some other
10671 language, then you need to know more about the details of how the GNAT
10672 implementation of these input-output facilities behaves.
10674 In this chapter we give a detailed description of exactly how GNAT
10675 interfaces to the file system. As always, the sources of the system are
10676 available to you for answering questions at an even more detailed level,
10677 but for most purposes the information in this chapter will suffice.
10679 Another reason that you may need to know more about how input-output is
10680 implemented arises when you have a program written in mixed languages
10681 where, for example, files are shared between the C and Ada sections of
10682 the same program. GNAT provides some additional facilities, in the form
10683 of additional child library packages, that facilitate this sharing, and
10684 these additional facilities are also described in this chapter.
10687 * Standard I/O Packages::
10693 * Wide_Wide_Text_IO::
10697 * Operations on C Streams::
10698 * Interfacing to C Streams::
10701 @node Standard I/O Packages
10702 @section Standard I/O Packages
10705 The Standard I/O packages described in Annex A for
10711 Ada.Text_IO.Complex_IO
10713 Ada.Text_IO.Text_Streams
10717 Ada.Wide_Text_IO.Complex_IO
10719 Ada.Wide_Text_IO.Text_Streams
10721 Ada.Wide_Wide_Text_IO
10723 Ada.Wide_Wide_Text_IO.Complex_IO
10725 Ada.Wide_Wide_Text_IO.Text_Streams
10735 are implemented using the C
10736 library streams facility; where
10740 All files are opened using @code{fopen}.
10742 All input/output operations use @code{fread}/@code{fwrite}.
10746 There is no internal buffering of any kind at the Ada library level. The
10747 only buffering is that provided at the system level in the
10748 implementation of the C library routines that support streams. This
10749 facilitates shared use of these streams by mixed language programs.
10752 @section FORM Strings
10755 The format of a FORM string in GNAT is:
10758 "keyword=value,keyword=value,@dots{},keyword=value"
10762 where letters may be in upper or lower case, and there are no spaces
10763 between values. The order of the entries is not important. Currently
10764 there are two keywords defined.
10772 The use of these parameters is described later in this section.
10778 Direct_IO can only be instantiated for definite types. This is a
10779 restriction of the Ada language, which means that the records are fixed
10780 length (the length being determined by @code{@var{type}'Size}, rounded
10781 up to the next storage unit boundary if necessary).
10783 The records of a Direct_IO file are simply written to the file in index
10784 sequence, with the first record starting at offset zero, and subsequent
10785 records following. There is no control information of any kind. For
10786 example, if 32-bit integers are being written, each record takes
10787 4-bytes, so the record at index @var{K} starts at offset
10788 (@var{K}@minus{}1)*4.
10790 There is no limit on the size of Direct_IO files, they are expanded as
10791 necessary to accommodate whatever records are written to the file.
10793 @node Sequential_IO
10794 @section Sequential_IO
10797 Sequential_IO may be instantiated with either a definite (constrained)
10798 or indefinite (unconstrained) type.
10800 For the definite type case, the elements written to the file are simply
10801 the memory images of the data values with no control information of any
10802 kind. The resulting file should be read using the same type, no validity
10803 checking is performed on input.
10805 For the indefinite type case, the elements written consist of two
10806 parts. First is the size of the data item, written as the memory image
10807 of a @code{Interfaces.C.size_t} value, followed by the memory image of
10808 the data value. The resulting file can only be read using the same
10809 (unconstrained) type. Normal assignment checks are performed on these
10810 read operations, and if these checks fail, @code{Data_Error} is
10811 raised. In particular, in the array case, the lengths must match, and in
10812 the variant record case, if the variable for a particular read operation
10813 is constrained, the discriminants must match.
10815 Note that it is not possible to use Sequential_IO to write variable
10816 length array items, and then read the data back into different length
10817 arrays. For example, the following will raise @code{Data_Error}:
10819 @smallexample @c ada
10820 package IO is new Sequential_IO (String);
10825 IO.Write (F, "hello!")
10826 IO.Reset (F, Mode=>In_File);
10833 On some Ada implementations, this will print @code{hell}, but the program is
10834 clearly incorrect, since there is only one element in the file, and that
10835 element is the string @code{hello!}.
10837 In Ada 95, this kind of behavior can be legitimately achieved using
10838 Stream_IO, and this is the preferred mechanism. In particular, the above
10839 program fragment rewritten to use Stream_IO will work correctly.
10845 Text_IO files consist of a stream of characters containing the following
10846 special control characters:
10849 LF (line feed, 16#0A#) Line Mark
10850 FF (form feed, 16#0C#) Page Mark
10854 A canonical Text_IO file is defined as one in which the following
10855 conditions are met:
10859 The character @code{LF} is used only as a line mark, i.e.@: to mark the end
10863 The character @code{FF} is used only as a page mark, i.e.@: to mark the
10864 end of a page and consequently can appear only immediately following a
10865 @code{LF} (line mark) character.
10868 The file ends with either @code{LF} (line mark) or @code{LF}-@code{FF}
10869 (line mark, page mark). In the former case, the page mark is implicitly
10870 assumed to be present.
10874 A file written using Text_IO will be in canonical form provided that no
10875 explicit @code{LF} or @code{FF} characters are written using @code{Put}
10876 or @code{Put_Line}. There will be no @code{FF} character at the end of
10877 the file unless an explicit @code{New_Page} operation was performed
10878 before closing the file.
10880 A canonical Text_IO file that is a regular file, i.e.@: not a device or a
10881 pipe, can be read using any of the routines in Text_IO@. The
10882 semantics in this case will be exactly as defined in the Ada 95 reference
10883 manual and all the routines in Text_IO are fully implemented.
10885 A text file that does not meet the requirements for a canonical Text_IO
10886 file has one of the following:
10890 The file contains @code{FF} characters not immediately following a
10891 @code{LF} character.
10894 The file contains @code{LF} or @code{FF} characters written by
10895 @code{Put} or @code{Put_Line}, which are not logically considered to be
10896 line marks or page marks.
10899 The file ends in a character other than @code{LF} or @code{FF},
10900 i.e.@: there is no explicit line mark or page mark at the end of the file.
10904 Text_IO can be used to read such non-standard text files but subprograms
10905 to do with line or page numbers do not have defined meanings. In
10906 particular, a @code{FF} character that does not follow a @code{LF}
10907 character may or may not be treated as a page mark from the point of
10908 view of page and line numbering. Every @code{LF} character is considered
10909 to end a line, and there is an implied @code{LF} character at the end of
10913 * Text_IO Stream Pointer Positioning::
10914 * Text_IO Reading and Writing Non-Regular Files::
10916 * Treating Text_IO Files as Streams::
10917 * Text_IO Extensions::
10918 * Text_IO Facilities for Unbounded Strings::
10921 @node Text_IO Stream Pointer Positioning
10922 @subsection Stream Pointer Positioning
10925 @code{Ada.Text_IO} has a definition of current position for a file that
10926 is being read. No internal buffering occurs in Text_IO, and usually the
10927 physical position in the stream used to implement the file corresponds
10928 to this logical position defined by Text_IO@. There are two exceptions:
10932 After a call to @code{End_Of_Page} that returns @code{True}, the stream
10933 is positioned past the @code{LF} (line mark) that precedes the page
10934 mark. Text_IO maintains an internal flag so that subsequent read
10935 operations properly handle the logical position which is unchanged by
10936 the @code{End_Of_Page} call.
10939 After a call to @code{End_Of_File} that returns @code{True}, if the
10940 Text_IO file was positioned before the line mark at the end of file
10941 before the call, then the logical position is unchanged, but the stream
10942 is physically positioned right at the end of file (past the line mark,
10943 and past a possible page mark following the line mark. Again Text_IO
10944 maintains internal flags so that subsequent read operations properly
10945 handle the logical position.
10949 These discrepancies have no effect on the observable behavior of
10950 Text_IO, but if a single Ada stream is shared between a C program and
10951 Ada program, or shared (using @samp{shared=yes} in the form string)
10952 between two Ada files, then the difference may be observable in some
10955 @node Text_IO Reading and Writing Non-Regular Files
10956 @subsection Reading and Writing Non-Regular Files
10959 A non-regular file is a device (such as a keyboard), or a pipe. Text_IO
10960 can be used for reading and writing. Writing is not affected and the
10961 sequence of characters output is identical to the normal file case, but
10962 for reading, the behavior of Text_IO is modified to avoid undesirable
10963 look-ahead as follows:
10965 An input file that is not a regular file is considered to have no page
10966 marks. Any @code{Ascii.FF} characters (the character normally used for a
10967 page mark) appearing in the file are considered to be data
10968 characters. In particular:
10972 @code{Get_Line} and @code{Skip_Line} do not test for a page mark
10973 following a line mark. If a page mark appears, it will be treated as a
10977 This avoids the need to wait for an extra character to be typed or
10978 entered from the pipe to complete one of these operations.
10981 @code{End_Of_Page} always returns @code{False}
10984 @code{End_Of_File} will return @code{False} if there is a page mark at
10985 the end of the file.
10989 Output to non-regular files is the same as for regular files. Page marks
10990 may be written to non-regular files using @code{New_Page}, but as noted
10991 above they will not be treated as page marks on input if the output is
10992 piped to another Ada program.
10994 Another important discrepancy when reading non-regular files is that the end
10995 of file indication is not ``sticky''. If an end of file is entered, e.g.@: by
10996 pressing the @key{EOT} key,
10998 is signaled once (i.e.@: the test @code{End_Of_File}
10999 will yield @code{True}, or a read will
11000 raise @code{End_Error}), but then reading can resume
11001 to read data past that end of
11002 file indication, until another end of file indication is entered.
11004 @node Get_Immediate
11005 @subsection Get_Immediate
11006 @cindex Get_Immediate
11009 Get_Immediate returns the next character (including control characters)
11010 from the input file. In particular, Get_Immediate will return LF or FF
11011 characters used as line marks or page marks. Such operations leave the
11012 file positioned past the control character, and it is thus not treated
11013 as having its normal function. This means that page, line and column
11014 counts after this kind of Get_Immediate call are set as though the mark
11015 did not occur. In the case where a Get_Immediate leaves the file
11016 positioned between the line mark and page mark (which is not normally
11017 possible), it is undefined whether the FF character will be treated as a
11020 @node Treating Text_IO Files as Streams
11021 @subsection Treating Text_IO Files as Streams
11022 @cindex Stream files
11025 The package @code{Text_IO.Streams} allows a Text_IO file to be treated
11026 as a stream. Data written to a Text_IO file in this stream mode is
11027 binary data. If this binary data contains bytes 16#0A# (@code{LF}) or
11028 16#0C# (@code{FF}), the resulting file may have non-standard
11029 format. Similarly if read operations are used to read from a Text_IO
11030 file treated as a stream, then @code{LF} and @code{FF} characters may be
11031 skipped and the effect is similar to that described above for
11032 @code{Get_Immediate}.
11034 @node Text_IO Extensions
11035 @subsection Text_IO Extensions
11036 @cindex Text_IO extensions
11039 A package GNAT.IO_Aux in the GNAT library provides some useful extensions
11040 to the standard @code{Text_IO} package:
11043 @item function File_Exists (Name : String) return Boolean;
11044 Determines if a file of the given name exists.
11046 @item function Get_Line return String;
11047 Reads a string from the standard input file. The value returned is exactly
11048 the length of the line that was read.
11050 @item function Get_Line (File : Ada.Text_IO.File_Type) return String;
11051 Similar, except that the parameter File specifies the file from which
11052 the string is to be read.
11056 @node Text_IO Facilities for Unbounded Strings
11057 @subsection Text_IO Facilities for Unbounded Strings
11058 @cindex Text_IO for unbounded strings
11059 @cindex Unbounded_String, Text_IO operations
11062 The package @code{Ada.Strings.Unbounded.Text_IO}
11063 in library files @code{a-suteio.ads/adb} contains some GNAT-specific
11064 subprograms useful for Text_IO operations on unbounded strings:
11068 @item function Get_Line (File : File_Type) return Unbounded_String;
11069 Reads a line from the specified file
11070 and returns the result as an unbounded string.
11072 @item procedure Put (File : File_Type; U : Unbounded_String);
11073 Writes the value of the given unbounded string to the specified file
11074 Similar to the effect of
11075 @code{Put (To_String (U))} except that an extra copy is avoided.
11077 @item procedure Put_Line (File : File_Type; U : Unbounded_String);
11078 Writes the value of the given unbounded string to the specified file,
11079 followed by a @code{New_Line}.
11080 Similar to the effect of @code{Put_Line (To_String (U))} except
11081 that an extra copy is avoided.
11085 In the above procedures, @code{File} is of type @code{Ada.Text_IO.File_Type}
11086 and is optional. If the parameter is omitted, then the standard input or
11087 output file is referenced as appropriate.
11089 The package @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} in library
11090 files @file{a-swuwti.ads} and @file{a-swuwti.adb} provides similar extended
11091 @code{Wide_Text_IO} functionality for unbounded wide strings.
11093 The package @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} in library
11094 files @file{a-szuzti.ads} and @file{a-szuzti.adb} provides similar extended
11095 @code{Wide_Wide_Text_IO} functionality for unbounded wide wide strings.
11098 @section Wide_Text_IO
11101 @code{Wide_Text_IO} is similar in most respects to Text_IO, except that
11102 both input and output files may contain special sequences that represent
11103 wide character values. The encoding scheme for a given file may be
11104 specified using a FORM parameter:
11111 as part of the FORM string (WCEM = wide character encoding method),
11112 where @var{x} is one of the following characters
11118 Upper half encoding
11130 The encoding methods match those that
11131 can be used in a source
11132 program, but there is no requirement that the encoding method used for
11133 the source program be the same as the encoding method used for files,
11134 and different files may use different encoding methods.
11136 The default encoding method for the standard files, and for opened files
11137 for which no WCEM parameter is given in the FORM string matches the
11138 wide character encoding specified for the main program (the default
11139 being brackets encoding if no coding method was specified with -gnatW).
11143 In this encoding, a wide character is represented by a five character
11151 where @var{a}, @var{b}, @var{c}, @var{d} are the four hexadecimal
11152 characters (using upper case letters) of the wide character code. For
11153 example, ESC A345 is used to represent the wide character with code
11154 16#A345#. This scheme is compatible with use of the full
11155 @code{Wide_Character} set.
11157 @item Upper Half Coding
11158 The wide character with encoding 16#abcd#, where the upper bit is on
11159 (i.e.@: a is in the range 8-F) is represented as two bytes 16#ab# and
11160 16#cd#. The second byte may never be a format control character, but is
11161 not required to be in the upper half. This method can be also used for
11162 shift-JIS or EUC where the internal coding matches the external coding.
11164 @item Shift JIS Coding
11165 A wide character is represented by a two character sequence 16#ab# and
11166 16#cd#, with the restrictions described for upper half encoding as
11167 described above. The internal character code is the corresponding JIS
11168 character according to the standard algorithm for Shift-JIS
11169 conversion. Only characters defined in the JIS code set table can be
11170 used with this encoding method.
11173 A wide character is represented by a two character sequence 16#ab# and
11174 16#cd#, with both characters being in the upper half. The internal
11175 character code is the corresponding JIS character according to the EUC
11176 encoding algorithm. Only characters defined in the JIS code set table
11177 can be used with this encoding method.
11180 A wide character is represented using
11181 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
11182 10646-1/Am.2. Depending on the character value, the representation
11183 is a one, two, or three byte sequence:
11186 16#0000#-16#007f#: 2#0xxxxxxx#
11187 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
11188 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
11192 where the xxx bits correspond to the left-padded bits of the
11193 16-bit character value. Note that all lower half ASCII characters
11194 are represented as ASCII bytes and all upper half characters and
11195 other wide characters are represented as sequences of upper-half
11196 (The full UTF-8 scheme allows for encoding 31-bit characters as
11197 6-byte sequences, but in this implementation, all UTF-8 sequences
11198 of four or more bytes length will raise a Constraint_Error, as
11199 will all invalid UTF-8 sequences.)
11201 @item Brackets Coding
11202 In this encoding, a wide character is represented by the following eight
11203 character sequence:
11210 where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal
11211 characters (using uppercase letters) of the wide character code. For
11212 example, @code{["A345"]} is used to represent the wide character with code
11214 This scheme is compatible with use of the full Wide_Character set.
11215 On input, brackets coding can also be used for upper half characters,
11216 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
11217 is only used for wide characters with a code greater than @code{16#FF#}.
11222 For the coding schemes other than Hex and Brackets encoding,
11223 not all wide character
11224 values can be represented. An attempt to output a character that cannot
11225 be represented using the encoding scheme for the file causes
11226 Constraint_Error to be raised. An invalid wide character sequence on
11227 input also causes Constraint_Error to be raised.
11230 * Wide_Text_IO Stream Pointer Positioning::
11231 * Wide_Text_IO Reading and Writing Non-Regular Files::
11234 @node Wide_Text_IO Stream Pointer Positioning
11235 @subsection Stream Pointer Positioning
11238 @code{Ada.Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
11239 of stream pointer positioning (@pxref{Text_IO}). There is one additional
11242 If @code{Ada.Wide_Text_IO.Look_Ahead} reads a character outside the
11243 normal lower ASCII set (i.e.@: a character in the range:
11245 @smallexample @c ada
11246 Wide_Character'Val (16#0080#) .. Wide_Character'Val (16#FFFF#)
11250 then although the logical position of the file pointer is unchanged by
11251 the @code{Look_Ahead} call, the stream is physically positioned past the
11252 wide character sequence. Again this is to avoid the need for buffering
11253 or backup, and all @code{Wide_Text_IO} routines check the internal
11254 indication that this situation has occurred so that this is not visible
11255 to a normal program using @code{Wide_Text_IO}. However, this discrepancy
11256 can be observed if the wide text file shares a stream with another file.
11258 @node Wide_Text_IO Reading and Writing Non-Regular Files
11259 @subsection Reading and Writing Non-Regular Files
11262 As in the case of Text_IO, when a non-regular file is read, it is
11263 assumed that the file contains no page marks (any form characters are
11264 treated as data characters), and @code{End_Of_Page} always returns
11265 @code{False}. Similarly, the end of file indication is not sticky, so
11266 it is possible to read beyond an end of file.
11268 @node Wide_Wide_Text_IO
11269 @section Wide_Wide_Text_IO
11272 @code{Wide_Wide_Text_IO} is similar in most respects to Text_IO, except that
11273 both input and output files may contain special sequences that represent
11274 wide wide character values. The encoding scheme for a given file may be
11275 specified using a FORM parameter:
11282 as part of the FORM string (WCEM = wide character encoding method),
11283 where @var{x} is one of the following characters
11289 Upper half encoding
11301 The encoding methods match those that
11302 can be used in a source
11303 program, but there is no requirement that the encoding method used for
11304 the source program be the same as the encoding method used for files,
11305 and different files may use different encoding methods.
11307 The default encoding method for the standard files, and for opened files
11308 for which no WCEM parameter is given in the FORM string matches the
11309 wide character encoding specified for the main program (the default
11310 being brackets encoding if no coding method was specified with -gnatW).
11315 A wide character is represented using
11316 UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
11317 10646-1/Am.2. Depending on the character value, the representation
11318 is a one, two, three, or four byte sequence:
11321 16#000000#-16#00007f#: 2#0xxxxxxx#
11322 16#000080#-16#0007ff#: 2#110xxxxx# 2#10xxxxxx#
11323 16#000800#-16#00ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
11324 16#010000#-16#10ffff#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
11328 where the xxx bits correspond to the left-padded bits of the
11329 21-bit character value. Note that all lower half ASCII characters
11330 are represented as ASCII bytes and all upper half characters and
11331 other wide characters are represented as sequences of upper-half
11334 @item Brackets Coding
11335 In this encoding, a wide wide character is represented by the following eight
11336 character sequence if is in wide character range
11342 and by the following ten character sequence if not
11345 [ " a b c d e f " ]
11349 where @code{a}, @code{b}, @code{c}, @code{d}, @code{e}, and @code{f}
11350 are the four or six hexadecimal
11351 characters (using uppercase letters) of the wide wide character code. For
11352 example, @code{["01A345"]} is used to represent the wide wide character
11353 with code @code{16#01A345#}.
11355 This scheme is compatible with use of the full Wide_Wide_Character set.
11356 On input, brackets coding can also be used for upper half characters,
11357 e.g.@: @code{["C1"]} for lower case a. However, on output, brackets notation
11358 is only used for wide characters with a code greater than @code{16#FF#}.
11363 If is also possible to use the other Wide_Character encoding methods,
11364 such as Shift-JIS, but the other schemes cannot support the full range
11365 of wide wide characters.
11366 An attempt to output a character that cannot
11367 be represented using the encoding scheme for the file causes
11368 Constraint_Error to be raised. An invalid wide character sequence on
11369 input also causes Constraint_Error to be raised.
11372 * Wide_Wide_Text_IO Stream Pointer Positioning::
11373 * Wide_Wide_Text_IO Reading and Writing Non-Regular Files::
11376 @node Wide_Wide_Text_IO Stream Pointer Positioning
11377 @subsection Stream Pointer Positioning
11380 @code{Ada.Wide_Wide_Text_IO} is similar to @code{Ada.Text_IO} in its handling
11381 of stream pointer positioning (@pxref{Text_IO}). There is one additional
11384 If @code{Ada.Wide_Wide_Text_IO.Look_Ahead} reads a character outside the
11385 normal lower ASCII set (i.e.@: a character in the range:
11387 @smallexample @c ada
11388 Wide_Wide_Character'Val (16#0080#) .. Wide_Wide_Character'Val (16#10FFFF#)
11392 then although the logical position of the file pointer is unchanged by
11393 the @code{Look_Ahead} call, the stream is physically positioned past the
11394 wide character sequence. Again this is to avoid the need for buffering
11395 or backup, and all @code{Wide_Wide_Text_IO} routines check the internal
11396 indication that this situation has occurred so that this is not visible
11397 to a normal program using @code{Wide_Wide_Text_IO}. However, this discrepancy
11398 can be observed if the wide text file shares a stream with another file.
11400 @node Wide_Wide_Text_IO Reading and Writing Non-Regular Files
11401 @subsection Reading and Writing Non-Regular Files
11404 As in the case of Text_IO, when a non-regular file is read, it is
11405 assumed that the file contains no page marks (any form characters are
11406 treated as data characters), and @code{End_Of_Page} always returns
11407 @code{False}. Similarly, the end of file indication is not sticky, so
11408 it is possible to read beyond an end of file.
11414 A stream file is a sequence of bytes, where individual elements are
11415 written to the file as described in the Ada 95 reference manual. The type
11416 @code{Stream_Element} is simply a byte. There are two ways to read or
11417 write a stream file.
11421 The operations @code{Read} and @code{Write} directly read or write a
11422 sequence of stream elements with no control information.
11425 The stream attributes applied to a stream file transfer data in the
11426 manner described for stream attributes.
11430 @section Shared Files
11433 Section A.14 of the Ada 95 Reference Manual allows implementations to
11434 provide a wide variety of behavior if an attempt is made to access the
11435 same external file with two or more internal files.
11437 To provide a full range of functionality, while at the same time
11438 minimizing the problems of portability caused by this implementation
11439 dependence, GNAT handles file sharing as follows:
11443 In the absence of a @samp{shared=@var{xxx}} form parameter, an attempt
11444 to open two or more files with the same full name is considered an error
11445 and is not supported. The exception @code{Use_Error} will be
11446 raised. Note that a file that is not explicitly closed by the program
11447 remains open until the program terminates.
11450 If the form parameter @samp{shared=no} appears in the form string, the
11451 file can be opened or created with its own separate stream identifier,
11452 regardless of whether other files sharing the same external file are
11453 opened. The exact effect depends on how the C stream routines handle
11454 multiple accesses to the same external files using separate streams.
11457 If the form parameter @samp{shared=yes} appears in the form string for
11458 each of two or more files opened using the same full name, the same
11459 stream is shared between these files, and the semantics are as described
11460 in Ada 95 Reference Manual, Section A.14.
11464 When a program that opens multiple files with the same name is ported
11465 from another Ada compiler to GNAT, the effect will be that
11466 @code{Use_Error} is raised.
11468 The documentation of the original compiler and the documentation of the
11469 program should then be examined to determine if file sharing was
11470 expected, and @samp{shared=@var{xxx}} parameters added to @code{Open}
11471 and @code{Create} calls as required.
11473 When a program is ported from GNAT to some other Ada compiler, no
11474 special attention is required unless the @samp{shared=@var{xxx}} form
11475 parameter is used in the program. In this case, you must examine the
11476 documentation of the new compiler to see if it supports the required
11477 file sharing semantics, and form strings modified appropriately. Of
11478 course it may be the case that the program cannot be ported if the
11479 target compiler does not support the required functionality. The best
11480 approach in writing portable code is to avoid file sharing (and hence
11481 the use of the @samp{shared=@var{xxx}} parameter in the form string)
11484 One common use of file sharing in Ada 83 is the use of instantiations of
11485 Sequential_IO on the same file with different types, to achieve
11486 heterogeneous input-output. Although this approach will work in GNAT if
11487 @samp{shared=yes} is specified, it is preferable in Ada 95 to use Stream_IO
11488 for this purpose (using the stream attributes)
11491 @section Open Modes
11494 @code{Open} and @code{Create} calls result in a call to @code{fopen}
11495 using the mode shown in the following table:
11498 @center @code{Open} and @code{Create} Call Modes
11500 @b{OPEN } @b{CREATE}
11501 Append_File "r+" "w+"
11503 Out_File (Direct_IO) "r+" "w"
11504 Out_File (all other cases) "w" "w"
11505 Inout_File "r+" "w+"
11509 If text file translation is required, then either @samp{b} or @samp{t}
11510 is added to the mode, depending on the setting of Text. Text file
11511 translation refers to the mapping of CR/LF sequences in an external file
11512 to LF characters internally. This mapping only occurs in DOS and
11513 DOS-like systems, and is not relevant to other systems.
11515 A special case occurs with Stream_IO@. As shown in the above table, the
11516 file is initially opened in @samp{r} or @samp{w} mode for the
11517 @code{In_File} and @code{Out_File} cases. If a @code{Set_Mode} operation
11518 subsequently requires switching from reading to writing or vice-versa,
11519 then the file is reopened in @samp{r+} mode to permit the required operation.
11521 @node Operations on C Streams
11522 @section Operations on C Streams
11523 The package @code{Interfaces.C_Streams} provides an Ada program with direct
11524 access to the C library functions for operations on C streams:
11526 @smallexample @c adanocomment
11527 package Interfaces.C_Streams is
11528 -- Note: the reason we do not use the types that are in
11529 -- Interfaces.C is that we want to avoid dragging in the
11530 -- code in this unit if possible.
11531 subtype chars is System.Address;
11532 -- Pointer to null-terminated array of characters
11533 subtype FILEs is System.Address;
11534 -- Corresponds to the C type FILE*
11535 subtype voids is System.Address;
11536 -- Corresponds to the C type void*
11537 subtype int is Integer;
11538 subtype long is Long_Integer;
11539 -- Note: the above types are subtypes deliberately, and it
11540 -- is part of this spec that the above correspondences are
11541 -- guaranteed. This means that it is legitimate to, for
11542 -- example, use Integer instead of int. We provide these
11543 -- synonyms for clarity, but in some cases it may be
11544 -- convenient to use the underlying types (for example to
11545 -- avoid an unnecessary dependency of a spec on the spec
11547 type size_t is mod 2 ** Standard'Address_Size;
11548 NULL_Stream : constant FILEs;
11549 -- Value returned (NULL in C) to indicate an
11550 -- fdopen/fopen/tmpfile error
11551 ----------------------------------
11552 -- Constants Defined in stdio.h --
11553 ----------------------------------
11554 EOF : constant int;
11555 -- Used by a number of routines to indicate error or
11557 IOFBF : constant int;
11558 IOLBF : constant int;
11559 IONBF : constant int;
11560 -- Used to indicate buffering mode for setvbuf call
11561 SEEK_CUR : constant int;
11562 SEEK_END : constant int;
11563 SEEK_SET : constant int;
11564 -- Used to indicate origin for fseek call
11565 function stdin return FILEs;
11566 function stdout return FILEs;
11567 function stderr return FILEs;
11568 -- Streams associated with standard files
11569 --------------------------
11570 -- Standard C functions --
11571 --------------------------
11572 -- The functions selected below are ones that are
11573 -- available in DOS, OS/2, UNIX and Xenix (but not
11574 -- necessarily in ANSI C). These are very thin interfaces
11575 -- which copy exactly the C headers. For more
11576 -- documentation on these functions, see the Microsoft C
11577 -- "Run-Time Library Reference" (Microsoft Press, 1990,
11578 -- ISBN 1-55615-225-6), which includes useful information
11579 -- on system compatibility.
11580 procedure clearerr (stream : FILEs);
11581 function fclose (stream : FILEs) return int;
11582 function fdopen (handle : int; mode : chars) return FILEs;
11583 function feof (stream : FILEs) return int;
11584 function ferror (stream : FILEs) return int;
11585 function fflush (stream : FILEs) return int;
11586 function fgetc (stream : FILEs) return int;
11587 function fgets (strng : chars; n : int; stream : FILEs)
11589 function fileno (stream : FILEs) return int;
11590 function fopen (filename : chars; Mode : chars)
11592 -- Note: to maintain target independence, use
11593 -- text_translation_required, a boolean variable defined in
11594 -- a-sysdep.c to deal with the target dependent text
11595 -- translation requirement. If this variable is set,
11596 -- then b/t should be appended to the standard mode
11597 -- argument to set the text translation mode off or on
11599 function fputc (C : int; stream : FILEs) return int;
11600 function fputs (Strng : chars; Stream : FILEs) return int;
11617 function ftell (stream : FILEs) return long;
11624 function isatty (handle : int) return int;
11625 procedure mktemp (template : chars);
11626 -- The return value (which is just a pointer to template)
11628 procedure rewind (stream : FILEs);
11629 function rmtmp return int;
11637 function tmpfile return FILEs;
11638 function ungetc (c : int; stream : FILEs) return int;
11639 function unlink (filename : chars) return int;
11640 ---------------------
11641 -- Extra functions --
11642 ---------------------
11643 -- These functions supply slightly thicker bindings than
11644 -- those above. They are derived from functions in the
11645 -- C Run-Time Library, but may do a bit more work than
11646 -- just directly calling one of the Library functions.
11647 function is_regular_file (handle : int) return int;
11648 -- Tests if given handle is for a regular file (result 1)
11649 -- or for a non-regular file (pipe or device, result 0).
11650 ---------------------------------
11651 -- Control of Text/Binary Mode --
11652 ---------------------------------
11653 -- If text_translation_required is true, then the following
11654 -- functions may be used to dynamically switch a file from
11655 -- binary to text mode or vice versa. These functions have
11656 -- no effect if text_translation_required is false (i.e. in
11657 -- normal UNIX mode). Use fileno to get a stream handle.
11658 procedure set_binary_mode (handle : int);
11659 procedure set_text_mode (handle : int);
11660 ----------------------------
11661 -- Full Path Name support --
11662 ----------------------------
11663 procedure full_name (nam : chars; buffer : chars);
11664 -- Given a NUL terminated string representing a file
11665 -- name, returns in buffer a NUL terminated string
11666 -- representing the full path name for the file name.
11667 -- On systems where it is relevant the drive is also
11668 -- part of the full path name. It is the responsibility
11669 -- of the caller to pass an actual parameter for buffer
11670 -- that is big enough for any full path name. Use
11671 -- max_path_len given below as the size of buffer.
11672 max_path_len : integer;
11673 -- Maximum length of an allowable full path name on the
11674 -- system, including a terminating NUL character.
11675 end Interfaces.C_Streams;
11678 @node Interfacing to C Streams
11679 @section Interfacing to C Streams
11682 The packages in this section permit interfacing Ada files to C Stream
11685 @smallexample @c ada
11686 with Interfaces.C_Streams;
11687 package Ada.Sequential_IO.C_Streams is
11688 function C_Stream (F : File_Type)
11689 return Interfaces.C_Streams.FILEs;
11691 (File : in out File_Type;
11692 Mode : in File_Mode;
11693 C_Stream : in Interfaces.C_Streams.FILEs;
11694 Form : in String := "");
11695 end Ada.Sequential_IO.C_Streams;
11697 with Interfaces.C_Streams;
11698 package Ada.Direct_IO.C_Streams is
11699 function C_Stream (F : File_Type)
11700 return Interfaces.C_Streams.FILEs;
11702 (File : in out File_Type;
11703 Mode : in File_Mode;
11704 C_Stream : in Interfaces.C_Streams.FILEs;
11705 Form : in String := "");
11706 end Ada.Direct_IO.C_Streams;
11708 with Interfaces.C_Streams;
11709 package Ada.Text_IO.C_Streams is
11710 function C_Stream (F : File_Type)
11711 return Interfaces.C_Streams.FILEs;
11713 (File : in out File_Type;
11714 Mode : in File_Mode;
11715 C_Stream : in Interfaces.C_Streams.FILEs;
11716 Form : in String := "");
11717 end Ada.Text_IO.C_Streams;
11719 with Interfaces.C_Streams;
11720 package Ada.Wide_Text_IO.C_Streams is
11721 function C_Stream (F : File_Type)
11722 return Interfaces.C_Streams.FILEs;
11724 (File : in out File_Type;
11725 Mode : in File_Mode;
11726 C_Stream : in Interfaces.C_Streams.FILEs;
11727 Form : in String := "");
11728 end Ada.Wide_Text_IO.C_Streams;
11730 with Interfaces.C_Streams;
11731 package Ada.Wide_Wide_Text_IO.C_Streams is
11732 function C_Stream (F : File_Type)
11733 return Interfaces.C_Streams.FILEs;
11735 (File : in out File_Type;
11736 Mode : in File_Mode;
11737 C_Stream : in Interfaces.C_Streams.FILEs;
11738 Form : in String := "");
11739 end Ada.Wide_Wide_Text_IO.C_Streams;
11741 with Interfaces.C_Streams;
11742 package Ada.Stream_IO.C_Streams is
11743 function C_Stream (F : File_Type)
11744 return Interfaces.C_Streams.FILEs;
11746 (File : in out File_Type;
11747 Mode : in File_Mode;
11748 C_Stream : in Interfaces.C_Streams.FILEs;
11749 Form : in String := "");
11750 end Ada.Stream_IO.C_Streams;
11754 In each of these six packages, the @code{C_Stream} function obtains the
11755 @code{FILE} pointer from a currently opened Ada file. It is then
11756 possible to use the @code{Interfaces.C_Streams} package to operate on
11757 this stream, or the stream can be passed to a C program which can
11758 operate on it directly. Of course the program is responsible for
11759 ensuring that only appropriate sequences of operations are executed.
11761 One particular use of relevance to an Ada program is that the
11762 @code{setvbuf} function can be used to control the buffering of the
11763 stream used by an Ada file. In the absence of such a call the standard
11764 default buffering is used.
11766 The @code{Open} procedures in these packages open a file giving an
11767 existing C Stream instead of a file name. Typically this stream is
11768 imported from a C program, allowing an Ada file to operate on an
11771 @node The GNAT Library
11772 @chapter The GNAT Library
11775 The GNAT library contains a number of general and special purpose packages.
11776 It represents functionality that the GNAT developers have found useful, and
11777 which is made available to GNAT users. The packages described here are fully
11778 supported, and upwards compatibility will be maintained in future releases,
11779 so you can use these facilities with the confidence that the same functionality
11780 will be available in future releases.
11782 The chapter here simply gives a brief summary of the facilities available.
11783 The full documentation is found in the spec file for the package. The full
11784 sources of these library packages, including both spec and body, are provided
11785 with all GNAT releases. For example, to find out the full specifications of
11786 the SPITBOL pattern matching capability, including a full tutorial and
11787 extensive examples, look in the @file{g-spipat.ads} file in the library.
11789 For each entry here, the package name (as it would appear in a @code{with}
11790 clause) is given, followed by the name of the corresponding spec file in
11791 parentheses. The packages are children in four hierarchies, @code{Ada},
11792 @code{Interfaces}, @code{System}, and @code{GNAT}, the latter being a
11793 GNAT-specific hierarchy.
11795 Note that an application program should only use packages in one of these
11796 four hierarchies if the package is defined in the Ada Reference Manual,
11797 or is listed in this section of the GNAT Programmers Reference Manual.
11798 All other units should be considered internal implementation units and
11799 should not be directly @code{with}'ed by application code. The use of
11800 a @code{with} statement that references one of these internal implementation
11801 units makes an application potentially dependent on changes in versions
11802 of GNAT, and will generate a warning message.
11805 * Ada.Characters.Latin_9 (a-chlat9.ads)::
11806 * Ada.Characters.Wide_Latin_1 (a-cwila1.ads)::
11807 * Ada.Characters.Wide_Latin_9 (a-cwila9.ads)::
11808 * Ada.Characters.Wide_Wide_Latin_1 (a-czila1.ads)::
11809 * Ada.Characters.Wide_Wide_Latin_9 (a-czila9.ads)::
11810 * Ada.Command_Line.Remove (a-colire.ads)::
11811 * Ada.Command_Line.Environment (a-colien.ads)::
11812 * Ada.Direct_IO.C_Streams (a-diocst.ads)::
11813 * Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)::
11814 * Ada.Exceptions.Traceback (a-exctra.ads)::
11815 * Ada.Sequential_IO.C_Streams (a-siocst.ads)::
11816 * Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)::
11817 * Ada.Strings.Unbounded.Text_IO (a-suteio.ads)::
11818 * Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)::
11819 * Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)::
11820 * Ada.Text_IO.C_Streams (a-tiocst.ads)::
11821 * Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)::
11822 * Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)::
11823 * GNAT.Array_Split (g-arrspl.ads)::
11824 * GNAT.AWK (g-awk.ads)::
11825 * GNAT.Bounded_Buffers (g-boubuf.ads)::
11826 * GNAT.Bounded_Mailboxes (g-boumai.ads)::
11827 * GNAT.Bubble_Sort (g-bubsor.ads)::
11828 * GNAT.Bubble_Sort_A (g-busora.ads)::
11829 * GNAT.Bubble_Sort_G (g-busorg.ads)::
11830 * GNAT.Calendar (g-calend.ads)::
11831 * GNAT.Calendar.Time_IO (g-catiio.ads)::
11832 * GNAT.CRC32 (g-crc32.ads)::
11833 * GNAT.Case_Util (g-casuti.ads)::
11834 * GNAT.CGI (g-cgi.ads)::
11835 * GNAT.CGI.Cookie (g-cgicoo.ads)::
11836 * GNAT.CGI.Debug (g-cgideb.ads)::
11837 * GNAT.Command_Line (g-comlin.ads)::
11838 * GNAT.Compiler_Version (g-comver.ads)::
11839 * GNAT.Ctrl_C (g-ctrl_c.ads)::
11840 * GNAT.Current_Exception (g-curexc.ads)::
11841 * GNAT.Debug_Pools (g-debpoo.ads)::
11842 * GNAT.Debug_Utilities (g-debuti.ads)::
11843 * GNAT.Directory_Operations (g-dirope.ads)::
11844 * GNAT.Dynamic_HTables (g-dynhta.ads)::
11845 * GNAT.Dynamic_Tables (g-dyntab.ads)::
11846 * GNAT.Exception_Actions (g-excact.ads)::
11847 * GNAT.Exception_Traces (g-exctra.ads)::
11848 * GNAT.Exceptions (g-except.ads)::
11849 * GNAT.Expect (g-expect.ads)::
11850 * GNAT.Float_Control (g-flocon.ads)::
11851 * GNAT.Heap_Sort (g-heasor.ads)::
11852 * GNAT.Heap_Sort_A (g-hesora.ads)::
11853 * GNAT.Heap_Sort_G (g-hesorg.ads)::
11854 * GNAT.HTable (g-htable.ads)::
11855 * GNAT.IO (g-io.ads)::
11856 * GNAT.IO_Aux (g-io_aux.ads)::
11857 * GNAT.Lock_Files (g-locfil.ads)::
11858 * GNAT.MD5 (g-md5.ads)::
11859 * GNAT.Memory_Dump (g-memdum.ads)::
11860 * GNAT.Most_Recent_Exception (g-moreex.ads)::
11861 * GNAT.OS_Lib (g-os_lib.ads)::
11862 * GNAT.Perfect_Hash_Generators (g-pehage.ads)::
11863 * GNAT.Regexp (g-regexp.ads)::
11864 * GNAT.Registry (g-regist.ads)::
11865 * GNAT.Regpat (g-regpat.ads)::
11866 * GNAT.Secondary_Stack_Info (g-sestin.ads)::
11867 * GNAT.Semaphores (g-semaph.ads)::
11868 * GNAT.Signals (g-signal.ads)::
11869 * GNAT.Sockets (g-socket.ads)::
11870 * GNAT.Source_Info (g-souinf.ads)::
11871 * GNAT.Spell_Checker (g-speche.ads)::
11872 * GNAT.Spitbol.Patterns (g-spipat.ads)::
11873 * GNAT.Spitbol (g-spitbo.ads)::
11874 * GNAT.Spitbol.Table_Boolean (g-sptabo.ads)::
11875 * GNAT.Spitbol.Table_Integer (g-sptain.ads)::
11876 * GNAT.Spitbol.Table_VString (g-sptavs.ads)::
11877 * GNAT.Strings (g-string.ads)::
11878 * GNAT.String_Split (g-strspl.ads)::
11879 * GNAT.UTF_32 (g-utf_32.ads)::
11880 * GNAT.Table (g-table.ads)::
11881 * GNAT.Task_Lock (g-tasloc.ads)::
11882 * GNAT.Threads (g-thread.ads)::
11883 * GNAT.Traceback (g-traceb.ads)::
11884 * GNAT.Traceback.Symbolic (g-trasym.ads)::
11885 * GNAT.Wide_String_Split (g-wistsp.ads)::
11886 * GNAT.Wide_Wide_String_Split (g-zistsp.ads)::
11887 * Interfaces.C.Extensions (i-cexten.ads)::
11888 * Interfaces.C.Streams (i-cstrea.ads)::
11889 * Interfaces.CPP (i-cpp.ads)::
11890 * Interfaces.Os2lib (i-os2lib.ads)::
11891 * Interfaces.Os2lib.Errors (i-os2err.ads)::
11892 * Interfaces.Os2lib.Synchronization (i-os2syn.ads)::
11893 * Interfaces.Os2lib.Threads (i-os2thr.ads)::
11894 * Interfaces.Packed_Decimal (i-pacdec.ads)::
11895 * Interfaces.VxWorks (i-vxwork.ads)::
11896 * Interfaces.VxWorks.IO (i-vxwoio.ads)::
11897 * System.Address_Image (s-addima.ads)::
11898 * System.Assertions (s-assert.ads)::
11899 * System.Memory (s-memory.ads)::
11900 * System.Partition_Interface (s-parint.ads)::
11901 * System.Restrictions (s-restri.ads)::
11902 * System.Rident (s-rident.ads)::
11903 * System.Task_Info (s-tasinf.ads)::
11904 * System.Wch_Cnv (s-wchcnv.ads)::
11905 * System.Wch_Con (s-wchcon.ads)::
11908 @node Ada.Characters.Latin_9 (a-chlat9.ads)
11909 @section @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
11910 @cindex @code{Ada.Characters.Latin_9} (@file{a-chlat9.ads})
11911 @cindex Latin_9 constants for Character
11914 This child of @code{Ada.Characters}
11915 provides a set of definitions corresponding to those in the
11916 RM-defined package @code{Ada.Characters.Latin_1} but with the
11917 few modifications required for @code{Latin-9}
11918 The provision of such a package
11919 is specifically authorized by the Ada Reference Manual
11922 @node Ada.Characters.Wide_Latin_1 (a-cwila1.ads)
11923 @section @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
11924 @cindex @code{Ada.Characters.Wide_Latin_1} (@file{a-cwila1.ads})
11925 @cindex Latin_1 constants for Wide_Character
11928 This child of @code{Ada.Characters}
11929 provides a set of definitions corresponding to those in the
11930 RM-defined package @code{Ada.Characters.Latin_1} but with the
11931 types of the constants being @code{Wide_Character}
11932 instead of @code{Character}. The provision of such a package
11933 is specifically authorized by the Ada Reference Manual
11936 @node Ada.Characters.Wide_Latin_9 (a-cwila9.ads)
11937 @section @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
11938 @cindex @code{Ada.Characters.Wide_Latin_9} (@file{a-cwila1.ads})
11939 @cindex Latin_9 constants for Wide_Character
11942 This child of @code{Ada.Characters}
11943 provides a set of definitions corresponding to those in the
11944 GNAT defined package @code{Ada.Characters.Latin_9} but with the
11945 types of the constants being @code{Wide_Character}
11946 instead of @code{Character}. The provision of such a package
11947 is specifically authorized by the Ada Reference Manual
11950 @node Ada.Characters.Wide_Wide_Latin_1 (a-czila1.ads)
11951 @section @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-czila1.ads})
11952 @cindex @code{Ada.Characters.Wide_Wide_Latin_1} (@file{a-czila1.ads})
11953 @cindex Latin_1 constants for Wide_Wide_Character
11956 This child of @code{Ada.Characters}
11957 provides a set of definitions corresponding to those in the
11958 RM-defined package @code{Ada.Characters.Latin_1} but with the
11959 types of the constants being @code{Wide_Wide_Character}
11960 instead of @code{Character}. The provision of such a package
11961 is specifically authorized by the Ada Reference Manual
11964 @node Ada.Characters.Wide_Wide_Latin_9 (a-czila9.ads)
11965 @section @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-czila9.ads})
11966 @cindex @code{Ada.Characters.Wide_Wide_Latin_9} (@file{a-czila9.ads})
11967 @cindex Latin_9 constants for Wide_Wide_Character
11970 This child of @code{Ada.Characters}
11971 provides a set of definitions corresponding to those in the
11972 GNAT defined package @code{Ada.Characters.Latin_9} but with the
11973 types of the constants being @code{Wide_Wide_Character}
11974 instead of @code{Character}. The provision of such a package
11975 is specifically authorized by the Ada Reference Manual
11978 @node Ada.Command_Line.Remove (a-colire.ads)
11979 @section @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
11980 @cindex @code{Ada.Command_Line.Remove} (@file{a-colire.ads})
11981 @cindex Removing command line arguments
11982 @cindex Command line, argument removal
11985 This child of @code{Ada.Command_Line}
11986 provides a mechanism for logically removing
11987 arguments from the argument list. Once removed, an argument is not visible
11988 to further calls on the subprograms in @code{Ada.Command_Line} will not
11989 see the removed argument.
11991 @node Ada.Command_Line.Environment (a-colien.ads)
11992 @section @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
11993 @cindex @code{Ada.Command_Line.Environment} (@file{a-colien.ads})
11994 @cindex Environment entries
11997 This child of @code{Ada.Command_Line}
11998 provides a mechanism for obtaining environment values on systems
11999 where this concept makes sense.
12001 @node Ada.Direct_IO.C_Streams (a-diocst.ads)
12002 @section @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
12003 @cindex @code{Ada.Direct_IO.C_Streams} (@file{a-diocst.ads})
12004 @cindex C Streams, Interfacing with Direct_IO
12007 This package provides subprograms that allow interfacing between
12008 C streams and @code{Direct_IO}. The stream identifier can be
12009 extracted from a file opened on the Ada side, and an Ada file
12010 can be constructed from a stream opened on the C side.
12012 @node Ada.Exceptions.Is_Null_Occurrence (a-einuoc.ads)
12013 @section @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
12014 @cindex @code{Ada.Exceptions.Is_Null_Occurrence} (@file{a-einuoc.ads})
12015 @cindex Null_Occurrence, testing for
12018 This child subprogram provides a way of testing for the null
12019 exception occurrence (@code{Null_Occurrence}) without raising
12022 @node Ada.Exceptions.Traceback (a-exctra.ads)
12023 @section @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
12024 @cindex @code{Ada.Exceptions.Traceback} (@file{a-exctra.ads})
12025 @cindex Traceback for Exception Occurrence
12028 This child package provides the subprogram (@code{Tracebacks}) to
12029 give a traceback array of addresses based on an exception
12032 @node Ada.Sequential_IO.C_Streams (a-siocst.ads)
12033 @section @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
12034 @cindex @code{Ada.Sequential_IO.C_Streams} (@file{a-siocst.ads})
12035 @cindex C Streams, Interfacing with Sequential_IO
12038 This package provides subprograms that allow interfacing between
12039 C streams and @code{Sequential_IO}. The stream identifier can be
12040 extracted from a file opened on the Ada side, and an Ada file
12041 can be constructed from a stream opened on the C side.
12043 @node Ada.Streams.Stream_IO.C_Streams (a-ssicst.ads)
12044 @section @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
12045 @cindex @code{Ada.Streams.Stream_IO.C_Streams} (@file{a-ssicst.ads})
12046 @cindex C Streams, Interfacing with Stream_IO
12049 This package provides subprograms that allow interfacing between
12050 C streams and @code{Stream_IO}. The stream identifier can be
12051 extracted from a file opened on the Ada side, and an Ada file
12052 can be constructed from a stream opened on the C side.
12054 @node Ada.Strings.Unbounded.Text_IO (a-suteio.ads)
12055 @section @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
12056 @cindex @code{Ada.Strings.Unbounded.Text_IO} (@file{a-suteio.ads})
12057 @cindex @code{Unbounded_String}, IO support
12058 @cindex @code{Text_IO}, extensions for unbounded strings
12061 This package provides subprograms for Text_IO for unbounded
12062 strings, avoiding the necessity for an intermediate operation
12063 with ordinary strings.
12065 @node Ada.Strings.Wide_Unbounded.Wide_Text_IO (a-swuwti.ads)
12066 @section @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
12067 @cindex @code{Ada.Strings.Wide_Unbounded.Wide_Text_IO} (@file{a-swuwti.ads})
12068 @cindex @code{Unbounded_Wide_String}, IO support
12069 @cindex @code{Text_IO}, extensions for unbounded wide strings
12072 This package provides subprograms for Text_IO for unbounded
12073 wide strings, avoiding the necessity for an intermediate operation
12074 with ordinary wide strings.
12076 @node Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO (a-szuzti.ads)
12077 @section @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
12078 @cindex @code{Ada.Strings.Wide_Wide_Unbounded.Wide_Wide_Text_IO} (@file{a-szuzti.ads})
12079 @cindex @code{Unbounded_Wide_Wide_String}, IO support
12080 @cindex @code{Text_IO}, extensions for unbounded wide wide strings
12083 This package provides subprograms for Text_IO for unbounded
12084 wide wide strings, avoiding the necessity for an intermediate operation
12085 with ordinary wide wide strings.
12087 @node Ada.Text_IO.C_Streams (a-tiocst.ads)
12088 @section @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
12089 @cindex @code{Ada.Text_IO.C_Streams} (@file{a-tiocst.ads})
12090 @cindex C Streams, Interfacing with @code{Text_IO}
12093 This package provides subprograms that allow interfacing between
12094 C streams and @code{Text_IO}. The stream identifier can be
12095 extracted from a file opened on the Ada side, and an Ada file
12096 can be constructed from a stream opened on the C side.
12098 @node Ada.Wide_Text_IO.C_Streams (a-wtcstr.ads)
12099 @section @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
12100 @cindex @code{Ada.Wide_Text_IO.C_Streams} (@file{a-wtcstr.ads})
12101 @cindex C Streams, Interfacing with @code{Wide_Text_IO}
12104 This package provides subprograms that allow interfacing between
12105 C streams and @code{Wide_Text_IO}. The stream identifier can be
12106 extracted from a file opened on the Ada side, and an Ada file
12107 can be constructed from a stream opened on the C side.
12109 @node Ada.Wide_Wide_Text_IO.C_Streams (a-ztcstr.ads)
12110 @section @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
12111 @cindex @code{Ada.Wide_Wide_Text_IO.C_Streams} (@file{a-ztcstr.ads})
12112 @cindex C Streams, Interfacing with @code{Wide_Wide_Text_IO}
12115 This package provides subprograms that allow interfacing between
12116 C streams and @code{Wide_Wide_Text_IO}. The stream identifier can be
12117 extracted from a file opened on the Ada side, and an Ada file
12118 can be constructed from a stream opened on the C side.
12121 @node GNAT.Array_Split (g-arrspl.ads)
12122 @section @code{GNAT.Array_Split} (@file{g-arrspl.ads})
12123 @cindex @code{GNAT.Array_Split} (@file{g-arrspl.ads})
12124 @cindex Array splitter
12127 Useful array-manipulation routines: given a set of separators, split
12128 an array wherever the separators appear, and provide direct access
12129 to the resulting slices.
12131 @node GNAT.AWK (g-awk.ads)
12132 @section @code{GNAT.AWK} (@file{g-awk.ads})
12133 @cindex @code{GNAT.AWK} (@file{g-awk.ads})
12138 Provides AWK-like parsing functions, with an easy interface for parsing one
12139 or more files containing formatted data. The file is viewed as a database
12140 where each record is a line and a field is a data element in this line.
12142 @node GNAT.Bounded_Buffers (g-boubuf.ads)
12143 @section @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
12144 @cindex @code{GNAT.Bounded_Buffers} (@file{g-boubuf.ads})
12146 @cindex Bounded Buffers
12149 Provides a concurrent generic bounded buffer abstraction. Instances are
12150 useful directly or as parts of the implementations of other abstractions,
12153 @node GNAT.Bounded_Mailboxes (g-boumai.ads)
12154 @section @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
12155 @cindex @code{GNAT.Bounded_Mailboxes} (@file{g-boumai.ads})
12160 Provides a thread-safe asynchronous intertask mailbox communication facility.
12162 @node GNAT.Bubble_Sort (g-bubsor.ads)
12163 @section @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
12164 @cindex @code{GNAT.Bubble_Sort} (@file{g-bubsor.ads})
12166 @cindex Bubble sort
12169 Provides a general implementation of bubble sort usable for sorting arbitrary
12170 data items. Exchange and comparison procedures are provided by passing
12171 access-to-procedure values.
12173 @node GNAT.Bubble_Sort_A (g-busora.ads)
12174 @section @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
12175 @cindex @code{GNAT.Bubble_Sort_A} (@file{g-busora.ads})
12177 @cindex Bubble sort
12180 Provides a general implementation of bubble sort usable for sorting arbitrary
12181 data items. Move and comparison procedures are provided by passing
12182 access-to-procedure values. This is an older version, retained for
12183 compatibility. Usually @code{GNAT.Bubble_Sort} will be preferable.
12185 @node GNAT.Bubble_Sort_G (g-busorg.ads)
12186 @section @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
12187 @cindex @code{GNAT.Bubble_Sort_G} (@file{g-busorg.ads})
12189 @cindex Bubble sort
12192 Similar to @code{Bubble_Sort_A} except that the move and sorting procedures
12193 are provided as generic parameters, this improves efficiency, especially
12194 if the procedures can be inlined, at the expense of duplicating code for
12195 multiple instantiations.
12197 @node GNAT.Calendar (g-calend.ads)
12198 @section @code{GNAT.Calendar} (@file{g-calend.ads})
12199 @cindex @code{GNAT.Calendar} (@file{g-calend.ads})
12200 @cindex @code{Calendar}
12203 Extends the facilities provided by @code{Ada.Calendar} to include handling
12204 of days of the week, an extended @code{Split} and @code{Time_Of} capability.
12205 Also provides conversion of @code{Ada.Calendar.Time} values to and from the
12206 C @code{timeval} format.
12208 @node GNAT.Calendar.Time_IO (g-catiio.ads)
12209 @section @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
12210 @cindex @code{Calendar}
12212 @cindex @code{GNAT.Calendar.Time_IO} (@file{g-catiio.ads})
12214 @node GNAT.CRC32 (g-crc32.ads)
12215 @section @code{GNAT.CRC32} (@file{g-crc32.ads})
12216 @cindex @code{GNAT.CRC32} (@file{g-crc32.ads})
12218 @cindex Cyclic Redundancy Check
12221 This package implements the CRC-32 algorithm. For a full description
12222 of this algorithm see
12223 ``Computation of Cyclic Redundancy Checks via Table Look-Up'',
12224 @cite{Communications of the ACM}, Vol.@: 31 No.@: 8, pp.@: 1008-1013,
12225 Aug.@: 1988. Sarwate, D.V@.
12228 Provides an extended capability for formatted output of time values with
12229 full user control over the format. Modeled on the GNU Date specification.
12231 @node GNAT.Case_Util (g-casuti.ads)
12232 @section @code{GNAT.Case_Util} (@file{g-casuti.ads})
12233 @cindex @code{GNAT.Case_Util} (@file{g-casuti.ads})
12234 @cindex Casing utilities
12235 @cindex Character handling (@code{GNAT.Case_Util})
12238 A set of simple routines for handling upper and lower casing of strings
12239 without the overhead of the full casing tables
12240 in @code{Ada.Characters.Handling}.
12242 @node GNAT.CGI (g-cgi.ads)
12243 @section @code{GNAT.CGI} (@file{g-cgi.ads})
12244 @cindex @code{GNAT.CGI} (@file{g-cgi.ads})
12245 @cindex CGI (Common Gateway Interface)
12248 This is a package for interfacing a GNAT program with a Web server via the
12249 Common Gateway Interface (CGI)@. Basically this package parses the CGI
12250 parameters, which are a set of key/value pairs sent by the Web server. It
12251 builds a table whose index is the key and provides some services to deal
12254 @node GNAT.CGI.Cookie (g-cgicoo.ads)
12255 @section @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
12256 @cindex @code{GNAT.CGI.Cookie} (@file{g-cgicoo.ads})
12257 @cindex CGI (Common Gateway Interface) cookie support
12258 @cindex Cookie support in CGI
12261 This is a package to interface a GNAT program with a Web server via the
12262 Common Gateway Interface (CGI). It exports services to deal with Web
12263 cookies (piece of information kept in the Web client software).
12265 @node GNAT.CGI.Debug (g-cgideb.ads)
12266 @section @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
12267 @cindex @code{GNAT.CGI.Debug} (@file{g-cgideb.ads})
12268 @cindex CGI (Common Gateway Interface) debugging
12271 This is a package to help debugging CGI (Common Gateway Interface)
12272 programs written in Ada.
12274 @node GNAT.Command_Line (g-comlin.ads)
12275 @section @code{GNAT.Command_Line} (@file{g-comlin.ads})
12276 @cindex @code{GNAT.Command_Line} (@file{g-comlin.ads})
12277 @cindex Command line
12280 Provides a high level interface to @code{Ada.Command_Line} facilities,
12281 including the ability to scan for named switches with optional parameters
12282 and expand file names using wild card notations.
12284 @node GNAT.Compiler_Version (g-comver.ads)
12285 @section @code{GNAT.Compiler_Version} (@file{g-comver.ads})
12286 @cindex @code{GNAT.Compiler_Version} (@file{g-comver.ads})
12287 @cindex Compiler Version
12288 @cindex Version, of compiler
12291 Provides a routine for obtaining the version of the compiler used to
12292 compile the program. More accurately this is the version of the binder
12293 used to bind the program (this will normally be the same as the version
12294 of the compiler if a consistent tool set is used to compile all units
12297 @node GNAT.Ctrl_C (g-ctrl_c.ads)
12298 @section @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
12299 @cindex @code{GNAT.Ctrl_C} (@file{g-ctrl_c.ads})
12303 Provides a simple interface to handle Ctrl-C keyboard events.
12305 @node GNAT.Current_Exception (g-curexc.ads)
12306 @section @code{GNAT.Current_Exception} (@file{g-curexc.ads})
12307 @cindex @code{GNAT.Current_Exception} (@file{g-curexc.ads})
12308 @cindex Current exception
12309 @cindex Exception retrieval
12312 Provides access to information on the current exception that has been raised
12313 without the need for using the Ada-95 exception choice parameter specification
12314 syntax. This is particularly useful in simulating typical facilities for
12315 obtaining information about exceptions provided by Ada 83 compilers.
12317 @node GNAT.Debug_Pools (g-debpoo.ads)
12318 @section @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
12319 @cindex @code{GNAT.Debug_Pools} (@file{g-debpoo.ads})
12321 @cindex Debug pools
12322 @cindex Memory corruption debugging
12325 Provide a debugging storage pools that helps tracking memory corruption
12326 problems. See section ``Finding memory problems with GNAT Debug Pool'' in
12327 the @cite{GNAT User's Guide}.
12329 @node GNAT.Debug_Utilities (g-debuti.ads)
12330 @section @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
12331 @cindex @code{GNAT.Debug_Utilities} (@file{g-debuti.ads})
12335 Provides a few useful utilities for debugging purposes, including conversion
12336 to and from string images of address values. Supports both C and Ada formats
12337 for hexadecimal literals.
12339 @node GNAT.Directory_Operations (g-dirope.ads)
12340 @section @code{GNAT.Directory_Operations} (g-dirope.ads)
12341 @cindex @code{GNAT.Directory_Operations} (g-dirope.ads)
12342 @cindex Directory operations
12345 Provides a set of routines for manipulating directories, including changing
12346 the current directory, making new directories, and scanning the files in a
12349 @node GNAT.Dynamic_HTables (g-dynhta.ads)
12350 @section @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
12351 @cindex @code{GNAT.Dynamic_HTables} (@file{g-dynhta.ads})
12352 @cindex Hash tables
12355 A generic implementation of hash tables that can be used to hash arbitrary
12356 data. Provided in two forms, a simple form with built in hash functions,
12357 and a more complex form in which the hash function is supplied.
12360 This package provides a facility similar to that of @code{GNAT.HTable},
12361 except that this package declares a type that can be used to define
12362 dynamic instances of the hash table, while an instantiation of
12363 @code{GNAT.HTable} creates a single instance of the hash table.
12365 @node GNAT.Dynamic_Tables (g-dyntab.ads)
12366 @section @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
12367 @cindex @code{GNAT.Dynamic_Tables} (@file{g-dyntab.ads})
12368 @cindex Table implementation
12369 @cindex Arrays, extendable
12372 A generic package providing a single dimension array abstraction where the
12373 length of the array can be dynamically modified.
12376 This package provides a facility similar to that of @code{GNAT.Table},
12377 except that this package declares a type that can be used to define
12378 dynamic instances of the table, while an instantiation of
12379 @code{GNAT.Table} creates a single instance of the table type.
12381 @node GNAT.Exception_Actions (g-excact.ads)
12382 @section @code{GNAT.Exception_Actions} (@file{g-excact.ads})
12383 @cindex @code{GNAT.Exception_Actions} (@file{g-excact.ads})
12384 @cindex Exception actions
12387 Provides callbacks when an exception is raised. Callbacks can be registered
12388 for specific exceptions, or when any exception is raised. This
12389 can be used for instance to force a core dump to ease debugging.
12391 @node GNAT.Exception_Traces (g-exctra.ads)
12392 @section @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
12393 @cindex @code{GNAT.Exception_Traces} (@file{g-exctra.ads})
12394 @cindex Exception traces
12398 Provides an interface allowing to control automatic output upon exception
12401 @node GNAT.Exceptions (g-except.ads)
12402 @section @code{GNAT.Exceptions} (@file{g-expect.ads})
12403 @cindex @code{GNAT.Exceptions} (@file{g-expect.ads})
12404 @cindex Exceptions, Pure
12405 @cindex Pure packages, exceptions
12408 Normally it is not possible to raise an exception with
12409 a message from a subprogram in a pure package, since the
12410 necessary types and subprograms are in @code{Ada.Exceptions}
12411 which is not a pure unit. @code{GNAT.Exceptions} provides a
12412 facility for getting around this limitation for a few
12413 predefined exceptions, and for example allow raising
12414 @code{Constraint_Error} with a message from a pure subprogram.
12416 @node GNAT.Expect (g-expect.ads)
12417 @section @code{GNAT.Expect} (@file{g-expect.ads})
12418 @cindex @code{GNAT.Expect} (@file{g-expect.ads})
12421 Provides a set of subprograms similar to what is available
12422 with the standard Tcl Expect tool.
12423 It allows you to easily spawn and communicate with an external process.
12424 You can send commands or inputs to the process, and compare the output
12425 with some expected regular expression. Currently @code{GNAT.Expect}
12426 is implemented on all native GNAT ports except for OpenVMS@.
12427 It is not implemented for cross ports, and in particular is not
12428 implemented for VxWorks or LynxOS@.
12430 @node GNAT.Float_Control (g-flocon.ads)
12431 @section @code{GNAT.Float_Control} (@file{g-flocon.ads})
12432 @cindex @code{GNAT.Float_Control} (@file{g-flocon.ads})
12433 @cindex Floating-Point Processor
12436 Provides an interface for resetting the floating-point processor into the
12437 mode required for correct semantic operation in Ada. Some third party
12438 library calls may cause this mode to be modified, and the Reset procedure
12439 in this package can be used to reestablish the required mode.
12441 @node GNAT.Heap_Sort (g-heasor.ads)
12442 @section @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
12443 @cindex @code{GNAT.Heap_Sort} (@file{g-heasor.ads})
12447 Provides a general implementation of heap sort usable for sorting arbitrary
12448 data items. Exchange and comparison procedures are provided by passing
12449 access-to-procedure values. The algorithm used is a modified heap sort
12450 that performs approximately N*log(N) comparisons in the worst case.
12452 @node GNAT.Heap_Sort_A (g-hesora.ads)
12453 @section @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
12454 @cindex @code{GNAT.Heap_Sort_A} (@file{g-hesora.ads})
12458 Provides a general implementation of heap sort usable for sorting arbitrary
12459 data items. Move and comparison procedures are provided by passing
12460 access-to-procedure values. The algorithm used is a modified heap sort
12461 that performs approximately N*log(N) comparisons in the worst case.
12462 This differs from @code{GNAT.Heap_Sort} in having a less convenient
12463 interface, but may be slightly more efficient.
12465 @node GNAT.Heap_Sort_G (g-hesorg.ads)
12466 @section @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
12467 @cindex @code{GNAT.Heap_Sort_G} (@file{g-hesorg.ads})
12471 Similar to @code{Heap_Sort_A} except that the move and sorting procedures
12472 are provided as generic parameters, this improves efficiency, especially
12473 if the procedures can be inlined, at the expense of duplicating code for
12474 multiple instantiations.
12476 @node GNAT.HTable (g-htable.ads)
12477 @section @code{GNAT.HTable} (@file{g-htable.ads})
12478 @cindex @code{GNAT.HTable} (@file{g-htable.ads})
12479 @cindex Hash tables
12482 A generic implementation of hash tables that can be used to hash arbitrary
12483 data. Provides two approaches, one a simple static approach, and the other
12484 allowing arbitrary dynamic hash tables.
12486 @node GNAT.IO (g-io.ads)
12487 @section @code{GNAT.IO} (@file{g-io.ads})
12488 @cindex @code{GNAT.IO} (@file{g-io.ads})
12490 @cindex Input/Output facilities
12493 A simple preelaborable input-output package that provides a subset of
12494 simple Text_IO functions for reading characters and strings from
12495 Standard_Input, and writing characters, strings and integers to either
12496 Standard_Output or Standard_Error.
12498 @node GNAT.IO_Aux (g-io_aux.ads)
12499 @section @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
12500 @cindex @code{GNAT.IO_Aux} (@file{g-io_aux.ads})
12502 @cindex Input/Output facilities
12504 Provides some auxiliary functions for use with Text_IO, including a test
12505 for whether a file exists, and functions for reading a line of text.
12507 @node GNAT.Lock_Files (g-locfil.ads)
12508 @section @code{GNAT.Lock_Files} (@file{g-locfil.ads})
12509 @cindex @code{GNAT.Lock_Files} (@file{g-locfil.ads})
12510 @cindex File locking
12511 @cindex Locking using files
12514 Provides a general interface for using files as locks. Can be used for
12515 providing program level synchronization.
12517 @node GNAT.MD5 (g-md5.ads)
12518 @section @code{GNAT.MD5} (@file{g-md5.ads})
12519 @cindex @code{GNAT.MD5} (@file{g-md5.ads})
12520 @cindex Message Digest MD5
12523 Implements the MD5 Message-Digest Algorithm as described in RFC 1321.
12525 @node GNAT.Memory_Dump (g-memdum.ads)
12526 @section @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
12527 @cindex @code{GNAT.Memory_Dump} (@file{g-memdum.ads})
12528 @cindex Dump Memory
12531 Provides a convenient routine for dumping raw memory to either the
12532 standard output or standard error files. Uses GNAT.IO for actual
12535 @node GNAT.Most_Recent_Exception (g-moreex.ads)
12536 @section @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
12537 @cindex @code{GNAT.Most_Recent_Exception} (@file{g-moreex.ads})
12538 @cindex Exception, obtaining most recent
12541 Provides access to the most recently raised exception. Can be used for
12542 various logging purposes, including duplicating functionality of some
12543 Ada 83 implementation dependent extensions.
12545 @node GNAT.OS_Lib (g-os_lib.ads)
12546 @section @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
12547 @cindex @code{GNAT.OS_Lib} (@file{g-os_lib.ads})
12548 @cindex Operating System interface
12549 @cindex Spawn capability
12552 Provides a range of target independent operating system interface functions,
12553 including time/date management, file operations, subprocess management,
12554 including a portable spawn procedure, and access to environment variables
12555 and error return codes.
12557 @node GNAT.Perfect_Hash_Generators (g-pehage.ads)
12558 @section @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
12559 @cindex @code{GNAT.Perfect_Hash_Generators} (@file{g-pehage.ads})
12560 @cindex Hash functions
12563 Provides a generator of static minimal perfect hash functions. No
12564 collisions occur and each item can be retrieved from the table in one
12565 probe (perfect property). The hash table size corresponds to the exact
12566 size of the key set and no larger (minimal property). The key set has to
12567 be know in advance (static property). The hash functions are also order
12568 preserving. If w2 is inserted after w1 in the generator, their
12569 hashcode are in the same order. These hashing functions are very
12570 convenient for use with realtime applications.
12572 @node GNAT.Regexp (g-regexp.ads)
12573 @section @code{GNAT.Regexp} (@file{g-regexp.ads})
12574 @cindex @code{GNAT.Regexp} (@file{g-regexp.ads})
12575 @cindex Regular expressions
12576 @cindex Pattern matching
12579 A simple implementation of regular expressions, using a subset of regular
12580 expression syntax copied from familiar Unix style utilities. This is the
12581 simples of the three pattern matching packages provided, and is particularly
12582 suitable for ``file globbing'' applications.
12584 @node GNAT.Registry (g-regist.ads)
12585 @section @code{GNAT.Registry} (@file{g-regist.ads})
12586 @cindex @code{GNAT.Registry} (@file{g-regist.ads})
12587 @cindex Windows Registry
12590 This is a high level binding to the Windows registry. It is possible to
12591 do simple things like reading a key value, creating a new key. For full
12592 registry API, but at a lower level of abstraction, refer to the Win32.Winreg
12593 package provided with the Win32Ada binding
12595 @node GNAT.Regpat (g-regpat.ads)
12596 @section @code{GNAT.Regpat} (@file{g-regpat.ads})
12597 @cindex @code{GNAT.Regpat} (@file{g-regpat.ads})
12598 @cindex Regular expressions
12599 @cindex Pattern matching
12602 A complete implementation of Unix-style regular expression matching, copied
12603 from the original V7 style regular expression library written in C by
12604 Henry Spencer (and binary compatible with this C library).
12606 @node GNAT.Secondary_Stack_Info (g-sestin.ads)
12607 @section @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
12608 @cindex @code{GNAT.Secondary_Stack_Info} (@file{g-sestin.ads})
12609 @cindex Secondary Stack Info
12612 Provide the capability to query the high water mark of the current task's
12615 @node GNAT.Semaphores (g-semaph.ads)
12616 @section @code{GNAT.Semaphores} (@file{g-semaph.ads})
12617 @cindex @code{GNAT.Semaphores} (@file{g-semaph.ads})
12621 Provides classic counting and binary semaphores using protected types.
12623 @node GNAT.Signals (g-signal.ads)
12624 @section @code{GNAT.Signals} (@file{g-signal.ads})
12625 @cindex @code{GNAT.Signals} (@file{g-signal.ads})
12629 Provides the ability to manipulate the blocked status of signals on supported
12632 @node GNAT.Sockets (g-socket.ads)
12633 @section @code{GNAT.Sockets} (@file{g-socket.ads})
12634 @cindex @code{GNAT.Sockets} (@file{g-socket.ads})
12638 A high level and portable interface to develop sockets based applications.
12639 This package is based on the sockets thin binding found in
12640 @code{GNAT.Sockets.Thin}. Currently @code{GNAT.Sockets} is implemented
12641 on all native GNAT ports except for OpenVMS@. It is not implemented
12642 for the LynxOS@ cross port.
12644 @node GNAT.Source_Info (g-souinf.ads)
12645 @section @code{GNAT.Source_Info} (@file{g-souinf.ads})
12646 @cindex @code{GNAT.Source_Info} (@file{g-souinf.ads})
12647 @cindex Source Information
12650 Provides subprograms that give access to source code information known at
12651 compile time, such as the current file name and line number.
12653 @node GNAT.Spell_Checker (g-speche.ads)
12654 @section @code{GNAT.Spell_Checker} (@file{g-speche.ads})
12655 @cindex @code{GNAT.Spell_Checker} (@file{g-speche.ads})
12656 @cindex Spell checking
12659 Provides a function for determining whether one string is a plausible
12660 near misspelling of another string.
12662 @node GNAT.Spitbol.Patterns (g-spipat.ads)
12663 @section @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
12664 @cindex @code{GNAT.Spitbol.Patterns} (@file{g-spipat.ads})
12665 @cindex SPITBOL pattern matching
12666 @cindex Pattern matching
12669 A complete implementation of SNOBOL4 style pattern matching. This is the
12670 most elaborate of the pattern matching packages provided. It fully duplicates
12671 the SNOBOL4 dynamic pattern construction and matching capabilities, using the
12672 efficient algorithm developed by Robert Dewar for the SPITBOL system.
12674 @node GNAT.Spitbol (g-spitbo.ads)
12675 @section @code{GNAT.Spitbol} (@file{g-spitbo.ads})
12676 @cindex @code{GNAT.Spitbol} (@file{g-spitbo.ads})
12677 @cindex SPITBOL interface
12680 The top level package of the collection of SPITBOL-style functionality, this
12681 package provides basic SNOBOL4 string manipulation functions, such as
12682 Pad, Reverse, Trim, Substr capability, as well as a generic table function
12683 useful for constructing arbitrary mappings from strings in the style of
12684 the SNOBOL4 TABLE function.
12686 @node GNAT.Spitbol.Table_Boolean (g-sptabo.ads)
12687 @section @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
12688 @cindex @code{GNAT.Spitbol.Table_Boolean} (@file{g-sptabo.ads})
12689 @cindex Sets of strings
12690 @cindex SPITBOL Tables
12693 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
12694 for type @code{Standard.Boolean}, giving an implementation of sets of
12697 @node GNAT.Spitbol.Table_Integer (g-sptain.ads)
12698 @section @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
12699 @cindex @code{GNAT.Spitbol.Table_Integer} (@file{g-sptain.ads})
12700 @cindex Integer maps
12702 @cindex SPITBOL Tables
12705 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table}
12706 for type @code{Standard.Integer}, giving an implementation of maps
12707 from string to integer values.
12709 @node GNAT.Spitbol.Table_VString (g-sptavs.ads)
12710 @section @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
12711 @cindex @code{GNAT.Spitbol.Table_VString} (@file{g-sptavs.ads})
12712 @cindex String maps
12714 @cindex SPITBOL Tables
12717 A library level of instantiation of @code{GNAT.Spitbol.Patterns.Table} for
12718 a variable length string type, giving an implementation of general
12719 maps from strings to strings.
12721 @node GNAT.Strings (g-string.ads)
12722 @section @code{GNAT.Strings} (@file{g-string.ads})
12723 @cindex @code{GNAT.Strings} (@file{g-string.ads})
12726 Common String access types and related subprograms. Basically it
12727 defines a string access and an array of string access types.
12729 @node GNAT.String_Split (g-strspl.ads)
12730 @section @code{GNAT.String_Split} (@file{g-strspl.ads})
12731 @cindex @code{GNAT.String_Split} (@file{g-strspl.ads})
12732 @cindex String splitter
12735 Useful string manipulation routines: given a set of separators, split
12736 a string wherever the separators appear, and provide direct access
12737 to the resulting slices. This package is instantiated from
12738 @code{GNAT.Array_Split}.
12740 @node GNAT.UTF_32 (g-utf_32.ads)
12741 @section @code{GNAT.UTF_32} (@file{g-table.ads})
12742 @cindex @code{GNAT.UTF_32} (@file{g-table.ads})
12743 @cindex Wide character codes
12746 This is a package intended to be used in conjunction with the
12747 @code{Wide_Character} type in Ada 95 and the
12748 @code{Wide_Wide_Character} type in Ada 2005 (available
12749 in @code{GNAT} in Ada 2005 mode). This package contains
12750 Unicode categorization routines, as well as lexical
12751 categorization routines corresponding to the Ada 2005
12752 lexical rules for identifiers and strings, and also a
12753 lower case to upper case fold routine corresponding to
12754 the Ada 2005 rules for identifier equivalence.
12756 @node GNAT.Table (g-table.ads)
12757 @section @code{GNAT.Table} (@file{g-table.ads})
12758 @cindex @code{GNAT.Table} (@file{g-table.ads})
12759 @cindex Table implementation
12760 @cindex Arrays, extendable
12763 A generic package providing a single dimension array abstraction where the
12764 length of the array can be dynamically modified.
12767 This package provides a facility similar to that of @code{GNAT.Dynamic_Tables},
12768 except that this package declares a single instance of the table type,
12769 while an instantiation of @code{GNAT.Dynamic_Tables} creates a type that can be
12770 used to define dynamic instances of the table.
12772 @node GNAT.Task_Lock (g-tasloc.ads)
12773 @section @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
12774 @cindex @code{GNAT.Task_Lock} (@file{g-tasloc.ads})
12775 @cindex Task synchronization
12776 @cindex Task locking
12780 A very simple facility for locking and unlocking sections of code using a
12781 single global task lock. Appropriate for use in situations where contention
12782 between tasks is very rarely expected.
12784 @node GNAT.Threads (g-thread.ads)
12785 @section @code{GNAT.Threads} (@file{g-thread.ads})
12786 @cindex @code{GNAT.Threads} (@file{g-thread.ads})
12787 @cindex Foreign threads
12788 @cindex Threads, foreign
12791 Provides facilities for creating and destroying threads with explicit calls.
12792 These threads are known to the GNAT run-time system. These subprograms are
12793 exported C-convention procedures intended to be called from foreign code.
12794 By using these primitives rather than directly calling operating systems
12795 routines, compatibility with the Ada tasking run-time is provided.
12797 @node GNAT.Traceback (g-traceb.ads)
12798 @section @code{GNAT.Traceback} (@file{g-traceb.ads})
12799 @cindex @code{GNAT.Traceback} (@file{g-traceb.ads})
12800 @cindex Trace back facilities
12803 Provides a facility for obtaining non-symbolic traceback information, useful
12804 in various debugging situations.
12806 @node GNAT.Traceback.Symbolic (g-trasym.ads)
12807 @section @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
12808 @cindex @code{GNAT.Traceback.Symbolic} (@file{g-trasym.ads})
12809 @cindex Trace back facilities
12812 Provides symbolic traceback information that includes the subprogram
12813 name and line number information.
12815 @node GNAT.Wide_String_Split (g-wistsp.ads)
12816 @section @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
12817 @cindex @code{GNAT.Wide_String_Split} (@file{g-wistsp.ads})
12818 @cindex Wide_String splitter
12821 Useful wide string manipulation routines: given a set of separators, split
12822 a wide string wherever the separators appear, and provide direct access
12823 to the resulting slices. This package is instantiated from
12824 @code{GNAT.Array_Split}.
12826 @node GNAT.Wide_Wide_String_Split (g-zistsp.ads)
12827 @section @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
12828 @cindex @code{GNAT.Wide_Wide_String_Split} (@file{g-zistsp.ads})
12829 @cindex Wide_Wide_String splitter
12832 Useful wide wide string manipulation routines: given a set of separators, split
12833 a wide wide string wherever the separators appear, and provide direct access
12834 to the resulting slices. This package is instantiated from
12835 @code{GNAT.Array_Split}.
12837 @node Interfaces.C.Extensions (i-cexten.ads)
12838 @section @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
12839 @cindex @code{Interfaces.C.Extensions} (@file{i-cexten.ads})
12842 This package contains additional C-related definitions, intended
12843 for use with either manually or automatically generated bindings
12846 @node Interfaces.C.Streams (i-cstrea.ads)
12847 @section @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
12848 @cindex @code{Interfaces.C.Streams} (@file{i-cstrea.ads})
12849 @cindex C streams, interfacing
12852 This package is a binding for the most commonly used operations
12855 @node Interfaces.CPP (i-cpp.ads)
12856 @section @code{Interfaces.CPP} (@file{i-cpp.ads})
12857 @cindex @code{Interfaces.CPP} (@file{i-cpp.ads})
12858 @cindex C++ interfacing
12859 @cindex Interfacing, to C++
12862 This package provides facilities for use in interfacing to C++. It
12863 is primarily intended to be used in connection with automated tools
12864 for the generation of C++ interfaces.
12866 @node Interfaces.Os2lib (i-os2lib.ads)
12867 @section @code{Interfaces.Os2lib} (@file{i-os2lib.ads})
12868 @cindex @code{Interfaces.Os2lib} (@file{i-os2lib.ads})
12869 @cindex Interfacing, to OS/2
12870 @cindex OS/2 interfacing
12873 This package provides interface definitions to the OS/2 library.
12874 It is a thin binding which is a direct translation of the
12875 various @file{<bse@.h>} files.
12877 @node Interfaces.Os2lib.Errors (i-os2err.ads)
12878 @section @code{Interfaces.Os2lib.Errors} (@file{i-os2err.ads})
12879 @cindex @code{Interfaces.Os2lib.Errors} (@file{i-os2err.ads})
12880 @cindex OS/2 Error codes
12881 @cindex Interfacing, to OS/2
12882 @cindex OS/2 interfacing
12885 This package provides definitions of the OS/2 error codes.
12887 @node Interfaces.Os2lib.Synchronization (i-os2syn.ads)
12888 @section @code{Interfaces.Os2lib.Synchronization} (@file{i-os2syn.ads})
12889 @cindex @code{Interfaces.Os2lib.Synchronization} (@file{i-os2syn.ads})
12890 @cindex Interfacing, to OS/2
12891 @cindex Synchronization, OS/2
12892 @cindex OS/2 synchronization primitives
12895 This is a child package that provides definitions for interfacing
12896 to the @code{OS/2} synchronization primitives.
12898 @node Interfaces.Os2lib.Threads (i-os2thr.ads)
12899 @section @code{Interfaces.Os2lib.Threads} (@file{i-os2thr.ads})
12900 @cindex @code{Interfaces.Os2lib.Threads} (@file{i-os2thr.ads})
12901 @cindex Interfacing, to OS/2
12902 @cindex Thread control, OS/2
12903 @cindex OS/2 thread interfacing
12906 This is a child package that provides definitions for interfacing
12907 to the @code{OS/2} thread primitives.
12909 @node Interfaces.Packed_Decimal (i-pacdec.ads)
12910 @section @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
12911 @cindex @code{Interfaces.Packed_Decimal} (@file{i-pacdec.ads})
12912 @cindex IBM Packed Format
12913 @cindex Packed Decimal
12916 This package provides a set of routines for conversions to and
12917 from a packed decimal format compatible with that used on IBM
12920 @node Interfaces.VxWorks (i-vxwork.ads)
12921 @section @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
12922 @cindex @code{Interfaces.VxWorks} (@file{i-vxwork.ads})
12923 @cindex Interfacing to VxWorks
12924 @cindex VxWorks, interfacing
12927 This package provides a limited binding to the VxWorks API.
12928 In particular, it interfaces with the
12929 VxWorks hardware interrupt facilities.
12931 @node Interfaces.VxWorks.IO (i-vxwoio.ads)
12932 @section @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
12933 @cindex @code{Interfaces.VxWorks.IO} (@file{i-vxwoio.ads})
12934 @cindex Interfacing to VxWorks' I/O
12935 @cindex VxWorks, I/O interfacing
12936 @cindex VxWorks, Get_Immediate
12937 @cindex Get_Immediate, VxWorks
12940 This package provides a binding to the ioctl (IO/Control)
12941 function of VxWorks, defining a set of option values and
12942 function codes. A particular use of this package is
12943 to enable the use of Get_Immediate under VxWorks.
12945 @node System.Address_Image (s-addima.ads)
12946 @section @code{System.Address_Image} (@file{s-addima.ads})
12947 @cindex @code{System.Address_Image} (@file{s-addima.ads})
12948 @cindex Address image
12949 @cindex Image, of an address
12952 This function provides a useful debugging
12953 function that gives an (implementation dependent)
12954 string which identifies an address.
12956 @node System.Assertions (s-assert.ads)
12957 @section @code{System.Assertions} (@file{s-assert.ads})
12958 @cindex @code{System.Assertions} (@file{s-assert.ads})
12960 @cindex Assert_Failure, exception
12963 This package provides the declaration of the exception raised
12964 by an run-time assertion failure, as well as the routine that
12965 is used internally to raise this assertion.
12967 @node System.Memory (s-memory.ads)
12968 @section @code{System.Memory} (@file{s-memory.ads})
12969 @cindex @code{System.Memory} (@file{s-memory.ads})
12970 @cindex Memory allocation
12973 This package provides the interface to the low level routines used
12974 by the generated code for allocation and freeing storage for the
12975 default storage pool (analogous to the C routines malloc and free.
12976 It also provides a reallocation interface analogous to the C routine
12977 realloc. The body of this unit may be modified to provide alternative
12978 allocation mechanisms for the default pool, and in addition, direct
12979 calls to this unit may be made for low level allocation uses (for
12980 example see the body of @code{GNAT.Tables}).
12982 @node System.Partition_Interface (s-parint.ads)
12983 @section @code{System.Partition_Interface} (@file{s-parint.ads})
12984 @cindex @code{System.Partition_Interface} (@file{s-parint.ads})
12985 @cindex Partition interfacing functions
12988 This package provides facilities for partition interfacing. It
12989 is used primarily in a distribution context when using Annex E
12992 @node System.Restrictions (s-restri.ads)
12993 @section @code{System.Restrictions} (@file{s-restri.ads})
12994 @cindex @code{System.Restrictions} (@file{s-restri.ads})
12995 @cindex Run-time restrictions access
12998 This package provides facilities for accessing at run-time
12999 the status of restrictions specified at compile time for
13000 the partition. Information is available both with regard
13001 to actual restrictions specified, and with regard to
13002 compiler determined information on which restrictions
13003 are violated by one or more packages in the partition.
13005 @node System.Rident (s-rident.ads)
13006 @section @code{System.Rident} (@file{s-rident.ads})
13007 @cindex @code{System.Rident} (@file{s-rident.ads})
13008 @cindex Restrictions definitions
13011 This package provides definitions of the restrictions
13012 identifiers supported by GNAT, and also the format of
13013 the restrictions provided in package System.Restrictions.
13014 It is not normally necessary to @code{with} this generic package
13015 since the necessary instantiation is included in
13016 package System.Restrictions.
13018 @node System.Task_Info (s-tasinf.ads)
13019 @section @code{System.Task_Info} (@file{s-tasinf.ads})
13020 @cindex @code{System.Task_Info} (@file{s-tasinf.ads})
13021 @cindex Task_Info pragma
13024 This package provides target dependent functionality that is used
13025 to support the @code{Task_Info} pragma
13027 @node System.Wch_Cnv (s-wchcnv.ads)
13028 @section @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
13029 @cindex @code{System.Wch_Cnv} (@file{s-wchcnv.ads})
13030 @cindex Wide Character, Representation
13031 @cindex Wide String, Conversion
13032 @cindex Representation of wide characters
13035 This package provides routines for converting between
13036 wide and wide wide characters and a representation as a value of type
13037 @code{Standard.String}, using a specified wide character
13038 encoding method. It uses definitions in
13039 package @code{System.Wch_Con}.
13041 @node System.Wch_Con (s-wchcon.ads)
13042 @section @code{System.Wch_Con} (@file{s-wchcon.ads})
13043 @cindex @code{System.Wch_Con} (@file{s-wchcon.ads})
13046 This package provides definitions and descriptions of
13047 the various methods used for encoding wide characters
13048 in ordinary strings. These definitions are used by
13049 the package @code{System.Wch_Cnv}.
13051 @node Interfacing to Other Languages
13052 @chapter Interfacing to Other Languages
13054 The facilities in annex B of the Ada 95 Reference Manual are fully
13055 implemented in GNAT, and in addition, a full interface to C++ is
13059 * Interfacing to C::
13060 * Interfacing to C++::
13061 * Interfacing to COBOL::
13062 * Interfacing to Fortran::
13063 * Interfacing to non-GNAT Ada code::
13066 @node Interfacing to C
13067 @section Interfacing to C
13070 Interfacing to C with GNAT can use one of two approaches:
13074 The types in the package @code{Interfaces.C} may be used.
13076 Standard Ada types may be used directly. This may be less portable to
13077 other compilers, but will work on all GNAT compilers, which guarantee
13078 correspondence between the C and Ada types.
13082 Pragma @code{Convention C} may be applied to Ada types, but mostly has no
13083 effect, since this is the default. The following table shows the
13084 correspondence between Ada scalar types and the corresponding C types.
13089 @item Short_Integer
13091 @item Short_Short_Integer
13095 @item Long_Long_Integer
13103 @item Long_Long_Float
13104 This is the longest floating-point type supported by the hardware.
13108 Additionally, there are the following general correspondences between Ada
13112 Ada enumeration types map to C enumeration types directly if pragma
13113 @code{Convention C} is specified, which causes them to have int
13114 length. Without pragma @code{Convention C}, Ada enumeration types map to
13115 8, 16, or 32 bits (i.e.@: C types @code{signed char}, @code{short},
13116 @code{int}, respectively) depending on the number of values passed.
13117 This is the only case in which pragma @code{Convention C} affects the
13118 representation of an Ada type.
13121 Ada access types map to C pointers, except for the case of pointers to
13122 unconstrained types in Ada, which have no direct C equivalent.
13125 Ada arrays map directly to C arrays.
13128 Ada records map directly to C structures.
13131 Packed Ada records map to C structures where all members are bit fields
13132 of the length corresponding to the @code{@var{type}'Size} value in Ada.
13135 @node Interfacing to C++
13136 @section Interfacing to C++
13139 The interface to C++ makes use of the following pragmas, which are
13140 primarily intended to be constructed automatically using a binding generator
13141 tool, although it is possible to construct them by hand. No suitable binding
13142 generator tool is supplied with GNAT though.
13144 Using these pragmas it is possible to achieve complete
13145 inter-operability between Ada tagged types and C class definitions.
13146 See @ref{Implementation Defined Pragmas}, for more details.
13149 @item pragma CPP_Class ([Entity =>] @var{local_NAME})
13150 The argument denotes an entity in the current declarative region that is
13151 declared as a tagged or untagged record type. It indicates that the type
13152 corresponds to an externally declared C++ class type, and is to be laid
13153 out the same way that C++ would lay out the type.
13155 @item pragma CPP_Constructor ([Entity =>] @var{local_NAME})
13156 This pragma identifies an imported function (imported in the usual way
13157 with pragma @code{Import}) as corresponding to a C++ constructor.
13159 @item pragma CPP_Vtable @dots{}
13160 One @code{CPP_Vtable} pragma can be present for each component of type
13161 @code{CPP.Interfaces.Vtable_Ptr} in a record to which pragma @code{CPP_Class}
13165 @node Interfacing to COBOL
13166 @section Interfacing to COBOL
13169 Interfacing to COBOL is achieved as described in section B.4 of
13170 the Ada 95 reference manual.
13172 @node Interfacing to Fortran
13173 @section Interfacing to Fortran
13176 Interfacing to Fortran is achieved as described in section B.5 of the
13177 reference manual. The pragma @code{Convention Fortran}, applied to a
13178 multi-dimensional array causes the array to be stored in column-major
13179 order as required for convenient interface to Fortran.
13181 @node Interfacing to non-GNAT Ada code
13182 @section Interfacing to non-GNAT Ada code
13184 It is possible to specify the convention @code{Ada} in a pragma
13185 @code{Import} or pragma @code{Export}. However this refers to
13186 the calling conventions used by GNAT, which may or may not be
13187 similar enough to those used by some other Ada 83 or Ada 95
13188 compiler to allow interoperation.
13190 If arguments types are kept simple, and if the foreign compiler generally
13191 follows system calling conventions, then it may be possible to integrate
13192 files compiled by other Ada compilers, provided that the elaboration
13193 issues are adequately addressed (for example by eliminating the
13194 need for any load time elaboration).
13196 In particular, GNAT running on VMS is designed to
13197 be highly compatible with the DEC Ada 83 compiler, so this is one
13198 case in which it is possible to import foreign units of this type,
13199 provided that the data items passed are restricted to simple scalar
13200 values or simple record types without variants, or simple array
13201 types with fixed bounds.
13203 @node Specialized Needs Annexes
13204 @chapter Specialized Needs Annexes
13207 Ada 95 defines a number of specialized needs annexes, which are not
13208 required in all implementations. However, as described in this chapter,
13209 GNAT implements all of these special needs annexes:
13212 @item Systems Programming (Annex C)
13213 The Systems Programming Annex is fully implemented.
13215 @item Real-Time Systems (Annex D)
13216 The Real-Time Systems Annex is fully implemented.
13218 @item Distributed Systems (Annex E)
13219 Stub generation is fully implemented in the GNAT compiler. In addition,
13220 a complete compatible PCS is available as part of the GLADE system,
13221 a separate product. When the two
13222 products are used in conjunction, this annex is fully implemented.
13224 @item Information Systems (Annex F)
13225 The Information Systems annex is fully implemented.
13227 @item Numerics (Annex G)
13228 The Numerics Annex is fully implemented.
13230 @item Safety and Security (Annex H)
13231 The Safety and Security annex is fully implemented.
13234 @node Implementation of Specific Ada Features
13235 @chapter Implementation of Specific Ada Features
13238 This chapter describes the GNAT implementation of several Ada language
13242 * Machine Code Insertions::
13243 * GNAT Implementation of Tasking::
13244 * GNAT Implementation of Shared Passive Packages::
13245 * Code Generation for Array Aggregates::
13246 * The Size of Discriminated Records with Default Discriminants::
13249 @node Machine Code Insertions
13250 @section Machine Code Insertions
13253 Package @code{Machine_Code} provides machine code support as described
13254 in the Ada 95 Reference Manual in two separate forms:
13257 Machine code statements, consisting of qualified expressions that
13258 fit the requirements of RM section 13.8.
13260 An intrinsic callable procedure, providing an alternative mechanism of
13261 including machine instructions in a subprogram.
13265 The two features are similar, and both are closely related to the mechanism
13266 provided by the asm instruction in the GNU C compiler. Full understanding
13267 and use of the facilities in this package requires understanding the asm
13268 instruction as described in @cite{Using the GNU Compiler Collection (GCC)}
13269 by Richard Stallman. The relevant section is titled ``Extensions to the C
13270 Language Family'' -> ``Assembler Instructions with C Expression Operands''.
13272 Calls to the function @code{Asm} and the procedure @code{Asm} have identical
13273 semantic restrictions and effects as described below. Both are provided so
13274 that the procedure call can be used as a statement, and the function call
13275 can be used to form a code_statement.
13277 The first example given in the GCC documentation is the C @code{asm}
13280 asm ("fsinx %1 %0" : "=f" (result) : "f" (angle));
13284 The equivalent can be written for GNAT as:
13286 @smallexample @c ada
13287 Asm ("fsinx %1 %0",
13288 My_Float'Asm_Output ("=f", result),
13289 My_Float'Asm_Input ("f", angle));
13293 The first argument to @code{Asm} is the assembler template, and is
13294 identical to what is used in GNU C@. This string must be a static
13295 expression. The second argument is the output operand list. It is
13296 either a single @code{Asm_Output} attribute reference, or a list of such
13297 references enclosed in parentheses (technically an array aggregate of
13300 The @code{Asm_Output} attribute denotes a function that takes two
13301 parameters. The first is a string, the second is the name of a variable
13302 of the type designated by the attribute prefix. The first (string)
13303 argument is required to be a static expression and designates the
13304 constraint for the parameter (e.g.@: what kind of register is
13305 required). The second argument is the variable to be updated with the
13306 result. The possible values for constraint are the same as those used in
13307 the RTL, and are dependent on the configuration file used to build the
13308 GCC back end. If there are no output operands, then this argument may
13309 either be omitted, or explicitly given as @code{No_Output_Operands}.
13311 The second argument of @code{@var{my_float}'Asm_Output} functions as
13312 though it were an @code{out} parameter, which is a little curious, but
13313 all names have the form of expressions, so there is no syntactic
13314 irregularity, even though normally functions would not be permitted
13315 @code{out} parameters. The third argument is the list of input
13316 operands. It is either a single @code{Asm_Input} attribute reference, or
13317 a list of such references enclosed in parentheses (technically an array
13318 aggregate of such references).
13320 The @code{Asm_Input} attribute denotes a function that takes two
13321 parameters. The first is a string, the second is an expression of the
13322 type designated by the prefix. The first (string) argument is required
13323 to be a static expression, and is the constraint for the parameter,
13324 (e.g.@: what kind of register is required). The second argument is the
13325 value to be used as the input argument. The possible values for the
13326 constant are the same as those used in the RTL, and are dependent on
13327 the configuration file used to built the GCC back end.
13329 If there are no input operands, this argument may either be omitted, or
13330 explicitly given as @code{No_Input_Operands}. The fourth argument, not
13331 present in the above example, is a list of register names, called the
13332 @dfn{clobber} argument. This argument, if given, must be a static string
13333 expression, and is a space or comma separated list of names of registers
13334 that must be considered destroyed as a result of the @code{Asm} call. If
13335 this argument is the null string (the default value), then the code
13336 generator assumes that no additional registers are destroyed.
13338 The fifth argument, not present in the above example, called the
13339 @dfn{volatile} argument, is by default @code{False}. It can be set to
13340 the literal value @code{True} to indicate to the code generator that all
13341 optimizations with respect to the instruction specified should be
13342 suppressed, and that in particular, for an instruction that has outputs,
13343 the instruction will still be generated, even if none of the outputs are
13344 used. See the full description in the GCC manual for further details.
13346 The @code{Asm} subprograms may be used in two ways. First the procedure
13347 forms can be used anywhere a procedure call would be valid, and
13348 correspond to what the RM calls ``intrinsic'' routines. Such calls can
13349 be used to intersperse machine instructions with other Ada statements.
13350 Second, the function forms, which return a dummy value of the limited
13351 private type @code{Asm_Insn}, can be used in code statements, and indeed
13352 this is the only context where such calls are allowed. Code statements
13353 appear as aggregates of the form:
13355 @smallexample @c ada
13356 Asm_Insn'(Asm (@dots{}));
13357 Asm_Insn'(Asm_Volatile (@dots{}));
13361 In accordance with RM rules, such code statements are allowed only
13362 within subprograms whose entire body consists of such statements. It is
13363 not permissible to intermix such statements with other Ada statements.
13365 Typically the form using intrinsic procedure calls is more convenient
13366 and more flexible. The code statement form is provided to meet the RM
13367 suggestion that such a facility should be made available. The following
13368 is the exact syntax of the call to @code{Asm}. As usual, if named notation
13369 is used, the arguments may be given in arbitrary order, following the
13370 normal rules for use of positional and named arguments)
13374 [Template =>] static_string_EXPRESSION
13375 [,[Outputs =>] OUTPUT_OPERAND_LIST ]
13376 [,[Inputs =>] INPUT_OPERAND_LIST ]
13377 [,[Clobber =>] static_string_EXPRESSION ]
13378 [,[Volatile =>] static_boolean_EXPRESSION] )
13380 OUTPUT_OPERAND_LIST ::=
13381 [PREFIX.]No_Output_Operands
13382 | OUTPUT_OPERAND_ATTRIBUTE
13383 | (OUTPUT_OPERAND_ATTRIBUTE @{,OUTPUT_OPERAND_ATTRIBUTE@})
13385 OUTPUT_OPERAND_ATTRIBUTE ::=
13386 SUBTYPE_MARK'Asm_Output (static_string_EXPRESSION, NAME)
13388 INPUT_OPERAND_LIST ::=
13389 [PREFIX.]No_Input_Operands
13390 | INPUT_OPERAND_ATTRIBUTE
13391 | (INPUT_OPERAND_ATTRIBUTE @{,INPUT_OPERAND_ATTRIBUTE@})
13393 INPUT_OPERAND_ATTRIBUTE ::=
13394 SUBTYPE_MARK'Asm_Input (static_string_EXPRESSION, EXPRESSION)
13398 The identifiers @code{No_Input_Operands} and @code{No_Output_Operands}
13399 are declared in the package @code{Machine_Code} and must be referenced
13400 according to normal visibility rules. In particular if there is no
13401 @code{use} clause for this package, then appropriate package name
13402 qualification is required.
13404 @node GNAT Implementation of Tasking
13405 @section GNAT Implementation of Tasking
13408 This chapter outlines the basic GNAT approach to tasking (in particular,
13409 a multi-layered library for portability) and discusses issues related
13410 to compliance with the Real-Time Systems Annex.
13413 * Mapping Ada Tasks onto the Underlying Kernel Threads::
13414 * Ensuring Compliance with the Real-Time Annex::
13417 @node Mapping Ada Tasks onto the Underlying Kernel Threads
13418 @subsection Mapping Ada Tasks onto the Underlying Kernel Threads
13421 GNAT's run-time support comprises two layers:
13424 @item GNARL (GNAT Run-time Layer)
13425 @item GNULL (GNAT Low-level Library)
13429 In GNAT, Ada's tasking services rely on a platform and OS independent
13430 layer known as GNARL@. This code is responsible for implementing the
13431 correct semantics of Ada's task creation, rendezvous, protected
13434 GNARL decomposes Ada's tasking semantics into simpler lower level
13435 operations such as create a thread, set the priority of a thread,
13436 yield, create a lock, lock/unlock, etc. The spec for these low-level
13437 operations constitutes GNULLI, the GNULL Interface. This interface is
13438 directly inspired from the POSIX real-time API@.
13440 If the underlying executive or OS implements the POSIX standard
13441 faithfully, the GNULL Interface maps as is to the services offered by
13442 the underlying kernel. Otherwise, some target dependent glue code maps
13443 the services offered by the underlying kernel to the semantics expected
13446 Whatever the underlying OS (VxWorks, UNIX, OS/2, Windows NT, etc.) the
13447 key point is that each Ada task is mapped on a thread in the underlying
13448 kernel. For example, in the case of VxWorks, one Ada task = one VxWorks task.
13450 In addition Ada task priorities map onto the underlying thread priorities.
13451 Mapping Ada tasks onto the underlying kernel threads has several advantages:
13455 The underlying scheduler is used to schedule the Ada tasks. This
13456 makes Ada tasks as efficient as kernel threads from a scheduling
13460 Interaction with code written in C containing threads is eased
13461 since at the lowest level Ada tasks and C threads map onto the same
13462 underlying kernel concept.
13465 When an Ada task is blocked during I/O the remaining Ada tasks are
13469 On multiprocessor systems Ada tasks can execute in parallel.
13473 Some threads libraries offer a mechanism to fork a new process, with the
13474 child process duplicating the threads from the parent.
13476 support this functionality when the parent contains more than one task.
13477 @cindex Forking a new process
13479 @node Ensuring Compliance with the Real-Time Annex
13480 @subsection Ensuring Compliance with the Real-Time Annex
13481 @cindex Real-Time Systems Annex compliance
13484 Although mapping Ada tasks onto
13485 the underlying threads has significant advantages, it does create some
13486 complications when it comes to respecting the scheduling semantics
13487 specified in the real-time annex (Annex D).
13489 For instance the Annex D requirement for the @code{FIFO_Within_Priorities}
13490 scheduling policy states:
13493 @emph{When the active priority of a ready task that is not running
13494 changes, or the setting of its base priority takes effect, the
13495 task is removed from the ready queue for its old active priority
13496 and is added at the tail of the ready queue for its new active
13497 priority, except in the case where the active priority is lowered
13498 due to the loss of inherited priority, in which case the task is
13499 added at the head of the ready queue for its new active priority.}
13503 While most kernels do put tasks at the end of the priority queue when
13504 a task changes its priority, (which respects the main
13505 FIFO_Within_Priorities requirement), almost none keep a thread at the
13506 beginning of its priority queue when its priority drops from the loss
13507 of inherited priority.
13509 As a result most vendors have provided incomplete Annex D implementations.
13511 The GNAT run-time, has a nice cooperative solution to this problem
13512 which ensures that accurate FIFO_Within_Priorities semantics are
13515 The principle is as follows. When an Ada task T is about to start
13516 running, it checks whether some other Ada task R with the same
13517 priority as T has been suspended due to the loss of priority
13518 inheritance. If this is the case, T yields and is placed at the end of
13519 its priority queue. When R arrives at the front of the queue it
13522 Note that this simple scheme preserves the relative order of the tasks
13523 that were ready to execute in the priority queue where R has been
13526 @node GNAT Implementation of Shared Passive Packages
13527 @section GNAT Implementation of Shared Passive Packages
13528 @cindex Shared passive packages
13531 GNAT fully implements the pragma @code{Shared_Passive} for
13532 @cindex pragma @code{Shared_Passive}
13533 the purpose of designating shared passive packages.
13534 This allows the use of passive partitions in the
13535 context described in the Ada Reference Manual; i.e. for communication
13536 between separate partitions of a distributed application using the
13537 features in Annex E.
13539 @cindex Distribution Systems Annex
13541 However, the implementation approach used by GNAT provides for more
13542 extensive usage as follows:
13545 @item Communication between separate programs
13547 This allows separate programs to access the data in passive
13548 partitions, using protected objects for synchronization where
13549 needed. The only requirement is that the two programs have a
13550 common shared file system. It is even possible for programs
13551 running on different machines with different architectures
13552 (e.g. different endianness) to communicate via the data in
13553 a passive partition.
13555 @item Persistence between program runs
13557 The data in a passive package can persist from one run of a
13558 program to another, so that a later program sees the final
13559 values stored by a previous run of the same program.
13564 The implementation approach used is to store the data in files. A
13565 separate stream file is created for each object in the package, and
13566 an access to an object causes the corresponding file to be read or
13569 The environment variable @code{SHARED_MEMORY_DIRECTORY} should be
13570 @cindex @code{SHARED_MEMORY_DIRECTORY} environment variable
13571 set to the directory to be used for these files.
13572 The files in this directory
13573 have names that correspond to their fully qualified names. For
13574 example, if we have the package
13576 @smallexample @c ada
13578 pragma Shared_Passive (X);
13585 and the environment variable is set to @code{/stemp/}, then the files created
13586 will have the names:
13594 These files are created when a value is initially written to the object, and
13595 the files are retained until manually deleted. This provides the persistence
13596 semantics. If no file exists, it means that no partition has assigned a value
13597 to the variable; in this case the initial value declared in the package
13598 will be used. This model ensures that there are no issues in synchronizing
13599 the elaboration process, since elaboration of passive packages elaborates the
13600 initial values, but does not create the files.
13602 The files are written using normal @code{Stream_IO} access.
13603 If you want to be able
13604 to communicate between programs or partitions running on different
13605 architectures, then you should use the XDR versions of the stream attribute
13606 routines, since these are architecture independent.
13608 If active synchronization is required for access to the variables in the
13609 shared passive package, then as described in the Ada Reference Manual, the
13610 package may contain protected objects used for this purpose. In this case
13611 a lock file (whose name is @file{___lock} (three underscores)
13612 is created in the shared memory directory.
13613 @cindex @file{___lock} file (for shared passive packages)
13614 This is used to provide the required locking
13615 semantics for proper protected object synchronization.
13617 As of January 2003, GNAT supports shared passive packages on all platforms
13618 except for OpenVMS.
13620 @node Code Generation for Array Aggregates
13621 @section Code Generation for Array Aggregates
13624 * Static constant aggregates with static bounds::
13625 * Constant aggregates with an unconstrained nominal types::
13626 * Aggregates with static bounds::
13627 * Aggregates with non-static bounds::
13628 * Aggregates in assignment statements::
13632 Aggregate have a rich syntax and allow the user to specify the values of
13633 complex data structures by means of a single construct. As a result, the
13634 code generated for aggregates can be quite complex and involve loops, case
13635 statements and multiple assignments. In the simplest cases, however, the
13636 compiler will recognize aggregates whose components and constraints are
13637 fully static, and in those cases the compiler will generate little or no
13638 executable code. The following is an outline of the code that GNAT generates
13639 for various aggregate constructs. For further details, the user will find it
13640 useful to examine the output produced by the -gnatG flag to see the expanded
13641 source that is input to the code generator. The user will also want to examine
13642 the assembly code generated at various levels of optimization.
13644 The code generated for aggregates depends on the context, the component values,
13645 and the type. In the context of an object declaration the code generated is
13646 generally simpler than in the case of an assignment. As a general rule, static
13647 component values and static subtypes also lead to simpler code.
13649 @node Static constant aggregates with static bounds
13650 @subsection Static constant aggregates with static bounds
13653 For the declarations:
13654 @smallexample @c ada
13655 type One_Dim is array (1..10) of integer;
13656 ar0 : constant One_Dim := ( 1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
13660 GNAT generates no executable code: the constant ar0 is placed in static memory.
13661 The same is true for constant aggregates with named associations:
13663 @smallexample @c ada
13664 Cr1 : constant One_Dim := (4 => 16, 2 => 4, 3 => 9, 1=> 1);
13665 Cr3 : constant One_Dim := (others => 7777);
13669 The same is true for multidimensional constant arrays such as:
13671 @smallexample @c ada
13672 type two_dim is array (1..3, 1..3) of integer;
13673 Unit : constant two_dim := ( (1,0,0), (0,1,0), (0,0,1));
13677 The same is true for arrays of one-dimensional arrays: the following are
13680 @smallexample @c ada
13681 type ar1b is array (1..3) of boolean;
13682 type ar_ar is array (1..3) of ar1b;
13683 None : constant ar1b := (others => false); -- fully static
13684 None2 : constant ar_ar := (1..3 => None); -- fully static
13688 However, for multidimensional aggregates with named associations, GNAT will
13689 generate assignments and loops, even if all associations are static. The
13690 following two declarations generate a loop for the first dimension, and
13691 individual component assignments for the second dimension:
13693 @smallexample @c ada
13694 Zero1: constant two_dim := (1..3 => (1..3 => 0));
13695 Zero2: constant two_dim := (others => (others => 0));
13698 @node Constant aggregates with an unconstrained nominal types
13699 @subsection Constant aggregates with an unconstrained nominal types
13702 In such cases the aggregate itself establishes the subtype, so that
13703 associations with @code{others} cannot be used. GNAT determines the
13704 bounds for the actual subtype of the aggregate, and allocates the
13705 aggregate statically as well. No code is generated for the following:
13707 @smallexample @c ada
13708 type One_Unc is array (natural range <>) of integer;
13709 Cr_Unc : constant One_Unc := (12,24,36);
13712 @node Aggregates with static bounds
13713 @subsection Aggregates with static bounds
13716 In all previous examples the aggregate was the initial (and immutable) value
13717 of a constant. If the aggregate initializes a variable, then code is generated
13718 for it as a combination of individual assignments and loops over the target
13719 object. The declarations
13721 @smallexample @c ada
13722 Cr_Var1 : One_Dim := (2, 5, 7, 11);
13723 Cr_Var2 : One_Dim := (others > -1);
13727 generate the equivalent of
13729 @smallexample @c ada
13735 for I in Cr_Var2'range loop
13736 Cr_Var2 (I) := =-1;
13740 @node Aggregates with non-static bounds
13741 @subsection Aggregates with non-static bounds
13744 If the bounds of the aggregate are not statically compatible with the bounds
13745 of the nominal subtype of the target, then constraint checks have to be
13746 generated on the bounds. For a multidimensional array, constraint checks may
13747 have to be applied to sub-arrays individually, if they do not have statically
13748 compatible subtypes.
13750 @node Aggregates in assignment statements
13751 @subsection Aggregates in assignment statements
13754 In general, aggregate assignment requires the construction of a temporary,
13755 and a copy from the temporary to the target of the assignment. This is because
13756 it is not always possible to convert the assignment into a series of individual
13757 component assignments. For example, consider the simple case:
13759 @smallexample @c ada
13764 This cannot be converted into:
13766 @smallexample @c ada
13772 So the aggregate has to be built first in a separate location, and then
13773 copied into the target. GNAT recognizes simple cases where this intermediate
13774 step is not required, and the assignments can be performed in place, directly
13775 into the target. The following sufficient criteria are applied:
13779 The bounds of the aggregate are static, and the associations are static.
13781 The components of the aggregate are static constants, names of
13782 simple variables that are not renamings, or expressions not involving
13783 indexed components whose operands obey these rules.
13787 If any of these conditions are violated, the aggregate will be built in
13788 a temporary (created either by the front-end or the code generator) and then
13789 that temporary will be copied onto the target.
13792 @node The Size of Discriminated Records with Default Discriminants
13793 @section The Size of Discriminated Records with Default Discriminants
13796 If a discriminated type @code{T} has discriminants with default values, it is
13797 possible to declare an object of this type without providing an explicit
13800 @smallexample @c ada
13802 type Size is range 1..100;
13804 type Rec (D : Size := 15) is record
13805 Name : String (1..D);
13813 Such an object is said to be @emph{unconstrained}.
13814 The discriminant of the object
13815 can be modified by a full assignment to the object, as long as it preserves the
13816 relation between the value of the discriminant, and the value of the components
13819 @smallexample @c ada
13821 Word := (3, "yes");
13823 Word := (5, "maybe");
13825 Word := (5, "no"); -- raises Constraint_Error
13830 In order to support this behavior efficiently, an unconstrained object is
13831 given the maximum size that any value of the type requires. In the case
13832 above, @code{Word} has storage for the discriminant and for
13833 a @code{String} of length 100.
13834 It is important to note that unconstrained objects do not require dynamic
13835 allocation. It would be an improper implementation to place on the heap those
13836 components whose size depends on discriminants. (This improper implementation
13837 was used by some Ada83 compilers, where the @code{Name} component above
13839 been stored as a pointer to a dynamic string). Following the principle that
13840 dynamic storage management should never be introduced implicitly,
13841 an Ada95 compiler should reserve the full size for an unconstrained declared
13842 object, and place it on the stack.
13844 This maximum size approach
13845 has been a source of surprise to some users, who expect the default
13846 values of the discriminants to determine the size reserved for an
13847 unconstrained object: ``If the default is 15, why should the object occupy
13849 The answer, of course, is that the discriminant may be later modified,
13850 and its full range of values must be taken into account. This is why the
13855 type Rec (D : Positive := 15) is record
13856 Name : String (1..D);
13864 is flagged by the compiler with a warning:
13865 an attempt to create @code{Too_Large} will raise @code{Storage_Error},
13866 because the required size includes @code{Positive'Last}
13867 bytes. As the first example indicates, the proper approach is to declare an
13868 index type of ``reasonable'' range so that unconstrained objects are not too
13871 One final wrinkle: if the object is declared to be @code{aliased}, or if it is
13872 created in the heap by means of an allocator, then it is @emph{not}
13874 it is constrained by the default values of the discriminants, and those values
13875 cannot be modified by full assignment. This is because in the presence of
13876 aliasing all views of the object (which may be manipulated by different tasks,
13877 say) must be consistent, so it is imperative that the object, once created,
13883 @node Project File Reference
13884 @chapter Project File Reference
13887 This chapter describes the syntax and semantics of project files.
13888 Project files specify the options to be used when building a system.
13889 Project files can specify global settings for all tools,
13890 as well as tool-specific settings.
13891 See the chapter on project files in the GNAT Users guide for examples of use.
13895 * Lexical Elements::
13897 * Empty declarations::
13898 * Typed string declarations::
13902 * Project Attributes::
13903 * Attribute References::
13904 * External Values::
13905 * Case Construction::
13907 * Package Renamings::
13909 * Project Extensions::
13910 * Project File Elaboration::
13913 @node Reserved Words
13914 @section Reserved Words
13917 All Ada95 reserved words are reserved in project files, and cannot be used
13918 as variable names or project names. In addition, the following are
13919 also reserved in project files:
13922 @item @code{extends}
13924 @item @code{external}
13926 @item @code{project}
13930 @node Lexical Elements
13931 @section Lexical Elements
13934 Rules for identifiers are the same as in Ada95. Identifiers
13935 are case-insensitive. Strings are case sensitive, except where noted.
13936 Comments have the same form as in Ada95.
13946 simple_name @{. simple_name@}
13950 @section Declarations
13953 Declarations introduce new entities that denote types, variables, attributes,
13954 and packages. Some declarations can only appear immediately within a project
13955 declaration. Others can appear within a project or within a package.
13959 declarative_item ::=
13960 simple_declarative_item |
13961 typed_string_declaration |
13962 package_declaration
13964 simple_declarative_item ::=
13965 variable_declaration |
13966 typed_variable_declaration |
13967 attribute_declaration |
13968 case_construction |
13972 @node Empty declarations
13973 @section Empty declarations
13976 empty_declaration ::=
13980 An empty declaration is allowed anywhere a declaration is allowed.
13983 @node Typed string declarations
13984 @section Typed string declarations
13987 Typed strings are sequences of string literals. Typed strings are the only
13988 named types in project files. They are used in case constructions, where they
13989 provide support for conditional attribute definitions.
13993 typed_string_declaration ::=
13994 @b{type} <typed_string_>_simple_name @b{is}
13995 ( string_literal @{, string_literal@} );
13999 A typed string declaration can only appear immediately within a project
14002 All the string literals in a typed string declaration must be distinct.
14008 Variables denote values, and appear as constituents of expressions.
14011 typed_variable_declaration ::=
14012 <typed_variable_>simple_name : <typed_string_>name := string_expression ;
14014 variable_declaration ::=
14015 <variable_>simple_name := expression;
14019 The elaboration of a variable declaration introduces the variable and
14020 assigns to it the value of the expression. The name of the variable is
14021 available after the assignment symbol.
14024 A typed_variable can only be declare once.
14027 a non typed variable can be declared multiple times.
14030 Before the completion of its first declaration, the value of variable
14031 is the null string.
14034 @section Expressions
14037 An expression is a formula that defines a computation or retrieval of a value.
14038 In a project file the value of an expression is either a string or a list
14039 of strings. A string value in an expression is either a literal, the current
14040 value of a variable, an external value, an attribute reference, or a
14041 concatenation operation.
14054 attribute_reference
14060 ( <string_>expression @{ , <string_>expression @} )
14063 @subsection Concatenation
14065 The following concatenation functions are defined:
14067 @smallexample @c ada
14068 function "&" (X : String; Y : String) return String;
14069 function "&" (X : String_List; Y : String) return String_List;
14070 function "&" (X : String_List; Y : String_List) return String_List;
14074 @section Attributes
14077 An attribute declaration defines a property of a project or package. This
14078 property can later be queried by means of an attribute reference.
14079 Attribute values are strings or string lists.
14081 Some attributes are associative arrays. These attributes are mappings whose
14082 domain is a set of strings. These attributes are declared one association
14083 at a time, by specifying a point in the domain and the corresponding image
14084 of the attribute. They may also be declared as a full associative array,
14085 getting the same associations as the corresponding attribute in an imported
14086 or extended project.
14088 Attributes that are not associative arrays are called simple attributes.
14092 attribute_declaration ::=
14093 full_associative_array_declaration |
14094 @b{for} attribute_designator @b{use} expression ;
14096 full_associative_array_declaration ::=
14097 @b{for} <associative_array_attribute_>simple_name @b{use}
14098 <project_>simple_name [ . <package_>simple_Name ] ' <attribute_>simple_name ;
14100 attribute_designator ::=
14101 <simple_attribute_>simple_name |
14102 <associative_array_attribute_>simple_name ( string_literal )
14106 Some attributes are project-specific, and can only appear immediately within
14107 a project declaration. Others are package-specific, and can only appear within
14108 the proper package.
14110 The expression in an attribute definition must be a string or a string_list.
14111 The string literal appearing in the attribute_designator of an associative
14112 array attribute is case-insensitive.
14114 @node Project Attributes
14115 @section Project Attributes
14118 The following attributes apply to a project. All of them are simple
14123 Expression must be a path name. The attribute defines the
14124 directory in which the object files created by the build are to be placed. If
14125 not specified, object files are placed in the project directory.
14128 Expression must be a path name. The attribute defines the
14129 directory in which the executables created by the build are to be placed.
14130 If not specified, executables are placed in the object directory.
14133 Expression must be a list of path names. The attribute
14134 defines the directories in which the source files for the project are to be
14135 found. If not specified, source files are found in the project directory.
14138 Expression must be a list of file names. The attribute
14139 defines the individual files, in the project directory, which are to be used
14140 as sources for the project. File names are path_names that contain no directory
14141 information. If the project has no sources the attribute must be declared
14142 explicitly with an empty list.
14144 @item Source_List_File
14145 Expression must a single path name. The attribute
14146 defines a text file that contains a list of source file names to be used
14147 as sources for the project
14150 Expression must be a path name. The attribute defines the
14151 directory in which a library is to be built. The directory must exist, must
14152 be distinct from the project's object directory, and must be writable.
14155 Expression must be a string that is a legal file name,
14156 without extension. The attribute defines a string that is used to generate
14157 the name of the library to be built by the project.
14160 Argument must be a string value that must be one of the
14161 following @code{"static"}, @code{"dynamic"} or @code{"relocatable"}. This
14162 string is case-insensitive. If this attribute is not specified, the library is
14163 a static library. Otherwise, the library may be dynamic or relocatable. This
14164 distinction is operating-system dependent.
14166 @item Library_Version
14167 Expression must be a string value whose interpretation
14168 is platform dependent. On UNIX, it is used only for dynamic/relocatable
14169 libraries as the internal name of the library (the @code{"soname"}). If the
14170 library file name (built from the @code{Library_Name}) is different from the
14171 @code{Library_Version}, then the library file will be a symbolic link to the
14172 actual file whose name will be @code{Library_Version}.
14174 @item Library_Interface
14175 Expression must be a string list. Each element of the string list
14176 must designate a unit of the project.
14177 If this attribute is present in a Library Project File, then the project
14178 file is a Stand-alone Library_Project_File.
14180 @item Library_Auto_Init
14181 Expression must be a single string "true" or "false", case-insensitive.
14182 If this attribute is present in a Stand-alone Library Project File,
14183 it indicates if initialization is automatic when the dynamic library
14186 @item Library_Options
14187 Expression must be a string list. Indicates additional switches that
14188 are to be used when building a shared library.
14191 Expression must be a single string. Designates an alternative to "gcc"
14192 for building shared libraries.
14194 @item Library_Src_Dir
14195 Expression must be a path name. The attribute defines the
14196 directory in which the sources of the interfaces of a Stand-alone Library will
14197 be copied. The directory must exist, must be distinct from the project's
14198 object directory and source directories, and must be writable.
14201 Expression must be a list of strings that are legal file names.
14202 These file names designate existing compilation units in the source directory
14203 that are legal main subprograms.
14205 When a project file is elaborated, as part of the execution of a gnatmake
14206 command, one or several executables are built and placed in the Exec_Dir.
14207 If the gnatmake command does not include explicit file names, the executables
14208 that are built correspond to the files specified by this attribute.
14210 @item Main_Language
14211 This is a simple attribute. Its value is a string that specifies the
14212 language of the main program.
14215 Expression must be a string list. Each string designates
14216 a programming language that is known to GNAT. The strings are case-insensitive.
14218 @item Locally_Removed_Files
14219 This attribute is legal only in a project file that extends another.
14220 Expression must be a list of strings that are legal file names.
14221 Each file name must designate a source that would normally be inherited
14222 by the current project file. It cannot designate an immediate source that is
14223 not inherited. Each of the source files in the list are not considered to
14224 be sources of the project file: they are not inherited.
14227 @node Attribute References
14228 @section Attribute References
14231 Attribute references are used to retrieve the value of previously defined
14232 attribute for a package or project.
14235 attribute_reference ::=
14236 attribute_prefix ' <simple_attribute_>simple_name [ ( string_literal ) ]
14238 attribute_prefix ::=
14240 <project_simple_name | package_identifier |
14241 <project_>simple_name . package_identifier
14245 If an attribute has not been specified for a given package or project, its
14246 value is the null string or the empty list.
14248 @node External Values
14249 @section External Values
14252 An external value is an expression whose value is obtained from the command
14253 that invoked the processing of the current project file (typically a
14259 @b{external} ( string_literal [, string_literal] )
14263 The first string_literal is the string to be used on the command line or
14264 in the environment to specify the external value. The second string_literal,
14265 if present, is the default to use if there is no specification for this
14266 external value either on the command line or in the environment.
14268 @node Case Construction
14269 @section Case Construction
14272 A case construction supports attribute declarations that depend on the value of
14273 a previously declared variable.
14277 case_construction ::=
14278 @b{case} <typed_variable_>name @b{is}
14283 @b{when} discrete_choice_list =>
14284 @{case_construction | attribute_declaration | empty_declaration@}
14286 discrete_choice_list ::=
14287 string_literal @{| string_literal@} |
14292 All choices in a choice list must be distinct. The choice lists of two
14293 distinct alternatives must be disjoint. Unlike Ada, the choice lists of all
14294 alternatives do not need to include all values of the type. An @code{others}
14295 choice must appear last in the list of alternatives.
14301 A package provides a grouping of variable declarations and attribute
14302 declarations to be used when invoking various GNAT tools. The name of
14303 the package indicates the tool(s) to which it applies.
14307 package_declaration ::=
14308 package_specification | package_renaming
14310 package_specification ::=
14311 @b{package} package_identifier @b{is}
14312 @{simple_declarative_item@}
14313 @b{end} package_identifier ;
14315 package_identifier ::=
14316 @code{Naming} | @code{Builder} | @code{Compiler} | @code{Binder} |
14317 @code{Linker} | @code{Finder} | @code{Cross_Reference} |
14318 @code{gnatls} | @code{IDE} | @code{Pretty_Printer}
14321 @subsection Package Naming
14324 The attributes of a @code{Naming} package specifies the naming conventions
14325 that apply to the source files in a project. When invoking other GNAT tools,
14326 they will use the sources in the source directories that satisfy these
14327 naming conventions.
14329 The following attributes apply to a @code{Naming} package:
14333 This is a simple attribute whose value is a string. Legal values of this
14334 string are @code{"lowercase"}, @code{"uppercase"} or @code{"mixedcase"}.
14335 These strings are themselves case insensitive.
14338 If @code{Casing} is not specified, then the default is @code{"lowercase"}.
14340 @item Dot_Replacement
14341 This is a simple attribute whose string value satisfies the following
14345 @item It must not be empty
14346 @item It cannot start or end with an alphanumeric character
14347 @item It cannot be a single underscore
14348 @item It cannot start with an underscore followed by an alphanumeric
14349 @item It cannot contain a dot @code{'.'} if longer than one character
14353 If @code{Dot_Replacement} is not specified, then the default is @code{"-"}.
14356 This is an associative array attribute, defined on language names,
14357 whose image is a string that must satisfy the following
14361 @item It must not be empty
14362 @item It cannot start with an alphanumeric character
14363 @item It cannot start with an underscore followed by an alphanumeric character
14367 For Ada, the attribute denotes the suffix used in file names that contain
14368 library unit declarations, that is to say units that are package and
14369 subprogram declarations. If @code{Spec_Suffix ("Ada")} is not
14370 specified, then the default is @code{".ads"}.
14372 For C and C++, the attribute denotes the suffix used in file names that
14373 contain prototypes.
14376 This is an associative array attribute defined on language names,
14377 whose image is a string that must satisfy the following
14381 @item It must not be empty
14382 @item It cannot start with an alphanumeric character
14383 @item It cannot start with an underscore followed by an alphanumeric character
14384 @item It cannot be a suffix of @code{Spec_Suffix}
14388 For Ada, the attribute denotes the suffix used in file names that contain
14389 library bodies, that is to say units that are package and subprogram bodies.
14390 If @code{Body_Suffix ("Ada")} is not specified, then the default is
14393 For C and C++, the attribute denotes the suffix used in file names that contain
14396 @item Separate_Suffix
14397 This is a simple attribute whose value satisfies the same conditions as
14398 @code{Body_Suffix}.
14400 This attribute is specific to Ada. It denotes the suffix used in file names
14401 that contain separate bodies. If it is not specified, then it defaults to same
14402 value as @code{Body_Suffix ("Ada")}.
14405 This is an associative array attribute, specific to Ada, defined over
14406 compilation unit names. The image is a string that is the name of the file
14407 that contains that library unit. The file name is case sensitive if the
14408 conventions of the host operating system require it.
14411 This is an associative array attribute, specific to Ada, defined over
14412 compilation unit names. The image is a string that is the name of the file
14413 that contains the library unit body for the named unit. The file name is case
14414 sensitive if the conventions of the host operating system require it.
14416 @item Specification_Exceptions
14417 This is an associative array attribute defined on language names,
14418 whose value is a list of strings.
14420 This attribute is not significant for Ada.
14422 For C and C++, each string in the list denotes the name of a file that
14423 contains prototypes, but whose suffix is not necessarily the
14424 @code{Spec_Suffix} for the language.
14426 @item Implementation_Exceptions
14427 This is an associative array attribute defined on language names,
14428 whose value is a list of strings.
14430 This attribute is not significant for Ada.
14432 For C and C++, each string in the list denotes the name of a file that
14433 contains source code, but whose suffix is not necessarily the
14434 @code{Body_Suffix} for the language.
14437 The following attributes of package @code{Naming} are obsolescent. They are
14438 kept as synonyms of other attributes for compatibility with previous versions
14439 of the Project Manager.
14442 @item Specification_Suffix
14443 This is a synonym of @code{Spec_Suffix}.
14445 @item Implementation_Suffix
14446 This is a synonym of @code{Body_Suffix}.
14448 @item Specification
14449 This is a synonym of @code{Spec}.
14451 @item Implementation
14452 This is a synonym of @code{Body}.
14455 @subsection package Compiler
14458 The attributes of the @code{Compiler} package specify the compilation options
14459 to be used by the underlying compiler.
14462 @item Default_Switches
14463 This is an associative array attribute. Its
14464 domain is a set of language names. Its range is a string list that
14465 specifies the compilation options to be used when compiling a component
14466 written in that language, for which no file-specific switches have been
14470 This is an associative array attribute. Its domain is
14471 a set of file names. Its range is a string list that specifies the
14472 compilation options to be used when compiling the named file. If a file
14473 is not specified in the Switches attribute, it is compiled with the
14474 settings specified by Default_Switches.
14476 @item Local_Configuration_Pragmas.
14477 This is a simple attribute, whose
14478 value is a path name that designates a file containing configuration pragmas
14479 to be used for all invocations of the compiler for immediate sources of the
14483 This is an associative array attribute. Its domain is
14484 a set of main source file names. Its range is a simple string that specifies
14485 the executable file name to be used when linking the specified main source.
14486 If a main source is not specified in the Executable attribute, the executable
14487 file name is deducted from the main source file name.
14490 @subsection package Builder
14493 The attributes of package @code{Builder} specify the compilation, binding, and
14494 linking options to be used when building an executable for a project. The
14495 following attributes apply to package @code{Builder}:
14498 @item Default_Switches
14504 @item Global_Configuration_Pragmas
14505 This is a simple attribute, whose
14506 value is a path name that designates a file that contains configuration pragmas
14507 to be used in every build of an executable. If both local and global
14508 configuration pragmas are specified, a compilation makes use of both sets.
14511 This is an associative array attribute, defined over
14512 compilation unit names. The image is a string that is the name of the
14513 executable file corresponding to the main source file index.
14514 This attribute has no effect if its value is the empty string.
14516 @item Executable_Suffix
14517 This is a simple attribute whose value is a suffix to be added to
14518 the executables that don't have an attribute Executable specified.
14521 @subsection package Gnatls
14524 The attributes of package @code{Gnatls} specify the tool options to be used
14525 when invoking the library browser @command{gnatls}.
14526 The following attributes apply to package @code{Gnatls}:
14533 @subsection package Binder
14536 The attributes of package @code{Binder} specify the options to be used
14537 when invoking the binder in the construction of an executable.
14538 The following attributes apply to package @code{Binder}:
14541 @item Default_Switches
14547 @subsection package Linker
14550 The attributes of package @code{Linker} specify the options to be used when
14551 invoking the linker in the construction of an executable.
14552 The following attributes apply to package @code{Linker}:
14555 @item Default_Switches
14561 @subsection package Cross_Reference
14564 The attributes of package @code{Cross_Reference} specify the tool options
14566 when invoking the library tool @command{gnatxref}.
14567 The following attributes apply to package @code{Cross_Reference}:
14570 @item Default_Switches
14576 @subsection package Finder
14579 The attributes of package @code{Finder} specify the tool options to be used
14580 when invoking the search tool @command{gnatfind}.
14581 The following attributes apply to package @code{Finder}:
14584 @item Default_Switches
14590 @subsection package Pretty_Printer
14593 The attributes of package @code{Pretty_Printer}
14594 specify the tool options to be used
14595 when invoking the formatting tool @command{gnatpp}.
14596 The following attributes apply to package @code{Pretty_Printer}:
14599 @item Default_switches
14605 @subsection package IDE
14608 The attributes of package @code{IDE} specify the options to be used when using
14609 an Integrated Development Environment such as @command{GPS}.
14613 This is a simple attribute. Its value is a string that designates the remote
14614 host in a cross-compilation environment, to be used for remote compilation and
14615 debugging. This field should not be specified when running on the local
14619 This is a simple attribute. Its value is a string that specifies the
14620 name of IP address of the embedded target in a cross-compilation environment,
14621 on which the program should execute.
14623 @item Communication_Protocol
14624 This is a simple string attribute. Its value is the name of the protocol
14625 to use to communicate with the target in a cross-compilation environment,
14626 e.g. @code{"wtx"} or @code{"vxworks"}.
14628 @item Compiler_Command
14629 This is an associative array attribute, whose domain is a language name. Its
14630 value is string that denotes the command to be used to invoke the compiler.
14631 The value of @code{Compiler_Command ("Ada")} is expected to be compatible with
14632 gnatmake, in particular in the handling of switches.
14634 @item Debugger_Command
14635 This is simple attribute, Its value is a string that specifies the name of
14636 the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.
14638 @item Default_Switches
14639 This is an associative array attribute. Its indexes are the name of the
14640 external tools that the GNAT Programming System (GPS) is supporting. Its
14641 value is a list of switches to use when invoking that tool.
14644 This is a simple attribute. Its value is a string that specifies the name
14645 of the @command{gnatls} utility to be used to retrieve information about the
14646 predefined path; e.g., @code{"gnatls"}, @code{"powerpc-wrs-vxworks-gnatls"}.
14649 This is a simple attribute. Its value is a string used to specify the
14650 Version Control System (VCS) to be used for this project, e.g CVS, RCS
14651 ClearCase or Perforce.
14653 @item VCS_File_Check
14654 This is a simple attribute. Its value is a string that specifies the
14655 command used by the VCS to check the validity of a file, either
14656 when the user explicitly asks for a check, or as a sanity check before
14657 doing the check-in.
14659 @item VCS_Log_Check
14660 This is a simple attribute. Its value is a string that specifies
14661 the command used by the VCS to check the validity of a log file.
14665 @node Package Renamings
14666 @section Package Renamings
14669 A package can be defined by a renaming declaration. The new package renames
14670 a package declared in a different project file, and has the same attributes
14671 as the package it renames.
14674 package_renaming ::==
14675 @b{package} package_identifier @b{renames}
14676 <project_>simple_name.package_identifier ;
14680 The package_identifier of the renamed package must be the same as the
14681 package_identifier. The project whose name is the prefix of the renamed
14682 package must contain a package declaration with this name. This project
14683 must appear in the context_clause of the enclosing project declaration,
14684 or be the parent project of the enclosing child project.
14690 A project file specifies a set of rules for constructing a software system.
14691 A project file can be self-contained, or depend on other project files.
14692 Dependencies are expressed through a context clause that names other projects.
14698 context_clause project_declaration
14700 project_declaration ::=
14701 simple_project_declaration | project_extension
14703 simple_project_declaration ::=
14704 @b{project} <project_>simple_name @b{is}
14705 @{declarative_item@}
14706 @b{end} <project_>simple_name;
14712 [@b{limited}] @b{with} path_name @{ , path_name @} ;
14719 A path name denotes a project file. A path name can be absolute or relative.
14720 An absolute path name includes a sequence of directories, in the syntax of
14721 the host operating system, that identifies uniquely the project file in the
14722 file system. A relative path name identifies the project file, relative
14723 to the directory that contains the current project, or relative to a
14724 directory listed in the environment variable ADA_PROJECT_PATH.
14725 Path names are case sensitive if file names in the host operating system
14726 are case sensitive.
14728 The syntax of the environment variable ADA_PROJECT_PATH is a list of
14729 directory names separated by colons (semicolons on Windows).
14731 A given project name can appear only once in a context_clause.
14733 It is illegal for a project imported by a context clause to refer, directly
14734 or indirectly, to the project in which this context clause appears (the
14735 dependency graph cannot contain cycles), except when one of the with_clause
14736 in the cycle is a @code{limited with}.
14738 @node Project Extensions
14739 @section Project Extensions
14742 A project extension introduces a new project, which inherits the declarations
14743 of another project.
14747 project_extension ::=
14748 @b{project} <project_>simple_name @b{extends} path_name @b{is}
14749 @{declarative_item@}
14750 @b{end} <project_>simple_name;
14754 The project extension declares a child project. The child project inherits
14755 all the declarations and all the files of the parent project, These inherited
14756 declaration can be overridden in the child project, by means of suitable
14759 @node Project File Elaboration
14760 @section Project File Elaboration
14763 A project file is processed as part of the invocation of a gnat tool that
14764 uses the project option. Elaboration of the process file consists in the
14765 sequential elaboration of all its declarations. The computed values of
14766 attributes and variables in the project are then used to establish the
14767 environment in which the gnat tool will execute.
14769 @node Obsolescent Features
14770 @chapter Obsolescent Features
14773 This chapter describes features that are provided by GNAT, but are
14774 considered obsolescent since there are preferred ways of achieving
14775 the same effect. These features are provided solely for historical
14776 compatibility purposes.
14779 * pragma No_Run_Time::
14780 * pragma Ravenscar::
14781 * pragma Restricted_Run_Time::
14784 @node pragma No_Run_Time
14785 @section pragma No_Run_Time
14787 The pragma @code{No_Run_Time} is used to achieve an affect similar
14788 to the use of the "Zero Foot Print" configurable run time, but without
14789 requiring a specially configured run time. The result of using this
14790 pragma, which must be used for all units in a partition, is to restrict
14791 the use of any language features requiring run-time support code. The
14792 preferred usage is to use an appropriately configured run-time that
14793 includes just those features that are to be made accessible.
14795 @node pragma Ravenscar
14796 @section pragma Ravenscar
14798 The pragma @code{Ravenscar} has exactly the same effect as pragma
14799 @code{Profile (Ravenscar)}. The latter usage is preferred since it
14800 is part of the new Ada 2005 standard.
14802 @node pragma Restricted_Run_Time
14803 @section pragma Restricted_Run_Time
14805 The pragma @code{Restricted_Run_Time} has exactly the same effect as
14806 pragma @code{Profile (Restricted)}. The latter usage is
14807 preferred since the Ada 2005 pragma @code{Profile} is intended for
14808 this kind of implementation dependent addition.
14811 @c GNU Free Documentation License
14813 @node Index,,GNU Free Documentation License, Top
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