lib/stdbool.in.h

   1 /* Copyright (C) 2001-2003, 2006-2011 Free Software Foundation, Inc.
   2    Written by Bruno Haible <haible@clisp.cons.org>, 2001.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  17
  18 #ifndef _GL_STDBOOL_H
  19 #define _GL_STDBOOL_H
  20
  21 /* ISO C 99 <stdbool.h> for platforms that lack it.  */
  22
  23 /* Usage suggestions:
  24
  25    Programs that use <stdbool.h> should be aware of some limitations
  26    and standards compliance issues.
  27
  28    Standards compliance:
  29
  30        - <stdbool.h> must be #included before 'bool', 'false', 'true'
  31          can be used.
  32
  33        - You cannot assume that sizeof (bool) == 1.
  34
  35        - Programs should not undefine the macros bool, true, and false,
  36          as C99 lists that as an "obsolescent feature".
  37
  38    Limitations of this substitute, when used in a C89 environment:
  39
  40        - <stdbool.h> must be #included before the '_Bool' type can be used.
  41
  42        - You cannot assume that _Bool is a typedef; it might be a macro.
  43
  44        - Bit-fields of type 'bool' are not supported.  Portable code
  45          should use 'unsigned int foo : 1;' rather than 'bool foo : 1;'.
  46
  47        - In C99, casts and automatic conversions to '_Bool' or 'bool' are
  48          performed in such a way that every nonzero value gets converted
  49          to 'true', and zero gets converted to 'false'.  This doesn't work
  50          with this substitute.  With this substitute, only the values 0 and 1
  51          give the expected result when converted to _Bool' or 'bool'.
  52
  53        - C99 allows the use of (_Bool)0.0 in constant expressions, but
  54          this substitute cannot always provide this property.
  55
  56    Also, it is suggested that programs use 'bool' rather than '_Bool';
  57    this isn't required, but 'bool' is more common.  */
  58
  59
  60 /* 7.16. Boolean type and values */
  61
  62 /* BeOS <sys/socket.h> already #defines false 0, true 1.  We use the same
  63    definitions below, but temporarily we have to #undef them.  */
  64 #if defined __BEOS__ && !defined __HAIKU__
  65 # include <OS.h> /* defines bool but not _Bool */
  66 # undef false
  67 # undef true
  68 #endif
  69
  70 /* For the sake of symbolic names in gdb, we define true and false as
  71    enum constants, not only as macros.
  72    It is tempting to write
  73       typedef enum { false = 0, true = 1 } _Bool;
  74    so that gdb prints values of type 'bool' symbolically. But if we do
  75    this, values of type '_Bool' may promote to 'int' or 'unsigned int'
  76    (see ISO C 99 6.7.2.2.(4)); however, '_Bool' must promote to 'int'
  77    (see ISO C 99 6.3.1.1.(2)).  So we add a negative value to the
  78    enum; this ensures that '_Bool' promotes to 'int'.  */
  79 #if defined __cplusplus || (defined __BEOS__ && !defined __HAIKU__)
  80   /* A compiler known to have 'bool'.  */
  81   /* If the compiler already has both 'bool' and '_Bool', we can assume they
  82      are the same types.  */
  83 # if !@HAVE__BOOL@
  84 typedef bool _Bool;
  85 # endif
  86 #else
  87 # if !defined __GNUC__
  88    /* If @HAVE__BOOL@:
  89         Some HP-UX cc and AIX IBM C compiler versions have compiler bugs when
  90         the built-in _Bool type is used.  See
  91           http://gcc.gnu.org/ml/gcc-patches/2003-12/msg02303.html
  92           http://lists.gnu.org/archive/html/bug-coreutils/2005-11/msg00161.html
  93           http://lists.gnu.org/archive/html/bug-coreutils/2005-10/msg00086.html
  94         Similar bugs are likely with other compilers as well; this file
  95         wouldn't be used if <stdbool.h> was working.
  96         So we override the _Bool type.
  97       If !@HAVE__BOOL@:
  98         Need to define _Bool ourselves. As 'signed char' or as an enum type?
  99         Use of a typedef, with SunPRO C, leads to a stupid
 100           "warning: _Bool is a keyword in ISO C99".
 101         Use of an enum type, with IRIX cc, leads to a stupid
 102           "warning(1185): enumerated type mixed with another type".
 103         Even the existence of an enum type, without a typedef,
 104           "Invalid enumerator. (badenum)" with HP-UX cc on Tru64.
 105         The only benefit of the enum, debuggability, is not important
 106         with these compilers.  So use 'signed char' and no enum.  */
 107 #  define _Bool signed char
 108 # else
 109    /* With this compiler, trust the _Bool type if the compiler has it.  */
 110 #  if !@HAVE__BOOL@
 111 typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool;
 112 #  endif
 113 # endif
 114 #endif
 115 #define bool _Bool
 116
 117 /* The other macros must be usable in preprocessor directives.  */
 118 #define false 0
 119 #define true 1
 120 #define __bool_true_false_are_defined 1
 121
 122 #endif /* _GL_STDBOOL_H */