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author | Jim Meyering <jim@meyering.net> | 2003-08-18 09:44:49 +0000 |
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committer | Jim Meyering <jim@meyering.net> | 2003-08-18 09:44:49 +0000 |
commit | b1b4af8047b2d6c2b2ea0d552969e25f872da675 (patch) | |
tree | ee8166cbc3f75e901def92c7c94473473d360165 /lib/stdbool_.h | |
parent | 84a9ab5a07427ab8322424cd0c401e847326e7e2 (diff) | |
download | coreutils-b1b4af8047b2d6c2b2ea0d552969e25f872da675.tar.xz |
Sync with gnulib.
Diffstat (limited to 'lib/stdbool_.h')
-rw-r--r-- | lib/stdbool_.h | 55 |
1 files changed, 47 insertions, 8 deletions
diff --git a/lib/stdbool_.h b/lib/stdbool_.h index c29958d4a..3dbb51b24 100644 --- a/lib/stdbool_.h +++ b/lib/stdbool_.h @@ -1,4 +1,4 @@ -/* Copyright (C) 2001-2003 Free Software Foundation, Inc. +/* Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc. Written by Bruno Haible <haible@clisp.cons.org>, 2001. This program is free software; you can redistribute it and/or modify @@ -20,6 +20,37 @@ /* ISO C 99 <stdbool.h> for platforms that lack it. */ +/* Usage suggestions: + + Programs that use <stdbool.h> should be aware of some limitations + and standards compliance issues. + + Standards compliance: + + - <stdbool.h> must be #included before 'bool', 'false', 'true' + can be used. + + - You cannot assume that sizeof (bool) == 1. + + - Programs should not undefine the macros bool, true, and false, + as C99 lists that as an "obsolescent feature". + + Limitations of this substitute, when used in a C89 environment: + + - <stdbool.h> must be #included before the '_Bool' type can be used. + + - You cannot assume that _Bool is a typedef; it might be a macro. + + - In C99, casts and automatic conversions to '_Bool' or 'bool' are + performed in such a way that every nonzero value gets converted + to 'true', and zero gets converted to 'false'. This doesn't work + with this substitute. With this substitute, only the values 0 and 1 + give the expected result when converted to _Bool' or 'bool'. + + Also, it is suggested that programs use 'bool' rather than '_Bool'; + this isn't required, but 'bool' is more common. */ + + /* 7.16. Boolean type and values */ /* BeOS <sys/socket.h> already #defines false 0, true 1. We use the same @@ -29,16 +60,24 @@ # undef true #endif -/* For the sake of symbolic names in gdb, define true and false as - enum constants. However, do not define _Bool as the enum type, - since the enum type might be compatible with unsigned int, whereas - _Bool must promote to int. Also, make _Bool a macro rather than a - typedef, to suppress warnings by the Sun Forte Developer 7 C - compiler that _Bool is a keyword in ISO C99. */ +/* For the sake of symbolic names in gdb, we define true and false as + enum constants, not only as macros. + It is tempting to write + typedef enum { false = 0, true = 1 } _Bool; + so that gdb prints values of type 'bool' symbolically. But if we do + this, values of type '_Bool' may promote to 'int' or 'unsigned int' + (see ISO C 99 6.7.2.2.(4)); however, '_Bool' must promote to 'int' + (see ISO C 99 6.3.1.1.(2)). So we add a negative value to the + enum; this ensures that '_Bool' promotes to 'int'. */ #ifndef __cplusplus # if !@HAVE__BOOL@ +# if defined __SUNPRO_C && (__SUNPRO_C < 0x550 || __STDC__ == 1) + /* Avoid stupid "warning: _Bool is a keyword in ISO C99". */ +# define _Bool signed char enum { false = 0, true = 1 }; -# define _Bool signed char +# else +typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool; +# endif # endif #else typedef bool _Bool; |