@node stdbool.h
@section @file{stdbool.h}

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/stdbool.h.html}

Gnulib module: stdbool-h-c99
@mindex stdbool-h-c99
@mindex bool

The @code{stdbool-h-c99} module is present only for programs that
formerly used the old @code{stdbool} module for C99 compatibility,
and that for some reason cannot use the current @code{bool} module
for C23 compatibility.

Portability problems fixed by Gnulib:
@itemize
@item
This header file is missing on some platforms:
AIX 5.1, HP-UX 11.
@item
This header file is not usable in C++ mode with the vendor compiler
on Solaris 10.
@item
Some compilers have bugs relating to @samp{bool}.
@item
This header file defines @code{true} incorrectly on some platforms:
OpenBSD 4.7 with gcc 2.95.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
@samp{_Bool} cannot be used before @code{<stdbool.h>} is included, or if
the program is intended to be compiled by a C++ compiler.
(With the advent of C23, @samp{_Bool} is obsolescent anyway.)
@item
You cannot assume that @code{_Bool} is a keyword or a typedef;
@c In ISO C 99 § 6.4.1.(1) it is listed as a keyword.
@c Older releases of Mac OS X and FreeBSD define it as a typedef.
it might be a macro.
For example, C23 allows @code{_Bool} to be a macro.
@c See ISO C 23 § 6.4.1.(3) footnote 63.
@item
Bit-fields of type @samp{bool} are not supported.  Portable code
should use @samp{unsigned int foo : 1;} rather than @samp{bool foo : 1;}.
@item
Casts and automatic conversions to @samp{bool} don't test against the
zero value or the null pointer, as they should.  Such casts should only
be used if the value is known to be equal to 0 or 1.
@item
You cannot assume that casting a floating point literal to @samp{bool} will
result in a constant expression.
@end itemize
