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9.48 stdbool.h

POSIX specification:
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdbool.h.html

Gnulib module: stdbool-c99

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

Portability problems fixed by Gnulib:

• This header file is missing on some platforms: AIX 5.1, HP-UX 11.
• This header file is not usable in C++ mode with the vendor compiler on Solaris 10.
• Some compilers have bugs relating to ‘bool’.
• This header file defines true incorrectly on some platforms: OpenBSD 4.7 with gcc 2.95.

Portability problems not fixed by Gnulib:

• ‘_Bool’ cannot be used before <stdbool.h> is included, or if the program is intended to be compiled by a C++ compiler. (With the advent of C23, ‘_Bool’ is obsolescent anyway.)
• You cannot assume that _Bool is a typedef; it might be a macro. For example, C23 allows _Bool to be a macro.
• Bit-fields of type ‘bool’ are not supported. Portable code should use ‘unsigned int foo : 1;’ rather than ‘bool foo : 1;’.
• Casts and automatic conversions to ‘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.
• You cannot assume that casting a floating point literal to ‘bool’ will result in a constant expression.