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9.50 stddef.h

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

Gnulib module: stddef

Portability problems fixed by Gnulib:

• Some platforms fail to provide unreachable, which was added in C23: GCC 13, clang 15, AIX with xlc 12.1, Solaris with Sun C 5.15, and others.
• Some platforms fail to provide max_align_t, which was added in C11: NetBSD 8.0, Solaris 11.0, and others.
• max_align_t does not have the expected alignment on some platforms: NetBSD 8.0/x86, AIX 7.2 with xlc in 64-bit mode.
• Some platforms provide a NULL macro that cannot be used in arbitrary expressions: NetBSD 5.0
• Some platforms provide a NULL macro whose value does not have the size of a pointer: AIX 7.2 with xlc in 64-bit mode.
• When this header file is provided by TinyCC 0.9.27 on glibc or macOS systems, it does not fulfil the expectations of other system header files.

Portability problems not fixed by Gnulib:

• Some platforms fail to provide nullptr_t, which Gnulib cannot usefully emulate: GCC 12, Clang 15, and other pre-2023 C compilers.
• Some platforms define nullptr_t even when <stddef.h> is not included: GCC 14.0.1 20240411 (Red Hat 14.0.1-0).
• Some platforms provide an offsetof macro that cannot be used in arbitrary expressions: Solaris 11.4 This problem can be worked around by parenthesizing the offsetof expression in the unlikely case you use it with sizeof or ‘[]’.