time.h (GNU Gnulib)

Gnulib module: time-h

Portability problems fixed by Gnulib:

‘struct timespec’ is not defined on some platforms.
The macro TIME_UTC is not defined on many platforms: glibc 2.15, macOS 10.13, FreeBSD 11.0, NetBSD 7.1, OpenBSD 6.0, Minix 3.1.8, AIX 7.1, HP-UX 11.31, Solaris 11.3, Cygwin 2.9, mingw, MSVC 14, Android 9.0.
Some platforms provide a NULL macro that cannot be used in arbitrary expressions: NetBSD 5.0.

Portability problems fixed by the Gnulib module year2038:

On some platforms where time_t defaults to 32-bit but can be changed to 64-bit, functions like stat can fail with errno == EOVERFLOW when a 32-bit timestamp is out of range, such as with a file timestamp in the far future or past: glibc 2.34+ atop 32-bit x86 or ARM Linux. See Avoiding the year 2038 problem.

Portability problems not fixed by Gnulib:

On some platforms struct tm lacks the the tm_gmtoff and tm_zone members: AIX 7.3, HP-UX 11, Solaris 11.4, mingw, MSVC 14.
On some platforms the global state variables daylight, timezone and tzname are not available. Even on platforms where they are available, their contents are often unreliable, even in single-threaded programs. Portable code can instead use struct tm’s tm_gmtoff and tm_zone members when available, and the strftime function with %z or %Z conversion specifiers otherwise.
On platforms where time_t is always 32-bit, functions like stat can fail with errno == EOVERFLOW when a timestamp is out of range, such as with a file timestamp in the far future or past; on other such platforms, the functions silently return the low-order 32 bits of the correct timestamp. These platforms will be obsolete when 32-bit time_t rolls around, which will occur in 2038 for the typical case when time_t is signed. See Avoiding the year 2038 problem.
On some platforms the tv_nsec member of struct timespec is not of type long, but is of type long long instead: glibc x32