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

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

Gnulib module: time-h
@mindex time-h

Portability problems fixed by Gnulib:
@itemize
@item
@samp{struct timespec} is not defined on some platforms.
@item
The macro @code{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.
@item
Some platforms provide a @code{NULL} macro that cannot be used in arbitrary
expressions:
NetBSD 5.0.
@end itemize

@mindex year2038
Portability problems fixed by the Gnulib module @code{year2038}:
@itemize
@item
On some platforms where @code{time_t} defaults to 32-bit but can be
changed to 64-bit, functions like @code{stat} can fail with
@code{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.
@xref{Avoiding the year 2038 problem}.
@end itemize

Portability problems not fixed by Gnulib:

@itemize
@item
On some platforms @code{struct tm} lacks the the @code{tm_gmtoff} and
@code{tm_zone} members:
AIX 7.3, HP-UX 11, Solaris 11.4, mingw, MSVC 14.

@item
On some platforms the global state variables @code{daylight},
@code{timezone} and @code{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 @code{struct tm}'s @code{tm_gmtoff} and
@code{tm_zone} members when available, and the @code{strftime} function
with @code{%z} or @code{%Z} conversion specifiers otherwise.

@item
On platforms where @code{time_t} is always 32-bit, functions like
@code{stat} can fail with @code{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 @code{time_t}
rolls around, which will occur in 2038 for the typical case when
@code{time_t} is signed.
@xref{Avoiding the year 2038 problem}.

@item
On some platforms the @code{tv_nsec} member of @code{struct timespec}
is not of type @code{long}, but is of type @code{long long} instead:
glibc x32
@end itemize
