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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
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TIME(2) Linux Programmer's Manual TIME(2)
time - get time in seconds
#include <time.h>
time_t time(time_t *tloc);
time() returns the time as the number of seconds since the Epoch,
1970-01-01 00:00:00 +0000 (UTC).
If tloc is non-NULL, the return value is also stored in the memory
pointed to by tloc.
On success, the value of time in seconds since the Epoch is returned.
On error, ((time_t) -1) is returned, and errno is set appropriately.
EFAULT tloc points outside your accessible address space (but see
BUGS).
On systems where the C library time() wrapper function invokes
an implementation provided by the vdso(7) (so that there is no
trap into the kernel), an invalid address may instead trigger
a SIGSEGV signal.
SVr4, 4.3BSD, C89, C99, POSIX.1-2001. POSIX does not specify any
error conditions.
POSIX.1 defines seconds since the Epoch using a formula that
approximates the number of seconds between a specified time and the
Epoch. This formula takes account of the facts that all years that
are evenly divisible by 4 are leap years, but years that are evenly
divisible by 100 are not leap years unless they are also evenly
divisible by 400, in which case they are leap years. This value is
not the same as the actual number of seconds between the time and the
Epoch, because of leap seconds and because system clocks are not
required to be synchronized to a standard reference. The intention
is that the interpretation of seconds since the Epoch values be
consistent; see POSIX.1-2008 Rationale A.4.15 for further rationale.
On Linux, a call to time() with tloc specified as NULL cannot fail
with the error EOVERFLOW, even on ABIs where time_t is a signed
32-bit integer and the clock ticks past the time 2**31 (2038-01-19
03:14:08 UTC, ignoring leap seconds). (POSIX.1 permits, but does not
require, the EOVERFLOW error in the case where the seconds since the
Epoch will not fit in time_t.) Instead, the behavior on Linux is
undefined when the system time is out of the time_t range.
Applications intended to run after 2038 should use ABIs with time_t
wider than 32 bits.
Error returns from this system call are indistinguishable from
successful reports that the time is a few seconds before the Epoch,
so the C library wrapper function never sets errno as a result of
this call.
The tloc argument is obsolescent and should always be NULL in new
code. When tloc is NULL, the call cannot fail.
C library/kernel differences
On some architectures, an implementation of time() is provided in the
vdso(7).
date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 TIME(2)
Pages that refer to this page: clock_getres(2), gettimeofday(2), seccomp(2), syscalls(2), ctime(3), difftime(3), ftime(3), getdate(3), misc_conv(3), pmtimeval(3), __ppc_get_timebase(3), pthread_tryjoin_np(3), strftime(3), strptime(3), tzset(3), uuid_time(3), rtc(4), tzfile(5), utmp(5), signal-safety(7), time(7), zic(8)
Copyright and license for this manual page
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