time — get time in seconds
time() returns the time as
the number of seconds since the Epoch, 1970-01-01 00:00:00
non-NULL, the return value is also stored in the memory
pointed to by
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.
outside your accessible address space (but see
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
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
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.
is obsolescent and should always be NULL in new code. When
tloc is NULL, the
call cannot fail.
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description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 1992 Drew Eckhardt (drewcs.colorado.edu), March 28, 1992
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Modified by Michael Haardt <michaelmoria.de>
Modified Sat Jul 24 14:13:40 1993 by Rik Faith <faithcs.unc.edu>
Additions by Joseph S. Myers <jsm28cam.ac.uk>, 970909