time - get time in seconds
#include <time.h>
long time(NULL);
Think of this function as returning a long
as output and as taking only NULL
as input.
This function gets the current date and time as seconds since January 1, 1970, 00:00:00 UTC, otherwise known as the Epoch.
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
.
This function returns the number of seconds since January 1, 1970, 00:00:00 UTC.
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.
#include <stdio.h>
#include <time.h>
int main(void)
{
printf("The time is now %li.\n", time(NULL));
}
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.
On some architectures, an implementation of time() is provided in the vdso(7).
This page is part of release 5.10 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/.