time - get time in seconds
Standard C library (
libc,
-lc)
#include <time.h>
time_t time(time_t *_Nullable 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 to indicate
the error.
- 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, 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 reaches or exceeds 2**31 seconds (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).
date(1),
gettimeofday(2),
ctime(3),
ftime(3),
time(7),
vdso(7)