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 to indicate the error.
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.
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).
This page is part of release 5.13 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/.
|
Copyright (c) 1992 Drew Eckhardt (drewcs.colorado.edu), March 28, 1992 %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END 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 |