time

TIME(2)                    Linux Programmer's Manual                   TIME(2)



NAME
       time - get time in seconds

SYNOPSIS
       #include <time.h>

       time_t time(time_t *tloc);

DESCRIPTION
       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.

RETURN VALUE
       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.

ERRORS
       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.

CONFORMING TO
       SVr4, 4.3BSD, C89, C99, POSIX.1-2001.  POSIX does not specify any error
       conditions.

NOTES
       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.

BUGS
       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).

SEE ALSO
       date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)

COLOPHON
       This page is part of release 5.03 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)