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 approxi-
       mates 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  ac-
       tual  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  Ratio-
       nale 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 inte-
       ger  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 success-
       ful  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 5.05 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)