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.

SEE ALSO

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

COLOPHON

   This page is part of release 4.09 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/.

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