TIME(3)                FreeBSD Library Functions Manual                TIME(3)

NAME
     time - get time of day

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <time.h>

     time_t
     time(time_t *tloc);

DESCRIPTION
     The time() function returns the value of time in seconds since 0 hours, 0
     minutes, 0 seconds, January 1, 1970, Coordinated Universal Time (UTC).
     If an error occurs, time() returns the value (time_t)-1.

     The return value is also stored in *tloc, provided that tloc is non-null.

ERRORS
     The time() function may fail for any of the reasons described in
     gettimeofday(2).

SEE ALSO
     clock_gettime(2), gettimeofday(2), ctime(3)

STANDARDS
     The time function conforms to IEEE Std 1003.1-2008 ("POSIX.1").

HISTORY
     The time() system call first appeared in Version 1 AT&T UNIX.  Through
     the Version 3 AT&T UNIX, it returned 60 Hz ticks since an epoch that
     changed occasionally, because it was a 32-bit value that overflowed in a
     little over 2 years.

     In Version 4 AT&T UNIX the granularity of the return value was reduced to
     whole seconds, delaying the aforementioned overflow until 2038.

     Version 7 AT&T UNIX introduced the ftime() system call, which returned
     time at a millisecond level, though retained the gtime() system call
     (exposed as time() in userland).  time() could have been implemented as a
     wrapper around ftime(), but that wasn't done.

     4.1cBSD implemented a higher-precision time function gettimeofday() to
     replace ftime() and reimplemented time() in terms of that.

     Since FreeBSD 9 the implementation of time() uses
     clock_gettime(CLOCK_SECOND) instead of gettimeofday() for performance
     reasons.

BUGS
     Neither ISO/IEC 9899:1999 ("ISO C99") nor IEEE Std 1003.1-2001
     ("POSIX.1") requires time() to set errno on failure; thus, it is
     impossible for an application to distinguish the valid time value -1
     (representing the last UTC second of 1969) from the error return value.

     Systems conforming to earlier versions of the C and POSIX standards
     (including older versions of FreeBSD) did not set *tloc in the error
     case.

FreeBSD 13.1-RELEASE-p6         April 14, 2022         FreeBSD 13.1-RELEASE-p6