TIME(3P)                    POSIX Programmer's Manual                   TIME(3P)

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the corresponding
       Linux manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       time — get time

       #include <time.h>

       time_t time(time_t *tloc);

       The functionality described on this reference page is aligned with the
       ISO C standard. Any conflict between the requirements described here and
       the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers
       to the ISO C standard.

       The time() function shall return the value of time in seconds since the

       The tloc argument points to an area where the return value is also
       stored. If tloc is a null pointer, no value is stored.

       Upon successful completion, time() shall return the value of time.
       Otherwise, (time_t)−1 shall be returned.

       The time() function may fail if:

              The number of seconds since the Epoch will not fit in an object of
              type time_t.

       The following sections are informative.

   Getting the Current Time
       The following example uses the time() function to calculate the time
       elapsed, in seconds, since the Epoch, localtime() to convert that value
       to a broken-down time, and asctime() to convert the broken-down time
       values into a printable string.

           #include <stdio.h>
           #include <time.h>

           int main(void)
           time_t result;

               result = time(NULL);
               printf("%s%ju secs since the Epoch\n",

       This example writes the current time to stdout in a form like this:

           Wed Jun 26 10:32:15 1996
           835810335 secs since the Epoch

   Timing an Event
       The following example gets the current time, prints it out in the user's
       format, and prints the number of minutes to an event being timed.

           #include <time.h>
           #include <stdio.h>
           time_t now;
           int minutes_to_event;
           minutes_to_event = ...;
           printf("The time is ");
           printf("There are %d minutes to the event.\n",


       The time() function returns a value in seconds while clock_gettime() and
       gettimeofday() return a struct timespec (seconds and nanoseconds) and
       struct timeval (seconds and microseconds), respectively, and are
       therefore capable of returning more precise times. The times() function
       is also capable of more precision than time() as it returns a value in
       clock ticks, although it returns the elapsed time since an arbitrary
       point such as system boot time, not since the epoch.

       Implementations in which time_t is a 32-bit signed integer (many
       historical implementations) fail in the year 2038. POSIX.1‐2008 does not
       address this problem. However, the use of the time_t type is mandated in
       order to ease the eventual fix.

       On some systems the time() function is implemented using a system call
       that does not return an error condition in addition to the return value.
       On these systems it is impossible to differentiate between valid and
       invalid return values and hence overflow conditions cannot be reliably

       The use of the <time.h> header instead of <sys/types.h> allows
       compatibility with the ISO C standard.

       Many historical implementations (including Version 7) and the 1984
       /usr/group standard use long instead of time_t.  This volume of
       POSIX.1‐2008 uses the latter type in order to agree with the ISO C

       In a future version of this volume of POSIX.1‐2008, time_t is likely to
       be required to be capable of representing times far in the future.
       Whether this will be mandated as a 64-bit type or a requirement that a
       specific date in the future be representable (for example, 10000 AD) is
       not yet determined. Systems purchased after the approval of this volume
       of POSIX.1‐2008 should be evaluated to determine whether their lifetime
       will extend past 2038.

       asctime(), clock(), clock_getres(), ctime(), difftime(), futimens(),
       gettimeofday(), gmtime(), localtime(), mktime(), strftime(), strptime(),
       times(), utime()

       The Base Definitions volume of POSIX.1‐2008, <time.h>

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical
       and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008
       with the 2013 Technical Corrigendum 1 applied.) In the event of any
       discrepancy between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee
       document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
       to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                   2013                              TIME(3P)