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



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

NAME
       time - get time

SYNOPSIS
       #include <time.h>

       time_t time(time_t *tloc);


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

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

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

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   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",
                      asctime(localtime(&result)),
                          (uintmax_t)result);
                  return(0);
              }

       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;
              ...
              time(&now);
              minutes_to_event = ...;
              printf("The time is ");
              puts(asctime(localtime(&now)));
              printf("There are %d minutes to the event.\n",
                  minutes_to_event);
              ...

APPLICATION USAGE
       None.

RATIONALE
       The  time()  function returns a value in seconds (type time_t) while times() returns a set of values in clock ticks (type
       clock_t).  Some historical implementations, such as 4.3 BSD, have mechanisms capable of returning more precise times (see
       below). A generalized timing scheme to unify these various timing mechanisms has been proposed but not adopted.

       Implementations  in  which  time_t  is  a  32-bit signed integer (many historical implementations) fail in the year 2038.
       IEEE Std 1003.1-2001 does not address this problem. However, the use of the time_t type is mandated in order to ease  the
       eventual fix.

       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 IEEE Std 1003.1-2001 uses the latter type in order to agree with the ISO C standard.

       4.3 BSD includes time() only as an alternate function to the more flexible gettimeofday() function.

FUTURE DIRECTIONS
       In a future version of this volume of IEEE Std 1003.1-2001, 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 vol-
       ume of IEEE Std 1003.1-2001 should be evaluated to determine whether their lifetime will extend past 2038.

SEE ALSO
       asctime(),  clock(),  ctime(),  difftime(),  gettimeofday(),  gmtime(),  localtime(),  mktime(),  strftime(), strptime(),
       utime(), the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      TIME(3P)