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 (consult 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 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
       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. Oth-
       erwise, (time_t)-1 shall be returned.

ERRORS
       The time() function may fail if:

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

       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	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  his-
       torical	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 reli-
       ably detected.

       The use of the <time.h> header instead of <sys/types.h> allows compati-
       bility 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
       standard.

FUTURE DIRECTIONS
       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.

SEE ALSO
       asctime(),  clock(),  clock_getres(),  ctime(), difftime(), futimens(),
       gettimeofday(),	gmtime(),  localtime(),	 mktime(),  strftime(),	 strp-
       time(), times(), utime()

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

COPYRIGHT
       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 Electri-
       cal  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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group		     2013			      TIME(3P)