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Linux 2.6 - man page for time (linux section 3posix)

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

       time - get time

       #include <time.h>

       time_t time(time_t *tloc);

       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.

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

       No errors are defined.

       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 (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 implementa-
       tions) fail in the year 2038.  IEEE Std 1003.1-2001 does not address  this  problem.  How-
       ever, 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()

       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  man-
       dated  as  a  64-bit  type  or  a requirement that a specific date in the future be repre-
       sentable (for example, 10000 AD) is not	yet  determined.   Systems  purchased  after  the
       approval  of  this volume of IEEE Std 1003.1-2001 should be evaluated to determine whether
       their lifetime will extend past 2038.

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

       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, Copyright (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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  TIME(P)

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