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. Oth-
       erwise, (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
              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  his-
       torical  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 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
       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 flex-
       ible 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  volume  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,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the