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.  Otherwise,  (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 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 detected.

       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 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(), strptime(), 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 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 .