# time

## 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.1‐2017 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.1‐2017 uses the latter type in order to agree with the ISO C
           standard.
    


## FUTURE DIRECTIONS



           In a future version of this volume of POSIX.1‐2017, **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.1‐2017 should be
           evaluated to determine whether their lifetime will extend past
           2038.
    


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