# mktime

## 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



           mktime — convert broken-down time into time since the Epoch
    


## SYNOPSIS



           #include <time.h>
    
           time_t mktime(struct tm *_timeptr_);
    


## 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 _mktime_() function shall convert the broken-down time,
           expressed as local time, in the structure pointed to by _timeptr_ ,
           into a time since the Epoch value with the same encoding as that
           of the values returned by _time_().  The original values of the
           _tm_wday_ and _tm_yday_ components of the structure shall be ignored,
           and the original values of the other components shall not be
           restricted to the ranges described in _< time.h>_.
    
           A positive or 0 value for _tm_isdst_ shall cause _mktime_() to presume
           initially that Daylight Savings Time, respectively, is or is not
           in effect for the specified time. A negative value for _tm_isdst_
           shall cause _mktime_() to attempt to determine whether Daylight
           Savings Time is in effect for the specified time.
    
           Local timezone information shall be set as though _mktime_() called
           _tzset_().
    
           The relationship between the **tm** structure (defined in the _< time.h>_
           header) and the time in seconds since the Epoch is that the result
           shall be as specified in the expression given in the definition of
           seconds since the Epoch (see the Base Definitions volume of
           POSIX.1‐2017, _Section 4.16_ , _Seconds Since the Epoch_) corrected for
           timezone and any seasonal time adjustments, where the names other
           than _tm_yday_ in the structure and in the expression correspond,
           and the _tm_yday_ value used in the expression is the day of the
           year from 0 to 365 inclusive, calculated from the other **tm**
           structure members specified in _< time.h>_ (excluding _tm_wday_).
    
           Upon successful completion, the values of the _tm_wday_ and _tm_yday_
           components of the structure shall be set appropriately, and the
           other components shall be set to represent the specified time
           since the Epoch, but with their values forced to the ranges
           indicated in the _< time.h>_ entry; the final value of _tm_mday_ shall
           not be set until _tm_mon_ and _tm_year_ are determined.
    


## RETURN VALUE



           The _mktime_() function shall return the specified time since the
           Epoch encoded as a value of type **time_t**.  If the time since the
           Epoch cannot be represented, the function shall return the value
           (**time_t**)-1 and set _errno_ to indicate the error.
    


## ERRORS



           The _mktime_() function shall fail if:
    
           **EOVERFLOW**
                  The result cannot be represented.
    
           _The following sections are informative._
    


## EXAMPLES



           What day of the week is July 4, 2001?
    
               #include <stdio.h>
               #include <time.h>
    
               struct tm time_str;
    
               char daybuf[20];
    
               int main(void)
               {
                   time_str.tm_year = 2001 — 1900;
                   time_str.tm_mon = 7 — 1;
                   time_str.tm_mday = 4;
                   time_str.tm_hour = 0;
                   time_str.tm_min = 0;
                   time_str.tm_sec = 1;
                   time_str.tm_isdst = -1;
                   if (mktime(&time_str) == -1)
                       (void)puts("-unknown-");
                   else {
                       (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
                       (void)puts(daybuf);
                   }
                   return 0;
               }
    


## APPLICATION USAGE



           None.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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