MKTIME(3)                  POSIX Programmer's Manual                 MKTIME(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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.

SEE ALSO
       asctime(), clock(), ctime(), difftime(), gmtime(), localtime(),
       strftime(), strptime(), time(), tzset(), utime()

       The Base Definitions volume of POSIX.1-2017, Section 4.16, Seconds
       Since the Epoch, <time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 original Standard can
       be obtained online at http://www.opengroup.org/unix/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 .



IEEE/The Open Group                  2017                            MKTIME(3)
