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.

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 .