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 .