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

       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.

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

       #include <time.h>

       time_t mktime(struct tm *timeptr);

       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

       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

       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.

       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.

       The mktime() function shall fail if:

              The result cannot be represented.

       The following sections are informative.

       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)
               else {
                   (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
               return 0;




       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>

       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 .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
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IEEE/The Open Group                   2017                            MKTIME(3P)