mktime(3p) — Linux manual page


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

PROLOG         top

       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         top

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

SYNOPSIS         top

       #include <time.h>

       time_t mktime(struct tm *timeptr);

DESCRIPTION         top

       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 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         top

       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         top

       The mktime() function shall fail if:

              The result cannot be represented.

       The following sections are informative.

EXAMPLES         top

       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;



RATIONALE         top




SEE ALSO         top

       asctime(3p), clock(3p), ctime(3p), difftime(3p), gmtime(3p),
       localtime(3p), strftime(3p), strptime(3p), time(3p), tzset(3p),

       The Base Definitions volume of POSIX.1‐2017, Section 4.16,
       Seconds Since the Epoch, time.h(0p)

COPYRIGHT         top

       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 to man page format. To report such errors, see .

IEEE/The Open Group               2017                        MKTIME(3P)

Pages that refer to this page: time.h(0p)asctime(3p)clock(3p)ctime(3p)difftime(3p)gmtime(3p)localtime(3p)strftime(3p)time(3p)tzset(3p)