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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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
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.
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:
EOVERFLOW
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)
(void)puts("-unknown-");
else {
(void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
(void)puts(daybuf);
}
return 0;
}
None.
None.
None.
asctime(3p), clock(3p), ctime(3p), difftime(3p), gmtime(3p),
localtime(3p), strftime(3p), strptime(3p), time(3p), tzset(3p),
utime(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds
Since the Epoch, time.h(0p)
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(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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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