MKTIME
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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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 broke-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 broke-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("-unknow-");
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.-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/ma-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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