MKTIME(P) POSIX Programmer's Manual MKTIME(P)NAMEmktime - convert broken-down time into time since the Epoch
SYNOPSIS
#include <time.h>
time_t mktime(struct tm *timeptr);
DESCRIPTION
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 are ignored, and the original values of the other compo‐
nents are not restricted to the ranges described in <time.h>.
A positive or 0 value for tm_isdst shall cause mktime() to presume ini‐
tially 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 sec‐
onds since the Epoch (see the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.14, Seconds Since the Epoch) corrected
for timezone and any seasonal time adjustments, where the names in the
structure and in the expression correspond.
Upon successful completion, the values of the tm_wday and tm_yday com‐
ponents of the structure shall be set appropriately, and the other com‐
ponents are 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.
ERRORS
No errors are defined.
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 ALSOasctime() , clock() , ctime() , difftime() , gmtime() , localtime() ,
strftime() , strptime() , time() , utime() , the Base Definitions vol‐
ume of IEEE Std 1003.1-2001, <time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 MKTIME(P)
