mktime
Defined in header
<time.h>
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Converts local calendar time to a time since epoch as a time_t object. time->tm_wday
and time->tm_yday
are ignored. The values in time
are not checked for being out of range.
A negative value of time->tm_isdst
causes mktime
to attempt to determine if Daylight Saving Time was in effect.
If the conversion is successful, the time
object is modified. All fields of time
are updated to fit their proper ranges. time->tm_wday
and time->tm_yday
are recalculated using information available in other fields.
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[edit] Parameters
time | - | pointer to a tm object specifying local calendar time to convert |
[edit] Return value
time since epoch as a time_t object on success or -1 if time
cannot be represented as a time_t object.
[edit] Notes
If the tm object was obtained from POSIX strptime or equivalent function, the value of tm_isdst
is indeterminate, and needs to be set explicitly before calling mktime
.
[edit] Example
Display the time 100 months ago
#include <stdio.h> #include <time.h> #include <stdlib.h> int main(void) { time_t t = time(NULL); struct tm *tmptr = localtime(&t); printf("Today is %s", asctime(tmptr)); tmptr->tm_mon -= 100; time_t result = mktime(tmptr); if (result == ((time_t)-1)) { fprintf(stderr,"mktime() failed in file %s at line # %d\n", __FILE__,__LINE__-3); exit(EXIT_FAILURE); } printf("100 months ago was %s", asctime(tmptr)); }
Output:
Today is Wed Oct 9 10:47:25 2013 100 months ago was Thu Jun 9 10:47:25 2005
[edit] See also
converts time since epoch to calendar time expressed as local time (function) |
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C++ documentation for mktime
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