mktime() - transform format of time value
#include <time.h>
time_t mktime (struct tm *tm)
The function mktime(3) converts the local time, expressed in the structure pointed to by tm into a time_t time value with the same encoding as that of the values returned by the time(2) function, that is, seconds from the Epoch, UTC.
The original values of the tm_wday and tm_yday components of the structure are ignored, and the original values of the other components are not restricted to their normal ranges. (A positive or zero value for tm_isdst causes mktime(3) to presume initially that summer time (for example, Daylight Saving Time) is or is not in effect for the specified time, respectively. A negative value for tm_isdst causes the mktime(3) function to attempt to divine whether summer time is in effect for the specified time.)
On successful completion, the values of the tm_wday and tm_yday components of the structure are set appropriately, and the other components are set to represent the specified calendar time, but with their values forced to their normal ranges; the final value of tm_mday is not set until tm_mon and tm_year are determined. Mktime(3) returns the specified calendar time; if the calendar time cannot be represented, it returns -1.
External declarations as well as the tm structure definition are in the <time.h> include file. The tm structure includes at least the following fields:
| int | tm_sec; | seconds (0 - 60) |
| int | tm_min; | minutes (0 - 59) |
| int | tm_hour; | hours (0 - 23) |
| int | tm_mday; | day of month (1 - 31) |
| int | tm_mon; | month of year (0 - 11) |
| int | tm_year; | year - 1900 |
| int | tm_wday; | day of week (Sunday = 0) |
| int | tm_yday; | day of year (0 - 365) |
| int | tm_isdst; | is summer time in effect? |
The field tm_isdst is non-zero if summer time is in effect.
date(1)
asctime(3)
ctime(3)
gmtime(3)
localtime(3)
difftime(3)
getenv(3)
time(2)
tzset(3)