7.23.2.3 The mktime function

Synopsis

1

#include <time.h>
time_t mktime(struct tm *timeptr);

Description

2

The mktime function converts the broken-down time, expressed as local time, in the structure pointed to by timeptr into a calendar time value with the same encoding as that of the values returned by the time function. 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 the ranges indicated above.[1] 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 the ranges indicated above; the final value of tm_mday is not set until tm_mon and tm_year are determined.

Returns

3

The mktime function returns the specified calendar time encoded as a value of type time_t. If the calendar time cannot be represented, the function returns the value (time_t)(-1).

4

EXAMPLE What day of the week is July 4, 2001?

#include <stdio.h>
#include <time.h>
static const char *const wday[] = {
        "Sunday", "Monday", "Tuesday", "Wednesday",
        "Thursday", "Friday", "Saturday", "-unknown-"
};
struct tm time_str;
/* ... */

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) == (time_t)(-1))
      time_str.tm_wday = 7;
printf("%s\n", wday[time_str.tm_wday]);

Footnotes