C mktime() function

Last update on December 21 2022 12:07:45 (UTC/GMT +8 hours)

C mktime() function - Convert broken-down time into time since the Epoch

Syntax:

time_t mktime(struct tm *timeptr)

The mktime() function is used to convert a stored tm structure (assume to be in job local time) pointed to by time, into a time_t structure suitable for use with other time functions.

The fields of the tm structure include:

tm_sec	Seconds (0-61)
tm_min	Minutes (0-59)
tm_hour	Hours (0-23)
tm_mday	Day of month (1-31)
tm_mon	Month (0-11; January = 0)
tm_year	Year (current year minus 1900)
tm_wday	Day of week (0-6; Sunday = 0)
tm_yday	Day of year (0-365; January 1 = 0)
tm_isdst	Zero if daylight saving time is not in effect; positive if daylight saving time is in effect; negative if the information is not available.

Parameters:

Name	Description	Required /Optional
timeptr	Pointer to time structure	Required

Return value from mktime()

Universal Coordinate Time (UTC) having type time_t.
The value (time_t)(-1) is returned if the Universal Coordinate Time cannot be represented.

Example: mktime() function

The following example shows the usage of mktime() function.

#include <stdio.h>
#include <time.h>
 
char *weekday[] = { "Sunday", "Monday", "Tuesday", "Wednesday",
                 "Thursday", "Friday", "Saturday" };
 
int main(void)
{
  time_t dt1, dt3;
  struct tm *t2;
 
  dt1 = time(NULL);
  t2 = localtime(&dt1);
  t2 -> tm_mday += 110;
  t2 -> tm_hour += 20;
  dt3 = mktime(t2);
 
  printf("It will be a %s after 110 days and 20 hours from now.\n",
          weekday[t2 -> tm_wday]);
}

Output:

It will be a Monday after 110 days and 20 hours from now.

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