mktime


function
<ctime>
time_t mktime ( struct tm * timeptr );

Convert tm structure to time_t

Interprets the contents of the tm structure pointed by timeptr as a calendar time expressed in local time. This calendar time is used to adjust the values of the members of timeptr accordingly and returned as an object of type time_t.

The original values of the members tm_wday and tm_yday of timeptr are ignored, and the ranges of values for the rest of its members are not restricted to their normal values (like tm_mday being between 1 and 31).

The object pointed by timeptr is modified, setting the tm_wday and tm_yday to their appropiate values, and modifying the other members as necessary to values within the normal range representing the specified time.

Parameters

timeptr
Pointer to a tm structure that contains a calendar time broken down into its components (see tm).


Return Value

A time_t value corresponding to the calendar time passed as argument.
On error, a -1 value is returned.

Example

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/* mktime example: weekday calculator */
#include <stdio.h>
#include <time.h>

int main ()
{
  time_t rawtime;
  struct tm * timeinfo;
  int year, month ,day;
  char * weekday[] = { "Sunday", "Monday",
                       "Tuesday", "Wednesday",
                       "Thursday", "Friday", "Saturday"};

  /* prompt user for date */
  printf ("Enter year: "); scanf ("%d",&year);
  printf ("Enter month: "); scanf ("%d",&month);
  printf ("Enter day: "); scanf ("%d",&day);

  /* get current timeinfo and modify it to the user's choice */
  time ( &rawtime );
  timeinfo = localtime ( &rawtime );
  timeinfo->tm_year = year - 1900;
  timeinfo->tm_mon = month - 1;
  timeinfo->tm_mday = day;

  /* call mktime: timeinfo->tm_wday will be set */
  mktime ( timeinfo );

  printf ("That day is a %s.\n", weekday[timeinfo->tm_wday]);
  
  return 0;
}


Output:

Enter year: 2000
Enter month: 5
Enter day: 20
That day is a Saturday.


See also.
asctime Convert tm structure to string (function)
gmtime Convert time_t to tm as UTC time (function)
localtime Convert time_t to tm as local time (function)
time Get current time (function)