mktime

time_t mktime (struct tm * timeptr);

Convert tm structure to time_t

Returns the value of type time_t that represents the local time described by the tm structure pointed by timeptr (which may be modified).

This function performs the reverse translation that localtime does.

The values of the members tm_wday and tm_yday of timeptr are ignored, and the values of the other members are interpreted even if out of their valid ranges (see struct tm). For example, tm_mday may contain values above 31, which are interpreted accordingly as the days that follow the last day of the selected month.

A call to this function automatically adjusts the values of the members of timeptr if they are off-range or -in the case of tm_wday and tm_yday- if they have values that do not match the date described by the other members.

Parameters

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

Return Value

A time_t value corresponding to the calendar time passed as argument.
If the calendar time cannot be represented, a value of -1 is returned.

Example

/* mktime example: weekday calculator */
#include <stdio.h>      /* printf, scanf */
#include <time.h>       /* time_t, struct tm, time, mktime */

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

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

Data races

The object pointed by timeptr is accessed, and potentially modified.

Exceptions (C++)

No-throw guarantee: this function never throws exceptions.

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types