mktime() function in C++ STL

The mktime() is an inbuilt C++ function which converts the local calendar time to the time since epoch and returns the value as an object of type time_t.

Syntax :

time_t  mktime( struct tm  *time_ptr )

Parameters: The function accepts a mandatory parameter pointer time_ptr that points to a tm object structure that contains a calendar time which is to be converted. 

Return Value: The function returns two type of values as described below: 

• It returns the time since epoch as an object of type time_t if the parameter passed is a success.
• It returns -1 on failure.

Below program illustrates the mktime() function: 

C++

// C++ program to demonstrate the
// mktime() function

#include <bits/stdc++.h>
using namespace std;

int main()
{
    time_t tim;
    tm* time_ptr;
    char weekday[7][20] = { "Sunday",
                            "Monday",
                            "Tuesday",
                            "Wednesday",
                            "Thursday",
                            "Friday",
                            "Saturday" };

    // Date
    int year = 2018;
    int month = 6;
    int day = 18;

    time(&tim);
    time_ptr = localtime(&tim);

    // tm_year is time since 1900
    time_ptr->tm_year = year - 1900;

    // Months calculated since January
    time_ptr->tm_mon = month - 1;

    // Day calculated in the month
    time_ptr->tm_mday = day;

    // time_ptr pointer to be pass
    mktime(time_ptr);

    cout << "The Day on 18th June 2018 was "
         << weekday[time_ptr->tm_wday];

    return 0;
}

Output

The Day on 18th June 2018 was Monday