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 which contains a calendar time whihc 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:

// CPP 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 << "Tha Day on 18th June 2018 was "
         << weekday[time_ptr->tm_wday]; 
  
    return 0; 
} 

Output:

Tha Day on 18th June 2018 was Monday

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