c++11 difftime() calculating leap year incorrectly?

Question

I make a simple program to calculate the number of day between two days:

#include <stdio.h>
#include <iostream>
#include <ctime>
#include <utility>

using namespace std;
int main(){
    struct tm t1 = {0,0,0,28,2,104};
    struct tm t2 = {0,0,0,1,3,104};
    time_t x = mktime(&t1);
    time_t y = mktime(&t2);
    cout << difftime(y,x)/3600/24 << endl;

}

The output is 4 however, my expected result is 1. May I know where is the problem is ?

Answer 1

In a struct tm, months are counted from 0 to 11 (not 1 to 12), thus 2 is March and 3 is April, you code output the number of days between March the 28^th and April 1^st, which is 4.

The correct version would be:

struct tm t1 = {0, 0, 0, 28, 1, 104};
struct tm t2 = {0, 0, 0,  1, 2, 104};

By the way, 2004 is a leap year and thus February had 29 days, there were two days between February the 28^th and March the 1^st (not one).

difftime gives you the number of seconds between 02/28/2004 00:00:00 and 03/01/2004 00:00:00 (the first day is accounted for in the difference).