Calculating the Difference Between Two Time Periods in C++

When working with time-based data in C++, you may need to determine the exact duration between two time values. Whether you're building scheduling features, logging user activity, or tracking time intervals for performance, this calculation plays an important role in many applications.

In this sub-article, we'll show you how to calculate the difference between two time periods in C++ using the time.h header.

This example continues the logic established in our C language lead article, adapting it to the C++ programming language using modern coding conventions.

Required Header File

To work with time functions, include:

#include <ctime>  // for time_t, tm, mktime, difftime

C++ Program: Calculate the Difference Between Two Time Periods

// DIFFERENCE BETWEEN TWO TIME PERIODS in C++ using time.h
#include <iostream>
#include <ctime>
using namespace std;

int main()
{
    // Step-1 Declare two time structures
    struct tm time1 = {0}, time2 = {0};

    // Step-2 Initialize the first time (YYYY-MM-DD HH:MM:SS)
    time1.tm_year = 2025 - 1900; // Year since 1900
    time1.tm_mon = 4;            // May (0-based index)
    time1.tm_mday = 1;
    time1.tm_hour = 10;
    time1.tm_min = 30;
    time1.tm_sec = 0;

    // Step-3 Initialize the second time
    time2.tm_year = 2025 - 1900;
    time2.tm_mon = 4;
    time2.tm_mday = 9;
    time2.tm_hour = 15;
    time2.tm_min = 45;
    time2.tm_sec = 0;

    // Step-4 Convert both structures to time_t (epoch time)
    time_t t1 = mktime(&time1);
    time_t t2 = mktime(&time2);

    // Step-5 Find the difference in seconds
    double seconds = difftime(t2, t1);

    // Step-6 Convert seconds to hours, minutes, seconds
    int hours = seconds / 3600;
    int minutes = ((int)seconds % 3600) / 60;
    int remainingSeconds = (int)seconds % 60;

    // Step-7 Display the result
    cout << "\nTIME DIFFERENCE: " << hours << " HOURS, "
         << minutes << " MINUTES, "
         << remainingSeconds << " SECONDS\n";

    return 0;
}

Run

Output

Explanation

In this C++ example:

• We used the tm structure to represent individual time components.

• The mktime() function converts these structures to time_t format, which is a numeric representation of time.

• The difftime() function gives us the difference in seconds between two time_t values.

• We then transformed the total seconds into hours, minutes, and seconds for easier readability.

This approach is efficient and portable for basic date and time calculations in C++.