developer-roadmap/src/data/roadmaps/cpp/content/110-stl/103-date-time.md

C++ Date Time

In C++, you can work with dates and times using the chrono library, which is part of the Standard Library (STL). The chrono library provides various data types and functions to represent and manipulate time durations, time points, and clocks.

Duration

A duration represents a span of time, which can be expressed in various units such as seconds, minutes, hours, etc. To create a duration, use the std::chrono::duration template class. Common predefined duration types are:

• std::chrono::seconds
• std::chrono::minutes
• std::chrono::hours

Example:

#include <iostream>
#include <chrono>

int main() {
    std::chrono::seconds sec(5);
    std::chrono::minutes min(2);
    std::chrono::hours hr(1);
    return 0;
}

Time Point

A time_point represents a specific point in time. It is usually created using a combination of duration and a clock. In C++, there are three clock types provided by the chrono library:

• std::chrono::system_clock: Represents the system-wide real time wall clock.
• std::chrono::steady_clock: Represents a monotonic clock that is guaranteed to never be adjusted.
• std::chrono::high_resolution_clock: Represents the clock with the shortest tick period.

Example:

#include <iostream>
#include <chrono>

int main() {
    std::chrono::system_clock::time_point tp = std::chrono::system_clock::now();
    return 0;
}

Clock

A clock provides access to the current time. It consists of the following elements:

• time_point: A specific point in time.
• duration: The time duration between two time points.
• now(): A static function that returns the current time point.

Example:

#include <iostream>
#include <chrono>

int main() {
    // Get the current time_point using system_clock
    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();

    // Get the time_point 1 hour from now
    std::chrono::system_clock::time_point one_hour_from_now = now + std::chrono::hours(1);
    return 0;
}

Converting Time Points to Calendar Time

To convert a time point to calendar representation, you can use the std::chrono::system_clock::to_time_t function.

Example:

#include <iostream>
#include <chrono>
#include <ctime>

int main() {
    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
    std::time_t now_c = std::chrono::system_clock::to_time_t(now);
    std::cout << "Current time: " << std::ctime(&now_c) << std::endl;
    return 0;
}

This summarizes the basic functionality of working with date and time in C++ using the chrono library. You can find more advanced features, such as casting durations and time arithmetic, in the C++ reference.