How to Get the Time in Milliseconds in C++: A Detailed Guide

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In modern C++ development, accurately measuring time and performance is crucial across various applications, including profiling, simulations, and real-time systems. C++ offers robust support for time measurements through its Standard Library, particularly with the <chrono> header introduced in C++11. This header provides a set of time utilities that can be used to get the current time in milliseconds, as well as perform high-precision time operations. This article explores how to retrieve the current time in milliseconds using C++.

Table of Contents

Understanding C++ Chrono Library

The <chrono> library is part of the C++ Standard Library that deals with time. It introduces several time-related classes, functions, and constants that can be used to represent specific points in time (time_points), durations, and clocks. A clock in the <chrono> library is a source of time, like the system clock or steady clock, providing access to the current time.

Using System Clock to Get Current Time in Milliseconds

The system clock, accessible via std::chrono::system_clock, represents the system-wide real-time clock. Here’s how you can use it to get the current time in milliseconds:

Step 1: Include the Chrono Header

Start by including the <chrono> header in your C++ program:

#include <chrono>

Step 2: Get the Current Time Point

Retrieve the current time point from the system clock:

auto now = std::chrono::system_clock::now();

The now variable holds the current time point.

Step 3: Convert Time Point to Milliseconds

To convert the time point to milliseconds since the epoch (00:00 hours, Jan 1, 1970), use std::chrono::time_point_cast along with std::chrono::milliseconds, and then subtract the epoch:

auto epoch = now.time_since_epoch();
auto milliseconds = std::chrono::duration_cast<std::chrono::milliseconds>(epoch).count();

milliseconds will now hold the current time in milliseconds since the epoch.

Complete Example

Combining the steps above, here’s a complete example program that prints the current time in milliseconds:

#include <iostream>
#include <chrono>

int main() {
    // Get the current time point
    auto now = std::chrono::system_clock::now();

    // Convert the time point to milliseconds since the epoch
    auto epoch = now.time_since_epoch();
    auto milliseconds = std::chrono::duration_cast<std::chrono::milliseconds>(epoch).count();

    // Print the current time in milliseconds
    std::cout << "Current time: " << milliseconds << " milliseconds since the epoch" << std::endl;

    return 0;
}

High-Resolution Clock for More Precise Time Measurement

For applications requiring higher precision, C++ provides std::chrono::high_resolution_clock. This clock offers the shortest tick period possible on the current system. The process to get the current time in milliseconds using the high-resolution clock is similar to that of the system clock.

Considerations and Best Practices

Clock Types: Choose the appropriate clock (system_clock, steady_clock, or high_resolution_clock) based on your application’s needs. system_clock is suitable for real-world time, while steady_clock is better for measuring intervals without adjustments for system clock changes.
Time Zones and Epoch: The epoch (00:00 hours, Jan 1, 1970) is universally used for Unix time, but be aware of time zone considerations when displaying or using time for user-facing features.
Precision and Performance: Higher precision time measurements, especially with high_resolution_clock, might come with performance costs. Measure and optimize based on your application’s requirements.

Conclusion

Retrieving the current time in milliseconds in C++ is straightforward with the <chrono> library, offering flexibility and precision for various time-related operations. By understanding how to use the different clocks and time points provided by the library, developers can accurately measure and work with time in their C++ applications, catering to a wide range of scenarios from performance profiling to real-time system monitoring.

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Anastasios Antoniadis

Anastasios Antoniadis is the founder and editor-in-chief of BORDERPOLAR... He is a software engineer, blogger, and avid gamer covering tech, gaming, and coding guides for over 4 years. He is a 2014 graduate of the Department of Informatics and Telecommunications of the University of Athens, an M.Sc. holder in Computer Science, and a Ph.D. student in Program Analysis.