Understanding the Value of chrono::steady_clock::now().time_since_epoch().count() in C++

Описание: Explore what the value of `chrono::steady_clock::now().time_since_epoch().count()` represents in C++, including its implications and how to use it correctly.
---
This video is based on the question https://stackoverflow.com/q/71022720/ asked by the user 'migo101' ( https://stackoverflow.com/u/18144036/ ) and on the answer https://stackoverflow.com/a/71022877/ provided by the user 'Drew Dormann' ( https://stackoverflow.com/u/16287/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: What the value of "chrono::steady_clock::now().time_since_epoch().count()" represents?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Value of chrono::steady_clock::now().time_since_epoch().count() in C++

In C++, the chrono library offers a powerful way to handle time-related tasks. One commonly asked question by developers is: What does the value returned by chrono::steady_clock::now().time_since_epoch().count() signify? This inquiry often arises in contexts where precise timing and elapsed duration measurement are critical.

This guide aims to provide clarity on this topic, breaking down the key concepts associated with chrono::steady_clock and helping you understand the significance of its output. Let's dive in!

What Does chrono::steady_clock::now() Return?

The chrono::steady_clock::now() function is used to obtain the current point in time from the system’s steady clock. The concept of a steady clock is important because it guarantees that the clock will never go backward, allowing for precise elapsed time measurement across various operations and processes.

Understanding Time Since Epoch

When you call .time_since_epoch(), it calculates the duration that has passed since a predefined point in time known as the epoch. The term "epoch" typically refers to a fixed point in time, but the exact starting point for steady_clock is not standardized, as it differs across implementations.

The Output of count()

When you invoke .count(), you're effectively casting the duration into a specific unit (although the unit is not inherently specified). The output is a numeric value that represents some duration passed since some time. But crucially, it's important to note:

The units of this duration, such as nanoseconds, milliseconds, or microseconds, are not explicitly defined by the steady_clock itself.

Thus, interpreting this value requires caution since it may not indicate any universal standard like the Unix epoch (January 1, 1970).

Is It the Number of Nanoseconds Since 1970?

In short, the answer is very unlikely. The value you receive from chrono::steady_clock::now().time_since_epoch().count() does not represent the number of nanoseconds since 1970. Instead, it’s primarily useful for measuring elapsed time when compared with another reading from steady_clock.

Useful Applications of Steady Clock

While it may seem that a single reading from steady_clock isn't very useful, this function can serve several practical purposes:

Elapsed Time Measurement: Comparing two readings to determine the duration of a specific operation or function in your program.

Seeding Random Number Generators: You can use the current time point as a seed value for random number generation to ensure varied outputs across different executions.

Conclusion

To summarize, the value returned by chrono::steady_clock::now().time_since_epoch().count() is not a universally interpretable measure, like the time since 1970. Instead, it is a raw duration value that's best utilized when compared with other clock readings to assess elapsed time in your applications. Understanding how to leverage this feature can greatly enhance timing functionality in your C++ programs.

Being informed about how chrono::steady_clock works will empower you to use it effectively, whether for performance measurement, profiling, or establishing unique timestamps in your programming endeavors.

Remember, always compare steady_clock readings if you're looking to compute time intervals rather than relying on a standalone count!