A blog, dealing with multithreading in modern C++ but not writing about the new time library is not complete. Especially, because I often used the time library in my posts to measure the performance of short code snippets. Therefore, I give in this post an overview of the components of the time library: time point, time duration, and clock. I will write in additional posts about each of this three components.
As ever before the practice is the theory.
Time point, time duration and clock
The time library consists of three parts which are dependent on each other.
- Time point: The time point is given by its starting point - the so called epoch - and the time duration which refers to the epoch.
- Time duration: The time duration is the difference between two time points. It's measured in the number of time ticks.
- Clock: The clock consists of a starting point and a time tick. This information enables you to calculate the current time.
You can compare time points. When you add a time duration to a time point you get a new time point. The time tick is the accuracy of the clock in which you measure the time duration. The birth of Christ is my culture the starting time point and a year a typically time tick.
I will use the three concepts to present the lifetime of the 2011 died father of the programming language C: Dennis Ritchie. For simplicity reasons I'm only interested in the years.
The time points 1941 and 2011 are defined by the birth of Christ and the time duration. Therefore, the birth of Christ is our epoch. Of course, the epoch is also a time point. When I subtract 1941 from 2011 I get the time duration. This dime duration is measured with the accuracy year. Dennis Ritchie became 70 years old.
Before I dive deeper in the time library in upcoming post a few remarks. A time points consists of a clock and a time duration. C++ has the clocks std::chrono::system_clock, std::chrono::steady_clock, and std::chrono::high_resolution_clock. The time duration can be positive and negative. The known time durations as std::chrono::seconds, std::chrono::minutes or std::chrono::hours are predefined in C++. Additionally, C++4 offers time literals: For example 1s, 1min or 1h. The clocks differ in their accuracy (time tick) and epoch. Although it's not defined but usually std::chrono::system_clock starts at the 1.1.1970. Each clock has a method now for returning the current time (time point).
I the next post I will write about the concept time point. Therefore, I will calculate in different time ticks how much time is past since 1.1.1970.
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