Time duration is the difference between two time points. It will be measured in time ticks.
Time duration is a class template. std::chrono::duration consists of the type of the tick Rep and the length of a tick Period.
The tick length is by default std::ratio<1>. std::ratio<1> stands for a second and can also be written as std::ratio<1,1>. Therefore, it’s quite easy. std::ratio<60> is a minute and std::ratio<1,1000> a millisecond. When Rep is a floating point number, you can use it to hold fractions of time ticks.
C++11 predefines the most important time durations:
How much time has passed since the UNIX epoch (1.1.1970)? Thanks to type aliases for the different time durations, I can answer the question quite easily. For simplicity reasons, I ignore leap years and assume that a year has 365 days.
In addition to the typical time duration’s microsecond (line 16), millisecond (line 20), second (line 24), minute (line 28), hour (line 32), and year (line 36), I define the German school hour (45 min) in line 45.
It’s quite convenient to calculate with time durations.
Calculations with time durations
The time durations support basic mathematics. In the case of multiplication or division, you can multiply or divide a time duration by a number. Of course, you can compare time durations. I explicitly want to emphasize that all these calculations and comparisons respect the units of the time durations.
It gets even better with C++14 because C++14 has a bunch of predefined time literals.
How much time does my 16 year old son need for his typical school day? I will answer the question in the example and show the result in different time durations.
The time literals are constant expressions; therefore, they can be evaluated at compile time. I have time durations for a German school hour (line 12), for a short break (line 14), for a long break (line 15), for his way to the school (line 17), and his homework (line 18). The result of the calculation schoolDaysInSeconds (line 20) is available at compile time.
Impressed? I’m not. His daily duty is only about 7 1/2 hours.
The used clock gives the accuracy of the time tick. In C++, we have the clocks std::chrono::system_clock, std::chrono::steady_clock, and std::chrono::high_resolution_clock. The three clocks will be the topic of my next post.
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I’m happy to give online seminars or face-to-face seminars worldwide. Please call me if you have any questions.
- Embedded Programmierung mit modernem C++ 12.12.2023 – 14.12.2023 (Präsenzschulung, Termingarantie)
Standard Seminars (English/German)
Here is a compilation of my standard seminars. These seminars are only meant to give you a first orientation.
- C++ – The Core Language
- C++ – The Standard Library
- C++ – Compact
- C++11 and C++14
- Concurrency with Modern C++
- Design Pattern and Architectural Pattern with C++
- Embedded Programming with Modern C++
- Generic Programming (Templates) with C++
- Clean Code with Modern C++
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