Professional C++, 5th Edition

22Date and Time Utilities

WHAT'S IN THIS CHAPTER?

• How to work with compile-time rational numbers
• How to work with time
• How to work with dates and calendars
• How to convert time points between different time zones

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This chapter discusses the time-related functionality provided by the C++ Standard Library, known collectively as the chrono library. It is a collection of classes and functions to work with time and dates. The library consists of the following components:

• Durations
• Clocks
• Time points
• Dates (C++20)
• Time zones (C++20)

Everything is defined in <chrono> in the std::chrono namespace. However, before we can start the discussion of each of these chrono library components, we need a small digression and need to take a look at the compile-time rational number support available in C++, as this is heavily used by the chrono library.

COMPILE-TIME RATIONAL NUMBERS

The Ratio library allows you to exactly represent any finite rational number that you can use at compile time. Everything is defined in <ratio> and is in the std namespace. The numerator and denominator of a rational number are represented as compile-time constants of type std::intmax_t, which is a signed integer type with the maximum width supported by a compiler. Because of the ...