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# C++ concepts: Clock

From cppreference.com
< cpp‎ | concept

The `Clock` concept describes a bundle consisting of a std::chrono::duration, a std::chrono::time_point, and a function now() to get the current time_point. The origin of the clock's time_point is referred to as the clock's epoch.

### [edit] Requirements

C1 and C2 denote clock types. t1 and t2 are values returned by C1::now() where the call returning t1 happens before the call returning t2 and both of these calls occur before C1::time_point::max().

Expression | Return type | Operational semantics
--- | --- | ---
C1::rep | An arithmetic type or a class emulating an arithmetic type | The representation type of C1::duration.
C1::period | A specialization of std::ratio | The tick period of the clock in seconds.
C1::duration | std::chrono::duration<C1::rep, C1::period> | The duration type of the clock.
C1::time_point | std::chrono::time_point<C1> or std::chrono::time_point<C2, C1::duration> | The std::chrono::time_point type of the clock. C1 and C2 shall refer to the same epoch.
C1::is_steady | const bool | True if t1 < t2 is always true and the time between clock ticks is constant, otherwise false
C1::now() | C1::time_point | Returns a time_point object representing the current point in time.

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