# C++ named requirements: Clock (since C++11)

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< cpp‎ | named req

The Clock requirements describe 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.

### 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 clock advances at a steady rate relative to real time (so the difference between two distinct reported times is approximately the elapsed real time between the clock updates), otherwise false
C1::now() | C1::time_point | Returns a time_point object representing the current point in time.

### See also

is_clock is_clock_v (C++20) | determines if a type is a Clock (class template) (variable template)

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