23 General utilities library [utilities]

23.17 Time utilities [time]

23.17.3 Clock requirements [time.clock.req]

A clock is a bundle consisting of a duration, a 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. A clock shall meet the requirements in Table 52.

In Table 52 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(). [Note: This means C1 did not wrap around between t1 and t2. end note]

Table 52 — Clock requirements
ExpressionReturn typeOperational semantics
C1​::​rep An arithmetic type or a class emulating an arithmetic type The representation type of C1​::​duration.
C1​::​period a specialization of ratio The tick period of the clock in seconds.
C1​::​duration chrono​::​duration<C1​::​rep, C1​::​period> The duration type of the clock.
C1​::​time_­point chrono​::​time_­point<C1> or chrono​::​time_­point<C2, C1​::​duration> The 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.

[Note: The relative difference in durations between those reported by a given clock and the SI definition is a measure of the quality of implementation. end note]

A type TC meets the TrivialClock requirements if: