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
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 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: