std::chrono::clock_time_conversion

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Defined in header`<chrono>`
template<class Dest,class Source> struct clock_time_conversion{};		(since C++20)

std::chrono::clock_time_conversion is a trait that specifies how to convert astd::chrono::time_point of theSource clock to that of theDest clock. It does so by providing a const-callableoperator() that accepts an argument of typestd::chrono::time_point<Source, Duration> and returns astd::chrono::time_point<Dest, OtherDuration> that represents an equivalent point in time. The duration of the returned time point is computed from the source duration in a manner that varies for each specialization.clock_time_conversion is normally only used indirectly, viastd::chrono::clock_cast.

A program may specializeclock_time_conversion if at least one of the template parameters is a user-defined clock type.

The primary template is an empty struct. The standard defines the following specializations:

template<class Clock> struct clock_time_conversion<Clock, Clock>;	(1)	(since C++20)
template<> struct clock_time_conversion<std::chrono::system_clock,std::chrono::system_clock>;	(2)	(since C++20)
template<> struct clock_time_conversion<std::chrono::utc_clock,std::chrono::utc_clock>;	(3)	(since C++20)
template<> struct clock_time_conversion<std::chrono::system_clock,std::chrono::utc_clock>;	(4)	(since C++20)
template<> struct clock_time_conversion<std::chrono::utc_clock,std::chrono::system_clock>;	(5)	(since C++20)
template<class Clock> struct clock_time_conversion<Clock,std::chrono::system_clock>;	(6)	(since C++20)
template<class Clock> struct clock_time_conversion<std::chrono::system_clock, Clock>;	(7)	(since C++20)
template<class Clock> struct clock_time_conversion<Clock,std::chrono::utc_clock>;	(8)	(since C++20)
template<class Clock> struct clock_time_conversion<std::chrono::utc_clock, Clock>;	(9)	(since C++20)

1-3) Identity conversion:operator() returns a copy of the argument.

4,5) Conversions betweenstd::chrono::sys_time andstd::chrono::utc_time:operator() callsstd::chrono::utc_clock::to_sys andstd::chrono::utc_clock::from_sys, respectively.

6,7) Conversions to and fromstd::chrono::sys_time whenClock supportsfrom_sys andto_sys:operator() callsClock::to_sys andClock::from_sys, respectively.

8,9) Conversions to and fromstd::chrono::utc_time whenClock supportsfrom_utc andto_utc:operator() callsClock::to_utc andClock::from_utc, respectively.

[edit]Member functions

Each specialization has an implicitly-declared default constructor, copy constructor, move constructor, copy assignment operator, move assignment operator, and destructor.

std::chrono::clock_time_conversion::operator()

template<class Duration> std::chrono::time_point<Clock, Duration> operator()(conststd::chrono::time_point<Clock, Duration>& t)const;	(1)	(member of specialization(1))
template<class Duration> std::chrono::sys_time<Duration> operator()(conststd::chrono::sys_time<Duration>& t)const;	(2)	(member of specialization(2))
template<class Duration> std::chrono::utc_time<Duration> operator()(conststd::chrono::utc_time<Duration>& t)const;	(3)	(member of specialization(3))
template<class Duration> std::chrono::sys_time<Duration> operator()(conststd::chrono::utc_time<Duration>& t)const;	(4)	(member of specialization(4))
template<class Duration> std::chrono::utc_time<Duration> operator()(conststd::chrono::sys_time<Duration>& t)const;	(5)	(member of specialization(5))
template<class Duration> auto operator()(conststd::chrono::sys_time<Duration>& t)const -> decltype(Clock::from_sys(t));	(6)	(member of specialization(6))
template<class Duration> auto operator()(conststd::chrono::time_point<SourceClock, Duration>& t)const -> decltype(Clock::to_sys(t));	(7)	(member of specialization(7))
template<class Duration> auto operator()(conststd::chrono::utc_time<Duration>& t)const -> decltype(Clock::from_utc(t));	(8)	(member of specialization(8))
template<class Duration> auto operator()(conststd::chrono::time_point<Clock, Duration>& t)const -> decltype(Clock::to_utc(t));	(9)	(member of specialization(9))

Converts the argumentstd::chrono::time_point to the destination clock.

1-3) Identity conversion. Returnst unchanged.

4) Returnsstd::chrono::utc_clock::to_sys(t).

5) Returnsstd::chrono::utc_clock::from_sys(t).

6) ReturnsClock::from_sys(t). This overload participates in overload resolution only if the expressionClock::from_sys(t) is well-formed. The program is ill-formed ifClock::from_sys(t) does not returnstd::chrono::time_point<Clock, Duration> whereDuration is some valid specialization ofstd::chrono::duration.

7) ReturnsClock::to_sys(t). This overload participates in overload resolution only if the expressionClock::to_sys(t) is well-formed. The program is ill-formed ifClock::to_sys(t) does not returnstd::chrono::sys_time<Duration> whereDuration is some valid specialization ofstd::chrono::duration.

8) ReturnsClock::from_utc(t). This overload participates in overload resolution only if the expressionClock::from_utc(t) is well-formed. The program is ill-formed ifClock::from_utc(t) does not returnstd::chrono::time_point<Clock, Duration> whereDuration is some valid specialization ofstd::chrono::duration.

9) ReturnsClock::to_utc(t). This overload participates in overload resolution only if the expressionClock::to_utc(t) is well-formed. The program is ill-formed ifClock::to_utc(t) does not returnstd::chrono::utc_time<Duration> whereDuration is some valid specialization ofstd::chrono::duration.