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 a std::chrono::time_point of the Source clock to that of the Dest clock. It does so by providing a const-callable operator() that accepts an argument of type std::chrono::time_point <Source, Duration> and returns a std::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, via std::chrono::clock_cast

A program may specialize clock_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 between std::chrono::sys_time and std::chrono::utc_time: operator() calls std::chrono::utc_clock::to_sys and std::chrono::utc_clock::from_sys
6,7) Conversions to and from std::chrono::sys_time when Clock supports from_sys and to_sys: operator() calls Clock::to_sys and Clock::from_sys
8,9) Conversions to and from std::chrono::utc_time when Clock supports from_utc and to_utc: operator() calls Clock::to_utc and Clock::from_utc

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( ) ( const std::chrono::time_point <Clock, Duration> & t ) const ;
(1) (member of specialization (1))
template < class Duration >

std::chrono::sys_time<Duration>

    operator( ) ( const std::chrono::sys_time <Duration> & t ) const ;
(2) (member of specialization (2))
template < class Duration >

std::chrono::utc_time<Duration>

    operator( ) ( const std::chrono::utc_time <Duration> & t ) const ;
(3) (member of specialization (3))
template < class Duration >

std::chrono::sys_time<Duration>

    operator( ) ( const std::chrono::utc_time <Duration> & t ) const ;
(4) (member of specialization (4))
template < class Duration >

std::chrono::utc_time<Duration>

    operator( ) ( const std::chrono::sys_time <Duration> & t ) const ;
(5) (member of specialization (5))
template < class Duration >

auto operator( ) ( const std::chrono::sys_time <Duration> & t ) const

- > decltype(Clock:: from_sys (t) ) ;
(6) (member of specialization (6))
template < class Duration >

auto operator( ) ( const std::chrono::time_point <SourceClock, Duration> & t ) const

- > decltype(Clock:: to_sys (t) ) ;
(7) (member of specialization (7))
template < class Duration >

auto operator( ) ( const std::chrono::utc_time <Duration> & t ) const

- > decltype(Clock:: from_utc (t) ) ;
(8) (member of specialization (8))
template < class Duration >

auto operator( ) ( const std::chrono::time_point <Clock, Duration> & t ) const

- > decltype(Clock:: to_utc (t) ) ;
(9) (member of specialization (9))

Converts the argument std::chrono::time_point to the destination clock.

1-3) Identity conversion. Returns t unchanged.
4) Returns std::chrono::utc_clock::to_sys (t)
5) Returns std::chrono::utc_clock::from_sys (t)
6) Returns Clock::from_sys(t) . This overload participates in overload resolution only if the expression Clock::from_sys(t) is well-formed. The program is ill-formed if Clock::from_sys(t) does not return std::chrono::time_point <Clock, Duration> where Duration is some valid specialization of std::chrono::duration
7) Returns Clock::to_sys(t) . This overload participates in overload resolution only if the expression Clock::to_sys(t) is well-formed. The program is ill-formed if Clock::to_sys(t) does not return std::chrono::sys_time <Duration> where Duration is some valid specialization of std::chrono::duration
8) Returns Clock::from_utc(t) . This overload participates in overload resolution only if the expression Clock::from_utc(t) is well-formed. The program is ill-formed if Clock::from_utc(t) does not return std::chrono::time_point <Clock, Duration> where Duration is some valid specialization of std::chrono::duration
9) Returns Clock::to_utc(t) . This overload participates in overload resolution only if the expression Clock::to_utc(t) is well-formed. The program is ill-formed if Clock::to_utc(t) does not return std::chrono::utc_time <Duration> where Duration is some valid specialization of std::chrono::duration

Parameters

t - time point to convert

Return value

The result of the conversion as described above:

1-3) t.
4) std::chrono::utc_clock::to_sys (t)
5) std::chrono::utc_clock::from_sys (t)
6) Clock::from_sys(t).
7) Clock::to_sys(t).
8) Clock::from_utc(t).
9) Clock::to_utc(t).

See also

(C++20)
 convert time points of one clock to another
(function template)
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