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 , respectively.
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 , respectively.
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 , respectively.

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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