NAME

std::chrono::clock_time_conversion - std::chrono::clock_time_conversion

Synopsis

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

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

std::chrono::sys_time<Duration> (2) (member of
specialization (2))
operator()(const std::chrono::sys_time<Duration> & t)
const;
template <class Duration>
(member of
std::chrono::utc_time<Duration> (3) specialization (3))

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

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

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

auto operator()(const std::chrono::sys_time<Duration>& t) (6) (member of
const specialization (6))

-> decltype(Clock::from_sys(t));
template <class Duration>

auto operator()(const std::chrono::time_point<SourceClock, (7) (member of
Duration>& t) const specialization (7))

-> decltype(Clock::to_sys(t));
template <class Duration>

auto operator()(const std::chrono::utc_time<Duration>& t) (8) (member of
const specialization (8))

-> decltype(Clock::from_utc(t));
template <class Duration>

auto operator()(const std::chrono::time_point<Clock, (9) (member of
Duration>& t) const specialization (9))

-> decltype(Clock::to_utc(t));

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

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