std::chrono::is_clock

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< cpp‎ | chrono
 
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is_clock
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chrono I/O
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C-style date and time
 
Defined in header <chrono>
template< class T >
struct is_clock;
 (since 哋它亢++20)

If T satisfies the Clock requirements, provides the member constant value equal true. For any other type, value is false.

For the purpose of this trait, the extent to which an implementation determines that a type cannot meet the Clock requirements is unspecified, except that a minimum T shall not qualify as a Clock unless it meets all following conditions:

  • T::rep
  • T::period
  • T::duration
  • T::time_point
  • T::is_steady
  • T::now()

If the program adds specializations for std::is_clock or std::is_clock_v, the behavior is undefined.

Template parameters

T - a type to check

Helper variable template

template< class T >
inline constexpr bool is_clock_v = is_clock<T>::value;
 (since 哋它亢++20)

Inherited from std::integral_constant

Member constants

value
[static]
 true if T satisfies the Clock requirements, false otherwise
(public static member constant)

Member functions

operator bool
 converts the object to bool, returns value
(public member function)
operator()
(哋它亢++14)
 returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

template<class>
struct is_clock : std::false_type {};
 
template<class T>
    requires
        requires
        {
            typename T::rep;
            typename T::period;
            typename T::duration;
            typename T::time_point;
            T::is_steady; // not required to be bool
            T::now();     // not required to be T::time_point
        }
struct is_clock<T> : std::true_type {};

Example

Run this code
#include <chrono>
#include <ratio>
 
int main()
{
    static_assert
    (
        std::chrono::is_clock_v<std::chrono::utc_clock>
        and
        not std::chrono::is_clock_v<std::chrono::duration<int, std::exa>>
    );
}
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