std::chrono::duration<Rep,Period>::duration

 

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std::chrono::duration

Member functions
duration::duration duration::operator= duration::count duration::zero duration::min duration::max duration::operator+duration::operator-	duration::operator++duration::operator-- duration::operator+=duration::operator-=duration::operator*=duration::operator/=duration::operator%=
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common_type treat_as_floating_point      duration_values	formatter<std::chrono::duration> (C++20) hash<std::chrono::duration> (C++26)

 

constexpr duration() = default;	(1)	(since C++11)
duration( const duration& ) = default;	(2)	(since C++11)
template< class Rep2 > constexpr explicit duration( const Rep2& r );	(3)	(since C++11)
template< class Rep2, class Period2 > constexpr duration( const duration<Rep2, Period2>& d );	(4)	(since C++11)

Constructs a new duration from one of several optional data sources.

1) The default constructor.

2) The copy constructor.

3) Constructs a duration with r ticks.

This overload participates in overload resolution only if all following conditions are satisfied:

• is_convertible<const Rep2&, Rep>::value is true.
• Any of the following conditions is satisfied:

• std::chrono::treat_as_floating_point<Rep>::value is true.
• std::chrono::treat_as_floating_point<Rep2>::value is false.

4) Constructs a duration by converting d to an appropriate period and tick count, as if by std::chrono::duration_cast<duration>(d).count().

This overload participates in overload resolution only if no overflow is induced in the conversion, and any of the following conditions is satisfied:

• std::chrono::treat_as_floating_point<Rep>::value is true.
• All following conditions are satisfied:

• std::ratio_divide<Period2, Period>::den is 1.
• std::chrono::treat_as_floating_point<Rep2>::value is false.

Parameters

r	-	a tick count
d	-	a duration to copy from

Example

The following code shows several examples (both valid and invalid) of how to construct durations:

Run this code

#include <chrono>
 
int main()
{
    std::chrono::hours h(1); // one hour
    std::chrono::milliseconds ms{3}; // 3 milliseconds
    std::chrono::duration<int, std::kilo> ks(3); // 3000 seconds
 
    // error: treat_as_floating_point<int>::value == false,
    // This duration allows whole tick counts only
//  std::chrono::duration<int, std::kilo> d3(3.5);
 
    // 30Hz clock using fractional ticks
    std::chrono::duration<double, std::ratio<1, 30>> hz30(3.5);
 
    // 3000 microseconds constructed from 3 milliseconds
    std::chrono::microseconds us = ms;
    // error: 1/1000000 is not divisible by 1/1000
//  std::chrono::milliseconds ms2 = us
    std::chrono::duration<double, std::milli> ms2 = us; // 3.0 milliseconds
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2094	C++11	for overload (4), std::ratio_divide<Period2, period>::num might overflow when evaluating std::ratio_divide<Period2, period>::den	overload (4) does not participate in overload resolution in this case
LWG 3050	C++11	convertibility constraint used non-const xvalue	use const lvalues instead

See also

operator=

assigns the contents (public member function)