NAME¶

std::chrono::duration::duration - std::chrono::duration::duration

Synopsis¶

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

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:^[1]

* 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:^[2]
* 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.
1. ↑ That is, a duration with an integer tick count cannot be constructed from a
floating-point value, but a duration with a floating-point tick count can be
constructed from an integer value.
2. ↑ That is, either the duration uses floating-point ticks, or Period2 is exactly
divisible by Period.

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

See also¶

operator= assigns the contents
(public member function)