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 is defaulted.
2) The copy constructor is defaulted (makes a bitwise copy of the tick count).
3) Constructs a duration with r ticks. Note that this constructor only participates
in overload resolution if const Rep2& (the argument type) is implicitly convertible
to rep (the type of this duration's ticks) and

* std::chrono::treat_as_floating_point<rep>::value is true,
or
* std::chrono::treat_as_floating_point<Rep2>::value is
false.

(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)
4) Constructs a duration by converting d to an appropriate period and tick count, as
if by std::chrono::duration_cast<duration>(d).count(). In order to prevent
truncation during conversion, this constructor only participates in overload
resolution if computation of the conversion factor (by std::ratio_divide<Period2,
Period>) does not overflow and:

* std::chrono::treat_as_floating_point<rep>::value == true

or both:

* std::ratio_divide<Period2, period>::den == 1, and
* std::chrono::treat_as_floating_point<Rep2>::value ==
false.

(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
LWG 3050 C++11 convertibility constraint used non-const use const lvalues
xvalue instead

See also

operator= assigns the contents
(public member function)