std::chrono::duration<Rep,Period>::duration (3) - Linux Manuals

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


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


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 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)


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


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

See also

          assigns the contents
operator= (public member function)