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std::chrono...on::duration(3)  C++ Standard Libary std::chrono...on::duration(3)

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.  a	That  is,  a  duration with an integer tick count cannot be con-
     structed from a
	    floating-point value, but a  duration  with  a  floating-point  tick
     count can be
	    constructed from an integer value.
	 2. a 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  millisec-
     onds
      }

	Defect reports

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

	   DR	 Applied to		Behavior as published		    Cor-
     rect behavior
									  over-
     load (4) does
			    for overload (4), std::ratio_divide<Period2,  not
	LWG  2094  C++11      period>::num				    par-
     ticipate in
			    might overflow when evaluating		   over-
     load
			    std::ratio_divide<Period2,	period>::den	   reso-
     lution in this
									  case
	LWG 3050 C++11	    convertibility constraint  used  non-const	     use
     const lvalues
			    xvalue					     in-
     stead

See also
	operator= assigns the contents
		  (public member function)

http://cppreference.com 	   2024.06.10	   std::chrono...on::duration(3)
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