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std::chrono...on::duration(3) C++ Standard Libarystd::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 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 implic- itly convertible to rep (the type of this duration's ticks) and * std::chrono::treat_as_float- ing_point<rep>::value is true, or * std::chrono::treat_as_float- ing_point<Rep2>::value is false. (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) 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::ra- tio_divide<Period2, Period>) does not overflow and: * std::chrono::treat_as_float- ing_point<rep>::value == true or both: * std::ratio_divide<Period2, period>::den == 1, and * std::chrono::treat_as_float- ing_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 mil- liseconds } Defect reports The following behavior-changing defect reports were applied retroac- tively 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) http://cppreference.com 2022.07.31 std::chrono...on::duration(3)
NAME | Synopsis | Parameters | Example | See also
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