std::chrono::round(std::chrono::duration)

 

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std::chrono::duration

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Defined in header <chrono>
template <class ToDuration, class Rep, class Period> constexpr ToDuration round(const duration<Rep, Period>& d);		(since C++17)

Returns the value t representable in ToDuration that is the closest to d. If there are two such values, returns the even value (that is, the value t such that t % 2 == 0).

The function does not participate in the overload resolution unless ToDuration is an instance of std::chrono::duration and std::chrono::treat_as_floating_point<typename ToDuration::rep>::value is false

Parameters

d

-

duration to convert

Return value

d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.

Possible implementation

template <class T> struct is_duration : std::false_type {}; template <class Rep, class Period> struct is_duration< std::chrono::duration<Rep, Period>> : std::true_type {};   template <class To, class Rep, class Period, class = std::enable_if_t<is_duration<To>{} && !std::chrono::treat_as_floating_point<typename To::rep>{}>> constexpr To round(const std::chrono::duration<Rep, Period>& d) { To t0 = std::chrono::duration::floor<To>(d); To t1 = t0 + To{1}; auto diff0 = d - t0; auto diff1 = t1 - d; if (diff0 == diff1) { if (t0.count() & 1) return t1; return t0; } else if (diff0 < diff1) { return t0; } return t1; }

See also

duration_cast	converts a duration to another, with a different tick interval (function template)
floor(std::chrono::duration) (C++17)	converts a duration to another, rounding down (function template)
ceil(std::chrono::duration) (C++17)	converts a duration to another, rounding up (function template)
round(std::chrono::time_point) (C++17)	converts a time_point to another, rounding to nearest, ties to even (function template)
roundlroundllround (C++11)(C++11)(C++11)	nearest integer, rounding away from zero in halfway cases (function)