std::chrono::round(std::chrono::duration)
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std::chrono::duration
Member functions
Non-member functions
(until C++20)(C++20)
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round
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Helper classes
Defined in header
<chrono>
template< class ToDuration, class Rep, class Period >
constexpr ToDuration round( const std::chrono::duration <Rep, Period>& d );
(since C++17)
constexpr ToDuration round( const std::chrono::duration <Rep, Period>& d );
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 a specialization of std::chrono::duration and std::chrono::treat_as_floating_point_v <typename ToDuration::rep> is false.
[edit] Parameters
d
-
duration to convert
[edit] Return value
d rounded to the nearest duration of type ToDuration, rounding to even in halfway cases.
[edit] Possible implementation
namespace detail { template<class> inline constexpr bool is_duration_v = false; template<class Rep, class Period> inline constexpr bool is_duration_v< std::chrono::duration <Rep, Period>> = true; } template<class To, class Rep, class Period, class = std::enable_if_t <detail::is_duration_v<To> && !std::chrono::treat_as_floating_point_v <typename To::rep>>> constexpr To round(const std::chrono::duration <Rep, Period>& d) { To t0 = std::chrono::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; }
[edit] Example
Run this code
#include <chrono> #include <iomanip> #include <iostream> int main() { using namespace std::chrono_literals; std::cout << "Duration\tFloor\tRound\tCeil\n"; for (using Sec = std::chrono::seconds ; auto const d : {+4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms, -4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms}) std::cout << std::showpos << d << "\t\t" << std::chrono::floor <Sec>(d) << '\t' << std::chrono::round<Sec>(d) << '\t' << std::chrono::ceil <Sec>(d) << '\n'; }
Output:
Duration Floor Round Ceil +4999ms +4s +5s +5s +5000ms +5s +5s +5s +5001ms +5s +5s +6s +5499ms +5s +5s +6s +5500ms +5s +6s +6s +5999ms +5s +6s +6s -4999ms -5s -5s -4s -5000ms -5s -5s -5s -5001ms -6s -5s -5s -5499ms -6s -5s -5s -5500ms -6s -6s -5s -5999ms -6s -6s -5s
[edit] See also
(C++17)
(function template) [edit]
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
(function) [edit]