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

 

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Time point time_point (C++11) clock_time_conversion (C++20)   clock_cast (C++20) Duration duration (C++11) Clocks system_clock (C++11) steady_clock (C++11) is_clock (C++20) utc_clock (C++20) tai_clock (C++20) high_resolution_clock (C++11) gps_clock (C++20) file_clock (C++20) local_t (C++20) Time of day is_amis_pm (C++20)(C++20) make12make24 (C++20)(C++20) hh_mm_ss (C++20)

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std::chrono::duration

Member functions
duration::duration duration::operator= duration::count duration::zero duration::min duration::max duration::operator+duration::operator-	duration::operator++duration::operator-- duration::operator+=duration::operator-=duration::operator*=duration::operator/=duration::operator%=
Non-member functions
operator+operator-operator*operator/operator% operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(C++20) operator<< (C++20)	duration_cast floor (C++17) ceil (C++17) round (C++17) abs (C++17) operator""h (C++14) operator""min (C++14) operator""s (C++14) operator""ms (C++14) operator""us (C++14) operator""ns (C++14) from_stream (C++20)
Helper classes
common_type treat_as_floating_point      duration_values	formatter<std::chrono::duration> (C++20) hash<std::chrono::duration> (C++26)

 

Defined in header <chrono>
template<class ToDuration, class Rep, class Period > constexpr ToDuration round(conststd::chrono::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 a specialization of std::chrono::duration and std::chrono::treat_as_floating_point_v<typename ToDuration::rep> 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

namespace detail {template<class>inlineconstexprbool is_duration_v =false;template<class Rep, class Period>inlineconstexprbool 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(conststd::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;}elseif(diff0 < diff1)return t0;return t1;}

Example

Run this code

#include <chrono>#include <iomanip>#include <iostream>   int main(){usingnamespace std::chrono_literals;std::cout<<"Duration\tFloor\tRound\tCeil\n";for(using Sec =std::chrono::seconds;autoconst 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

See also

duration_cast (C++11)	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)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)	nearest integer, rounding away from zero in halfway cases (function)