# std::chrono::round(std::chrono::time_point)

From cppreference.com
< cpp‎ | chrono‎ | time point

Defined in header `<chrono>` |  |
template< class ToDuration, class Clock, class Duration > constexpr std::chrono::time_point <Clock, ToDuration> round( const std::chrono::time_point <Clock, Duration>& tp ); |  | (since C++17)

Returns the nearest time point to tp representable in `ToDuration`, rounding to even in halfway cases.

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

tp | - | time point to round to nearest

### Return value

tp rounded to nearest time point using duration of type `ToDuration`, rounding to even in halfway cases.

### 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 Clock, class FromDuration,
             class = std::enable_if_t<detail::is_duration_v<To> &&
                    !std::chrono::treat_as_floating_point_v<typename To::rep>>>
    constexpr std::chrono::time_point<Clock, To> round(
        const std::chrono::time_point<Clock, FromDuration>& tp)
    {
        return std::chrono::time_point<Clock, To>{
            std::chrono::round<To>(tp.time_since_epoch())};
    }

### Example

Run this code

    #include <chrono>
    #include <iostream>
    #include <string>

    template<typename TimePoint>
    std::string to_string(const TimePoint& time_point)
    {
        return std::to_string(time_point.time_since_epoch().count());
    }

    int main()
    {
        using namespace std::literals::chrono_literals;
        using Sec = std::chrono::seconds;

        std::cout << "Time point\t" "Cast\t" "Floor\t" "Round\t" "Ceil\n";
        std::cout << "(ms)\t\t"     "(s)\t"  "(s)\t"   "(s)\t"   "(s)\n";
        for (const auto value_ms : {5432ms, 5678ms})
        {
            std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds>
                time_point_ms(value_ms);

            std::cout
                << to_string(time_point_ms) << "\t\t"
                << to_string(std::chrono::time_point_cast<Sec>(time_point_ms)) << '\t'
                << to_string(std::chrono::floor<Sec>(time_point_ms)) << '\t'
                << to_string(std::chrono::round<Sec>(time_point_ms)) << '\t'
                << to_string(std::chrono::ceil<Sec>(time_point_ms)) << '\n';
        }
    }

Output:

    Time point	Cast	Floor	Round	Ceil
    (ms)		(s)	(s)	(s)	(s)
    5432		5	5	5	6
    5678		5	5	6	6

### See also

time_point_cast (C++11) | converts a time point to another time point on the same clock, with a different duration (function template)
ceil(std::chrono::time_point) (C++17) | converts a time_point to another, rounding up (function template)
floor(std::chrono::time_point) (C++17) | converts a time_point to another, rounding down (function template)
round(std::chrono::duration) (C++17) | converts a duration 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)

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