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

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< cpp‎ | chrono‎ | duration

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;
    }

### Example

| This section is incomplete Reason: no example

### 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)
round lround llround (C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function)

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- Todo no example