# std::chrono::floor(std::chrono::duration)

From cppreference.com
< cpp‎ | chrono‎ | duration

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

Returns the greatest duration `t` representable in `ToDuration` that is less or equal to d.

The function does not participate in the overload resolution unless `ToDuration` is a specialization of std::chrono::duration.

### Parameters

d | - | duration to convert

### Return value

d rounded down to a duration of type `ToDuration`.

### 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>>>
    constexpr To floor(const duration<Rep, Period>& d)
    {
        To t = std::chrono::duration_cast<To>(d);
        if (t > d)
            return t - To{1};
        return t;
    }

### 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

### See also

duration_cast (C++11) | converts a duration to another, with a different tick interval (function template)
ceil(std::chrono::duration) (C++17) | converts a duration to another, rounding up (function template)
round(std::chrono::duration) (C++17) | converts a duration to another, rounding to nearest, ties to even (function template)
floor(std::chrono::time_point) (C++17) | converts a time_point to another, rounding down (function template)
floorfloorffloorl (C++11)(C++11) | nearest integer not greater than the given value (function)

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