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

 

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std::chrono::duration

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duration::duration
duration::operator=
duration::count
duration::zero
duration::min
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duration::operator++duration::operator--
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operator+operator-operator*operator/operator% operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 前)(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)
辅助类
common_type treat_as_floating_point duration_values formatter<std::chrono::duration> (C++20)

 

定义于头文件 <chrono>
template <class ToDuration, class Rep, class Period> constexpr ToDuration floor(const std::chrono::duration<Rep, Period>& d);		(C++17 起)

返回可表示为 ToDuration 的小于或等于 d 的最大时长 t 。

函数不参与重载决议，除非 ToDuration 是 std::chrono::duration 的特化。

参数

d

-

要转换的时长

返回值

向下取整到 ToDuration 类型时长的 d 。

可能的实现

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; }

示例

运行此代码

#include <iostream>
#include <iomanip>
#include <chrono>
 
int main()
{
    using namespace std::chrono_literals;
    using Sec = std::chrono::seconds;
    for (std::cout << "Duration\tFloor\tRound\tCeil\n"
                      "(ms)\t\t(sec)\t(sec)\t(sec)\n";
        auto const d: {
            +4999ms, +5000ms, +5001ms, +5499ms, +5500ms, +5999ms,
            -4999ms, -5000ms, -5001ms, -5499ms, -5500ms, -5999ms, }) {
        std::cout << std::showpos << d.count() << "\t\t"
                  << std::chrono::floor<Sec>(d).count() << '\t'
                  << std::chrono::round<Sec>(d).count() << '\t'
                  << std::chrono::ceil <Sec>(d).count() << '\n';
    }
}

输出：

Duration   Floor   Round   Ceil
(ms)       (sec)   (sec)   (sec)
+4999      +4      +5      +5
+5000      +5      +5      +5
+5001      +5      +5      +6
+5499      +5      +5      +6
+5500      +5      +6      +6
+5999      +5      +6      +6
-4999      -5      -5      -4
-5000      -5      -5      -5
-5001      -6      -5      -5
-5499      -6      -5      -5
-5500      -6      -6      -5
-5999      -6      -6      -5

参阅

duration_cast (C++11)	转换时长到另一个拥有不同嘀嗒间隔的时长 (函数模板)
ceil(std::chrono::duration) (C++17)	以向上取整的方式，将一个时长转换为另一个时长 (函数模板)
round(std::chrono::duration) (C++17)	转换时长到另一个时长，就近取整，偶数优先 (函数模板)
floor(std::chrono::time_point) (C++17)	转换 time_point 到另一个，向下取整 (函数模板)
floorfloorffloorl (C++11)(C++11)	不大于给定值的最接近整数 (函数)