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

 

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std::chrono::time_point

成员函数

time_point::time_point

time_point::time_since_epoch

time_point::operator+time_point::operator-

time_point::operator++time_point::operator-- (C++20)(C++20)

time_point::min

time_point::max

非成员函数

operator+operator-

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 前)(C++20)

time_point_cast

floor (C++17)

ceil (C++17)

round (C++17)

辅助类

common_type

 

定义于头文件 <chrono>
template <class ToDuration, class Clock, class Duration> constexpr std::chrono::time_point<Clock, ToDuration>     round(const std::chrono::time_point<Clock, Duration>& tp);		(C++17 起)

返回能以 ToDuration 表示的最接近 tp 的时间点，中点情况下向偶数舍入。

函数不参与重载决议，除非 ToDuration 是 std::chrono::duration 的特化且 std::chrono::treat_as_floating_point_v<typename ToDuration::rep> 为 false 。

参数

tp

-

要舍入到最近值的时间点

返回值

舍入到使用 ToDuration 类型时长的最近时间点的 tp ，中点情况下向偶数舍入。

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 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())}; }

示例

运行此代码

#include <iostream>
#include <chrono>
#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";
    }
}

输出：

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

参阅

time_point_cast (C++11)	转换时间点为同一时钟上拥有不同时长的另一时间点 (函数模板)
ceil(std::chrono::time_point) (C++17)	转换 time_point 到另一个，向上取整 (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)
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)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)	最接近整数，中间情况下向远离零舍入 (函数)