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

 

C++

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功能特性测试宏 (C++20)

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技术规范

符号索引

外部库

 

日期和时间库

时间点 time_point (C++11) clock_time_conversion (C++20)   clock_cast (C++20) 时长 duration (C++11) 时钟 system_clock (C++11) steady_clock (C++11) is_clock (C++20) utc_clock (C++20) tai_clock (C++20) high_resolution_clock (C++11) gps_clock (C++20) file_clock (C++20) local_t (C++20) 当天时刻 is_amis_pm (C++20)(C++20) make12make24 (C++20)(C++20) hh_mm_ss (C++20)

日历 day (C++20) month (C++20) year (C++20) weekday (C++20) operator/ (C++20) year_month_day (C++20) year_month_day_last (C++20) year_month_weekday (C++20) year_month_weekday_last (C++20)   weekday_indexed (C++20) weekday_last (C++20) month_day (C++20) month_day_last (C++20) month_weekday (C++20) month_weekday_last (C++20) year_month (C++20) last_speclast (C++20)(C++20) chrono I/O parse (C++20)

时区 tzdb (C++20) tzdb_list (C++20) get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20) sys_info (C++20) local_info (C++20) nonexistent_local_time (C++20) ambiguous_local_time (C++20) locate_zone (C++20) current_zone (C++20) time_zone (C++20) choose (C++20) zoned_traits (C++20) zoned_time (C++20) time_zone_link (C++20) leap_second (C++20) leap_second_info (C++20) get_leap_second_info (C++20) C 风格日期和时间

 

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

hash<std::chrono::time_point> (C++26)

 

在标头 <chrono> 定义
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。

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

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)