std::chrono::time_point_cast

 

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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

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

 

在标头 <chrono> 定义
template< class ToDuration, class Clock, class Duration > std::chrono::time_point<Clock, ToDuration>     time_point_cast( const std::chrono::time_point<Clock, Duration> &t );		(C++11 起) (C++14 前)
template< class ToDuration, class Clock, class Duration > constexpr std::chrono::time_point<Clock, ToDuration>     time_point_cast( const std::chrono::time_point<Clock, Duration> &t );		(C++14 起)

将 std::chrono::time_point 从一个时长转换到另一个。

time_point_cast 仅当 ToDuration 为 std::chrono::duration 的特化时才参与重载决议。

示例

t

-

转换来源的 time_point

返回值

std::chrono::time_point<Clock, ToDuration>(
    std::chrono::duration_cast<ToDuration>(t.time_since_epoch()))。

示例

运行此代码

#include <chrono>
#include <iostream>
using namespace std::chrono_literals;
 
using Clock = std::chrono::high_resolution_clock;
using Ms = std::chrono::milliseconds;
using Sec = std::chrono::seconds;
 
template<class Duration>
using TimePoint = std::chrono::time_point<Clock, Duration>;
 
inline void print_ms(const TimePoint<Ms>& time_point)
{
    std::cout << time_point.time_since_epoch().count() << " ms\n";
}
 
int main()
{
    TimePoint<Sec> time_point_sec{4s};
 
    // 隐式转换，无精度损失
    TimePoint<Ms> time_point_ms{time_point_sec};
    print_ms(time_point_ms); // 4000 ms
 
    time_point_ms = TimePoint<Ms>{5756ms};
    print_ms(time_point_ms); // 5756 ms
 
    // 显式转换，在可能发生精度损失时需要
    // 5756 截断为 5000
    time_point_sec = std::chrono::time_point_cast<Sec>(time_point_ms);
    print_ms(time_point_sec); // 5000 ms
}

输出：

4000 ms
5756 ms
5000 ms

参阅

floor(std::chrono::time_point) (C++17)	转换 time_point 到另一个，向下取整 (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)
round(std::chrono::time_point) (C++17)	转换 time_point 到另一个，就近取整，偶数优先 (函数模板)
duration_cast (C++11)	转换时长到另一个拥有不同计次间隔的时长 (函数模板)