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std::chrono:: time_point_cast

From cppreference.net
C++
Date and time library
std::chrono::time_point
定义于头文件 <chrono>
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 从一种时长类型转换为另一种时长类型。

time_point_cast 仅当 ToDuration 是 std::chrono::duration 的特化时才会参与重载决议。

目录

参数

t - 要转换的 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 被截断为 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

参见

(C++17)
将 time_point 转换为另一种精度，向下取整
(函数模板)
(C++17)
将 time_point 转换为另一种精度，向上取整
(函数模板)
(C++17)
将 time_point 转换为另一种精度，四舍五入到最近值，中间值向偶数取整
(函数模板)
(C++11)
将 duration 转换为具有不同时间间隔精度的类型
(函数模板)