std::chrono::time_point_cast

 

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std::chrono::time_point

成員函式

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

非成員函式

operator+operator-

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

time_point_cast

floor (C++17)

ceil (C++17)

round (C++17)

輔助類

common_type

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

 

定義於標頭檔案 <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) (until C++14)
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)

將 std::chrono::time_point 從一個 duration 轉換為另一個。

time_point_cast 僅當 ToDuration 是 std::chrono::duration 的特化時才參與過載決議。

引數

t

-

要轉換的 time_point

返回值

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

示例

執行此程式碼

#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};
 
    // implicit conversion, no precision loss
    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
 
    // explicit cast, need when precision loss may happen
    // 5756 truncated to 5000
    time_point_sec = std::chrono::time_point_cast<Sec>(time_point_ms);
    print_ms(time_point_sec); // 5000 ms
}

輸出

4000 ms
5756 ms
5000 ms

參閱

floor(std::chrono::time_point) (C++17)	將一個 time_point 轉換為另一個，向下取整 (函式模板)
ceil(std::chrono::time_point) (C++17)	將一個 time_point 轉換為另一個，向上取整 (函式模板)
round(std::chrono::time_point) (C++17)	將一個 time_point 轉換為另一個，四捨五入到最接近的值，平局時取偶數 (函式模板)
duration_cast (C++11)	將一個 duration 轉換為另一個，具有不同的時鐘間隔 (函式模板)