floor和duration_cast有什么区别？ [英] What's the Difference Between floor and duration_cast?

问题描述

因此在c ++ 11 计时库提供了 duration_cast ：

So in c++11 the Chrono Library provides, duration_cast:

计算以可用的最大类型进行，并像通过static_cast一样转换为结果类型仅在完成后

Computations are done in the widest type available and converted, as if by static_cast, to the result type only when finished

然后 c ++ 17 的 地板 ：

返回小于或等于d的ToDuration可表示的最大持续时间t

Returns the greatest duration t representable in ToDuration that is less or equal to d

因此对于所有 x 这两个调用的结果将相等：

So for all x will the result of these 2 calls be equal:

1. chrono :: duration_cast< ; chrono :: se conds>（x）


2. chrono :: floor< chrono :: seconds>（x）

1. chrono::duration_cast<chrono::seconds>(x)
2. chrono::floor<chrono::seconds>(x)

推荐答案

据我所知，与之间的区别相同static_cast 和 std :: floor ：负数会四舍五入，而不是被截断为零。

As far as I can tell, same as the difference between static_cast and std::floor: Negatives are rounded down instead of truncated toward zero.

#include <iostream>
#include <chrono>
using namespace std::chrono_literals;

int main() {
    std::cout << "duration_cast:" << std::endl;
    std::cout << "1.4s: " << std::chrono::duration_cast<std::chrono::seconds>(1400ms).count() << std::endl;
    std::cout << "1.5s: " << std::chrono::duration_cast<std::chrono::seconds>(1500ms).count() << std::endl;
    std::cout << "1.6s: " << std::chrono::duration_cast<std::chrono::seconds>(1600ms).count() << std::endl;
    std::cout << "-1.4s: " << std::chrono::duration_cast<std::chrono::seconds>(-1400ms).count() << std::endl;
    std::cout << "-1.5s: " << std::chrono::duration_cast<std::chrono::seconds>(-1500ms).count() << std::endl;
    std::cout << "-1.6s: " << std::chrono::duration_cast<std::chrono::seconds>(-1600ms).count() << std::endl;

    std::cout << "floor:" << std::endl;
    std::cout << "1.4s: " << std::chrono::floor<std::chrono::seconds>(1400ms).count() << std::endl;
    std::cout << "1.5s: " << std::chrono::floor<std::chrono::seconds>(1500ms).count() << std::endl;
    std::cout << "1.6s: " << std::chrono::floor<std::chrono::seconds>(1600ms).count() << std::endl;
    std::cout << "-1.4s: " << std::chrono::floor<std::chrono::seconds>(-1400ms).count() << std::endl;
    std::cout << "-1.5s: " << std::chrono::floor<std::chrono::seconds>(-1500ms).count() << std::endl;
    std::cout << "-1.6s: " << std::chrono::floor<std::chrono::seconds>(-1600ms).count() << std::endl;
    return 0;
}

。

duration_cast:
1.4s: 1
1.5s: 1
1.6s: 1
-1.4s: -1
-1.5s: -1
-1.6s: -1
floor:
1.4s: 1
1.5s: 1
1.6s: 1
-1.4s: -2
-1.5s: -2
-1.6s: -2

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