duration_cast如何进行 [英] How does duration_cast round

问题描述

如果我将时间单位转换为较粗略的时间（例如，将 std :: chrono ::分钟转换为 std :: chrono ::小时） duration_cast 将如何取整？例如，如果转换为 std :: chrono :: hours std :: chrono :: minutes（91）会变成什么值$ c>？ 2h，1h？

If I convert to a coarser unit of time (say std::chrono::minutes to std::chrono::hours) how will duration_cast round? For example, what value will std::chrono::minutes(91) become if converted to std::chrono::hours? 2h, 1h?

推荐答案

duration_cast 总是四舍五入。即正值向下取整，负值向上取整。

duration_cast always rounds towards zero. I.e. positive values round down and negative values round up.

有关其他取整选项，请参见：

For other rounding options see:

http://howardhinnant.github.io/duration_io/chrono_util.html

楼层，天花板和回合当前在C ++ 1z（希望是C ++ 17）草稿中。同时，请随时使用 chrono_util.html 中的代码，请让我知道您是否有任何问题。

floor, ceil, and round are currently in the draft C++ 1z (hopefully C++17) draft working paper. In the meantime feel free to use the code at chrono_util.html, and please let me know if you have any problems with it.

• std :: chrono :: floor


• std :: chrono :: ceil


• std :: chrono :: round

• std::chrono::floor
• std::chrono::ceil
• std::chrono::round

std::chrono::floor<std::chrono::seconds>(1400ms)  ==  1s
std::chrono::floor<std::chrono::seconds>(1500ms)  ==  1s
std::chrono::floor<std::chrono::seconds>(1600ms)  ==  1s
std::chrono::floor<std::chrono::seconds>(-1400ms) == -2s
std::chrono::floor<std::chrono::seconds>(-1500ms) == -2s
std::chrono::floor<std::chrono::seconds>(-1600ms) == -2s

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