特定于平台的 std::chrono::high_resolution_clock::period::num [英] platform-specific std::chrono::high_resolution_clock::period::num

问题描述

我注意到对于我测试过的每个系统，std::chrono::high_resolution_clock::period::num = 1.是否存在任何系统(嵌入式、桌面、移动或其他)恰好是其他数字?(在这样的系统上，1 秒不能用刻度表示.)

I've noticed that std::chrono::high_resolution_clock::period::num = 1 for every system I've tested. Does there exist any system (embedded, desktop, mobile, or otherwise) where it happens to be some other number? (On such a system, 1 second would not be representable in ticks.)

推荐答案

我知道 std::chrono::high_resolution_clock 的三种实现:Visual Studio、gcc 和 clang(当与 libc++ 一起使用).

There are three implementations of std::chrono::high_resolution_clock that I am aware of: Visual Studio, gcc and clang (when used with libc++).

所有这三个都具有纳秒精度(std::chrono::high_resolution_clock::period::num = 1).对于 VS 和 libc++，high_resolution_clock 被类型别名为 steady_clock.在 gcc 上，它被类型别名为 system_clock.

All three of these have nanosecond-precision (std::chrono::high_resolution_clock::period::num = 1). For VS and libc++, high_resolution_clock is type-aliased to steady_clock. On gcc it is type-aliased to system_clock.

规范中没有任何内容可以阻止 std::chrono::high_resolution_clock::period::num != 1，您是对的，在这样的系统上 1 秒是无法表示的在滴答声"中.这进一步转化为:

There is nothing in the spec that prevents std::chrono::high_resolution_clock::period::num != 1, and you are correct that on such a system 1 second would not be representable in "ticks". This further translates to:

seconds 不会隐式转换为 high_resolution_clock::duration.

要找到 seconds 和 high_resolution_clock::duration 可转换为的最粗略持续时间，您可以使用:

To find the coarsest duration to which both seconds and high_resolution_clock::duration are convertible to, you can portably use:

using CT = common_type_t<seconds, high_resolution_clock::duration>;

对于我所知道的所有实现，CT 是 nanoseconds 的类型别名.

For all of the implementations I'm aware of, CT is a type-alias for nanoseconds.

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