使用比较运算符比较 time_t 值 [英] Comparing time_t values using comparison operators

问题描述

我有 2 个 time_t 值，我想找出哪个值更大.

I have 2 time_t values and I want to find out which one is greater.

time_t 在我的平台上内部是 __int64.我可以使用 <、> 和 == 运算符来比较值吗?我不想知道两个时间值之间的差异.

time_t is internally __int64 on my platform. Can I use <, > and == operators to compare the values? I don't want to know the difference between the two time values.

代码只会在 Windows 上运行，所以我不关心可移植性.

The code will just run on Windows, so I don't care about portability.

以这种方式比较值是否正确?

Is it correct to compare the values in this way?

推荐答案

根据 C 标准的 7.27.1(3) 部分(在这种情况下 C++ 标准指的是)time_t 是实型，在6.2.5(17)中定义为整型或浮点型.

According to section 7.27.1(3) of the C standard (which the C++ standard refers to in this case) time_t is a real type, which is defined in 6.2.5(17) as either integer or floating type.

只要您不明确假设整数(即通过执行 time_t t; int x = t;)，这可能会失去精度，您就是安全的.

As long as you don't explicitly assume integers (i.e. by doing time_t t; int x = t;) which could lose precision you are safe.

编辑:我实际上收回了.如果你去这个链接，发布#6，你可以阅读以下内容:

EDIT: I take that back actually. If you go to this link, post #6, you can read the following:

仅仅因为 time_t 是算术，这并不意味着它存储时间作为随着时间的推移单调递增的值.事实上，我们的标准C 库不保证 t1

Just because time_t is arithmetic, that doesn't mean it stores time as monotone increasing values for advancing time. In fact, our Standard C library does not guarantee t1 < t2 for t2 later than t1. We fold a limited range of representable values different ways for different systems.

P.J.普拉格
Dinkumware, Ltd.
http://www.dinkumware.com

由于 Dinkumware 广泛用于 Windows 系统(虽然我不知道这是否也适用于 C++ 标准库)我认为这很相关.

Since Dinkumware is widely used on Windows systems (although I don't know whether this also holds for the C++ standard library) I consider this relevant.

tl;dr: 按照其他答案中的建议使用 std::difftime.

tl;dr: Use std::difftime as suggested in the other answers.

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