获取C中的时区GMT偏移量 [英] Get the time zone GMT offset in C

问题描述

我正在使用标准的 mktime 功能将 struct tm 转换为时代时间值。 tm 字段在本地填充，我需要将时代时间作为GMT。 tm 有一个 gmtoff 字段，只允许您设置本地GMT偏移量（以秒为单位）。

I'm using the standard mktime function to turn a struct tm into an epoch time value. The tm fields are populated locally, and I need to get the epoch time as GMT. tm has a gmtoff field to allow you to set the local GMT offset in seconds for just this purpose.

但是我无法弄清楚如何获取这些信息。当然肯定会有一个标准的功能，会返回偏移量？

But I can't figure out how to get that information. Surely there must be a standard function somewhere that will return the offset? How does localtime do it?

推荐答案

我想我应该做的在询问之前要多一点搜索。事实证明，有一个已知的 timegm 功能与 gmtime 相反。它支持GNU和BSD，这对我来说足够好。一个更便携的解决方案是将 TZ 环境变量的值临时设置为UTC，然后使用 mktime 然后设置 TZ 。

I guess I should have done a bit more searching before asking. It turns out there's a little known timegm function which does the opposite of gmtime. It's supported on GNU and BSD which is good enough for my purposes. A more portable solution is to temporarily set the value of the TZ environment variable to "UTC" and then use mktime, then set TZ back.

但是 timegm 适用于我

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