获取时区GMT在C的失调 [英] Get the time zone GMT offset in C

问题描述

我使用的是标准的 mktime 功能把一个结构TM 进入一个划时代的时间值。在 TM 字段是本地人口的，我需要得到划时代的时间为北京时间。 TM 有一个 gmtoff 字段，允许您设置的当地GMT以秒为抵消这个目的。

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.

但我不能想出如何的获得的信息。当然，必须有一个标准功能的地方，将返回偏移？如何本地时间呢？

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

我想我应该做得更多一点提问前搜索。原来，有一个鲜为人知的 timegm 功能，它确实 gmtime的相反。它支持GNU和BSD是够用了我的目的。一个更通用的解决方案是临时设置 TZ 环境变量UTC的值，然后使用 mktime ，然后设置 TZ 回来了。

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 timegm 为我工作。

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