本地时间和GMT / UTC之间的转换在C / C ++ [英] Converting Between Local Times and GMT/UTC in C/C++

问题描述

什么是转换用C本地时间和UTC / C ++？

What's the best way to convert datetimes between local time and UTC in C/C++?

通过日期时间，我的意思是包含日期和时间的日一段时间再presentation。我会很乐意与 time_t的，结构TM ，或任何其他重presentation，使之成为可能。

By "datetime", I mean some time representation that contains date and time-of-day. I'll be happy with time_t, struct tm, or any other representation that makes it possible.

我的平台是Linux操作系统。

My platform is Linux.

下面是我试图解决具体的问题：我找一双含Julian日期和若干秒到一天的值。这些值都在GMT。我需要将其转换成一个本地时区YYYYMMDDHHMMSS的价值。我知道如何Julian日期为Y-M-D转换，显然很容易秒转换为HHMMSS。但是，棘手的部分是时区转换。我敢肯定，我可以想出一个解决方案，但我想preFER找到一个标准或知名的方式，而不是绊脚石左右。

Here's the specific problem I'm trying to solve: I get a pair of values containing a julian date and a number of seconds into the day. Those values are in GMT. I need to convert that to a local-timezone "YYYYMMDDHHMMSS" value. I know how to convert the julian date to Y-M-D, and obviously it is easy to convert seconds into HHMMSS. However, the tricky part is the timezone conversion. I'm sure I can figure out a solution, but I'd prefer to find a "standard" or "well-known" way rather than stumbling around.

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一个可能相关的问题是<一个href=\"http://stackoverflow.com/questions/678445/get-daylight-saving-transition-dates-for-time-zones-in-c\">Get夏令过渡日期时区用C

A possibly related question is Get Daylight Saving Transition Dates For Time Zones in C

推荐答案

你应该使用组合 gmtime的 / 本地时间和 timegm / mktime 。这应该给你正交工具做之间的转换结构TM 和 time_t的。

You're supposed to use combinations of gmtime/localtime and timegm/mktime. That should give you the orthogonal tools to do conversions between struct tm and time_t.

有关UTC / GMT：

For UTC/GMT:

time_t t;
struct tm tm;
struct tm * tmp;
...
t = timegm(&tm);
...
tmp = gmtime(t);

有关本地时间：

t = mktime(&tm);
...
tmp = localtime(t);

所有 tzset（）是否设置为从 TZ 环境变量中的内部时区变量。我不认为这是应该被称为一次以上。

All tzset() does is set the internal timezone variable from the TZ environment variable. I don't think this is supposed to be called more than once.

如果你想时区之间进行转换，您应该修改结构TM 的 tm_gmtoff 。

If you're trying to convert between timezones, you should modify the struct tm's tm_gmtoff.

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