在 C/C++ 中在本地时间和 GMT/UTC 之间转换
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Converting Between Local Times and GMT/UTC in C/C++
提问by Kristopher Johnson
What's the best way to convert datetimes between local time and UTC in C/C++?
在 C/C++ 中，在本地时间和 UTC 之间转换日期时间的最佳方法是什么？
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.
“日期时间”是指包含日期和时间的某种时间表示。我会很乐意用time_t，struct tm或任何其他的表示，使之成为可能。
My platform is Linux.
我的平台是Linux。
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.
这是我要解决的具体问题：我得到一对包含朱利安日期和一天中的秒数的值。这些值采用格林威治标准时间。我需要将其转换为本地时区“YYYYMMDDHHMMSS”值。我知道如何将朱利安日期转换为 YMD，显然很容易将秒转换为 HHMMSS。然而，棘手的部分是时区转换。我确信我能找到解决方案，但我更愿意找到一种“标准”或“众所周知”的方式，而不是四处游荡。
A possibly related question is Get Daylight Saving Transition Dates For Time Zones in C
一个可能相关的问题是在 C 中获取时区的夏令时转换日期
采纳答案by Rick C. Petty
You're supposed to use combinations of gmtime/localtimeand timegm/mktime. That should give you the orthogonal tools to do conversions between struct tmand time_t.
您应该使用gmtime/localtime和timegm/ 的组合mktime。这应该为您提供在struct tm和之间进行转换的正交工具time_t。
For UTC/GMT:
对于 UTC/GMT：
time_t t;
struct tm tm;
struct tm * tmp;
...
t = timegm(&tm);
...
tmp = gmtime(t);
For localtime:
对于本地时间：
t = mktime(&tm);
...
tmp = localtime(t);
All tzset()does is set the internal timezone variable from the TZenvironment variable. I don't think this is supposed to be called more than once.
所有tzset()没有设置为从内部时区变量TZ的环境变量。我不认为这应该被多次调用。
If you're trying to convert between timezones, you should modify the struct tm's tm_gmtoff.
如果你想时区之间进行转换，您应该修改struct tm的tm_gmtoff。
回答by Rick C. Petty
If on Windows, you don't have timegm() available to you:
如果在 Windows 上，您没有 timegm() 可用：
struct tm *tptr;
time_t secs, local_secs, gmt_secs;
time( &secs ); // Current time in GMT
// Remember that localtime/gmtime overwrite same location
tptr = localtime( &secs );
local_secs = mktime( tptr );
tptr = gmtime( &secs );
gmt_secs = mktime( tptr );
long diff_secs = long(local_secs - gmt_secs);
or something similar...
或类似的东西...
