将UTC时间转换为在C中的unix时间戳。

I need to know the current UTC time and convert it to Unix time stamp. I tried using combination of time(), mktime(), gmtime() but not getting correct UTC time Following is the snippet I am using:

我需要知道当前UTC时间，并将其转换为Unix时间戳。我尝试使用时间的组合()、mktime()、gmtime()但是没有得到正确的UTC时间，以下是我使用的代码片段:

time_t now;
struct tm  ts;
char buf[80];
now = time(NULL);
ts = *gmtime(&now);
strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S %Z", &ts);

This gives me following output as --> Time :: Sat 2015-01-10 00:14:34 CST which is adding 5 Hr 30 minutes into local time instead of subtracting 5 Hr 30 min. Can anyone tell me why this is happening ?

这给了我如下的输出:>时间:Sat 2015-01-10 00:14:34 CST，在当地时间里增加了5小时30分钟，而不是减去5小时30分钟。谁能告诉我为什么会发生这种情况?

3 个解决方案

#1

[edit] Re-thought the issue.

[编辑]反思这个问题。

OP wants a Unix time stamp. Such a time stamp is the seconds since Jan 1, 1970. This is likely nothing more than the below.

OP需要Unix时间戳。这样的时间戳是自1970年1月1日以来的几秒钟。这很可能只是下面的情况。

sprintf(buffer, "%lld", (long long) time(NULL));

OTOH, OP also seems to want year-month-day hour:minute:second. This is not a UNIX time stamp. It is simply a time stamp which the rest of this answer discusses a portable way to derive.

OTOH, OP也似乎想要每年一个月的时间:分钟:第二。这不是一个UNIX时间戳。这只是一个时间戳，剩下的答案讨论了一种可移植的派生方式。

---

time() returns some real type capable of representing time. It is very often some integer type representing the numbers of seconds since Jan 1, 1970 0:00:00 UTC (or GMT).

time()返回一些能够表示时间的真正类型。它通常是一些整数类型，表示自1970年1月1日以来的秒数(或GMT)。

 now = time(NULL);

gmtime() coverts time_t into a year, month, day, etc. structure for the UTC (GMT) timezone.

gmtime()将time_t包含到UTC (GMT)时区的年、月、日等结构中。

ts = *gmtime(&now);

---

Now comes a coding problem:

现在出现了一个编码问题:

strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S %Z", &ts);

strftime() may (@Jasen) not known the timezone from &ts. Instead, it gets the locale's timezone. That result is adjusted per the is_daylight_time field ts.tm_isdst. So the following does not make sense.

strftime()可以(@Jasen)不知道来自&ts的时区。相反，它会获取语言环境的时区。这个结果是根据is_daylight_time字段。tm_isdst进行调整的。所以下面的内容是没有意义的。

ts = *gmtime(&now);  // UTC/GMT time
strftime(buf, sizeof(buf), "... %Z ...", &ts);  // print local standard time name

Instead use

而不是使用

ts = *gmtime(&now);
strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S UTC", &ts);

---

Consider ISO 8601 formats

考虑ISO 8601格式

strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%SZ", &ts);
//  2015-01-06T03:51:57Z

#2

The return value of time() already is in UTC:

时间()的返回值已经在UTC中:

time() returns the time as the number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

时间()返回的时间为自纪元以来的秒数，1970-01-01 00:00 +0000 (UTC)。

It's not clear to me why you're doing further processing.

我不清楚你为什么要做进一步的处理。

#3

Fix Your Clock

Your time zone is IST "Asia/Calcutta" (I couldn't find anything else with a 5:30 offset from GMT)

您的时区是“Asia/Calcutta”(我在格林尼治标准时间下午5:30的时候找不到其他东西)

But it's printing as GMT as CST ths suggests that your computers clock is badly misconfigured.

但它的印刷时间是格林尼治标准时间，这表明你的电脑时钟被严重错误配置了。

The code you posted works fine here. I cannot provoke it to print CST instead of GMT.

你发布的代码在这里很好。我不能让它印刷CST而不是GMT。