2

我必须在我的应用程序中处理一些时间转换。我想尽可能地坚持使用标准库函数。现在我使用 time_t 结构作为我的系统时基。但是，某些设备可以将时间同步到我的设备，该时间可能是也可能不是 UTC。此外，我的设备会将时间同步到另一台设备，并且该时间将始终为 UTC。

无论如何，我可以询问用户正在同步到我的设备的时间的时区是什么，以及他们是否使用 DST。当我的设备获得时间同步时，我可以使用 mktime 直接生成我的时间戳（我的设备系统时间需要与它们同步的时间相匹配以用于时间戳目的，否则我必须不断进行转换），然后我可以如果我知道我的时间同步来自非 UTC 来源，请使用 gmtime() 获取 UTC 时间。问题是默认情况下 localtime() 和 gmtime() 将返回相同的值，因为默认情况下库会认为它是直接 UTC 时间并且没有 DST 或时区偏移。

所以，我认为解决这个问题的方法是实现并覆盖库 __getzone 函数。

来自 EW430_CompilerReference.pdf 第 106 页

要使 __time32、__time64 和 date 函数工作，您必须实现函数 clock、__time32、__time64 和 __getzone。使用 __time32 还是 __time64 取决于您使用哪个接口用于 time_t，请参见 time.h，第 304 页。

...

__getzone 的默认实现将 UTC（协调世界时）指定为时区。

Q1：我的推理是否正确，做我想做的最好的方法是实现这个 __getzone 函数？

我犹豫的原因是因为 __getzone 返回的值是一个奇怪的字符串，格式如下：

:[XXX[:YYY[:NNN[:DST[:DST ...]]]]]

其中 XXX 是标准时区名称（例如 GMT-5 表示 EST），YYY 是夏令时时区名称（例如 GMT-4 表示 EST），NNN 是与 UTC 的数字偏移量，格式为 HHMM（并且可以有 - 符号).，然后 DST 为夏令时规则指定了一系列选项，这些规则具有自己令人讨厌的格式。

无论如何，这对我来说现在应该很简单，因为我只担心拥有相同 DST 规则的加拿大和美国。

Q2：有没有人有任何用于形成该字符串的示例代码，以便我可以检查我对此的理解？

4

4 回答 4

2

这是我对 __getzone() 的实现。所以现在我的系统时基将是 UTC。当用户配置我的系统时，如果时间源不提供 UTC，我会询问他们的当地时间。然后，当他们向我的系统提供时间同步时，他们提供的时间将通过调用 MKTIME 转换为 UTC（这将考虑 DST 规则）。然后，当时间返回给用户时，它将通过调用 localtime() 来完成。

我们在实现这个过程中学到的另一件事是，IAR 的 MKTIME() 实现将调用 __getzone()，但除非将 tm_isdst 设置为'-1'，否则不会考虑 DST 规则。-1 调用 MKTIME() 根据规则确定是否应用 DST。

/*!
* \brief Overrides default library function __getzone to support different time
* zones and DST rules.
* \returns Pointer to a const string containing the timezone + dst rules
*
* This function supports all time zones and DST rules for the U.S. and Canada.
*
* \par IAR Notes
* The return value should be a string on the following form:
* \code
* :[XXX[:YYY[:NNN[:DST[:DST ...]]]]]
* \endcode
* \par
* Where \b XXX is the standard time-zone name, \b YYY is the daylight
* savings time-zone name, \b NNN is the time zone offset, and the DSTs
* are the daylight savings time rules. Daylight savings time will add
* one hour to the normal time.
* \par
* The time zone offset \b NNN is specified as a number relative to UTC,
* possibly negative (east is positive), on the format HHMM, where HH
* is hours and MM is minutes.
* \par
* The DSTs specifes a set of rules for how daylight savings time is
* applied. The rules must be sorted in increasing date order starting
* from the earliest date. The first rule for a specific year will
* enable DST, the next will disable it, and so on. Each rule is on
* the following form:
* \code
*   [(YYYY)]MMDD[HH][-W|+W]
* \endcode
*
* * \b (YYYY) is the first year the daylight savings rule was applied.
*      It is optional. If not specified it will default to the same
*      year as the previous rule or zero if no previous rule.
* * \b MM is the month number (1-12).
* * \b DD is the day of the month (1-31).
* * \b HH is the hour number in a 24-hour day (optional, defaults to 0).
* * \b +/-W specifies the day of the week the rule takes effect (where
*      Sunday = 0, Monday = 1, etc). +W means that the rule applies
*      to the first such day on or after the specified date and -W
*      strictly before the date. If this is not specified, the rule
*      will take effect on the exact date, regardless of the day of
*      the week.
*
* \par Example
* U.S. Eastern Standard time is UTC -5. Eastern Daylight time is UTC -4.
* Daylight time goes into affect on the second sunday of March at 2:00AM local
* time. Daylight time ends on the first sunday of November at 2:00AM local
* time. The law that defines this went into affect in 2007.
* Therefore here is how the DST string is constructed:
* | \| | STD Time | \| | DST Time | \| | UTC Offset | \| | DST Rule Year | Month DST Starts | Day DST Starts | Hour DST Starts | Day of Week | \| | Month DST Ends | Day DST Ends | Hour DST Ends | Day of Week |
* |----|----------|----|----------|----|------------|----|---------------|------------------|----------------|-----------------|-------------|----|----------------|--------------|---------------|-------------|
* | :  |  XXX     | :  | YYY      | :  | NNN        | :  | (YYYY)        | MM               | DD*            | HH              | +/-W**      | :  | MM             | DD           | HH            | +/-W        |
* | :  |  GMT-5   | :  | GMT-4    | :  | -0500      | :  | (2007)        | 03               | 08             | 02              | +0          | :  | 11             | 01           | 02            | +0          |
* - * An 8 for the day means that DST will start around the 8th day of the
*   month. Or that the +/-W parameter is relative to the 8th day of the month.
* - ** A + here means that the DST rule will start \b on or \b after the
*   previously specified day (the 8th). 0 means that it should happen on a
*   sunday. Therefore if the 8th is a sunday (and the 8th cannot be the first
*   sunday of the month) then the rule will take affect on that day - or it
*   will happen on the very next sunday.
* \par
* Result:
* \code
* :GMT-5:GMT-4:-0500:(2007)030802+0:110102+0
* \endcode
*
* \sa
* - time_zones - Supported time zones
*/
const char8_t * __getzone(void)
{
    const char8_t *current_zone = NULL;
    static const char8_t dst_time_zones[][50] =
    {
        // UTC time
        ":GMT+0:GMT+0:0000:0",
        // Newfoundland Standard Time UTC – 3:30
        ":GMT-3:GMT-2:-0330:(2007)030802+0:110102+0",
        // Atlantic Standard Time, UTC – 4
        ":GMT-4:GMT-3:-0400:(2007)030802+0:110102+0",
        // Eastern Standard Time, UTC – 5
        ":GMT-5:GMT-4:-0500:(2007)030802+0:110102+0",
        // Central Standard Time, UTC – 6
        ":GMT-6:GMT-5:-0600:(2007)030802+0:110102+0",
        // Mountain Standard Time, UTC – 7
        ":GMT-7:GMT-6:-0700:(2007)030802+0:110102+0",
        // Pacific Standard Time, UTC – 8
        ":GMT-8:GMT-7:-0800:(2007)030802+0:110102+0",
        // Alaska Standard Time, UTC – 9
        ":GMT-9:GMT-8:-0900:(2007)030802+0:110102+0",
        // Hawaii-Aleutian Standard Time, UTC – 10
        ":GMT-10:GMT-9:-1000:(2007)030802+0:110102+0"
    };

    static const char8_t std_time_zones[][20] =
    {
        // UTC time
        ":GMT+0:GMT+0:0000",
        // Newfoundland Standard Time UTC – 3:30
        ":GMT-3:GMT-2:-0330",
        // Atlantic Standard Time, UTC – 4
        ":GMT-4:GMT-3:-0400",
        // Eastern Standard Time, UTC – 5
        ":GMT-5:GMT-4:-0500",
        // Central Standard Time, UTC – 6
        ":GMT-6:GMT-5:-0600",
        // Mountain Standard Time, UTC – 7
        ":GMT-7:GMT-6:-0700",
        // Pacific Standard Time, UTC – 8
        ":GMT-8:GMT-7:-0800",
        // Alaska Standard Time, UTC – 9
        ":GMT-9:GMT-8:-0900",
        // Hawaii-Aleutian Standard Time, UTC – 10
        ":GMT-10:GMT-9:-1000"
    };

    switch(get_config()->time_zone)
    {
        case NST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[NST];
            }
            else
            {
                current_zone = std_time_zones[NST];
            }
        }
        break;

        case AST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[AST];
            }
            else
            {
                current_zone = std_time_zones[AST];
            }
        }
        break;

        case EST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[EST];
            }
            else
            {
                current_zone = std_time_zones[EST];
            }
        }
        break;

        case CST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[CST];
            }
            else
            {
                current_zone = std_time_zones[CST];
            }
        }
        break;

        case MST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[MST];
            }
            else
            {
                current_zone = std_time_zones[MST];
            }
        }
        break;

        case PST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[PST];
            }
            else
            {
                current_zone = std_time_zones[PST];
            }
        }
        break;

        case AKST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[AKST];
            }
            else
            {
                current_zone = std_time_zones[AKST];
            }
        }
        break;

        case HAST:
        {
            if(get_config()->b_dst)
            {
                current_zone = dst_time_zones[HAST];
            }
            else
            {
                current_zone = std_time_zones[HAST];
            }
        }
        break;

        case UTC:
        default:
            current_zone = std_time_zones[UTC];
        break;
    }

    return current_zone;
}
于 2014-07-08T20:02:55.483 回答
2

上面的乌克兰规则并不完全正确，因为它不适用于 31 日的星期日。如果您阅读 getzone.c 中的规则，则 -W 表示此日期之前的星期日。

+/-W specifies the day of the week the rule takes effect (where
    Sunday = 0, Monday = 1, etc). +W means that the rule applies
    to the first such day on or after the specified date and -W
    strictly before the date. If this is not specified, the rule
    will take effect on the exact date, regardless of the day of
    the week.

正确的规则如下

char const * __getzone()
{
    return ":GMT+2:GMT+3:0200:(1996)032503+0:102504+0";
  // Ukraine; rule: (last Sun (March | October) )
}
于 2015-08-21T15:25:12.697 回答
1 
char const * __getzone()
{
        return ":GMT+2:GMT+3:0200:(1996)033103-0:103104-0";



    // Ukraine; rule: (last Sun (March | October) )
}
于 2014-06-12T14:09:46.000 回答
1

对于德国，您可以使用：

char const * __getzone() {
  return ":GMT+1:GMT+2:0100:032502+0:102502+0";
}

乌克兰的错误或我的错误，但我用实际设备测试了我的并得到了正确的结果。这是我的测试：

//Forward
time_t ts = 1490489997L;//26.03.2017-01:59:57 3 seconds before dst
struct tm* pre = localtime(&ts);

time_t after = ts + 5L;//wait 5 seconds -> 26.03.2017-03:00:02
struct tm* post = localtime(&after);

//Backward
time_t ts = 1509238797L;//29.10.2017-02:59:57 3 seconds before dst
struct tm* pre = localtime(&ts);

time_t after = ts + 5L;//wait 5 seconds -> 29.10.2017-02:00:02
struct tm* post = localtime(&after);

最好的问候迈克尔

于 2017-07-13T12:15:16.870 回答