C++ 使用WinAPI进行夏令时和UTC到本地时间的转换

我想看看从本地时间转换到UTC时间的WindAPI和从UTC时间转换到本地时间的WindAPI是否精确到夏令时。例如，让我们以API为例。其说明如下：

LocalFileTimeToFileTime使用时区的当前设置 还有夏时制。所以如果是夏时制,， 此功能将考虑夏令时，即使 转换的时间是标准时间

所以我用以下代码测试它：

//Say, if DST change takes place on Mar-8-2015 at 2:00:00 AM
//when the clock is set 1 hr forward

//Let's check the difference between two times:
SYSTEMTIME st1_local = {2015, 3, 0, 8, 1, 30, 0, 0};    //Mar-8-2015 1:30:00 AM
SYSTEMTIME st2_local = {2015, 3, 0, 8, 3, 30, 0, 0};    //Mar-8-2015 3:30:00 AM

//Convert to file-time format
FILETIME ft1_local, ft2_local;
VERIFY(::SystemTimeToFileTime(&st1_local, &ft1_local));
VERIFY(::SystemTimeToFileTime(&st2_local, &ft2_local));

//Then convert from local to UTC time
FILETIME ft1_utc, ft2_utc;
VERIFY(::LocalFileTimeToFileTime(&ft1_local, &ft1_utc));
VERIFY(::LocalFileTimeToFileTime(&ft2_local, &ft2_utc));

//Get the difference
LONGLONG iiDiff100ns = (((LONGLONG)ft2_utc.dwHighDateTime << 32) | ft2_utc.dwLowDateTime) -
    (((LONGLONG)ft1_utc.dwHighDateTime << 32) | ft1_utc.dwLowDateTime);

//Convert from 100ns to seconds
LONGLONG iiDiffSecs = iiDiff100ns / 10000000LL;

//I would expect 1 hr
ASSERT(iiDiffSecs == 3600); //But I get 7200, which is 2 hrs!

//如果DST变更发生在2015年3月8日凌晨2:00:00
//当时钟设置为向前1小时时
//让我们检查两次之间的差异：
SYSTEMTIME st1_local={2015,3,0,8,1,30,0,0}//2015年3月8日凌晨1:30:00
SYSTEMTIME st2_local={2015,3,0,8,3,30,0,0}//2015年3月8日凌晨3:30:00
//转换为文件时间格式
文件时ft1_本地，ft2_本地；
验证（：：SystemTimeToFileTime（&st1_local，&ft1_local））；
验证（：：SystemTimeToFileTime（&st2_local，&ft2_local））；
//然后将本地时间转换为UTC时间
文件时间ft1_utc，ft2_utc；
验证（：：LocalFileTimeToFileTime（&ft1_local，&ft1_utc））；
验证（：：LocalFileTimeToFileTime（&ft2_local，&ft2_utc））；
//明白了吗
LONGLONG iiDiff100ns=（（LONGLONG）ft2_utc.dwHighDateTime
SystemTimeToFileTime（）
将其第一个参数解释为utc时间（它没有DST的概念），因此您的
ft1_local
和
ft2_local
对象将始终相隔两小时，因为您正在更改数据格式，而不是实际的时间点。
LocalFileTimeToFileTime（）
然后将对传递给它的任何内容应用相同的偏移量，因此
ft1_utc
和
ft2_utc
也将始终相隔两小时

如文档所述，“
LocalFileTimeToFileTime
使用时区和夏令时的当前设置”（emphasis mine），因此，如果当前时间比UTC晚四个小时，那么它将从您传递给它的任何时间中扣除四个小时，而不管该时间最初是否代表DST另一端的某个时间

编辑：根据评论，以下是如何获得标准C中两个本地时间的秒差：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    struct tm start_time;
    start_time.tm_year = 115;
    start_time.tm_mon = 2;
    start_time.tm_mday = 8;
    start_time.tm_hour = 1;
    start_time.tm_min = 30;
    start_time.tm_sec = 0;
    start_time.tm_isdst = -1;

    struct tm end_time;
    end_time.tm_year = 115;
    end_time.tm_mon = 2;
    end_time.tm_mday = 8;
    end_time.tm_hour = 3;
    end_time.tm_min = 30;
    end_time.tm_sec = 0;
    end_time.tm_isdst = -1;

    time_t start_tm = mktime(&start_time);
    time_t end_tm = mktime(&end_time);

    if ( start_tm == -1 || end_tm == -1 ) {
        fputs("Couldn't get local time.", stderr);
        exit(EXIT_FAILURE);
    }

    double seconds_diff = difftime(end_tm, start_tm);
    printf("There are %.1f seconds difference.\n", seconds_diff);

    return EXIT_SUCCESS;
}

正如你所期待的

请注意，对于
struct tm
：


tm_year
表示自1900年以来的年份，因此为了得到2015年，我们写115

tm_mon
在0到11之间，所以三月是2，而不是3

其他时间成员如您所料

当
tm_isdst
设置为
-1
时，
mktime（）
将尝试自行查明DST是否在我们提供的本地时间生效，这是我们希望它执行的操作

尽管“解决方案”非常漂亮，但由于明显的区域设置限制，我无法使用它。（C显然显示了它的年龄。）因此我不得不采用纯WinAPI方法。接下来是我想到的。如果我错了，请纠正我（尤其是那些可以访问除美国以外的时区的人，而微软的
mktime
似乎更喜欢这个时区）：

那么这就是实际的实现。这里需要注意的一个重要方面是，由于缺少检索特定年份时区信息的API，下面的方法在Windows XP上可能无法可靠地工作

一些声明首先：

enum DST_STATUS{
    DST_ERROR = TIME_ZONE_ID_INVALID,           //Error
    DST_NONE = TIME_ZONE_ID_UNKNOWN,            //Daylight Saving Time is NOT observed
    DST_OFF = TIME_ZONE_ID_STANDARD,            //Daylight Saving Time is observed, but the system is currently not on it
    DST_ON = TIME_ZONE_ID_DAYLIGHT,             //Daylight Saving Time is observed, and the system is currently on it
};

#define FILETIME_TO_100NS(f) (((LONGLONG)f.dwHighDateTime << 32) | f.dwLowDateTime)

BOOL GetLocalDateTimeDifference(SYSTEMTIME* pStBegin_Local, SYSTEMTIME* pStEnd_Local, LONGLONG* pOutDiffMs = NULL);
BOOL ConvertLocalTimeToUTCTime(SYSTEMTIME* pSt_Local, SYSTEMTIME* pOutSt_UTC = NULL);
DST_STATUS GetDSTInfoForYear(USHORT uYear, TIME_ZONE_INFORMATION* pTZI = NULL);

SystemTimeToFileTime不会将其第一个参数解释为UTC时间。它会按原样将其转换，或者换句话说，
1:30 AM
变为
1:30 AM
。您可以通过手动将FILETIME值转换为人类可读的格式来检查这一点。从1601年1月1日起，它以
100纳秒的间隔表示。您如何解释这来自第一个参数的文档，然后是：“一个指向SYSTEMTIME结构的指针，该结构包含要从UTC转换为文件时间格式的系统时间。”我将如何解释它？混乱的Microsoft文档：）不过，我喜欢你的第二个论点，关于
使用了当前设置
。似乎
LocalFileTimeToFileTime
确实采用了当前的DST设置并应用了它，而不考虑转换的日期。哇，那太糟糕了。你是如何调整我查找两个日期之间时间差的方法的呢>FILETIME结构包含从1601年1月1日UTC开始的时间间隔，因此如果
1:30AM
始终变为
1:30AM
，这表明
SystemTimeToFileTime（）< /代码>将它的第一个参数解释为UTC，它不驳斥这一点。保罗的答案是SPOT，但您也可以考虑使用.@ MattJangson的日期和时间API：是的，它是有效的。但是，除了C实现之外，“代码”> LoopFielTimeToFieltTime//Case> API本身有什么问题？它是否真的使用DST调整？就在“现在”调用它时？@ahmd0:是的，如文档所述。无需调用GetDynamicTimeZoneInformation（）。只需将NULL传递给GetTimeZoneInformation ForYear（）的第二个参数。
SYSTEMTIME st1 = {2015, 3, 0, 8, 1, 30, 0, 0};    //Mar-8-2015 1:30:00 AM
SYSTEMTIME st2 = {2015, 3, 0, 8, 3, 30, 0, 0};    //Mar-8-2015 3:30:00 AM

LONGLONG iiDiffNs;
if(GetLocalDateTimeDifference(&st1, &st2, &iiDiffNs))
{
    _tprintf(L"Difference is %.02f sec\n", (double)iiDiffNs / 1000.0);
}
else
{
    _tprintf(L"ERROR (%d) calculating the difference.\n", ::GetLastError());
}

enum DST_STATUS{
    DST_ERROR = TIME_ZONE_ID_INVALID,           //Error
    DST_NONE = TIME_ZONE_ID_UNKNOWN,            //Daylight Saving Time is NOT observed
    DST_OFF = TIME_ZONE_ID_STANDARD,            //Daylight Saving Time is observed, but the system is currently not on it
    DST_ON = TIME_ZONE_ID_DAYLIGHT,             //Daylight Saving Time is observed, and the system is currently on it
};

#define FILETIME_TO_100NS(f) (((LONGLONG)f.dwHighDateTime << 32) | f.dwLowDateTime)

BOOL GetLocalDateTimeDifference(SYSTEMTIME* pStBegin_Local, SYSTEMTIME* pStEnd_Local, LONGLONG* pOutDiffMs = NULL);
BOOL ConvertLocalTimeToUTCTime(SYSTEMTIME* pSt_Local, SYSTEMTIME* pOutSt_UTC = NULL);
DST_STATUS GetDSTInfoForYear(USHORT uYear, TIME_ZONE_INFORMATION* pTZI = NULL);

BOOL GetLocalDateTimeDifference(SYSTEMTIME* pStBegin_Local, SYSTEMTIME* pStEnd_Local, LONGLONG* pOutDiffMs)
{
    //Calculate difference between two local dates considering DST adjustments between them
    //INFO: May not work correctly on Windows XP for a year other than the current year!
    //'pStBegin_Local' = local date/time to start from
    //'pStEnd_Local' = local date/time to end with
    //'pOutDiffMs' = if not NULL, receives the difference in milliseconds (if success)
    //RETURN:
    //      = TRUE if success
    //      = FALSE if error (check GetLastError() for info)
    BOOL bRes = FALSE;
    LONGLONG iiDiffMs = 0;
    int nOSError = NO_ERROR;

    if(pStBegin_Local &&
        pStEnd_Local)
    {
        //Convert both dates to UTC
        SYSTEMTIME stBeginUTC;
        if(ConvertLocalTimeToUTCTime(pStBegin_Local, &stBeginUTC))
        {
            SYSTEMTIME stEndUTC;
            if(ConvertLocalTimeToUTCTime(pStEnd_Local, &stEndUTC))
            {
                //Then convert into a more manageable format: FILETIME
                //It will represent number of 100-nanosecond intervals since January 1, 1601 for each date
                FILETIME ftBeginUTC;
                if(::SystemTimeToFileTime(&stBeginUTC, &ftBeginUTC))
                {
                    FILETIME ftEndUTC;
                    if(::SystemTimeToFileTime(&stEndUTC, &ftEndUTC))
                    {
                        //Now get the difference in ms
                        //Convert from 100-ns intervals = 10^7, where ms = 10^3
                        iiDiffMs = (FILETIME_TO_100NS(ftEndUTC) - FILETIME_TO_100NS(ftBeginUTC)) / 10000LL;

                        //Done
                        bRes = TRUE;
                    }
                    else
                        nOSError = ::GetLastError();
                }
                else
                    nOSError = ::GetLastError();
            }
            else
                nOSError = ::GetLastError();
        }
        else
            nOSError = ::GetLastError();
    }
    else
        nOSError = ERROR_INVALID_PARAMETER;

    if(pOutDiffMs)
        *pOutDiffMs = iiDiffMs;

    ::SetLastError(nOSError);
    return bRes;
}

BOOL ConvertLocalTimeToUTCTime(SYSTEMTIME* pSt_Local, SYSTEMTIME* pOutSt_UTC)
{
    //Convert local date/time from 'pSt_Local'
    //'pOutSt_UTC' = if not NULL, receives converted UTC time
    //RETURN:
    //      = TRUE if success
    //      = FALSE if error (check GetLastError() for info)
    BOOL bRes = FALSE;
    SYSTEMTIME stUTC = {0};
    int nOSError = NO_ERROR;

    if(pSt_Local)
    {
        //First get time zone info
        TIME_ZONE_INFORMATION tzi;
        if(GetDSTInfoForYear(pSt_Local->wYear, &tzi) != DST_ERROR)
        {
            if(::TzSpecificLocalTimeToSystemTime(&tzi, pSt_Local, &stUTC))
            {
                //Done
                bRes = TRUE;
            }
            else
                nOSError = ::GetLastError();
        }
        else
            nOSError = ::GetLastError();
    }
    else
        nOSError = ERROR_INVALID_PARAMETER;

    if(pOutSt_UTC)
        *pOutSt_UTC = stUTC;

    ::SetLastError(nOSError);
    return bRes;
}

DST_STATUS GetDSTInfoForYear(USHORT uYear, TIME_ZONE_INFORMATION* pTZI)
{
    //Get DST info for specific 'uYear'
    //INFO: Year is not used on the OS prior to Vista SP1
    //'pTZI' = if not NULL, will receive the DST data currently set for the time zone for the year
    //RETURN:
    //      = Current DST status, or an error
    //        If error (check GetLastError() for info)
    DST_STATUS tzStat = DST_ERROR;
    int nOSError = NO_ERROR;

    //Define newer APIs
    DWORD (WINAPI *pfnGetDynamicTimeZoneInformation)(PDYNAMIC_TIME_ZONE_INFORMATION);
    BOOL (WINAPI *pfnGetTimeZoneInformationForYear)(USHORT, PDYNAMIC_TIME_ZONE_INFORMATION, LPTIME_ZONE_INFORMATION);

    //Load APIs dynamically (in case of Windows XP)
    HMODULE hKernel32 = ::GetModuleHandle(L"Kernel32.dll");
    ASSERT(hKernel32);
    (FARPROC&)pfnGetDynamicTimeZoneInformation = ::GetProcAddress(hKernel32, "GetDynamicTimeZoneInformation");
    (FARPROC&)pfnGetTimeZoneInformationForYear = ::GetProcAddress(hKernel32, "GetTimeZoneInformationForYear");

    TIME_ZONE_INFORMATION tzi = {0};

    //Use newer API if possible
    if(pfnGetDynamicTimeZoneInformation &&
        pfnGetTimeZoneInformationForYear)
    {
        //Use new API for dynamic time zone
        DYNAMIC_TIME_ZONE_INFORMATION dtzi = {0};
        tzStat = (DST_STATUS)pfnGetDynamicTimeZoneInformation(&dtzi);
        if(tzStat == DST_ERROR)
        {
            //Failed -- try old method
            goto lbl_fallback_method;
        }

        //Get TZ info for a year
        if(!pfnGetTimeZoneInformationForYear(uYear, &dtzi, &tzi))
        {
            //Failed -- try old method
            goto lbl_fallback_method;
        }
    }
    else
    {
lbl_fallback_method:
        //Older API (also used as a fall-back method)
        tzStat = (DST_STATUS)GetTimeZoneInformation(&tzi);
        if(tzStat == DST_ERROR)
            nOSError = ::GetLastError();
        else
            nOSError = ERROR_NOT_SUPPORTED;
    }

    if(pTZI)
    {
        *pTZI = tzi;
    }

    ::SetLastError(nOSError);
    return tzStat;
}