获取两指定日期的时间差

代码如下，

double TimeDiff(const char* szTime1, const char* szTime2)
{
    if(0 == szTime1)        return -1.0f;
    if(0 == szTime1[0])     return -1.0f;
    if(0 == szTime2)        return -1.0f;
    if(0 == szTime2[0])     return -1.0f;

    int nRetCount;
    SYSTEMTIME sysTime1 = {0};
    nRetCount = sscanf(szTime1, "%hd-%hd-%hd %hd:%hd:%hd.%hd",
        &sysTime1.wYear, &sysTime1.wMonth, &sysTime1.wDay,
        &sysTime1.wHour, &sysTime1.wMinute, &sysTime1.wSecond, &sysTime1.wMilliseconds);
    if(7 != nRetCount)
    {
        return -1.0f;
    }

    SYSTEMTIME sysTime2 = {0};
    nRetCount = sscanf(szTime2, "%hd-%hd-%hd %hd:%hd:%hd.%hd",
        &sysTime2.wYear, &sysTime2.wMonth, &sysTime2.wDay,
        &sysTime2.wHour, &sysTime2.wMinute, &sysTime2.wSecond, &sysTime2.wMilliseconds);
    if(7 != nRetCount)
    {
        return -1.0f;
    }

    //将时间转换为FILETIME，然后拷贝到ULARGE_INTEGER中，再进行数学运算
    FILETIME fileTime1 = {0}, fileTime2 = {0};
    ::SystemTimeToFileTime(&sysTime1, &fileTime1);
    ::SystemTimeToFileTime(&sysTime2, &fileTime2);

    ULARGE_INTEGER uliTime1= {0}, uliTime2 = {0};
    memcpy(&uliTime1, &fileTime1, sizeof(FILETIME));
    memcpy(&uliTime2, &fileTime2, sizeof(FILETIME));
    //计算毫秒结果
    __int64 iSpan = ((__int64)(uliTime1.QuadPart - uliTime2.QuadPart))/10000;

    if(0 == iSpan)
    {
        return 0.0f;
    }
    return iSpan/(24.0f*3600.0f*1000.0f);
}

 

之前用过COleDateTime类，但是精度不够。

FILETIME的精度为100纳秒，除以10000时得到毫秒的结果，除以10时得微秒结果。