c++ - 如何从 ULONGLONG 毫秒创建 SYSTEMTIME 结构？

Question

我不想使用 WMI 获取上次启动时间，而是想使用 ::GetSystemTime() 和 ::GetTickCount64 来计算它。但是一旦达到毫秒，我就不知道如何返回到 FILETIME 对象。

我试过这个:

static ULONGLONG FileTimeToMillis(const FILETIME &ft)
{
    ULARGE_INTEGER uli;
    uli.LowPart = ft.dwLowDateTime; // could use memcpy here!
    uli.HighPart = ft.dwHighDateTime;

    return uli.QuadPart/10000;
}

static void MillisToSystemTime(ULONGLONG millis, SYSTEMTIME *st)
{
   UINT64 t = static_cast<UINT64>(-10000) * static_cast<UINT64>(millis);

   FILETIME ft;
   ft.dwLowDateTime = static_cast<DWORD(t & 0xFFFFFFFF);
   ft.dwHighDateTime = static_cast<DWORD>(t >> 32);

   ::FileTimeToSystemTime(&ft, st);
}

void main()
{
    SYSTEMTIME st, lt, st2, lt2;

    ::GetSystemTime(&st);
    ::GetLocalTime(&lt);

    cout << "The system time is: " << st.wHour << ":" << st.wMinute << ":" << st.wSecond << endl;
    cout << "The local time is: "  << lt.wHour << ":" << lt.wMinute << ":" << lt.wSecond << endl;

    FILETIME sft, lft;
    ::SystemTimeToFileTime(&st, &sft);
    ::SystemTimeToFileTime(&lt, &lft);  

    cout << "The system time in millis is: " << FileTimeToMillis(sft) << endl;
    cout << "The local time in millis is: "  << FileTimeToMillis(lft) << endl;

    MillisToSystemTime(FileTimeToMillis(sft), &st2);
    MillisToSystemTime(FileTimeToMillis(sft), &lt2);

    cout << "The system time (post conversion) is: " << st2.wHour << ":" << st2.wMinute << ":" << st2.wSecond << endl;
    cout << "The local time (post conversion) is: "  << lt2.wHour << ":" << lt2.wMinute << ":" << lt2.wSecond << endl;
}

但我肯定没有得到预期的结果。相反，我得到:

The system time is: 15:5:2
The local time is: 10:5:2
The system time in millis is: 12984678302935
The local time in millis is: 12984660302935
The system time (post conversion) is: 52428:52428:52428
The local time (post conversion) is: 52428:52428:52428

有什么想法吗？请不要告诉我使用 Boost 或因为它对我不可用。

Answer 1

The system time (post conversion) is: 52428:52428:52428

当你得到奇怪的值时，总是先转换为十六进制。 52428 == 0xcccc。这是调试版本生成的代码用来初始化变量的值。所以你正在查看未初始化的内存。

下一个防御策略是从不忽略 Windows api 函数的返回值。使用 VERIFY() 宏，就像 MFC 中可用的宏一样。然后您会很容易地看到 FileTimeToSystemTime() 失败。

错误是-10000。