將clock_gettime移植到Windows

clock_gettime函數是POSIX標準函數，它提供了一種以納秒精度獲取當前時間的方法。但是，Windows 本身不支援它。

將程式碼移植到 Windows

要將使用clock_gettime 的程式碼移植到 Windows，您可以使用 Win32 實作替換函數API。以下是如何執行此操作的範例：

#include <Windows.h>

// Returns the file time offset for Windows.
LARGE_INTEGER getFILETIMEoffset() {
    SYSTEMTIME s;
    FILETIME f;
    LARGE_INTEGER t;

    s.wYear = 1970;
    s.wMonth = 1;
    s.wDay = 1;
    s.wHour = 0;
    s.wMinute = 0;
    s.wSecond = 0;
    s.wMilliseconds = 0;
    SystemTimeToFileTime(&s, &f);
    t.QuadPart = f.dwHighDateTime;
    t.QuadPart <<= 32;
    t.QuadPart |= f.dwLowDateTime;
    return (t);
}

// Replacement for clock_gettime function.
int clock_gettime(int X, struct timeval *tv) {
    LARGE_INTEGER t;
    FILETIME f;
    double microseconds;
    static LARGE_INTEGER offset;
    static double frequencyToMicroseconds;
    static int initialized = 0;
    static BOOL usePerformanceCounter = 0;

    if (!initialized) {
        LARGE_INTEGER performanceFrequency;
        initialized = 1;
        usePerformanceCounter = QueryPerformanceFrequency(&performanceFrequency);
        if (usePerformanceCounter) {
            QueryPerformanceCounter(&offset);
            frequencyToMicroseconds = (double)performanceFrequency.QuadPart / 1000000.;
        } else {
            offset = getFILETIMEoffset();
            frequencyToMicroseconds = 10.;
        }
    }
    if (usePerformanceCounter) QueryPerformanceCounter(&t);
    else {
        GetSystemTimeAsFileTime(&f);
        t.QuadPart = f.dwHighDateTime;
        t.QuadPart <<= 32;
        t.QuadPart |= f.dwLowDateTime;
    }

    t.QuadPart -= offset.QuadPart;
    microseconds = (double)t.QuadPart / frequencyToMicroseconds;
    t.QuadPart = microseconds;
    tv->tv_sec = t.QuadPart / 1000000;
    tv->tv_usec = t.QuadPart % 1000000;
    return (0);
}

實現替換函數後，您可以在程式碼中使用它來取得奈秒精度的當前時間。請注意，您可能需要對程式碼進行額外的修改，以解決不同平台上 Clock_gettime 行為的任何差異。