C get system time to microsecond accuracy on windows? [duplicate]

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measuring time with re开发者_高级运维solution of microseconds in c++?

Hi,

Is there a simple way i can get the system time on a Windows machine, down to microsecond accuracy?

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Look at GetSystemTimeAsFileTime

It gives you accuracy in 0.1 microseconds or 100 nanoseconds.

Note that it's Epoch different from POSIX Epoch.

So to get POSIX time in microseconds you need:

    FILETIME ft;
    GetSystemTimeAsFileTime(&ft);
    unsigned long long tt = ft.dwHighDateTime;
    tt <<=32;
    tt |= ft.dwLowDateTime;
    tt /=10;
    tt -= 11644473600000000ULL;

So in such case time(0) == tt / 1000000

---

Like this

unsigned __int64 freq;
QueryPerformanceFrequency((LARGE_INTEGER*)&freq);
double timerFrequency = (1.0/freq);

unsigned __int64 startTime;
QueryPerformanceCounter((LARGE_INTEGER *)&startTime);

//do something...

unsigned __int64 endTime;
QueryPerformanceCounter((LARGE_INTEGER *)&endTime);
double timeDifferenceInMilliseconds = ((endTime-startTime) * timerFrequency);

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What we really need is a high-resolution GetTickCount(). As far as I know, this doesn't really exist.

If you're willing to use a hackish way to solve this (that would probably only work on some versions of Windows like XP), look here at ReactOS. Then try this code:

long long GetTickCount64()
{
    return (long long)
        ((((unsigned long long)*(unsigned long int*)0x7FFE0000
           * (unsigned long long)*(unsigned long int*)0x7FFE0004)
         * (unsigned long long)10000) >> 0x18);
}

Tweaking it might give you what you need in some versions of Windows.