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

Question

Possible Duplicate:
measuring time with resolution of microseconds in c++?

Hi,

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

Answer 1

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

Answer 2

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);