difference between two SYSTEMTIME variable

Question

I want to get difference between two SYSTEMTIME variable. I saw someone asked this question here before, but he was told to convert both SYSTEMTIME structures to FILETIME.. Is there another way to get the difference?

SYSTEMTIME st;
GetSystemTime(&st);

---some code here---

  SYSTEMTIME st2;
  GetSystemTime(&st2);

st-st2?

Answer 1

SYSTEMTIME operator-(const SYSTEMTIME& pSr,const SYSTEMTIME& pSl)
{
    SYSTEMTIME t_res;
    FILETIME v_ftime;
    ULARGE_INTEGER v_ui;
    __int64 v_right,v_left,v_res;
    SystemTimeToFileTime(&pSr,&v_ftime);
    v_ui.LowPart=v_ftime.dwLowDateTime;
    v_ui.HighPart=v_ftime.dwHighDateTime;
    v_right=v_ui.QuadPart;

    SystemTimeToFileTime(&pSl,&v_ftime);
    v_ui.LowPart=v_ftime.dwLowDateTime;
    v_ui.HighPart=v_ftime.dwHighDateTime;
    v_left=v_ui.QuadPart;

    v_res=v_right-v_left;

    v_ui.QuadPart=v_res;
    v_ftime.dwLowDateTime=v_ui.LowPart;
    v_ftime.dwHighDateTime=v_ui.HighPart;
    FileTimeToSystemTime(&v_ftime,&t_res);
    return t_res;
}

Answer 2

It says pretty clearly on the MSDN documentation:

It is not recommended that you add and subtract values from the SYSTEMTIME structure to obtain relative times. Instead, you should

• Convert the SYSTEMTIME structure to a FILETIME structure.
• Copy the resulting FILETIME structure to a ULARGE_INTEGER structure.
• Use normal 64-bit arithmetic on the ULARGE_INTEGER value.

Why not do exactly that?

Answer 3

ft1 and ft2 are filetime structures

ULARGE_INTEGER ul1;
    ul1.LowPart = ft1.dwLowDateTime;
    ul1.HighPart = ft1.dwHighDateTime;

ULARGE_INTEGER ul2;
    ul2.LowPart = ft2.dwLowDateTime;
    ul2.HighPart = ft2.dwHighDateTime;


ul2.QuadPart -= ul1.QuadPart;

Difference in Milliseconds...

ULARGE_INTEGER uliRetValue;
    uliRetValue.QuadPart = 0;


    uliRetValue = ul2;
    uliRetValue.QuadPart /= 10;
    uliRetValue.QuadPart /= 1000; // To Milliseconds