time interval in milliseconds

Hi ,
I need to calculate difference between two time intervals. I have to set a timer for this time interval using SetTimer(......)
iam using SYSTEMTIME,FILETIME and ULARGE_INTEGER for this.
Iam getting the current time(start time) using GetLocalTime(...) and setting the end time in SYSTEMTIME structure for 31st Dec,2005 as follows:
l_SystemTime.wDay=31;
l_SystemTime.wDayOfWeek=0;
l_SystemTime.wHour=0;
l_SystemTime.wMilliseconds=0;
l_SystemTime.wMinute=0;
l_SystemTime.wMonth=12;
l_SystemTime.wSecond=0;
l_SystemTime.wYear=2005;
i have converted both start and end times to FILETIME and then to ULARGE_INTEGER for subtracting. iam subtracting high and low parts of both the time intervals separately(or can i subtract the quadparts?) .i wanted to know if the difference here can be obtained in milli seconds, so that i can directly use this value for setting a timer. If yes, how do I extract the value as SetTimer takes the interval as UINT?
Can anyone help me on this
Regards,
Anu

If you really need millisecond-resolution, use GetTickCount(). There's a reference:

http://msdn.microsoft.com/library/de...ttickcount.asp

Thank u for the reply.
But the GetTickCount function retrieves the number of milliseconds that have elapsed since the system was started. I need to set the timer for a particular time. for that i have to obtain the difference between the current (local) system time and the specified time. Is there any API that can do this?

Quote:

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Originally Posted by allu_anuradha

Thank u for the reply.
But the GetTickCount function retrieves the number of milliseconds that have elapsed since the system was started. I need to set the timer for a particular time. for that i have to obtain the difference between the current (local) system time and the specified time. Is there any API that can do this?

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No There is no API specified for this.
anyway just follow this link u will get your answere

http://www.codeproject.com/datetime/winapi_datetime_ops.asp
:thumb:

Your first assumptions are correct (see also my example below), i.e. to get the time interval in milliseconds you may:

• use SystemTimeToFileTime to "convert" SYSTEMTIME to FILETIME;
• because it's not so "convenient" to obtain the time interval from FILETIME, copy the FILETIME members in a ULARGE_INTEGER structure;
• substract QuadPart members of ULARGE_INTEGER and obtain the time interval.

Last one is not:

• store the obtained time interval in an UINT variable; this may be and may be not possible (without loss of data) depending of UINT_MAX value (see UINT_MAX defined in LIMITS.H); for sure from this very moment its not enough for an 32-bit UINT.

Code:

---

  // get current local time
  SYSTEMTIME stNow;
  ::GetLocalTime(&stNow);

  // set time to 01/01/2006 0:0:0 - 000
  SYSTEMTIME stTo;
  ::ZeroMemory(&stTo, sizeof(SYSTEMTIME));
  stTo.wYear = 2006;
  stTo.wMonth = 1;
  stTo.wDay = 1;

  // convert each to FILETIME
  FILETIME ftNow, ftTo;

  ::SystemTimeToFileTime(&stNow, &ftNow);
  ::SystemTimeToFileTime(&stTo, &ftTo);

  // copy in FILETIME in ULARGE_INTEGER structure
  ULARGE_INTEGER uliNow, uliTo;

  uliNow.LowPart  = ftNow.dwLowDateTime;
  uliNow.HighPart = ftNow.dwHighDateTime;

  uliTo.LowPart  = ftTo.dwLowDateTime;
  uliTo.HighPart = ftTo.dwHighDateTime;

  // substract QuadPart and get time left in milliseconds
  ULONGLONG ullLeft = uliTo.QuadPart - uliNow.QuadPart;

  // just for testing: can we cast to UINT?
  if(ullLeft <= (ULONGLONG)UINT_MAX)
  {
      // Maybe, but not always.
      ::MessageBox(NULL, _T("Fits UINT"), _T("Test"), MB_OK);
  }

  LPTSTR pszBuff = new TCHAR[128];

  _stprintf(pszBuff, _T("Estimated time left: %I64d ms"), ullLeft);
  ::MessageBox(NULL, pszBuff, _T("Test"), MB_OK);

  delete[] pszBuff;

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BTW, why do you want to pass the time interval until 31 December 2005 in milliseconds. You want to wake up with 1 millisecond precision? ;)
Well, just as an ideea: Set a timer with, let's say, 1 second resolution (value 1000 for uElapse argument); in WM_TIMER handler take the current time and compare with final time; when this time is reached... "bang!". Of course some precsion is lost, but still is good. ;)

Quote:

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Originally Posted by ovidiucucu

Well, just as an ideea: Set a timer with, let's say, 1 second resolution (value 1000 for uElapse argument); in WM_TIMER handler take the current time and compare with final time; when this time is reached... "bang!". Of course some precsion is lost, but still is good. ;)

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But WM_TIMER is a low priority message. There's no guarantee that the handler will get invoked every one second. :)

Quote:

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Originally Posted by Wombat

But WM_TIMER is a low priority message. There's no guarantee that the handler will get invoked every one second. :)

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Correct. But what we gonna do without the hope?.. :)

Hi ovidiucucu,
I tried checking if ullLeft <= (ULONGLONG)UINT_MAX as given in your code. But that doesnt seem to work.
Regards,
Anu

Quote:

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Originally Posted by allu_anuradha

Hi ovidiucucu,
I tried checking if ullLeft <= (ULONGLONG)UINT_MAX as given in your code. But that doesnt seem to work.
Regards,
Anu

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Doesn't work what?
I put that test in the example to simple demonstrate that you cannot store the milliseconds from now till 31 December 2005 in a UINT variable.