Hello!
I use class which inherits QApplication and implements its own winEventFilter(MSG* msg, long* result) to capture WM_INPUT messages and to process raw input data from keyboard in Qt 4.8.4.
Qt Code: 
  1. bool Application::winEventFilter(MSG *msg, long *result)
  2. {
  3.   UINT dwSize;
  4.   WCHAR keyChar;
  5.   switch(msg->message)
  6.   {
  7.     case WM_INPUT:
  8.     {
  9.       if (GetRawInputData((HRAWINPUT)msg->lParam,
  10.                           RID_INPUT,
  11.                           NULL,
  12.                           &dwSize,
  13.                           sizeof(RAWINPUTHEADER)) == -1) return false;
  14.       LPBYTE lpb = new BYTE[dwSize];
  15.       if (lpb == NULL) return false;
  16.       if (GetRawInputData((HRAWINPUT)msg->lParam,
  17.                           RID_INPUT,
  18.                           lpb,
  19.                           &dwSize,
  20.                           sizeof(RAWINPUTHEADER)) != dwSize)
  21.       {
  22.         delete[] lpb;
  23.         return false;
  24.       }
  25.       PRAWINPUT raw = (PRAWINPUT)lpb;
  26.       UINT Event;
  27.       Event = raw->data.keyboard.Message;
  28.       keyChar = GetSymbol(raw->data.keyboard.VKey);
  29.       char keyCharLO = (char)keyChar;
  30.       delete[] lpb;
  31.       if (!iswprint(keyChar))
  32.         return false;
  33.       // process data from keyboard
  34.       keyStrokeHandle->ProcessNextKeyStroke(Event, keyChar);
  35.  
  36.       *result = 0;
  37.       QApplication::winEventFilter(msg, result);
  38.       return true;
  39.     }
  40.     default:
  41.     {
  42.       return false;
  43.     }
  44.   }
  45. }
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After RegisterRawInputDevices call, application starts to recieve WM_INPUT messages.
The problem is: when user types in qt application, data from keyboard don't get to input which is used to type data, it is "blocked" by winEventFilter.
According to Qt Documentation:
If you don't want the event to be processed by Qt, then return true and set result to the value that the window procedure should return. Otherwise return false.
And MSDN:
Return value
If an application processes this message, it should return zero.
But I can't receive my input in application whether I return true/false from winEventFilter, change *result value or invoke inhedited QApplcation::winEventFilter.
What do I have to do to get data in application after WM_INPUT processing?