Thread: Invalid windowhandle

  1. #1
    Politics&Cpp geek Da-Nuka's Avatar
    Join Date
    Oct 2004

    Invalid windowhandle

    I have done errorchekcing all and that, but at SOME points in my program, MoveWindow() returns error 1400, which is invalid windowhandle. Sometimes, later in the program, it works, even i havent done anything new to the handle!

    I post some relevant code, and the full code included
    The function which creates the window and return a handle
    HWND CreateInputWindow(const char* AppName) {
         HWND returnHWND;
         WNDCLASS wndclass;         = CS_HREDRAW | CS_VREDRAW;
         wndclass.cbClsExtra    = 0 ;
         wndclass.cbWndExtra    = 0 ;
         wndclass.lpfnWndProc   = InputProc;
         wndclass.hIcon         = NULL;
         wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
         wndclass.lpszMenuName  = NULL;
         wndclass.lpszClassName = AppName;
         wndclass.hInstance     = g_hInstance ;
         wndclass.hbrBackground = (HBRUSH)CreateSolidBrush(RGB(255,255,255));
                if (!RegisterClass (&wndclass)) {
                MessageBox (NULL, TEXT ("Could not register windows class. Shutting down.."), AppName, MB_ICONERROR) ;
                return (HWND)NULL ; // Error, exit and return
         returnHWND=CreateWindow(AppName,AppName,WS_CHILD|WS_VISIBLE,0,0,0,0,output_W,(HMENU) ID_INPUT_W,g_hInstance,NULL);
                if(returnHWND==NULL) {
                MessageBox(NULL,"Call to CreateWindow() failed", "Error", MB_OK);
                return (HWND) NULL; // Error, exit and return
    return returnHWND;
    In the WinMain() function:
         ShowWindow (input_W, g_CmdShow) ;
         UpdateWindow (input_W) ;
    In the MessageProcedure:
    case WM_SIZE:
      if(MoveWindow(input_W,0,0,200,200,true)==0) {
         ReportError(GetLastError(),"MoveWindow()"); //This returns 1400...
    return 0;

  2. #2
    Join Date
    Jan 2002
    Sometimes WM_SIZE messages are issued before WM_CREATE or during system processing of CreateWindowEx, hence the invalid handle error.

    I wouldn't worry about it; if MoveWindow fails in the context you're using it then it's not a problem but, if perfectionism is your thing, then just check for a non-NULL window handle prior to issuing the MoveWindow call.

    edit: Alternatively, set the value of HWND variable, input_W within your WM_CREATE handler; as this message is sent during system processing of CreateWindowEx there's a good chance that handle will be valid for the first WM_SIZE - or just use the window handle delivered to your window procedure as it will be valid.
    Last edited by Ken Fitlike; 03-06-2005 at 06:44 AM.
    CProgramming FAQ
    Caution: this person may be a carrier of the misinformation virus.

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