RegisterClass fails the 2nd time it is called

[codercoder]

I have on method call another method NotificationWndProc to create a notification window, which will receive messages. At the first time, things are running OK, but in the second time, it returns error:

RegisterClass returned 1410.

Please help me out!

In .cpp file:

{
...
 
long  (CALLBACK *WndProcPointer ) ( HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam ) = NotificationWndProc    ;
wc.lpfnWndProc   = WndProcPointer;    
wc.lpszClassName = NOTIFICATION_CLASS;
wc.lpszMenuName  = NULL;
wc.hInstance     = gVars.g_hInst;
wc.hIcon         = NULL;
wc.hCursor       = NULL;
wc.hbrBackground = NULL;
wc.cbWndExtra    = sizeof(PSNMP_MGR_SESSION);
wc.cbClsExtra    = 0;
wc.style         = 0;    // register class
fOk = RegisterClass(&wc);
 
if (!fOk) 
{
     TRACE( "RegisterClass returned %d.\n", GetLastError() );
     return (FALSE);
}
 
...
}
 
LRESULT CALLBACK CACSSnmpUtil::NotificationWndProc(    
                                                    HWND   hWnd,
                                                    UINT   uMsg,
                                                    WPARAM wParam,
                                                    LPARAM lParam
                                                   )
{
 
    if (uMsg == WM_MSG_INCOMING) 
    {
 
        PSNMP_MGR_SESSION pSession;
        // retrieve session pointer from window
   pSession = (PSNMP_MGR_SESSION)GetWindowLong(hWnd, 0);
 
        // validate session ptr
        if ( pSession == NULL )
            return (LRESULT)0;
 
        // process notification message
        if ( ProcessNotification( pSession ) ) 
        {
            // post message to break out of message pump
            PostMessage( pSession->hWnd, WM_MSG_DONE, (WPARAM)0, (LPARAM)0 );
        }
        return (LRESULT)0;
 
    } 
    else 
    {
        // forward all other messages to windows
        return DefWindowProc(hWnd, uMsg, wParam, lParam);
 
    }
 
} // end of NotificationWndProc
 

In .h file:
static LRESULT CALLBACK NotificationWndProc( HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam );

[Banfa]

You can look up the error code here where you will find it is ERROR_CLASS_ALREADY_EXISTS.

Once you have registered a class then there is no need to do so again unless you unregister it.

It is normal to only register classes once for an application not everytime it tries to create a window of that class.