Win32中如何让窗口大小不可变

case WM_NCHITTEST: 
   {
   switch(DefWindowProc(hWnd, msg, wParam, lParam))
   {
   case HTLEFT:
    return HTCLIENT;
   case HTBOTTOM:  
     return HTCLIENT;
   case HTBOTTOMLEFT:  
     return HTCLIENT;
   case HTBOTTOMRIGHT:  
     return HTCLIENT;
   case HTRIGHT:  
     return HTCLIENT;
   case HTTOP:  
     return HTCLIENT;
   case HTTOPLEFT:  
     return HTCLIENT;
   case HTTOPRIGHT:  
     return HTCLIENT;  
   } 
   }
   return DefWindowProc(hWnd, msg, wParam, lParam);