Windows: Provide widget style hint to create dialog without system icon but close button in the titlebar

That's the default configuration for dialogs in most Windows application, but it is not possible to achive that with any combintation of Qt::WindowFlags. Ie. setting only Qt::Dialog on a toplevel dialog with parent results in system icon, "what's this" and close button. OR'ing with Qt::WindowTitleHint removes everything, and adding any other flag also enables the unwanted system menu.

The following Win32 code creates a window with closing box and without system menu:

• Set the icon in the class struct to 0
• Use exStyle WS_EX_DLGMODALFRAME
• Use Style WS_POPUPWINDOW ( WS_POPUP | WS_BORDER | WS_SYSMENU [! although it does not show])

  #include <windows.h>
  
  LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
  {
      switch (message) 
      {
      case WM_DESTROY:
   PostQuitMessage(0);
   break;
  
      default:
   return DefWindowProc(hWnd, message, wParam, lParam);
      }
      return 0;
  }
  
  int APIENTRY wWinMain(HINSTANCE hInstance,
          HINSTANCE /*hPrevInstance*/,
          LPTSTR    /*lpCmdLine*/,
          int       nCmdShow)
  {
      WNDCLASSEX wcex;
      
      wcex.cbSize = sizeof(WNDCLASSEX); 
      
      wcex.style  = CS_HREDRAW | CS_VREDRAW;
      wcex.lpfnWndProc = (WNDPROC)WndProc;
      wcex.cbClsExtra = 0;
      wcex.cbWndExtra = 0;
      wcex.hInstance = hInstance;
      wcex.hIcon  = NULL;
      wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
      wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
      wcex.lpszMenuName = NULL;
      wcex.lpszClassName = L"qtest";
      wcex.hIconSm = NULL;
      
      ATOM windowClass = RegisterClassEx(&wcex);
  
      HWND hWnd = CreateWindowEx(WS_EX_DLGMODALFRAME,
          (TCHAR*)windowClass, L"Example",
   WS_POPUPWINDOW | WS_CLIPSIBLINGS | WS_DLGFRAME | WS_OVERLAPPED | WS_SIZEBOX, 
          CW_USEDEFAULT, CW_USEDEFAULT, 200, 100, 0, 0, hInstance, 0);
      if (!hWnd)
   return FALSE;
      SendMessage(hWnd, WM_SETICON, 0, 0);
  
      ShowWindow(hWnd, nCmdShow);
      UpdateWindow(hWnd);
  
      MSG msg;
      while (GetMessage(&msg, 0, 0, 0)) {
          TranslateMessage(&msg);
          DispatchMessage(&msg);
      }
      return 0;
  }