How to check if a window is maximized? (Gdk::Window_State_Maximized from a Gtk::Window)

[<Lukas Orlowski dlr de>]

Good morning community

I've been googling myself senseless while trying to find a solution for
my problem.

I want to check if a Gtk::Window is maximized using Gtkmm.
The following does not work:

Gtk::Window* wMainWindow;
// snip...
Glib::RefPtr<Gdk::Window> pGDK = wMainWindow->get_frame();
if ( Gdk::WINDOW_STATE_MAXIMIZED == pGDK->get_state() )
	cout << "true" << endl;

Neither does the following declaration:

Gdk::WINDOW_STATE wstate;


Any help is welcome.

Best regards Luke