Addendum...

I discovered that I can obtain pointer 'p' by moving the position of const - i.e. this doesn't compile...

Code:
void functionB() const
{
	const Glib::RefPtr<Gdk::Window> p = canvas_event_box.get_window();
}
but this does compile...

Code:
void functionB() const
{
	Glib::RefPtr<const Gdk::Window> p = canvas_event_box.get_window();
}
The problem now is that having succesfully obtained the pointer, I can't use it !!!

My ultimate aim is to find the 'x' and 'y' co-ordinates for this window's mouse pointer:-

Code:
void functionB() const
{
gint x, y;
Gdk::ModifierType state;

	Glib::RefPtr<const Gdk::Window> p = canvas_event_box.get_window();

	p->get_pointer (x, y, state);
}
But the red line now gives me this error

error C2662: 'Gdk::Window::get_pointer' : cannot convert 'this' pointer from 'const Gdk::Window' to 'Gdk::Window &'
1> Conversion loses qualifiers