void gtk_window_set_deletable ( GtkWindow* window, gboolean setting )
Sets whether the window should be deletable.
By default, windows have a close button in the window frame.
Some window managers allow GTK to disable this button. If you
set the deletable property to
FALSE using this function, GTK
will do its best to convince the window manager not to show a
close button. Depending on the system, this function may not
have any effect when called on a window that is already visible,
so you should call it before calling gtk_widget_show().
On Windows, this function always works, since there’s no window manager policy involved.