Accessing the window inside the widget

A simple program:

---SNIP---
GtkWidget *my_window;
GtkBuilder *builder_handler;


builder_handler = gtk_builder_new();
gtk_builder_add_from_file(builder_handler, GUI_XML_FILENAME, NULL);

my_window = GTK_WIDGET(gtk_builder_get_object(builder_handler, "window"));
---PINS---


Now my_window is a GtkWidget and its class hierarchy tree is the following:

+GtkWidget
|+GtkContainer
  |+GtkBin
   |+GtkWindow

Almost every function to manipulate windows requires a GtkWindow 
pointer, i.e.:
void gtk_window_set_resizable(GtkWindow *window, gboolean resizable);

How do I get the GtkWindow pointer from the GtkWidget I get after the 
builder?

Thanks in advance.
-- 
Regards,
Manuel Ferrero
R&D department

Reer SpA	
Tel.  +39 011 2482215
Fax. +39 011 859867

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