Question about GtkWidget pointer?

["David Wang (Wang Xin-lu)" <davidwang lucent com>]

Hi,

I wrote a function to create menu: 
void setupMenu(GtkWidget *window, GtkWidget *menu_bar, GtkWidget *menu_vbox,
        GtkWidget *root_menu, GtkWidget *menu, char *labelname, gboolean boo)
{
	if (menu_vbox == 0) {
                menu_vbox = gtk_vbox_new(FALSE, 1);
                gtk_container_border_width (GTK_CONTAINER(menu_vbox), 1);
                gtk_container_add(GTK_CONTAINER (window), menu_vbox);
                gtk_widget_show(menu_vbox);
                printf("menu_vbox is 0\n");
                printf("menu_vbox is %x\n", menu_vbox);
        }
....
}

In the main function, I call it like this:
int main( int argc, char *argv[] )
{

...
GtkWidget *menu_vbox;
menu_vbox = 0;
...

setupMenu(window, menu_bar, menu_vbox,
                        root_menu, menu, "File", FALSE);
printf("after one menu_vbox is %x\n", menu_vbox);
..
}

I found that "menu_vbox" has value in setupMenu function, but it is "0" after
it.
If I call setupMenu more than 1 time, there has error:
: before menu_vbox is 0
menu_vbox is 0
menu_vbox is 3b090
menu_bar is 0
new root_menu with label
after one menu_vbox is 0

Gtk-CRITICAL **: file gtkbin.c: line 217 (gtk_bin_add): assertion `bin->child ==
NULL' failed.
menu_vbox is 0
menu_vbox is 3b320
menu_bar is 0
new root_menu with label
justify root_menu
after two menu_vbox is 0

why GtkWidget pointer can not take back value in a function?
How can I do if I want to use the value initialized in a function?

Thanks!
David