Get MenuElem by name ?

["schmirrwurst free fr" <schmirrwurst free fr>]

Hi,

I try to modify a program to add some features. I would like to add some
menu element...
Those elements are added that way :

 menu_partition .items() .push_back(
Gtk::Menu_Helpers::MenuElem( _("manage flags"),
 sigc::mem_fun( *this, &Win_GParted::activate_manage_flags ) ) );

So I've added my element with the same syntax
menu_partition .items() .push_back(
Gtk::Menu_Helpers::MenuElem( _("Make Image"),
 sigc::mem_fun( *this, &Win_GParted::on_make_image ) ) );

The Problem is that it is not appearing, I guess I have to .show it, but
in the code, it is done later, and with an ID number, and I don't know
it : 

menu_partition .items()[ installer_mode ? 9 : 10 ] .show() ;

Is there a way to .show the item by name ? like
menu_partition .items()["Make Image"] .show();
???

Other question, I'm pretty new in gtkmm, can somebody explain me what
the sentense "installer_mode ? 9 : 10" means ??