Gtk::ComboBox::get_active_id() documentation

[Phil Wolff <adiabat hughes net>]

The documentation says

    void Gtk::ComboBox::get_active_id(const Glib::ustring & active_id)
    ...
    Changes the active row of combo_box...
    ...
    Returns: true if a row with a matching ID was found...

Void, but it returns a value?

g++ says no, it can't return a value.

If it can't return a value, and it changes the active row, why is it 
called "get..." rather than "set..."?