ComboBoxText and getting the index

[Sean Kelley <sean sweng gmail com>]

Hi,

I am porting my Qt application to Gtkmm in order to learn more about
Gtkmm.  I am not particularly clear on how to get an index into my
ComboBoxText.  So if I have a combo box of a number of text items,
in my case Irish Gaelic prepositions, how do get the index on a changed
signal?

    //Child widgets:
    Gtk::ComboBoxText    m_pronBox;
    Gtk::ComboBoxText    m_prepBox;

....

      //Fill the combo:
      m_prepBox.append_text("ag");
      m_prepBox.append_text("ar");
      m_prepBox.append_text("as");
      m_prepBox.append_text("chun");
 ...
      //Connect signal handler:
    m_prepBox.signal_changed().connect( sigc::mem_fun(*this, &IrishPrep::on_combobox_changed) );
...

All I can get from the combo box is the text selected.  In Qt I
had used a QtComboBox, where I could access the member function
currentItem.  I would rather have the actual index into it and not
the string.

Thanks in advance!

Sean