How do I catch a combo box change?

The entry which is associated to your GtkCombo send a "changed" signal when:

• some text is typed in

• the selection of the combo box is changed

To catch any combo box change, simply connect your signal handler with

      g_signal_connect(GTK_COMBO(cb)->entry,
                       "changed",
                       G_CALLBACK(my_cb_change_handler),
                       NULL);