The set_text_column() method defines the what column of the GtkTreeModel (set by set_model() method) will be used as list for GtkEntryCompletion. This method creates and adds a GtkCellRendererText using the column specified by column as the source for completion strings. If you don't use this method you will have to install a GtkCellRendererText in the GtkEntryCompletion and set a match function using the set_match_func() method to display the completion strings.