Gets the logical sort_column_id that the model sorts on when this column is selected for sorting. See gtk_tree_view_column_set_sort_column_id().
the current sort_column_id for this column, or -1 if this column can't be used for sorting.
See Implementation
Gets the logical sort_column_id that the model sorts on when this column is selected for sorting. See gtk_tree_view_column_set_sort_column_id().