GtkTreeViewColumn::set_resizable

void set_resizable(bool resizable);

If resizable is true, then the user can explicitly resize the column by grabbing the outer edge of the column button. If resizable is true and sizing mode of the column is Gtk::TREE_VIEW_COLUMN_AUTOSIZE, then the sizing mode is changed to Gtk::TREE_VIEW_COLUMN_GROW_ONLY.

See also: get_resizable()