e that different graph classes can have different associated vertex
iterator types, which is why we need the <tt>graph_traits</tt> class. Given some
graph type, the <tt>graph_traits</tt> class will provide access to the <tt>vertex_iterator</tt>
type.
<p>The following example prints out the index for each of the vertices in the
graph. All vertex and edge properties, including index, are accessed via
property map objects. The <a href="property_map.html"><tt>property_map</tt></a>
class is used to obtain the pr