All the other container classes considered in this text
have only one associated iterator.
When dealing with graphs,
it is convenient to have at least four iterators:
The first two are used to enumerate the sets and ,
and the last two are used to enumerate the sets and
associated with a given vertex *v*.

Each of the following member functions allocates dynamically a new iterator instance as follows:

`Vertices`-
This member function of the
`Graph`class returns an iterator that can be used to traverse the elements of . `Edges`-
This member function of the
`Graph`class returns an iterator that can be used to traverse the elements of . `IncidentEdges`-
This member function takes a reference to
a vertex, say
*v*, and returns an iterator that can be used to traverse the elements of . The vertex*v*must be contained by the graph. `EmanatingEdges`-
This member function takes a reference to
a vertex, say
*v*, and returns an iterator that can be used to traverse the elements of . The vertex*v*must be contained by the graph.

Copyright © 1997 by Bruno R. Preiss, P.Eng. All rights reserved.