Version 5.0 The LEDA User Manual

• Iterators are not bound to a loop, which means that the user has finer control over
the iteration process. For example, the continuation condition it.valid() in the above
loop could be replaced by another condition to terminate the loop once a specific
node has been found (and the loop may be re-started at the same position later on).
• The meaning of iteration may be modified seamlessly. For example, the filter iterators
defined in sect. 13.9 restrict the iteration to a subset that is specified by an
arbitrary logical condition (predicate). In other words, the nodes or edges that do
not fulfill this predicate are filtered out automatically during iteration.
• The functionality of iteration may be extended seamlessly. For example, the observer
iterators defined in sect. 13.11 can be used to record details of the iteration. A
concrete example is given in sect. 13.11: an observer iterator can be initialized such
that it records the number of iterations performed by the iterator.
• Iterator-based implementations of algorithms can be easily integrated into environments
that are implemented according to the STL style [69], (this style has been
adopted for the standard C++ library). For this purpose, sect. 13.12 define adapters,
which convert graph iterators into STL iterators.
13.1.2 Handles and Iterators
Iterators can be used whenever the corresponding handle can be used. For example, node
iterators can be used where a node is requested or edge iterators can be used where an
edge is requested. For adjacency iterators, it is possible to use them whenever an edge is
requested 1 .
An example shows how iterators can be used as handles:
NodeIt it(G);
leda::node_array index(G);
leda::node v;
int i=0;
forall_nodes(v,G) index[v]=++i;
while (it.valid()) {
cout