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<title>AddEdgeVisitor Concept</title>
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<img src="../../../boost.png" alt="C++ Boost" height="86" width="277"> 

<br clear="">

<h1>AddEdgeVisitor Concept</h1>

The AddEdgeVisitor concept exists to allow for some indirection in algorithms
that modify graphs by adding edges. In such algorithms, it may be convenient
to perform additional operations (such as updating an edge index map) at 
points in the algorithm where an edge addition occurs. Replacing calls to
to <tt>add_edge</tt> with calls to <tt>AddEdgeVisitor::visit_vertex_pair</tt>
allows for such operations to be defined independently from the algorithm.

<h3>Notation</h3>

<table>
<tbody>

<tr>
<td> <tt>Visitor</tt> </td>
<td> is a type that models the AddEdgeVisitor concept </td>
</tr>

<tr> 
<td> <tt>vis</tt> </td>  
<td> is an object of type Visitor </td>
</tr>

<tr>
<td> <tt>Graph</tt> </td>
<td> is the type of a graph </td>
</tr>

<tr> 
<td> <tt>u,v</tt> </td>  
<td> are objects of type <tt>graph_traits&lt;Graph&gt;::vertex_descriptor</tt>
</td>
</tr>

<tr> 
<td> <tt>e</tt> </td>  
<td> is an object of type <tt>graph_traits&lt;Graph&gt;::edge_descriptor</tt> 
</td>
</tr>

<tr>
<td> <tt>v</tt> </td>
<td> is an object of type <tt>graph_traits&lt;Graph&gt;::vertex_descriptor</tt>
</td>

</tr><tr>
<td> 

</td></tr></tbody></table>


<h3>Associated Types</h3>

None

<h3>Valid Expressions</h3>

<p>

<table border="1">

<tbody><tr><th>Name</th><th>Expression</th><th>Return Type</th>
<th>Description</th>

</tr><tr> 
<td> Add an Edge </td>
<td> <tt>vis.visit_vertex_pair(u, v, g)</tt>  </td>
<td> <tt>void</tt></td>
<td> Invoked every time an edge between vertices <tt>u</tt> and <tt>v</tt>
     should be added to the graph <tt>g</tt>.
</td></tr>

</tbody></table>

</p><h3>Models</h3>

Two models of this concept are defined in the file 
<a href="../../../boost/graph/planar_detail/add_edge_visitors.hpp">
<tt>add_edge_visitors.hpp</tt></a>:

<ul>
<li><tt>default_add_edge_visitor</tt>: The constructor of this class takes
no arguments.<tt>visit_vertex_pair(u, v, g)</tt> is just a dispatch to
<tt>add_edge(u, v, g)</tt>. 
<li><tt>edge_index_update_visitor</tt>: The constructor of this class takes
two arguments: the first, an EdgeIndexMap,
is a <a href="../../property_map/doc/ReadWritePropertyMap.html">
ReadWritePropertyMap</a> that maps each edge in the associated graph 
<tt>g</tt> to a distinct integer in the range <tt>[0, num_edges(g))</tt>. 
The second argument is the number of edges in the underlying graph, which 
serves as the "next available index" counter within the visitor.
For example, in the case the graph used has an initialized interior 
edge index, the <tt>edge_index_update_visitor</tt> constructor should be 
called with <tt>get(edge_index, g)</tt> as the edge index and 
<tt>num_edges(g)</tt> as the next available index. When 
<tt>visit_vertex_pair(u, v, g)</tt> is called, the 
<tt>edge_index_update_visitor</tt> will add the edge <i>(u,v)</i> to the graph
and update the edge index for the newly created edge.
</ul>

<p>

<br>
</p><hr>
Copyright © 2007 Aaron Windsor (<a href="mailto:aaron.windsor@gmail.com">
aaron.windsor@gmail.com</a>) 

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