<HTML> <!-- Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000 Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> <Head> <Title>Boost Graph Library: EventVisitor</Title> <BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" ALINK="#ff0000"> <IMG SRC="../../../boost.png" ALT="C++ Boost" width="277" height="86"> <BR Clear> <H1>EventVisitor Concept</H1> This concept defines the interface for single-event visitors. An EventVisitor has an apply member function (<tt>operator()</tt>) which is invoked within the graph algorithm at the event-point specified by the <tt>event_filter</tt> typedef within the EventVisitor. EventVisitor's can be combined into an <a href="./EventVisitorList.html">EventVistorList</a>. <p> The following is the list of event tags that can be invoked in BGL algorithms. Each tag corresponds to a member function of the visitor for an algorithm. For example, the <a href="./BFSVisitor.html">BFSVisitor</a> of <a href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a> has a <tt>cycle_edge()</tt> member function. The corresponding tag is <tt>on_cycle_edge</tt>. The first argument is the event visitor's <tt>operator()</tt> must be either an edge or vertex descriptor depending on the event tag. <pre> namespace boost { struct on_initialize_vertex { }; struct on_start_vertex { }; struct on_discover_vertex { }; struct on_examine_edge { }; struct on_tree_edge { }; struct on_cycle_edge { }; struct on_finish_vertex { }; struct on_forward_or_cross_edge { }; struct on_back_edge { }; struct on_edge_relaxed { }; struct on_edge_not_relaxed { }; struct on_edge_minimized { }; struct on_edge_not_minimized { }; } // namespace boost </pre> <h3>Refinement of</h3> <a href="../../utility/CopyConstructible.html">Copy Constructible</a> (copying a visitor should be a lightweight operation). <h3>Notation</h3> <Table> <TR> <TD><tt>G</tt></TD> <TD>A type that is a model of <a href="./Graph.html">Graph</a>.</TD> </TR> <TR> <TD><tt>g</tt></TD> <TD>An object of type <tt>G</tt>.</TD> </TR> <TR> <TD><tt>V</tt></TD> <TD>A type that is a model of EventVisitor.</TD> </TR> <TR> <TD><tt>vis</tt></TD> <TD>An object of type <tt>V</tt>.</TD> </TR> <TR> <TD><tt>x</tt></TD> <TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt> or <tt>boost::graph_traits<G>::edge_descriptor</tt>.</TD> </TR> </table> <h3>Associated Types</h3> <Table border> <TR> <TD>Event Filter </TD> <TD><TT>V::event_filter</TT></TD> <TD> A tag struct to specify on which event the visitor should be invoked. </TD> </TR> </table> <h3>Valid Expressions</h3> <Table border> <tr> <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> </tr> <tr> <td>Apply Visitor</td> <td><TT>vis(x, g)</TT></TD> <TD><TT>void</TT></TD> <TD> Invokes the visitor operation on object <tt>x</tt>, which is either a vertex or edge descriptor of the graph. </TD> </TR> </table> <h3>Models</h3> <ul> <li><a href="./predecessor_recorder.html"><tt>predecessor_recorder</tt></a> <li><a href="./distance_recorder.html"><tt>distance_recorder</tt></a> <li><a href="./time_stamper.html"><tt>time_stamper</tt></a> <li><a href="./property_writer.html"><tt>property_writer</tt></a> <li><a href="./null_visitor.html"><tt>null_visitor</tt></a> </ul> <h3>See Also</h3> <a href="./EventVisitorList.html">EventVisitorList</a>, <a href="./visitor_concepts.html">Visitor concepts</a> <br> <HR> <TABLE> <TR valign=top> <TD nowrap>Copyright © 2000-2001</TD><TD> <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> <A HREF="http://www.boost.org/people/liequan_lee.htm">Lie-Quan Lee</A>, Indiana University (<A HREF="mailto:llee@cs.indiana.edu">llee@cs.indiana.edu</A>)<br> <A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, Indiana University (<A HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) </TD></TR></TABLE> </BODY> </HTML>