1<HTML> 2<!-- 3 Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000 4 5 Distributed under the Boost Software License, Version 1.0. 6 (See accompanying file LICENSE_1_0.txt or copy at 7 http://www.boost.org/LICENSE_1_0.txt) 8 --> 9<Head> 10<Title>Boost Graph Library: EventVisitor</Title> 11<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" 12 ALINK="#ff0000"> 13<IMG SRC="../../../boost.png" 14 ALT="C++ Boost" width="277" height="86"> 15 16<BR Clear> 17 18<H1>EventVisitor Concept</H1> 19 20This concept defines the interface for single-event visitors. An 21EventVisitor has an apply member function (<tt>operator()</tt>) which 22is invoked within the graph algorithm at the event-point specified by 23the <tt>event_filter</tt> typedef within the 24EventVisitor. EventVisitor's can be combined into an <a 25href="./EventVisitorList.html">EventVistorList</a>. 26 27<p> 28The following is the list of event tags that can be invoked in BGL 29algorithms. Each tag corresponds to a member function of the visitor 30for an algorithm. For example, the <a 31href="./BFSVisitor.html">BFSVisitor</a> of <a 32href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a> 33has a <tt>cycle_edge()</tt> member function. The corresponding tag is 34<tt>on_cycle_edge</tt>. The first argument is the event visitor's 35<tt>operator()</tt> must be either an edge or vertex descriptor 36depending on the event tag. 37 38<pre> 39namespace boost { 40 struct on_initialize_vertex { }; 41 struct on_start_vertex { }; 42 struct on_discover_vertex { }; 43 struct on_examine_edge { }; 44 struct on_tree_edge { }; 45 struct on_cycle_edge { }; 46 struct on_finish_vertex { }; 47 struct on_forward_or_cross_edge { }; 48 struct on_back_edge { }; 49 struct on_edge_relaxed { }; 50 struct on_edge_not_relaxed { }; 51 struct on_edge_minimized { }; 52 struct on_edge_not_minimized { }; 53} // namespace boost 54</pre> 55 56 57<h3>Refinement of</h3> 58 59<a href="../../utility/CopyConstructible.html">Copy Constructible</a> 60(copying a visitor should be a lightweight operation). 61 62<h3>Notation</h3> 63 64<Table> 65<TR> 66<TD><tt>G</tt></TD> 67<TD>A type that is a model of <a href="./Graph.html">Graph</a>.</TD> 68</TR> 69 70<TR> 71<TD><tt>g</tt></TD> 72<TD>An object of type <tt>G</tt>.</TD> 73</TR> 74 75<TR> 76<TD><tt>V</tt></TD> 77<TD>A type that is a model of EventVisitor.</TD> 78</TR> 79 80<TR> 81<TD><tt>vis</tt></TD> 82<TD>An object of type <tt>V</tt>.</TD> 83</TR> 84 85<TR> 86<TD><tt>x</tt></TD> 87<TD>An object of type 88<tt>boost::graph_traits<G>::vertex_descriptor</tt> 89or <tt>boost::graph_traits<G>::edge_descriptor</tt>.</TD> 90</TR> 91 92</table> 93 94<h3>Associated Types</h3> 95 96<Table border> 97 98<TR> 99<TD>Event Filter </TD> 100<TD><TT>V::event_filter</TT></TD> 101<TD> 102A tag struct to specify on which event the visitor should be invoked. 103</TD> 104</TR> 105 106</table> 107 108<h3>Valid Expressions</h3> 109 110<Table border> 111 112<tr> 113<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> 114</tr> 115 116<tr> 117<td>Apply Visitor</td> 118<td><TT>vis(x, g)</TT></TD> 119<TD><TT>void</TT></TD> 120<TD> 121Invokes the visitor operation on object <tt>x</tt>, which is 122either a vertex or edge descriptor of the graph. 123</TD> 124</TR> 125 126 127</table> 128 129 130<h3>Models</h3> 131 132<ul> 133 <li><a 134 href="./predecessor_recorder.html"><tt>predecessor_recorder</tt></a> 135 <li><a href="./distance_recorder.html"><tt>distance_recorder</tt></a> 136 <li><a href="./time_stamper.html"><tt>time_stamper</tt></a> 137 <li><a href="./property_writer.html"><tt>property_writer</tt></a> 138 <li><a href="./null_visitor.html"><tt>null_visitor</tt></a> 139</ul> 140 141<h3>See Also</h3> 142 143<a href="./EventVisitorList.html">EventVisitorList</a>, 144<a href="./visitor_concepts.html">Visitor concepts</a> 145 146<br> 147<HR> 148<TABLE> 149<TR valign=top> 150<TD nowrap>Copyright © 2000-2001</TD><TD> 151<A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, 152Indiana University (<A 153HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> 154<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> 155<A HREF="https://homes.cs.washington.edu/~al75">Andrew Lumsdaine</A>, 156Indiana University (<A 157HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) 158</TD></TR></TABLE> 159 160</BODY> 161</HTML> 162
