projects / ceph.git / blame
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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: BFSVisitor</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><img src="figs/python.gif" alt="(Python)"/>BFS Visitor Concept</H1> | |
| 19 | ||
| 20 | This concept defines the visitor interface for <a | |
| 21 | href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a>. | |
| 22 | Users can define a class with the BFS Visitor interface and pass and | |
| 23 | object of the class to <tt>breadth_first_search()</tt>, thereby | |
| 24 | augmenting the actions taken during the graph search. | |
| 25 | ||
| 26 | <h3>Refinement of</h3> | |
| 27 | ||
| 28 | <a href="../../utility/CopyConstructible.html">Copy Constructible</a> | |
| 29 | (copying a visitor should be a lightweight operation). | |
| 30 | ||
| 31 | ||
| 32 | <h3>Notation</h3> | |
| 33 | ||
| 34 | <Table> | |
| 35 | <TR> | |
| 36 | <TD><tt>V</tt></TD> | |
| 37 | <TD>A type that is a model of BFS Visitor.</TD> | |
| 38 | </TR> | |
| 39 | ||
| 40 | <TR> | |
| 41 | <TD><tt>vis</tt></TD> | |
| 42 | <TD>An object of type <tt>V</tt>.</TD> | |
| 43 | </TR> | |
| 44 | ||
| 45 | <TR> | |
| 46 | <TD><tt>G</tt></TD> | |
| 47 | <TD>A type that is a model of Graph.</TD> | |
| 48 | </TR> | |
| 49 | ||
| 50 | <TR> | |
| 51 | <TD><tt>g</tt></TD> | |
| 52 | <TD>An object of type <tt>G</tt>.</TD> | |
| 53 | </TR> | |
| 54 | ||
| 55 | <TR> | |
| 56 | <TD><tt>e</tt></TD> | |
| 57 | <TD>An object of type <tt>boost::graph_traits<G>::edge_descriptor</tt>.</TD> | |
| 58 | </TR> | |
| 59 | ||
| 60 | <TR> | |
| 61 | <TD><tt>s,u</tt></TD> | |
| 62 | <TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt>.</TD> | |
| 63 | </TR> | |
| 64 | ||
| 65 | </table> | |
| 66 | ||
| 67 | <h3>Associated Types</h3> | |
| 68 | ||
| 69 | none | |
| 70 | <p> | |
| 71 | ||
| 72 | <h3>Valid Expressions</h3> | |
| 73 | ||
| 74 | <table border> | |
| 75 | <tr> | |
| 76 | <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> | |
| 77 | </tr> | |
| 78 | ||
| 79 | <tr> | |
| 80 | <td>Initialize Vertex</td> | |
| 81 | <td><tt>vis.initialize_vertex(s, g)</tt></td> | |
| 82 | <td><tt>void</tt></td> | |
| 83 | <td> | |
| 84 | This is invoked on every vertex of the graph before the start of the | |
| 85 | graph search. | |
| 86 | </td> | |
| 87 | </tr> | |
| 88 | ||
| 89 | <tr> | |
| 90 | <td>Discover Vertex</td> | |
| 91 | <td><tt>vis.discover_vertex(u, g)</tt></td> | |
| 92 | <td><tt>void</tt></td> | |
| 93 | <td> | |
| 94 | This is invoked when a vertex is encountered for the first time. | |
| 95 | </td> | |
| 96 | </tr> | |
| 97 | ||
| 98 | <tr> | |
| 99 | <td>Examine Vertex</td> | |
| 100 | <td><tt>vis.examine_vertex(u, g)</tt></td> | |
| 101 | <td><tt>void</tt></td> | |
| 102 | <td> | |
| 103 | This is invoked on a vertex as it is popped from the queue. This | |
| 104 | happens immediately before <tt>examine_edge()</tt> is invoked | |
| 105 | on each of the out-edges of vertex <tt>u</tt>. | |
| 106 | </td> | |
| 107 | </tr> | |
| 108 | ||
| 109 | <tr> | |
| 110 | <td>Examine Edge</td> | |
| 111 | <td><tt>vis.examine_edge(e, g)</tt></td> | |
| 112 | <td><tt>void</tt></td> | |
| 113 | <td> | |
| 114 | This is invoked on every out-edge of each vertex after it is discovered. | |
| 115 | </td> | |
| 116 | </tr> | |
| 117 | ||
| 118 | ||
| 119 | <tr> | |
| 120 | <td>Tree Edge</td> | |
| 121 | <td><tt>vis.tree_edge(e, g)</tt></td> | |
| 122 | <td><tt>void</tt></td> | |
| 123 | <td> | |
| 124 | This is invoked on each edge as it becomes a member of the edges that | |
| 125 | form the search tree.</td> | |
| 126 | </tr> | |
| 127 | ||
| 128 | <tr> | |
| 129 | <td>Non-Tree Edge</td> | |
| 130 | <td><tt>vis.non_tree_edge(e, g)</tt></td> | |
| 131 | <td><tt>void</tt></td> | |
| 132 | <td> | |
| 133 | This is invoked on back or cross edges for directed graphs and cross | |
| 134 | edges for undirected graphs. | |
| 135 | </td> | |
| 136 | </tr> | |
| 137 | ||
| 138 | <tr> | |
| 139 | <td>Gray Target</td> | |
| 140 | <td><tt>vis.gray_target(e, g)</tt></td> | |
| 141 | <td><tt>void</tt></td> | |
| 142 | <td> | |
| 143 | This is invoked on the subset of non-tree edges whose target vertex is | |
| 144 | colored gray at the time of examination. The color gray indicates | |
| 145 | that the vertex is currently in the queue. | |
| 146 | </td> | |
| 147 | </tr> | |
| 148 | ||
| 149 | <tr> | |
| 150 | <td>Black Target</td> | |
| 151 | <td><tt>vis.black_target(e, g)</tt></td> | |
| 152 | <td><tt>void</tt></td> | |
| 153 | <td> | |
| 154 | This is invoked on the subset of non-tree edges whose target vertex is | |
| 155 | colored black at the time of examination. The color black indicates | |
| 156 | that the vertex has been removed from the queue. | |
| 157 | </td> | |
| 158 | </tr> | |
| 159 | ||
| 160 | <tr> | |
| 161 | <td>Finish Vertex</td> | |
| 162 | <td><tt>vis.finish_vertex(u, g)</tt></td> | |
| 163 | <td><tt>void</tt></td> | |
| 164 | <td> | |
| 165 | This invoked on a vertex after all of its out edges have been added to the | |
| 166 | search tree and all of the adjacent vertices have been discovered | |
| 167 | (but before the out-edges of the adjacent vertices have been examined). | |
| 168 | </td> | |
| 169 | </tr> | |
| 170 | ||
| 171 | </table> | |
| 172 | ||
| 173 | <h3>Models</h3> | |
| 174 | ||
| 175 | <ul> | |
| 176 | <li><a href="./bfs_visitor.html"><tt>bfs_visitor</tt></a> | |
| 177 | </ul> | |
| 178 | ||
| 179 | <a name="python"></a><h3>Python</h3> | |
| 180 | To implement a model of the <tt>BFSVisitor</tt> concept in Python, | |
| 181 | create a new class that derives from the <tt>BFSVisitor</tt> type of | |
| 182 | the graph, which will be | |
| 183 | named <tt><i>GraphType</i>.BFSVisitor</tt>. The events and syntax are | |
| 184 | the same as with visitors in C++. Here is an example for the | |
| 185 | Python <tt>bgl.Graph</tt> graph type: | |
| 186 | ||
| 187 | <pre> | |
| 188 | class count_tree_edges_bfs_visitor(bgl.Graph.BFSVisitor): | |
| 189 | def __init__(self, name_map): | |
| 190 | bgl.Graph.BFSVisitor.__init__(self) | |
| 191 | self.name_map = name_map | |
| 192 | ||
| 193 | def tree_edge(self, e, g): | |
| 194 | (u, v) = (g.source(e), g.target(e)) | |
| 195 | print "Tree edge ", | |
| 196 | print self.name_map[u], | |
| 197 | print " -> ", | |
| 198 | print self.name_map[v] | |
| 199 | </pre> | |
| 200 | ||
| 201 | <h3>See also</h3> | |
| 202 | ||
| 203 | <a href="./visitor_concepts.html">Visitor concepts</a> | |
| 204 | ||
| 205 | <br> | |
| 206 | <HR> | |
| 207 | <TABLE> | |
| 208 | <TR valign=top> | |
| 209 | <TD nowrap>Copyright © 2000-2001</TD><TD> | |
| 210 | <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, | |
| 211 | Indiana University (<A | |
| 212 | HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> | |
| 213 | <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> | |
| 214 | <A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, | |
| 215 | Indiana University (<A | |
| 216 | HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) | |
| 217 | </TD></TR></TABLE> | |
| 218 | ||
| 219 | </BODY> | |
| 220 | </HTML> |