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: EventVisitorList</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>EventVisitorList Concept</H1> | |
| 19 | ||
| 20 | An EventVisitorList is either an <a | |
| 21 | href="./EventVisitor.html">EventVisitor</a>, or a list of | |
| 22 | EventVisitors combined using <tt>std::pair</tt>. Each graph algorithm | |
| 23 | defines visitor adaptors that convert an EventVisitorList into the | |
| 24 | particular kind of visitor needed by the algorithm. | |
| 25 | ||
| 26 | In the following example we will show how to combine event visitors | |
| 27 | into a list using <tt>std::pair</tt> and how to use an algorithm's | |
| 28 | visitor adaptor class. | |
| 29 | ||
| 30 | <p> | |
| 31 | Suppose we would like to print out the parenthesis | |
| 32 | structure of the discover/finish times of vertices in a <a | |
| 33 | href="./graph_theory_review.html#sec:dfs-algorithm">depth-first | |
| 34 | search</a>. We can use the BGL algorithm <a | |
| 35 | href="./depth_first_search.html"><tt>depth_first_search()</tt></a> and | |
| 36 | two event visitors to accomplish this. The complete source code for | |
| 37 | the following example is in <a href="../example/dfs_parenthesis.cpp"> | |
| 38 | <tt>examples/dfs_parenthesis.cpp</tt></a>. First we define the two | |
| 39 | event visitors. We use <tt>on_discover_vertex</tt> and | |
| 40 | <tt>on_finish_vertex</tt> as the event points, selected from the list | |
| 41 | of event points specified in <a | |
| 42 | href="./DFSVisitor.html">DFSVisitor</a>. | |
| 43 | ||
| 44 | <pre> | |
| 45 | struct open_paren : public base_visitor<open_paren> { | |
| 46 | typedef on_discover_vertex event_filter; | |
| 47 | template <class Vertex, class Graph> | |
| 48 | void operator()(Vertex v, Graph& G) { | |
| 49 | std::cout << "(" << v; | |
| 50 | } | |
| 51 | }; | |
| 52 | struct close_paren : public base_visitor<close_paren> { | |
| 53 | typedef on_finish_vertex event_filter; | |
| 54 | template <class Vertex, class Graph> | |
| 55 | void operator()(Vertex v, Graph& G) { | |
| 56 | std::cout << v << ")"; | |
| 57 | } | |
| 58 | }; | |
| 59 | </pre> | |
| 60 | ||
| 61 | Next we create two event visitor objects and make an EventVisitorList | |
| 62 | out of them using a <tt>std::pair</tt> which created by | |
| 63 | <tt>std::make_pair</tt>. | |
| 64 | ||
| 65 | <pre> | |
| 66 | std::make_pair(open_paren(), close_paren()) | |
| 67 | </pre> | |
| 68 | ||
| 69 | Next we want to pass this list into <tt>depth_first_search()</tt>, but | |
| 70 | <tt>depth_first_search()</tt> is expecting a <a | |
| 71 | href="./DFSVisitor.html">DFSVisitor</a>, not a EventVisitorList. We | |
| 72 | therefore use the <a | |
| 73 | href="./dfs_visitor.html"><tt>dfs_visitor</tt></a> adaptor which turns | |
| 74 | an EventVisitor list into a DFSVisitor. Like all of the visitor | |
| 75 | adaptors, <tt>dfs_visitor</tt> has a creation function called | |
| 76 | <tt>make_dfs_visitor()</tt>. | |
| 77 | ||
| 78 | <pre> | |
| 79 | make_dfs_visitor(std::make_pair(open_paren(), close_paren())) | |
| 80 | </pre> | |
| 81 | ||
| 82 | Now we can pass the resulting visitor object into | |
| 83 | <tt>depth_first_search()</tt> as follows. | |
| 84 | ||
| 85 | <pre> | |
| 86 | // graph object G is created ... | |
| 87 | ||
| 88 | std::vector<default_color_type> color(num_vertices(G)); | |
| 89 | ||
| 90 | depth_first_search(G, make_dfs_visitor(std::make_pair(open_paren(), close_paren())), | |
| 91 | color.begin()); | |
| 92 | </pre> | |
| 93 | ||
| 94 | For creating a list of more than two event visitors, you can nest calls to | |
| 95 | <tt>std::make_pair</tt> in the following way: | |
| 96 | ||
| 97 | <pre> | |
| 98 | std::make_pair(<i>visitor1</i>, | |
| 99 | std::make_pair(<i>visitor2</i>, | |
| 100 | ... | |
| 101 | std::make_pair(<i>visitorN-1</i>, <i>visitorN</i>)...)); | |
| 102 | </pre> | |
| 103 | ||
| 104 | ||
| 105 | ||
| 106 | <h3>See Also</h3> | |
| 107 | ||
| 108 | <a href="./EventVisitor.html">EventVisitor</a>, | |
| 109 | <a href="./visitor_concepts.html">Visitor concepts</a> | |
| 110 | ||
| 111 | ||
| 112 | <br> | |
| 113 | <HR> | |
| 114 | <TABLE> | |
| 115 | <TR valign=top> | |
| 116 | <TD nowrap>Copyright © 2000-2001</TD><TD> | |
| 117 | <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, | |
| 118 | Indiana University (<A | |
| 119 | HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> | |
| 120 | <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> | |
| 121 | <A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, | |
| 122 | Indiana University (<A | |
| 123 | HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) | |
| 124 | </TD></TR></TABLE> | |
| 125 | ||
| 126 | </BODY> | |
| 127 | </HTML> |