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11<div class="document" id="logo-read-graphml">
12<h1 class="title"><a class="reference external" href="../../../index.htm"><img align="middle" alt="Boost" class="align-middle" src="../../../boost.png" /></a> <tt class="docutils literal"><span class="pre">read_graphml</span></tt></h1>
13
14<!-- Copyright (C) 2006 Tiago de Paula Peixoto <tiago@forked.de>
15
16Distributed under the Boost Software License, Version 1.0. (See
17accompanying file LICENSE_1_0.txt or copy at
18http://www.boost.org/LICENSE_1_0.txt)
19
20Authors: Tiago de Paula Peixoto -->
21<pre class="literal-block">
22void read_graphml(std::istream&amp; in, MutableGraph&amp; graph,
23 dynamic_properties&amp; dp, size_t graph_index = 0);
24</pre>
25<p>The <tt class="docutils literal"><span class="pre">read_graphml</span></tt> function interprets a graph described using the
26<a class="reference external" href="http://graphml.graphdrawing.org/">GraphML</a> format and builds a BGL graph that captures that
27description. Using this function, you can initialize a graph using
28data stored as text.</p>
29<p>The GraphML format can specify both directed and undirected graphs, and
30<tt class="docutils literal"><span class="pre">read_graphml</span></tt> differentiates between the two. One must pass
31<tt class="docutils literal"><span class="pre">read_graphml</span></tt> an undirected graph when reading an undirected graph;
32the same is true for directed graphs. Furthermore, <tt class="docutils literal"><span class="pre">read_graphml</span></tt>
33will throw an exception if it encounters parallel edges and cannot add
34them to the graph.</p>
35<p>To handle attributes expressed in the GraphML format, <tt class="docutils literal"><span class="pre">read_graphml</span></tt>
36takes a <a class="reference external" href="../../property_map/doc/dynamic_property_map.html">dynamic_properties</a> object and operates on its collection of
37property maps. The reader passes all the properties encountered to
38this object, using the GraphML attribute names as the property names,
39and with the appropriate C++ value type based on the GraphML attribute type
40definition. Graph properties are also set with the same
41<a class="reference external" href="../../property_map/doc/dynamic_property_map.html">dynamic_properties</a> object, where the key type is the type of the graph itself.</p>
42<p>If the file contains multiple graphs, the <tt class="docutils literal"><span class="pre">graph_index</span></tt> parameter controls
43which graph will be loaded. It defaults to <tt class="docutils literal"><span class="pre">0</span></tt>, meaning that the first graph
44in the file will be loaded. If <tt class="docutils literal"><span class="pre">graph_index</span></tt> is greater than or equal to the
45number of graphs in the file, an empty graph will be returned.</p>
46<dl class="docutils">
47<dt>Requirements:</dt>
48<dd><ul class="first last simple">
49<li>The type of the graph must model the <a class="reference external" href="MutableGraph.html">Mutable Graph</a> concept.</li>
50<li>The type of the iterator must model the <a class="reference external" href="../../iterator/index.html">Multi-Pass Iterator</a>
51concept.</li>
52<li>The property map value types must be default-constructible.</li>
53</ul>
54</dd>
55</dl>
56<div class="contents topic" id="contents">
57<p class="topic-title first">Contents</p>
58<ul class="simple">
59<li><a class="reference internal" href="#where-defined" id="id2">Where Defined</a></li>
60<li><a class="reference internal" href="#exceptions" id="id3">Exceptions</a></li>
61<li><a class="reference internal" href="#building-the-graphml-reader" id="id4">Building the GraphML reader</a></li>
62<li><a class="reference internal" href="#notes" id="id5">Notes</a></li>
63<li><a class="reference internal" href="#see-also" id="id6">See Also</a></li>
64</ul>
65</div>
66<div class="section" id="where-defined">
67<h1><a class="toc-backref" href="#id2">Where Defined</a></h1>
68<p><tt class="docutils literal"><span class="pre">&lt;boost/graph/graphml.hpp&gt;</span></tt></p>
69</div>
70<div class="section" id="exceptions">
71<h1><a class="toc-backref" href="#id3">Exceptions</a></h1>
72<pre class="literal-block">
73struct graph_exception : public std::exception {
74 virtual ~graph_exception() throw();
75 virtual const char* what() const throw() = 0;
76};
77
78struct bad_parallel_edge : public graph_exception {
79 std::string from;
80 std::string to;
81
82 bad_parallel_edge(const std::string&amp;, const std::string&amp;);
83 virtual ~bad_parallel_edge() throw();
84 const char* what() const throw();
85};
86
87struct directed_graph_error : public graph_exception {
88 virtual ~directed_graph_error() throw();
89 virtual const char* what() const throw();
90};
91
92struct undirected_graph_error : public graph_exception {
93 virtual ~undirected_graph_error() throw();
94 virtual const char* what() const throw();
95};
96
97struct parse_error : public graph_exception {
98 parse_error(const std::string&amp;);
99 virtual ~parse_error() throw() {}
100 virtual const char* what() const throw();
101 std::string statement;
102 std::string error;
103};
104</pre>
105<p>Under certain circumstances, <tt class="docutils literal"><span class="pre">read_graphml</span></tt> will throw one of the
106above exceptions. The three concrete exceptions can all be caught
107using the general <tt class="docutils literal"><span class="pre">graph_exception</span></tt> moniker when greater precision
108is not needed. In addition, all of the above exceptions derive from
109the standard <tt class="docutils literal"><span class="pre">std::exception</span></tt> for even more generalized error
110handling.</p>
111<p>The <tt class="docutils literal"><span class="pre">bad_parallel_edge</span></tt> exception is thrown when an attempt to add a
112parallel edge to the supplied MutableGraph fails. The GraphML format
113supports parallel edges, but some BGL-compatible graph types do not.
114One example of such a graph is <tt class="docutils literal"><span class="pre">boost::adjacency_list&lt;setS,vecS&gt;</span></tt>,
115which allows at most one edge can between any two vertices.</p>
116<p>The <tt class="docutils literal"><span class="pre">directed_graph_error</span></tt> exception occurs when an undirected graph
117type is passed to <tt class="docutils literal"><span class="pre">read_graph</span></tt>, but the graph defined in the GraphML
118file contains at least one directed edge.</p>
119<p>The <tt class="docutils literal"><span class="pre">undirected_graph_error</span></tt> exception occurs when a directed graph
120type is passed to <tt class="docutils literal"><span class="pre">read_graph</span></tt>, but the graph defined in the GraphML
121file contains at least one undirected edge.</p>
122<p>The <tt class="docutils literal"><span class="pre">parse_error</span></tt> exception occurs when a syntax error is
123encountered in the GraphML file. The error string will contain the
124line and column where the error was encountered.</p>
125</div>
126<div class="section" id="building-the-graphml-reader">
127<h1><a class="toc-backref" href="#id4">Building the GraphML reader</a></h1>
128<p>To use the GraphML reader, you will need to build and link against
129the &quot;boost_graph&quot; library. The library can be built by following the
130<a class="reference external" href="../../../more/getting_started.html#Build_Install">Boost Jam Build Instructions</a> for the subdirectory <tt class="docutils literal"><span class="pre">libs/graph/build</span></tt>.</p>
131</div>
132<div class="section" id="notes">
133<h1><a class="toc-backref" href="#id5">Notes</a></h1>
134<blockquote>
135<ul class="simple">
136<li>On successful reading of a graph, every vertex and edge will have
137an associated value for every respective edge and vertex property
138encountered while interpreting the graph. These values will be set
139using the <tt class="docutils literal"><span class="pre">dynamic_properties</span></tt> object. Some properties may be
140<tt class="docutils literal"><span class="pre">put</span></tt> multiple times during the course of reading in order to
141ensure the GraphML semantics. Those edges and vertices that are
142not explicitly given a value for a property (and that property has
143no default) will be given the default constructed value of the
144value type. <strong>Be sure that property map value types are default
145constructible.</strong></li>
146<li>Nested graphs are supported as long as they are exactly of the same
147type as the root graph, i.e., are also directed or undirected. Note
148that since nested graphs are not directly supported by BGL, they
149are in fact completely ignored when building the graph, and the
150internal vertices or edges are interpreted as belonging to the root
151graph.</li>
152<li>Hyperedges and Ports are not supported.</li>
153</ul>
154</blockquote>
155</div>
156<div class="section" id="see-also">
157<h1><a class="toc-backref" href="#id6">See Also</a></h1>
158<p><a class="reference external" href="write_graphml.html">write_graphml</a></p>
159</div>
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