Rel.07 NEWS - 2. round
3 * This file is a part of LEMON, a generic C++ optimization library
5 * Copyright (C) 2003-2008
6 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
7 * (Egervary Research Group on Combinatorial Optimization, EGRES).
9 * Permission to use, modify and distribute this software is granted
10 * provided that this copyright notice appears in all copies. For
11 * precise terms see the accompanying LICENSE file.
13 * This software is provided "AS IS" with no warranty of any kind,
14 * express or implied, and with no claim as to its suitability for any
21 \page read_write_bg Background of Reading and Writing
23 To read a map (on the nodes or edges)
24 the \ref lemon::GraphReader "GraphReader"
25 should know how to read a Value from the given map.
26 By the default implementation the input operator reads a value from
27 the stream and the type of the read value is the value type of the given map.
28 When the reader should skip a value in the stream, because you do not
29 want to store it in a map, the reader skips a character sequence without
32 If you want to change the functionality of the reader, you can use
33 template parameters to specialize it. When you give a reading
34 command for a map you can give a Reader type as template parameter.
35 With this template parameter you can control how the Reader reads
36 a value from the stream.
38 The reader has the next structure:
41 typedef TypeName Value;
43 void read(std::istream& is, Value& value);
47 For example, the \c "strings" nodemap contains strings and you do not need
48 the value of the string just the length. Then you can implement an own Reader
55 void read(std::istream& is, Value& value) {
62 reader.readNodeMap<LengthReader>("strings", lengthMap);
65 The global functionality of the reader class can be changed by giving a
66 special template parameter to the GraphReader class. By default, the
67 template parameter is \c DefaultReaderTraits. A reader traits class
68 should provide a nested template class Reader for each type, and a
69 DefaultReader for skipping a value.
71 The specialization of writing is very similar to that of reading.
73 \section u Undirected graphs
75 In a file describing an undirected graph (ugraph, for short) you find an
76 \c uedgeset section instead of the \c edgeset section. The first line of
77 the section describes the names of the maps on the undirected egdes and all
78 next lines describe one undirected edge with the the incident nodes and the
81 The format handles directed edge maps as a syntactical sugar???, if there
82 are two maps with names being the same with a \c '+' and a \c '-' prefix
83 then this will be read as a directed map.
87 label capacity +flow -flow
93 The \c edges section is changed to \c uedges section. This section
94 describes labeled edges and undirected edges. The directed edge label
95 should start with a \c '+' or a \c '-' prefix to decide the direction
105 There are similar classes to the \ref lemon::GraphReader "GraphReader" and
106 \ref lemon::GraphWriter "GraphWriter" which
107 handle the undirected graphs. These classes are
108 the \ref lemon::UGraphReader "UGraphReader"
109 and \ref lemon::UGraphWriter "UGraphWriter".
111 The \ref lemon::UGraphReader::readUEdgeMap() "readUEdgeMap()"
112 function reads an undirected map and the
113 \ref lemon::UGraphReader::readUEdge() "readUEdge()"
114 reads an undirected edge from the file,
117 reader.readUEdgeMap("capacity", capacityMap);
118 reader.readEdgeMap("flow", flowMap);
120 reader.readUEdge("u_edge", u_edge);
121 reader.readEdge("edge", edge);
124 \section advanced Advanced features
126 The graph reader and writer classes give an easy way to read and write
127 graphs. But sometimes we want more advanced features. In this case we can
128 use the more general <tt>lemon reader and writer</tt> interface.
130 The LEMON file format is a section oriented file format. It contains one or
131 more sections, each starting with a line identifying its type
132 (the word starting with the \c \@ character).
133 The content of the section this way cannot contain line with \c \@ first
134 character. The file may contains comment lines with \c # first character.
136 The \ref lemon::LemonReader "LemonReader"
137 and \ref lemon::LemonWriter "LemonWriter"
138 gives a framework to read and
139 write sections. There are various section reader and section writer
140 classes which can be attached to a \ref lemon::LemonReader "LemonReader"
141 or a \ref lemon::LemonWriter "LemonWriter".
143 There are default section readers and writers for reading and writing
144 item sets, and labeled items in the graph. These read and write
145 the format described above. Other type of data can be handled with own
146 section reader and writer classes which are inherited from the
147 \c LemonReader::SectionReader or the
148 \ref lemon::LemonWriter::SectionWriter "LemonWriter::SectionWriter"
151 The next example defines a special section reader which reads the
152 \c \@description sections into a string:
155 class DescriptionReader : LemonReader::SectionReader {
157 virtual bool header(const std::string& line) {
158 std::istringstream ls(line);
161 return head == "@description";
164 virtual void read(std::istream& is) {
166 while (getline(is, line)) {
172 typedef LemonReader::SectionReader Parent;
174 DescriptionReader(LemonReader& reader) : Parent(reader) {}
176 const std::string& description() const {
185 The other advanced stuff of the generalized file format is that
186 multiple edgesets can be stored to the same nodeset. It can be used
187 for example as a network traffic matrix.
189 In our example there is a network with symmetric links and there are assymetric
190 traffic request on the network. This construction can be stored in an
191 undirected graph and in a directed \c ListEdgeSet class. The example
192 shows the input with the \ref lemon::LemonReader "LemonReader" class:
196 ListUGraph::UEdgeMap<double> capacity;
197 ListEdgeSet<ListUGraph> traffic(network);
198 ListEdgeSet<ListUGraph>::EdgeMap<double> request(network);
200 LemonReader reader(std::cin);
201 NodeSetReader<ListUGraph> nodesetReader(reader, network);
202 UEdgeSetReader<ListUGraph>
203 uEdgesetReader(reader, network, nodesetReader);
204 uEdgesetReader.readEdgeMap("capacity", capacity);
205 EdgeSetReader<ListEdgeSet<ListUGraph> >
206 edgesetReader(reader, traffic, nodesetReader, "traffic");
207 edgesetReader.readEdgeMap("request", request);
212 Because both the \ref lemon::GraphReader "GraphReader"
213 and the \ref lemon::UGraphReader "UGraphReader" can be converted
214 to \ref lemon::LemonReader "LemonReader"
215 and it can resolve the label's of the items, the previous
216 result can be achived with the \ref lemon::UGraphReader "UGraphReader"
222 ListUGraph::UEdgeSet<double> capacity;
223 ListEdgeSet<ListUGraph> traffic(network);
224 ListEdgeSet<ListUGraph>::EdgeMap<double> request(network);
226 UGraphReader<ListUGraph> reader(std::cin, network);
227 reader.readEdgeMap("capacity", capacity);
228 EdgeSetReader<ListEdgeSet<ListUGraph> >
229 edgesetReader(reader, traffic, reader, "traffic");
230 edgesetReader.readEdgeMap("request", request);