namespace lemon {

 /*!

 \page graph-io-page Graph Input-Output

 The standard graph IO enables to store graphs and additional maps

 in a flexible and efficient way. 

 \section format The general file format

 The file contains sections in the following order:

 \li nodeset

 \li edgeset

 \li nodes

 \li edges

 \li attributes

 The nodeset section starts with the following line:

 <tt>\@nodeset</tt>

 The next line contains the names of the nodemaps, separated by whitespaces.  Each

 following line describes a node in the graph: it contains the values of the

 maps in the right order. The map named "id" should contain unique values

 because it is regarded as an ID-map. For example:

 \code

 @nodeset

 id  x-coord  y-coord  color

 3   1.0      4.0      blue

 5   2.3      5.7      red

 12  7.8      2.3      green

 \endcode

 The edgeset section is very similar to the nodeset section, it has

 the same coloumn oriented structure. It starts with the line 

 <tt>\@edgeset</tt>

 The next line contains the whitespace separated list of names of the maps.

 Each of the next lines describes one edge. The first two elements in the line

 are the IDs of the source and target (or tail and head) node of the edge as they occur in the ID node

 map. You can also have an optional ID map on the edges for later reference.

 \code

 @edgeset

              id    weight   label

 3   5        a     4.3      a-edge

 5   12       c     2.6      c-edge

 3   12       g     3.4      g-edge

 \endcode

 The next section contains <em>labeled nodes</em> (i.e. nodes having a special

 label on them). The section starts with

 <tt> \@nodes </tt>

 Each of the next lines contains a label for a node in the graph 

 and then the ID described in the nodeset section.

 \code

 @nodes 

 source 3

 target 12

 \endcode

 The last section describes the <em>labeled edges</em>

 (i.e. edges having a special label on them). It starts with \c \@edges

 and then each line contains the name of the edge and the ID.

 \code

 @nodes 

 observed c

 \endcode

 The file may contain empty lines and comment lines. The comment lines

 start with an \c # character.

 The attributes section can handle some information about the graph. It

 contains in each line an key and the mapped value to key. The key should

 be a string without whitespace, the value can be from various type.

 \code

 @attributes

 title "Four colored plan graph"

 author "Balazs DEZSO"

 copyright "Lemon Library"

 version 12

 \endcode

 \code

 @end

 \endcode

 =======

 The file ends with the 

 <tt> \@end </tt>

 line.

 \section use Using graph input-output

 The graph input and output is based on reading and writing  commands. The user

 adds reading and writing commands to the reader or writer class, then he

 calls the \c run() method that executes all the given commands.

 \subsection write Writing a graph

 The \c GraphWriter class provides the graph output. To write a graph

 you should first give writing commands to the writer. You can declare

 write command as \c NodeMap or \c EdgeMap writing and labeled Node and

 Edge writing.

 \code

 GraphWriter<ListGraph> writer(std::cout, graph);

 \endcode

 The \c writeNodeMap() function declares a \c NodeMap writing command in the

 \c GraphWriter. You should give a name of the map and the map

 object as parameters. The NodeMap writing command with name "id" should write a 

 unique map because it is regarded as ID map.

 \see IdMap, DescriptorMap  

 \code

 IdMap<ListGraph, Node> nodeIdMap;

 writer.writeNodeMap("id", nodeIdMap);

 writer.writeNodeMap("x-coord", xCoordMap);

 writer.writeNodeMap("y-coord", yCoordMap);

 writer.writeNodeMap("color", colorMap);

 \endcode

 With the \c writeEdgeMap() member function you can give an edge map

 writing command similar to the NodeMaps.

 \see IdMap, DescriptorMap  

 \code

 DescriptorMap<ListGraph, Edge, ListGraph::EdgeMap<int> > edgeDescMap(graph);

 writer.writeEdgeMap("descriptor", edgeDescMap);

 writer.writeEdgeMap("weight", weightMap);

 writer.writeEdgeMap("label", labelMap);

 \endcode

 With \c writeNode() and \c writeEdge() functions you can designate Nodes and

 Edges in the graph. For example, you can write out the source and target node

 of a maximum flow instance.

 \code

 writer.writeNode("source", sourceNode);

 writer.writeNode("target", targetNode);

 writer.writeEdge("observed", edge);

 \endcode

 With \c writeAttribute() function you can write an attribute to the file.

 \code

 writer.writeAttribute("author", "Balazs DEZSO");

 writer.writeAttribute("version", 12);

 \endcode

 After you give all write commands you must call the \c run() member

 function, which executes all the writing commands.

 \code

 writer.run();

 \endcode

 \subsection reading Reading a graph

 The given file format may contain several maps and labeled nodes or edges.

 If you read a graph you need not read all the maps and items just those

 that you need. The interface of the \c GraphReader is very similar to

 the GraphWriter but the reading method does not depend on the order of the

 given commands.

 The reader object assumes that each not readed value does not contain 

 whitespaces, therefore it has some extra possibilities to control how

 it should skip the values when the string representation contains spaces.

 \code

 GraphReader<ListGraph> reader(std::cin, graph);

 \endcode

 The \c readNodeMap() function reads a map from the \c \@nodeset section.

 If there is a map that you do not want to read from the file and there are

 whitespaces in the string represenation of the values then you should

 call the \c skipNodeMap() template member function with proper parameters.

 \see QuotedStringReader

 \code

 reader.readNodeMap("x-coord", xCoordMap);

 reader.readNodeMap("y-coord", yCoordMap);

 reader.readNodeMap<QuotedStringReader>("label", labelMap);

 reader.skipNodeMap<QuotedStringReader>("description");

 reader.readNodeMap("color", colorMap);

 \endcode

 With the \c readEdgeMap() member function you can give an edge map

 reading command similar to the NodeMaps. 

 \code

 reader.readEdgeMap("weight", weightMap);

 reader.readEdgeMap("label", labelMap);

 \endcode

 With \c readNode() and \c readEdge() functions you can read labeled Nodes and

 Edges.

 \code

 reader.readNode("source", sourceNode);

 reader.readNode("target", targetNode);

 reader.readEdge("observed", edge);

 \endcode

 With \c readAttribute() function you can read an attribute from the file.

 \code

 std::string author;

 writer.readAttribute("author", author);

 int version;

 writer.writeAttribute("version", version);

 \endcode

 After you give all read commands you must call the \c run() member

 function, which executes all the commands.

 \code

 reader.run();

 \endcode

 \section types Background of Reading and Writing

 To read a map (on the nodes or edges)

 the \c GraphReader should know how to read a Value from the given map.

 By the default implementation the input operator reads a value from

 the stream and the type of the readed value is the value type of the given map.

 When the reader should skip a value in the stream, because you do not

 want to store it in a map, the reader skips a character sequence without 

 whitespace. 

 If you want to change the functionality of the reader, you can use

 template parameters to specialize it. When you give a reading

 command for a map you can give a Reader type as template parameter.

 With this template parameter you can control how the Reader reads

 a value from the stream.

 The reader has the next structure: 

 \code

 struct TypeReader {

   typedef TypeName Value;

   void read(std::istream& is, Value& value);

 };

 \endcode

 For example, the \c "strings" nodemap contains strings and you do not need

 the value of the string just the length. Then you can implement own Reader

 struct.

 \code

 struct LengthReader {

   typedef int Value;

   void read(std::istream& is, Value& value) {

     std::string tmp;

     is >> tmp;

     value = tmp.length();

   }

 };

 ...

 reader.readNodeMap<LengthReader>("strings", lengthMap);

 \endcode  

 The global functionality of the reader class can be changed by giving a

 special template parameter to the GraphReader class. By default, the

 template parameter is \c DefaultReaderTraits. A reader traits class 

 should provide an inner template class Reader for each type, and an 

 DefaultReader for skipping a value.

 The specialization of  writing should be very similar to that of reading.

 \section undir Undir graphs

 In the undir graph format there is an \c undiredgeset section instead of

 the \c edgeset section. The first line of the section describes the 

 undirected egdes' names and all next lines describes one undirected edge

 with the the incident nodes and the values of the map.

 The format handles the directed edge maps as a syntactical sugar, if there

 is two map which names are the same with a \c '+' and a \c '-' prefix

 then it can be read as an directed map.

 \code

 @undiredgeset

              id    capacity +flow -flow

 32   2       1     4.3      2.0	  0.0

 21   21      5     2.6      0.0   2.6

 21   12      8     3.4      0.0   0.0

 \endcode

 The \c edges section changed to \c undiredges section. This section

 describes labeled edges and undirected edges. The directed edge label

 should start with a \c '+' and a \c '-' prefix what decide the direction

 of the edge. 

 \code

 @undiredges

 undiredge 1

 +edge 5

 -back 5

 \endcode

 There are similar classes to the \c GraphReader ans \c GraphWriter

 which handle the undirected graphs. These classes are the 

 \c UndirGraphReader and \UndirGraphWriter.

 The \c readUndirMap() function reads an undirected map and the

 \c readUndirEdge() reads an undirected edge from the file, 

 \code

 reader.readUndirEdgeMap("capacity", capacityMap);

 reader.readEdgeMap("flow", flowMap);

 ...

 reader.readUndirEdge("undir_edge", undir_edge);

 reader.readEdge("edge", edge);

 \endcode

 \section advanced Advanced features

 The graph reader and writer classes gives an easy way to read and write

 graphs. But sometimes we want more advanced features. This way we can

 use the more general lemon reader and writer interface.

 The lemon format is an section oriented file format. It contains one or

 more section, each starts with a line with \c \@ first character.

 The content of the section this way cannot contain line with \c \@ first

 character. The file may contains comment lines with \c # first character.

 The \c LemonReader and \c LemonWriter gives a framework to read and

 write sections. There are various section reader and section writer

 classes which can be attached to a \c LemonReader or a \c LemonWriter.

 There are default section readers and writers for reading and writing

 item sets, and labeled items in the graph. These reads and writes

 the format described above. Other type of data can be handled with own

 section reader and writer classes which are inherited from the

 \c LemonReader::SectionReader or the \c LemonWriter::SectionWriter classes.

 The next example defines a special section reader which reads the

 \c \@description sections into a string:

 \code 

 class DescriptionReader : LemonReader::SectionReader {

 protected:

   virtual bool header(const std::string& line) {

     std::istringstream ls(line);

     std::string head;

     ls >> head;

     return head == "@description";

   }

   virtual void read(std::istream& is) {

     std::string line;

     while (getline(is, line)) {

       desc += line;

     }

   }

 public:

   typedef LemonReader::SectionReader Parent;

   DescriptionReader(LemonReader& reader) : Parent(reader) {}

   const std::string& description() const {

     return description;

   }

 private:

   std::string desc;

 };

 \endcode

 The other advanced stuff of the generalized file format is that 

 multiple edgesets can be stored to the same nodeset. It can be used 

 by example as a network traffic matrix.

 In example there is a network with symmetric links and there are assymetric

 traffic request on the network. This construction can be stored in an

 undirected graph and in an directed NewEdgeSetAdaptor class. The example

 shows the input with the LemonReader class:

 \code

 UndirListGraph network;

 UndirListGraph::UndirEdgeSet<double> capacity;

 NewEdgeSetAdaptor<UndirListGraph> traffic(network);

 NewEdgeSetAdaptor<UndirListGraph>::EdgeSet<double> request(network);

 LemonReader reader(std::cin);

 NodeSetReader nodesetReader(reader, network);

 UndirEdgeSetReader undirEdgesetReader(reader, network, nodesetReader);

 undirEdgesetReader.readEdgeMap("capacity", capacity);

 EdgeSetReader edgesetReader(reader, traffic, nodesetReader);

 edgesetReader.readEdgeMap("request", request);

 reader.run();

 \endcode

 Because the GraphReader and the UndirGraphReader can be converted

 to LemonReader and it can resolve the ID's of the items, the previous

 result can be achived with the UndirGraphReader class also.

 \code

 UndirListGraph network;

 UndirListGraph::UndirEdgeSet<double> capacity;

 NewEdgeSetAdaptor<UndirListGraph> traffic(network);

 NewEdgeSetAdaptor<UndirListGraph>::EdgeSet<double> request(network);

 UndirGraphReader reader(std::cin, network);

 reader.readEdgeMap("capacity", capacity);

 EdgeSetReader edgesetReader(reader, traffic, reader);

 edgesetReader.readEdgeMap("request", request);

 reader.run();

 \endcode

 \author Balazs Dezso

 */

 }