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 at most four sections in the following order:

 \li nodeset

 \li edgeset

 \li nodes

 \li edges

 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 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

 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

 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.

 \author Balazs Dezso

 */

 }