source: lemon-0.x/lemon/graph_reader.h @ 1534:b86aad11f842

/* -*- C++ -*-
 * lemon/graph_reader.h - Part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */

///\ingroup io_group
///\file
///\brief Lemon Graph Format reader.

#ifndef LEMON_GRAPH_READER_H
#define LEMON_GRAPH_READER_H

#include <iostream>

#include <lemon/error.h>
#include <lemon/lemon_reader.h>

namespace lemon {

  /// \addtogroup io_group
  /// @{

  /// \brief The graph reader class.
  ///
  /// The \c GraphReader class provides the graph input. 
  /// Before you read this documentation it might be useful to read the general
  /// description of  \ref graph-io-page "Graph Input-Output".
  /// If you don't need very sophisticated
  /// behaviour then you can use the versions of the public function
  /// \ref readGraph() to read a graph (or a max flow instance etc).
  ///
  /// 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 the
  /// given commands.
  ///
  /// The reader object suppose 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 is
  /// whitespace in the string represenation of the values then you should
  /// call the \c skipNodeMap() template member function with proper 
  /// parameters.
  ///
  /// \code
  /// reader.readNodeMap("coords", coords);
  ///
  /// 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 the \c readAttribute() functions you can read an attribute
  /// in a variable. You can specify the reader for the attribute as
  /// the nodemaps.
  ///
  /// After you give all read commands you must call the \c run() member
  /// function, which execute all the commands.
  ///
  /// \code
  /// reader.run();
  /// \endcode
  ///
  /// \see DefaultReaderTraits
  /// \see QuotedStringReader
  /// \see \ref GraphWriter
  /// \see \ref graph-io-page
  /// \author Balazs Dezso
  template <typename _Graph, typename _ReaderTraits = DefaultReaderTraits> 
  class GraphReader {
  public:
    
    typedef _Graph Graph;
    typedef typename Graph::Node Node;
    typedef typename Graph::Edge Edge;

    typedef _ReaderTraits ReaderTraits;
    typedef typename ReaderTraits::Skipper DefaultSkipper;

    /// \brief Construct a new GraphReader.
    ///
    /// Construct a new GraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    GraphReader(std::istream& _is, 
                typename SmartParameter<Graph>::Type _graph, 
                const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(new LemonReader(_is)), own_reader(true), skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        edgeset_reader(*reader, _graph, nodeset_reader, 
                       std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        edge_reader(*reader, edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Construct a new GraphReader.
    ///
    /// Construct a new GraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    GraphReader(const std::string& _filename, 
                typename SmartParameter<Graph>::Type _graph, 
                const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(new LemonReader(_filename)), own_reader(true), 
        skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        edgeset_reader(*reader, _graph, nodeset_reader, 
                       std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        edge_reader(*reader, edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Construct a new GraphReader.
    ///
    /// Construct a new GraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    GraphReader(LemonReader& _reader, 
                typename SmartParameter<Graph>::Type _graph, 
                const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(_reader), own_reader(false), skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        edgeset_reader(*reader, _graph, nodeset_reader, 
                       std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        edge_reader(*reader, edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Destruct the graph reader.
    ///
    /// Destruct the graph reader.
    ~GraphReader() {
      if (own_reader) 
        delete reader;
    }

    /// \brief Add a new node map reader command for the reader.
    ///
    /// Add a new node map reader command for the reader.
    template <typename Map>
    GraphReader& readNodeMap(std::string name, Map& map) {
      nodeset_reader.readNodeMap(name, map);
      return *this;
    }

    template <typename Map>
    GraphReader& readNodeMap(std::string name, const Map& map) {
      nodeset_reader.readNodeMap(name, map);
      return *this;
    }

    /// \brief Add a new node map reader command for the reader.
    ///
    /// Add a new node map reader command for the reader.
    template <typename Reader, typename Map>
    GraphReader& readNodeMap(std::string name, Map& map, 
                             const Reader& reader = Reader()) {
      nodeset_reader.readNodeMap(name, map, reader);
      return *this;
    }

    template <typename Reader, typename Map>
    GraphReader& readNodeMap(std::string name, const Map& map, 
                             const Reader& reader = Reader()) {
      nodeset_reader.readNodeMap(name, map, reader);
      return *this;
    }

    /// \brief Add a new node map skipper command for the reader.
    ///
    /// Add a new node map skipper command for the reader.
    template <typename Reader>
    GraphReader& skipNodeMap(std::string name, 
                             const Reader& reader = Reader()) {
      nodeset_reader.skipNodeMap(name, reader);
      return *this;
    }

    /// \brief Add a new edge map reader command for the reader.
    ///
    /// Add a new edge map reader command for the reader.
    template <typename Map>
    GraphReader& readEdgeMap(std::string name, Map& map) { 
      edgeset_reader.readEdgeMap(name, map);
      return *this;
    }

    template <typename Map>
    GraphReader& readEdgeMap(std::string name, const Map& map) { 
      edgeset_reader.readEdgeMap(name, map);
      return *this;
    }


    /// \brief Add a new edge map reader command for the reader.
    ///
    /// Add a new edge map reader command for the reader.
    template <typename Reader, typename Map>
    GraphReader& readEdgeMap(std::string name, Map& map,
                             const Reader& reader = Reader()) {
      edgeset_reader.readEdgeMap(name, map, reader);
      return *this;
    }

    template <typename Reader, typename Map>
    GraphReader& readEdgeMap(std::string name, const Map& map,
                             const Reader& reader = Reader()) {
      edgeset_reader.readEdgeMap(name, map, reader);
      return *this;
    }

    /// \brief Add a new edge map skipper command for the reader.
    ///
    /// Add a new edge map skipper command for the reader.
    template <typename Reader>
    GraphReader& skipEdgeMap(std::string name, 
                             const Reader& reader = Reader()) {
      edgeset_reader.skipEdgeMap(name, reader);
      return *this;
    }

    /// \brief Add a new labeled node reader for the reader.
    ///
    /// Add a new labeled node reader for the reader.
    GraphReader& readNode(std::string name, Node& node) {
      node_reader.readNode(name, node);
      return *this;
    }

    /// \brief Add a new labeled edge reader for the reader.
    ///
    /// Add a new labeled edge reader for the reader.
    GraphReader& readEdge(std::string name, Edge& edge) {
      edge_reader.readEdge(name, edge);
      return *this;
    }

    /// \brief Add a new attribute reader command.
    ///
    ///  Add a new attribute reader command.
    template <typename Value>
    GraphReader& readAttribute(std::string name, Value& value) {
      attribute_reader.readAttribute(name, value);
      return *this;
    }
    
    /// \brief Add a new attribute reader command.
    ///
    ///  Add a new attribute reader command.
    template <typename Reader, typename Value>
    GraphReader& readAttribute(std::string name, Value& value, 
                               const Reader& reader) {
      attribute_reader.readAttribute<Reader>(name, value, reader);
      return *this;
    }

    /// \brief Conversion operator to LemonReader.
    ///
    /// Conversion operator to LemonReader. It make possible
    /// to access the encapsulated \e LemonReader, this way
    /// you can attach to this reader new instances of 
    /// \e LemonReader::SectionReader.
    operator LemonReader&() {
      return *reader;
    }

    /// \brief Executes the reader commands.
    ///
    /// Executes the reader commands.
    void run() {
      reader->run();
    }

    /// \brief Gives back the node by its id.
    ///
    /// It reads an id from the stream and gives back which node belongs to
    /// it. It is possible only if there was read an "id" named node map.
    Node readId(std::istream& is, Node) const {
      return nodeset_reader.readId(is, Node());
    } 

    /// \brief Gives back the edge by its id.
    ///
    /// It reads an id from the stream and gives back which edge belongs to
    /// it. It is possible only if there was read an "id" named edge map.
    Edge readId(std::istream& is, Edge) const {
      return edgeset_reader.readId(is, Edge());
    } 

  private:

    LemonReader* reader;
    bool own_reader;

    DefaultSkipper skipper;

    NodeSetReader<Graph, ReaderTraits> nodeset_reader;
    EdgeSetReader<Graph, ReaderTraits> edgeset_reader;

    NodeReader<Graph> node_reader;
    EdgeReader<Graph> edge_reader;
    
    AttributeReader<ReaderTraits> attribute_reader;
  };


  ///\anchor readGraph()
  ///
  /// \brief Read a graph from an input stream.
  ///
  /// Read a graph from an input stream.
  /// \param is The input stream.
  /// \param g The graph.
  template<typename Graph>
  void readGraph(std::istream& is, Graph &g) {
    GraphReader<Graph> reader(is, g);
    reader.run();
  }

  /// \brief Read a capacitated graph instance from an input stream.
  /// 
  /// Read a capacitated graph (graph+capacity on the
  /// edges) from an input stream.
  /// \param is The input stream.
  /// \param g The graph.
  /// \param capacity The capacity map.
  template<typename Graph, typename CapacityMap>
  void readGraph(std::istream& is, Graph &g, CapacityMap& capacity) {
    GraphReader<Graph> reader(is, g);
    reader.readEdgeMap("capacity", capacity);
    reader.run();
  }

  /// \brief Read a shortest path instance from an input stream.
  /// 
  /// Read a shortest path instance (graph+capacity on the
  /// edges+designated source) from an input stream.
  /// \param is The input stream.
  /// \param g The graph.
  /// \param capacity The capacity map.
  /// \param s The source node.
  template<typename Graph, typename CapacityMap>
  void readGraph(std::istream& is, Graph &g, CapacityMap& capacity, 
                  typename Graph::Node &s) {
    GraphReader<Graph> reader(is, g);
    reader.readEdgeMap("capacity", capacity);
    reader.readNode("source", s);
    reader.run();
  }



  /// \brief Read a max flow instance from an input stream.
  ///
  /// Read a max flow instance (graph+capacity on the
  /// edges+designated source and target) from an input stream.
  ///
  /// \param is The input stream.
  /// \param g The graph.
  /// \param capacity The capacity map.
  /// \param s The source node.
  /// \param t The target node.
  template<typename Graph, typename CapacityMap>
  void readGraph(std::istream& is, Graph &g, CapacityMap& capacity, 
                  typename Graph::Node &s, typename Graph::Node &t) {
    GraphReader<Graph> reader(is, g);
    reader.readEdgeMap("capacity", capacity);
    reader.readNode("source", s);
    reader.readNode("target", t);
    reader.run();
  }

  /// \brief Read a min cost flow instance from an input stream.
  ///
  /// Read a min cost flow instance (graph+capacity on the edges+cost
  /// function on the edges+designated source and target) from an input stream.
  ///
  /// \param is The input stream.
  /// \param g The graph.
  /// \param capacity The capacity map.
  /// \param s The source node.
  /// \param t The target node.
  /// \param cost The cost map.
  template<typename Graph, typename CapacityMap, typename CostMap>
  void readGraph(std::istream& is, Graph &g, CapacityMap& capacity, 
                  typename Graph::Node &s, typename Graph::Node &t, 
                  CostMap& cost) {
    GraphReader<Graph> reader(is, g);
    reader.readEdgeMap("capacity", capacity);
    reader.readEdgeMap("cost", cost);
    reader.readNode("source", s);
    reader.readNode("target", t);
    reader.run();
  }


  /// \brief The undir graph reader class.
  ///
  /// 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 the
  /// given commands.
  ///
  /// The reader object suppose 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
  /// UndirGraphReader<UndirListGraph> 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 is
  /// whitespace in the string represenation of the values then you should
  /// call the \c skipNodeMap() template member function with proper 
  /// parameters.
  ///
  /// \code
  /// reader.readNodeMap("coords", coords);
  ///
  /// reader.readNodeMap<QuotedStringReader>("label", labelMap);
  /// reader.skipNodeMap<QuotedStringReader>("description");
  ///
  /// reader.readNodeMap("color", colorMap);
  /// \endcode
  ///
  /// With the \c readUndirEdgeMap() member function you can give an 
  /// undir edge map reading command similar to the NodeMaps. 
  ///
  /// \code
  /// reader.readUndirEdgeMap("capacity", capacityMap);
  /// \endcode
  ///
  /// The reading of the directed edge maps is just a syntactical sugar.
  /// It reads two undirected edgemaps into a directed edge map. The 
  /// undirected edge maps' name should be start with the \c '+' and the
  /// \c '-' character and the same.
  ///
  /// \code
  /// reader.readEdgeMap("flow", flowMap);
  /// \endcode 
  ///
  /// With \c readNode() and \c readUndirEdge() functions you can read 
  /// labeled Nodes and UndirEdges.
  ///
  /// \code
  /// reader.readNode("source", sourceNode);
  /// reader.readNode("target", targetNode);
  ///
  /// reader.readUndirEdge("observed", undirEdge);
  /// \endcode
  ///
  /// With the \c readAttribute() functions you can read an attribute
  /// in a variable. You can specify the reader for the attribute as
  /// the nodemaps.
  ///
  /// After you give all read commands you must call the \c run() member
  /// function, which execute all the commands.
  ///
  /// \code
  /// reader.run();
  /// \endcode
  ///
  /// \see GraphReader
  /// \see DefaultReaderTraits
  /// \see \ref UndirGraphWriter
  /// \see \ref graph-io-page
  ///
  /// \author Balazs Dezso
  template <typename _Graph, typename _ReaderTraits = DefaultReaderTraits> 
  class UndirGraphReader {
  public:
    
    typedef _Graph Graph;
    typedef typename Graph::Node Node;
    typedef typename Graph::Edge Edge;
    typedef typename Graph::UndirEdge UndirEdge;

    typedef _ReaderTraits ReaderTraits;
    typedef typename ReaderTraits::Skipper DefaultSkipper;

    /// \brief Construct a new UndirGraphReader.
    ///
    /// Construct a new UndirGraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    UndirGraphReader(std::istream& _is, Graph& _graph, 
                     const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(new LemonReader(_is)), own_reader(true), skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        undir_edgeset_reader(*reader, _graph, nodeset_reader, 
                             std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        undir_edge_reader(*reader, undir_edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Construct a new UndirGraphReader.
    ///
    /// Construct a new UndirGraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    UndirGraphReader(const std::string& _filename, Graph& _graph, 
                     const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(new LemonReader(_filename)), own_reader(true), 
        skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        undir_edgeset_reader(*reader, _graph, nodeset_reader, 
                             std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        undir_edge_reader(*reader, undir_edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Construct a new UndirGraphReader.
    ///
    /// Construct a new UndirGraphReader. It reads into the given graph
    /// and it use the given reader as the default skipper.
    UndirGraphReader(LemonReader& _reader, Graph& _graph, 
                     const DefaultSkipper& _skipper = DefaultSkipper()) 
      : reader(_reader), own_reader(false), skipper(_skipper),
        nodeset_reader(*reader, _graph, std::string(), skipper),
        undir_edgeset_reader(*reader, _graph, nodeset_reader, 
                             std::string(), skipper),
        node_reader(*reader, nodeset_reader, std::string()),
        undir_edge_reader(*reader, undir_edgeset_reader, std::string()),
        attribute_reader(*reader, std::string()) {}

    /// \brief Destruct the graph reader.
    ///
    /// Destruct the graph reader.
    ~UndirGraphReader() {
      if (own_reader) 
        delete reader;
    }

    /// \brief Add a new node map reader command for the reader.
    ///
    /// Add a new node map reader command for the reader.
    template <typename Map>
    UndirGraphReader& readNodeMap(std::string name, Map& map) {
      nodeset_reader.readNodeMap(name, map);
      return *this;
    }

    template <typename Map>
    UndirGraphReader& readNodeMap(std::string name, const Map& map) {
      nodeset_reader.readNodeMap(name, map);
      return *this;
    }

    /// \brief Add a new node map reader command for the reader.
    ///
    /// Add a new node map reader command for the reader.
    template <typename Reader, typename Map>
    UndirGraphReader& readNodeMap(std::string name, Map& map, 
                                  const Reader& reader = Reader()) {
      nodeset_reader.readNodeMap(name, map, reader);
      return *this;
    }

    template <typename Reader, typename Map>
    UndirGraphReader& readNodeMap(std::string name, const Map& map, 
                                  const Reader& reader = Reader()) {
      nodeset_reader.readNodeMap(name, map, reader);
      return *this;
    }

    /// \brief Add a new node map skipper command for the reader.
    ///
    /// Add a new node map skipper command for the reader.
    template <typename Reader>
    UndirGraphReader& skipNodeMap(std::string name, 
                             const Reader& reader = Reader()) {
      nodeset_reader.skipNodeMap(name, reader);
      return *this;
    }

    /// \brief Add a new undirected edge map reader command for the reader.
    ///
    /// Add a new undirected edge map reader command for the reader.
    template <typename Map>
    UndirGraphReader& readUndirEdgeMap(std::string name, Map& map) { 
      undir_edgeset_reader.readUndirEdgeMap(name, map);
      return *this;
    }

    template <typename Map>
    UndirGraphReader& readUndirEdgeMap(std::string name, const Map& map) { 
      undir_edgeset_reader.readUndirEdgeMap(name, map);
      return *this;
    }


    /// \brief Add a new undirected edge map reader command for the reader.
    ///
    /// Add a new undirected edge map reader command for the reader.
    template <typename Reader, typename Map>
    UndirGraphReader& readUndirEdgeMap(std::string name, Map& map,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.readUndirEdgeMap(name, map, reader);
      return *this;
    }

    template <typename Reader, typename Map>
    UndirGraphReader& readUndirEdgeMap(std::string name, const Map& map,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.readUndirEdgeMap(name, map, reader);
      return *this;
    }

    /// \brief Add a new undirected edge map skipper command for the reader.
    ///
    /// Add a new undirected edge map skipper command for the reader.
    template <typename Reader>
    UndirGraphReader& skipUndirEdgeMap(std::string name,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.skipUndirMap(name, reader);
      return *this;
    }


    /// \brief Add a new edge map reader command for the reader.
    ///
    /// Add a new edge map reader command for the reader.
    template <typename Map>
    UndirGraphReader& readEdgeMap(std::string name, Map& map) { 
      undir_edgeset_reader.readEdgeMap(name, map);
      return *this;
    }

    template <typename Map>
    UndirGraphReader& readEdgeMap(std::string name, const Map& map) { 
      undir_edgeset_reader.readEdgeMap(name, map);
      return *this;
    }


    /// \brief Add a new edge map reader command for the reader.
    ///
    /// Add a new edge map reader command for the reader.
    template <typename Reader, typename Map>
    UndirGraphReader& readEdgeMap(std::string name, Map& map,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.readEdgeMap(name, map, reader);
      return *this;
    }

    template <typename Reader, typename Map>
    UndirGraphReader& readEdgeMap(std::string name, const Map& map,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.readEdgeMap(name, map, reader);
      return *this;
    }

    /// \brief Add a new edge map skipper command for the reader.
    ///
    /// Add a new edge map skipper command for the reader.
    template <typename Reader>
    UndirGraphReader& skipEdgeMap(std::string name,
                                       const Reader& reader = Reader()) {
      undir_edgeset_reader.skipEdgeMap(name, reader);
      return *this;
    }

    /// \brief Add a new labeled node reader for the reader.
    ///
    /// Add a new labeled node reader for the reader.
    UndirGraphReader& readNode(std::string name, Node& node) {
      node_reader.readNode(name, node);
      return *this;
    }

    /// \brief Add a new labeled edge reader for the reader.
    ///
    /// Add a new labeled edge reader for the reader.
    UndirGraphReader& readEdge(std::string name, Edge& edge) {
      undir_edge_reader.readEdge(name, edge);
    }

    /// \brief Add a new labeled undirected edge reader for the reader.
    ///
    /// Add a new labeled undirected edge reader for the reader.
    UndirGraphReader& readUndirEdge(std::string name, UndirEdge& edge) {
      undir_edge_reader.readUndirEdge(name, edge);
    }

    /// \brief Add a new attribute reader command.
    ///
    ///  Add a new attribute reader command.
    template <typename Value>
    UndirGraphReader& readAttribute(std::string name, Value& value) {
      attribute_reader.readAttribute(name, value);
      return *this;
    }
    
    /// \brief Add a new attribute reader command.
    ///
    ///  Add a new attribute reader command.
    template <typename Reader, typename Value>
    UndirGraphReader& readAttribute(std::string name, Value& value, 
                               const Reader& reader) {
      attribute_reader.readAttribute<Reader>(name, value, reader);
      return *this;
    }

    /// \brief Conversion operator to LemonReader.
    ///
    /// Conversion operator to LemonReader. It make possible
    /// to access the encapsulated \e LemonReader, this way
    /// you can attach to this reader new instances of 
    /// \e LemonReader::SectionReader.
    operator LemonReader&() {
      return *reader;
    }

    /// \brief Executes the reader commands.
    ///
    /// Executes the reader commands.
    void run() {
      reader->run();
    }

    /// \brief Gives back the node by its id.
    ///
    /// It reads an id from the stream and gives back which node belongs to
    /// it. It is possible only if there was read an "id" named node map.
    Node readId(std::istream& is, Node) const {
      return nodeset_reader.readId(is, Node());
    } 

    /// \brief Gives back the edge by its id.
    ///
    /// It reads an id from the stream and gives back which edge belongs to
    /// it. It is possible only if there was read an "id" named edge map.
    Edge readId(std::istream& is, Edge) const {
      return undir_edgeset_reader.readId(is, Edge());
    } 

    /// \brief Gives back the undirected edge by its id.
    ///
    /// It reads an id from the stream and gives back which undirected edge 
    /// belongs to it. It is possible only if there was read an "id" named 
    /// edge map.
    UndirEdge readId(std::istream& is, UndirEdge) const {
      return undir_edgeset_reader.readId(is, UndirEdge());
    } 
    

  private:

    LemonReader* reader;
    bool own_reader;

    DefaultSkipper skipper;

    NodeSetReader<Graph, ReaderTraits> nodeset_reader;
    UndirEdgeSetReader<Graph, ReaderTraits> undir_edgeset_reader;

    NodeReader<Graph> node_reader;
    UndirEdgeReader<Graph> undir_edge_reader;
    
    AttributeReader<ReaderTraits> attribute_reader;
  };

  /// \brief Read an undirected graph from an input stream.
  ///
  /// Read an undirected graph from an input stream.
  /// \param is The input stream.
  /// \param g The graph.
  template<typename Graph>
  void readUndirGraph(std::istream& is, Graph &g) {
    UndirGraphReader<Graph> reader(is, g);
    reader.run();
  }

  /// \brief Read an undirected multigraph (undirected graph + capacity
  /// map on the edges) from an input stream.
  ///
  /// Read an undirected multigraph (undirected graph + capacity
  /// map on the edges) from an input stream.
  /// \param is The input stream.
  /// \param g The graph.
  /// \param capacity The capacity map.
  template<typename Graph, typename CapacityMap>
  void readUndirGraph(std::istream& is, Graph &g, CapacityMap& capacity) {
    UndirGraphReader<Graph> reader(is, g);
    reader.readUndirEdgeMap("capacity", capacity);
    reader.run();
  }


  /// @}
}

#endif