/* -*- mode: C++; indent-tabs-mode: nil; -*-

  *

  * This file is a part of LEMON, a generic C++ optimization library.

  *

  * Copyright (C) 2003-2009

  * 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 lemon_io

 ///\file

 ///\brief \ref lgf-format "LEMON Graph Format" reader.

 #ifndef LEMON_LGF_READER_H

 #define LEMON_LGF_READER_H

 #include <iostream>

 #include <fstream>

 #include <sstream>

 #include <set>

 #include <map>

 #include <lemon/core.h>

 #include <lemon/lgf_writer.h>

 #include <lemon/concept_check.h>

 #include <lemon/concepts/maps.h>

 namespace lemon {

   namespace _reader_bits {

     template <typename Value>

     struct DefaultConverter {

       Value operator()(const std::string& str) {

         std::istringstream is(str);

         Value value;

         if (!(is >> value)) {

           throw FormatError("Cannot read token");

         }

         char c;

         if (is >> std::ws >> c) {

           throw FormatError("Remaining characters in token");

         }

         return value;

       }

     };

     template <>

     struct DefaultConverter<std::string> {

       std::string operator()(const std::string& str) {

         return str;

       }

     };

     template <typename _Item>

     class MapStorageBase {

     public:

       typedef _Item Item;

     public:

       MapStorageBase() {}

       virtual ~MapStorageBase() {}

       virtual void set(const Item& item, const std::string& value) = 0;

     };

     template <typename _Item, typename _Map,

               typename _Converter = DefaultConverter<typename _Map::Value> >

     class MapStorage : public MapStorageBase<_Item> {

     public:

       typedef _Map Map;

       typedef _Converter Converter;

       typedef _Item Item;

     private:

       Map& _map;

       Converter _converter;

     public:

       MapStorage(Map& map, const Converter& converter = Converter())

         : _map(map), _converter(converter) {}

       virtual ~MapStorage() {}

       virtual void set(const Item& item ,const std::string& value) {

         _map.set(item, _converter(value));

       }

     };

     template <typename _GR, bool _dir, typename _Map,

               typename _Converter = DefaultConverter<typename _Map::Value> >

     class GraphArcMapStorage : public MapStorageBase<typename _GR::Edge> {

     public:

       typedef _Map Map;

       typedef _Converter Converter;

       typedef _GR GR;

       typedef typename GR::Edge Item;

       static const bool dir = _dir;

     private:

       const GR& _graph;

       Map& _map;

       Converter _converter;

     public:

       GraphArcMapStorage(const GR& graph, Map& map,

                          const Converter& converter = Converter())

         : _graph(graph), _map(map), _converter(converter) {}

       virtual ~GraphArcMapStorage() {}

       virtual void set(const Item& item ,const std::string& value) {

         _map.set(_graph.direct(item, dir), _converter(value));

       }

     };

     class ValueStorageBase {

     public:

       ValueStorageBase() {}

       virtual ~ValueStorageBase() {}

       virtual void set(const std::string&) = 0;

     };

     template <typename _Value, typename _Converter = DefaultConverter<_Value> >

     class ValueStorage : public ValueStorageBase {

     public:

       typedef _Value Value;

       typedef _Converter Converter;

     private:

       Value& _value;

       Converter _converter;

     public:

       ValueStorage(Value& value, const Converter& converter = Converter())

         : _value(value), _converter(converter) {}

       virtual void set(const std::string& value) {

         _value = _converter(value);

       }

     };

     template <typename Value>

     struct MapLookUpConverter {

       const std::map<std::string, Value>& _map;

       MapLookUpConverter(const std::map<std::string, Value>& map)

         : _map(map) {}

       Value operator()(const std::string& str) {

         typename std::map<std::string, Value>::const_iterator it =

           _map.find(str);

         if (it == _map.end()) {

           std::ostringstream msg;

           msg << "Item not found: " << str;

           throw FormatError(msg.str());

         }

         return it->second;

       }

     };

     template <typename GR>

     struct GraphArcLookUpConverter {

       const GR& _graph;

       const std::map<std::string, typename GR::Edge>& _map;

       GraphArcLookUpConverter(const GR& graph,

                               const std::map<std::string,

                                              typename GR::Edge>& map)

         : _graph(graph), _map(map) {}

       typename GR::Arc operator()(const std::string& str) {

         if (str.empty() || (str[0] != '+' && str[0] != '-')) {

           throw FormatError("Item must start with '+' or '-'");

         }

         typename std::map<std::string, typename GR::Edge>

           ::const_iterator it = _map.find(str.substr(1));

         if (it == _map.end()) {

           throw FormatError("Item not found");

         }

         return _graph.direct(it->second, str[0] == '+');

       }

     };

     inline bool isWhiteSpace(char c) {

       return c == ' ' || c == '\t' || c == '\v' ||

         c == '\n' || c == '\r' || c == '\f';

     }

     inline bool isOct(char c) {

       return '0' <= c && c <='7';

     }

     inline int valueOct(char c) {

       LEMON_ASSERT(isOct(c), "The character is not octal.");

       return c - '0';

     }

     inline bool isHex(char c) {

       return ('0' <= c && c <= '9') ||

         ('a' <= c && c <= 'z') ||

         ('A' <= c && c <= 'Z');

     }

     inline int valueHex(char c) {

       LEMON_ASSERT(isHex(c), "The character is not hexadecimal.");

       if ('0' <= c && c <= '9') return c - '0';

       if ('a' <= c && c <= 'z') return c - 'a' + 10;

       return c - 'A' + 10;

     }

     inline bool isIdentifierFirstChar(char c) {

       return ('a' <= c && c <= 'z') ||

         ('A' <= c && c <= 'Z') || c == '_';

     }

     inline bool isIdentifierChar(char c) {

       return isIdentifierFirstChar(c) ||

         ('0' <= c && c <= '9');

     }

     inline char readEscape(std::istream& is) {

       char c;

       if (!is.get(c))

         throw FormatError("Escape format error");

       switch (c) {

       case '\\':

         return '\\';

       case '\"':

         return '\"';

       case '\'':

         return '\'';

       case '\?':

         return '\?';

       case 'a':

         return '\a';

       case 'b':

         return '\b';

       case 'f':

         return '\f';

       case 'n':

         return '\n';

       case 'r':

         return '\r';

       case 't':

         return '\t';

       case 'v':

         return '\v';

       case 'x':

         {

           int code;

           if (!is.get(c) || !isHex(c))

             throw FormatError("Escape format error");

           else if (code = valueHex(c), !is.get(c) || !isHex(c)) is.putback(c);

           else code = code * 16 + valueHex(c);

           return code;

         }

       default:

         {

           int code;

           if (!isOct(c))

             throw FormatError("Escape format error");

           else if (code = valueOct(c), !is.get(c) || !isOct(c))

             is.putback(c);

           else if (code = code * 8 + valueOct(c), !is.get(c) || !isOct(c))

             is.putback(c);

           else code = code * 8 + valueOct(c);

           return code;

         }

       }

     }

     inline std::istream& readToken(std::istream& is, std::string& str) {

       std::ostringstream os;

       char c;

       is >> std::ws;

       if (!is.get(c))

         return is;

       if (c == '\"') {

         while (is.get(c) && c != '\"') {

           if (c == '\\')

             c = readEscape(is);

           os << c;

         }

         if (!is)

           throw FormatError("Quoted format error");

       } else {

         is.putback(c);

         while (is.get(c) && !isWhiteSpace(c)) {

           if (c == '\\')

             c = readEscape(is);

           os << c;

         }

         if (!is) {

           is.clear();

         } else {

           is.putback(c);

         }

       }

       str = os.str();

       return is;

     }

     class Section {

     public:

       virtual ~Section() {}

       virtual void process(std::istream& is, int& line_num) = 0;

     };

     template <typename Functor>

     class LineSection : public Section {

     private:

       Functor _functor;

     public:

       LineSection(const Functor& functor) : _functor(functor) {}

       virtual ~LineSection() {}

       virtual void process(std::istream& is, int& line_num) {

         char c;

         std::string line;

         while (is.get(c) && c != '@') {

           if (c == '\n') {

             ++line_num;

           } else if (c == '#') {

             getline(is, line);

             ++line_num;

           } else if (!isWhiteSpace(c)) {

             is.putback(c);

             getline(is, line);

             _functor(line);

             ++line_num;

           }

         }

         if (is) is.putback(c);

         else if (is.eof()) is.clear();

       }

     };

     template <typename Functor>

     class StreamSection : public Section {

     private:

       Functor _functor;

     public:

       StreamSection(const Functor& functor) : _functor(functor) {}

       virtual ~StreamSection() {}

       virtual void process(std::istream& is, int& line_num) {

         _functor(is, line_num);

         char c;

         std::string line;

         while (is.get(c) && c != '@') {

           if (c == '\n') {

             ++line_num;

           } else if (!isWhiteSpace(c)) {

             getline(is, line);

             ++line_num;

           }

         }

         if (is) is.putback(c);

         else if (is.eof()) is.clear();

       }

     };

   }

   template <typename DGR>

   class DigraphReader;

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, std::istream& is = std::cin);

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, const std::string& fn);

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, const char *fn);

   /// \ingroup lemon_io

   ///

   /// \brief \ref lgf-format "LGF" reader for directed graphs

   ///

   /// This utility reads an \ref lgf-format "LGF" file.

   ///

   /// The reading method does a batch processing. The user creates a

   /// reader object, then various reading rules can be added to the

   /// reader, and eventually the reading is executed with the \c run()

   /// member function. A map reading rule can be added to the reader

   /// with the \c nodeMap() or \c arcMap() members. An optional

   /// converter parameter can also be added as a standard functor

   /// converting from \c std::string to the value type of the map. If it

   /// is set, it will determine how the tokens in the file should be

   /// converted to the value type of the map. If the functor is not set,

   /// then a default conversion will be used. One map can be read into

   /// multiple map objects at the same time. The \c attribute(), \c

   /// node() and \c arc() functions are used to add attribute reading

   /// rules.

   ///

   ///\code

   /// DigraphReader<DGR>(digraph, std::cin).

   ///   nodeMap("coordinates", coord_map).

   ///   arcMap("capacity", cap_map).

   ///   node("source", src).

   ///   node("target", trg).

   ///   attribute("caption", caption).

   ///   run();

   ///\endcode

   ///

   /// By default, the reader uses the first section in the file of the

   /// proper type. If a section has an optional name, then it can be

   /// selected for reading by giving an optional name parameter to the

   /// \c nodes(), \c arcs() or \c attributes() functions.

   ///

   /// The \c useNodes() and \c useArcs() functions are used to tell the reader

   /// that the nodes or arcs should not be constructed (added to the

   /// graph) during the reading, but instead the label map of the items

   /// are given as a parameter of these functions. An

   /// application of these functions is multipass reading, which is

   /// important if two \c \@arcs sections must be read from the

   /// file. In this case the first phase would read the node set and one

   /// of the arc sets, while the second phase would read the second arc

   /// set into an \e ArcSet class (\c SmartArcSet or \c ListArcSet).

   /// The previously read label node map should be passed to the \c

   /// useNodes() functions. Another application of multipass reading when

   /// paths are given as a node map or an arc map.

   /// It is impossible to read this in

   /// a single pass, because the arcs are not constructed when the node

   /// maps are read.

   template <typename DGR>

   class DigraphReader {

   public:

     typedef DGR Digraph;

   private:

     TEMPLATE_DIGRAPH_TYPEDEFS(DGR);

     std::istream* _is;

     bool local_is;

     std::string _filename;

     DGR& _digraph;

     std::string _nodes_caption;

     std::string _arcs_caption;

     std::string _attributes_caption;

     typedef std::map<std::string, Node> NodeIndex;

     NodeIndex _node_index;

     typedef std::map<std::string, Arc> ArcIndex;

     ArcIndex _arc_index;

     typedef std::vector<std::pair<std::string,

       _reader_bits::MapStorageBase<Node>*> > NodeMaps;

     NodeMaps _node_maps;

     typedef std::vector<std::pair<std::string,

       _reader_bits::MapStorageBase<Arc>*> >ArcMaps;

     ArcMaps _arc_maps;

     typedef std::multimap<std::string, _reader_bits::ValueStorageBase*>

       Attributes;

     Attributes _attributes;

     bool _use_nodes;

     bool _use_arcs;

     bool _skip_nodes;

     bool _skip_arcs;

     int line_num;

     std::istringstream line;

   public:

     /// \brief Constructor

     ///

     /// Construct a directed graph reader, which reads from the given

     /// input stream.

     DigraphReader(DGR& digraph, std::istream& is = std::cin)

       : _is(&is), local_is(false), _digraph(digraph),

         _use_nodes(false), _use_arcs(false),

         _skip_nodes(false), _skip_arcs(false) {}

     /// \brief Constructor

     ///

     /// Construct a directed graph reader, which reads from the given

     /// file.

     DigraphReader(DGR& digraph, const std::string& fn)

       : _is(new std::ifstream(fn.c_str())), local_is(true),

         _filename(fn), _digraph(digraph),

         _use_nodes(false), _use_arcs(false),

         _skip_nodes(false), _skip_arcs(false) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Constructor

     ///

     /// Construct a directed graph reader, which reads from the given

     /// file.

     DigraphReader(DGR& digraph, const char* fn)

       : _is(new std::ifstream(fn)), local_is(true),

         _filename(fn), _digraph(digraph),

         _use_nodes(false), _use_arcs(false),

         _skip_nodes(false), _skip_arcs(false) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Destructor

     ~DigraphReader() {

       for (typename NodeMaps::iterator it = _node_maps.begin();

            it != _node_maps.end(); ++it) {

         delete it->second;

       }

       for (typename ArcMaps::iterator it = _arc_maps.begin();

            it != _arc_maps.end(); ++it) {

         delete it->second;

       }

       for (typename Attributes::iterator it = _attributes.begin();

            it != _attributes.end(); ++it) {

         delete it->second;

       }

       if (local_is) {

         delete _is;

       }

     }

   private:

     template <typename TDGR>

     friend DigraphReader<TDGR> digraphReader(TDGR& digraph, std::istream& is);

     template <typename TDGR>

     friend DigraphReader<TDGR> digraphReader(TDGR& digraph, 

                                              const std::string& fn);

     template <typename TDGR>

     friend DigraphReader<TDGR> digraphReader(TDGR& digraph, const char *fn);

     DigraphReader(DigraphReader& other)

       : _is(other._is), local_is(other.local_is), _digraph(other._digraph),

         _use_nodes(other._use_nodes), _use_arcs(other._use_arcs),

         _skip_nodes(other._skip_nodes), _skip_arcs(other._skip_arcs) {

       other._is = 0;

       other.local_is = false;

       _node_index.swap(other._node_index);

       _arc_index.swap(other._arc_index);

       _node_maps.swap(other._node_maps);

       _arc_maps.swap(other._arc_maps);

       _attributes.swap(other._attributes);

       _nodes_caption = other._nodes_caption;

       _arcs_caption = other._arcs_caption;

       _attributes_caption = other._attributes_caption;

     }

     DigraphReader& operator=(const DigraphReader&);

   public:

     /// \name Reading Rules

     /// @{

     /// \brief Node map reading rule

     ///

     /// Add a node map reading rule to the reader.

     template <typename Map>

     DigraphReader& nodeMap(const std::string& caption, Map& map) {

       checkConcept<concepts::WriteMap<Node, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Node>* storage =

         new _reader_bits::MapStorage<Node, Map>(map);

       _node_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Node map reading rule

     ///

     /// Add a node map reading rule with specialized converter to the

     /// reader.

     template <typename Map, typename Converter>

     DigraphReader& nodeMap(const std::string& caption, Map& map,

                            const Converter& converter = Converter()) {

       checkConcept<concepts::WriteMap<Node, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Node>* storage =

         new _reader_bits::MapStorage<Node, Map, Converter>(map, converter);

       _node_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Arc map reading rule

     ///

     /// Add an arc map reading rule to the reader.

     template <typename Map>

     DigraphReader& arcMap(const std::string& caption, Map& map) {

       checkConcept<concepts::WriteMap<Arc, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Arc>* storage =

         new _reader_bits::MapStorage<Arc, Map>(map);

       _arc_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Arc map reading rule

     ///

     /// Add an arc map reading rule with specialized converter to the

     /// reader.

     template <typename Map, typename Converter>

     DigraphReader& arcMap(const std::string& caption, Map& map,

                           const Converter& converter = Converter()) {

       checkConcept<concepts::WriteMap<Arc, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Arc>* storage =

         new _reader_bits::MapStorage<Arc, Map, Converter>(map, converter);

       _arc_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Attribute reading rule

     ///

     /// Add an attribute reading rule to the reader.

     template <typename Value>

     DigraphReader& attribute(const std::string& caption, Value& value) {

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Value>(value);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Attribute reading rule

     ///

     /// Add an attribute reading rule with specialized converter to the

     /// reader.

     template <typename Value, typename Converter>

     DigraphReader& attribute(const std::string& caption, Value& value,

                              const Converter& converter = Converter()) {

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Value, Converter>(value, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Node reading rule

     ///

     /// Add a node reading rule to reader.

     DigraphReader& node(const std::string& caption, Node& node) {

       typedef _reader_bits::MapLookUpConverter<Node> Converter;

       Converter converter(_node_index);

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Node, Converter>(node, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Arc reading rule

     ///

     /// Add an arc reading rule to reader.

     DigraphReader& arc(const std::string& caption, Arc& arc) {

       typedef _reader_bits::MapLookUpConverter<Arc> Converter;

       Converter converter(_arc_index);

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Arc, Converter>(arc, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// @}

     /// \name Select Section by Name

     /// @{

     /// \brief Set \c \@nodes section to be read

     ///

     /// Set \c \@nodes section to be read

     DigraphReader& nodes(const std::string& caption) {

       _nodes_caption = caption;

       return *this;

     }

     /// \brief Set \c \@arcs section to be read

     ///

     /// Set \c \@arcs section to be read

     DigraphReader& arcs(const std::string& caption) {

       _arcs_caption = caption;

       return *this;

     }

     /// \brief Set \c \@attributes section to be read

     ///

     /// Set \c \@attributes section to be read

     DigraphReader& attributes(const std::string& caption) {

       _attributes_caption = caption;

       return *this;

     }

     /// @}

     /// \name Using Previously Constructed Node or Arc Set

     /// @{

     /// \brief Use previously constructed node set

     ///

     /// Use previously constructed node set, and specify the node

     /// label map.

     template <typename Map>

     DigraphReader& useNodes(const Map& map) {

       checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_nodes, "Multiple usage of useNodes() member");

       _use_nodes = true;

       _writer_bits::DefaultConverter<typename Map::Value> converter;

       for (NodeIt n(_digraph); n != INVALID; ++n) {

         _node_index.insert(std::make_pair(converter(map[n]), n));

       }

       return *this;

     }

     /// \brief Use previously constructed node set

     ///

     /// Use previously constructed node set, and specify the node

     /// label map and a functor which converts the label map values to

     /// \c std::string.

     template <typename Map, typename Converter>

     DigraphReader& useNodes(const Map& map,

                             const Converter& converter = Converter()) {

       checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_nodes, "Multiple usage of useNodes() member");

       _use_nodes = true;

       for (NodeIt n(_digraph); n != INVALID; ++n) {

         _node_index.insert(std::make_pair(converter(map[n]), n));

       }

       return *this;

     }

     /// \brief Use previously constructed arc set

     ///

     /// Use previously constructed arc set, and specify the arc

     /// label map.

     template <typename Map>

     DigraphReader& useArcs(const Map& map) {

       checkConcept<concepts::ReadMap<Arc, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_arcs, "Multiple usage of useArcs() member");

       _use_arcs = true;

       _writer_bits::DefaultConverter<typename Map::Value> converter;

       for (ArcIt a(_digraph); a != INVALID; ++a) {

         _arc_index.insert(std::make_pair(converter(map[a]), a));

       }

       return *this;

     }

     /// \brief Use previously constructed arc set

     ///

     /// Use previously constructed arc set, and specify the arc

     /// label map and a functor which converts the label map values to

     /// \c std::string.

     template <typename Map, typename Converter>

     DigraphReader& useArcs(const Map& map,

                            const Converter& converter = Converter()) {

       checkConcept<concepts::ReadMap<Arc, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_arcs, "Multiple usage of useArcs() member");

       _use_arcs = true;

       for (ArcIt a(_digraph); a != INVALID; ++a) {

         _arc_index.insert(std::make_pair(converter(map[a]), a));

       }

       return *this;

     }

     /// \brief Skips the reading of node section

     ///

     /// Omit the reading of the node section. This implies that each node

     /// map reading rule will be abandoned, and the nodes of the graph

     /// will not be constructed, which usually cause that the arc set

     /// could not be read due to lack of node name resolving.

     /// Therefore \c skipArcs() function should also be used, or

     /// \c useNodes() should be used to specify the label of the nodes.

     DigraphReader& skipNodes() {

       LEMON_ASSERT(!_skip_nodes, "Skip nodes already set");

       _skip_nodes = true;

       return *this;

     }

     /// \brief Skips the reading of arc section

     ///

     /// Omit the reading of the arc section. This implies that each arc

     /// map reading rule will be abandoned, and the arcs of the graph

     /// will not be constructed.

     DigraphReader& skipArcs() {

       LEMON_ASSERT(!_skip_arcs, "Skip arcs already set");

       _skip_arcs = true;

       return *this;

     }

     /// @}

   private:

     bool readLine() {

       std::string str;

       while(++line_num, std::getline(*_is, str)) {

         line.clear(); line.str(str);

         char c;

         if (line >> std::ws >> c && c != '#') {

           line.putback(c);

           return true;

         }

       }

       return false;

     }

     bool readSuccess() {

       return static_cast<bool>(*_is);

     }

     void skipSection() {

       char c;

       while (readSuccess() && line >> c && c != '@') {

         readLine();

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readNodes() {

       std::vector<int> map_index(_node_maps.size());

       int map_num, label_index;

       char c;

       if (!readLine() || !(line >> c) || c == '@') {

         if (readSuccess() && line) line.putback(c);

         if (!_node_maps.empty())

           throw FormatError("Cannot find map names");

         return;

       }

       line.putback(c);

       {

         std::map<std::string, int> maps;

         std::string map;

         int index = 0;

         while (_reader_bits::readToken(line, map)) {

           if (maps.find(map) != maps.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of node map: " << map;

             throw FormatError(msg.str());

           }

           maps.insert(std::make_pair(map, index));

           ++index;

         }

         for (int i = 0; i < static_cast<int>(_node_maps.size()); ++i) {

           std::map<std::string, int>::iterator jt =

             maps.find(_node_maps[i].first);

           if (jt == maps.end()) {

             std::ostringstream msg;

             msg << "Map not found: " << _node_maps[i].first;

             throw FormatError(msg.str());

           }

           map_index[i] = jt->second;

         }

         {

           std::map<std::string, int>::iterator jt = maps.find("label");

           if (jt != maps.end()) {

             label_index = jt->second;

           } else {

             label_index = -1;

           }

         }

         map_num = maps.size();

       }

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::vector<std::string> tokens(map_num);

         for (int i = 0; i < map_num; ++i) {

           if (!_reader_bits::readToken(line, tokens[i])) {

             std::ostringstream msg;

             msg << "Column not found (" << i + 1 << ")";

             throw FormatError(msg.str());

           }

         }

         if (line >> std::ws >> c)

           throw FormatError("Extra character at the end of line");

         Node n;

         if (!_use_nodes) {

           n = _digraph.addNode();

           if (label_index != -1)

             _node_index.insert(std::make_pair(tokens[label_index], n));

         } else {

           if (label_index == -1)

             throw FormatError("Label map not found");

           typename std::map<std::string, Node>::iterator it =

             _node_index.find(tokens[label_index]);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Node with label not found: " << tokens[label_index];

             throw FormatError(msg.str());

           }

           n = it->second;

         }

         for (int i = 0; i < static_cast<int>(_node_maps.size()); ++i) {

           _node_maps[i].second->set(n, tokens[map_index[i]]);

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readArcs() {

       std::vector<int> map_index(_arc_maps.size());

       int map_num, label_index;

       char c;

       if (!readLine() || !(line >> c) || c == '@') {

         if (readSuccess() && line) line.putback(c);

         if (!_arc_maps.empty())

           throw FormatError("Cannot find map names");

         return;

       }

       line.putback(c);

       {

         std::map<std::string, int> maps;

         std::string map;

         int index = 0;

         while (_reader_bits::readToken(line, map)) {

           if (maps.find(map) != maps.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of arc map: " << map;

             throw FormatError(msg.str());

           }

           maps.insert(std::make_pair(map, index));

           ++index;

         }

         for (int i = 0; i < static_cast<int>(_arc_maps.size()); ++i) {

           std::map<std::string, int>::iterator jt =

             maps.find(_arc_maps[i].first);

           if (jt == maps.end()) {

             std::ostringstream msg;

             msg << "Map not found: " << _arc_maps[i].first;

             throw FormatError(msg.str());

           }

           map_index[i] = jt->second;

         }

         {

           std::map<std::string, int>::iterator jt = maps.find("label");

           if (jt != maps.end()) {

             label_index = jt->second;

           } else {

             label_index = -1;

           }

         }

         map_num = maps.size();

       }

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::string source_token;

         std::string target_token;

         if (!_reader_bits::readToken(line, source_token))

           throw FormatError("Source not found");

         if (!_reader_bits::readToken(line, target_token))

           throw FormatError("Target not found");

         std::vector<std::string> tokens(map_num);

         for (int i = 0; i < map_num; ++i) {

           if (!_reader_bits::readToken(line, tokens[i])) {

             std::ostringstream msg;

             msg << "Column not found (" << i + 1 << ")";

             throw FormatError(msg.str());

           }

         }

         if (line >> std::ws >> c)

           throw FormatError("Extra character at the end of line");

         Arc a;

         if (!_use_arcs) {

           typename NodeIndex::iterator it;

           it = _node_index.find(source_token);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Item not found: " << source_token;

             throw FormatError(msg.str());

           }

           Node source = it->second;

           it = _node_index.find(target_token);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Item not found: " << target_token;

             throw FormatError(msg.str());

           }

           Node target = it->second;

           a = _digraph.addArc(source, target);

           if (label_index != -1)

             _arc_index.insert(std::make_pair(tokens[label_index], a));

         } else {

           if (label_index == -1)

             throw FormatError("Label map not found");

           typename std::map<std::string, Arc>::iterator it =

             _arc_index.find(tokens[label_index]);

           if (it == _arc_index.end()) {

             std::ostringstream msg;

             msg << "Arc with label not found: " << tokens[label_index];

             throw FormatError(msg.str());

           }

           a = it->second;

         }

         for (int i = 0; i < static_cast<int>(_arc_maps.size()); ++i) {

           _arc_maps[i].second->set(a, tokens[map_index[i]]);

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readAttributes() {

       std::set<std::string> read_attr;

       char c;

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::string attr, token;

         if (!_reader_bits::readToken(line, attr))

           throw FormatError("Attribute name not found");

         if (!_reader_bits::readToken(line, token))

           throw FormatError("Attribute value not found");

         if (line >> c)

           throw FormatError("Extra character at the end of line");

         {

           std::set<std::string>::iterator it = read_attr.find(attr);

           if (it != read_attr.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of attribute: " << attr;

             throw FormatError(msg.str());

           }

           read_attr.insert(attr);

         }

         {

           typename Attributes::iterator it = _attributes.lower_bound(attr);

           while (it != _attributes.end() && it->first == attr) {

             it->second->set(token);

             ++it;

           }

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

       for (typename Attributes::iterator it = _attributes.begin();

            it != _attributes.end(); ++it) {

         if (read_attr.find(it->first) == read_attr.end()) {

           std::ostringstream msg;

           msg << "Attribute not found: " << it->first;

           throw FormatError(msg.str());

         }

       }

     }

   public:

     /// \name Execution of the Reader

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing

     void run() {

       LEMON_ASSERT(_is != 0, "This reader assigned to an other reader");

       bool nodes_done = _skip_nodes;

       bool arcs_done = _skip_arcs;

       bool attributes_done = false;

       line_num = 0;

       readLine();

       skipSection();

       while (readSuccess()) {

         try {

           char c;

           std::string section, caption;

           line >> c;

           _reader_bits::readToken(line, section);

           _reader_bits::readToken(line, caption);

           if (line >> c)

             throw FormatError("Extra character at the end of line");

           if (section == "nodes" && !nodes_done) {

             if (_nodes_caption.empty() || _nodes_caption == caption) {

               readNodes();

               nodes_done = true;

             }

           } else if ((section == "arcs" || section == "edges") &&

                      !arcs_done) {

             if (_arcs_caption.empty() || _arcs_caption == caption) {

               readArcs();

               arcs_done = true;

             }

           } else if (section == "attributes" && !attributes_done) {

             if (_attributes_caption.empty() || _attributes_caption == caption) {

               readAttributes();

               attributes_done = true;

             }

           } else {

             readLine();

             skipSection();

           }

         } catch (FormatError& error) {

           error.line(line_num);

           error.file(_filename);

           throw;

         }

       }

       if (!nodes_done) {

         throw FormatError("Section @nodes not found");

       }

       if (!arcs_done) {

         throw FormatError("Section @arcs not found");

       }

       if (!attributes_done && !_attributes.empty()) {

         throw FormatError("Section @attributes not found");

       }

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref DigraphReader class

   ///

   /// This function just returns a \ref DigraphReader class.

   ///

   /// With this function a digraph can be read from an 

   /// \ref lgf-format "LGF" file or input stream with several maps and

   /// attributes. For example, there is network flow problem on a

   /// digraph, i.e. a digraph with a \e capacity map on the arcs and

   /// \e source and \e target nodes. This digraph can be read with the

   /// following code:

   ///

   ///\code

   ///ListDigraph digraph;

   ///ListDigraph::ArcMap<int> cm(digraph);

   ///ListDigraph::Node src, trg;

   ///digraphReader(digraph, std::cin).

   ///  arcMap("capacity", cap).

   ///  node("source", src).

   ///  node("target", trg).

   ///  run();

   ///\endcode

   ///

   /// For a complete documentation, please see the \ref DigraphReader

   /// class documentation.

   /// \warning Don't forget to put the \ref DigraphReader::run() "run()"

   /// to the end of the parameter list.

   /// \relates DigraphReader

   /// \sa digraphReader(TDGR& digraph, const std::string& fn)

   /// \sa digraphReader(TDGR& digraph, const char* fn)

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, std::istream& is) {

     DigraphReader<TDGR> tmp(digraph, is);

     return tmp;

   }

   /// \brief Return a \ref DigraphReader class

   ///

   /// This function just returns a \ref DigraphReader class.

   /// \relates DigraphReader

   /// \sa digraphReader(TDGR& digraph, std::istream& is)

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, const std::string& fn) {

     DigraphReader<TDGR> tmp(digraph, fn);

     return tmp;

   }

   /// \brief Return a \ref DigraphReader class

   ///

   /// This function just returns a \ref DigraphReader class.

   /// \relates DigraphReader

   /// \sa digraphReader(TDGR& digraph, std::istream& is)

   template <typename TDGR>

   DigraphReader<TDGR> digraphReader(TDGR& digraph, const char* fn) {

     DigraphReader<TDGR> tmp(digraph, fn);

     return tmp;

   }

   template <typename GR>

   class GraphReader;

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, std::istream& is = std::cin);

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, const std::string& fn);

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, const char *fn);

   /// \ingroup lemon_io

   ///

   /// \brief \ref lgf-format "LGF" reader for undirected graphs

   ///

   /// This utility reads an \ref lgf-format "LGF" file.

   ///

   /// It can be used almost the same way as \c DigraphReader.

   /// The only difference is that this class can handle edges and

   /// edge maps as well as arcs and arc maps.

   ///

   /// The columns in the \c \@edges (or \c \@arcs) section are the

   /// edge maps. However, if there are two maps with the same name

   /// prefixed with \c '+' and \c '-', then these can be read into an

   /// arc map.  Similarly, an attribute can be read into an arc, if

   /// it's value is an edge label prefixed with \c '+' or \c '-'.

   template <typename GR>

   class GraphReader {

   public:

     typedef GR Graph;

   private:

     TEMPLATE_GRAPH_TYPEDEFS(GR);

     std::istream* _is;

     bool local_is;

     std::string _filename;

     GR& _graph;

     std::string _nodes_caption;

     std::string _edges_caption;

     std::string _attributes_caption;

     typedef std::map<std::string, Node> NodeIndex;

     NodeIndex _node_index;

     typedef std::map<std::string, Edge> EdgeIndex;

     EdgeIndex _edge_index;

     typedef std::vector<std::pair<std::string,

       _reader_bits::MapStorageBase<Node>*> > NodeMaps;

     NodeMaps _node_maps;

     typedef std::vector<std::pair<std::string,

       _reader_bits::MapStorageBase<Edge>*> > EdgeMaps;

     EdgeMaps _edge_maps;

     typedef std::multimap<std::string, _reader_bits::ValueStorageBase*>

       Attributes;

     Attributes _attributes;

     bool _use_nodes;

     bool _use_edges;

     bool _skip_nodes;

     bool _skip_edges;

     int line_num;

     std::istringstream line;

   public:

     /// \brief Constructor

     ///

     /// Construct an undirected graph reader, which reads from the given

     /// input stream.

     GraphReader(GR& graph, std::istream& is = std::cin)

       : _is(&is), local_is(false), _graph(graph),

         _use_nodes(false), _use_edges(false),

         _skip_nodes(false), _skip_edges(false) {}

     /// \brief Constructor

     ///

     /// Construct an undirected graph reader, which reads from the given

     /// file.

     GraphReader(GR& graph, const std::string& fn)

       : _is(new std::ifstream(fn.c_str())), local_is(true),

         _filename(fn), _graph(graph),

         _use_nodes(false), _use_edges(false),

         _skip_nodes(false), _skip_edges(false) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Constructor

     ///

     /// Construct an undirected graph reader, which reads from the given

     /// file.

     GraphReader(GR& graph, const char* fn)

       : _is(new std::ifstream(fn)), local_is(true),

         _filename(fn), _graph(graph),

         _use_nodes(false), _use_edges(false),

         _skip_nodes(false), _skip_edges(false) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Destructor

     ~GraphReader() {

       for (typename NodeMaps::iterator it = _node_maps.begin();

            it != _node_maps.end(); ++it) {

         delete it->second;

       }

       for (typename EdgeMaps::iterator it = _edge_maps.begin();

            it != _edge_maps.end(); ++it) {

         delete it->second;

       }

       for (typename Attributes::iterator it = _attributes.begin();

            it != _attributes.end(); ++it) {

         delete it->second;

       }

       if (local_is) {

         delete _is;

       }

     }

   private:

     template <typename TGR>

     friend GraphReader<TGR> graphReader(TGR& graph, std::istream& is);

     template <typename TGR>

     friend GraphReader<TGR> graphReader(TGR& graph, const std::string& fn); 

     template <typename TGR>

     friend GraphReader<TGR> graphReader(TGR& graph, const char *fn);

     GraphReader(GraphReader& other)

       : _is(other._is), local_is(other.local_is), _graph(other._graph),

         _use_nodes(other._use_nodes), _use_edges(other._use_edges),

         _skip_nodes(other._skip_nodes), _skip_edges(other._skip_edges) {

       other._is = 0;

       other.local_is = false;

       _node_index.swap(other._node_index);

       _edge_index.swap(other._edge_index);

       _node_maps.swap(other._node_maps);

       _edge_maps.swap(other._edge_maps);

       _attributes.swap(other._attributes);

       _nodes_caption = other._nodes_caption;

       _edges_caption = other._edges_caption;

       _attributes_caption = other._attributes_caption;

     }

     GraphReader& operator=(const GraphReader&);

   public:

     /// \name Reading Rules

     /// @{

     /// \brief Node map reading rule

     ///

     /// Add a node map reading rule to the reader.

     template <typename Map>

     GraphReader& nodeMap(const std::string& caption, Map& map) {

       checkConcept<concepts::WriteMap<Node, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Node>* storage =

         new _reader_bits::MapStorage<Node, Map>(map);

       _node_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Node map reading rule

     ///

     /// Add a node map reading rule with specialized converter to the

     /// reader.

     template <typename Map, typename Converter>

     GraphReader& nodeMap(const std::string& caption, Map& map,

                            const Converter& converter = Converter()) {

       checkConcept<concepts::WriteMap<Node, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Node>* storage =

         new _reader_bits::MapStorage<Node, Map, Converter>(map, converter);

       _node_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Edge map reading rule

     ///

     /// Add an edge map reading rule to the reader.

     template <typename Map>

     GraphReader& edgeMap(const std::string& caption, Map& map) {

       checkConcept<concepts::WriteMap<Edge, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Edge>* storage =

         new _reader_bits::MapStorage<Edge, Map>(map);

       _edge_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Edge map reading rule

     ///

     /// Add an edge map reading rule with specialized converter to the

     /// reader.

     template <typename Map, typename Converter>

     GraphReader& edgeMap(const std::string& caption, Map& map,

                           const Converter& converter = Converter()) {

       checkConcept<concepts::WriteMap<Edge, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Edge>* storage =

         new _reader_bits::MapStorage<Edge, Map, Converter>(map, converter);

       _edge_maps.push_back(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Arc map reading rule

     ///

     /// Add an arc map reading rule to the reader.

     template <typename Map>

     GraphReader& arcMap(const std::string& caption, Map& map) {

       checkConcept<concepts::WriteMap<Arc, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Edge>* forward_storage =

         new _reader_bits::GraphArcMapStorage<Graph, true, Map>(_graph, map);

       _edge_maps.push_back(std::make_pair('+' + caption, forward_storage));

       _reader_bits::MapStorageBase<Edge>* backward_storage =

         new _reader_bits::GraphArcMapStorage<GR, false, Map>(_graph, map);

       _edge_maps.push_back(std::make_pair('-' + caption, backward_storage));

       return *this;

     }

     /// \brief Arc map reading rule

     ///

     /// Add an arc map reading rule with specialized converter to the

     /// reader.

     template <typename Map, typename Converter>

     GraphReader& arcMap(const std::string& caption, Map& map,

                           const Converter& converter = Converter()) {

       checkConcept<concepts::WriteMap<Arc, typename Map::Value>, Map>();

       _reader_bits::MapStorageBase<Edge>* forward_storage =

         new _reader_bits::GraphArcMapStorage<GR, true, Map, Converter>

         (_graph, map, converter);

       _edge_maps.push_back(std::make_pair('+' + caption, forward_storage));

       _reader_bits::MapStorageBase<Edge>* backward_storage =

         new _reader_bits::GraphArcMapStorage<GR, false, Map, Converter>

         (_graph, map, converter);

       _edge_maps.push_back(std::make_pair('-' + caption, backward_storage));

       return *this;

     }

     /// \brief Attribute reading rule

     ///

     /// Add an attribute reading rule to the reader.

     template <typename Value>

     GraphReader& attribute(const std::string& caption, Value& value) {

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Value>(value);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Attribute reading rule

     ///

     /// Add an attribute reading rule with specialized converter to the

     /// reader.

     template <typename Value, typename Converter>

     GraphReader& attribute(const std::string& caption, Value& value,

                              const Converter& converter = Converter()) {

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Value, Converter>(value, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Node reading rule

     ///

     /// Add a node reading rule to reader.

     GraphReader& node(const std::string& caption, Node& node) {

       typedef _reader_bits::MapLookUpConverter<Node> Converter;

       Converter converter(_node_index);

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Node, Converter>(node, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Edge reading rule

     ///

     /// Add an edge reading rule to reader.

     GraphReader& edge(const std::string& caption, Edge& edge) {

       typedef _reader_bits::MapLookUpConverter<Edge> Converter;

       Converter converter(_edge_index);

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Edge, Converter>(edge, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// \brief Arc reading rule

     ///

     /// Add an arc reading rule to reader.

     GraphReader& arc(const std::string& caption, Arc& arc) {

       typedef _reader_bits::GraphArcLookUpConverter<GR> Converter;

       Converter converter(_graph, _edge_index);

       _reader_bits::ValueStorageBase* storage =

         new _reader_bits::ValueStorage<Arc, Converter>(arc, converter);

       _attributes.insert(std::make_pair(caption, storage));

       return *this;

     }

     /// @}

     /// \name Select Section by Name

     /// @{

     /// \brief Set \c \@nodes section to be read

     ///

     /// Set \c \@nodes section to be read.

     GraphReader& nodes(const std::string& caption) {

       _nodes_caption = caption;

       return *this;

     }

     /// \brief Set \c \@edges section to be read

     ///

     /// Set \c \@edges section to be read.

     GraphReader& edges(const std::string& caption) {

       _edges_caption = caption;

       return *this;

     }

     /// \brief Set \c \@attributes section to be read

     ///

     /// Set \c \@attributes section to be read.

     GraphReader& attributes(const std::string& caption) {

       _attributes_caption = caption;

       return *this;

     }

     /// @}

     /// \name Using Previously Constructed Node or Edge Set

     /// @{

     /// \brief Use previously constructed node set

     ///

     /// Use previously constructed node set, and specify the node

     /// label map.

     template <typename Map>

     GraphReader& useNodes(const Map& map) {

       checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_nodes, "Multiple usage of useNodes() member");

       _use_nodes = true;

       _writer_bits::DefaultConverter<typename Map::Value> converter;

       for (NodeIt n(_graph); n != INVALID; ++n) {

         _node_index.insert(std::make_pair(converter(map[n]), n));

       }

       return *this;

     }

     /// \brief Use previously constructed node set

     ///

     /// Use previously constructed node set, and specify the node

     /// label map and a functor which converts the label map values to

     /// \c std::string.

     template <typename Map, typename Converter>

     GraphReader& useNodes(const Map& map,

                             const Converter& converter = Converter()) {

       checkConcept<concepts::ReadMap<Node, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_nodes, "Multiple usage of useNodes() member");

       _use_nodes = true;

       for (NodeIt n(_graph); n != INVALID; ++n) {

         _node_index.insert(std::make_pair(converter(map[n]), n));

       }

       return *this;

     }

     /// \brief Use previously constructed edge set

     ///

     /// Use previously constructed edge set, and specify the edge

     /// label map.

     template <typename Map>

     GraphReader& useEdges(const Map& map) {

       checkConcept<concepts::ReadMap<Edge, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_edges, "Multiple usage of useEdges() member");

       _use_edges = true;

       _writer_bits::DefaultConverter<typename Map::Value> converter;

       for (EdgeIt a(_graph); a != INVALID; ++a) {

         _edge_index.insert(std::make_pair(converter(map[a]), a));

       }

       return *this;

     }

     /// \brief Use previously constructed edge set

     ///

     /// Use previously constructed edge set, and specify the edge

     /// label map and a functor which converts the label map values to

     /// \c std::string.

     template <typename Map, typename Converter>

     GraphReader& useEdges(const Map& map,

                             const Converter& converter = Converter()) {

       checkConcept<concepts::ReadMap<Edge, typename Map::Value>, Map>();

       LEMON_ASSERT(!_use_edges, "Multiple usage of useEdges() member");

       _use_edges = true;

       for (EdgeIt a(_graph); a != INVALID; ++a) {

         _edge_index.insert(std::make_pair(converter(map[a]), a));

       }

       return *this;

     }

     /// \brief Skip the reading of node section

     ///

     /// Omit the reading of the node section. This implies that each node

     /// map reading rule will be abandoned, and the nodes of the graph

     /// will not be constructed, which usually cause that the edge set

     /// could not be read due to lack of node name

     /// could not be read due to lack of node name resolving.

     /// Therefore \c skipEdges() function should also be used, or

     /// \c useNodes() should be used to specify the label of the nodes.

     GraphReader& skipNodes() {

       LEMON_ASSERT(!_skip_nodes, "Skip nodes already set");

       _skip_nodes = true;

       return *this;

     }

     /// \brief Skip the reading of edge section

     ///

     /// Omit the reading of the edge section. This implies that each edge

     /// map reading rule will be abandoned, and the edges of the graph

     /// will not be constructed.

     GraphReader& skipEdges() {

       LEMON_ASSERT(!_skip_edges, "Skip edges already set");

       _skip_edges = true;

       return *this;

     }

     /// @}

   private:

     bool readLine() {

       std::string str;

       while(++line_num, std::getline(*_is, str)) {

         line.clear(); line.str(str);

         char c;

         if (line >> std::ws >> c && c != '#') {

           line.putback(c);

           return true;

         }

       }

       return false;

     }

     bool readSuccess() {

       return static_cast<bool>(*_is);

     }

     void skipSection() {

       char c;

       while (readSuccess() && line >> c && c != '@') {

         readLine();

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readNodes() {

       std::vector<int> map_index(_node_maps.size());

       int map_num, label_index;

       char c;

       if (!readLine() || !(line >> c) || c == '@') {

         if (readSuccess() && line) line.putback(c);

         if (!_node_maps.empty())

           throw FormatError("Cannot find map names");

         return;

       }

       line.putback(c);

       {

         std::map<std::string, int> maps;

         std::string map;

         int index = 0;

         while (_reader_bits::readToken(line, map)) {

           if (maps.find(map) != maps.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of node map: " << map;

             throw FormatError(msg.str());

           }

           maps.insert(std::make_pair(map, index));

           ++index;

         }

         for (int i = 0; i < static_cast<int>(_node_maps.size()); ++i) {

           std::map<std::string, int>::iterator jt =

             maps.find(_node_maps[i].first);

           if (jt == maps.end()) {

             std::ostringstream msg;

             msg << "Map not found: " << _node_maps[i].first;

             throw FormatError(msg.str());

           }

           map_index[i] = jt->second;

         }

         {

           std::map<std::string, int>::iterator jt = maps.find("label");

           if (jt != maps.end()) {

             label_index = jt->second;

           } else {

             label_index = -1;

           }

         }

         map_num = maps.size();

       }

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::vector<std::string> tokens(map_num);

         for (int i = 0; i < map_num; ++i) {

           if (!_reader_bits::readToken(line, tokens[i])) {

             std::ostringstream msg;

             msg << "Column not found (" << i + 1 << ")";

             throw FormatError(msg.str());

           }

         }

         if (line >> std::ws >> c)

           throw FormatError("Extra character at the end of line");

         Node n;

         if (!_use_nodes) {

           n = _graph.addNode();

           if (label_index != -1)

             _node_index.insert(std::make_pair(tokens[label_index], n));

         } else {

           if (label_index == -1)

             throw FormatError("Label map not found");

           typename std::map<std::string, Node>::iterator it =

             _node_index.find(tokens[label_index]);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Node with label not found: " << tokens[label_index];

             throw FormatError(msg.str());

           }

           n = it->second;

         }

         for (int i = 0; i < static_cast<int>(_node_maps.size()); ++i) {

           _node_maps[i].second->set(n, tokens[map_index[i]]);

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readEdges() {

       std::vector<int> map_index(_edge_maps.size());

       int map_num, label_index;

       char c;

       if (!readLine() || !(line >> c) || c == '@') {

         if (readSuccess() && line) line.putback(c);

         if (!_edge_maps.empty())

           throw FormatError("Cannot find map names");

         return;

       }

       line.putback(c);

       {

         std::map<std::string, int> maps;

         std::string map;

         int index = 0;

         while (_reader_bits::readToken(line, map)) {

           if (maps.find(map) != maps.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of edge map: " << map;

             throw FormatError(msg.str());

           }

           maps.insert(std::make_pair(map, index));

           ++index;

         }

         for (int i = 0; i < static_cast<int>(_edge_maps.size()); ++i) {

           std::map<std::string, int>::iterator jt =

             maps.find(_edge_maps[i].first);

           if (jt == maps.end()) {

             std::ostringstream msg;

             msg << "Map not found: " << _edge_maps[i].first;

             throw FormatError(msg.str());

           }

           map_index[i] = jt->second;

         }

         {

           std::map<std::string, int>::iterator jt = maps.find("label");

           if (jt != maps.end()) {

             label_index = jt->second;

           } else {

             label_index = -1;

           }

         }

         map_num = maps.size();

       }

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::string source_token;

         std::string target_token;

         if (!_reader_bits::readToken(line, source_token))

           throw FormatError("Node u not found");

         if (!_reader_bits::readToken(line, target_token))

           throw FormatError("Node v not found");

         std::vector<std::string> tokens(map_num);

         for (int i = 0; i < map_num; ++i) {

           if (!_reader_bits::readToken(line, tokens[i])) {

             std::ostringstream msg;

             msg << "Column not found (" << i + 1 << ")";

             throw FormatError(msg.str());

           }

         }

         if (line >> std::ws >> c)

           throw FormatError("Extra character at the end of line");

         Edge e;

         if (!_use_edges) {

           typename NodeIndex::iterator it;

           it = _node_index.find(source_token);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Item not found: " << source_token;

             throw FormatError(msg.str());

           }

           Node source = it->second;

           it = _node_index.find(target_token);

           if (it == _node_index.end()) {

             std::ostringstream msg;

             msg << "Item not found: " << target_token;

             throw FormatError(msg.str());

           }

           Node target = it->second;

           e = _graph.addEdge(source, target);

           if (label_index != -1)

             _edge_index.insert(std::make_pair(tokens[label_index], e));

         } else {

           if (label_index == -1)

             throw FormatError("Label map not found");

           typename std::map<std::string, Edge>::iterator it =

             _edge_index.find(tokens[label_index]);

           if (it == _edge_index.end()) {

             std::ostringstream msg;

             msg << "Edge with label not found: " << tokens[label_index];

             throw FormatError(msg.str());

           }

           e = it->second;

         }

         for (int i = 0; i < static_cast<int>(_edge_maps.size()); ++i) {

           _edge_maps[i].second->set(e, tokens[map_index[i]]);

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

     void readAttributes() {

       std::set<std::string> read_attr;

       char c;

       while (readLine() && line >> c && c != '@') {

         line.putback(c);

         std::string attr, token;

         if (!_reader_bits::readToken(line, attr))

           throw FormatError("Attribute name not found");

         if (!_reader_bits::readToken(line, token))

           throw FormatError("Attribute value not found");

         if (line >> c)

           throw FormatError("Extra character at the end of line");

         {

           std::set<std::string>::iterator it = read_attr.find(attr);

           if (it != read_attr.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of attribute: " << attr;

             throw FormatError(msg.str());

           }

           read_attr.insert(attr);

         }

         {

           typename Attributes::iterator it = _attributes.lower_bound(attr);

           while (it != _attributes.end() && it->first == attr) {

             it->second->set(token);

             ++it;

           }

         }

       }

       if (readSuccess()) {

         line.putback(c);

       }

       for (typename Attributes::iterator it = _attributes.begin();

            it != _attributes.end(); ++it) {

         if (read_attr.find(it->first) == read_attr.end()) {

           std::ostringstream msg;

           msg << "Attribute not found: " << it->first;

           throw FormatError(msg.str());

         }

       }

     }

   public:

     /// \name Execution of the Reader

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing

     void run() {

       LEMON_ASSERT(_is != 0, "This reader assigned to an other reader");

       bool nodes_done = _skip_nodes;

       bool edges_done = _skip_edges;

       bool attributes_done = false;

       line_num = 0;

       readLine();

       skipSection();

       while (readSuccess()) {

         try {

           char c;

           std::string section, caption;

           line >> c;

           _reader_bits::readToken(line, section);

           _reader_bits::readToken(line, caption);

           if (line >> c)

             throw FormatError("Extra character at the end of line");

           if (section == "nodes" && !nodes_done) {

             if (_nodes_caption.empty() || _nodes_caption == caption) {

               readNodes();

               nodes_done = true;

             }

           } else if ((section == "edges" || section == "arcs") &&

                      !edges_done) {

             if (_edges_caption.empty() || _edges_caption == caption) {

               readEdges();

               edges_done = true;

             }

           } else if (section == "attributes" && !attributes_done) {

             if (_attributes_caption.empty() || _attributes_caption == caption) {

               readAttributes();

               attributes_done = true;

             }

           } else {

             readLine();

             skipSection();

           }

         } catch (FormatError& error) {

           error.line(line_num);

           error.file(_filename);

           throw;

         }

       }

       if (!nodes_done) {

         throw FormatError("Section @nodes not found");

       }

       if (!edges_done) {

         throw FormatError("Section @edges not found");

       }

       if (!attributes_done && !_attributes.empty()) {

         throw FormatError("Section @attributes not found");

       }

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref GraphReader class

   ///

   /// This function just returns a \ref GraphReader class. 

   ///

   /// With this function a graph can be read from an 

   /// \ref lgf-format "LGF" file or input stream with several maps and

   /// attributes. For example, there is weighted matching problem on a

   /// graph, i.e. a graph with a \e weight map on the edges. This

   /// graph can be read with the following code:

   ///

   ///\code

   ///ListGraph graph;

   ///ListGraph::EdgeMap<int> weight(graph);

   ///graphReader(graph, std::cin).

   ///  edgeMap("weight", weight).

   ///  run();

   ///\endcode

   ///

   /// For a complete documentation, please see the \ref GraphReader

   /// class documentation.

   /// \warning Don't forget to put the \ref GraphReader::run() "run()"

   /// to the end of the parameter list.

   /// \relates GraphReader

   /// \sa graphReader(TGR& graph, const std::string& fn)

   /// \sa graphReader(TGR& graph, const char* fn)

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, std::istream& is) {

     GraphReader<TGR> tmp(graph, is);

     return tmp;

   }

   /// \brief Return a \ref GraphReader class

   ///

   /// This function just returns a \ref GraphReader class.

   /// \relates GraphReader

   /// \sa graphReader(TGR& graph, std::istream& is)

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, const std::string& fn) {

     GraphReader<TGR> tmp(graph, fn);

     return tmp;

   }

   /// \brief Return a \ref GraphReader class

   ///

   /// This function just returns a \ref GraphReader class.

   /// \relates GraphReader

   /// \sa graphReader(TGR& graph, std::istream& is)

   template <typename TGR>

   GraphReader<TGR> graphReader(TGR& graph, const char* fn) {

     GraphReader<TGR> tmp(graph, fn);

     return tmp;

   }

   class SectionReader;

   SectionReader sectionReader(std::istream& is);

   SectionReader sectionReader(const std::string& fn);

   SectionReader sectionReader(const char* fn);

   /// \ingroup lemon_io

   ///

   /// \brief Section reader class

   ///

   /// In the \ref lgf-format "LGF" file extra sections can be placed,

   /// which contain any data in arbitrary format. Such sections can be

   /// read with this class. A reading rule can be added to the class

   /// with two different functions. With the \c sectionLines() function a

   /// functor can process the section line-by-line, while with the \c

   /// sectionStream() member the section can be read from an input

   /// stream.

   class SectionReader {

   private:

     std::istream* _is;

     bool local_is;

     std::string _filename;

     typedef std::map<std::string, _reader_bits::Section*> Sections;

     Sections _sections;

     int line_num;

     std::istringstream line;

   public:

     /// \brief Constructor

     ///

     /// Construct a section reader, which reads from the given input

     /// stream.

     SectionReader(std::istream& is)

       : _is(&is), local_is(false) {}

     /// \brief Constructor

     ///

     /// Construct a section reader, which reads from the given file.

     SectionReader(const std::string& fn)

       : _is(new std::ifstream(fn.c_str())), local_is(true),

         _filename(fn) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Constructor

     ///

     /// Construct a section reader, which reads from the given file.

     SectionReader(const char* fn)

       : _is(new std::ifstream(fn)), local_is(true),

         _filename(fn) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Destructor

     ~SectionReader() {

       for (Sections::iterator it = _sections.begin();

            it != _sections.end(); ++it) {

         delete it->second;

       }

       if (local_is) {

         delete _is;

       }

     }

   private:

     friend SectionReader sectionReader(std::istream& is);

     friend SectionReader sectionReader(const std::string& fn);

     friend SectionReader sectionReader(const char* fn);

     SectionReader(SectionReader& other)

       : _is(other._is), local_is(other.local_is) {

       other._is = 0;

       other.local_is = false;

       _sections.swap(other._sections);

     }

     SectionReader& operator=(const SectionReader&);

   public:

     /// \name Section Readers

     /// @{

     /// \brief Add a section processor with line oriented reading

     ///

     /// The first parameter is the type descriptor of the section, the

     /// second is a functor, which takes just one \c std::string

     /// parameter. At the reading process, each line of the section

     /// will be given to the functor object. However, the empty lines

     /// and the comment lines are filtered out, and the leading

     /// whitespaces are trimmed from each processed string.

     ///

     /// For example, let's see a section, which contain several

     /// integers, which should be inserted into a vector.

     ///\code

     ///  @numbers

     ///  12 45 23

     ///  4

     ///  23 6

     ///\endcode

     ///

     /// The functor is implemented as a struct:

     ///\code

     ///  struct NumberSection {

     ///    std::vector<int>& _data;

     ///    NumberSection(std::vector<int>& data) : _data(data) {}

     ///    void operator()(const std::string& line) {

     ///      std::istringstream ls(line);

     ///      int value;

     ///      while (ls >> value) _data.push_back(value);

     ///    }

     ///  };

     ///

     ///  // ...

     ///

     ///  reader.sectionLines("numbers", NumberSection(vec));

     ///\endcode

     template <typename Functor>

     SectionReader& sectionLines(const std::string& type, Functor functor) {

       LEMON_ASSERT(!type.empty(), "Type is empty.");

       LEMON_ASSERT(_sections.find(type) == _sections.end(),

                    "Multiple reading of section.");

       _sections.insert(std::make_pair(type,

         new _reader_bits::LineSection<Functor>(functor)));

       return *this;

     }

     /// \brief Add a section processor with stream oriented reading

     ///

     /// The first parameter is the type of the section, the second is

     /// a functor, which takes an \c std::istream& and an \c int&

     /// parameter, the latter regard to the line number of stream. The

     /// functor can read the input while the section go on, and the

     /// line number should be modified accordingly.

     template <typename Functor>

     SectionReader& sectionStream(const std::string& type, Functor functor) {

       LEMON_ASSERT(!type.empty(), "Type is empty.");

       LEMON_ASSERT(_sections.find(type) == _sections.end(),

                    "Multiple reading of section.");

       _sections.insert(std::make_pair(type,

          new _reader_bits::StreamSection<Functor>(functor)));

       return *this;

     }

     /// @}

   private:

     bool readLine() {

       std::string str;

       while(++line_num, std::getline(*_is, str)) {

         line.clear(); line.str(str);

         char c;

         if (line >> std::ws >> c && c != '#') {

           line.putback(c);

           return true;

         }

       }

       return false;

     }

     bool readSuccess() {

       return static_cast<bool>(*_is);

     }

     void skipSection() {

       char c;

       while (readSuccess() && line >> c && c != '@') {

         readLine();

       }

       if (readSuccess()) {

         line.putback(c);

       }

     }

   public:

     /// \name Execution of the Reader

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing.

     void run() {

       LEMON_ASSERT(_is != 0, "This reader assigned to an other reader");

       std::set<std::string> extra_sections;

       line_num = 0;

       readLine();

       skipSection();

       while (readSuccess()) {

         try {

           char c;

           std::string section, caption;

           line >> c;

           _reader_bits::readToken(line, section);

           _reader_bits::readToken(line, caption);

           if (line >> c)

             throw FormatError("Extra character at the end of line");

           if (extra_sections.find(section) != extra_sections.end()) {

             std::ostringstream msg;

             msg << "Multiple occurence of section: " << section;

             throw FormatError(msg.str());

           }

           Sections::iterator it = _sections.find(section);

           if (it != _sections.end()) {

             extra_sections.insert(section);

             it->second->process(*_is, line_num);

           }

           readLine();

           skipSection();

         } catch (FormatError& error) {

           error.line(line_num);

           error.file(_filename);

           throw;

         }

       }

       for (Sections::iterator it = _sections.begin();

            it != _sections.end(); ++it) {

         if (extra_sections.find(it->first) == extra_sections.end()) {

           std::ostringstream os;

           os << "Cannot find section: " << it->first;

           throw FormatError(os.str());

         }

       }

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref SectionReader class

   ///

   /// This function just returns a \ref SectionReader class.

   ///

   /// Please see SectionReader documentation about the custom section

   /// input.

   ///

   /// \relates SectionReader

   /// \sa sectionReader(const std::string& fn)

   /// \sa sectionReader(const char *fn)

   inline SectionReader sectionReader(std::istream& is) {

     SectionReader tmp(is);

     return tmp;

   }

   /// \brief Return a \ref SectionReader class

   ///

   /// This function just returns a \ref SectionReader class.

   /// \relates SectionReader

   /// \sa sectionReader(std::istream& is)

   inline SectionReader sectionReader(const std::string& fn) {

     SectionReader tmp(fn);

     return tmp;

   }

   /// \brief Return a \ref SectionReader class

   ///

   /// This function just returns a \ref SectionReader class.

   /// \relates SectionReader

   /// \sa sectionReader(std::istream& is)

   inline SectionReader sectionReader(const char* fn) {

     SectionReader tmp(fn);

     return tmp;

   }

   /// \ingroup lemon_io

   ///

   /// \brief Reader for the contents of the \ref lgf-format "LGF" file

   ///

   /// This class can be used to read the sections, the map names and

   /// the attributes from a file. Usually, the LEMON programs know

   /// that, which type of graph, which maps and which attributes

   /// should be read from a file, but in general tools (like glemon)

   /// the contents of an LGF file should be guessed somehow. This class

   /// reads the graph and stores the appropriate information for

   /// reading the graph.

   ///

   ///\code

   /// LgfContents contents("graph.lgf");

   /// contents.run();

   ///

   /// // Does it contain any node section and arc section?

   /// if (contents.nodeSectionNum() == 0 || contents.arcSectionNum()) {

   ///   std::cerr << "Failure, cannot find graph." << std::endl;

   ///   return -1;

   /// }

   /// std::cout << "The name of the default node section: "

   ///           << contents.nodeSection(0) << std::endl;

   /// std::cout << "The number of the arc maps: "

   ///           << contents.arcMaps(0).size() << std::endl;

   /// std::cout << "The name of second arc map: "

   ///           << contents.arcMaps(0)[1] << std::endl;

   ///\endcode

   class LgfContents {

   private:

     std::istream* _is;

     bool local_is;

     std::vector<std::string> _node_sections;

     std::vector<std::string> _edge_sections;

     std::vector<std::string> _attribute_sections;

     std::vector<std::string> _extra_sections;

     std::vector<bool> _arc_sections;

     std::vector<std::vector<std::string> > _node_maps;

     std::vector<std::vector<std::string> > _edge_maps;

     std::vector<std::vector<std::string> > _attributes;

     int line_num;

     std::istringstream line;

   public:

     /// \brief Constructor

     ///

     /// Construct an \e LGF contents reader, which reads from the given

     /// input stream.

     LgfContents(std::istream& is)

       : _is(&is), local_is(false) {}

     /// \brief Constructor

     ///

     /// Construct an \e LGF contents reader, which reads from the given

     /// file.

     LgfContents(const std::string& fn)

       : _is(new std::ifstream(fn.c_str())), local_is(true) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Constructor

     ///

     /// Construct an \e LGF contents reader, which reads from the given

     /// file.

     LgfContents(const char* fn)

       : _is(new std::ifstream(fn)), local_is(true) {

       if (!(*_is)) {

         delete _is;

         throw IoError("Cannot open file", fn);

       }

     }

     /// \brief Destructor

     ~LgfContents() {

       if (local_is) delete _is;

     }

   private:

     LgfContents(const LgfContents&);

     LgfContents& operator=(const LgfContents&);

   public:

     /// \name Node Sections

     /// @{

     /// \brief Gives back the number of node sections in the file.

     ///

     /// Gives back the number of node sections in the file.

     int nodeSectionNum() const {

       return _node_sections.size();

     }

     /// \brief Returns the node section name at the given position.

     ///

     /// Returns the node section name at the given position.

     const std::string& nodeSection(int i) const {

       return _node_sections[i];

     }

     /// \brief Gives back the node maps for the given section.

     ///

     /// Gives back the node maps for the given section.

     const std::vector<std::string>& nodeMapNames(int i) const {

       return _node_maps[i];

     }

     /// @}

     /// \name Arc/Edge Sections

     /// @{

     /// \brief Gives back the number of arc/edge sections in the file.

     ///

     /// Gives back the number of arc/edge sections in the file.

     /// \note It is synonym of \c edgeSectionNum().

     int arcSectionNum() const {

       return _edge_sections.size();

     }

     /// \brief Returns the arc/edge section name at the given position.

     ///

     /// Returns the arc/edge section name at the given position.

     /// \note It is synonym of \c edgeSection().

     const std::string& arcSection(int i) const {

       return _edge_sections[i];

     }

     /// \brief Gives back the arc/edge maps for the given section.

     ///

     /// Gives back the arc/edge maps for the given section.

     /// \note It is synonym of \c edgeMapNames().

     const std::vector<std::string>& arcMapNames(int i) const {

       return _edge_maps[i];

     }

     /// @}

     /// \name Synonyms

     /// @{

     /// \brief Gives back the number of arc/edge sections in the file.

     ///

     /// Gives back the number of arc/edge sections in the file.

     /// \note It is synonym of \c arcSectionNum().

     int edgeSectionNum() const {

       return _edge_sections.size();

     }

     /// \brief Returns the section name at the given position.

     ///

     /// Returns the section name at the given position.

     /// \note It is synonym of \c arcSection().

     const std::string& edgeSection(int i) const {

       return _edge_sections[i];

     }

     /// \brief Gives back the edge maps for the given section.

     ///

     /// Gives back the edge maps for the given section.

     /// \note It is synonym of \c arcMapNames().

     const std::vector<std::string>& edgeMapNames(int i) const {

       return _edge_maps[i];

     }

     /// @}

     /// \name Attribute Sections

     /// @{

     /// \brief Gives back the number of attribute sections in the file.

     ///

     /// Gives back the number of attribute sections in the file.

     int attributeSectionNum() const {

       return _attribute_sections.size();

     }

     /// \brief Returns the attribute section name at the given position.

     ///

     /// Returns the attribute section name at the given position.

     const std::string& attributeSectionNames(int i) const {

       return _attribute_sections[i];

     }

     /// \brief Gives back the attributes for the given section.

     ///

     /// Gives back the attributes for the given section.

     const std::vector<std::string>& attributes(int i) const {

       return _attributes[i];

     }

     /// @}

     /// \name Extra Sections

     /// @{

     /// \brief Gives back the number of extra sections in the file.

     ///

     /// Gives back the number of extra sections in the file.

     int extraSectionNum() const {

       return _extra_sections.size();

     }

     /// \brief Returns the extra section type at the given position.

     ///

     /// Returns the section type at the given position.

     const std::string& extraSection(int i) const {

       return _extra_sections[i];

     }

     /// @}

   private:

     bool readLine() {

       std::string str;

       while(++line_num, std::getline(*_is, str)) {

         line.clear(); line.str(str);

         char c;

         if (line >> std::ws >> c && c != '#') {

           line.putback(c);

           return true;

         }

       }

       return false;

     }