/* -*- 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" writer.

 #ifndef LEMON_LGF_WRITER_H

 #define LEMON_LGF_WRITER_H

 #include <iostream>

 #include <fstream>

 #include <sstream>

 #include <algorithm>

 #include <vector>

 #include <functional>

 #include <lemon/core.h>

 #include <lemon/maps.h>

 #include <lemon/concept_check.h>

 #include <lemon/concepts/maps.h>

 namespace lemon {

   namespace _writer_bits {

     template <typename Value>

     struct DefaultConverter {

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

         std::ostringstream os;

         os << value;

         return os.str();

       }

     };

     template <typename T>

     bool operator<(const T&, const T&) {

       throw FormatError("Label map is not comparable");

     }

     template <typename _Map>

     class MapLess {

     public:

       typedef _Map Map;

       typedef typename Map::Key Item;

     private:

       const Map& _map;

     public:

       MapLess(const Map& map) : _map(map) {}

       bool operator()(const Item& left, const Item& right) {

         return _map[left] < _map[right];

       }

     };

     template <typename _Graph, bool _dir, typename _Map>

     class GraphArcMapLess {

     public:

       typedef _Map Map;

       typedef _Graph Graph;

       typedef typename Graph::Edge Item;

     private:

       const Graph& _graph;

       const Map& _map;

     public:

       GraphArcMapLess(const Graph& graph, const Map& map)

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

       bool operator()(const Item& left, const Item& right) {

         return _map[_graph.direct(left, _dir)] <

           _map[_graph.direct(right, _dir)];

       }

     };

     template <typename _Item>

     class MapStorageBase {

     public:

       typedef _Item Item;

     public:

       MapStorageBase() {}

       virtual ~MapStorageBase() {}

       virtual std::string get(const Item& item) = 0;

       virtual void sort(std::vector<Item>&) = 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:

       const Map& _map;

       Converter _converter;

     public:

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

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

       virtual ~MapStorage() {}

       virtual std::string get(const Item& item) {

         return _converter(_map[item]);

       }

       virtual void sort(std::vector<Item>& items) {

         MapLess<Map> less(_map);

         std::sort(items.begin(), items.end(), less);

       }

     };

     template <typename _Graph, bool _dir, typename _Map,

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

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

     public:

       typedef _Map Map;

       typedef _Converter Converter;

       typedef _Graph Graph;

       typedef typename Graph::Edge Item;

       static const bool dir = _dir;

     private:

       const Graph& _graph;

       const Map& _map;

       Converter _converter;

     public:

       GraphArcMapStorage(const Graph& graph, const Map& map,

                          const Converter& converter = Converter())

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

       virtual ~GraphArcMapStorage() {}

       virtual std::string get(const Item& item) {

         return _converter(_map[_graph.direct(item, dir)]);

       }

       virtual void sort(std::vector<Item>& items) {

         GraphArcMapLess<Graph, dir, Map> less(_graph, _map);

         std::sort(items.begin(), items.end(), less);

       }

     };

     class ValueStorageBase {

     public:

       ValueStorageBase() {}

       virtual ~ValueStorageBase() {}

       virtual std::string get() = 0;

     };

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

     class ValueStorage : public ValueStorageBase {

     public:

       typedef _Value Value;

       typedef _Converter Converter;

     private:

       const Value& _value;

       Converter _converter;

     public:

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

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

       virtual std::string get() {

         return _converter(_value);

       }

     };

     template <typename Value>

     struct MapLookUpConverter {

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

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

         : _map(map) {}

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

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

           _map.find(str);

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

           throw FormatError("Item not found");

         }

         return it->second;

       }

     };

     template <typename Graph>

     struct GraphArcLookUpConverter {

       const Graph& _graph;

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

       GraphArcLookUpConverter(const Graph& graph,

                               const std::map<typename Graph::Edge,

                                              std::string>& map)

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

       std::string operator()(const typename Graph::Arc& val) {

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

           ::const_iterator it = _map.find(val);

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

           throw FormatError("Item not found");

         }

         return (_graph.direction(val) ? '+' : '-') + it->second;

       }

     };

     inline bool isWhiteSpace(char c) {

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

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

     }

     inline bool isEscaped(char c) {

       return c == '\\' || c == '\"' || c == '\'' ||

         c == '\a' || c == '\b';

     }

     inline static void writeEscape(std::ostream& os, char c) {

       switch (c) {

       case '\\':

         os << "\\\\";

         return;

       case '\"':

         os << "\\\"";

         return;

       case '\a':

         os << "\\a";

         return;

       case '\b':

         os << "\\b";

         return;

       case '\f':

         os << "\\f";

         return;

       case '\r':

         os << "\\r";

         return;

       case '\n':

         os << "\\n";

         return;

       case '\t':

         os << "\\t";

         return;

       case '\v':

         os << "\\v";

         return;

       default:

         if (c < 0x20) {

           std::ios::fmtflags flags = os.flags();

           os << '\\' << std::oct << static_cast<int>(c);

           os.flags(flags);

         } else {

           os << c;

         }

         return;

       }

     }

     inline bool requireEscape(const std::string& str) {

       if (str.empty() || str[0] == '@') return true;

       std::istringstream is(str);

       char c;

       while (is.get(c)) {

         if (isWhiteSpace(c) || isEscaped(c)) {

           return true;

         }

       }

       return false;

     }

     inline std::ostream& writeToken(std::ostream& os, const std::string& str) {

       if (requireEscape(str)) {

         os << '\"';

         for (std::string::const_iterator it = str.begin();

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

           writeEscape(os, *it);

         }

         os << '\"';

       } else {

         os << str;

       }

       return os;

     }

     class Section {

     public:

       virtual ~Section() {}

       virtual void process(std::ostream& os) = 0;

     };

     template <typename Functor>

     class LineSection : public Section {

     private:

       Functor _functor;

     public:

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

       virtual ~LineSection() {}

       virtual void process(std::ostream& os) {

         std::string line;

         while (!(line = _functor()).empty()) os << line << std::endl;

       }

     };

     template <typename Functor>

     class StreamSection : public Section {

     private:

       Functor _functor;

     public:

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

       virtual ~StreamSection() {}

       virtual void process(std::ostream& os) {

         _functor(os);

       }

     };

   }

   template <typename DGR>

   class DigraphWriter;

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, 

                                    std::ostream& os = std::cout);

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, const std::string& fn);

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, const char* fn);

   /// \ingroup lemon_io

   ///

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

   ///

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

   ///

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

   /// writer object, then various writing rules can be added to the

   /// writer, and eventually the writing is executed with the \c run()

   /// member function. A map writing rule can be added to the writer

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

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

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

   /// is set, it will determine how the value type of the map is written to

   /// the output stream. If the functor is not set, then a default

   /// conversion will be used. The \c attribute(), \c node() and \c

   /// arc() functions are used to add attribute writing rules.

   ///

   ///\code

   /// DigraphWriter<DGR>(digraph, std::cout).

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

   ///   nodeMap("size", size).

   ///   nodeMap("title", title).

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

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

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

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

   ///   run();

   ///\endcode

   ///

   ///

   /// By default, the writer does not write additional captions to the

   /// sections, but they can be give as an optional parameter of

   /// the \c nodes(), \c arcs() or \c

   /// attributes() functions.

   ///

   /// The \c skipNodes() and \c skipArcs() functions forbid the

   /// writing of the sections. If two arc sections should be written

   /// to the output, it can be done in two passes, the first pass

   /// writes the node section and the first arc section, then the

   /// second pass skips the node section and writes just the arc

   /// section to the stream. The output stream can be retrieved with

   /// the \c ostream() function, hence the second pass can append its

   /// output to the output of the first pass.

   template <typename DGR>

   class DigraphWriter {

   public:

     typedef DGR Digraph;

     TEMPLATE_DIGRAPH_TYPEDEFS(DGR);

   private:

     std::ostream* _os;

     bool local_os;

     const DGR& _digraph;

     std::string _nodes_caption;

     std::string _arcs_caption;

     std::string _attributes_caption;

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

     NodeIndex _node_index;

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

     ArcIndex _arc_index;

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

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

     NodeMaps _node_maps;

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

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

     ArcMaps _arc_maps;

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

       _writer_bits::ValueStorageBase*> > Attributes;

     Attributes _attributes;

     bool _skip_nodes;

     bool _skip_arcs;

   public:

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output stream.

     DigraphWriter(const DGR& digraph, std::ostream& os = std::cout)

       : _os(&os), local_os(false), _digraph(digraph),

         _skip_nodes(false), _skip_arcs(false) {}

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output file.

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

       : _os(new std::ofstream(fn.c_str())), local_os(true), _digraph(digraph),

         _skip_nodes(false), _skip_arcs(false) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output file.

     DigraphWriter(const DGR& digraph, const char* fn)

       : _os(new std::ofstream(fn)), local_os(true), _digraph(digraph),

         _skip_nodes(false), _skip_arcs(false) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Destructor

     ~DigraphWriter() {

       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_os) {

         delete _os;

       }

     }

   private:

     template <typename TDGR>

     friend DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, 

                                              std::ostream& os);

     template <typename TDGR>

     friend DigraphWriter<TDGR> digraphWriter(const TDGR& digraph,

                                              const std::string& fn);

     template <typename TDGR>

     friend DigraphWriter<TDGR> digraphWriter(const TDGR& digraph,

                                              const char *fn);

     DigraphWriter(DigraphWriter& other)

       : _os(other._os), local_os(other.local_os), _digraph(other._digraph),

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

       other._os = 0;

       other.local_os = 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;

     }

     DigraphWriter& operator=(const DigraphWriter&);

   public:

     /// \name Writing Rules

     /// @{

     /// \brief Node map writing rule

     ///

     /// Add a node map writing rule to the writer.

     template <typename Map>

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

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

       _writer_bits::MapStorageBase<Node>* storage =

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

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

       return *this;

     }

     /// \brief Node map writing rule

     ///

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

     /// writer.

     template <typename Map, typename Converter>

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

                            const Converter& converter = Converter()) {

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

       _writer_bits::MapStorageBase<Node>* storage =

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

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

       return *this;

     }

     /// \brief Arc map writing rule

     ///

     /// Add an arc map writing rule to the writer.

     template <typename Map>

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

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

       _writer_bits::MapStorageBase<Arc>* storage =

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

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

       return *this;

     }

     /// \brief Arc map writing rule

     ///

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

     /// writer.

     template <typename Map, typename Converter>

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

                           const Converter& converter = Converter()) {

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

       _writer_bits::MapStorageBase<Arc>* storage =

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

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

       return *this;

     }

     /// \brief Attribute writing rule

     ///

     /// Add an attribute writing rule to the writer.

     template <typename Value>

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

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Attribute writing rule

     ///

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

     /// writer.

     template <typename Value, typename Converter>

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

                              const Converter& converter = Converter()) {

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Node writing rule

     ///

     /// Add a node writing rule to the writer.

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

       typedef _writer_bits::MapLookUpConverter<Node> Converter;

       Converter converter(_node_index);

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Arc writing rule

     ///

     /// Add an arc writing rule to writer.

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

       typedef _writer_bits::MapLookUpConverter<Arc> Converter;

       Converter converter(_arc_index);

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \name Section Captions

     /// @{

     /// \brief Add an additional caption to the \c \@nodes section

     ///

     /// Add an additional caption to the \c \@nodes section.

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

       _nodes_caption = caption;

       return *this;

     }

     /// \brief Add an additional caption to the \c \@arcs section

     ///

     /// Add an additional caption to the \c \@arcs section.

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

       _arcs_caption = caption;

       return *this;

     }

     /// \brief Add an additional caption to the \c \@attributes section

     ///

     /// Add an additional caption to the \c \@attributes section.

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

       _attributes_caption = caption;

       return *this;

     }

     /// \name Skipping Section

     /// @{

     /// \brief Skip writing the node set

     ///

     /// The \c \@nodes section will not be written to the stream.

     DigraphWriter& skipNodes() {

       LEMON_ASSERT(!_skip_nodes, "Multiple usage of skipNodes() member");

       _skip_nodes = true;

       return *this;

     }

     /// \brief Skip writing arc set

     ///

     /// The \c \@arcs section will not be written to the stream.

     DigraphWriter& skipArcs() {

       LEMON_ASSERT(!_skip_arcs, "Multiple usage of skipArcs() member");

       _skip_arcs = true;

       return *this;

     }

     /// @}

   private:

     void writeNodes() {

       _writer_bits::MapStorageBase<Node>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       *_os << "@nodes";

       if (!_nodes_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _nodes_caption);

       }

       *_os << std::endl;

       if (label == 0) {

         *_os << "label" << '\t';

       }

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

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

         _writer_bits::writeToken(*_os, it->first) << '\t';

       }

       *_os << std::endl;

       std::vector<Node> nodes;

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

         nodes.push_back(n);

       }

       if (label == 0) {

         IdMap<DGR, Node> id_map(_digraph);

         _writer_bits::MapLess<IdMap<DGR, Node> > id_less(id_map);

         std::sort(nodes.begin(), nodes.end(), id_less);

       } else {

         label->sort(nodes);

       }

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

         Node n = nodes[i];

         if (label == 0) {

           std::ostringstream os;

           os << _digraph.id(n);

           _writer_bits::writeToken(*_os, os.str());

           *_os << '\t';

           _node_index.insert(std::make_pair(n, os.str()));

         }

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

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

           std::string value = it->second->get(n);

           _writer_bits::writeToken(*_os, value);

           if (it->first == "label") {

             _node_index.insert(std::make_pair(n, value));

           }

           *_os << '\t';

         }

         *_os << std::endl;

       }

     }

     void createNodeIndex() {

       _writer_bits::MapStorageBase<Node>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       if (label == 0) {

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

           std::ostringstream os;

           os << _digraph.id(n);

           _node_index.insert(std::make_pair(n, os.str()));

         }

       } else {

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

           std::string value = label->get(n);

           _node_index.insert(std::make_pair(n, value));

         }

       }

     }

     void writeArcs() {

       _writer_bits::MapStorageBase<Arc>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       *_os << "@arcs";

       if (!_arcs_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _arcs_caption);

       }

       *_os << std::endl;

       *_os << '\t' << '\t';

       if (label == 0) {

         *_os << "label" << '\t';

       }

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

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

         _writer_bits::writeToken(*_os, it->first) << '\t';

       }

       *_os << std::endl;

       std::vector<Arc> arcs;

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

         arcs.push_back(n);

       }

       if (label == 0) {

         IdMap<DGR, Arc> id_map(_digraph);

         _writer_bits::MapLess<IdMap<DGR, Arc> > id_less(id_map);

         std::sort(arcs.begin(), arcs.end(), id_less);

       } else {

         label->sort(arcs);

       }

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

         Arc a = arcs[i];

         _writer_bits::writeToken(*_os, _node_index.

                                  find(_digraph.source(a))->second);

         *_os << '\t';

         _writer_bits::writeToken(*_os, _node_index.

                                  find(_digraph.target(a))->second);

         *_os << '\t';

         if (label == 0) {

           std::ostringstream os;

           os << _digraph.id(a);

           _writer_bits::writeToken(*_os, os.str());

           *_os << '\t';

           _arc_index.insert(std::make_pair(a, os.str()));

         }

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

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

           std::string value = it->second->get(a);

           _writer_bits::writeToken(*_os, value);

           if (it->first == "label") {

             _arc_index.insert(std::make_pair(a, value));

           }

           *_os << '\t';

         }

         *_os << std::endl;

       }

     }

     void createArcIndex() {

       _writer_bits::MapStorageBase<Arc>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       if (label == 0) {

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

           std::ostringstream os;

           os << _digraph.id(a);

           _arc_index.insert(std::make_pair(a, os.str()));

         }

       } else {

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

           std::string value = label->get(a);

           _arc_index.insert(std::make_pair(a, value));

         }

       }

     }

     void writeAttributes() {

       if (_attributes.empty()) return;

       *_os << "@attributes";

       if (!_attributes_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _attributes_caption);

       }

       *_os << std::endl;

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

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

         _writer_bits::writeToken(*_os, it->first) << ' ';

         _writer_bits::writeToken(*_os, it->second->get());

         *_os << std::endl;

       }

     }

   public:

     /// \name Execution of the Writer

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing.

     void run() {

       if (!_skip_nodes) {

         writeNodes();

       } else {

         createNodeIndex();

       }

       if (!_skip_arcs) {

         writeArcs();

       } else {

         createArcIndex();

       }

       writeAttributes();

     }

     /// \brief Give back the stream of the writer

     ///

     /// Give back the stream of the writer.

     std::ostream& ostream() {

       return *_os;

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref DigraphWriter class

   ///

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

   ///

   /// With this function a digraph can be write to a file or output

   /// stream in \ref lgf-format "LGF" format with several maps and

   /// attributes. For example, with the following code a network flow

   /// problem can be written to the standard output, i.e. a digraph

   /// with a \e capacity map on the arcs and \e source and \e target

   /// nodes:

   ///

   ///\code

   ///ListDigraph digraph;

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

   ///ListDigraph::Node src, trg;

   ///  // Setting the capacity map and source and target nodes

   ///digraphWriter(digraph, std::cout).

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

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

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

   ///  run();

   ///\endcode

   ///

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

   /// class documentation.

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

   /// to the end of the parameter list.

   /// \relates DigraphWriter

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

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

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, std::ostream& os) {

     DigraphWriter<TDGR> tmp(digraph, os);

     return tmp;

   }

   /// \brief Return a \ref DigraphWriter class

   ///

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

   /// \relates DigraphWriter

   /// \sa digraphWriter(const TDGR& digraph, std::ostream& os)

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, 

                                     const std::string& fn) {

     DigraphWriter<TDGR> tmp(digraph, fn);

     return tmp;

   }

   /// \brief Return a \ref DigraphWriter class

   ///

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

   /// \relates DigraphWriter

   /// \sa digraphWriter(const TDGR& digraph, std::ostream& os)

   template <typename TDGR>

   DigraphWriter<TDGR> digraphWriter(const TDGR& digraph, const char* fn) {

     DigraphWriter<TDGR> tmp(digraph, fn);

     return tmp;

   }

   template <typename GR>

   class GraphWriter;

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, std::ostream& os = std::cout);

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, const std::string& fn);

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, const char* fn);

   /// \ingroup lemon_io

   ///

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

   ///

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

   ///

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

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

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

   ///

   /// The arc maps are written into the file as two columns, the

   /// caption of the columns are the name of the map prefixed with \c

   /// '+' and \c '-'. The arcs are written into the \c \@attributes

   /// section as a \c '+' or a \c '-' prefix (depends on the direction

   /// of the arc) and the label of corresponding edge.

   template <typename GR>

   class GraphWriter {

   public:

     typedef GR Graph;

     TEMPLATE_GRAPH_TYPEDEFS(GR);

   private:

     std::ostream* _os;

     bool local_os;

     const GR& _graph;

     std::string _nodes_caption;

     std::string _edges_caption;

     std::string _attributes_caption;

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

     NodeIndex _node_index;

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

     EdgeIndex _edge_index;

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

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

     NodeMaps _node_maps;

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

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

     EdgeMaps _edge_maps;

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

       _writer_bits::ValueStorageBase*> > Attributes;

     Attributes _attributes;

     bool _skip_nodes;

     bool _skip_edges;

   public:

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output stream.

     GraphWriter(const GR& graph, std::ostream& os = std::cout)

       : _os(&os), local_os(false), _graph(graph),

         _skip_nodes(false), _skip_edges(false) {}

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output file.

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

       : _os(new std::ofstream(fn.c_str())), local_os(true), _graph(graph),

         _skip_nodes(false), _skip_edges(false) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Constructor

     ///

     /// Construct a directed graph writer, which writes to the given

     /// output file.

     GraphWriter(const GR& graph, const char* fn)

       : _os(new std::ofstream(fn)), local_os(true), _graph(graph),

         _skip_nodes(false), _skip_edges(false) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Destructor

     ~GraphWriter() {

       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_os) {

         delete _os;

       }

     }

   private:

     template <typename TGR>

     friend GraphWriter<TGR> graphWriter(const TGR& graph, std::ostream& os);

     template <typename TGR>

     friend GraphWriter<TGR> graphWriter(const TGR& graph, 

                                         const std::string& fn);

     template <typename TGR>

     friend GraphWriter<TGR> graphWriter(const TGR& graph, const char *fn);

     GraphWriter(GraphWriter& other)

       : _os(other._os), local_os(other.local_os), _graph(other._graph),

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

       other._os = 0;

       other.local_os = 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;

     }

     GraphWriter& operator=(const GraphWriter&);

   public:

     /// \name Writing Rules

     /// @{

     /// \brief Node map writing rule

     ///

     /// Add a node map writing rule to the writer.

     template <typename Map>

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

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

       _writer_bits::MapStorageBase<Node>* storage =

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

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

       return *this;

     }

     /// \brief Node map writing rule

     ///

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

     /// writer.

     template <typename Map, typename Converter>

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

                            const Converter& converter = Converter()) {

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

       _writer_bits::MapStorageBase<Node>* storage =

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

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

       return *this;

     }

     /// \brief Edge map writing rule

     ///

     /// Add an edge map writing rule to the writer.

     template <typename Map>

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

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

       _writer_bits::MapStorageBase<Edge>* storage =

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

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

       return *this;

     }

     /// \brief Edge map writing rule

     ///

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

     /// writer.

     template <typename Map, typename Converter>

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

                           const Converter& converter = Converter()) {

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

       _writer_bits::MapStorageBase<Edge>* storage =

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

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

       return *this;

     }

     /// \brief Arc map writing rule

     ///

     /// Add an arc map writing rule to the writer.

     template <typename Map>

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

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

       _writer_bits::MapStorageBase<Edge>* forward_storage =

         new _writer_bits::GraphArcMapStorage<GR, true, Map>(_graph, map);

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

       _writer_bits::MapStorageBase<Edge>* backward_storage =

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

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

       return *this;

     }

     /// \brief Arc map writing rule

     ///

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

     /// writer.

     template <typename Map, typename Converter>

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

                           const Converter& converter = Converter()) {

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

       _writer_bits::MapStorageBase<Edge>* forward_storage =

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

         (_graph, map, converter);

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

       _writer_bits::MapStorageBase<Edge>* backward_storage =

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

         (_graph, map, converter);

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

       return *this;

     }

     /// \brief Attribute writing rule

     ///

     /// Add an attribute writing rule to the writer.

     template <typename Value>

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

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Attribute writing rule

     ///

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

     /// writer.

     template <typename Value, typename Converter>

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

                              const Converter& converter = Converter()) {

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Node writing rule

     ///

     /// Add a node writing rule to the writer.

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

       typedef _writer_bits::MapLookUpConverter<Node> Converter;

       Converter converter(_node_index);

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Edge writing rule

     ///

     /// Add an edge writing rule to writer.

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

       typedef _writer_bits::MapLookUpConverter<Edge> Converter;

       Converter converter(_edge_index);

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \brief Arc writing rule

     ///

     /// Add an arc writing rule to writer.

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

       typedef _writer_bits::GraphArcLookUpConverter<GR> Converter;

       Converter converter(_graph, _edge_index);

       _writer_bits::ValueStorageBase* storage =

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

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

       return *this;

     }

     /// \name Section Captions

     /// @{

     /// \brief Add an additional caption to the \c \@nodes section

     ///

     /// Add an additional caption to the \c \@nodes section.

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

       _nodes_caption = caption;

       return *this;

     }

     /// \brief Add an additional caption to the \c \@arcs section

     ///

     /// Add an additional caption to the \c \@arcs section.

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

       _edges_caption = caption;

       return *this;

     }

     /// \brief Add an additional caption to the \c \@attributes section

     ///

     /// Add an additional caption to the \c \@attributes section.

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

       _attributes_caption = caption;

       return *this;

     }

     /// \name Skipping Section

     /// @{

     /// \brief Skip writing the node set

     ///

     /// The \c \@nodes section will not be written to the stream.

     GraphWriter& skipNodes() {

       LEMON_ASSERT(!_skip_nodes, "Multiple usage of skipNodes() member");

       _skip_nodes = true;

       return *this;

     }

     /// \brief Skip writing edge set

     ///

     /// The \c \@edges section will not be written to the stream.

     GraphWriter& skipEdges() {

       LEMON_ASSERT(!_skip_edges, "Multiple usage of skipEdges() member");

       _skip_edges = true;

       return *this;

     }

     /// @}

   private:

     void writeNodes() {

       _writer_bits::MapStorageBase<Node>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       *_os << "@nodes";

       if (!_nodes_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _nodes_caption);

       }

       *_os << std::endl;

       if (label == 0) {

         *_os << "label" << '\t';

       }

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

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

         _writer_bits::writeToken(*_os, it->first) << '\t';

       }

       *_os << std::endl;

       std::vector<Node> nodes;

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

         nodes.push_back(n);

       }

       if (label == 0) {

         IdMap<GR, Node> id_map(_graph);

         _writer_bits::MapLess<IdMap<GR, Node> > id_less(id_map);

         std::sort(nodes.begin(), nodes.end(), id_less);

       } else {

         label->sort(nodes);

       }

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

         Node n = nodes[i];

         if (label == 0) {

           std::ostringstream os;

           os << _graph.id(n);

           _writer_bits::writeToken(*_os, os.str());

           *_os << '\t';

           _node_index.insert(std::make_pair(n, os.str()));

         }

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

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

           std::string value = it->second->get(n);

           _writer_bits::writeToken(*_os, value);

           if (it->first == "label") {

             _node_index.insert(std::make_pair(n, value));

           }

           *_os << '\t';

         }

         *_os << std::endl;

       }

     }

     void createNodeIndex() {

       _writer_bits::MapStorageBase<Node>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       if (label == 0) {

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

           std::ostringstream os;

           os << _graph.id(n);

           _node_index.insert(std::make_pair(n, os.str()));

         }

       } else {

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

           std::string value = label->get(n);

           _node_index.insert(std::make_pair(n, value));

         }

       }

     }

     void writeEdges() {

       _writer_bits::MapStorageBase<Edge>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       *_os << "@edges";

       if (!_edges_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _edges_caption);

       }

       *_os << std::endl;

       *_os << '\t' << '\t';

       if (label == 0) {

         *_os << "label" << '\t';

       }

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

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

         _writer_bits::writeToken(*_os, it->first) << '\t';

       }

       *_os << std::endl;

       std::vector<Edge> edges;

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

         edges.push_back(n);

       }

       if (label == 0) {

         IdMap<GR, Edge> id_map(_graph);

         _writer_bits::MapLess<IdMap<GR, Edge> > id_less(id_map);

         std::sort(edges.begin(), edges.end(), id_less);

       } else {

         label->sort(edges);

       }

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

         Edge e = edges[i];

         _writer_bits::writeToken(*_os, _node_index.

                                  find(_graph.u(e))->second);

         *_os << '\t';

         _writer_bits::writeToken(*_os, _node_index.

                                  find(_graph.v(e))->second);

         *_os << '\t';

         if (label == 0) {

           std::ostringstream os;

           os << _graph.id(e);

           _writer_bits::writeToken(*_os, os.str());

           *_os << '\t';

           _edge_index.insert(std::make_pair(e, os.str()));

         }

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

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

           std::string value = it->second->get(e);

           _writer_bits::writeToken(*_os, value);

           if (it->first == "label") {

             _edge_index.insert(std::make_pair(e, value));

           }

           *_os << '\t';

         }

         *_os << std::endl;

       }

     }

     void createEdgeIndex() {

       _writer_bits::MapStorageBase<Edge>* label = 0;

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

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

         if (it->first == "label") {

           label = it->second;

           break;

         }

       }

       if (label == 0) {

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

           std::ostringstream os;

           os << _graph.id(e);

           _edge_index.insert(std::make_pair(e, os.str()));

         }

       } else {

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

           std::string value = label->get(e);

           _edge_index.insert(std::make_pair(e, value));

         }

       }

     }

     void writeAttributes() {

       if (_attributes.empty()) return;

       *_os << "@attributes";

       if (!_attributes_caption.empty()) {

         _writer_bits::writeToken(*_os << ' ', _attributes_caption);

       }

       *_os << std::endl;

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

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

         _writer_bits::writeToken(*_os, it->first) << ' ';

         _writer_bits::writeToken(*_os, it->second->get());

         *_os << std::endl;

       }

     }

   public:

     /// \name Execution of the Writer

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing.

     void run() {

       if (!_skip_nodes) {

         writeNodes();

       } else {

         createNodeIndex();

       }

       if (!_skip_edges) {

         writeEdges();

       } else {

         createEdgeIndex();

       }

       writeAttributes();

     }

     /// \brief Give back the stream of the writer

     ///

     /// Give back the stream of the writer

     std::ostream& ostream() {

       return *_os;

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref GraphWriter class

   ///

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

   ///

   /// With this function a graph can be write to a file or output

   /// stream in \ref lgf-format "LGF" format with several maps and

   /// attributes. For example, with the following code a weighted

   /// matching problem can be written to the standard output, i.e. a

   /// graph with a \e weight map on the edges:

   ///

   ///\code

   ///ListGraph graph;

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

   ///  // Setting the weight map

   ///graphWriter(graph, std::cout).

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

   ///  run();

   ///\endcode

   ///

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

   /// class documentation.

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

   /// to the end of the parameter list.

   /// \relates GraphWriter

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

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

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, std::ostream& os) {

     GraphWriter<TGR> tmp(graph, os);

     return tmp;

   }

   /// \brief Return a \ref GraphWriter class

   ///

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

   /// \relates GraphWriter

   /// \sa graphWriter(const TGR& graph, std::ostream& os)

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, const std::string& fn) {

     GraphWriter<TGR> tmp(graph, fn);

     return tmp;

   }

   /// \brief Return a \ref GraphWriter class

   ///

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

   /// \relates GraphWriter

   /// \sa graphWriter(const TGR& graph, std::ostream& os)

   template <typename TGR>

   GraphWriter<TGR> graphWriter(const TGR& graph, const char* fn) {

     GraphWriter<TGR> tmp(graph, fn);

     return tmp;

   }

   class SectionWriter;

   SectionWriter sectionWriter(std::istream& is);

   SectionWriter sectionWriter(const std::string& fn);

   SectionWriter sectionWriter(const char* fn);

   /// \ingroup lemon_io

   ///

   /// \brief Section writer class

   ///

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

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

   /// written with this class. A writing rule can be added to the

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

   /// function a generator can write the section line-by-line, while

   /// with the \c sectionStream() member the section can be written to

   /// an output stream.

   class SectionWriter {

   private:

     std::ostream* _os;

     bool local_os;

     typedef std::vector<std::pair<std::string, _writer_bits::Section*> >

     Sections;

     Sections _sections;

   public:

     /// \brief Constructor

     ///

     /// Construct a section writer, which writes to the given output

     /// stream.

     SectionWriter(std::ostream& os)

       : _os(&os), local_os(false) {}

     /// \brief Constructor

     ///

     /// Construct a section writer, which writes into the given file.

     SectionWriter(const std::string& fn)

       : _os(new std::ofstream(fn.c_str())), local_os(true) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Constructor

     ///

     /// Construct a section writer, which writes into the given file.

     SectionWriter(const char* fn)

       : _os(new std::ofstream(fn)), local_os(true) {

       if (!(*_os)) {

         delete _os;

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

       }

     }

     /// \brief Destructor

     ~SectionWriter() {

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

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

         delete it->second;

       }

       if (local_os) {

         delete _os;

       }

     }

   private:

     friend SectionWriter sectionWriter(std::ostream& os);

     friend SectionWriter sectionWriter(const std::string& fn);

     friend SectionWriter sectionWriter(const char* fn);

     SectionWriter(SectionWriter& other)

       : _os(other._os), local_os(other.local_os) {

       other._os = 0;

       other.local_os = false;

       _sections.swap(other._sections);

     }

     SectionWriter& operator=(const SectionWriter&);

   public:

     /// \name Section Writers

     /// @{

     /// \brief Add a section writer with line oriented writing

     ///

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

     /// second is a generator with std::string values. At the writing

     /// process, the returned \c std::string will be written into the

     /// output file until it is an empty string.

     ///

     /// For example, an integer vector is written into a section.

     ///\code

     ///  @numbers

     ///  12 45 23 78

     ///  4 28 38 28

     ///  23 6 16

     ///\endcode

     ///

     /// The generator is implemented as a struct.

     ///\code

     ///  struct NumberSection {

     ///    std::vector<int>::const_iterator _it, _end;

     ///    NumberSection(const std::vector<int>& data)

     ///      : _it(data.begin()), _end(data.end()) {}

     ///    std::string operator()() {

     ///      int rem_in_line = 4;

     ///      std::ostringstream ls;

     ///      while (rem_in_line > 0 && _it != _end) {

     ///        ls << *(_it++) << ' ';

     ///        --rem_in_line;

     ///      }

     ///      return ls.str();

     ///    }

     ///  };

     ///

     ///  // ...

     ///

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

     ///\endcode

     template <typename Functor>

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

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

       _sections.push_back(std::make_pair(type,

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

       return *this;

     }

     /// \brief Add a section writer with stream oriented writing

     ///

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

     /// a functor, which takes a \c std::ostream& parameter. The

     /// functor writes the section to the output stream.

     /// \warning The last line must be closed with end-line character.

     template <typename Functor>

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

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

       _sections.push_back(std::make_pair(type,

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

       return *this;

     }

     /// @}

   public:

     /// \name Execution of the Writer

     /// @{

     /// \brief Start the batch processing

     ///

     /// This function starts the batch processing.

     void run() {

       LEMON_ASSERT(_os != 0, "This writer is assigned to an other writer");

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

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

         (*_os) << '@' << it->first << std::endl;

         it->second->process(*_os);

       }

     }

     /// \brief Give back the stream of the writer

     ///

     /// Returns the stream of the writer

     std::ostream& ostream() {

       return *_os;

     }

     /// @}

   };

   /// \ingroup lemon_io

   ///

   /// \brief Return a \ref SectionWriter class

   ///

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

   ///

   /// Please see SectionWriter documentation about the custom section

   /// output.

   ///

   /// \relates SectionWriter

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

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

   inline SectionWriter sectionWriter(std::ostream& os) {

     SectionWriter tmp(os);

     return tmp;

   }

   /// \brief Return a \ref SectionWriter class

   ///

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

   /// \relates SectionWriter

   /// \sa sectionWriter(std::ostream& os)

   inline SectionWriter sectionWriter(const std::string& fn) {

     SectionWriter tmp(fn);

     return tmp;

   }

   /// \brief Return a \ref SectionWriter class

   ///

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

   /// \relates SectionWriter

   /// \sa sectionWriter(std::ostream& os)

   inline SectionWriter sectionWriter(const char* fn) {

     SectionWriter tmp(fn);

     return tmp;

   }

 }

 #endif