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

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

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

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

   ///   run();

   ///   run();

   ///\endcode

   ///\endcode

   ///

   ///

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

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

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

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

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

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

   ///

   ///

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

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

   private:

   private:

     template <typename TDGR>

     template <typename TDGR>

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

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

     template <typename TDGR>

     template <typename TDGR>

                                              const std::string& fn);

                                              const std::string& fn);

     template <typename TDGR>

     template <typename TDGR>

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

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

     DigraphReader(DigraphReader& other)

     DigraphReader(DigraphReader& other)

     }

     }

     /// @}

     /// @}

   };

   };

   /// \ingroup lemon_io

   /// \ingroup lemon_io

   ///

   ///

   /// \brief Return a \ref DigraphReader class

   /// \brief Return a \ref DigraphReader class

   ///

   ///

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

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

   ///

   ///

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

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

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

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

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

   /// 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

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

   /// following code:

   /// following code:

     return tmp;

     return tmp;

   }

   }

   template <typename GR>

   template <typename GR>

   class GraphReader;

   class GraphReader;

   template <typename TGR>

   template <typename TGR>

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

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

   template <typename TGR>

   template <typename TGR>

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

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

   template <typename TGR>

   template <typename TGR>

   private:

   private:

     template <typename TGR>

     template <typename TGR>

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

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

     template <typename TGR>

     template <typename TGR>

     template <typename TGR>

     template <typename TGR>

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

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

     GraphReader(GraphReader& other)

     GraphReader(GraphReader& other)

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

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

   /// \ingroup lemon_io

   /// \ingroup lemon_io

   ///

   ///

   /// \brief Return a \ref GraphReader class

   /// \brief Return a \ref GraphReader class

   ///

   ///

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

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

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

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

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

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

   ///

   ///

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

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

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

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

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

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

     /// whitespaces are trimmed from each processed string.

     /// whitespaces are trimmed from each processed string.

     ///

     ///

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

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

     ///\code

     ///\code

     ///  @numbers

     ///  @numbers

     ///  12 45 23

     ///  12 45 23

     ///  4

     ///  4