diff --git a/demo/lgf_demo.cc b/demo/lgf_demo.cc
--- a/demo/lgf_demo.cc
+++ b/demo/lgf_demo.cc
@@ -44,7 +44,7 @@
   SmartDigraph::Node s, t;
 
   try {
-    digraphReader("digraph.lgf", g). // read the directed graph into g
+    digraphReader(g, "digraph.lgf"). // read the directed graph into g
       arcMap("capacity", cap).       // read the 'capacity' arc map into cap
       node("source", s).             // read 'source' node to s
       node("target", t).             // read 'target' node to t
@@ -60,7 +60,7 @@
 
   std::cout << "We can write it to the standard output:" << std::endl;
 
-  digraphWriter(std::cout, g).     // write g to the standard output
+  digraphWriter(g).                // write g to the standard output
     arcMap("capacity", cap).       // write cap into 'capacity'
     node("source", s).             // write s to 'source'
     node("target", t).             // write t to 'target'
diff --git a/lemon/lgf_reader.h b/lemon/lgf_reader.h
--- a/lemon/lgf_reader.h
+++ b/lemon/lgf_reader.h
@@ -390,13 +390,14 @@
   class DigraphReader;
 
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(std::istream& is, Digraph& digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph,
+                                       std::istream& is = std::cin);
 
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(const std::string& fn, Digraph& digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph, const std::string& fn);
 
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(const char *fn, Digraph& digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph, const char *fn);
 
   /// \ingroup lemon_io
   ///
@@ -419,7 +420,7 @@
   /// rules.
   ///
   ///\code
-  /// DigraphReader<Digraph>(std::cin, digraph).
+  /// DigraphReader<Digraph>(digraph, std::cin).
   ///   nodeMap("coordinates", coord_map).
   ///   arcMap("capacity", cap_map).
   ///   node("source", src).
@@ -499,7 +500,7 @@
     ///
     /// Construct a directed graph reader, which reads from the given
     /// input stream.
-    DigraphReader(std::istream& is, Digraph& digraph)
+    DigraphReader(Digraph& 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) {}
@@ -508,7 +509,7 @@
     ///
     /// Construct a directed graph reader, which reads from the given
     /// file.
-    DigraphReader(const std::string& fn, Digraph& digraph)
+    DigraphReader(Digraph& digraph, const std::string& fn)
       : _is(new std::ifstream(fn.c_str())), local_is(true), _digraph(digraph),
         _use_nodes(false), _use_arcs(false),
         _skip_nodes(false), _skip_arcs(false) {}
@@ -517,7 +518,7 @@
     ///
     /// Construct a directed graph reader, which reads from the given
     /// file.
-    DigraphReader(const char* fn, Digraph& digraph)
+    DigraphReader(Digraph& digraph, const char* fn)
       : _is(new std::ifstream(fn)), local_is(true), _digraph(digraph),
         _use_nodes(false), _use_arcs(false),
         _skip_nodes(false), _skip_arcs(false) {}
@@ -547,12 +548,12 @@
 
   private:
 
-    friend DigraphReader<Digraph> digraphReader<>(std::istream& is,
-                                                  Digraph& digraph);
-    friend DigraphReader<Digraph> digraphReader<>(const std::string& fn,
-                                                  Digraph& digraph);
-    friend DigraphReader<Digraph> digraphReader<>(const char *fn,
-                                                  Digraph& digraph);
+    friend DigraphReader<Digraph> digraphReader<>(Digraph& digraph,
+                                                  std::istream& is);
+    friend DigraphReader<Digraph> digraphReader<>(Digraph& digraph,
+                                                  const std::string& fn);
+    friend DigraphReader<Digraph> digraphReader<>(Digraph& digraph,
+                                                  const char *fn);
 
     DigraphReader(DigraphReader& other)
       : _is(other._is), local_is(other.local_is), _digraph(other._digraph),
@@ -1180,8 +1181,9 @@
   /// This function just returns a \ref DigraphReader class.
   /// \relates DigraphReader
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(std::istream& is, Digraph& digraph) {
-    DigraphReader<Digraph> tmp(is, digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph,
+                                       std::istream& is = std::cin) {
+    DigraphReader<Digraph> tmp(digraph, is);
     return tmp;
   }
 
@@ -1190,9 +1192,9 @@
   /// This function just returns a \ref DigraphReader class.
   /// \relates DigraphReader
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(const std::string& fn,
-                                       Digraph& digraph) {
-    DigraphReader<Digraph> tmp(fn, digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph,
+                                       const std::string& fn) {
+    DigraphReader<Digraph> tmp(digraph, fn);
     return tmp;
   }
 
@@ -1201,8 +1203,8 @@
   /// This function just returns a \ref DigraphReader class.
   /// \relates DigraphReader
   template <typename Digraph>
-  DigraphReader<Digraph> digraphReader(const char* fn, Digraph& digraph) {
-    DigraphReader<Digraph> tmp(fn, digraph);
+  DigraphReader<Digraph> digraphReader(Digraph& digraph, const char* fn) {
+    DigraphReader<Digraph> tmp(digraph, fn);
     return tmp;
   }
 
@@ -1210,13 +1212,14 @@
   class GraphReader;
 
   template <typename Graph>
-  GraphReader<Graph> graphReader(std::istream& is, Graph& graph);
+  GraphReader<Graph> graphReader(Graph& graph,
+                                 std::istream& is = std::cin);
 
   template <typename Graph>
-  GraphReader<Graph> graphReader(const std::string& fn, Graph& graph);
+  GraphReader<Graph> graphReader(Graph& graph, const std::string& fn);
 
   template <typename Graph>
-  GraphReader<Graph> graphReader(const char *fn, Graph& graph);
+  GraphReader<Graph> graphReader(Graph& graph, const char *fn);
 
   /// \ingroup lemon_io
   ///
@@ -1283,7 +1286,7 @@
     ///
     /// Construct an undirected graph reader, which reads from the given
     /// input stream.
-    GraphReader(std::istream& is, Graph& graph)
+    GraphReader(Graph& 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) {}
@@ -1292,7 +1295,7 @@
     ///
     /// Construct an undirected graph reader, which reads from the given
     /// file.
-    GraphReader(const std::string& fn, Graph& graph)
+    GraphReader(Graph& graph, const std::string& fn)
       : _is(new std::ifstream(fn.c_str())), local_is(true), _graph(graph),
         _use_nodes(false), _use_edges(false),
         _skip_nodes(false), _skip_edges(false) {}
@@ -1301,7 +1304,7 @@
     ///
     /// Construct an undirected graph reader, which reads from the given
     /// file.
-    GraphReader(const char* fn, Graph& graph)
+    GraphReader(Graph& graph, const char* fn)
       : _is(new std::ifstream(fn)), local_is(true), _graph(graph),
         _use_nodes(false), _use_edges(false),
         _skip_nodes(false), _skip_edges(false) {}
@@ -1330,10 +1333,10 @@
     }
 
   private:
-    friend GraphReader<Graph> graphReader<>(std::istream& is, Graph& graph);
-    friend GraphReader<Graph> graphReader<>(const std::string& fn,
-                                            Graph& graph);
-    friend GraphReader<Graph> graphReader<>(const char *fn, Graph& graph);
+    friend GraphReader<Graph> graphReader<>(Graph& graph, std::istream& is);
+    friend GraphReader<Graph> graphReader<>(Graph& graph,
+                                            const std::string& fn);
+    friend GraphReader<Graph> graphReader<>(Graph& graph, const char *fn);
 
     GraphReader(GraphReader& other)
       : _is(other._is), local_is(other.local_is), _graph(other._graph),
@@ -2006,8 +2009,8 @@
   /// This function just returns a \ref GraphReader class.
   /// \relates GraphReader
   template <typename Graph>
-  GraphReader<Graph> graphReader(std::istream& is, Graph& graph) {
-    GraphReader<Graph> tmp(is, graph);
+  GraphReader<Graph> graphReader(Graph& graph, std::istream& is = std::cin) {
+    GraphReader<Graph> tmp(graph, is);
     return tmp;
   }
 
@@ -2016,9 +2019,8 @@
   /// This function just returns a \ref GraphReader class.
   /// \relates GraphReader
   template <typename Graph>
-  GraphReader<Graph> graphReader(const std::string& fn,
-                                       Graph& graph) {
-    GraphReader<Graph> tmp(fn, graph);
+  GraphReader<Graph> graphReader(Graph& graph, const std::string& fn) {
+    GraphReader<Graph> tmp(graph, fn);
     return tmp;
   }
 
@@ -2027,8 +2029,8 @@
   /// This function just returns a \ref GraphReader class.
   /// \relates GraphReader
   template <typename Graph>
-  GraphReader<Graph> graphReader(const char* fn, Graph& graph) {
-    GraphReader<Graph> tmp(fn, graph);
+  GraphReader<Graph> graphReader(Graph& graph, const char* fn) {
+    GraphReader<Graph> tmp(graph, fn);
     return tmp;
   }
 
diff --git a/lemon/lgf_writer.h b/lemon/lgf_writer.h
--- a/lemon/lgf_writer.h
+++ b/lemon/lgf_writer.h
@@ -352,16 +352,16 @@
   class DigraphWriter;
 
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(std::ostream& os,
-                                       const Digraph& digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       std::ostream& os = std::cout);
 
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(const std::string& fn,
-                                       const Digraph& digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       const std::string& fn);
 
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(const char *fn,
-                                       const Digraph& digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       const char *fn);
 
   /// \ingroup lemon_io
   ///
@@ -382,7 +382,7 @@
   /// arc() functions are used to add attribute writing rules.
   ///
   ///\code
-  /// DigraphWriter<Digraph>(std::cout, digraph).
+  /// DigraphWriter<Digraph>(digraph, std::cout).
   ///   nodeMap("coordinates", coord_map).
   ///   nodeMap("size", size).
   ///   nodeMap("title", title).
@@ -452,15 +452,15 @@
     ///
     /// Construct a directed graph writer, which writes to the given
     /// output stream.
-    DigraphWriter(std::ostream& is, const Digraph& digraph)
-      : _os(&is), local_os(false), _digraph(digraph),
+    DigraphWriter(const Digraph& 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 std::string& fn, const Digraph& digraph)
+    DigraphWriter(const Digraph& digraph, const std::string& fn)
       : _os(new std::ofstream(fn.c_str())), local_os(true), _digraph(digraph),
         _skip_nodes(false), _skip_arcs(false) {}
 
@@ -468,7 +468,7 @@
     ///
     /// Construct a directed graph writer, which writes to the given
     /// output file.
-    DigraphWriter(const char* fn, const Digraph& digraph)
+    DigraphWriter(const Digraph& digraph, const char* fn)
       : _os(new std::ofstream(fn)), local_os(true), _digraph(digraph),
         _skip_nodes(false), _skip_arcs(false) {}
 
@@ -496,12 +496,12 @@
 
   private:
 
-    friend DigraphWriter<Digraph> digraphWriter<>(std::ostream& os,
-                                                  const Digraph& digraph);
-    friend DigraphWriter<Digraph> digraphWriter<>(const std::string& fn,
-                                                  const Digraph& digraph);
-    friend DigraphWriter<Digraph> digraphWriter<>(const char *fn,
-                                                  const Digraph& digraph);
+    friend DigraphWriter<Digraph> digraphWriter<>(const Digraph& digraph,
+                                                  std::ostream& os);
+    friend DigraphWriter<Digraph> digraphWriter<>(const Digraph& digraph,
+                                                  const std::string& fn);
+    friend DigraphWriter<Digraph> digraphWriter<>(const Digraph& digraph,
+                                                  const char *fn);
 
     DigraphWriter(DigraphWriter& other)
       : _os(other._os), local_os(other.local_os), _digraph(other._digraph),
@@ -908,9 +908,9 @@
   /// This function just returns a \ref DigraphWriter class.
   /// \relates DigraphWriter
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(std::ostream& os,
-                                       const Digraph& digraph) {
-    DigraphWriter<Digraph> tmp(os, digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       std::ostream& os = std::cout) {
+    DigraphWriter<Digraph> tmp(digraph, os);
     return tmp;
   }
 
@@ -919,9 +919,9 @@
   /// This function just returns a \ref DigraphWriter class.
   /// \relates DigraphWriter
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(const std::string& fn,
-                                       const Digraph& digraph) {
-    DigraphWriter<Digraph> tmp(fn, digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       const std::string& fn) {
+    DigraphWriter<Digraph> tmp(digraph, fn);
     return tmp;
   }
 
@@ -930,9 +930,9 @@
   /// This function just returns a \ref DigraphWriter class.
   /// \relates DigraphWriter
   template <typename Digraph>
-  DigraphWriter<Digraph> digraphWriter(const char* fn,
-                                       const Digraph& digraph) {
-    DigraphWriter<Digraph> tmp(fn, digraph);
+  DigraphWriter<Digraph> digraphWriter(const Digraph& digraph,
+                                       const char* fn) {
+    DigraphWriter<Digraph> tmp(digraph, fn);
     return tmp;
   }
 
@@ -940,13 +940,14 @@
   class GraphWriter;
 
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(std::ostream& os, const Graph& graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph,
+                                 std::ostream& os = std::cout);
 
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(const std::string& fn, const Graph& graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph, const std::string& fn);
 
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(const char *fn, const Graph& graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph, const char *fn);
 
   /// \ingroup lemon_io
   ///
@@ -1008,15 +1009,15 @@
     ///
     /// Construct a directed graph writer, which writes to the given
     /// output stream.
-    GraphWriter(std::ostream& is, const Graph& graph)
-      : _os(&is), local_os(false), _graph(graph),
+    GraphWriter(const Graph& 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 std::string& fn, const Graph& graph)
+    GraphWriter(const Graph& graph, const std::string& fn)
       : _os(new std::ofstream(fn.c_str())), local_os(true), _graph(graph),
         _skip_nodes(false), _skip_edges(false) {}
 
@@ -1024,7 +1025,7 @@
     ///
     /// Construct a directed graph writer, which writes to the given
     /// output file.
-    GraphWriter(const char* fn, const Graph& graph)
+    GraphWriter(const Graph& graph, const char* fn)
       : _os(new std::ofstream(fn)), local_os(true), _graph(graph),
         _skip_nodes(false), _skip_edges(false) {}
 
@@ -1052,12 +1053,12 @@
 
   private:
 
-    friend GraphWriter<Graph> graphWriter<>(std::ostream& os,
-                                            const Graph& graph);
-    friend GraphWriter<Graph> graphWriter<>(const std::string& fn,
-                                            const Graph& graph);
-    friend GraphWriter<Graph> graphWriter<>(const char *fn,
-                                            const Graph& graph);
+    friend GraphWriter<Graph> graphWriter<>(const Graph& graph,
+                                            std::ostream& os);
+    friend GraphWriter<Graph> graphWriter<>(const Graph& graph,
+                                            const std::string& fn);
+    friend GraphWriter<Graph> graphWriter<>(const Graph& graph,
+                                            const char *fn);
 
     GraphWriter(GraphWriter& other)
       : _os(other._os), local_os(other.local_os), _graph(other._graph),
@@ -1510,8 +1511,9 @@
   /// This function just returns a \ref GraphWriter class.
   /// \relates GraphWriter
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(std::ostream& os, const Graph& graph) {
-    GraphWriter<Graph> tmp(os, graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph,
+                                 std::ostream& os = std::cout) {
+    GraphWriter<Graph> tmp(graph, os);
     return tmp;
   }
 
@@ -1520,8 +1522,8 @@
   /// This function just returns a \ref GraphWriter class.
   /// \relates GraphWriter
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(const std::string& fn, const Graph& graph) {
-    GraphWriter<Graph> tmp(fn, graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph, const std::string& fn) {
+    GraphWriter<Graph> tmp(graph, fn);
     return tmp;
   }
 
@@ -1530,8 +1532,8 @@
   /// This function just returns a \ref GraphWriter class.
   /// \relates GraphWriter
   template <typename Graph>
-  GraphWriter<Graph> graphWriter(const char* fn, const Graph& graph) {
-    GraphWriter<Graph> tmp(fn, graph);
+  GraphWriter<Graph> graphWriter(const Graph& graph, const char* fn) {
+    GraphWriter<Graph> tmp(graph, fn);
     return tmp;
   }
 
diff --git a/test/bfs_test.cc b/test/bfs_test.cc
--- a/test/bfs_test.cc
+++ b/test/bfs_test.cc
@@ -144,7 +144,7 @@
   Node s, t;
 
   std::istringstream input(test_lgf);
-  digraphReader(input, G).
+  digraphReader(G, input).
     node("source", s).
     node("target", t).
     run();
diff --git a/test/dfs_test.cc b/test/dfs_test.cc
--- a/test/dfs_test.cc
+++ b/test/dfs_test.cc
@@ -146,7 +146,7 @@
   Node s, t;
 
   std::istringstream input(test_lgf);
-  digraphReader(input, G).
+  digraphReader(G, input).
     node("source", s).
     node("target", t).
     run();
diff --git a/test/dijkstra_test.cc b/test/dijkstra_test.cc
--- a/test/dijkstra_test.cc
+++ b/test/dijkstra_test.cc
@@ -142,7 +142,7 @@
   LengthMap length(G);
 
   std::istringstream input(test_lgf);
-  digraphReader(input, G).
+  digraphReader(G, input).
     arcMap("length", length).
     node("source", s).
     node("target", t).
diff --git a/test/heap_test.cc b/test/heap_test.cc
--- a/test/heap_test.cc
+++ b/test/heap_test.cc
@@ -167,7 +167,7 @@
   Node source;
 
   std::istringstream input(test_lgf);
-  digraphReader(input, digraph).
+  digraphReader(digraph, input).
     arcMap("capacity", length).
     node("source", source).
     run();