I have written a custom iterator based on boost::iterator_facade, and I'm trying to use this with the std::partial_sort_copy algorithm. However, when compiling with g++ I get an error message saying that there is no matching function for a call to counting_iterator(Vertex<3>&). The way I interpret this is that my code is trying to construct a Vertex_Iterator from a Vertex object, but that was not my intenton. Is there something obvious that I have missed in my definition of Vertex_Iterator, which should be a bidirectional iterator? A Vertex_Iterator iterates over the vertices of a mesh, and therefore it needs a pointer to the mesh in question. Does an iterator which returns a Vertex<3>& when dereferenced need a constructor which takes only a Vertex<3>& argument? If so, how can I supply it with the pointer to its parent mesh? I hope that some of this makes sense. ////////////////////////////////////////////// // Some typedefs from the parent class 'Mesh': ////////////////////////////////////////////// class Mesh { public: class Vertex_Iterator; //... private: friend class Vertex_Iterator; typedef boost::property< boost::vertex_root_t, Vertex<3> > Vertex_Property; typedef boost::adjacency_list < boost::vecS, boost::vecS, boost::undirectedS, Vertex_Property > Vertex_Graph; typedef boost::property_map::type Vertex_Data_Map; Vertex_Data_Map its_vertex_data; //... }; ////////////////////////////////////////////// // Definition of my custom iterator: ////////////////////////////////////////////// class Mesh::Vertex_Iterator: public boost::iterator_facade & > { public: Vertex_Iterator() {} explicit Vertex_Iterator( const Mesh* const mesh, Vertex_Graph::vertex_iterator p ) : its_parent( mesh ), its_vertex( p ) {} private: friend class boost::iterator_core_access; Vertex<3>& dereference() const { return its_parent->its_vertex_data[*its_vertex]; } void increment() { ++its_vertex; } void decrement() { --its_vertex; } bool equal( Vertex_Iterator const& other) const { return this->its_vertex == other.its_vertex; } const Mesh* const its_parent; Vertex_Graph::vertex_iterator its_vertex; }; ////////////////////////////////////////////// // The call with an error looks like this: ////////////////////////////////////////////// void Mesh::subset() { //... Compare_Normals compare( its_mean_normal ); Vertex<3> temp_holder[size]; Vertex_Iterator first_vertex( this, boost::vertices( its_vertices ).first ); Vertex_Iterator last_vertex( this, boost::vertices( its_vertices ).second ); std::partial_sort_copy( first_vertex, last_vertex, temp_holder, temp_holder + size, compare ); //... } ////////////////////////////////////////////// // This is gcc's error message: ////////////////////////////////////////////// Building object file Mesh.o... /usr/include/c++/3.3.1/bits/stl_algo.h: In function `_RandomAccessIter std::partial_sort_copy(_InputIter, _InputIter, _RandomAccessIter, _RandomAccessIter, _Compare) [with _InputIter = Mesh::Vertex_Iterator, _RandomAccessIter = Vertex<3>*, _Compare = Mesh::Compare_Normals]': /home/martin/source/scan-match/Mesh.cpp:532: instantiated from here /usr/include/c++/3.3.1/bits/stl_algo.h:2661: error: no matching function for call to `boost::counting_iterator::counting_iterator(Vertex<3>&)' /usr/local/include/boost/iterator/counting_iterator.hpp:169: error: candidates are: boost::counting_iterator::counting_iterator(Incrementable) [with Incrementable = size_t, CategoryOrTraversal = boost::use_default, Difference = boost::use_default] /usr/local/include/boost/iterator/counting_iterator.hpp:166: error: boost::counting_iterator::counting_iterator(const boost::counting_iterator&) [with Incrementable = size_t, CategoryOrTraversal = boost::use_default, Difference = boost::use_default] /usr/local/include/boost/iterator/counting_iterator.hpp:164: error: boost::counting_iterator::counting_iterator() [with Incrementable = size_t, CategoryOrTraversal = boost::use_default, Difference = boost::use_default] make[1]: *** [Mesh.o] Error 1 make: *** [default_target] Error 2 Thanks / martin