бинарный ‘[‘: оператор не найден, который принимает левый операнд типа ‘const std :: map & lt; _Kty, _Ty & gt;’

Я не знаю, откуда исходит ошибка. Кажется, я передаю действительные данные в оператор [].

template <class VertexType>
typename map< Vertex<VertexType>, int >::iterator Graph<VertexType>::findEdge( const VertexType& v, const VertexType& w ) const
{
map<Vertex<VertexType>, int>::const_iterator iter = vertices[v].second.adjList.find(w);

return iter;
}  // end findEdge

Ошибка:

error C2678: binary '[' : no operator found which takes a left-hand operand of type 'const std::map<_Kty,_Ty>' (or there is no acceptable conversion)
1>          with
1>          [
1>              _Kty=unsigned int,
1>              _Ty=Vertex<unsigned int>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(164): could be 'Vertex<VertexType> &std::map<_Kty,_Ty>::operator [](unsigned int &&)'
1>          with
1>          [
1>              VertexType=unsigned int,
1>              _Kty=unsigned int,
1>              _Ty=Vertex<unsigned int>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(209): or       'Vertex<VertexType> &std::map<_Kty,_Ty>::operator [](const unsigned int &)'
1>          with
1>          [
1>              VertexType=unsigned int,
1>              _Kty=unsigned int,
1>              _Ty=Vertex<unsigned int>
1>          ]
1>          while trying to match the argument list '(const std::map<_Kty,_Ty>, const unsigned int)'
1>          with
1>          [
1>              _Kty=unsigned int,
1>              _Ty=Vertex<unsigned int>
1>          ]
1>          c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\graph.h(146) : while compiling class template member function 'std::_Tree_iterator<_Mytree> Graph<VertexType>::findEdge(const VertexType &,const VertexType &) const'
1>          with
1>          [
1>              _Mytree=std::_Tree_val<std::_Tmap_traits<Vertex<unsigned int>,int,std::less<Vertex<unsigned int>>,std::allocator<std::pair<const Vertex<unsigned int>,int>>,false>>,
1>              VertexType=unsigned int
1>          ]
1>          c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\graph.h(52) : while compiling class template member function 'Graph<VertexType>::Graph(unsigned int)'
1>          with
1>          [
1>              VertexType=unsigned int
1>          ]
1>          c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\topicg.cpp(17) : see reference to class template instantiation 'Graph<VertexType>' being compiled
1>          with
1>          [
1>              VertexType=unsigned int
1>          ]

И Graph учебный класс:

template <class VertexType>
class Graph
{
private:
// list of all vertices in the graph. assumes non-duplicate data.
map< VertexType, Vertex<VertexType> > vertices;

const unsigned MAX_VERTICES;  // Maximum number of vertices the graph can hold.
unsigned numVertices;         /** Current number of vertices in the graph. */
unsigned numEdges;            /** Number of edges in the graph. */

typename map< Vertex<VertexType>, int >::iterator findEdge( const VertexType& v, const VertexType& w ) const;

public:
Graph( unsigned max );

unsigned getNumVertices() const;
unsigned getMaxNumVertices() const;
unsigned getNumEdges() const;
int getWeight( const VertexType& v, const VertexType& w ) const;

Graph<VertexType>& addVertex( const VertexType& newValue );
Graph<VertexType>& addEdge( const VertexType& v, const VertexType& w, int weight );
void removeEdge( const VertexType& v, const VertexType& w );
void BFS( const VertexType& v ) const;
void display() const;
}; // end Graph