Question

The definition below is failing… I’m thinking it has something to do with specializing a class template (Vector) within another class template (Graph). Thanks!

this is the part giving me trouble (defined in Graph below) -> 
std::map<KeyType, Vertex<KeyType, ObjectType> > vertexes;

template <class KeyType, class ObjectType>
class Vertex
{
private:
    KeyType key;
    const ObjectType* object;
public:
    Vertex(const KeyType& key, const ObjectType& object);
    const KeyType getKey();
};

template <class KeyType, class ObjectType> 
class Graph
{
private:
    std::map<KeyType, Vertex<KeyType, ObjectType> > vertexes;
public:
    const Vertex<KeyType, ObjectType>& createVertex(const KeyType& key, const ObjectType& object);
};

template <class KeyType, class ObjectType>
const Vertex<KeyType, ObjectType>& Graph<KeyType, ObjectType>::createVertex(const KeyType& key, const ObjectType& object)
{
    Vertex<KeyType, ObjectType> *vertex = new Vertex<KeyType, ObjectType>(key, object);
    vertexes.insert(pair<KeyType, Vertex<KeyType, ObjectType> >(vertex.getKey(), vertex));
    return *vertex;
};

Visual Studio 10 reports:

Error 1 error C2228: left of ‘.getKey’ must have class/struct/union c:\documents\visual studio 2010\projects\socialnetwork\socialnetwork\graph.h 46 1 SocialNetwork

The line mentioned in the error corresponds to the the vertexes.insert call near the end.

UPDATE: made correction as suggested by 2 posters of changing the >> to > >. No difference. Error persists.

Answer 1

Your vertex is a pointer. To access getKey you need to use -> operator, not .. Plus, you can use std::make_pair to avoid repeating the types.

vertexes.insert(std::make_pair(vertex->getKey(), *vertex));