Question

I have a vector of type template class and I am trying to print it, but getting a weird error.

Here is my class:

template <typename VertexType, typename EdgeType> class Vertex{
private:
    typedef std::vector<std::pair<int, EdgeType> > VertexList;
    std::vector<Vertex<VertexType, EdgeType>> Vertice;

public:
    void Add(Vertex);
};

Add Method and Print Statement:

template <typename VertexType, typename EdgeType> void Vertex<VertexType, EdgeType> ::Add(Vertex v)
{
    int count = 5;
    //std::vector<string>temp;

    for(int i=0; i<count; i++)
    Vertice.push_back(v);

    for(int i=0; i<Vertice.size(); i++)
        cout<< Vertice[i] <<endl;
}

Main() Method:

int main()
{
    Vertex<std::string, std::string> v1;

    v1.Add(v1);

    std::getchar();
}

Error am getting is:

error C2679: binary ‘<<‘ : no operator
found which takes a right-hand operand
of type ‘Vertex’
(or there is no acceptable conversion)

Answer 1

You aren’t defining an operator << anywhere. You should define it like this out of your class :

template <typename VertexType, typename EdgeType>
std::ostream& operator << (std::ostream& out, const Vertex<VertexType,EdgeType>& v);
// implementation
template <typename VertexType, typename EdgeType>
std::ostream& operator << (std::ostream& out, const Vertex<VertexType,EdgeType>& v) {
    // print whatever you want that represents your vertex

    // please don't forget to return this reference.
    return out;
}

Also, having a class with a vector of instances of it inside is a call for trouble. Remember that “vector<Vertice<VertexType,EdgeType> >” is an array of instances, not an array of references. If you want a array of ‘references’ to Vertex, use an array of pointers.

And consider using boost’s graph library instead of redefining yet another one and coming to all pitfall associated with graphs (like memory management for instance). The boost library also have some useful algorithms that you could want to use..