C++ undefined reference to template class method [duplicate]

Answer 1

You need to define member functions in a header file, because when instantiating a template, the compiler needs to have access to the implementation of the methods, to instantiate them with the template argument.

In your example:

template  
class Graph  {    
public:
    void InsertVertex(T val) {
        Node *temp = new Node(val);

        if(head == NULL) 
            head = temp;

        // ... 
    }

    // ...

private:
    Node *head;
};