template errors

This is a discussion on template errors within the C++ Programming forums, part of the General Programming Boards category; Code: template<class Type> class Tree { private: struct Node { Type item; // node[0] = parent; // node[1] = left ...

  1. #1
    -bleh-
    Join Date
    Aug 2010
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    somewhere in this universe
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    template errors

    Code:
    template<class Type>
    class Tree
    {
    private:
      struct Node
      {
        Type item;
        //  node[0] = parent;
        //  node[1] = left child;
        //  node[2] = right child;
        Node * node[3];
      };
      
      Node * root;
    public:
      Tree():root(NULL) {}
      Node* search_tree(Type x);
      
      
        
    };
    
    template<class Type>
    Tree<Type>::Node *  Tree<Type>::search_tree(Type x)
    {
      if( this == NULL) return NULL;
      if(this->item == x)
        return this;
      else if( this->item < x )
        return this->node[1].search_tree(x);
      else
        return this->node[2].search_tree(x);
    }
    That class template keeps giving me the errors;
    Code:
    error: expected constructor, destructor, or type conversion before * token
    does anyone know how to fix that error?
    "All that we see or seem
    Is but a dream within a dream." - Poe

  2. #2
    Registered User
    Join Date
    Jun 2005
    Posts
    6,676
    Code:
    template<class Type>
    typename Tree<Type>::Node *  Tree<Type>::search_tree(Type x)
    In rough terms, without the typename keyword present, the standard says that the compiler must interpret TreeType<Node> as a non-type name while parsing the template code. That is the reason for your error message.

    As to the reason the standard says that - view finding and understanding that as a homework challenge. The reason is not trivial, and a complete explanation gives most people a headache.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

  3. #3
    -bleh-
    Join Date
    Aug 2010
    Location
    somewhere in this universe
    Posts
    460
    Thank you grumpy for the answer. I keep forgetting the use of "typename" for a user-defined type inside a class.
    "All that we see or seem
    Is but a dream within a dream." - Poe

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