Accessing a Private struct from child class

Question

I am required to implement these two methods in this class. Elem& operator*() and Elem* operator->(). The only issue whoever is that the Iterator class is defined within a Map Class. While the Elem is defined in the private section of the parent class. The catch is that I am not allowed to modify the the .h file of the class.

class Iterator{
    public:
        Iterator(){}
        explicit Iterator(Elem *cur):_cur(cur) {}
        Elem& operator*();
        Elem* operator->();
        // Iterator operator++(int);
        bool operator==(Iterator it);
        bool operator!=(Iterator it);
    private:
        Elem* _cur;
    };

Here is my attempted implemnetation of the function. However does not work as it says the struct is private.

Map::Elem& Map::Iterator::operator*(Iterator it){
//do stuff
}

The class is defined within another class. Which the struct is defined in under the private section. I am not really sure how I am supposed to be returning an Elem& or Elem* from within the Iterator class, if the Elem structure is private. However I suspect it has something to do with the Elem* _cur; defined within the private function of the Iterator class.

Here is the struct defined within the Map class. If that makes sense.. its private...

private:
    struct Elem {
        KEY_TYPE key;
        VALUE_TYPE data;
        Elem *left;
        Elem *right;
    };
    Elem *_root;  // a dummy root sentinel 
    int _size;

In case what I included does not work, here is the full class definition. Just wanted to include the examples above to include less code.

#ifndef MAP_H
#define MAP_H
#include <iostream>
#include <string>

using namespace std;

typedef string KEY_TYPE;
typedef string VALUE_TYPE;

class Map{
    struct Elem; //declaration of an interal structure needed below...

  public:
    //---Constructors and destructors---
    Map();               // constructs empty Map
    Map(const Map &rhs); // copy constructor 
    ~Map();              // destructor

    // assignment operator
    Map& operator=(const Map &rhs);

    // insert an element; return true if successful
    bool insert(KEY_TYPE, VALUE_TYPE);

    // remove an element; return true if successful
    bool erase(KEY_TYPE);

    // return size of the Map
    int size() const;

    // return an iterator pointing to the end if an element is not found,
    // otherwise, return an iterator to the element
    class Iterator;
    Iterator find(KEY_TYPE) const;

    // Iterators for accessing beginning and end of collection
    Iterator begin() const;
    Iterator end() const;

    // overloaded subscript operator
    VALUE_TYPE& operator[](KEY_TYPE);

    // output the undering BST
    ostream& dump(ostream& out) const;

    // a simple Iterator, won't traverse the collection
    class Iterator{
    public:
        Iterator(){}
        explicit Iterator(Elem *cur):_cur(cur) {}
        Elem& operator*();
        Elem* operator->();
        // Iterator operator++(int);
        bool operator==(Iterator it);
        bool operator!=(Iterator it);
    private:
        Elem* _cur;
    };

private:
    struct Elem {
        KEY_TYPE key;
        VALUE_TYPE data;
        Elem *left;
        Elem *right;
    };
    Elem *_root;  // a dummy root sentinel 
    int _size;

    // helper method for inserting record into tree.
    bool insert(Elem *& root, const KEY_TYPE& key, const VALUE_TYPE& data);

    // helper method for print tree
    void printTree(ostream& out, int level, Elem *p) const;

    // common code for deallocation
    void destructCode(Elem *& p);

    // common code for copy tree
    void copyCode(Elem* &newRoot, Elem* origRoot); 
};

ostream& operator<< (ostream&, const Map&);

#endif

Any help would be awesome. Been making the rounds on google with no such luck.

Answer 1

The issues is not that Elm is private. Change

Map::Elem& Map::Iterator::operator*(Iterator it){
//do stuff
}

to

Map::Elem& Map::Iterator::operator*(){
//do stuff
}

because the former does not match the signature declared in the header. That causes the defined operator overload to not be in the scope of the class.