如何组织类以共享数据成员但保留封装c ++？

Question

I want to build a tree breadth first in c++ using a queue. I have the files Queue.h, Queue.cpp, Tree.h, Tree.cpp, and main.cpp. My main class #includes "Tree.cpp". How do I structure these files using the #include keyword so that my Queue can push and pop tree nodes, and my tree can manipulate the Queue? It seems that part of the problem I am having is that the struct in each class is private. My Queue cannot define a treePtr in its struct, and my tree cannot instantiate new queue nodes. Should I make the structs in each class public so they can access each other across classes? In general, how am I suppose to organize these classes to make use of encapsulation?

class Tree{
private:
    typedef struct tree {
        int data;
        tree* left;
        tree* right;
    }* treePtr;

    treePtr root;
    int numNodes;
    void addTree(int n, treePtr child);
    treePtr addTree(int n);


public:

    Tree();
    void addTreeNode(int integer);
    treePtr getRoot();
    void printTreeNode(int n, treePtr treeRoot);

};


class Queue {
private:
    typedef struct node {
        Tree::treePtr treeNode;
        node* next;
    }* nodePtr;

    nodePtr head;
    nodePtr current;

public:
    Queue();
    void push(treePtr t);
    int pop();
};

Answer 1

Per @Eugene, the answer is to make Tree and Queue mutual friends. This is done in the header files for each class inside the class body.