c++二叉树问题

#include <iostream>

template<class DataType>
struct BiNode
{
    DataType data;
    BiNode<DataType>* lchild;
    BiNode<DataType>* rchild;

    BiNode( const DataType& data ) : data(data), lchild(), rchild()
    {
    }
    ~BiNode()
    {
        delete lchild;
        delete rchild;
    }

protected: // no-implement
    BiNode( const BiNode& );
    BiNode& operator=( const BiNode& );
};

template<class DataType>
class BiTree
{
public:
    BiTree() : root()
    {
    }
    ~BiTree()
    {
        delete root;
    }

protected: // no-implement
    BiTree( const BiTree& );
    BiTree& operator=( const BiTree& );

private:
    BiNode<DataType>* root;

    friend std::istream& operator>>( std::istream& is, BiTree<DataType>& tree )
    {
        struct foo
        {
            std::istream& operator()( std::istream& is, BiNode<DataType>*& pnode )
            {
                DataType data;
                if( !(is>>data) || data=='#' )
                    return is;
                pnode = new BiNode<DataType>( data );
                operator()( is, pnode->lchild );
                operator()( is, pnode->rchild );
                return is;
            }
        } foo;

        delete tree.root;
        tree.root = NULL;
        return foo( is, tree.root );
    }
    friend std::ostream& operator<<( std::ostream& os, const BiTree<DataType>& tree )
    {
        struct foo
        {
            std::ostream& operator()( std::ostream& os, BiNode<DataType>* const& pnode )
            {
                if( pnode )
                {
                    os << pnode->data;
                    operator()( os, pnode->lchild );
                    operator()( os, pnode->rchild );
                }
                else
                    os << '#';
                return os;
            }
        } foo;

        return foo( os, tree.root );
    }
};

int main( void )
{
    using namespace std;

    BiTree<char> bt;
    cin >> bt; // AB#D##C##
    cout << bt << endl;
}