C++:[class]未在此作用域中声明

-----------------------------------使用.h-------------------

#ifndef QUEUE_H
#define QUEUE_H
#include <iostream>
#include "MyException.h"
using namespace std;
template<class T>
class Queue;
template<class T>
ostream& operator<<(ostream&,Queue<T>&);
template<class T>
class Queue
{
    public:
        friend ostream& operator<< <T>(ostream&,Queue<T>&);
        Queue();
        Queue(const Queue<T>& other);
        Queue<T>& operator=(const Queue<T>& other);
        ~Queue();
    void enqueue(const T& el);
        T dequeue();
        void increasePriority(const T& el);
        bool isEmpty();
    private:
        class Node
        {
            public:
                Node(const T& data, Node* n = 0)
                {
                    element = data;
                    next = n;
                }
                T element;
                Node* next;
        };
        Node* head;
};
#include "Queue.C"
#endif

我们根本不允许更改.h(以上(文件。

---------------------队列.C-------------------

 #include "Queue.h"
    template<class T>
    ostream& operator << (ostream &strm, Queue<T> &obj)
    {
        if (obj.isEmpty())
        {
            strm << "[]";
            return strm;
        }
        else
        {
            strm << '[';
 //line 28
    Node* tmp = new Node();
            tmp = obj.head;
            strm << tmp.element + ',';
            while (tmp->next != 0)
            {
                tmp = tmp->next;
                if (tmp-next != 0)
                {
                    strm << tmp.element + ',';
                }
                else
                {
                    strm << tmp.element;
                }
            }
            strm << ']';
            delete [] tmp;
            tmp = 0;
            return strm;
        }
        return strm;
    }
    //...more code
    Queue::Queue()
    {
//line 54
    head = new Node();
        }

因此，从该代码中，我收到的一些错误如下：

Queue.C: In function ‘std::ostream& operator<<(std::ostream&, Queue<T>&)’:
Queue.C:28: error: ‘Node’ was not declared in this scope
Queue.C:28: error: ‘tmp’ was not declared in this scope
Queue.C:28: error: expected type-specifier before ‘Node’
Queue.C:28: error: expected ‘;’ before ‘Node’
Queue.C:34: error: ‘next’ was not declared in this scope
Queue.C: At global scope:
Queue.C:54: error: ‘head’ was not declared in this scope
Queue.C:54: error: expected type-specifier before ‘Node’
Queue.C:54: error: expected ‘;’ before ‘Node’