C++primer一个类模板有关问题

C++primer一个类模板问题！
#include <iostream>
using namespace std;
template <typename Type> class Queue;
template <typename T> ostream& operator<< (ostream&,const Queue<T>&);
template <typename Type> class QueueItem
{
friend class Queue<Type>;
friend ostream& 
operator<< <Type> (ostream&,const Queue<Type>&);

QueueItem(const Type &t):item(t),next(0){}
Type item;
QueueItem *next;
};

template <typename Type> class Queue
{
  friend ostream& 
operator<< <Type> (ostream&,const Queue<Type>&);

private:
  QueueItem<Type> *head;
  QueueItem<Type> *tail;
  void destroy();
  void copy_elems(const Queue&);
public:
  Queue():head(0),tail(0){}
  Queue(const Queue &Q):head(0),tail(0)
{
copy_elems(Q);
}
Queue& operator=(const Queue &Q)
{

destroy();
Queue<Type> *pp=new Queue<Type>(Q);

return *pp;

}
~Queue(){destroy();}

Type& front(){return head->item;}
void push(const Type&);
void pop();
bool empty() const { return head==0;}


};
template <typename Type> 
ostream& operator<<(ostream &os,const Queue<Type> &q)
{
os<< "<";
QueueItem<Type>* p;
for(p=q.head;p;p->next)
{
os<< p->item << " ";
}
os<<">";
return os;
}
template <typename Type> void Queue<Type>::destroy()
{
while(!empty())
pop();
}

template <typename Type> void Queue<Type>::pop()
{
QueueItem<Type>* p=head; //keep pointer to head so we can delete it
head=head->next; //head now points to next element
delete p; //delete old head element
}

template <typename Type> void Queue<Type>::push(const Type &val)
{
QueueItem<Type>* pt =new QueueItem<Type>(val);
if(empty())
head=tail=pt;
else
{
tail->next=pt;
tail=pt;
}
}

template <typename Type> void Queue<Type>::copy_elems(const Queue &orig)
{
for(QueueItem<Type> *pt=orig.head;pt;pt=pt->next)
{
push(pt->item);
}
}

int main()
{
int a=5;
int b=6;
Queue<int> tt,tt1;
tt.push(a);
tt.push(a);
tt1.push(b);
tt1.push(b);
tt1.push(b);
tt=tt1;
cout<<tt; //问题出在输出这一块
return 0;
}
高手们帮忙看看输出问题出在哪里了~

[解决办法]
你用的VC6吧？
[解决办法]
用Dev C++运行没错，换一个版本

C/C++ code

 
 #include  <iostream>  
 using namespace std;  
 template  <typename Type> class Queue;  
 template  <typename T> ostream& operator  < < (ostream&,const Queue  <T>&);  
 template  <typename Type> class QueueItem  
 {  
 friend class Queue  <Type>;  
 friend ostream&  
 operator  < <  <Type> (ostream&,const Queue  <Type>&);  
  
 QueueItem(const Type  &t):item(t),next(0){}  
 Type item;  
 QueueItem *next;  
 };  
  
 template  <typename Type> class Queue  
 {  
     friend ostream&  
 operator  < <  <Type> (ostream&,const Queue  <Type>&);  
  
 private:  
   QueueItem  <Type> *head;   
 
   QueueItem  <Type> *tail;  
   void destroy();  
   void copy_elems(const Queue&);  
 public:  
   Queue():head(0),tail(0){}  
   Queue(const Queue &Q):head(0),tail(0)  
 {  
 copy_elems(Q);  
 }  
 Queue& operator=(const Queue &Q)  
 {  
  
 destroy();  
 Queue  <Type> *pp=new Queue  <Type>(Q);  
  
 return *pp;  
  
 }  
 ~Queue(){destroy();}  
  
 Type& front() {return head->item;}  
 void push(const Type&);  
 void pop();  
 bool empty() const { return head==0;}  
  
  
 };  
 template  <typename Type>  
 ostream& operator  < <(ostream &os,const Queue  <Type> &q)  
 {  
 os  < < "  <";  
 QueueItem  <Type>* p;  
 for(p=q.head;p;p->next)  
 {  
 os  < < p->item  < < " ";  
 }  
 os  < <">";  
 return os;  
 }  
 template  <typename Type> void Queue  <Type>::destroy()  
 {  
 while(!empty())  
 pop();  
 }  
  
 template  <typename Type> void Queue  <Type>::pop()  
 {  
 QueueItem  <Type>* p=head;  //keep pointer to head so we can delete it  
 head=head->next;    //head now points to next element  
 delete p;        //delete old head element  
 }  
  
 template  <typename Type> void Queue  <Type>::push(const Type &val)  
 {  
 QueueItem  <Type>* pt =new QueueItem  <Type>(val);  
 if(empty())  
 head=tail=pt;  
 else  
 {  
 tail->next=pt;  
 tail=pt;  
 }  
 }  
  
 template  <typename Type> void Queue  <Type>::copy_elems(const Queue &orig)  
 {  
 for(QueueItem  <Type> *pt=orig.head;pt;pt=pt->next)  
 {  
 push(pt->item);  
 }  
 }  
  
 int main()  
 {  
 int a=5;  
 int b=6;  
 Queue  <int> tt,tt1;  
 tt.push(a);  
 tt.push(a);  
 tt1.push(b);  
 tt1.push(b);  
 tt1.push(b);  
 tt=tt1;  
 cout  < <tt;  //问题出在输出这一块  
 cin.get();  
 return 0;  
 }