Chapter 2 templates and generic programming (10)

16.4.4 friends declaration of Queue and QueueItem

1. Set the class template to youyuan

Template <class Type>
Class QueueItem
{
QueueItem (const Type & t): item (t), next (0 ){}
Type item;
QueueItem * next;
Friend class Queue <Type>;
};
Template <class Type>
Class QueueItem
{
QueueItem (const Type & t): item (t), next (0 ){}
Type item;
QueueItem * next;
Friend class Queue <Type>;
}; 2. Queue output Operator

Template <class Type>
Ostream & operator <(ostream & OS, const Queue <Type> & q)
{
OS <"<";
QueueItem <Type> * p;
For (p = q. head; p! = 0; p = p-> next)
{
OS <p-> item <"";
}
OS <"> ";
Return OS;
}
Template <class Type>
Ostream & operator <(ostream & OS, const Queue <Type> & q)
{
OS <"<";
QueueItem <Type> * p;
For (p = q. head; p! = 0; p = p-> next)
{
OS <p-> item <"";
}
OS <"> ";
Return OS;
} 3. Set the function template to youyuan

Template <class Type>
Class QueueItem
{
Type item;
QueueItem * next;
QueueItem (const Type & t): item (t), next (0 ){}
Friend class Queue <Type>;
Friend ostream & operator <Type> (ostream & OS, const Queue <Type> & q );
};
Template <class Type>
Class QueueItem
{
Type item;
QueueItem * next;
QueueItem (const Type & t): item (t), next (0 ){}
Friend class Queue <Type>;
Friend ostream & operator <Type> (ostream & OS, const Queue <Type> & q );
}; Template <class Type>
Class Queue
{
Public:
Queue (): head (0), tail (0 ){}
Queue (const Queue & Q): head (0), tail (0)
{Copy_elems (Q );}
Queue & operator = (const Queue &);
~ Queue () {destroy ();}
Type & front ()
{Return head-> item ;}
Const Type & front () const {return head-> item ;}
Void push (const Type &);
Void pop ();
Bool empty () const
{Return head = 0 ;}
Friend ostream & operator <Type> (ostream & OS, const Queue <Type> & q );
Private:
QueueItem <Type> * head;
QueueItem <Type> * tail;
Void destroy ();
Void copy_elems (const Queue &);
};
Template <class Type>
Class Queue
{
Public:
Queue (): head (0), tail (0 ){}
Queue (const Queue & Q): head (0), tail (0)
{Copy_elems (Q );}
Queue & operator = (const Queue &);
~ Queue () {destroy ();}
Type & front ()
{Return head-> item ;}
Const Type & front () const {return head-> item ;}
Void push (const Type &);
Void pop ();
Bool empty () const
{Return head = 0 ;}
Friend ostream & operator <Type> (ostream & OS, const Queue <Type> & q );
Private:
QueueItem <Type> * head;
QueueItem <Type> * tail;
Void destroy ();
Void copy_elems (const Queue &);
}; 4. Type dependency and output Operator

Each type bound to a Queue that uses the Queue output operator must have an output operator.

From xufei96's column