шаблоны в си++

#ifndef LIST_H 
#define LIST_H 
 
#include<iostream>
#include<ostream>
#include<istream>
#include<ostream>
#include<string>
#include<fstream>
#include<list>
 
using namespace std; 
 
 
template <class TData> 
class List
{
 class Node
  {
    public:
    TData d;
    Node *next, *prev;
    Node(TData dat = NULL){d = dat; next = NULL; prev = NULL;}
  };//end class Node
Node *pbeg, *pend;
public:
    
    List(){pbeg = NULL; pend = NULL;}
     ~List();
    void add(TData d);
    Node * find(TData d);
    Node * insert(TData key, TData d);
    bool remove(TData key);
    void print();
    void print_back();
};//end class List
 
#endif //LIST_H

#include"list.h"
 
 
 
template <class TData> List <TData>::~List()
{
if (pbeg !=0)
  {
     Node *pv = pbeg;
      while (pv)
    {
      pv = pv->next;
      delete pbeg;
     pbeg = pv;
   }
  }
}
//-------------------------
template <class TData> void List <TData>::print()
{
Node *pv = pbeg;
cout << endl << "list: ";
while (pv)
  {
  cout << pv->d << ' ';
  pv = pv->next;
  }
cout << endl;
}
//-------------------------
template <class TData> void List <TData>::print_back()
{
Node *pv = pend;
cout << endl << " list back: ";
while (pv)
  {
  cout << pv->d << ' ';
  pv = pv->prev;
  }
cout << endl;
}
 
//-------------------------
template <class TData> void List <TData>::add(TData d)
{
Node *pv = new Node(d);
if (pbeg == NULL)
 pbeg = pend = pv;
  else
  {
  pv->prev = pend;
  pend->next = pv;
  pend = pv;
  }
}
//-------------------------
 
template <class TData> Node * List <TData>::find( TData d)
{
Node *pv = pbeg;
while (pv)
  {
  if(pv->d == d)break;
  pv = pv->next;
  }
return pv;
}
 
//-------------------------
 
template <class TData> Node * List <TData>::insert(TData key, TData d)
{
if(Node *pkey = find(key))
  {
  Node *pv = new Node(d);
  pv->next = pkey->next;
  pv->prev = pkey;
  pkey->next = pv;
  if( pkey != pend)(pv->next)->prev = pv;
    else pend = pv;
  return pv;
  }
return 0;
}
 
//-------------------------
template <class TData> bool List <TData>::remove(TData key)
{
if(Node *pkey = find(key))
{
if (pkey == pbeg)
  {
  pbeg = pbeg->next; pbeg->prev = 0;
  }
  else if (pkey == pend)
    {
    pend = pend->prev; pend->next = 0;
    }
    else 
    {
    (pkey->prev)->next = pkey->next;
    (pkey->next)->prev = pkey->prev;
    }
delete pkey; return true;
}
return false; 
}