C + + templates implement a doubly linked list

#include <iostream> #include <string>using namespace std;template<typename T> Struct node{     node (const t& d)           :_data (d)          ,_next (NULL)           , _prev (NULL)      {}      T _data;     Node<T>* _next;      Node<T>* _prev;}; Template<typename t>class dlist{public:     dlist ();      ~dlist ();      dlist (const dlist<t>& list);      dlist<t>& operator= (const dlist<t> list);      void pushback (const t& d);      void  Popback ();      void pushfront (const t& d);      void popfront ();      node<t>* find (const T& d);      void insert (node<t>* pos, const t& d);      void reverse ();      void sort ();      void remove (const t& d);      void removeall (const &NBSP;T&AMP;&NBSP;D);      void erase (Node<t>* pos);      friend ostream& operator<<<T> (ostream& output, const  Dlist<t>& s);p rivate:     node<t>* _head;      Node<T>* _tail;}; Template<typename t>    dlist<t>::D list ()      :_head (NULL)     ,_tail (NULL)     {}template< Typename t>dlist<t>::~dlist () {     node<t>* cur =  _head;     while  (cur)      {           Node<T>* del = cur;           cur = cur->_next;           delete del;     }}template<typename t> dlist<t ::D list (const dlist<t>& list)     :_head (NULL)      ,_tail (NULL) {         node<t>* cur =  list._head;         while  (cur)     {        Pushback (Cur->_data);      cur = cur->_next;      }}template<typename t>dlist<t>& dlist<t>::operator= (const  Dlist<t> list) {     swap ((node<t>*) _head,  (Node<T>*) list. _head)      swap ((node<t>*) _tail,  (node<t>*) list._tail);      return *this;} Template<typename t>void dlist<t&gt::P ushback (const t& d) {      if  (_head == null)      {           _head = new Node<T> (d);           _tail = _head;     }      Else     {         &nbSp Node<t>* newnode = new node<t> (d);           _tail->_next = NewNode;           newnode->_prev = _tail;          _tail  = newnode;     }}template<typename t>void dlist<t>:: Popback () {     if  (_head == null)      {           return;     }      else if  (_head== _tail)      {           delete _head;           _tail = NULL;          _head =  null;     }     else     {           _tail = _tail->_prev;           delete _tail->_next;          _ Tail->_next = null;     }}template<typename t>void dlist <t&gt::P ushfront (const t& d) {     node<t>* newnode  = new node<t> (d);     if  (_head == null)       {          _head = NewNode;           _tail = _head;           return; }     NewNode->_next =  _head;      _head->_prev = newnode;     _head = newnode;} Template<typename t>void dlist<t>::P Opfront () {     if  (_ Head == null)       return;     else if   (_head==_tail)      {           delete _head;          _head = NULL;           _tail = NULL;       }     else     {           _head = _head->_next;           delete _head->_prev;     }}template<typename T> ostream& operator<< (ostream& output, const dlist<t>& s) {     node<t>*  cur = s._head;     while  (cur)      {       cout<< cur->_data <<  "<->";       cur = cur->_next;     }      output <<  "over";      return output;} Template<typename t>node<t>* dlist<t>::find (const t& d) {      Node<T>* cur = _head;     while  (cur)     {          if  (Cur->_data &NBSP;==&NBSP;D)            return cur;           cur = cur->_next;     }     return  NULL;} Template<typename t>void dlist<t>::insert (node<t>* pos, const t &AMP;&NBSP;D) {     if  (pos == null)        return;     Node<T>* NewNode = new Node<T> (d);      if  (Pos == _tail)      {           _tail->_next = NewNode;           NewNode->_prev = _tail;           _tail = NewNode;     }      else     {          newnode- >_next = pos->_next;          newnode->_prev = pos;           pos->_next = NewNode;           NewNode->_next->_prev = NewNode;      }}template<typename t>void dlist<t>::reverse () {     node <T>* cur = _head;     while  (cur)       {          swap (Cur->_next, cur->_prev);           cur = cur->_prev;      }     swap (_head, _tail);} Template<typename t>void dlist<t>::sort () {     node<t>*  cur = _head;     node<t>* end = null;     while  (cur != end)       {      while  (Cur && cur->_next  != end)       {            if  (Cur->_data > cur->_next->_data)             {            T  Tmp = cur->_data;            cur-> _data = cur->_next->_data;             cur->_next->_data = tmp;            }           cur = cur->_next;      &nbSP;}       end = cur;      cur = _ Head;     }}template<typename t>void dlist<t>::remove (const &NBSP;T&AMP;&NBSP;D) {     node<t>* cur = _head;      while  (cur)      {         Node<T>* del = cur;      if  (cur->_data  ==&NBSP;D)       {       if  (cur ==  _head)        {             _head = _head->_next;             _head->_prev = NULL;       }        else if  (Cur!=_head && cur==_tail)        {             _tail = _tail->_prev;             _tail->_next = NULL;        }       else        {            cur->_ prev->_next = cur->_next;       }        delete del;       break;       }      cur = cur->_next; }}template<typename  t>void dlist<t>::removeall (const t& d) {     node <t>* cur = _head;     while  (cur)      {       node<t>* del = cur;      if  (cur->_data == &NBSP;D)       {       if  (cur ==  _head)        {             _head = _head->_next;             _head->_prev = NULL;             cur = _head;       }        else if  (Cur != _head && cur == _tail)         {            _ Tail = _tail->_prev;            _tail->_next = null;             cur = NULL;        }       else        {            cur->_prev->_next  = cur->_next;            cur->_ next->_prev = cur->_prev;             cur = cur->_next;       }        delete del;      }  else       cur = cur->_next; }}template<typename t>void dlist<t>:: Erase (Node<t>* pos) {     if  (pos == null)       return;      if  (Pos == _head && pos == _tail)       {          _head = NULL;           _tail = NULL;           return;     }     if  (POS  == _head)      {           _head = _head->_next;          _head-> _prev = null;     }     else if  (POS  == _tail)      {           _tail = _tail->_prev;          _tail->_next = null;      }     else     {           pos->_prev->_next = pos->_next;           pos->_next->_prev = pos->_prev;      } delete pos;}

C + + templates implement a doubly linked list