KISS(Keep It Simple, Standard)

#ifndef _DOUBLE_H_
#define _DOUBLE_H_

template<class T>
class Double;

template<class T>
class DoubleNode
{
 friend class Double<T>;
private:
 T data;
 DoubleNode<T> *pre;
 DoubleNode<T> *next;
};

template<class T>
class Double
{
 public:
  Double();//{head=end=NULL;}
  ~Double();
  void Erase();
  void reverse();
  int GetLength()const;
  bool IsEmpty()const;
  bool Find(int k, T& x)const;
  int Search(T& x)const;
  Double<T>& Delete(int k, T& x);
  Double<T>& Insert(int k, const T& x);
  void output(ostream& out)const;
  friend ostream& operator << (ostream& out, const Double<T>& x);
 private:
  DoubleNode<T> *head;
  DoubleNode<T> *end;
  int length;
};

template<class T>
Double<T>::Double()
{
 head = new DoubleNode<T>;
 end = new DoubleNode<T>;
 head->pre = NULL;
 head->next = end;
 end->pre = head;
 end->next = NULL;

 length = 0;
}

template<class T>
Double<T>::~Double()
{
 Erase();
}

template<class T>
void Double<T>::Erase()
{
 DoubleNode<T> *current = head;
 while (current)
 {
  head = head->next;
  delete current;
  current = head;
 }
 length = 0;
}

template<class T>
int Double<T>::GetLength()const
{
 return length;
}

template<class T>
bool Double<T>::IsEmpty()const
{
 return length == 0;
}

template<class T>
bool Double<T>::Find(int k, T& x)const
{

 if (length == 0)
 {
  throw exception("DoubleNode is empty!");
 }
 else if(k<1 || k>length)
 {
  throw exception("no find the position of k");
 }

 DoubleNode<T> *current = head->next;
 for (int i=1; (i<k)&&current; ++i)
 {
  current = current->next;
 }

 if (current)
 {
  x = current->data;
  return true;
 }

 return false;
}

template<class T>
int Double<T>::Search(T& x)const
{
 int nIndex = 1;
 DoubleNode<T> *current = head->next;
 while (current && current->data != x)
 {
  ++nIndex;
  current = current->next;
 }

 if (current)
 {
  return nIndex;
 }

 return -1;
}

template<class T>
Double<T>& Double<T>::Delete(int k, T& x)
{
 if (length == 0)
 {
  throw exception("DoubleNode is empty!");
 }
 else if(k<1 || k>length)
 {
  throw exception("no find the position of k, so can't delete!");
 }

 DoubleNode<T> *current = head->next; 
 for (int i=1; (i<k)&&current; ++i)
 {
  current = current->next;
 }

 DoubleNode<T> * p = current;
 current->pre->next = current->next;
 current->next->pre = current->pre;

 x = p->data;
 delete p;
 p = NULL;
 --length;

 return *this;
}

template<class T>
Double<T>& Double<T>::Insert(int k, const T& x)
{
 if (k>=0 && k<= length)
 {
  DoubleNode<T> *newNode = new DoubleNode<T>;
  newNode->data = x;

  DoubleNode<T> *current = head;
  for (int i=0; i<k; ++i)
  {
   current = current->next;
  }

  newNode->pre = current;
  newNode->next = current->next;
  current->next->pre = newNode;
  current->next = newNode;
  
  
  ++length;
 }
 else
 {
  throw exception("no find the position of k, so can't insert!");
 }

 return *this;
}

template<class T>
void Double<T>::output(ostream& out)const
{
 DoubleNode<T> *current = head->next;
 while (current!=end)
 {
  out << current->data << " ";
  current = current->next;
 }
}

template<class T>
ostream& operator<< (ostream& out, const Double<T>& x)
{
 x.output(out);
 return out;
}

template<class T>
void Double<T>::reverse()
{
 DoubleNode<T> *p1 = head;
 DoubleNode<T> *p2 = NULL;
 DoubleNode<T> *pNode;

 while (p1 != NULL)
 {
  pNode = p1;
  pNode->pre = p1->next;
  p1 = p1->next;
  pNode->next = p2;
  p2 = pNode;
 }

 end = head;
 head = p2;
}

#endif

以上為雙鏈表的基本操作，代碼已經測試過了，可以直接用！
其中，head. end在構造函數時，New了兩個對象，是為了Insert 和 Delete操作的方便！
更好的方式是:把指針和數據分開，這樣head,end就可以節省存貯空間了！
方式如下：
//指針數據部分（后續指針和前驅指針）
struct Node_base
{
 Node_base *next;
 Node_base *pre;
};

//添加實際數據部分
template <class T>
struct Node : public Node_base
{
 T m_data;
};