0001 template <typename T> void Quadlist<T>::init() { //Quadlist初始化，创建Quadlist对象时统一调用
0002    head = new QNode<T>; //创建头哨兵节点
0003    tail = new QNode<T>; //创建尾哨兵节点
0004    head->succ = tail; head->pred = NULL; //沿横向联接哨兵
0005    tail->pred = head; tail->succ = NULL; //沿横向联接哨兵
0006    head->above = tail->above = NULL; //纵向的后继置空
0007    head->below = tail->below = NULL; //纵向的前驱置空
0008    _size = 0; //记录规模
0009 } //如此构造的四联表，不含任何实质的节点，且暂时与其它四联表相互独立