C++双向循环链表

#include<iostream>
using namespace std;
typedef int elemType;

typedef struct DulNode
{
elemType data;
DulNode *prior;
DulNode *next;
}*DuList;

void InitList(DuList *L)
{
*L = new DulNode;
(*L)->next = (*L)->prior = *L;
}

int LengthList(DuList *L)//获取表长
{
DuList p = (*L)->next;
int length = 0;
while((p!=NULL) && (p!=*L))
{
p = p->next;
length++;
}
return length;
}

//获取第pos个位置的元素，若正确获取返回1，否则返回0
int GetElem(DuList *L, int pos, elemType *x)
{
DuList p = (*L)->next;
int i=1;
while(p!=(*L) && i<pos)
{
p=p->next;
i++;
}
if(p==*L || i>pos)
{
cout<<"get position error"<<endl;
return 0;
}
*x = p->data;
return 1;
}

//在带头结点的双向循环链表的第pos个位置前插入元素e
bool InsertList(DuList *L, int pos, elemType e)
{
DuList p,q;
int i=1;
p = (*L)->next;
while(p!=*L && i<pos-1)
{
p = p->next;
i++;
}
if((p==*L|| i>pos-1) && ((*L)->next!=(*L)->prior))
return false;
q = new DulNode;
q->data = e;

q->prior = p;
q->next = p->next;
p->next->prior = q;
p->next = q;
}

//删除第pos个位置的元素
bool DeleteList(DuList *L, int pos)
{
DuList p,q;
int i=1;
p = (*L)->next;
while(p!=*L && i<pos)
{
p = p->next;
i++;
}
if((p==*L|| i>pos) && ((*L)->next!=(*L)->prior))
return false;

p->prior->next = p->next;
p->next->prior = p->prior;
}

void PrintList(DuList *L)
{
DuList p;
int i=1;
p = (*L)->next;
while(p!=*L)
{
cout<< i <<":\t"<< p->data << endl;
p = p->next;
i++;
}
}

int main()
{
DuList L;
InitList(&L);
int length;
for(int i=1;i<6;i++)
InsertList(&L,i,i);
cout<<"the length of Dulist is: "<< LengthList(&L) <<endl;
PrintList(&L);
cout<<endl;

int num;
GetElem(&L, 2, &num);
cout<<"the 2th item of list is: "<< num <<endl;

DeleteList(&L, 3);
cout<<"after delete the 3th item:"<<endl;
PrintList(&L);
cout<<endl;

return 0;
}