双向循环链表，deleitem函数中free(p)是不是错的啊，释放后p=p->next是不是就不行了

Question

void deleitem(Node* L, int item)
{
    Node* p;
    p = L->next;
    while (p != L)
    {
        if (p->date == item)
        {
            p->prior->next = p->next;
            p->next->prior = p->prior;
            free(p);
        }
        p = p->next;
    }
}

全代码：

#include"stdio.h"
#include"stdlib.h"
typedef struct Node
{
    int date;
    struct Node* prior;
    struct Node* next;
}Node;
Node* create(int data[], int n)
{
    Node* head, * s, * rear;
    int i;
    head = (Node*)malloc(sizeof(Node));
    head->prior = NULL;
    head->next = NULL;
    rear = head;
    for (i = 0; i < n; i++)
    {
        s = (Node*)malloc(sizeof(Node));
        s->date = data[i];
        s->prior = rear;
        s->next = NULL;
        rear->next = s;
        rear = s;
    }
    rear->next = head;
    head->prior = rear;
    return head;
}
void display(Node* L)
{
    Node* p;
    p = L->next;
    while (p != L)
    {
        printf("%d ", p->date);
        p = p->next;
    }
    printf("\n");
}
void deleitem(Node* L, int item)
{
    Node* p;
    p = L->next;
    while (p != L)
    {
        if (p->date == item)
        {
            p->prior->next = p->next;
            p->next->prior = p->prior;
            free(p);
        }
        p = p->next;
    }
}
int main()
{
    Node* list = NULL;
    int item, i, a[10], num;
    printf("输入集合a中元素数：");
    scanf_s("%d", &num);
    printf("输入集合a中数据元素：");
    for (i = 0; i < num; i++)
        scanf_s("%d", &a[i]);
    list = create(a, num);
    printf("输入删除元素item：");
    scanf_s("%d", &item);
    printf("循环链表中元素为：\n");
    display(list);
    deleitem(list, item);
    printf("删除item元素后：\n");
    display(list);
}

Answer 1

因为你free(p)之后p的空间就不能使用了。所以就没有p->next了。所以最简单的解决方法就是在if之前用一个新的指针newNode保存一下p->next，最后那句赋值改成p=newNode. 而且写链表，循环改成操作三个指针就几乎没这种问题。