双链表的插入

typedef struct dnode
{
        int data;
        struct dnode *prior;
        struct dnode *next;
}DNode;

/*在所指定位置之前插入*/
void before_insert(DNode *head, int position, int value)
{
        DNode *p = head;
        DNode *q = NULL;
        int i = 0;
        while(p && i++ < position - 1)
                p = p->next;
        if((q = (DNode *)malloc(sizeof(DNode)))==NULL)
        {
                printf("分配内存失败\n");
                exit(0);
        }
        q->data = value;
        q->next = p->next;
        p->next = q;
        p->next->prior = q;
        q->prior = p;
}

/*在所指定位置之后插入*/
void behind_insert(DNode *head, int position, int value)
{
        DNode *p = head;
        DNode *q = NULL;
        int i = 0;
        while(p && i++ < position)
                p = p->next;
        if((q = (DNode *)malloc(sizeof(DNode)))==NULL)
        {
                printf("分配内存失败\n");
                exit(0);
        }
        q->data = value;
        q->next = p->next;
        p->next = q;
        p->next->prior = q;
        q->prior = p;
}