C 循环双链表

双链表比单链表多了一个prev指针域，用来指向一个节点的前一个节点，操作起来比单链表快捷许多，可以从前从后遍历整个链表。

程序：

#include<stdio.h>

#include<stdlib.h>


typedef struct dbnode
{
int num;
struct dbnode *prev;
struct dbnode *next;
}DbNode;
typedef DbNode * DbLink;


void create_empty_list(DbLink * head);
void create_newnode(DbLink * new_node);
void is_malloc_ok(DbLink new_node);
void display_list(DbLink head);
void indisplay_list(DbLink head);
void insert_node_head(DbLink  head, DbLink new_node);
void insert_node_tail(DbLink head, DbLink new_node);
void insert_node_tailhead(DbLink head, DbLink new_node);
void insert_node_mid(DbLink head, DbLink new_node, int num);
void insert_node_sort(DbLink head, DbLink new_node, int num);
void delete_node(DbLink head, int num);
void free_list(DbLink head);
//void revers_list(DbLink head);


int main()
{
DbLink head = NULL;
DbLink new_node = NULL;
int i;
int arr[5] = { 2,3,-1,43,10 };
int num;
create_empty_list(&head);
srand(time(NULL));
for (i = 0; i < 10; i++)
{
create_newnode(&new_node);
insert_node_sort(head, new_node, rand() % 100);
//new_node->num = arr[i];
//insert_node_head(head,new_node);
//insert_node_tailhead(head, new_node);
}
display_list(head);
printf("please input a num!\n");
scanf("%d", &num);
create_newnode(&new_node);
new_node->num =  num;
insert_node_mid(head,new_node,3);
delete_node(head, 5);
display_list(head);
//revers_list(head);
//printf("\n");
display_list(head);
free_list(head);
display_list(head);
return 0;
}


void create_empty_list(DbLink *head)
{
create_newnode(head);
(*head)->next = (*head)->prev = *head;
}


void create_newnode(DbLink * new_node)
{
*new_node = (DbLink)malloc(sizeof(DbNode));
is_malloc_ok(*new_node);
}


void is_malloc_ok(DbLink new_node)
{
if (new_node == NULL)
{
printf("malloc error!\n");
exit(-1);
}
}
void display_list(DbLink head)
{
DbLink p;
p = head->next;
if (head->next == head)
{
printf("list is empty!\n");
return;
}
while (p != head)
{
printf("num = %d\n", p->num);
p = p->next;
}
}


void indisplay_list(DbLink head)
{
DbLink p;
if (head->next == head)
{
printf("list is empty!\n");
return;
}
while (p != head)
{
printf("num = %d\n", p->num);
p = p->prev;
}
}


void insert_node_head(DbLink  head, DbLink new_node)
{
new_node->next = head->next;
new_node->prev = head;
head->next->prev = new_node;
head->next = new_node;
}


void insert_node_tail(DbLink head, DbLink new_node)
{
DbLink p;
p = head;
while (p->next != head)
{
p = p->next;
}
new_node->next = p->next;
new_node->prev = p;
p->next->prev = new_node;
p->next = new_node;
}
void insert_node_tailhead(DbLink head, DbLink new_node)
{
new_node->next = head;
new_node->prev = head->prev;
head->prev->next = new_node;
head->prev = new_node;
}


void insert_node_mid(DbLink head, DbLink new_node, int num)
{
DbLink p;
p = head;
if (head->next == head)
{
printf("list is empty!\n");
return;
}
while (p->num != num&&p->next != head)
{
p = p->next;
}
if (p->num == num)
{
new_node->next = p->next;
new_node->prev = p;
p->next->prev = new_node;
p->next = new_node;
}
else
{
printf("no such node!\n");
}
}


void delete_node(DbLink head, int num)
{
DbLink p = head;
if (head == head->next)
{
printf("list is empty!\n");
return;
}
while (p->num != num && p->next != head)
{
p = p->next;
}
if (p->num == num)
{
p->next->prev = p->prev;
p->prev->next = p->next;
free(p);
}
else
{
printf("no such node!\n");
}
}


void insert_node_sort(DbLink head, DbLink new_node, int num)
{
DbLink p;
p = head->next;
while (p != head && num >= p->num)
{
p = p->next;
}
new_node->num = num;
new_node->next = p;
new_node->prev = p->prev;
p->prev->next = new_node;
p->prev = new_node;




}


void free_list(DbLink head)
{
DbLink p;
p = head->next;
if (head->next == head)
{
printf("list is empty,release error!\n");
return;
}
while (p!= head)
{
p->prev->next = p->next;
p->next->prev = p->prev;
free(p);
p = head->next;
}
printf("release success!\n");
}