linux内核链表使用
Linux内核链表的核心思想是：在用户自定义的结构A中声明list_head类型的成员p，这样每个结构类型为A的变量a中，都拥有同样的成员p，如下：
struct A{
int property;
struct list_head p;
}
其中，list_head结构类型定义如下：
struct list_head {
struct list_head *next,*prev;
};
list_head拥有两个指针成员，其类型都为list_head，分别为前驱指针prev和后驱指针next。
假设：
（1）多个结构类型为A的变量a1...an，其list_head结构类型的成员为p1...pn
（2）一个list_head结构类型的变量head，代表头节点
使：
（1）head.next= p1 ; head.prev = pn
（2） p1.prev = head，p1.next = p2;
（3）p2.prev= p1 , p2.next = p3;
…
（n）pn.prev= pn-1 , pn.next = head
以上，则构成了一个循环链表。
因p是嵌入到a中的，p与a的地址偏移量可知，又因为head的地址可知，所以每个结构类型为A的链表节点a1...an的地址也是可以计算出的，从而可实现链表的遍历，在此基础上，则可以实现链表的各种操作。
下面是从linux内核中移植出来的简单链表，list.h和list.c:
list.h:
#ifndef _INIT_LIST_H_
#define _INIT_LIST_H_
#ifndef offsetof
/* Offset of member MEMBER in a struct of type TYPE. */
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif
struct listnode
{
struct listnode *next;
struct listnode *prev;
};
#define node_to_item(node, container, member) \
(container *) (((char*) (node)) - offsetof(container, member))
#define list_declare(name) \
struct listnode name = { \
.next = &name, \
.prev = &name, \
}
#define list_for_each(node, list) \
for (node = (list)->next; node != (list); node = node->next)
#define list_for_each_reverse(node, list) \
for (node = (list)->prev; node != (list); node = node->prev)
void list_init(struct listnode *list);
void list_add_tail(struct listnode *list, struct listnode *item);
void list_remove(struct listnode *item);
#define list_empty(list) ((list) == (list)->next)
#define list_head(list) ((list)->next)
#define list_tail(list) ((list)->prev)
#endiflist.c：
#include "list.h"
void list_init(struct listnode *node)
{
node->next = node;
node->prev = node;
}
void list_add_tail(struct listnode *head, struct listnode *item)
{
item->next = head;
item->prev = head->prev;
head->prev->next = item;
head->prev = item;
}
void list_remove(struct listnode *item)
{
item->next->prev = item->prev;
item->prev->next = item->next;
}
测试代码list_test.c:
#include
#include
#include "list.h"
#define STUDENT_FREE_MEMORY
//声明链表节点
typedef struct {
int id;
char *name;
struct listnode _list;
}student;
//遍历函数指针
typedef void (*student_foreach_fun)(student *stu,void *data);
//声明链表
static list_declare(student_list);
//添加节点
int student_add(struct listnode *list,student *stu)
{
list_init(&stu->_list);
list_add_tail(list,&stu->_list);
}
//删除节点，释放节点空间
int student_del(struct listnode *list,int id)
{
struct listnode *node;
student *stu;
list_for_each(node,list){
stu = node_to_item(node,student,_list);
if(id == stu->id){
printf("list_del, id:%d,name:%s\n",stu->id,stu->name);
list_remove(node);
#ifdef STUDENT_FREE_MEMORY
//释放节点空间
free(stu);
stu = NULL;
#endif
return 1;
}
}
return 0;
}
//节点遍历
void student_foreach(struct listnode *list,student_foreach_fun fun,void *data)
{
struct listnode *node;
student *stu;
list_for_each(node,list){
stu = node_to_item(node,student,_list);
fun(stu,data);
}
}
//打印节点信息
void student_print(student *stu,void *data)
{
printf("id:%d,name:%s\n",stu->id,stu->name);
}
int main()
{
int i,len;
student *stu;
char *stu_name[]={"tonny","andy","michael","leslie","john"};
len = sizeof(stu_name)/sizeof(stu_name[0]);
//添加节点
for(i=0;iid = i + 1;
stu->name = stu_name[i];
student_add(&student_list,stu);
}
//打印所有节点
student_foreach(&student_list,student_print,(void *)0);
//删除节点
student_del(&student_list,1);
student_foreach(&student_list,student_print,(void *)0);
//删除节点
student_del(&student_list,5);
student_foreach(&student_list,student_print,(void *)0);
return 0;
}
Makefile:
TARGET=list_test
SRC=list_test.c list.c
#SRC=$(wildcard *.c)
OBJ=$(SRC:.c=.o)
CFLAGS=-g -Wall -o
$(TARGET):$(SRC)
gcc $(SRC) $(CFLAGS) $(TARGET)
clean:
rm $(OBJ) $(TARGET)