标签：head 01 struct LIST list pos next entry LinuxAPI
LIST的使用
1. list_head
双向列表list_head结构体定义：
struct list_head {
struct list_head *next, *prev;
};
2. 创建链表
下列的接口都可以用于链表的初始化。
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)
#define INIT_LIST_HEAD(ptr) do { \
(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)
2.1 例子
可以通过LIST_HEAD(student_list)初始化一个链表，student_list的next和prev都是指向自己。
将这个student_list放到一个有意义的结构体重，作为这个结构体的宿主。
//初始化链表
LIST_HEAD(student_list);
//声明应用结构体
typedef struct student
{
string name;
int id;
struct list_head student_list;
}Student;
3. 加入节点
3.1. __list_add
在已知的两个节点中创建插入一个新的节点
/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static void __list_add(struct list_head *newer, struct list_head *prev, struct list_head *next)
{
next->prev = newer;
newer->next = next;
newer->prev = prev;
prev->next = newer;
}
3.2. list_add
在头结点之后插入一个新节点
/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static void list_add(struct list_head *newer, struct list_head *head)
{
__list_add(newer, head, head->next);
}
3.3. list_add_tail
在链表尾部插入新节点
/**
* list_add_tail - add a new entry
* @new: new entry to be added
* @head: list head to add it before
*
* Insert a new entry before the specified head.
* This is useful for implementing queues.
*/
static void list_add_tail(struct list_head *newer, struct list_head *head)
{
__list_add(newer, head->prev, head);
}
3.4. 例子
//创建一个节点
Student stu1 = {"stu1",1,LIST_HEAD_INIT(stu1.student_list)};
//加到头结点后面
//student_list相当于一个头结点，在后面创建一个stu1，进行连接
__list_add(&stu1.student_list,&student_list,&student_list);
4. 删除节点
4.1. __list_del
/*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static void __list_del(struct list_head *prev, struct list_head *next)
{
next->prev = prev;
prev->next = next;
}
4.2. list_del
删除链表中的任意节点，
/**
* list_del - deletes entry from list.
* @entry: the element to delete from the list.
* Note: list_empty on entry does not return true after this, the entry is in an undefined state.
*/
static void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = (struct list_head *)0;
entry->prev = (struct list_head *)0;
}
4.3. list_del_init
从链表中删除任一节点，并将其初始化。
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static void list_del_init(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
INIT_LIST_HEAD(entry);
}
5. 遍历链表
5.1. list_for_each
以链表的头结点为标志位，从前往后循环遍历链表
static inline void prefetch(const void *x) { ; }
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each(pos, head) \
for (pos = (head)->next, prefetch(pos->next); pos != (head); \
pos = pos->next, prefetch(pos->next))
5.2. list_for_each_prev
以链表的头结点为标志位，从后向前遍历链表
/**
* list_for_each_prev - iterate over a list backwards
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each_prev(pos, head) \
for (pos = (head)->prev, prefetch(pos->prev); pos != (head); \
pos = pos->prev, prefetch(pos->prev))
5.3. list_for_each_safe
更安全的方式遍历链表，n是一个临时变量，用来存储pos的下一个变量，
作用是，在遍历过程中如果删除了pos所指的变量，这个函数可以继续遍历下去
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* @pos: the &struct list_head to use as a loop counter.
* @n: another &struct list_head to use as temporary storage(临时变量)
* @head: the head for your list.
*/
#define list_for_each_safe(pos, n, head) \
for (pos = (head)->next, n = pos->next; pos != (head); \
pos = n, n = pos->next)
5.4. list_for_each_entry
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
prefetch(pos->member.next); \
&pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member), \
prefetch(pos->member.next))
6. 找出宿主结构体
6.1. list_entry
如上，typedef struct student { string name; int id; struct head_list student_list }Student;结构体中，对我们有意义的是name和id字段,student_list只是一个用于遍历的手段，所以我们需要借助一个函数来获得宿主结构体的其他数据。
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.（list_head结构，）
* @type: the type of the struct this is embedded in. （宿主结构体）
* @member: the name of the list_struct within the struct. （宿主结构体中我们需要的字段）
*/
#define list_entry(ptr, type, member) \
((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member)))
6.2. list_entry举例
struct head_list *pos = NULL;
//取值pos指针所在的宿主结构体的name字段
string name = list_entry(pos,Student,name)
7. 宿主结构体的遍历
7.1. list_for_each_entry
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
prefetch(pos->member.next); \
&pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member), \
prefetch(pos->member.next))
7.2. list_for_each_entry_safe
/**
* list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
* @pos: the type * to use as a loop counter.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe(pos, n, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
8. 大作业
8.1 Windows上编译通过
Windows上无法识别typeof()所以没有使用宿主结构体遍历的函数。
#include "sdp_list.h"
#include <iostream>
#include <mutex>
#include <string>
using namespace std;
mutex sdp_lock;
//初始化链表
LIST_HEAD(student_list);
//声明应用结构体
typedef struct student
{
string name;
int id;
struct list_head list;
}Student;
int main()
{
Student stu1 = { "name1",1, LIST_HEAD_INIT(stu1.list) };
Student stu2 = { "name2",2, LIST_HEAD_INIT(stu2.list) };
Student stu3 = { "name3",3, LIST_HEAD_INIT(stu3.list) };
sdp_lock.lock();
__list_add(&stu1.list, &student_list, &student_list);
list_add_tail(&stu2.list, &student_list);
list_add_tail(&stu3.list, &student_list);
struct list_head *pos = NULL, *tmp = NULL;
Student *stu = NULL;
//遍历
list_for_each_safe(pos, tmp, &student_list)
{
stu = list_entry(pos, Student, list);
{
if (stu)
{
cout << stu->name << " " << stu->id << endl;
}
}
}
//删除第二个元素
list_del(&stu2.list);
//遍历
list_for_each_safe(pos, tmp, &student_list)
{
stu = list_entry(pos, Student, list);
{
if (stu)
{
cout << stu->name << " " << stu->id << endl;
}
}
}
system("pause");
return 0;
}
8.2 Linux上运行通过
使用了list_for_each_entry_safe函数
#include <linux/types.h>
#include "list.h"
#include <stdio.h>
//初始化链表
LIST_HEAD(student_list);
//声明应用结构体
typedef struct student
{
char name[10];
int id;
struct list_head list;
}Student;
int main()
{
Student stu1 = { "name1",1, LIST_HEAD_INIT(stu1.list) };
Student stu2 = { "name2",2, LIST_HEAD_INIT(stu2.list) };
Student stu3 = { "name3",3, LIST_HEAD_INIT(stu3.list) };
__list_add(&stu1.list, &student_list, &student_list);
list_add_tail(&stu2.list, &student_list);
list_add_tail(&stu3.list, &student_list);
struct list_head *pos = NULL, *tmp = NULL;
Student *stu = NULL;
//遍历
list_for_each_safe(pos, tmp, &student_list)
{
stu = list_entry(pos, Student, list);
{
if (stu)
{
printf("name = %s,id = %d\n",stu->name,stu->id);
}
}
}
list_del(&stu2.list);
Student *stu_tmp = NULL;
list_for_each_entry_safe(stu, stu_tmp, &student_list, list)
{
if (stu)
{
printf("name = %s,id = %d\n",stu->name,stu->id);
}
}
return 0;
}
标签：head,01,struct,LIST,list,pos,next,entry,LinuxAPI 来源： https://blog.csdn.net/qq_38973710/article/details/113683927
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