一、链表代码
下面链表代码并不完整，完整代码可以到github上linux内核下载，网址linux/include at master · torvalds/linux · GitHub，在linux目录路径为 linux-master\include\linux\list.h
注：下面链表代码只能在linux环境运行，windows运行不了
/*
* Copy from linux/list.h
*/
#ifndef _GCP_MISC_LIST_H_
#define _GCP_MISC_LIST_H_
#ifdef __cplusplus
extern "C" {
#endif
#include <stddef.h>
#define LIST_POISON1 NULL
#define LIST_POISON2 NULL
#define container_of(ptr, type, member) \
({ \
const typeof(((type *)0)->member) *__mptr = (ptr); \
(type *)((char *)__mptr - offsetof(type, member)); \
})
struct list_head {
struct list_head *prev;
struct list_head *next;
};
#define LIST_HEAD_INIT(name) \
{ &(name), &(name) }
#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)
/**
* init_list_head - Initialize a list_head structure
* @list: list_head structure to be initialized.
*
* Initializes the list_head to point to itself. If it is a list header,
* the result is an empty list.
*/
static inline void init_list_head(struct list_head *list) {
list->prev = list;
list->next = list;
}
static inline void __list_add(struct list_head *new_entry, struct list_head *prev,
struct list_head *next) {
next->prev = new_entry;
new_entry->next = next;
new_entry->prev = prev;
prev->next = new_entry;
}
/**
* list_add - add a new_entry entry after the specified head
* @new_entry: new_entry entry to be added
* @head: list head to add it after
*
* Insert a new_entry entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new_entry, struct list_head *head) {
__list_add(new_entry, head, head->next);
}
/**
* list_add_tail - add a new_entry entry before the specified head
* @new_entry: new_entry entry to be added
* @head: list head to add it before
*
* Insert a new_entry entry before the specified head.
* This is useful for implementing queues.
*/
static inline void list_add_tail(struct list_head *new_entry, struct list_head *head) {
__list_add(new_entry, head->prev, head);
}
static inline void __list_del(struct list_head *prev, struct list_head *next) {
prev->next = next;
next->prev = prev;
}
/**
* 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 inline void list_del(struct list_head *entry) {
__list_del(entry->prev, entry->next);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
static inline void __list_splice(struct list_head *list, struct list_head *head) {
struct list_head *first = list->next;
struct list_head *last = list->prev;
struct list_head *at = head->next;
first->prev = head;
head->next = first;
last->next = at;
at->prev = last;
}
/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(const struct list_head *head) {
return head->next == head;
}
/**
* list_splice - join two lists
* @list: the new_entry list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(struct list_head *list, struct list_head *head) {
if (!list_empty(list))
__list_splice(list, head);
}
/**
* list_replace - replace old entry by new_entry one
* @old : the element to be replaced
* @new_entry : the new_entry element to insert
*
* If @old was empty, it will be overwritten.
*/
static inline void list_replace(struct list_head *old, struct list_head *new_entry) {
new_entry->next = old->next;
new_entry->next->prev = new_entry;
new_entry->prev = old->prev;
new_entry->prev->next = new_entry;
}
/**
* list_replace_init - replace old entry by new one and initialize the old one
* @old : the element to be replaced
* @new : the new element to insert
*
* If @old was empty, it will be overwritten.
*/
static inline void list_replace_init(struct list_head *old, struct list_head *new_entry) {
list_replace(old, new_entry);
init_list_head(old);
}
/**
* list_move - delete from one list and add as another's head
* @list: the entry to move
* @head: the head that will precede our entry
*/
static inline void list_move(struct list_head *list, struct list_head *head) {
__list_del(list->prev, list->next);
list_add(list, head);
}
/**
* list_move_tail - delete from one list and add as another's tail
* @list: the entry to move
* @head: the head that will follow our entry
*/
static inline void list_move_tail(struct list_head *list, struct list_head *head) {
__list_del(list->prev, list->next);
list_add_tail(list, head);
}
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*/
#define list_entry(ptr, type, member) container_of(ptr, type, member)
/**
* list_first_entry - get the first element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_first_entry(ptr, type, member) list_entry((ptr)->next, type, member)
/**
* list_last_entry - get the last element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_last_entry(ptr, type, member) list_entry((ptr)->prev, type, member)
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop cursor.
* @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); &pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_prev - iterate over a list backwards
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each_prev(pos, head) for (pos = (head)->prev; pos != (head); pos = pos->prev)
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* @pos: the &struct list_head to use as a loop cursor.
* @n: another &struct list_head to use as temporary storage
* @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)
/**
* 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 cursor.
* @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))
#ifdef __cplusplus
}
#endif
#endif /* _GCP_MISC_LIST_H_ */
二、简单演示
#include <stdio.h>
#include <stdlib.h>
#include "list.h"
typedef struct node{
int id;
struct list_head list
} Node;
int main() {
struct list_head list_node_head;
init_list_head(&list_node_head); // 初始化链表
for(int i = 0; i < 10; i ++){
Node* newNode = (Node*)malloc(sizeof(Node));
newNode->id = i;
list_add(&newNode->list, &list_node_head); // 添加节点
}
Node* currentNode, *nextNode; // 临时变量
list_for_each_entry(currentNode, &list_node_head, list){ // 遍历节点
printf("Node ID: %d\n", currentNode->id);
}
list_for_each_entry_safe(currentNode, nextNode, &list_node_head, list) { // 释放内存
list_del(¤tNode->list);
free(currentNode);
}
return 0;
}
三、详细解释
linux内核链表是其他结构体中来包含struct list_head来实现的，巧妙的运用了宏和链表元素list_head在结构体内的位置关系构。
1.该宏通过struct list_head在结构体的相对位置来确定节点头位置。
比如这样的结构体
struct node{
int id;
struct list_head list
} ; list_node_head->list，通过list与id相对位置关系来得出struct node的地址，最后 获取id的值。
#define container_of(ptr, type, member) \
({ \
const typeof(((type *)0)->member) *__mptr = (ptr); \
(type *)((char *)__mptr - offsetof(type, member)); \
})
2.链表初始化，两种初始化方式
#define LIST_HEAD_INIT(name) \
{ &(name), &(name) }
#define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)
static inline void init_list_head(struct list_head *list) {
list->prev = list;
list->next = list;
}
3.遍历
/**
* @pos 是临时指针，记录遍历节点的，类型：你定义的结构体，如举例的 Node 结构体
* @head 是头指针，类型：struct list_head
* @member 是在结构体中，struct list_head 的名称，如举例中Node结构体的list
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); &pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
list_for_each_entry(currentNode, &list_node_head, list)
内容不过多说，大家自己看英文注释，都很清楚。