0. 環境說明

本文的實驗環境是：
win7操作系統+Keil 5 IDE.
非常適合嵌入式軟件開發

1. 打造自己的“list.h”

在單片機程序開發中，有時候會用到隊列。能否設計一個通用的隊列呢？我想，可以把內核鏈表用起來。

以下代碼是我從內核里面扒拉出來的，再稍微改改，就可以在工程中使用了。

#ifndef _LIST_H #define _LIST_H /*/usr/src/linux-headers-4.8.0-36-generic/include/linux/stddef.h *///求偏移量 #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)/*/usr/src/linux-headers-4.8.0-36-generic/include/linux/kernel.h */ /*** container_of - cast a member of a structure out to the containing structure* @ptr: the pointer to the member.* @type: the type of the container struct this is embedded in.* @member: the name of the member within the struct.**///小指針轉大指針 #define container_of(ptr, type, member) ({ \const typeof( ((type *)0)->member ) *__mptr = (ptr); \(type *)( (char *)__mptr - offsetof(type,member) );})/*/usr/src/linux-headers-4.8.0-36-generic/include/linux/types.h */ struct list_head {struct list_head *next, *prev; };/*/usr/src/linux-headers-4.8.0-36-generic/include/linux/list.h */#define LIST_HEAD_INIT(name) { &(name), &(name) }//以下這個宏用來定義并且初始化頭結點 #define LIST_HEAD(name) \struct list_head name = LIST_HEAD_INIT(name)//這個函數不知道內核里面有沒有，我自己加的 static inline void node_init(struct list_head *node) {node->next = node;node->prev = node; }/* kernel 3.14 */ static inline void __list_add(struct list_head *new,struct list_head *prev,struct list_head *next) {next->prev = new;new->next = next;new->prev = prev;prev->next = new; // kernel 4.8中 這句話是 WRITE_ONCE(prev->next, new); } /*** 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 inline void list_add(struct list_head *new, struct list_head *head) {__list_add(new, head, head->next); //頭插 }/*** 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 inline void list_add_tail(struct list_head *new, struct list_head *head) {__list_add(new, head->prev, head); //尾插 }/** 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 inline void __list_del(struct list_head * prev, struct list_head * next) {next->prev = prev;prev->next = next; //WRITE_ONCE(prev->next, next); }static inline void list_del(struct list_head *entry) {__list_del(entry->prev, entry->next);node_init(entry); //add by me//entry->next = LIST_POISON1;//entry->prev = LIST_POISON2; }/*** 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;//return READ_ONCE(head->next) == head; } /*** 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_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_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_next_entry - get the next element in list* @pos: the type * to cursor* @member: the name of the list_head within the struct.*/ #define list_next_entry(pos, member) \list_entry((pos)->member.next, typeof(*(pos)), member)/*** 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_head within the struct.*/ #define list_for_each_entry(pos, head, member) \for (pos = list_first_entry(head, typeof(*pos), member); \&pos->member != (head); \pos = list_next_entry(pos, member)) /*** 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_head within the struct.*/ #define list_for_each_entry_safe(pos, n, head, member) \for (pos = list_first_entry(head, typeof(*pos), member), \n = list_next_entry(pos, member); \&pos->member != (head); \pos = n, n = list_next_entry(n, member))/*** list_for_each_entry_from - iterate over list of given type from the current point* @pos: the type * to use as a loop cursor.* @head: the head for your list.* @member: the name of the list_head within the struct.** Iterate over list of given type, continuing from current position.*///從pos指向的結構體開始遍歷 #define list_for_each_entry_from(pos, head, member) \for (; &pos->member != (head); \pos = list_next_entry(pos, member)) /*** list_for_each_entry_safe_from - iterate over list from current point safe against removal* @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_head within the struct.** Iterate over list of given type from current point, safe against* removal of list entry.*/ #define list_for_each_entry_safe_from(pos, n, head, member) \for (n = list_next_entry(pos, member); \&pos->member != (head); \pos = n, n = list_next_entry(n, member)) /*** list_for_each_entry_continue - continue iteration 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_head within the struct.** Continue to iterate over list of given type, continuing after* the current position.*///從pos的下一個開始遍歷 #define list_for_each_entry_continue(pos, head, member) \for (pos = list_next_entry(pos, member); \&pos->member != (head); \pos = list_next_entry(pos, member))/*** list_for_each_entry_safe_continue - continue list iteration safe against removal* @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_head within the struct.** Iterate over list of given type, continuing after current point,* safe against removal of list entry.*/ #define list_for_each_entry_safe_continue(pos, n, head, member) \for (pos = list_next_entry(pos, member), \n = list_next_entry(pos, member); \&pos->member != (head); \pos = n, n = list_next_entry(n, member))#endif

2. 接口設計

#ifndef _QUEUE_H #define _QUEUE_H #include "list.h"struct queue_info {struct list_head *head;void (*push)(struct queue_info *info, struct list_head *new_node);struct list_head *(*top)(struct queue_info *info);struct list_head *(*pop)(struct queue_info *info);int (*for_each)(struct queue_info *info, void (*todo)(struct list_head *node));int (*is_empty)(struct queue_info *info); };void queue_init(struct queue_info *info,struct list_head * head); void queue_destroy(struct queue_info *info);#endif

struct queue_info中，首先有一個struct list_head *head，這是一個指針，指向鏈表的頭結點。這個頭結點需要用戶分配空間；其次是隊列具有的方法（指向函數的指針）。

• void (*push)(struct queue_info *info, struct list_head *new_node);
  入隊操作

• struct list_head *(*top)(struct queue_info *info);
  得到隊列的首元素（有別于出隊）

• struct list_head *(*pop)(struct queue_info *info);
  出隊

• int (*for_each)(struct queue_info *info, void (*todo)(struct list_head *node));
  遍歷隊列，todo由用戶實現

• int (*is_empty)(struct queue_info *info);
  判斷隊列是否為空

3. 具體實現

3.1 入隊

static void queue_push (struct queue_info *info, struct list_head *new_node) {list_add_tail(new_node,info->head); }

直接調用內核鏈表的尾插函數list_add_tail就行。

3.2 得到隊首的元素

struct list_head *queue_top(struct queue_info *info) {if (queue_is_empty(info)) {return NULL; //隊列為空}else{return info->head->next;} }

因為是通用隊列，無法預測隊列中元素的數據形態，所以返回指向struct list_head的指針。為了得到數據，需要用戶自己轉換（通過宏container_of）.

3.3 出隊

struct list_head *queue_pop(struct queue_info *info) {if (queue_is_empty(info)) {return NULL; //隊列為空}else{struct list_head *temp = info->head->next;list_del(temp); //刪除隊列的首元素return temp;} }

注意，list_del(temp);這句話僅僅使隊首元素脫離鏈表，隊首元素的空間需要用戶自己回收。

3.4 遍歷隊列的每個元素

static int queue_for_each(struct queue_info *info, void (*todo)(struct list_head *node)) {if(queue_is_empty(info)){printf("the queue is empty\n");return -1;}else{struct list_head *pos = NULL;struct list_head *n = NULL;list_for_each_safe(pos, n, info->head)todo(pos);return 0;} }

如果隊列為空，打印出錯信息并返回-1；否則，調用用戶傳入的todo函數，對每個元素進行操作（list_for_each_safe是內核鏈表的安全遍歷，用普通遍歷也是可以的，因為todo函數一般不會進行刪除。刪除沒有道理啊，我實在想不出應用場景）。

其實，我設計這個接口的初衷是為了測試，比如打印隊列每個元素，看看入隊順序是否正確等。

3.5 隊列的初始化

void queue_init(struct queue_info *info,struct list_head * head) {info->head = head;node_init(head); //頭結點的next和prev都指向自身info->push = queue_push;info->pop = queue_pop;info->top = queue_top;info->is_empty = queue_is_empty;info->for_each = queue_for_each; }

此函數應該在最初調用。用戶需要定義struct queue_info結構體和struct list_head結構體，然后傳入二者的地址。

3.6 隊列的析構

void queue_destroy(struct queue_info *info) { }

我想了想，覺得此函數只能為空。理由是：
1. 不需要回收空間，所以真的沒啥可以做的；
2. 本打算不斷出隊直到為空，發現出隊是用戶的事情，不需要越俎代庖。

4. 測試代碼及結果

#include "stdio.h" #include "queue.h"#define NAME_MAX_LEN 20struct data_info {char name[NAME_MAX_LEN];int age;struct list_head list; };//此函數用于打印結點信息 void print_node(struct list_head *node) {struct data_info *pdata;pdata = container_of(node, struct data_info, list);printf("name:%s, age:%d\n",pdata->name, pdata->age); }int main(void) {struct data_info s[] = {{"A", 34},{"B", 42},{"C", 36},{"D", 100},{"E", 18},};struct list_head head;struct queue_info queue;queue_init(&queue,&head);//測試入隊int i;for (i = 0; i < sizeof s/ sizeof s[0]; ++i) {queue.push(&queue,&s[i].list);}//測試遍歷queue.for_each(&queue,print_node);//測試topprintf("top method\n");struct list_head *p_node = queue.top(&queue);if(p_node==NULL){printf("top test failed\n");}else{print_node(p_node);}//再次遍歷，驗證top并不是出隊 queue.for_each(&queue,print_node);//測試出隊while(!queue.is_empty(&queue)){p_node = queue.pop(&queue);printf("out queue:");print_node(p_node);}while(1);//單片機程序，沒有操作系統，只能在這里死循環了 }

在keil5上調試（use simulator），測試結果截圖如下：

5. 需要注意的問題

普通的編譯器是無法編譯list.h的，必須支持gnu語法才行。對于Keil，可以添加對gnu的支持，如下圖，輸入--gnu.

【完】

總結

以上是生活随笔為你收集整理的队列的C语言实现（通过内核链表）的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。