【数据结构】——较规范的链表操作方法
net小伙曾在文章【数据结构】双向链表的创建和读取和【数据结构】链式线性表的几种常用用法中写过关于线性表的操作方法，重新阅读发现代码很是稚嫩，现重新整理。
一般情况下我们会使用一个结构体head来作为双向链表的头部，head有两个指针域，一个指向链表的开始，一个指向链表的末尾。双向链表的指针域也有两个，一个指向前一个节点，一个指向后一个节点。两个结构体定义如下：
1 #define TAILQ_HEAD(name, type) \ 2 struct name { \ 3 struct type *tqh_first; /* first element */ \ 4 struct type **tqh_last; /* addr of last next element */ \ 5 } 6 #define TAILQ_ENTRY(type) \ 7 struct { \ 8 struct type *tqe_next; /* next element */ \ 9 struct type **tqe_prev; /* address of previous next element */ \ 10 }
使用二级指针是为了在遍历链表和删除链表的时候，代码更具有可读性。
完整的链表拓扑如下：
接下来直接给出代码，并附上一个小例子：
1 #define TAILQ_HEAD(name, type) \ 2 struct name { \ 3 struct type *tqh_first; /* first element */ \ 4 struct type **tqh_last; /* addr of last next element */ \ 5 } 6 #define TAILQ_ENTRY(type) \ 7 struct { \ 8 struct type *tqe_next; /* next element */ \ 9 struct type **tqe_prev; /* address of previous next element */ \ 10 } 11 12 #define TAILQ_FIRST(head) ((head)->tqh_first) 13 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next) 14 #define TAILQ_EMPTY(head) ((head)->tqh_first == NULL) 15 #define TRASHIT(x) do {(x) = (void *)-1;} while (0) 16 17 #define TAILQ_INIT(head) do { \ 18 TAILQ_FIRST((head)) = NULL; \ 19 (head)->tqh_last = &TAILQ_FIRST((head)); \ 20 } while (0) 21 22 #define TAILQ_INSERT_HEAD(head, elm, field) do { \ 23 if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL) \ 24 TAILQ_FIRST((head))->field.tqe_prev = \ 25 &TAILQ_NEXT((elm), field); \ 26 else \ 27 (head)->tqh_last = &TAILQ_NEXT((elm), field); \ 28 TAILQ_FIRST((head)) = (elm); \ 29 (elm)->field.tqe_prev = &TAILQ_FIRST((head)); \ 30 } while (0) 31 32 #define TAILQ_INSERT_TAIL(head, elm, field) do { \ 33 TAILQ_NEXT((elm), field) = NULL; \ 34 (elm)->field.tqe_prev = (head)->tqh_last; \ 35 *(head)->tqh_last = (elm); \ 36 (head)->tqh_last = &TAILQ_NEXT((elm), field); \ 37 } while (0) 38 39 #define TAILQ_FOREACH(var, head, field) \ 40 for ((var) = TAILQ_FIRST((head)); \ 41 (var); \ 42 (var) = TAILQ_NEXT((var), field)) 43 44 #define TAILQ_REMOVE(head, elm, field) do { \ 45 if ((TAILQ_NEXT((elm), field)) != NULL) \ 46 TAILQ_NEXT((elm), field)->field.tqe_prev = \ 47 (elm)->field.tqe_prev; \ 48 else { \ 49 (head)->tqh_last = (elm)->field.tqe_prev; \ 50 } \ 51 *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field); \ 52 TRASHIT((elm)->field.tqe_next); \ 53 TRASHIT((elm)->field.tqe_prev); \ 54 } while (0)
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <string.h> 4 5 #include "queue.h" 6 7 typedef struct _student_data { 8 char name[64]; 9 int age; 10 }student_data_t; 11 12 typedef struct _student_info{ 13 struct _student_data student_data; 14 TAILQ_ENTRY(_student_info) next_student; 15 }student_info_t; 16 17 #define MAX_NUM 4 18 19 TAILQ_HEAD(student_head, _student_info) student_list; 20 21 static student_data_t std[MAX_NUM] = { 22 {"lilei", 10}, 23 {"hanmeimei", 12}, 24 {"lili", 20}, 25 {"lucy", 21} 26 }; 27 28 void insert_info(int num) { 29 int i; 30 student_info_t *student = NULL; 31 32 for (i = 0; i < num; i++) { 33 student = (student_info_t *)malloc(sizeof(student_info_t)); 34 strncpy(student->student_data.name, std[i].name, strlen(std[i].name)); 35 student->student_data.age = std[i].age; 36 37 TAILQ_INSERT_TAIL(&student_list, student, next_student); 38 } 39 } 40 41 void show_info() { 42 student_info_t *tmp_info = NULL; 43 44 printf("--------------------------------------------------\n"); 45 TAILQ_FOREACH(tmp_info, &student_list, next_student) { 46 printf("name:%s age:%x\n", 47 tmp_info->student_data.name, 48 tmp_info->student_data.age 49 ); 50 } 51 printf("--------------------------------------------------\n"); 52 } 53 54 void delete_info() { 55 student_info_t *tmp_info = NULL; 56 57 #if 0 58 TAILQ_FOREACH(tmp_info, &student_list, next_student) { 59 TAILQ_REMOVE(&student_list, tmp_info, next_student); 60 free(tmp_info); 61 } 62 #else 63 while(1) { 64 TAILQ_FOREACH(tmp_info, &student_list, next_student) { 65 TAILQ_REMOVE(&student_list, tmp_info, next_student); 66 free(tmp_info); 67 break; 68 } 69 if (!tmp_info) 70 break; 71 } 72 #endif 73 } 74 75 int main(int argc, char *argv[]) { 76 77 TAILQ_INIT(&student_list); 78 79 insert_info(MAX_NUM); 80 show_info(); 81 delete_info(); 82 show_info(); 83 84 return 0; 85 }
需要注意的是在删除的所有list的时候，不可以直接使用FOREACH遍历，并使用REMOVE进行循环删除。因为REMOVE会把tmp_info的指针域全部置空，FOREACH在下次遍历的时候会直接段错误。
