二级指针删除单向链表

今晚在这里看到一篇文章，http://coolshell.cn/articles/8990.html，原文给的是代码片段，本着动手实践的原则，另外顺便复习一下链表，写了下代码

#include <stdio.h>#include <stdlib.h>typedef struct _node {int n;struct _node *next;} node;typedef int (* remove_fn)(node const *n);node *create_link();void destory_link(node *head);void print_link(node *head);int should_remove(node const *n);node *remove_if(node *head, remove_fn should_remove);void remove_if2(node **head, remove_fn should_remove);int main() {node *head = create_link();print_link(head);//head = remove_if(head, should_remove);remove_if2(&head, should_remove);print_link(head);destory_link(head);return 0;}node *create_link() {node *head = malloc(sizeof(node));if (head == NULL) {printf("malloc head failed\n");return NULL;}head->n = 0;head->next = NULL;node *pre = head;for (int i=1; i<10; i++) {node *cur = malloc(sizeof(node));if (cur == NULL) {printf("malloc node %d failed\n", i);return NULL;}pre->next = cur;cur->n = i;cur->next = NULL;pre = cur;}return head;}void destory_link(node *head) {node *cur = head;while (cur) {node *next = cur->next;free(cur);cur = next;}}void print_link(node *head) {node *cur = head;while (cur) {printf("%d\t", cur->n);cur = cur->next;}printf("\n");}int should_remove(node const *n) {if (n == NULL) {return 0;}return (n->n)%2 == 0;}node *remove_if(node *head, remove_fn should_remove) {for (node *pre = NULL, *cur = head; cur;) {node * const next = cur->next;if (should_remove(cur)) {if (pre) {pre->next= next;} else {head = next;}free(cur);} else {pre = cur;}cur = next;}return head;}void remove_if2(node **head, remove_fn should_remove) {for (node **cur = head; *cur;) {node *entry = *cur;if (should_remove(entry)) {*cur = entry->next;free(entry);} else {cur = &(entry->next);}}}

编译运行一下

1zrj@zrj-desktop:~/c$ gcc -g -std=gnu99 link.c && ./a.out

20    1    2    3    4    5    6    7    8    9

31    3    5    7    9

其实道理不复杂，自己多读两遍代码就懂了，不得不承认这种写法确实很巧妙，而且就可读性来说，其实也没有下降多少

总结：

这里熟悉一下：指向函数的指针的用法。

typedef int (* remove_fn)(node const *n); 之后，remove_fn声明的类型 就是指向 这样函数的指针。

调用int should_remove(node const *n);的名字 should_remove 就是一个指针了。