C-函数指针

来源：互联网发布：牛津大学本科知乎编辑：程序博客网时间：2024/06/16 18:31

C中函数指针最重要的两个用途：

(1)作为另一个函数的参数

(2)转换表(jump table)

C语言中，()的优先级大于*，因此函数int *f()与int (*f)()，前者返回值为int型的指针，后者f为指向函数的指针。

编写一个简单的链表测试用例，测试函数指针作为另一个函数的参数的用途。

#include <stdio.h>#include <stdlib.h>#include <string.h>#include <assert.h>typedef struct node{void *data;struct node *next;}Node;typedef struct list{Node *head;Node *tail;int list_len;}List;typedef struct test{char *dest_addr;char *local_addr;int link_quality;}Test;int compare_str(const void *s1, const void *s2){Test *a, *b;a = (Test *)s1;b = (Test *)s2;if (!memcmp(a, b, sizeof(Test))){return 0;}return 1;}void handle(void * data){Test *n;n = (Test *)data;printf("dest_addr: %s\n", n->dest_addr);printf("local_addr: %s\n", n->local_addr);printf("link_quality: %d\n\n", n->link_quality);}void list_init(List *list){list->head = NULL;list->tail = NULL;list->list_len = 0;}void list_destroy(List *list, void(*destroy)(void *)){list->list_len = 0;Node *n, *tmp;n = list->head;while (n){tmp = n->next;if (destroy){destroy(n->data);}free(n);n = tmp;}}void list_traverse(List *list, void(*handle)(void *)){Node *p;p = list->head;while (p){handle(p->data);p = p->next;}}Node* make_node(void *data){Node *n;n = malloc(sizeof(struct node));assert(n != NULL);n->next = NULL;n->data = data;return n;}void list_insert(List *list, void *data){Node *n;n = make_node(data);if (list->head == NULL){list->head = n;list->tail = n;n->next = NULL;}else{list->tail->next = n;list->tail = n;n->next = NULL;}list->list_len++;}void* list_search(List *list, void *key, int(*compare)(const void *, const void *)){int i = 1;Node *n;n = list->head;while (n){if (!compare(n->data, key)){printf("List Node Number: %d\n", i);return n->data;}n = n->next;i++;}return NULL;}void main(){Node *n;List *list;list = (List *)malloc(sizeof(List));list_init(list);Test n1 = { "192.168.5.10", "192.168.5.12", 1};Test n2 = { "192.168.5.20", "192.168.5.22", 2 };Test n3 = { "192.168.5.30", "192.168.5.32", 3 };Test nt = { "192.168.5.20", "192.168.5.22", 2 };list_insert(list, &n1);list_insert(list, &n2);list_insert(list, &n3);printf("list_length: %d\n", list->list_len);list_traverse(list, handle);n = list_search(list, &nt, compare_str);if (n != NULL){printf("Find List Node \n");}list_destroy(list, 0);system("pause");}

程序运行结果为：

使用到的函数指针有两个：void (*handle)(void *)和int (*compare)(const void *, const void *)

分别用于遍历时的数据处理以及结点数据比较。

第二种转移表的用途主要用于取代switch，定义int (*func[])(int, int)。其意义为元素函数指针的数组。

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