C/C++里的函数指针功能属于重要但平时用的不多,语法又比较难记,值的记录、学习一下。
写法一: 直接申明
//该代码申明了一个函数指针fn_b,他对应的函数的参数类型为void*,返回值类型为void*
void *(*fn_b)(void *);
也支持在申明的时候同时赋值,如下:
void *(*fn_b)(void *) = test_fn1;
写法二:先通过typedef定义类型,在申明变量
typedef void *(*fn_void_void)(void *);
fn_void_void fn_a = fn1;
这样写虽然多了一步,但可读性有了很大提高。
而且如果要定义多个变量的话,也是能减少重复的代码,所以更建议第二种写法。
其他类型的函数指针的定义示例
//下面函数指针类型表示,函数的两个参数类型分别为void*和int,返回值为void*
//写法1,直接申明
void *(*fn_d)(void *, int) = test_fn2;
//写法2,先typedef
typedef void *(*fn_void_void_int)(void *, int);
fn_void_void_int fn_c = test_fn2;
示例代码
#include <stdio.h>
void *fn1(void *args)
{
char *tmp = (char *)(args);
printf("%s is printing in %s\n", tmp, __func__);
return (void *)0;
}
void *fn2(void *args, int i)
{
char *tmp = (char *)(args);
printf("%s:%d is printing in %s\n", tmp, i, __func__);
return (void *)0;
}
typedef void *(*fn_void_void)(void *);
typedef void *(*fn_void_void_int)(void *, int);
int main()
{
fn_void_void fn_a = fn1;
void *(*fn_b)(void *) = fn1;
// void *(*fn_b)(void *);
// fn_b = fn1;
fn_void_void_int fn_c = fn2;
void *(*fn_d)(void *, int) = fn2;
char *p_hello = (char *)"hello";
fn_a(p_hello);
fn_b(p_hello);
fn_c(p_hello, 1);
fn_d(p_hello, 2);
return 0;
}