函数指针使用演示样例（參考Linux-内核代码）

近期阅读Linux-内核代码。发现非常多地方使用了函数指针，遂自己写一个演示样例程序。以供參阅：

#include <stdlib.h>
#include <stdio.h>

#define ADDONE 0
#define MINUSONE 1
#define S_OK 0
#define S_ERR -1

typedef int(*dir_fn)(int *data); //函数指针

//实际函数1
int add_func(int *data)
{
  (*data)++;
  return S_OK;
}

//实际函数2
int minus_func(int *data)
{
  (*data)--;
  return S_OK;
}

//核心：依据參数cmd，获取相应的func
dir_fn lookup_ctl(int cmd)
{
  dir_fn fn = NULL;
  switch(cmd)
  {
    case ADDONE:
      fn = add_func;
      break;
    case MINUSONE:
      fn = minus_func;
      break;
    default:
      break;
  }

  return fn;
}


int main(void)
{
  int data = 100; 
  int cmd = -1;
  dir_fn fn = NULL;

  printf("Input the cmd<0 add, 1 minus>\n");
  scanf("%d", &cmd);

  fn = lookup_ctl(cmd);

  fn(&data);

  printf("Result is: %d\n", data);

  return 0;
}