C语言回调函数的含义与核心使用场景详解

typedef int (*my_calculate_t)(int a, int b);
static int cal_sum(int a, int b)
{
    printf("now is sum\r\n");
    return a + b;
}
static int cal_sub(int a, int b)
{
    printf("now is sub\r\n");
    return a - b;
}
static int cal_mul(int a, int b)
{
    printf("now is mul\r\n");
    return a * b;
}
// 默认指向加法运算
static my_calculate_t s_cal = cal_sum;

static int test2_cal (int a, int b)
{
    int result = 0;
    if(s_cal) {
        // 执行回调
        result = s_cal(a ,b);
        printf("result=%d\r\n", result);
    }
    return result;
}
void app_main(void)
{
    printf("init done\r\n");
    int m = 10, n = 1, ret;
    ret = test2_cal(m, n);
}

typedef int (*my_calculate_t)(int a, int b);
// ... (省略 cal_sum, cal_sub, cal_mul 定义及 test2_cal 定义) ...

// 注册函数：允许外部改变实际执行的逻辑
static void my_cal_register(my_calculate_t cal)
{
    s_cal = cal;
}
// 解除注册：清空逻辑
static void my_cal_unregister(void)
{
    s_cal = NULL;
}

void app_main(void)
{
    printf("init done\r\n");
    int m = 10, n = 2, ret;

    // 第一次执行，默认是加法
    ret = test2_cal(m, n); 
    
    // 第二次执行前，动态改为减法
    my_cal_register(cal_sub);
    ret = test2_cal(m, n);
    
    // 清除配置后再改为乘法
    my_cal_unregister();
    my_cal_register(cal_mul);
    ret = test2_cal(m, n);
}

typedef int (*my_calculate_t)(int a, int b);
// ... (省略函数定义) ...

// 将函数指针作为参数接收
static int test1_cal (my_calculate_t actual_cal, int a, int b)
{
    int result = 0;
    if(actual_cal) {
        // 直接调用传入的参数函数
        result = actual_cal(a ,b);
        printf("result=%d\r\n", result);
    }
    return result;
}
void app_main(void)
{
    printf("init done\r\n");
    int m = 10, n = 2, ret;
    // 每次调用都明确指定要执行哪类逻辑
    ret = test1_cal(cal_sum, m, n);
    ret = test1_cal(cal_sub, m, n);
    ret = test1_cal(cal_mul, m, n);
}