嵌入式八股C语言---面向对象篇

面向对象与面向过程

面向过程
就是把整个业务逻辑分成多个步骤,每步或每一个功能都可以使用一个函数来实现
面向对象
对象是类的实例化,此时一个类就内部有属性和相应的方法

封装

在C语言里实现封装就是实现一个结构体,里面包括的成员变量和函数指针,然后在构造函数中,为结构体的函数指针赋初值
对于这个函数指针往往会把自身传入,因为只是在模仿class

#include <stdio.h>
#include <stdlib.h>
struct student
{int height;char* name;void(*add_height)(struct student *, int);
};void ADD_HEIGHT(struct student * stu, int add)
{stu->height += add;
}
struct student * Student(int height,char *name)
{struct student * stu = malloc(sizeof(struct student));if(stu) {stu->height = height;stu->name = name;stu->add_height = ADD_HEIGHT;}return stu;
}
void freeStudent(struct student * stu )
{if(stu) {free(stu);stu = NULL;}
}
int main()
{struct student * stu = Student(180,"LCS");printf("%d\r\n",stu->height);stu->add_height(stu,50);printf("%d\r\n",stu->height);return 0;
}

继承

实现方案一: 子类中嵌套父类结构体指针
C语言模仿继承就是子类的结构体里嵌套一个父类的结构体
那如何实现类似虚函数的效果呢–修改父类的函数指针的指向就行

 		#include <stdio.h>#include <stdlib.h>struct animal{/* data */int age;void (*speak)(void);};void cat_speak() {printf("speak miaomiao\r\n");}void dog_speak() {printf("speak wangwang\r\n");}struct cat {struct animal * anm;int like_nothing;};struct dog {struct animal * anm;int like_eat_shit;};struct animal* Animal(int age) {struct animal* anm = malloc(sizeof(struct animal));anm->age = age;anm->speak = NULL;return anm;}struct cat* Cat(int age) {struct cat* new_cat = malloc(sizeof(struct cat));new_cat->anm = Animal(age); // 这就意味着等会你释放内存是真麻烦new_cat->like_nothing = 1;new_cat->anm->speak = cat_speak;return new_cat;}struct dog* Dog(int age) {struct dog* new_dog = malloc(sizeof(struct dog));new_dog->anm = Animal(age); // 这就意味着等会你释放内存是真麻烦new_dog->like_eat_shit = 1;new_dog->anm->speak = dog_speak;return new_dog;}int main(){struct cat* new_cat = Cat(5);struct dog* new_dog = Dog(10);new_cat->anm->speak();new_dog->anm->speak();return 0;}

继承的妙用: struct list_head 双向链表
当我们想要实现自己的列表的实现就把自己的链表中嵌入这个双向列表就行
实现方案二: 父类提供一个void * 私有指针不同的子类把void * 做不同的实现

#include <stdio.h>
#include <stdlib.h>// 基类定义
typedef struct {int age;void (*speak)(void*); // 虚函数指针void* private_data;   // 用于存储子类特定数据
} Animal;// Cat的私有数据结构
typedef struct {int like_nothing;
} CatPrivate;// Dog的私有数据结构
typedef struct {int like_eat_shit;
} DogPrivate;// 实现虚函数：猫叫声
static void cat_speak(void* obj) {CatPrivate* private_data = ((Animal*)obj)->private_data;printf("Cat says: miaomiao, like_nothing=%d\n", private_data->like_nothing);
}// 实现虚函数：狗叫声
static void dog_speak(void* obj) {DogPrivate* private_data = ((Animal*)obj)->private_data;printf("Dog says: wangwang, like_eat_shit=%d\n", private_data->like_eat_shit);
}// 创建Animal实例
Animal* create_animal(int age, void (*speak_func)(void*), void* private_data) {Animal* animal = malloc(sizeof(Animal));animal->age = age;animal->speak = speak_func;animal->private_data = private_data; // 设置私有数据return animal;
}// 创建Cat实例
Animal* create_cat(int age) {CatPrivate* cat_private = malloc(sizeof(CatPrivate));cat_private->like_nothing = 1; // 设定Cat私有数据Animal* animal = create_animal(age, cat_speak, cat_private);return animal;
}// 创建Dog实例
Animal* create_dog(int age) {DogPrivate* dog_private = malloc(sizeof(DogPrivate));dog_private->like_eat_shit = 1; // 设定Dog私有数据Animal* animal = create_animal(age, dog_speak, dog_private);return animal;
}int main() {Animal* new_cat = create_cat(5);Animal* new_dog = create_dog(10);// 调用虚函数new_cat->speak(new_cat);new_dog->speak(new_dog);// 清理资源free(((CatPrivate*)new_cat->private_data));free(((DogPrivate*)new_dog->private_data));free(new_cat);free(new_dog);return 0;
}