【每日一题】做菜顺序

宏：offsetof的使用

//offsetof (type,member)
//type是结构体的类型名，member是结构体中的成员名。

struct Student
{
	char name[5]; // 姓名
	int age;       // 年龄
	float score;   // 成绩
};

int main()
{
	struct Student s;

	printf("%zd\n", offsetof(struct	Student, name));
	printf("%zd\n", offsetof(struct	Student, age));
	printf("%zd\n", offsetof(struct	Student, score));

	return 0;
}

 我们通过画图可以只管看出结构体是如何存储数据的：

 offsetof宏的实现

#define my_offsetof(TYPE,MEMBER)      (size_t)&(((TYPE*)0)->MEMBER)

 来使用一下：

#define my_offsetof(TYPE,MEMBER)      (size_t)&(((TYPE*)0)->MEMBER)
struct Student
{
	char name[5]; // 姓名
	int age;       // 年龄
	float score;   // 成绩
};
int main()
{
	struct Student s;

	printf("%p\n", &s);
	printf("%p\n", &(s.name));
	printf("%p\n", &(s.age));
	printf("%p\n", &(s.score));


	printf("%zd\n", my_offsetof(struct	Student, name));
	printf("%zd\n", my_offsetof(struct	Student, age));
	printf("%zd\n", my_offsetof(struct	Student, score));
	return 0;
}

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