Structure offset

The use of offsetof() 

#include<stdio.h>
#include<stddef.h>

struct Person{

	char  a; //0~3
	int b; //4~7
};

void test01()
{
	struct Person p1;
	struct Person* p = &p1;

	printf("b的偏移量为：%d\n",(int)&(p->b)-(int)p);
	printf("b的偏移量为：%d\n",offsetof(struct Person,b));
}

//通过偏移量获取到数据
void test02()
{
	struct Person p1 = {'a',10};

	printf("p.b = %d\n",*(int*)((char*)&p1+offsetof(struct Person,b))); //char* 步长
	printf("p.b = %d\n",*(int*)((int*)&p1 + 1));
}

int main()
{
	test01();
	test02();
	return 0;
}

operation result:

The offset of b is: 4
The offset of b is: 4
pb = 10
pb = 10
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