结构体偏移量

结构体偏移量

• 可以利用offsetof来计算结构体中属性的偏移
• 也可以通过地址的相加运算 计算偏移量
• 结构体嵌套结构体

代码示例：

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.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)));
        printf("p.b=%d\n", *(int*)(int*)&p1 + 1);
}
//结构体嵌套结构体
struct Person2
{
   
        char a;
        int b;
        struct Person c;
};
void test03()
{
   
        struct Person2 p = {
    'a',10,'b',20 };
        int offset1 = offsetof(struct Person2,c);
        int offset2 = offsetof(struct Person, b);
        printf("%d\n",*(int*)((char*)&p+offset1+offset2));
        printf("%d\n",((struct Person*)((char*)&p+offset1))->b);
}
int main()
{
   
        //test01();
        //test02();
        test03();
        return EXIT_SUCCESS;
}