offsetof和container_of学习

#include <stdlib.h>
#include <iostream>
// #include <stddef.h>
#define offsetof(TYPE,MEMBER)   ((size_t) &((TYPE *)0)->MEMBER)
#define container_of(PTR,TYPE,MEMBER)    ({  \
    const typeof(((TYPE *)0)->MEMBER) *__mptr=(PTR);  \
    (TYPE *) ((char *)__mptr - offsetof(TYPE,MEMBER)); })
using namespace std;
struct sNode{
    int a;
    int b;
    char c;
    sNode():a(1),b(2){}
    sNode(int a,int b):a(3),b(4){}
};

class cNode{
public:
    int a;
    int b;
    int d;
    cNode(int a,int b):a(a),b(b),c(11){}
private:
    int c;
    int f;
public:
    int p(){return 1;} 
    int e;
};

int main()
{
    sNode s;
    sNode s1(1,2);
    cNode c(1,2);
    cout << s.a << c.b << s1.a << endl;
    cout << offsetof(sNode, b) << endl;
    cout << offsetof(cNode, d) << endl;
    // cout << offsetof(cNode, c) << endl;//无法访问
    cout << offsetof(cNode, e) << endl;

    int *p = (int*)&c.a;
    cNode *ptt=container_of(p,cNode,a);//通过成员的地址来得到类或结构体的首地址
    cout << ptt->a << endl;
    char* pc =(char*) ptt;

    cout << (*((int*)(pc+12))) << endl;//输出了c的内容
    //cout << c.c << endl;//自然是错误的

    return 0;
}

//参考：https://www.cnblogs.com/litifeng/p/7690585.html

c++的类这么久自然说明上面的代码没啥意义，不过熟悉下整个流程还是好的