Android源码中中一种常见的struct使用方法

#include<iostream>
#include<stdlib.h>
using namespace std;

struct Base{
    int ba;
    int bb;
    void printB(){
        cout<<"base print"<<endl;
    }
};

struct A{
    struct Base b;
    int aa;
    void printA(){
        cout<<"A print"<<endl;
    }
};

int main(){
    //A类型的指针
    struct A *a;
    
    //按A类型创建对象
    a = (struct A *)calloc(1, sizeof(*a));
    a->b.ba = 12;
    a->b.bb = 34;
    a->aa = 65;
    
    //将其传换为Base类型变量
    struct Base  *bp = &(a->b);
    bp->printB();
    cout<<bp->ba<<"  "<<bp->bb<<endl;
    
    //上面的都很常见，但注意这里：将其直接转换回A类型
    struct A *ap = (struct A *)bp;
    ap->printA();
    cout<<ap->b.ba<<"  "<<ap->b.bb<<"  "<<ap->aa<<endl;
}