C++关于类结构体大小和构造顺序,析构顺序的测试详解

#include <iostream>
using namespace std;

class A{
public:
    A()
    {
        cout<<"A constructor"<<endl;
    }
    ~A()
    {
        cout<<"A destructor"<<endl;
    }
};
class B:A{
public:
    B()
    {
        cout<<"B constructor"<<endl;
    }
    ~B()
    {
        cout<<"B destructor"<<endl;
    }
};
class C:B{
public:
    C()
    {
        cout<<"C constructor"<<endl;
    }
    ~C()
    {
        cout<<"C destructor"<<endl;
    }
    virtual void eat()=0;//纯虚函数会存在一个虚函数指针。64bit系统上故大小为8
};
class D:B{
    void eat()
    {
        cout<<"D eat"<<endl;
    }
};
class E:B{
    int age;//不加修饰符的话，默认是private
public:
    int num;
    E(int a,int b):age(a),num(b){
        cout<<"E constructor"<<endl;
    };
    ~E()
    {
        cout<<"E destructor"<<endl;
    }
    void eat()
    {
        cout<<"E eat"<<endl;
    }
};
class F:C{
    //继承的类中有虚函数，存在一个虚函数指针，64bit系统上占8字节
    int age;//不加修饰符的话，默认是private
public:
    int num;
    F(int a,int b):age(a),num(b){
        cout<<"F constructor"<<endl;
    };
    ~F()
    {
        cout<<"F destructor"<<endl;
    }
    void eat()
    {
        cout<<"F eat"<<endl;
    }
};

//C++关于类结构体大小和构造顺序、析构顺序的测试。
int main()
{
    cout<<"run"<<endl;
    cout<<"sizeof(A)="<<sizeof(A)<<endl;//大小为1
    cout<<"sizeof(B)="<<sizeof(B)<<endl;//大小为1
    cout<<"sizeof(C)="<<sizeof(C)<<endl;//虚函数会存在一个虚函数指针。64bit系统上故大小为8
    cout<<"sizeof(D)="<<sizeof(D)<<endl;//大小为1,非虚函数不占用类大小。
    cout<<"sizeof(E)="<<sizeof(E)<<endl;//大小为4+4
    E e(11,22);
    cout<<"e.num="<<e.num<<endl;
    E* e2=new E(33,44);
    cout<<"e2->num="<<e2->num<<endl;
    delete e2;
    cout<<"sizeof(F)="<<sizeof(F)<<endl;//大小为8+4+4

    F f(55,66);
    cout<<"f.num="<<f.num<<endl;
    f.eat();
    return 0;
}