C++ Child类不能从Father类继承私有成员？

Question

我正在使用Win8 VC++ 2012.

上面的代码是为了表明在任何情况下子类B都可以访问A :: a.我也不能改变A :: a但是A :: b和A :: c的访问属性.

所以A :: c不是从A继承到B.但sizeof(A)和sizeof(B)分别是12和24,这意味着A :: a DO占用B中的内存.

1. B怎么能在其内存中存储A :: a而从不能访问它？
2. C++ Primer一书中说,我们可以恢复基类成员的访问属性但不能更改它.在这里,我的代码显示我可以在B中将A :: b的访问属性从protected更改为public.为什么？

这是代码:

#include <iostream>
using namespace std;

class A
{
private:
    int a;
protected:
    int b;
public:
    int c;

    A(int a, int b, int c): a(a), b(b), c(c)
    {
        cout << "A: ";
        cout << a << " ";
        cout << b << " ";
        cout << c << endl;
    }
};

class B: protected A
{
private:
    int d;
protected:
    int e;
    //using A::a; COMPILE ERROR
public:
    int f;
    //A::a;  COMPILE ERROR
    using A::c; //RESTORE A::c public access
    A::b; // change A::b from protected to public

    B(int d, int e, int f): A(d, e, f), d(d), e(e), f(f)
    {
        cout << "B\n";
        //cout << a << endl; COMPILE ERROR
        cout << b << " ";
        cout << c << " ";
        cout << d << " ";
        cout << e << " ";
        cout << f << endl;
    }
};
int main()
{
    A a(1,2,3);
    B b(4,5,6);

    cout << "sizeof(A)=" << sizeof(A) << endl; //OUTPUT 12
    cout << "sizeof(B)=" << sizeof(B) << endl; //OUTPUT 24
    return 0;
}

Answer 1

孩子继承父母的私人成员,但他们无法访问它们.要访问它们protected

class A
{
protected: // <<------------ make `a` as protected in parent
    int a;