C++内部类

#include <iostream>
using namespace std;

class A
{
    public:
        A() : _a(10) {}
    private:
        class B
        {
            public:
                void show(const A &aa) { cout << "_a: " << aa._a <<endl ;}
        };
    private:
        int _a ;
    public:
        B bb ;
};

int main(int argc, char *argv[])
{
    cout<<"Hello, world"<<'\n';
    A a ;
    a.bb.show(a) ;
    return 0;
}

内部类可以访问外部类的私有成员，外部类不能访问内部类的私有成员！