C++中虚函数的实现不受访问控制符的影响

#include <iostream>
#include <string>
using namespace std;
class Base{
    private:
        virtual string classID()const{
            return string("Base");
        }
    protected:
        virtual void dowork()=0;
    public:
        void work(){
            cout<<"this class id is "<<classID()<<endl;
            dowork();
        }
        virtual ~Base(){}
};
class DerivedA:public Base{
    private:                                                    
        virtual string classID()const{
            return string("DerivedA");
        }
    protected:
        void dowork(){
            cout<<"this is DerivedA dowork !"<<endl;
        }
};
int main(){
    Base* bp=new DerivedA();
    bp->work();
//    string s=bp->classID(); //这儿无法直接调用classID来实现多态，因为这个函数是private的，如果改成public之后就可了
//    cout<<s<<endl;
    delete bp;
}