多态性与虚函数2

#include <iostream>#include <string>using namespace std;class A{public:virtual int f() const{cout << "A::f()" << endl;return 1;}virtual void f(string) const {}virtual void g() const {}};class B : public A{public:void g() const {}};class C : public A{public:int f() const // 重写的时候返回的类型不能改变，{cout << "C::f()" << endl;return 1;}};class D :public A{public:int f(int) const{cout << "D::A" << endl;return 2;}};class A1{public:virtual string foodType() const = 0;};class A2{public:virtual string type() const = 0;virtual A1* eats() = 0;};class A3 : public A2{public:string type() const{return "A3";}class A33 : public A1{public:string foodType() const{return "A3 to 3";}};A1* eats(){return &bf;}private:A33 bf;};int main(){C c;c.f();D d;d.f(3); // d.f();  // 这里就不能调用基函数中虚函数int f() return 0;}