使用方法重写的c ++继承

Question

Very simple example of c++ inheritance :

#include <iostream>
using namespace std;

class A{
 public :
 virtual void print(A a){
  cout<<"a"<<endl;
 }
};
class B : public A {
 public :
  virtual void print(A a){
  cout<<"a2"<<endl;
 }
virtual void print(B b){
  cout<<"b"<<endl;
}
};

int main(){
 B b;
 A &a = b;
 a.print(b);
 return 0;
}

Why does this output a2? I would have expected this to be effectively the same as : b.print(b) thanks!

Answer 1

Because your reference is a type A , only the A methods will be considered when deciding what to call. Since print(A) was virtual, it will actually call the method from B that matches the signature from A .

If this is confusing, consider if you had added a method foo to B . What would happen if you tried to call a.foo() ? It would fail, because objects of type A don't have a foo method.