Copy assignment operator of subclass not overwriting parent class

[Heymid]

#include <iostream>

using namespace std;

struct A {
    void operator=(const A& rhs) {
        cout<<"A"<<endl;
    }
};

struct B : public A {
    void operator=(const A& rhs) {
        cout<<"B"<<endl;
    }
};

int main() {
    B b1;
    B b2;
    b1 = b2;
    return 0;
}

Why does this program call A's copy assignment operator instead of B's?

[Repeater]

Because you didn't provide one, your B class gets a default copy assignment created for you, of this form:

void operator=(const B& rhs);

That function, created for you, calls the base copy assignment operator.