Access child members within parent class, C++

#include <stdio.h>
class B;
class A {
    public:
        A();
        void print();
    private:
        B *child;
};

class B : public A {
    friend class A;
    public:
        B();
    private:
        int value;
};

A::A(){
    child = static_cast<B*>(this);
}

void A::print(){
    printf("value = %d\n", child->value);
}

B::B(){
    value = 10;
}

int main(){
    B b;
    b.A::print();
}