C++ operator overriding

#include <stdio.h>

struct A {
    A();
    virtual bool operator==(const A&) const { printf("A==A\n"); return false; }
};

struct B : public A {
            bool operator==(const A&) const override { printf("B==A\n"); return false; }
    virtual bool operator==(const B&) const          { printf("B==B\n"); return false; }
};

struct C final : public B {
    bool operator==(const B&) const override { printf("C==B\n"); return false; }
    bool operator==(const C&) const          { printf("C==C\n"); return false; }
};

A::A() {
    static bool comparing = false;
    if(!comparing) {
        comparing = true;
        *this == B();
        comparing = false;
    }
}

int main() {
//  const A &a = B();
//  a == B(); printf("\n");
//  B() == a; printf("\n");
    B() == B(); printf("\n");
//  B() == C(); printf("\n");
//  C() == B(); printf("\n");
    C() == C(); printf("\n");
    return 0;
}