Access protected member function in C-CodePudding

There are two external class (A and B)that I cannot change. I would like to access protected member of the class A:: doSomething in C (which I can do edit). Is there any way to access it. I understand its not good practice but I did not find any other way of doing it.

// External code starts
struct A {
    friend class B;
protected:
    void doSomething() {
        std::cout << "A" << std::endl;
    }
};

struct B {
protected:
    void doSomething() {
        A a;
        a.doSomething();
    }
};

// External code ends

// This will not compile as doSomething is a protected member.
struct C : B {
protected:
    void doSomethingElse() {
        A a;
        a.doSomething();
    }
};

CodePudding user response：

Friendship is not transitive, so inheriting from B doesn't help with this.

Inherit from A and form a pointer-to-member to doSomething:

struct Helper : A
{
    static constexpr auto ptr = &Helper::doSomething;
};

Use that pointer to call a function on a:

void doSomethingElse()
{
    A a;
    (a.*Helper::ptr)();
}