Access child members within parent class, C++

Question

I am facing a situation where I need to access child member variables inside the parent class. I know this is against OO principles but I have to deal with a scenario where

Answer 1

Apparently you have some subset of derived classes which utilise childMember. For these classes you have some method "DoSomething()" which can be called. I guess for all other derived classes the method DoSomething() is not applicable. Why don't you create another abstraction level for this set of derived classes?

class Parent
{
    // no DoSomething()
}

class ChildMemberClasses : Parent
{
    int childMember;

    void DoSomething()
    {
        // code that uses childMember
    }
}

class ChildWithChildMember : ChildMemberClasses
{
    // other stuff
}

If DoSomething() has some meaning for classes without childMember, you can still define the it as virtual method in Parent. Like this:

class Parent
{
    virtual void DoSomething()
    {
        // code that does not use childMember
    }
}

class ChildMemberClasses : Parent
{
    int childMember;

    void DoSomething()
    {
        // code that uses childMember
    }
}

class ChildWithChildMember : ChildMemberClasses
{
    // other stuff
}