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

If you're allowed to change your child classes source code, you can do something like that:

class Parent
{
public:
    void DoSomething()
    {
        getMember() = 0;
    }
    virtual int & getMember() = 0;
};

class Child1 : public Parent
{
    int childMember;
public:
    int & getMember()
    {
        return childMember;
    }
};

class Child2 : public Parent
{
    int childMember;
public:
    int & getMember()
    {
        return childMember;
    }
};

Otherwise, if your object has virtual table (at least one virtual method), you can use static_cast() in combination with C++11 typeid, because it's about three times faster than dynamic_cast:

#include 

class Parent
{
public:
    virtual void DoSomething();
};

class Child1 : public Parent
{
public:
    int childMember;
};

class Child2 : public Parent
{
public:
    int childMember;
};

void Parent::DoSomething()
{
    if (typeid(Child1) == typeid(*this))
    {
        auto child = static_cast(this);
        child->childMember = 0;
    }
    else if (typeid(Child2) == typeid(*this))
    {
        auto child = static_cast(this);
        child->childMember = 0;
    }
};