Re: Copy a Base Class to a Derived Class

Hello everybody,
first of all, sorry if the question I'm about to ask have been already
answered, but after some hours spent bothering google, I did not work
it out.

I have two classes:

class Base
{
public:
        Base() { k = 0; };
        ~Base() {};

        int k;
        void setK(int p) { k = p; };
        int getK() { return k; };

        void myMethod() { /* Code here */ };
};

class Derived : public Base
{
public:
        Derived() : Base() { i = 0; };
        ~Derived() {};

        int i;
        void setI(int p) { i = p; };
        int getI() { return i; };

        void myCoolMethod() { /* Code here */ };
};

Suppose I need to work with the derived class because I have to
implement many methods and I cannot touch the Base class since it's a
Qt class.

What I would like to do is find a way to "merge" an implementation of
a Derived class with another implementation of Base class, due to have
all the data for the Base class avaiable in the Derived class.

Casting is not sufficient since if I cast, I can use the Derived class
but I will lose all the personal data referred to it.

Let me explain with an tiny working example:

/* ### EXAMPLE STARTS ### */
#include <iostream>

class Base
{
public:
        Base() { k = 0; };
        ~Base() {};

        int k;
        void setK(int p) { k = p; };
        int getK() { return k; };

        void myMethod() { /* Code here */ };
};

class Derived : public Base
{
public:
        Derived() : Base() { i = 0; };
        ~Derived() {};

        int i;
        void setI(int p) { i = p; };
        int getI() { return i; };

        void myCoolMethod() { /* Code here */ };
};

int main() {
        Derived * d = new Derived();

        d->setI(10);
        printf("i: %d\n", d->getI());
        /* prints 10 */

        Base * b = new Base();

        b->setK(2);
        printf("k: %d\n", b->getK());
        /* prints 2 */

        d = reinterpret_cast<Derived *>(b);

        printf("i: %d -- k: %d\n", d->getI(), d->getK());
        /* prints 0 -- 2 !!! I want 10 -- 2 !!!*/

        return 0;
}
/* ### EXAMPLE STOPS ### */

Casting from Base to Derived loses all the Derived class information!!

I feel like there is a solution but I cannot imagine what is it.

Any suggestion is appreciated, thanks.

--
Iacopo