C++ How to make derived class to take base class parameters automatically

Question

When I change a value in base class and then, later on, create an object of the child class, child class created with an empty parameter instead of the changed value. Is there a way to object of derived class with the parameters of the base class?

Example:

Base.h

class Base
{

class Child;

public:
    int number = 0;
    Child *chilObject;

    void Setup()
    {
         number = 5;
         childObject = new Child;
    }
};

Child.h

class Child :
    public Base
    {

    };

main

int main()
{
    Base base;   
    base.Setup();

    cout << base.number << " : " << base->chilObject.number << endl;
    cout <<  << endl;        
}

Output: 5 : 0

I am simply asking if there is a way to make the derived class object to take Base class variables automatically.

Answer 1

Here is how it is typically done in C++:

#include <iostream>

class Base
{

public:

    int number = 0;

    virtual ~Base() = default;

    void Setup()
    {
        number = 5;
    }
};

class Child : public Base
{
    // number exists here because of inheritance.
};

int main()
{
    // Child object seen as Base object:
    Base* base = new Child;
    base->Setup();

    // Child object seen as Child object:
    Child* child = static_cast< Child* >( base );

    // Both share the same 'number' variable, so:

    std::cout << base->number << " : " << child->number << std::endl;
    std::cout << std::endl;

    // Free memory taken by 'new'.
    delete base;

    return 0;
}

yields:

5 : 5

In real code, you would probably make Setup virtual and not cast though.