Question

I have:

VirtualClass : public QObject
{
public:
    int m_number;
}

DerivedClass : public VirtualClass 
{
public:
    DerivedClass(int number) : m_number(number) {};
    int m_number;
    // some content goes here..
}

client code:

f(VirtualClass* instance)
{
std::cout << instance->m_number;
}

DerivedClass der(100);

I want f(der) to return m_number that relates to DerivedClass , but *I get m_number of VirtualClass*.
What I am doing wrong?!!

Answer 1

Remove int m_number; from the DerivedClass. Otherwise you have to different m_number members. One is from VirtualClass and other is from DerivedClass.

When you add int m_number; in the DerivedClass you hide m_number; of VirtualClass

Here is an example how it works:

struct Foo
{
    int a;
};

struct Bar : Foo
{
    int a; //another a
};

int main()
{
    Bar *f = new Bar();
    f->a = 10; //Bar::a

    Foo *b = f;
    b->a = 20; //Foo::a

    cout << f->a << endl; //prints 10
    cout << b->a << endl; //prints 20
}