Question

This title has been used many times but after searching around 5-6 examples, I couldn’t find anything that matches my problem:

I have a simple inheritance practice.

Class A is a base class, classes B & C inherit from it:

class A {

};

class B : public A { public:    int i; };

class C : public A { public:    int j; };

And a class P containing overloaded functions like this:

class P
{
public:
    void change(B *b)
    {
        b->i =1;
    }

    void change(C *c)
    {
        c->j =1;
    }
};

And when I use the functions like the following:

int main()
{
    A *b = new B();
    A *c = new C();
    P p;
    p.change(b);
    p.change(c);
    return 0;
}

it gives an error saying:

inherit2.cpp: In function ‘int main()’:
inherit2.cpp:37:12: error: call of overloaded ‘change(A*&)’ is ambiguous
inherit2.cpp:37:12: note: candidates are:
inherit2.cpp:21:7: note: void P::change(B*) <near match>
inherit2.cpp:21:7: note:   no known conversion for argument 1 from ‘A*’ to ‘B*’
inherit2.cpp:26:7: note: void P::change(C*) <near match>
inherit2.cpp:26:7: note:   no known conversion for argument 1 from ‘A*’ to ‘C*’
inherit2.cpp:38:12: error: call of overloaded ‘change(A*&)’ is ambiguous
inherit2.cpp:38:12: note: candidates are:
inherit2.cpp:21:7: note: void P::change(B*) <near match>
inherit2.cpp:21:7: note:   no known conversion for argument 1 from ‘A*’ to ‘B*’
inherit2.cpp:26:7: note: void P::change(C*) <near match>
inherit2.cpp:26:7: note:   no known conversion for argument 1 from ‘A*’ to ‘C*’

I will appreciate if you please help me solve the problem.
rahman

Answer 1

Polymorphism is one answer

class A
{
public:
    virtual void set() = 0;
};


class B : public A
{
public:
    virtual void set() { i = 1; }
private:
    int i;
};

class C : public A
{
public:
    virtual void set() { j = 1; }
private:
    int j;
};

class P
{
public:
    void change(A *a)
    {
        a->set();
    }
};

int main()
{
    A *b = new B();
    A *c = new C();
    P p;
    p.change(b);
    p.change(c);
    return 0;
}

With polymorphism there is no need for multiple change methods.