Overload a virtual method in a derived class so it takes more parameters in C++

Question

I have an abstract class A with the pure virtual method void foo(int a) = 0

Then I have several classes that inherit from A and all of them define the method foo. But I need one of them, B, to make it so foo takes an extra parameter, int b, so sort of an overload.

Then I would like to do this:

A *bInstance = new B();
bInstance -> foo(1, 2);

But I get an error telling me that foo is taking too many parameters.

Writing this, I realize it's kind of a weird thing to do so maybe you can't do this and it's good that you can't do it. But in case it is possible, please do tell me how I should go about it.

Answer 1

You can use the overloaded function of B only if the pointer to use is of type B.

See:

#include <iostream>
#include <memory>

class A{
public:
  virtual void foo(int a) = 0;
};

class B : public A
{
public:
    virtual void foo(int a) override
    {

    }
    void foo(int a, int b)
    {
        std::cout << a << "," << b;
    }
};

int main(){
    auto b = std::make_shared<B>();
    b->foo(1, 2);
    
    //to use a:
    A* aPtr = b.get();
    aPtr->foo(1);

    return 0;
}