Question

Okay, so I’m trying to override a function in a parent class, and getting some errors. here’s a test case

#include <iostream>
using namespace std; 

class A{
public:
    int aba;
    void printAba();
};

class B: public A{
    public:
    void printAba() new;
};

void A::printAba(){
    cout << "aba1" << endl;
}

void B::printAba() new{
    cout << "aba2" << endl;
}

int main(){
    A a = B();

    a.printAba();

    return 0;
}

And here’s the errors I’m getting:

Error   1   error C3662: 'B::printAba' : override specifier 'new' only allowed on member functions of managed classes   c:\users\test\test\test.cpp 12  test
Error   2   error C2723: 'B::printAba' : 'new' storage-class specifier illegal on function definition   c:\users\test\test\test.cpp 19  test

How the heck do I do this?

Answer 1

There’s no need to put any keywords in the derived class to override a function.

class B: public A{
    public:
    void printAba();
};

But the base class’s method should be virtual, to allow the method be selected depending on the actual identity of the variable.

class A{
public:
    int aba;
    virtual void printAba();
};

---

And if you create an B on stack and copy into A, slicing would occur. You should create a B on heap and cast the pointer as A.

A* a = new B();
a->printAba();  // if printAba is not virtual, A::printAba will be called.
delete a;