Question

Normal overriding would work this way:

class Fruit {
public:
    string color();
};

string Fruit::color() {
    return "Unkown";
};

class Apple : public Fruit {
public:
    string color();
};

string Apple::color() {
    return "Green";
};

Now, you’ld call this like:

Apple *apple = new Apple();
std::cout << apple->color();

This will output Green, which is correct! However, running it in the following situation (which is just an example, of course):

Apple *apple = new Apple();
printHealthy(apple);

// Method printHealthy:

void printHealthy(Fruit *fruit) {
    std::cout << fruit->color();
};

This will output Unkown, which I can understand, since you’re casting Apple to Fruit, and thus ‘replace’ its methods. But how can I still get to know its real color?
Requirements:

• I need to know what its real color is.
• I cannot rely on the Apple-class. There will be lots of more Apple‘s, which are assigned on the go.
• every Apple-class (eg. Tomato, they have different names of course) is a subclass of Fruit.
• not every class implements all methods. For example, there might be an Apple which color is ‘unkown’, so it doesn’t override that method and instead, run Fruit‘s method.

Answer 1

Mark the function virtual in the base class.

class Fruit {
public:
    virtual string color();
};