CODEWITHSUNDEEP
c++classinheritancepolymorphism
nedla2004
nedla2004

Reputation: 1145

Inherited Function Using Child Function

I was looking to have a base class and multiple child classes each with a separate implementations of one function used in many shared functions. This would be similar to this

class A {
    public:
    int a() {
        return 6;
    }
    int b() {
        return a() - 2;
    }
};

class B: public A {
    public:
    int a() {
        return 10;
    }
};

int main() {
    B x;
    std::cout << x.b() << std::endl;
}

How would I get x.b() to be 8 instead of 4?

Upvotes: 1

Views: 47

Answers (1)

Christophe
Christophe

Reputation: 73376

You need to make your function virtual, so that a() always refers to the implementation of a() in the object's real class: 

class A {
    public:
    virtual int a() {         //<<<<<<<<--------
        return 6;
    }
    int b() {
        return a() - 2;
    }
    virtual ~A() = default;  
};

In you version with a non-virtual function, the body of b() calls the only a() it knows, which is the A::a().

As a good practice, and to avoid nasty errors, when you define a virtual function indicate in the derived classes that you override the virtual function: 

class B: public A {
    public:
    int a() override {
        return 10;
    }
};

Another good practice is also to foresee a virtual destructor in the base class.

Upvotes: 2

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