Calling a derived function from an array of the base class

Question

How do you call a derived function from an array of the base class?

Ex:

#include <iostream>
#include <string>

class a{

public:
    virtual void prnt(){
        std::cout<<"a"<<std::endl;
    }
};

class b: public a{

public:
    virtual void prnt(){
        std::cout<<"B"<<std::endl;
    }
};

int main()
{
    a array[3];
    array[0] = a();
    array[1] = b();
    array[2] = a();

    array[1].prnt();
}

The output for this example is a.

is there anyway to fix this?

`b` is not a possible output for this code. Did you mean `a` ? — M.M, Jul 24 '17 at 04:19
You can't because it's an array of the base class, which means the objects in it are of the base class, not the derived class, so you can't call derived class functions on it because it's not the derived class. — user253751, Jul 24 '17 at 04:43

score 0 · Accepted Answer · answered Jul 24 '17 at 04:22

As Justin commented, you're witnessing a case of object slicing. One way to get the behavior you're expecting is to use pointers:

int main() {
    a* array[3];
    array[0] = new a();
    array[1] = new b();
    array[2] = new a();

    array[1]->prnt();

    // Don't forget to delete them!
    for (int i = 0; i < 3; ++i) {
        delete array[i];
    }
}

score 0 · Answer 2 · answered Jul 24 '17 at 04:23

0

 array[1] = b();

The above is object slicing.Read about it here

Polymorphism works with pointers and references only.

 a *array[3];
 array[0] = new a();
 array[1] = new b();
 array[2] = new a();

 array[1]->print()

answered Jul 24 '17 at 04:23

Gaurav Sehgal

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Calling a derived function from an array of the base class

2 Answers2