0

Is there a way to access superclass methods from a subclass? I made Apple class as a subclass of Fruit class, but I can not access to setName function in Fruit class from an object of Apple class. Could you give me any advice?

#include <iostream>
#include <string>
using namespace std;

class Fruit {
public:
    Fruit(string str)
    {
        cout << "Fruit class" << endl;
        name = str;
        cout << name << endl;
    }

    void setName(string str) {
        name = str;
    }
private:
    string name;
};

class Apple:Fruit {
public:
    Apple() :Fruit("apple"){
        cout << "Apple class" << endl;

    }
    void setName(string str) {
        name = str;
    }
};

int main()
{
    Apple apple;

    apple.setName("Orange");  //I can not access to setName function from apple
    return 0;
}
Miria
  • 1
  • 1

4 Answers4

2

Use public inheritance like this:

class Apple : public Fruit

The default visibility for class is private if it's not specified. That is why you're not able to access the public members of the base class because they're now private due to their private visibility.

Contrary to a class, the default visibility for a struct is public i.e.:

struct Base {};
struct Derived : Base {}; // public inheritance

In your code, the overridden setName() method in the derived class is redundant as it cannot manipulate the private data member name directly. You'll have to use the base class method to set the name in your overridden method. As of now, you're not doing anything else in that method so you don't need it.

Here's your working code (live):

#include <iostream>
#include <string>
using namespace std;

class Fruit {
public:
    Fruit(string str)
    {
        cout << "Fruit class" << endl;
        name = str;
        cout << name << endl;
    }

    void setName(string str) {
        name = str;
    }
private:
    string name;
};

class Apple : public Fruit {       // public inheritance
public:
    Apple() :Fruit("apple"){
        cout << "Apple class" << endl;
    }
    // void setName(string str) {  // Redundant!
    //     name = str;             // `name` is not accessible here!
    // }
};

int main()
{
    Apple apple;
    apple.setName("Orange");      // Accessible here
    return 0;
}

For more relevant information, refer to this:
Difference between private, public, and protected inheritance

Azeem
  • 11,148
  • 4
  • 27
  • 40
  • 1
    Small nitpick: private inheritance is only used by default for `class`es because `private` is the default visibility for `class` members. In `struct Apple : Fruit {};` Fruit will be a public parent of Apple. – bitmask Mar 27 '20 at 04:52
  • @bitmask: Thank you for the input! I kept it focused on class as the OP's question didn't have any reference to the structs. – Azeem Mar 27 '20 at 04:53
  • @bitmask: I've updated my answer regarding `struct` also. Thanks, again! – Azeem Mar 27 '20 at 05:02
0

Your Apple class is using private inheritance (the default when the type of inheritance is not specified), so all of Fruit's public methods are private in Apple and thus are not accessible for main() to call. You need to use public inheritance instead to fix that.

Also, there is no need to re-implement setName() in Apple. The inherited setName() from Fruit will suffice, once it is inherited as a public method in Apple.

class Apple : public Fruit {
public:
    Apple() : Fruit("apple"){
        cout << "Apple class" << endl;
    }
};
Remy Lebeau
  • 555,201
  • 31
  • 458
  • 770
0

Use public inheritance 

class Apple:public Fruit

in class Default is Private 

class Apple:Fruit

is same as

class Apple:private Fruit

You made private here, So you can not access member of Fruit by object of Apple even if it is public.

class Apple:public Fruit
{
public:
    Apple() :Fruit("apple")
    {
        cout << "Apple class" << endl;
    }
};

Or if you want it is to private use like this

class Apple:Fruit 
{
public:
    Apple() :Fruit("apple")
    {
        cout << "Apple class" << endl;
    }
    void setName(string str) 
    {
      Fruit::setName(str);
    }
};
srilakshmikanthanp
  • 2,231
  • 1
  • 8
  • 25
0

First, change class Apple to

class Apple: public Fruit

then, use this method

apple.Fruit::setname()
Idea Wang
  • 1
  • 2