How to call base class's function that is not defined in derived class?

Question

I always thought public methods of base class do get inherited by the derived class, even thought the derived class did not had definition of that particular method. For example

#include <iostream>

using namespace std;


    class A {
    public:
        int f() { cout << 3; return 0;}
        int f(int x) {cout << x; return 0;}
    }; 

    class B: public A {
    public:
        int f() {std::cout << 5; return 0;}

    };


    int main(){
       B ob;
       ob.f(7); 

       return 0;
    }

I was expecting the result to be : 7 , but I get compilation error saying

" error: too many arguments to function call, expected 0, have 1; did you mean 'A::f'?"

I know what the error is trying to say but I am little confused that the fuction from the Base class is not called.

overloading a function in derived class hides all base class versions — Gaurav Sehgal, Jun 14 '16 at 04:57
I found a link from stackoverflow - http://stackoverflow.com/questions/411103/function-with-same-name-but-different-signature-in-derived-class which explains the question lucidly. — pokche, Jun 14 '16 at 05:01

score 7 · Answer 1 · answered Jun 14 '16 at 05:01

Overloading a method in a derived class hides all base class versions.Even if the signature is different.If a method with the same name as in base class, exists in derived class then you won't be able to directly call base class versions.

You can do

  ob.A::f(7);

score 2 · Answer 2 · answered Jun 14 '16 at 05:09

2

With your posted code, B::f shadows all versions of A::f. You can call A::f(int) from an object of type B by using couple of methods.

Use A::f explicitly.
```
B ob;
ob.A::f(7); 
```

Bring all versions of A::f into the scope of B.

class B: public A {
   public:
      using A::f;
      int f() {std::cout << 5; return 0;}

};

Now you can use:

B ob;
ob.f(7);

answered Jun 14 '16 at 05:09

R Sahu

204,454
14
159
270

@ R Sahu ,but the above case works in Java. – asad_hussain Jun 14 '16 at 05:26
@a874, I am not familiar with Java. I can't comment on that. However, that has nothing to do with whether it works in C++. – R Sahu Jun 14 '16 at 05:28

score 2 · Answer 3 · answered Jun 14 '16 at 05:13

2

You can use another way:

class B: public A {
    public:
        using A::f;
        int f() {std::cout << 5; return 0;}

    };

answered Jun 14 '16 at 05:13

Sumeet

779
6
20

How to call base class's function that is not defined in derived class?

3 Answers3