views:

113

answers:

2

Hi all,
I am trying to inherit two equally named methods with different parameter lists to a derived class. One of them is virtual and overridden in the derived class, the other one is non-virtual. Doing so, i get a compile error while trying to access the non-virtual method of the base class from an derived class object.

Here is the code snippet

class Base {
public: 
    void f() {
        cout << "[Base::f()]" << endl;
    }

    virtual void f(int arg) {
        cout << "[Base::f(" << arg << ")]" << endl;
    }
};


class Deriv : public Base {
public:
    virtual void f(int arg) {
        cout << "[Deriv::f(" << arg << ")]" << endl;
    }
};


int main() {
    Deriv d;
    d.f(-1);    
    d.f();  // <<-- compile error   
    return 0;
}

which produces the following compile error:

error: no matching function for call to ‘Deriv::f()’
note: candidates are: virtual void Deriv::f(int)

I am not an expert in C++, but until now I thought to be right in making the assumption that member methods can be completely distinguished by their signatures. Thus, the non-virtual method Base::f() should not be overridden and should remain accessible. Am I wrong with this?

Here are some interesting/additional comments on that:

    - the overriding method Deriv::f(int arg) could be non-virtual as well; the error occurs in either way
    - the error disappears/can be circumvented...
      ... by casting the Deriv object to the Base class
      ... when not overriding Base::f(int arg) in Deriv
      ... by adding the command "Base::f;" to the public part of Deriv

So, since I already know how to avoid this compile error, I am mainly interested in why this error happens! Please help me to shed light on that...

Thanks in advanvce! emme

+2  A: 

In Deriv, add this:

using Base::f;

In addition to the link given by @DumbCoder, you can find more details in my answer to a similar question: http://stackoverflow.com/questions/888235/overriding-a-bases-overloaded-function-in-c/888313#888313

Fred Larson
yeah, i already know this (see my comments below the code snippet). but why do have to add this and what does this do?
Emme
ok, thank you very much for this link! helped a lot!
Emme
+2  A: 

Derived class function hides the base function defintion. Detailed explaination as to why and how

DumbCoder
"name hiding" is the "official" term you may want to google.
Alexandre C.