Question

Consider this demo program:

#include <stdio.h>

class Base
{
public:
    virtual int f(int) =0;
    virtual int f(){ return f(0); }

    virtual ~Base(){ }
};

class Derived : public Base
{
public:
    int f(int i)
    {
        return (10 + i);
    }
};

int main(void)
{
    Derived obj;
    printf("%d\n", obj.f(1));  // This works, and returns 11
    printf("%d\n", obj.f());   // Adding this line gives me the error listed below
}

Which gives me the following compilation error:

virtualfunc.cpp: In function ‘int main()’:
virtualfunc.cpp:25:26: error: no matching function for call to ‘Derived::f()’
virtualfunc.cpp:15:9: note: candidate is: virtual int Derived::f(int)

My hope was that a call to obj.f() would result in a call to Base::obj.f() since the derived class doesn’t define it, which would then result in a call to Derived::obj.f(0) per the definition in class Base.

What am I doing wrong here? Is there a way to accomplish this? Specifically, I’d like the call to obj.f() to return 10.

(Also please note that I realize I could use a default argument to solve this, but this code is simply a concise example of my issue, so please don’t tell me to use default arguments.)

Thanks.

Answer 1

The reason is, that the defined f (in Derived ) hides the f functions from the Base class. The solution is to add using. Like this:

class Derived : public Base
{
public:
    int f(int i)
    {
        return (10 + i);
    }

//  vvvvvvvvvvvvvv
    using Base::f;
};