Why are the inherited functions hidden in base class in this code?

Question

Possible Duplicate:
C++: rationale behind hiding rule

In this code sample from http://www.gotw.ca/gotw/005.htm, I was shocked to learn that in class Derived, f(int) and f(double) are not visible!

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

    virtual void f( double ) {
        cout << "Base::f(double)" << endl;
    }

    virtual void g( int i = 10 ) {
        cout << i << endl;
    }
};

class Derived: public Base {
public:
    void f( complex<double> ) {
        cout << "Derived::f(complex)" << endl;
    }

    void g( int i = 20 ) {
        cout << "Derived::g() " << i << endl;
    }
};

What is the reasoning behind this?

As I understand f( complex<double> ) has a different signature than the other two inherited versions of f().

Why are all three not visible in this scenario?
What are the ways to make sure the Base functions are visible in this case?

I can recommend Effective C++: Tip 33 – Stephan Dollberg Mar 18 '12 at 11:53 — Stephan Dollberg, Mar 18 '12 at 11:53

score 2 · Answer 1 · answered Mar 18 '12 at 11:52

2

1) Why are all three not visible in this scenario?

This is how name hiding works. Names in an inner scope hide all names from outer scopes (and this happens before overload resolution or anything else occurs).

2) What are the ways to make sure the Base functions are visible in this case?

Bring their names into the inner scope with using declarations (using Base::f;, using Base::g;), or change their names so that they are not hidden by the names in the derived class.

answered Mar 18 '12 at 11:52

Mankarse

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(regarding 1) but the signatures are different! How can one signature hide another one? – Lazer Mar 18 '12 at 11:55
@Lazer: The signatures are different, but the names are the same. Name hiding works on names. – Mankarse Mar 18 '12 at 12:00
@Lazer Because it’s *name hiding*, not *signature* hiding. – Konrad Rudolph Mar 18 '12 at 12:02
@KonradRudolph: wow, C++ is a black hole. – Lazer Mar 18 '12 at 12:14

Oliver Charlesworth · Answer 2 · 2012-03-18T12:00:04.963

1

See http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.9.

Essentially, Derived::f(complex<Double>) hides Base::f(int) and Base::f(double). You re-expose them by adding using Base::f to your definition of Derived.

The rationale for this is explained quite well in Item 33 of Effective C++.

edited Mar 18 '12 at 12:00

answered Mar 18 '12 at 11:49

Oliver Charlesworth

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Why are the inherited functions hidden in base class in this code?

2 Answers2