C++ inheritance: virtual member needs redeclaring?

Question

I'm sure this question has already been asked in one form or another, but I couldn't find the clue. Please consider the following C++-code:

// A.h
class A
{
    public:
        A();
        virtual ~A();
        virtual void setVisibility(bool v);
        virtual bool setVisibility();

    protected:
        bool visibility;
};

// B.h
class B : public A
{
    public:
        B();
        virtual ~B();
};


// C.h
class C : public B
{
    public:
        C();
        virtual ~C();
        virtual void setVisibility(bool v);
        virtual bool setVisibility();
};

// A.cpp
#include "common.h"
A::A() {}
A::~A() {}
void A::setVisibility(bool v) { this->visibility = v; }
bool A::setVisibility() { return this->visibility; }

// B.cpp
#include "common.h"
B::B() {}
B::~B() {}

// C.cpp
#include "common.h"
C::C() {}
C::~C() {}
void C::setVisibility(bool v) { /* do nothing */ }
bool C::setVisibility() { return false; }

// common.h - does nothing else than joining the header files together
#include "A.h"
#include "B.h"
#include "C.h"

calling:

C* myC = new C();
cout << "Set visibility true" << endl;
myC->setVisibility(true);

I tried several things. If I declare both methods virtually in C, it compiles but I get a segmentation fault at myC->setVisibility(true). If I remove the declaration (which shouldn't be necessary anyway, as they're inherited from B and A, right?), then it tells me that C doesn't have these methods.

And I don't want to reimplement the methods in B. If I declare them everywhere including B, it tells me that there's no implementation of these methods in B.

What should I do now? I need virtual, because I'm not always gonna use C as variable type in the calling example.

I'm using GCC on a 64 bit machine.

Edit: Corrected the copy/paste-mistake. I named the classes A, B and C for simplicity and didn't copy the code correctly. But unfortunately, the problem remains

Edit 2: Added common.h

Edit 3: Hmm... copying this code actually works fluently. But the architecture is the same. Except that I compile my code into a shared library using the flags -shared -fPIC. The calling code is in the application that uses this library. Nothing else is different. Gotta check again.

Thanks for any tips pointing me to the right direction. regards

also look this question http://stackoverflow.com/questions/4891139/inheritance-of-virtual-member-functions-with-the-same-name/4891406#4891406 — UmmaGumma, Feb 06 '11 at 14:06
in C.cpp you are defining A::setVisibility, is it an error you made in posting the question ? otherwise you are violating the One definition Rule.. — Francesco, Feb 06 '11 at 14:07
Your C::setVisibility looks like a violation of Liskov Substitution Principle. — Sjoerd, Feb 06 '11 at 14:29
The point is that I actually don't want to define it again but I'd like to **override** it. — Atmocreations, Feb 07 '11 at 20:18
vote for close as "storno" because of asking the wrong question. — Atmocreations, Feb 10 '11 at 20:23

score 4 · Answer 1 · answered Feb 06 '11 at 14:03

4

in C.cpp, don't define A::setVisibility(), it should be C::setVisibility()

answered Feb 06 '11 at 14:03

Javier

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sorry. typing mistake. please check my comment and the updated version – Atmocreations Feb 07 '11 at 13:09

score 1 · Answer 2 · answered Feb 06 '11 at 14:04

1

In C.cpp, you're defining A::setVisibility, not C::setVisibility.

answered Feb 06 '11 at 14:04

robert

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sorry. typing mistake. please check my comment and the updated version – Atmocreations Feb 07 '11 at 13:09

score 0 · Answer 3 · answered Feb 06 '11 at 14:48

0

You can change your class C to:

// C.h
class C : public B
{
     public:
        C();
        virtual ~C();
        using A::setVisibility;
        virtual bool setVisibility();
};

This will "reintroduce" all kinds of setVisibility defined in A.

answered Feb 06 '11 at 14:48

mmmmmmmm

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sorry, it was a typing mistake. is this still required if you check the updated version? – Atmocreations Feb 07 '11 at 13:10

score 0 · Accepted Answer · answered Feb 10 '11 at 20:21

The other answers are all correct before the correction. But it's not the solution to the problem. There actually isn't any problem at all. The problem lies in my implementation of the setVisibility-method, that's where the segfault occurs. Therefore the solution can't be found here.

Thanks to all who tried to help! regards

C++ inheritance: virtual member needs redeclaring?

4 Answers4