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.

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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

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Edit 2: Added common.h

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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

Answer 1

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