Does destructor of derived class remove virtual table?

[Martin Koller]

Hi list,

I have a small example which gives me "pure virtual function called".

I'm calling a virtual function in the destructor of the base class, where
the pointer used is effectively pointing to a derived class, but the whole
thing is in the process of being destroyed.

Interesting for me is also, that I get the same error if I call b->isA() in
the constructor of Base.

I just wanted to know, if this behavior is correct in C++ terms or is it a
compiler issue ? (using gcc-2.3.2 on Linux)

(Please CC me on mail)

#include <iostream>

class Base
{
public:
Base(Base *x) { b = x; };
virtual ~Base()
{
b->isA();
};

virtual int isA() = 0;

private:
Base *b;
};

class Derived : public Base
{
public:
Derived() : Base(this) { std::cerr << isA() << std::endl; };

virtual int isA() { return 1; }
};


main()
{
Derived *d = new Derived();

delete d;
}

Thanks,

Martin

[Rolf Magnus]

Re: Does destructor of derived class remove virtual table?

Martin Koller wrote:
[color=blue]
> Hi list,
>
> I have a small example which gives me "pure virtual function called".
>
> I'm calling a virtual function in the destructor of the base class,
> where the pointer used is effectively pointing to a derived class, but
> the whole thing is in the process of being destroyed.[/color]

In the destructor of the base class, the derived part of the objects is
already destroyed, so it isn't anymore an instance of the derived
class.
[color=blue]
> Interesting for me is also, that I get the same error if I call
> b->isA() in the constructor of Base.[/color]

Same principle. In the base class constructor, the derived part of the
object does not yet exist. Therefore a polymorphic call won't call the
derived implementation of the virtual function.
[color=blue]
> I just wanted to know, if this behavior is correct in C++ terms or is
> it a compiler issue ? (using gcc-2.3.2 on Linux)[/color]

It is correct.

[David Harmon]

Re: Does destructor of derived class remove virtual table?

On Sat, 21 Feb 2004 17:03:32 +0100 in comp.lang.c++, Martin Koller
<m.koller@surfe u.at> was alleged to have written:[color=blue]
>I have a small example which gives me "pure virtual function called".
>
>I'm calling a virtual function in the destructor of the base class,[/color]

See also the topic "[23.3] When my base class's constructor calls a
virtual function on its this object, why doesn't my derived class's
override of that virtual function get invoked?" in Marshall Cline's C++
FAQ. The remarks regarding constructors mostly apply for the same
reasons to destructors. You can get the FAQ at:

http://www.parashift.com/c++-faq-lite/

[Martin Koller]

Re: Does destructor of derived class remove virtual table?

[color=blue]
> It is correct.[/color]

Thanks a lot for all replies.

Martin