[cfe-dev] is delete on abstract with non-virtal ever safe?

[Richard Smith]

On 4 Oct 2013 02:49, "emmanuel.attia" <emmanuel.attia at philips.com> wrote:
>
> > This has undefined behavior. You're calling a virtual function on an
object
> whose lifetime has ended (the destructor has already been called).
>
> my_destroy_interface has no destructor so the vtable is not cleared until
> the memory is released (since nothing alters it before i get in the
operator
> delete overload).
>
> Referring to the standards (i'm not sure its the right pdf):
> "The lifetime of an object of type T ends when:
> — if T is a class type with a non-trivial destructor (12.4), the
destructor
> call starts, or
> — the storage which the object occupies is reused or released."
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1905.pdf
>
> And that make totally sense since if i add a  (non-virtual) destructor it
> still flies, unless the destructor is non trivial (in that case i get as
> expected a pure virtual function call).

This is sort of beside the point, since you had undefined behaviour earlier:

> > This has undefined behavior (you're using 'delete', the static and
dynamic
> > types don't match, and your base class does not have a virtual
> > destructor).
>
> That's the point, i call the overload "my_destroy_interface::operator
> delete" and not the global delete operator. Since my_destroy_interface has
> no (non trivial) destructor this is the only thing happening when calling
> delete on a pointer to my_destroy_interface.

You can't reason like that about undefined behaviour. You deleted an object
thorough the wrong static type and the dtor is not virtual, so you've
already lost.

> > Nope. See above. Or try giving my_destroy_interface a user-declared
> > (non-virtual) destructor, and watch as it either gets called twice or
your
> > program starts to die due to a pure virtual function call (depending on
> > implementation details).
>
> Giving to my_destructor_interface a virtual destructor would make it
called
> twice as you said, thats why it's not there in this construct (and it
makes
> sense since its an interface).
>
>
>
>
> --
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http://clang-developers.42468.n3.nabble.com/is-delete-on-abstract-with-non-virtal-ever-safe-tp4025653p4034880.html
> Sent from the Clang Developers mailing list archive at Nabble.com.
>
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