Re: [Boost-users] [shared_ptr] Multiple enable_shared_from_this in inheritance tree

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De: "Edward Diener" À: boost-users@lists.boost.org Envoyé: Dimanche 25 Mars 2012 21:37:55 Objet: [Boost-users] [shared_ptr] Multiple enable_shared_from_this in inheritance tree

There was a Code Project article (http://www.codeproject.com/Articles/286304/Solution-for-multiple-enable_shar...) about a problem using multiple enable_shared_from_this derivations in an inheritance tree.

Does this problem actually exist in the current Boost implementation ?

I've been trapped by this two years ago, and now under 1.48 code below throws under VS2010 when calling B::shared_from_this(). // BEGIN #include #include struct A : boost::enable_shared_from_this <A> {}; struct B : boost::enable_shared_from_this <B> {}; struct C : A, B {}; int main() { boost::make_shared <C>()->A::shared_from_this(); boost::make_shared <C>()->B::shared_from_this(); return 0; } // END weak_this_ is null so you have a bad_weak_ptr exception in shared_count::shared_count( weak_count const & r ). Root problem seems to be that template function sp_enable_shared_from_this is only called for first matching specialization. Following code does not throw : (*DISCLAIMER* this could make your computer explode, and is probably utterly wrong anyway) boost::shared_ptr <C> c = boost::make_shared <C>(); c->A::shared_from_this(); boost::detail::sp_enable_shared_from_this (&c, c.get(), static_cast (c.get())); c->B::shared_from_this(); Regards, Ivan