Subject: Re: [boost] [smart_ptr] enable_shared_from_this and shared_ptr to a base class
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-06-24 02:52:37
On Mon, Jun 24, 2013 at 10:28 AM, Adam Romanek <romanek.adam_at_[hidden]>wrote:
> I have a question related to using shared_from_this() and a shared_ptr
> to a base class.
> Here's a modified version of the enable_shared_from_this usage example
> from its documentation web page:
> #include <boost/enable_shared_from_**this.hpp>
> #include <boost/shared_ptr.hpp>
> #include <cassert>
> class X
> virtual void foo() = 0;
> class Y: public X, public boost::enable_shared_from_**this<Y>
> virtual void foo()
> int main()
> X* x_ptr = new Y;
> boost::shared_ptr<X> sp(x_ptr);
> First, class Y is now derived from class X. Secondly, shared_ptr's
> template argument is now X and the parameter to the shared_ptr's
> constructor is now a pointer to X.
> Now, calling shared_from_this() in X and/or Y throws boost::bad_weak_ptr.
> Is this correct behavior? Is it documented somewhere?
This is expected, given the way it's implemented and described.
shared_from_this() description  mentions that there must be at least one
shared_ptr that owns the object. I didn't find any formal definition of the
"owns" relation but it doesn't look to me that it applies to your example,
because there is no shared_ptr pointing to Y in your code.
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