Re: [boost] [smart_ptr] enable_shared_from_this and shared_ptr to a base class

On Mon, Jun 24, 2013 at 10:28 AM, Adam Romanek wrote:

Hi,

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 #include #include <cassert>

class X { public: virtual void foo() = 0; };

class Y: public X, public boost::enable_shared_from_**this<Y> { virtual void foo() { shared_from_this(); } };

int main() { X* x_ptr = new Y; boost::shared_ptr<X> sp(x_ptr); sp->foo(); }

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 [1] 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. [1] http://www.boost.org/doc/libs/release/libs/smart_ptr/enable_shared_from_this...