Boost logo

Boost :

Subject: [boost] [smart_ptr] enable_shared_from_this and shared_ptr to a base class
From: Adam Romanek (romanek.adam_at_[hidden])
Date: 2013-06-24 02:28:43


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?

I know that the example is a bit unrealistic since most of the time
shared_ptr is constructed directly from the pointer returned by 'new Y'
or created by make_shared() but still, this is something that bothers me.

Adam Romanek

Boost list run by bdawes at, gregod at, cpdaniel at, john at