[C++-sig] Attempt to Return Dangling Reference Error -- What'sthe solution?

[Bilokon, Paul]

Hi Dave,

Thought I should give more background. The library I'm wrapping is using
a custom smart pointer, which is really unfortunate. It would be
difficult (though desirable) to replace these custom shared pointers
with shared_ptr. Therefore I'm trying to provide a mechanism for calling
the functions expecting CustomPtr with a CustomPtr-to-copy by calling
clone and wrapping the copy into CustomPtr, wherever this has reasonable
semantics. Therefore I cannot wrap the return of clone into shared_ptr.
Is there any way to cheat the dangling reference detection mechanism?
(Of course, shared_ptr does not do release().)

Many thanks,
Paul

-----Original Message-----
From: Bilokon, Paul 
Sent: Wednesday, September 03, 2008 9:09 AM
To: 'Development of Python/C++ integration'
Subject: RE: [C++-sig] Attempt to Return Dangling Reference Error --
What'sthe solution?

Hi Dave,

Thanks a lot. Changing clone's signature to...

    virtual boost::shared_ptr<Animal> clone() const

did the trick. However, since I'm wrapping an existing library, I'm
trying to find a non-intrusive solution. I'd rather keep the current
signature of clone. Are there any other options?

Many thanks,
Paul

-----Original Message-----
From: c++-sig-bounces+paul.bilokon=lehman.com at python.org
[mailto:c++-sig-bounces+paul.bilokon=lehman.com at python.org] On Behalf Of
David Abrahams
Sent: Friday, August 29, 2008 3:53 PM
To: Development of Python/C++ integration
Subject: Re: [C++-sig] Attempt to Return Dangling Reference Error --
What'sthe solution?


on Fri Aug 29 2008, "Bilokon, Paul" <paul.bilokon-AT-lehman.com> wrote:

> Hi,
>
> I'm looking at this:
>
> http://www.boost.org/doc/libs/1_36_0/libs/python/doc/v2/faq.html#dangl
> in
> g
>
> ('I'm getting the "attempt to return dangling reference" error. What 
> am I doing wrong?')
>
> I understand the statement of the problem. However, suppose I need to 
> hold on to the new Python object and the C++ object contained therein.
> How do I achieve that?
>
> Let me give you the specific context.
>
>
> 	void takesAnimalRawPtr(Animal * animalRawPtr)
> 	{
> 	    cout << "This is " << animalRawPtr->whatIsIt() << endl;
> 	    Animal * clone = animalRawPtr->clone();
> 	    cout << "Now this is " << clone->whatIsIt() << endl;
> 	    delete clone;
> 	}

I suggest you make your clone() functions return a
boost::shared_ptr<Animal>.  That would make all your problems disappear.

HTH,

--
Dave Abrahams
BoostPro Computing
http://www.boostpro.com
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