-----Original Message----- From: David Klein [mailto:d.klein@ascaron.com] Sent: 20 March 2006 10:27 To: boost-users@lists.boost.org Subject: Re: [Boost-users] enable_shared_from_this - or an alternative..

boost-users-bounces@lists.boost.org wrote:

...

Hello All,

I have a couple of classes that I want to self register themselves with a monitoring class. To do this they must pass a shared_ptr of themselves to the monitor register function.

Therefore I need to make a shared_ptr form the this pointer, in the constructor.

I have derived my classes from enabled_shared_from_this...(code to get monitor omitted)

//psuedo code.. monitor::AddSource1(boost::shared_ptr<CSource1>); monitor::AddSource2(boost::shared_ptr<CSource2>);

class CSource1 : public enable_shared_from_this<CSource1> { CSource1() { Monitor->AddSource(shared_from_this()); }; }

and

class CSource2 : public base1, public enable_shared_from_this<CSource2> { CSource2() { Monitor->AddSource(shared_from_this()); };} }

This all compile fine, but when run, the shared_from_this call asserts with a bad weak ptr - at the time of calling the weak_ptr has no content, and looking at the boost code, I cannot see where it is supposed to get set to access the this value.

Should I be using enable_shared_from_this in this way or is there a better way to convert the this ptr to a shared_ptr in a constructor that I need to use.

James _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

hi james,

see: http://boost.org/libs/smart_ptr/sp_techniques.html#in_constructor

HTH dave _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Thanks Dave, that does cover the problem well. However, I cannot use the null deleter mechanism suggested as the shared_ptr is passed on to monitor and is used there. The second scheme, using a factory fucntion, would seem to be approriate, however, how to I handle creation when the CSource1 class is actually to be used as a base class? If the factory function is in CSource1, it doesnt know about any derived classes. I don't want to have to write factory functions in every dervied class - that seems a waste. Is there a correct technique for getting around this issue? I am assuming a template of some description, but now sure what that entails. James