Re: [Boost-users] enable_shared_from_this - or an alternative..

From: Stuart Dootson (stuart.dootson_at_[hidden])
Date: 2006-03-20 05:28:20

On 3/20/06, James Hughes <JHughes_at_[hidden]> 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

I suspect you're running foul of this condition on
enable_shared_from_this: "There must exist at least one shared_ptr
instance p that owns  t." If you're using something like:

boost::shared_ptr<CSource1> pSource(new CSource1);

then when the CSource1 constructor is executed, the raw pointer hasn't
been assigned to the shared pointer yet.

HTH

Stuart Dootson