[Boost-users] Newby question re (boost::shared_ptr) enable_shared_from_this

From: ethann.castell_at_[hidden]
Date: 2007-01-20 22:00:35

Hi,

I'm still fairly new to C++ and I'm in the process of converting pointers 
to boost shared pointers. I have a question regarding the use of 
enable_shared_from_this.

I would like to store a self-referencing pointer within the object. 
Something like:

class someclass : public boost::enable_shared_from_this<someclass>
{
        protected: boost::shared_ptr<someclass> m_ptr_this;
        someclass()
        {
                m_ptr_this = shared_from_this(); 
        }
}

And then access m_ptr_this in classes derived from someclass, and pass as 
a parameter to methods of other (derived or non-derived) classes. eg.

class someclass2 : public someclass
{
...
        some_func(){
                someclass3* f = new someclass3();
                someclass3->do_something( m_ptr_this );
        }
}

I understand that using a shared_ptr (without enable_shared_from_this) to 
self-reference will lead to problems because the reference count of the 
pointer will never reach zero and therefore the memory will never get 
released.  But as enable_shared_from_this uses a weak pointer internally, 
does this get around the problem? I'm getting a little confused because it 
gets typecast from weak_ptr to shared_ptr and I'm not sure what this leads 
to.

I've also considered having a member function return the pointer:

boost::shared_ptr<someclass> someclass::get_this()
{
        return shared_from_this();
}

and then calling the routine like this;

someclass3->do_something( get_this() );

but I think that this will cause a problem because the documentation says 
not to use boost pointers which are only created as temporary variables. 
i.e. store all boost pointers in vars.

What I'm hoping to do is avoid having to declare extra shared_ptr vars all 
over the place.

Any help will be most appreciated. And I'll owe you a beer!

Regards
Ethann Castell