Re: Smart Pointer Issue

From:

"Thomas J. Gritzan" <phygon_antispam@gmx.de>

Newsgroups:

comp.lang.c++

Date:

Fri, 13 Feb 2009 10:17:41 +0100

Message-ID:

<gn3ds4$mqb$1@newsreader2.netcologne.de>

anon schrieb:

SG wrote:

On 12 Feb., 14:00, anon <sfdhrt...@ebay.de> wrote:

kmakaro...@gmail.com wrote:

Hello, I have the following classes:
class ServiceBase
{
        public:
                ServiceBase() {}
                ~ServiceBase() {}

[...]

ServicePtr& operator=( ServicePtr<ServiceBase>& r)
         {
             release();

             ServicePtr cpyObj( dynamic_cast<X*> (r.get()));
             r.release();
             acquire(cpyObj);
             cpyObj.release();

             return *this;
         }

dynamic_castis not going to work on non-polymorphic types.

Cheers!
SG

This solves the problem. Anyone trying something stupid with the
template will notice :

Doesn't work.

ServicePtr& operator=( ServicePtr<ServiceBase>& r)
          {
              release();

              X *tmp = dynamic_cast<X*> (r.get());
              assert( NULL != tmp );

              ServicePtr cpyObj( tmp );

This will make a smart pointer which owns the tmp pointer.

r.release();

This lets r release its pointee, after that either its pointee is
deleted, or there's another smart pointer holding ownership.

              acquire(cpyObj);
              cpyObj.release();

              return *this;
          }

Here the class either stores an already deleted pointer, or there are
two families of smart pointers who owns the pointee.

Altough this smart pointer doesn't delete the pointee but call its
Stop() function, I don't think it's a good idea to call Stop() while
still using it.

--
Thomas