[Boost-users] Boost::shared_ptr from void

From: Dave Nay (dave.nay_at_[hidden])
Date: 2007-02-14 17:37:26

Hi All!

I am using a third party library where I enqueue a series of events.  Each
of these events allows the passing of a user context void*.  I am attempting
to pass the address of a boost::shared_ptr as my context.

        typedef boost::shared_ptr<CBuffer> CBufferPtr;

        for (i = 0; i < PREQUEUESIZE; i++)
        {
                handle = RegisterBuffer(buffer->m_pBCAMBuffer, m_AOISize);
                QueueBuffer( handle, &buffer ); // The second parameter is a
void* user context data
        }

In the above code "buffer" is my shared_ptr.

Later, in my event handler I have the following:

        CBufferPtr buffer = static_cast<CBufferPtr>(result.Context());

This does not compile due to the following error in VS2005:

1>c:\boost\include\boost-1_33_1\boost\shared_ptr.hpp(125) : error C2440:
'initializing' : cannot convert from 'const void *' to 'CBuffer *'
1>        Conversion from 'void*' to pointer to non-'void' requires an
explicit cast
1>        d:\sourcecode\test.cpp(1572) : see reference to function template
instantiation 'boost::shared_ptr<T>::shared_ptr<const void>(Y *)' being
compiled
1>        with
1>        [
1>            T=CBuffer,
1>            Y=const void
1>        ]

The problem seems to be that the third party library call to
result.Context() is returing a const void*.  It also seems to me that my
handler code is actually executing the overloaded operator=, and can never
actually cast from a void* to a shared_ptr<T>.

What can I do to successfully cast a void* to a shared_ptr<T>?

Thanks,
Dave