[Boost-users] Copy a smart pointer into allocated memory

Subject: [Boost-users] Copy a smart pointer into allocated memory
From: Tiago Alves (talves_at_[hidden])
Date: 2009-06-12 07:22:08

Hi, and sorry for the probable newbieness of this question!

I want to put weak_ptr into a piece of memory previously allocated.

this is my code:

// construct a weak_ptr from a share_ptr
boost::weak_ptr<Obj>* cameraPtr = new boost::weak_ptr<Obj>(obj_share_ptr);
// lua_newuserdata allocs memory and returns a pointer to it, just like 
malloc.
boost::weak_ptr<Obj>* camera = 
static_cast<boost::weak_ptr<Obj>*>(lua_newuserdata(pLuaState,sizeof(boost::weak_ptr<Obj>)));

Now i want camera to be a weak_ptr of ObjPtr.
I tried different ways to do this, such as
*camera = boost::weak_ptr<Obj>(obj_share_ptr);
or
camera->swap(*cameraPtr);
or
*camera = *cameraPtr;

I think none of these work because in fact they all do a swap() between 
camera and cameraPtr. Since camera is just an malloc, it will try to 
swap dirty memory and segfault sometimes (yes, sometimes this worked).

Out of desperation, i did this:
memcpy(camera,cameraPtr,sizeof(boost::weak_ptr<Obj>));

Which seems to work but it stinks. It's copying an object with memcpy 
instead of using its constructor.

Is there a better way to do this?
Thanks,
Tiago Alves