[vtkusers] using vtkSmartPtrs

[Sean McInerney]

Eric,

   You may be overlooking *all* incrementing of your object's reference 
count. vtkSmartPtr increments its object's reference count on 
construction and decrements it on destruction, but you may be forgetting 
that a vtkObject sets its own reference count to 1 in its constructor.

e.g.

void f()
{
   vtkSmartPtr<vtkObject> ptr(vtkObject::New());

   // Even though the smart pointer is destroyed when this function
   // goes out of scope and consequently decrements the reference count
   // of the object created above, the object itself is not destroyed.
   // Its reference count is still 1 and, therefore, a memory leak!
}

To avoid such a leak, the above function should be composed like this:

void f()
{
   vtkObject* object = vtkObject::New();
   vtkSmartPtr<vtkObject> ptr(object);

   object->Delete(); // The object's reference count is now 1

   // The smart pointer as well as the object that it references will
   // be destroyed when this function goes out of scope.
}

   Hopefully, your woes are a simple matter of book keeping. If you are 
already addressing the issue that I have outlined, something more 
sinister may be at work.

-Sean

Harlow Eric D Contr 412 TW/ENR wrote:
> 1.  How common is it to wrap vtk objects in vtkSmartPtrs?  This is causing a
> memory leak in our code.
> 
> vtkSmartPtr<OpenGLRenderWindow>  RenderWindow_;  
> 
> 
> 2.  We are placing all of the VTK functions in our VTK Application in a C++
> dll library so that the end user doesn't have to be vtk expert.  Are there
> some VTK developers out there that have had success in wrapping the VTK
> member functions/objects in a C++ MFC dll?  It was easy enough when we were
> building our test Application by calling the vtk functions either from the
> MFC ViewClass or classes in the Application project space.     
> 
> Thanks
> 
> -Eric