[vtkusers] Recreating a smart pointer object after deletion

[David Gobbi]

On Tue, Nov 23, 2010 at 10:04 AM, David Doria <daviddoria at gmail.com> wrote:

> Once you Delete() a smart pointer, how do you create a new object with
> the same pointer?
>
> Below is a demo. Can someone please confirm or correct the comments?
>
> // Create a smart pointer to a vtkFloatArray object
>  vtkSmartPointer<vtkFloatArray> distances =
>    vtkSmartPointer<vtkFloatArray>::New();
>  std::cout << distances->GetNumberOfComponents() << std::endl;
>
> // Delete the vtkFloatArray object, but the smart pointer still exists
>  distances->Delete();
>  //std::cout << distances->GetNumberOfComponents() << std::endl; //
> Of course this will crash
>

Yeah, calling Delete() on a smart pointer is not a good thing.


> // This is wrong, because this creates another smart pointer AND another
> object
>  distances = vtkSmartPointer<vtkFloatArray>::New();
>  std::cout << distances->GetNumberOfComponents() << std::endl; //
> Even though it is wrong, it seems like it should still work, but it
> crashes
>

Like you, my first guess is that it should work. But I suspect that it
breaks because it doesn't do reference count additions/subtractions in the
correct order, what with the creation of a temporary smart pointer followed
by assignment to another smart pointer and deletion of the temporary.


> // This is right because it leaves the smart pointer alone and gives
> it a new vtkFloatArray object
>  distances.Take(vtkFloatArray::New());
>  std::cout << distances->GetNumberOfComponents() << std::endl; // It
> still crashes (Deleting unknown object: vtkObjectBase)
>

The method you want is TakeReference().  The Take() method is a static
method.

  David
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