[vtkusers] clarification on smart pointer usage

[Richard Frank]

Ah i see, thanks. I wasn't using the smart pointer template ::New(). 

Rick Frank

On Jan 2, 2013, at 5:08 PM, David Lonie <david.lonie at kitware.com> wrote:

> On Fri, Dec 28, 2012 at 11:57 PM, Richard Frank <rickfrank at me.com> wrote:
>> Thanks- I'm doing that. Given two smart pointers allocated with ::New() macro, what should happen to the lhs on assignment?
> 
> If I remember correctly, this is what's happening:
>  
> >> vtkSmartPointer<vtkVolumeRayCastCompositionFunction> one = vtkVolumeRayCastCompositionFunction::New();
> 
> one's reference count is 2 -- once from vtkVolumeRayCastCompositionFunction::New(), and again from vtkSmartPointer::operator=().
> 
> >> vtkSmartPointer<vtkVolumeRayCastCompositionFunction> two = vtkVolumeRayCastCompositionFunction::New();
> 
> two's reference count is also 2.
> 
> >> one = two;
> 
> one should get decref'd to 1, while two gets increased to 3. Since one's refcount never gets to zero, the destructor never gets called.
> 
>  Using the method David mentioned:
> 
>> > vtkSmartPointer<vtkVolumeRayCastCompositionFunction> one =
>> >  vtkSmartPointer<vtkVolumeRayCastCompositionFunction>::New();
>  
> one has 1 reference. You can check this by calling GetReferenceCount on the pointers.
> 
> If you don't need to reassign the pointer, vtkNew is another useful smart pointer class that you may find useful. This article provides a nice short summary of these classes, and also vtkWeakPointer:
> 
> http://www.kitware.com/source/home/post/7
> 
> Hope this helps,
> Dave
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