[vtkusers] When to delete objects?

[Mike Jackson]

Also you can use the vtkSmartPointer class to wrap your local  
objects, so taking some of the examples from below:

void myfunction()
{
   vtkSmartPointer<vtkSomething> something =  
vtkSmartPointer<vtkSomething>::New(); //ref count starts as 1
   //do some things here
  // 'something' will be deleted when this method returns, saving a  
line of code and ensuring that the object is cleaned up.
}


Just my two cents..
-- 
Mike Jackson   Senior Research Engineer
Innovative Management & Technology Services


On May 21, 2007, at 9:40 AM, David E DeMarle wrote:

> Hello,
>
> This is what I do:
> 1)  Make sure there is a Delete() for each New() around each  
> temporary (local) use.
>
> void myfunction()
> {
>   vtkSomething *something = vtkSomething::New(); //ref count starts  
> as 1
>   //do some things here
>   something->Delete(); //ref count -- = 0 which will call  
> something's destructor to and deallocate it
> }
>
> 2) When I want to keep the object around and use it later, I save  
> it in an ivar within a class, and destroy it in the classes  
> destructor, or whenever the instance of the object is replaced with  
> another one.
>
> class MyClass {
>   MyClass()
>   {
>     this->MySomething = NULL;
>   }
>   ~MyClass()
>   {
>     if (this->MySomething != NULL)
>       {
>       this->MySomething->Delete();
>       }
>   }
>
>   void MyFunction()
>   {
>    if (this->MySomething != NULL) //Delete what I might have made  
> before
>    {
>       this->MySomething->Delete();
>    }
>    this->MySomething = vtkSomething::New();//Create a new thing it  
> starts with ref count 1
>
>    //now you can use it and not call Delete(), because the  
> destructor will eventually
>    for (int i = 0; i < 99; i++)
>    {
>       this->MySomething->CallAMethod();
>       ...
>       this->UseIt();
>       ...
>    }
>   }
>
>   void UseIt()
>   {
>     if (this->MySomething) //sanity check
>     {
>       this->MySomething->DoSomething();
>     }
>   }
> }
>
> 3) If I need to pass a reference to another object I register it.
> MyClass::PassItOff(AnotherClass *other)
> {
>    if (this->MySomething)
>    {
>       other->HisCopy == this->MySomething();
>       this->MySomething->Register(); //ref count goes to 2, so now  
> it will only be freed when this, and other Delete() it to make ref  
> count 0
>    }
> }
>
> Note:
> For subclasses of vtkObject you don't have to go through the steps  
> of checking the old pointer, saving the new pointer and  
> incrementing the reference count manually, you can just use the  
> vtkSetObject Macro in VTK/Common/vtkSetGet.h
> So
>
> Also note: to test if you've got it right, turn on the  
> VTK_DEBUG_LEAKS flag in cmake. When on, the program will check for  
> any vtkObjects that have not been Delete()'d thoroughly as it ends  
> and print them.
>
> hth,
> Dave DeMarle
>
>
>
> On 5/21/07, burlen <burlen at apollo.sr.unh.edu> wrote:
> Hi,
> Here is what I do,
>
> 1) when ever you ::New() something you also Delete() it.
>
> 2a) When ever you need to keep the output of a filter longer than  
> the filter itself call Register(0) on the output then Delete() the  
> filter. Make sure you Delete() the output later.
>
> 2b) alternatively you could DeepCopy the output of filters you want  
> to keep around.
>
> Burlen
>
>
> Godofredo wrote:
>> Hi everyone. I'm trying to make the triangulation of a point cloud  
>> using
>> vtkDelaunay2D. What I don't know is when to exactly delete filters  
>> and other
>> objects such as PolyDatas that aren't used anymore. I've made some  
>> tries but
>>
>> with bad results. For example, if I use vtkDelaunay2D, update it  
>> and then
>> save its output in a vtkPolyData, can I delete the vtkDelaunay2D  
>> filter?
>> Many thanks.
>>
>
> -- 
>
>
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