On Apr 2, 4:47 pm, David Fanning <n...@[EMAIL PROTECTED]
> wrote:
> Spon writes:
> > I think I'm already doing what you suggest, but just to be sure:
>
> > Graphs = PTR_NEW([-1L])
>
> I wouldn't do this. If there is nothing in it, I would
> probably make it a null pointer:
>
> graphs = PTR_NEW()
>
> Then check to see if I had a valid pointer in my code
> before I used it.
>
> Or, if you *want* a valid pointer, but don't have anything
> to put in it, you can just do this:
>
> graphs = Ptr_New(/ALLOCATE_HEAP)
>
> Now, you have a valid pointer:
>
> IDL> Print, Ptr_Valid(graphs)
> 1
>
> But, the thing inside it is an undefined variable:
>
> IDL> help, *graphs
> <PtrHeapVar1> UNDEFINED = <Undefined>
>
> You can stick something in it:
>
> *graphs = [widgetID]
>
> You can even find out how many things are in it:
>
> IDL> Print, N_Elements(*graphs)
>
> > Oh, and another question while I'm at it: I'm trying to check if a
> > widget still exists before trying to load its UVal, I thought that
>
> > IF WIDGET_INFO(GraphUVal.GroupLeader, /ACTIVE) THEN BEGIN
>
> > would do what I want, but apparently the /ACTIVE keyword doesn't work
> > with an argument.
>
> I don't know what ACTIVE does. The keyword you want
> is VALID_ID.
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming (www.dfanning.com)
> Se****e ma de ni thui. ("Perhaps thou speakest truth.")
Thanks David, you're a great help as usual :-)
Chris
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