Re: Object Data and pointer assignments

["J.D. Smith" <jdsmith(at)astro.cornell.edu>]

Ben Tupper wrote:
> 
> David Fanning wrote:
> 
> > You don't leak any memory because IDL is managing this
> > whole process for you. (Remember, these pointers are
> > not real pointers in the C sense. They are really
> > glorified variables in the IDL sense.) This is the
> > bestest feature of IDL pointers. :-)
> >
> 
> Thanks for the tips.  It's probably a good thing that I don't know much about
> C (no bad habits, eh?)
> 
> >
> > If you overwrite the pointer like this:
> >
> >    self.InArray = Ptr_New(newStruct)
> >
> > you *will* leak memory because now you destroyed the
> > only reference to that pointer area of memory. You could
> > do this:
> >
> >
> 
> So, if I am following your instruction correctly, I should only see ...
> 
>       self.InArray = Ptr_New(newStruct)
> 
> once in my code in the INIT function.  Thereafter (in SetProperty for
> example) it is simply derefence....
> 
>      *self.inarray = newStruct
> 

Just to be clear... you are free to free self.inarray, and point it somewhere
else, at any time.  This can be useful if you have a list which is either empty
(NULL pointer a.k.a. a dangling reference), or not (pointer to a list of finite
size).  If the list changes size, and becomes empty again, you can simply free
it, which indicates its emptiness.  If it then grows again, simply use ptr_new()
to get another heap variable for it.  So, while it might be easiest in some
cases only to call ptr_new() once, in other cases it is useful to let a single
member variable like self.inarray point to different heap variables over its
life.

Good Luck,

JD


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