Re: pointer question

[Jaco van Gorkom <j.c.van.gorkom(at)fz-juelich.de>]

Mark Hadfield wrote:
> 
> "Ted Graves" <egraves@socrates.Berkeley.EDU> wrote in message
> 99blck$ko7$1@agate.berkeley.edu">news:99blck$ko7$1@agate.berkeley.edu...
 ...
> > result = TEST(PTR_NEW(value))
> >
> > where value is whatever i want the heap variable to be. What happens toth e
> > heap variable assigned in this statement after TEST returns?  I'm assuming
> > from that because of the way it was created, a heap variable now exists that i
> > can't easily get rid of without using HEAP_GC.
> 
> Yes.
> 
> But if you have access to the code of TEST you could do this:
> 
> pro test, a
> 
>     ; Do something with a
> 
>     if not arg_present(a) then if ptr_valid(a) then ptr_free, a
> 
> end

Very nice! However, what if you pass in 'a' by value, e.g., from an
array of pointers?
If I call test like 
  for i=0, n_elements(PointerArray)-1 do test(PointerArray[i])
then I lose all the heap variables, right?

I would prefer to avoid the problem altogether by making TEST accept
both pointers and values, something like:

pro test, a
    if size(a, /type) ne 10 then begin
        a = ptr_new(a, /no_copy)
        a2ptr = 1
    endif else a2ptr = 0

    ; Do something with a, pointer-based.

    if a2ptr and ptr_valid(a) then begin
        a_copy = a
        a = temporary(*a)
        ptr_free, a_copy
    endif
end

If TEST is not your own code, this could easily be done in a wrapper
routine as well. The flexibility of not having to bother about
pointers-or-not is great for command-line use. But then again,  using
heap_gc on the command line every once in a while is not a big problem
either... 

  Jaco

  ----------------
Jaco van Gorkom                               gorkom@rijnh.nl
FOM-Instituut voor Plasmafysica "Rijnhuizen", The Netherlands