| Re: Structure field concatenation [message #21663 is a reply to message #21614] |
Wed, 06 September 2000 08:13   |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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David Fanning wrote:
>
> Martin Schultz (martin.schultz@dkrz.de) writes:
>
>> Only if you want
>> to replace the data in a structure element, then you need to free
>> the pointer beforehand:
>>
>> ;; Replace data of first structure
>> IF Ptr_Valid(periodcube.freq) THEN Ptr_Free,
>> periodcube.freq
>> periodcube.freq = Ptr_New( DIndgen(200)*0.1 )
>
> Actually, as I've been trying to point out for
> months now to no avail, it is NOT necessary to
> free the pointer in this instance. IDL *takes
> care of the memory management for you*. :-)
>
> IF Ptr_Valid(periodcube.freq) THEN $
> *periodcube.freq = newThingy
>
> Cheers,
>
> David
>
> P.S. I'm sure Martin knows this. He is just being
> thorough. A trait I have noticed among Germans. :-)
Actually, I didn't know! Well, I've heard this before, but I never
believed it would be that easy. Maybe I am just old-fashioned, but I
always feel like an equilibrist with no safety net if I replace the
contents of a pointer before actually deallocationg the memory it
occupies. And I think I will stick to this habit if only for
compatibility reasons with FORTRAN. Just imagine I would allow our
models to deallocate memory automatically - ain't never gonna happen I
fear...
The second motive for doing it my way is that you will need to have
two statements anyhow. In your example: what happens if the pointer is
not valid? Well, then you need to allocate memory for it, so you
write:
IF Ptr_Valid(periodcube[0].freq) THEN $
*periodcube[0].freq = newThingy $
ELSE $
periodcube[0].freq = Ptr_New(newthingy)
The only reason to do this that I could accept without further
quirking is if you tell me there is a lot of penalty if you manually
deallocate and reallocate the memory instead of letting IDL do it.
Haven't tested, but I would doubt that it makes a big difference.
Cheers,
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
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