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Re: null array [message #36544 is a reply to message #36471]

Tue, 30 September 2003 12:36

Stein Vidar Hagfors H[2] is currently offline

Stein Vidar Hagfors H[2]
Messages: 28
Registered: October 2002

Junior Member

Well, David, always pluggin' the pointers, eh?

Using pointers simply because of their ability to point to undefined
variables seems a bit overkill to me, though. A variable in itself
is just as good at representing an undefined variable... as in:

if n_elements(variable) eq 0 then print,"Variable undefined" $
else variable = [initValue]

And the way to "undefine" a variable is the good old

dummy = temporary(variable)

David Fanning <david@dfanning.com> writes:
> Tomson writes:
>
>> But What I want to do is to initialize several arrays which are in common
>> block and their length will be changed for different call and the lengths
>> of them may be zero. If the lengthes of them are zero, the process will be
>> changed. If there isnot any initialization, the array return to the main
>> program may be the former ones.
>
> If I understand you correctly, you may find a pointer
> useful in this situation. A pointer could point to
> a "null array", in the sense that it would point to
> an "undefined variable":
>
> ptr = Ptr_New(/Allocate_Heap)
> IF N_Elements(*ptr) EQ 0 THEN Print, 'Pointer undefined' ELSE $
> *ptr = [initValue]
>
> Cheers,
>
> David
>
> --
> David W. Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Phone: 970-221-0438, E-mail: david@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155

--
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Stein Vidar Hagfors Haugan
ESA SOHO SOC/European Space Agency Science Operations Coordinator for SOHO

NASA Goddard Space Flight Center, Tel.: 1-301-286-9028
Mail Code 682.3, Bld. 26, Room G-1, Cell: 1-240-354-6066
Greenbelt, Maryland 20771, USA. Fax: 1-301-286-0264
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[Message index]

		Re: null array By: David Fanning on Wed, 24 September 2003 18:35
		Re: null array By: tomson on Wed, 24 September 2003 17:47
		Re: null array By: JD Smith on Wed, 24 September 2003 09:17
		Re: null array By: R.Bauer on Wed, 24 September 2003 08:11
		Re: null array By: Paul Van Delst[1] on Wed, 24 September 2003 06:52
		Re: null array By: Ben Panter on Wed, 24 September 2003 02:08
		Re: null array By: Ben Panter on Wed, 24 September 2003 01:33
		Re: null array By: R.Bauer on Tue, 23 September 2003 20:21
		Re: null array By: David Fanning on Tue, 23 September 2003 20:04
		Re: null array By: David Fanning on Fri, 26 September 2003 02:24
		Re: null array By: Stein Vidar Hagfors H[2] on Tue, 30 September 2003 12:36

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