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Re: structures, arrays of pointers and assignment [message #53746 is a reply to message #53745]

Wed, 02 May 2007 09:08

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Ingo von Borstel writes:

> But now I wonder why deleting an entry works:
>
> PRO delete_entry, trackvalues, number
> IF NOT PTR_VALID(trackvalues.value[number]) THEN BEGIN
> MESSAGE, "Trackvalues number is not a valid record. Nothing done",
> /CONTINUE
> RETURN
> ENDIF
> PTR_FREE, trackvalues.value[number]
> trackvalues.used[number] = 0
> trackvalues.description[number] = ''
> END
>
> IDL>delete_entry, sep213.trackvalues, 3
> will result in the deletion of the 3rd (or 4th, depends upon where you
> start counting) entry... Why the hell does this work then? Shouldn't
> work, if this was also passed by value...

Ah, because pointers are variables and are passed by reference:

http://www.dfanning.com/misc_tips/pointers.html

Isn't it exciting to learn about IDL? :-)

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: structures, arrays of pointers and assignment By: David Fanning on Wed, 02 May 2007 09:24
		Re: structures, arrays of pointers and assignment By: David Fanning on Wed, 02 May 2007 09:08
		Re: structures, arrays of pointers and assignment By: Ingo von Borstel on Wed, 02 May 2007 08:50
		Re: structures, arrays of pointers and assignment By: David Fanning on Wed, 02 May 2007 06:47
		Re: structures, arrays of pointers and assignment By: Ingo von Borstel on Wed, 02 May 2007 23:57
		Re: structures, arrays of pointers and assignment By: Ingo von Borstel on Wed, 02 May 2007 23:54

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