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Re: Pass by value and performance [message #46711 is a reply to message #46707]

Wed, 14 December 2005 07:53

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Kenneth P. Bowman writes:

> True, and I considered that possibility. It would work fine for passing
> the arrays amongst my own routines, but I have to dereference the
> pointer to pass the array itself into system routines. Dereferencing a
> pointer is an expression, is it not?, and expressions are passed by
> value.

Ah, you would be interested to read the new pointer
section of my book that I just completely yesterday!
(Well, actually, you could read the damn pointer tutorial
where I learned about this, too.) Here is the news that
even I didn't fully appreciate until I put it down in my
own words. Pointers are just regular IDL variables!!

Consider this function:

PRO JUNK, var
var = var * 5
END

And do this:

IDL> a = Ptr_New(5)
IDL> junk, *a

Here is the question. What is the result of this command?

IDL> Print, *a

The answer might surprise you! :-)

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: Pass by value and performance By: JD Smith on Wed, 14 December 2005 11:04
		Re: Pass by value and performance By: David Fanning on Wed, 14 December 2005 09:54
		Re: Pass by value and performance By: Kenneth P. Bowman on Wed, 14 December 2005 09:28
		Re: Pass by value and performance By: David Fanning on Wed, 14 December 2005 09:08
		Re: Pass by value and performance By: Paul Van Delst[1] on Wed, 14 December 2005 09:02
		Re: Pass by value and performance By: David Fanning on Wed, 14 December 2005 07:53
		Re: Pass by value and performance By: Kenneth P. Bowman on Wed, 14 December 2005 07:09
		Re: Pass by value and performance By: peter.albert@gmx.de on Tue, 13 December 2005 23:38
		Re: Pass by value and performance By: Antonio Santiago on Wed, 14 December 2005 22:56

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