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Re: weird behaviour with cgdemodata [message #76611]

Tue, 21 June 2011 10:53

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jeremy Bailin writes:

> I'm sure there's a good reason why this happens, but it has me very confused:
>
> IDL> i = 5
> IDL> print, i, n_elements(cgdemodata(i))
> 4 65536
>
> Okay, that looks fine. Now what if I put that in a for loop?
>
>
> IDL> for i=0,5 do print, i, n_elements(cgdemodata(i))
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> 0 101
> ...repeat ad infinutm, i.e. until you hit Ctrl-C
>
>
> What is going on???

This is one of those "pass by reference" things that
drives you crazy every once in awhile. It turns out
I am actually *changing* the value of the variable
number in the code. (It never occurred to me someone
would call this function in a loop, for God's sake!!)

If you pass the value "i" by value, you should get
what you expect:

IDL> for i=0,5 do print, i, n_elements(cgdemodata(i[0]))
0 101
1 101
2 1681
3 1681
4 65536
5 65536

Cheers,

David

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

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[Message index]

		Re: weird behaviour with cgdemodata By: David Fanning on Tue, 21 June 2011 10:53
		Re: weird behaviour with cgdemodata By: Jeremy Bailin on Tue, 21 June 2011 09:28
		Re: weird behaviour with cgdemodata By: Foldy Lajos on Tue, 21 June 2011 09:10
		Re: weird behaviour with cgdemodata By: Jeremy Bailin on Tue, 21 June 2011 08:49
		Re: weird behaviour with cgdemodata By: Jeremy Bailin on Tue, 21 June 2011 08:28
		Re: weird behaviour with cgdemodata By: ben.bighair on Tue, 21 June 2011 08:27
		Re: weird behaviour with cgdemodata By: wlandsman on Tue, 21 June 2011 08:19

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