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Re: pointer question [message #24283 is a reply to message #24276]

Sun, 25 March 2001 14:16

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

"Pavel A. Romashkin" <pavel.romashkin@noaa.gov> wrote in message
news:3ABA272F.538D0EB0@noaa.gov...
> Mark Hadfield wrote:
>
>> pro test, a
>>
>> ; Do something with a
>>
>> if not arg_present(a) then if ptr_valid(a) then ptr_free, a
>>
>> end
>
> I am sorry, I have not had my first cup of coffe yet. How is that
> supposed to work? If there is *no* argument present, *then* try to check
> if the missing argument is a pointer? What am I missing?

The question answered by ARG_PRESENT is not "Is this argument present", it
is "If I change this variable, will it be passed back to the caller?". So
the intention of the code in routine "test" was to see whether the calling
program holds a reference to variable a.

I have never used this in my own code, but tt seemed like a clever idea when
I suggested it. Jaco has pointed out the flaw: what if the caller holds the
pointer heap variable (say in an array) but chooses to pass it by value?

---
Mark Hadfield
m.hadfield@niwa.cri.nz http://katipo.niwa.cri.nz/~hadfield
National Institute for Water and Atmospheric Research

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[Message index]

		Re: pointer question By: Martin Schultz on Mon, 26 March 2001 01:05
		Re: pointer question By: Mark Hadfield on Sun, 25 March 2001 14:16
		Re: pointer question By: Mark Hadfield on Sun, 25 March 2001 14:07
		Re: pointer question By: R.Bauer on Sun, 25 March 2001 09:24
		Re: pointer question By: Craig Markwardt on Thu, 22 March 2001 20:15
		Re: pointer question By: Paul van Delst on Thu, 22 March 2001 10:00
		Re: pointer question By: Pavel A. Romashkin on Thu, 22 March 2001 09:21
		Re: pointer question By: John-David T. Smith on Thu, 22 March 2001 08:56
		Re: pointer question By: Pavel A. Romashkin on Thu, 22 March 2001 08:24
		Re: pointer question By: Paul van Delst on Thu, 22 March 2001 06:52
		Re: pointer question By: Jaco van Gorkom on Thu, 22 March 2001 06:01
		Re: pointer question By: Mark Hadfield on Wed, 21 March 2001 19:47
		Re: pointer question By: Craig Markwardt on Mon, 26 March 2001 04:56
		Re: pointer question By: egraves on Mon, 26 March 2001 17:06

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