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Re: Bug in N_PARAMS? [message #63986 is a reply to message #63983]

Tue, 25 November 2008 06:29

Kenneth P. Bowman
Messages: 585
Registered: May 2000

Senior Member

In article <MPG.2394d6a934f41609989775@news.giganews.com>,
David Fanning <news@dfanning.com> wrote:

> Kenneth P. Bowman writes:
>
>> I have been having some very odd problems with the N_PARAMS function lately.
>> ...
>> Am I missing something obvious here?
>
> N_PARAMS only tells you *how many* parameters the
> command is called with. It tells you nothing about
> the *type* of the parameter. Since "undefined" is
> a valid variable type in IDL, it is possible to
> pass an "undefined" variable and have it counted
> as a passed *number* of variables by N_PARAMS.
>
> If you are concerned with if a variable is undefined
> or not, you can't use N_PARAMS to determine this. The
> only way to tell is to use N_ELEMENTS.

Ah. That significantly restricts the utility of

SWITCH N_PARAMS() OF
0 : ...

ENDSWITCH

to provide default values for optional parameters. I suppose
that is the only way it could work with positional parameters,
as you might have an undefined parameter in the middle of the
list.

Ken

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[Message index]

		Re: Bug in N_PARAMS? By: David Fanning on Wed, 26 November 2008 07:49
		Re: Bug in N_PARAMS? By: Carsten Lechte on Tue, 25 November 2008 23:53
		Re: Bug in N_PARAMS? By: Kenneth P. Bowman on Tue, 25 November 2008 06:29
		Re: Bug in N_PARAMS? By: David Fanning on Mon, 24 November 2008 14:20
		Re: Bug in N_PARAMS? By: Mark[1] on Thu, 27 November 2008 13:53
		Re: Bug in N_PARAMS? By: Brian Larsen on Tue, 02 December 2008 07:03
		Re: Bug in N_PARAMS? By: David Fanning on Wed, 03 December 2008 09:06

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