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Re: How to judge a Function's parameters ? [message #66470 is a reply to message #66271]

Thu, 07 May 2009 15:32

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

mgalloy wrote:
> Hu wrote:
>> Hi,folks,
>>
>> I created a function 'RectArea' to calculate the rectangle area, and
>> two parameters, side a and b, are needed when the function is
>> employed.
>>
>> I want to do something like this: if a and b are omitted by the user,
>> then the function will use the default values.
>>
>> But, How can I judge that the parameters are omitted?
>>
>> Thanks
>>
>> function RectArea,a,b
>> return,a*b
>> end
>
> Use N_ELEMENTS to determine if a particular parameter is omitted. I
> usually do something like the following:
>
> function RectArea, a, b
> compile_opt strictarr
>
> _a = n_elements(a) eq 0L ? 1.0 : a
> _b = n_elements(a) eq 0L ? 1.0 : b
>
> return, _a * _b
> end
>
> I don't do:
>
> if (n_elements(a) eq 0L) then a = 1.0
>
> because I don't want change an input variable from the user.

Excellent point.

Being a Fortran programmer, I rely on the INTENT(IN) attribute for input-only dummy
arguments in my Fortran code. I'm much lazier in my IDL dabblings.

To the OP: do what Mike says. :o)

cheers,

paulv

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[Message index]

		Re: How to judge a Function's parameters ? By: Michael Galloy on Thu, 07 May 2009 15:02
		Re: How to judge a Function's parameters ? By: Paul Van Delst[1] on Thu, 07 May 2009 15:01
		Re: How to judge a Function's parameters ? By: Paul Van Delst[1] on Thu, 07 May 2009 15:32

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