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Re: CALL_EXTERNAL [message #31524 is a reply to message #1268]

Sat, 20 July 2002 06:25

ronn
Messages: 123
Registered: April 1999

Senior Member

in article onofd3ml8d.fsf@cow.physics.wisc.edu, Craig Markwardt at
craigmnet@cow.physics.wisc.edu wrote on 7/19/02 6:00 PM:

>
>
> "Ian Dean" <Ian.d.dean@baesystems.com> writes:
>
>> Hi,
>> I'm running IDL 5.4 under VMS (!!!), and would like some help using
>> CALL_EXTERNAL to a C routine.
>>
>> The C routine has a sinle parameter passed to it, but it is a structure
>> (similar to that below)
>> The routine returns to the caller a variable sized array starting at the
>> address of item buffer and the number of elements in buff_size. (Other
>> control fields are also used but I won't cloudy the water with these).
>
> The answer to your question is simple. You can't use CALL_EXTERNAL to
> pass IDL structures to an external routine. In fact, I don't believe
> you can do this with the DLM or LINK_IMAGE facilities either. IDL
> structures are intentionally a black box not meant to be interrogated.
>
Hi Ian,

Craig is correct in that you can't use CALL_EXTERNAL to pass a structure,
but you CAN use a DLM to do it. The details are in my "IDL calling C" book,
but the trick is to create a structure in C and mimick it exactly on the IDL
side. This means IDL ints must be C shorts, etc.

I also agree that you don't want to pass raw memory from C to IDL. IDL just
doesn't know what to do with a memory address. Instead you would want to
create an IDL structure on the C side and fill one of the fields with your
data. Then you can use the structure in IDL just like normal.

Hope that helps a little.

-Ronn

--
Ronn Kling
KRS, inc.
email: ronn@rlkling.com
"Application Development with IDL"ï¿½ programming book updated for IDL5.5!
"Calling C from IDL, Using DLM's to extend your IDL code"!
http://www.rlkling.com/

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[Message index]

		CALL_EXTERNAL By: dean on Wed, 18 August 1993 09:38
		Re: Call_external By: Inigo Garcia on Thu, 12 June 1997 00:00
		Re: call_external By: Vap User on Wed, 05 August 1998 00:00
		Re: call_external By: rivers on Wed, 12 August 1998 00:00
		Re: CALL_EXTERNAL By: menakkis on Mon, 22 February 1999 00:00
		Re: CALL_EXTERNAL By: ashmall on Wed, 03 March 1999 00:00
		Re: CALL_EXTERNAL By: Nigel Wade on Mon, 22 July 2002 01:44
		Re: CALL_EXTERNAL By: ronn on Sat, 20 July 2002 06:25
		Re: CALL_EXTERNAL By: Craig Markwardt on Fri, 19 July 2002 15:00
		Re: CALL_EXTERNAL By: zaygula on Wed, 31 July 2002 07:35
		Re: CALL_EXTERNAL By: Mark Rivers on Tue, 30 July 2002 19:26
		Re: CALL_EXTERNAL By: Randall Skelton on Wed, 05 February 2003 00:47
		Re: Call_external By: Karl Schultz on Wed, 10 March 2004 11:02
		Re: Call_external By: Haje Korth on Wed, 10 March 2004 09:20
		Re: Call_external By: Dr Paul Ducksbury on Wed, 10 March 2004 06:39
		Re: Call_external By: scuaic on Thu, 11 March 2004 14:32
		Re: Call_external By: Haje Korth on Wed, 10 March 2004 05:11
		Re: Call_external By: Pepijn Kenter on Wed, 10 March 2004 05:19
		Re: Call_external By: Dr Paul Ducksbury on Wed, 10 March 2004 05:02
		Re: call_external By: Haje Korth on Sun, 17 February 2013 05:53
		Re: call_external By: Katerina Yakimenko on Thu, 07 March 2013 05:55
		Re: call_external By: David Fanning on Thu, 07 March 2013 06:42
		Re: call_external By: Katerina Yakimenko on Thu, 07 March 2013 06:23
		Re: call_external By: David Fanning on Thu, 07 March 2013 06:10

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