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Re: CALL_EXTERNAL [message #31530 is a reply to message #1268]

Fri, 19 July 2002 15:00

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

"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.

Also, it's not as straightforward as you think to pass raw memory,
such as your "void *buffer", to and from IDL. You'll have to
investigate the External Developers Guide and find out how to insert
user data into an IDL variable.

The much easier approach is to make two wrapper routines, written in
both IDL and C. On the IDL side, this routine would transfer IDL
structure values into simple IDL variables which can then be passed
easily to CALL_EXTERNAL. On the C side, you would need a similar
wrapper which would pack those values back into your own C structure,
and proceed on your merry way.

Good luck,
Craig

--
------------------------------------------------------------ --------------
Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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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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