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Re: CALL_EXTERNAL [message #31523 is a reply to message #1268]

Mon, 22 July 2002 01:44

Nigel Wade
Messages: 286
Registered: March 1998

Senior Member

Ian Dean wrote:

> 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).
>
> typedef struct
> {
> void *buffer;
> int buff_size;
> }ACCESS
>
> This routine and structure are already in use between several other C
> routines. I just want to use the same idea in IDL.

Unfortunately that won't be possible as IDL has no concept of void
pointers. Even the pointers it does have are pointers to IDL variables, not
raw memory addresses (at least I think that's correct).

What is that you are trying to achieve?

If you want to access the data in IDL then you'll have to create a variable
of the appropriate type and either use your data from C as its data, or
copy it, whichever you prefer.

If you want to pass on this structure to some other C function then you
will need to create an IDL variable which can hold the pointer.

The former requires a DLM (or LINK_IMAGE) whilst the latter could be
achieved via CALL_EXTERNAL provided you can be certain how much memory is
required to hold your void pointer.

--
-----------------------------------------------------------
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523568, Fax : +44 (0)116 2523555

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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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