Re: CALL_EXTERNAL and IDL_STRING

[Nigel Wade <nmw(at)ion.le.ac.uk>]

Mark Rivers wrote:
> 
> Frederique Soulard wrote in message
> <91vttb$tpn$1@s1.read.news.oleane.net>...
> >We are trying to use the CALL_EXTERNAL function in order to get strings
> from
> >a C routine. The variables are defined as IDL_STRING and have to be
> >modifyable into the C routine. Our C routine reads strings from a binary
> >file into C string variables. Then we are trying to copy the C strings into
> >the IDL_STRING pointers (copy byte after byte). We encounter problems while
> >doing this (memory overlaping probably). Does someone has any advice to
> give
> >in order to solve our problems (no question to re-develop the reading in
> IDL
> >routine) ? Is a ByteArr method a solution ?
> 
> Yes, I always use byte arrays for this.  In IDL dimension your byte arrays
> so that the dimension
> which is the string length is greater than it will ever need to be in the C
> code.  Have the C code
> fill in the byte array with trailing NULLs.  On return to IDL convert to a
> string or string array using the string() function.
> 
> Mark Rivers

Please pass the length of the IDL string to the C routine and make sure 
you don't copy more than the string can hold. Todays huge string is
tomorrows
buffer overrun. I don't use CALL_EXTERNAL so I don't really know much
about it, 
but if you have an IDL_STRING pointer can you use IDL_StrStore to put
your 
string into the IDL variable?

The alternative would be to write a "system routine" (i.e. using
LINKIMAGE
or a DLM). System routines can create IDL variables of any type. 

-- 
-----------------------------------------------------------
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