| Re: CALL_EXTERNAL and strarr() [message #18212] |
Fri, 10 December 1999 00:00 |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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Richard Tyc wrote:
>
> I need to call an external C function (unix/shared lib method) which
> will collect a string array of different size strings. I have been
> using call_external with success on returning other types (floats,
> strings etc) but this seems more challenging. The problem being I don't
> know how large each string will be in the string array so it needs to be
> dynamically allocated.
>
> I know the following can pass IN a string array and return a single
> string:
>
> replyStr = CALL_EXTERNAL('IDLquery_call.so','GetPatientList',strarr,$
> N_ELEMENTS(strarr), /S_VALUE)
>
> the key point in the C function being to make the returned string static
> to avoid memory leaks.
>
> Anyone care to point out how I might be able to retrieve a string array.
>
> I was thinking about IDL_ImportArray or IDL_ImportNamedArray to create
> an IDL Array.
>
> so lets say in my C function I have
>
> char *list[100] ; or should it be IDL_STRING *list100 ; ??????
>
> and the function has gone off an filled this list with various sized
> array strings.
> (eg. list[0] = strdup("5char") list[1] = strdup("06char") where strdup
> is using malloc implicitly)
>
> Assuming I create an IDL array from this data, what mechanism do I have
> of returning this data in the call_external function.
>
> Thanks in Advance
> Rich
First off, I'm not really a CALL_EXTERNAL user, I generally use
LINKIMAGE
or DLMs, but here goes anyway.
From the call structure you've outlined above, it looks as though you
know when you call the routine how many strings you are going to return
and pass in an array of strings. Is that right?
If so, within the external code can you not just step through the string
array and change the strings using IDL_StrStore? Something like:
IDL_ARRAY string_array;
IDL_STRING *strings;
string_array = argv[1]->value.arr;
strings = (IDL_STRING *)string_array->data;
for ( i=0; i<string_array->n_elts; i++ ) {
IDL_StrStore(&strings[i], list[i]);
/* if you don't need list any longer, free the string
IDL_StrStore creates its own copy */
free(list[i]);
}
Now, I'm not saying this will work. It's just a suggestion as something
to try. It may cause IDL to die horribly, or on Windows give the
infamous
BSOD, when you try to store the strings into the string array since the
array was created by IDL. If I were using LINKIMAGE/DLM then I would
create the string array in the C code and pass it back to IDL.
--
-----------------------------------------------------------
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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| Re: CALL_EXTERNAL and strarr() [message #18229 is a reply to message #18212] |
Thu, 09 December 1999 00:00  |
rivers
Messages: 228
Registered: March 1991
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Senior Member |
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In article <384E7B7E.6672F751@sbrc.umanitoba.ca>, Richard Tyc <richt@sbrc.umanitoba.ca> writes:
> I need to call an external C function (unix/shared lib method) which
> will collect a string array of different size strings. I have been
> using call_external with success on returning other types (floats,
> strings etc) but this seems more challenging. The problem being I don't
> know how large each string will be in the string array so it needs to be
> dynamically allocated.
>
>
> I know the following can pass IN a string array and return a single
> string:
>
> replyStr = CALL_EXTERNAL('IDLquery_call.so','GetPatientList',strarr,$
> N_ELEMENTS(strarr), /S_VALUE)
>
> the key point in the C function being to make the returned string static
> to avoid memory leaks.
>
> Anyone care to point out how I might be able to retrieve a string array.
I have done this by having IDL pass a 2-D byte array, where the first dimension
is the maximum length string which can be returned. Null terminate each string
in your C code, and then convert the byte to array into a string with
s = string(byte_array)
after it is returned to IDL.
Mark Rivers
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