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From: Martin Krischik <martin@krischik.com>
Subject: Re: Getting length of array from C
Newsgroups: comp.lang.ada
Reply-To: martin@krischik.com
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Date: Tue, 01 Feb 2005 15:17:19 +0100
Xref: g2news1.google.com comp.lang.ada:8113
Date: 2005-02-01T15:17:19+01:00
List-Id: <comp.lang.ada>

Chuck wrote:

> Here's the deal.  I currently have some Ada code.  Quite a bit of it.
> The originators of the code had done some C interfacing with the Ada
> code.  So, I have some procedures like the following:
> 
> procedure Write_Array( my_array : in My_Array_Type );
> pragma Import( C, Write_Array, "c_write_array" );

Well, at least GNAT is very upset if My_Array_Type is not a fixed array
type. You are allowed to do it - but there is warning about the use of the
dope vector.

http://en.wikipedia.org/wiki/Dope_vector
 
> The C function prototype from the header file I was given is:
> void c_write_array( void *array );

That does not look right. If My_Array_Type is fixed then there should be
typedef documenting that. If My_Array_Type in not fixed then indeed a
length parameter is missing.

> In the C code is there anyway I can get the length of the incoming
> array?  So, is Ada actually passing in a structure or an array?
> Hope this clears things up.

If My_Array_Type is fixed the the size is fixed. If My_Array_Type is not
fixed then the code is broken because someone forgot to pass on the dope
vector.

Martin
-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com