From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,68b2e2c0309a6e88
X-Google-Attributes: gid103376,public
Path: 
 controlnews3.google.com!news2.google.com!newsfeed2.dallas1.level3.net!news.level3.com!newsfeed.gamma.ru!Gamma.RU!newsfeed.icl.net!newsfeed.fjserv.net!news.tele.dk!news.tele.dk!small.news.tele.dk!newsfeed00.sul.t-online.de!newsmm00.sul.t-online.de!t-online.de!news.t-online.com!not-for-mail
From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: Question on interface Ada to C
Date: Wed, 26 May 2004 09:34:29 +0200
Organization: AdaCL
Message-ID: <14104353.udXiIW5mdD@linux1.krischik.com>
References: <rac7b0tnlsoauhcharlguhr7v3g30npk6b@4ax.com>
Reply-To: krischik@users.sourceforge.net
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit
X-Trace: news.t-online.com 1085557132 00 1515 z8KMGhqOKVG+PKf 040526 07:38:52
X-Complaints-To: usenet-abuse@t-online.de
X-ID: GndhOqZHweu-4Zw26bji7Lbhi-TXtRuJeXNVZHCCrb1ThLjKEtgeck
User-Agent: KNode/0.7.7
Xref: controlnews3.google.com comp.lang.ada:841
Date: 2004-05-26T09:34:29+02:00
List-Id: <comp.lang.ada>

James Alan Farrell wrote:

> Hello all,

> I've inherited a project that is half written in C and Ada.

Nothing wrong with that. You should carfully read Annex B. Currently I do a
lot of Ada / C mixed programming as well. It works quite well.

> My boss at first thought this was good code but when he took a second
> look he wasn't so sure.  So he's asked me to investigate.  What
> exactly happens with the memory used by list in this situation?

The code is indeed not very good.

> We're using GNAT, but I don't think that's an issue -- I would think
> this code would behave (or misbehave) the same no matter what
> compiler.

That depends if you use GNAT with gcc's own C or GNAT with some other C. 

> Thanks,
> James Alan Farrell
> GrammaTech.
> 
>  type stuff is integer; -- just for example
> 
>  type List_Type is array(Integer range <>) of stuff;
>  
>  package MyPointers is
>               new System.Address_To_Access_Conversions(List_Type);
>  subtype List_Pointer is MyPointers.Object_Pointer;
> 
>  procedure MyProc
>      (Items     : in out List_Pointer;
>       Nitems    : in out Integer) is
> 
>       List : List_Type := function_that_returns_a_list;
> 
>    begin
>       Nitems := List'Length;
>       Items  := MyPointers.To_Pointer(List'Address);
>    end;

List will be short lived after MyProc ends. Also list is indefinite - C has
no conzept of indefinite.

You should return a record like this (Example for Character):

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

   --
   --  C/Ada String Type
   --
   type C_Array
   is array
      (Natural range <>)
   of aliased
      Character;

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

   package C_Pointers
   is new
      Interfaces.C.Pointers (
         Index              => Natural,
         Element            => Character,
         Element_Array      => C_Array,
         Default_Terminator => Character'First);

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

   type C_String
   is record
      Data : C_Pointers.Pointer;
      Size : Interfaces.C.size_t;
   end record;

With GNAT you can use function as well. Returning a record from Ada to C
work OK.

C_String.Data should be allocated and freed with malloc. See:

http://cvs.sourceforge.net/viewcvs.py/adacl/CUnicode/Include/c-generic_strings.adb?rev=1.5&view=auto

If you use GNAT only then you can import malloc directly.

With Regards

Martin

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