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=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
X-Received: by 2002:a6b:2191:: with SMTP id
 h139-v6mr17961680ioh.27.1537185701927;
        Mon, 17 Sep 2018 05:01:41 -0700 (PDT)
X-Received: by 2002:a9d:2306:: with SMTP id j6-v6mr182048otb.3.1537185701815;
 Mon, 17 Sep 2018 05:01:41 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.uzoreto.com!weretis.net!feeder6.news.weretis.net!feeder.usenetexpress.com!feeder-in1.iad1.usenetexpress.com!border1.nntp.dca1.giganews.com!nntp.giganews.com!x188-v6no27346ite.0!news-out.google.com!z5-v6ni36ite.0!nntp.google.com!x188-v6no27342ite.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Mon, 17 Sep 2018 05:01:41 -0700 (PDT)
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=121.45.194.120;
 posting-account=3BDb0woAAAAxEpy0UNGOioOboBRjpqqT
NNTP-Posting-Host: 121.45.194.120
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <b3f11b70-002a-490b-8a67-9df4b2aeecb8@googlegroups.com>
Subject: Interface To C Struct That Includes An Array
From: rogermc@iinet.net.au
Injection-Date: Mon, 17 Sep 2018 12:01:41 +0000
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Xref: reader02.eternal-september.org comp.lang.ada:54337
Date: 2018-09-17T05:01:41-07:00
List-Id: <comp.lang.ada>


 I'm having problems interfacing the following record to C.

   type API_String is record
      Length  : Interfaces.C.size_t :=3D 0;
      Data    : API_String_Data_Array :=3D (others =3D> Interfaces.C.char'V=
al (0));
   end record;
   pragma Convention (C_Pass_By_Copy, API_String);

In general it seems OK, however, the following function in which Assimp_Pat=
h'Access is returned=20
from a C function produces a strange result=20

 Result :=3D API_Get_Material_Texture (Material'Access, Tex_Type, unsigned =
(Tex_Index), Assimp_Path'Access);

The returned Assimp_Path is Length: 16, Data: =0BB000phoenix.pcx0000
in which B is a series of four small zeros inside a rectangle.
I haven't been able to find a syntactical explanation for the four small ze=
ros inside a rectangle.

The expected Assimp_Path is Length: 11, Data: phoenix.pcx
Memory inspection indicates that the Length 16 includes both the expected l=
ength and character string.

(gdb) print Assimp_Path
$8 =3D (length =3D> 16, data =3D> (0 =3D> 11, 0, 0, 0, 112, 104, 111, 101, =
110, 105, 120, 46, 112, 99, 120, 0 <repeats 1009 times>)

If I shift the Data characters left by four places and change Length to 12,=
 the resultant Assimp_Path is
Length: 16, Data: =0BBphoenix.pcx

The C interface is:

      function API_Get_Material_Texture (aMaterial : access API_Material_Te=
x;
                                         Tex_Type  : AI_Texture_Type;
                                         Index     : Interfaces.C.unsigned;
                                         Path      : access Assimp_Types.AP=
I_String :=3D null;
                                         Mapping   : access AI_Texture_Mapp=
ing :=3D null;
                                         UV_Index  : access Interfaces.C.un=
signed :=3D null;
                                         Blend     : access Interfaces.C.C_=
float :=3D null;
                                         Op        : access AI_Texture_Op :=
=3D null;
                                         Map_Mode  : access AI_Texture_Map_=
Mode :=3D null)
                                         return Assimp_Types.API_Return;
      pragma Import (C, API_Get_Material_Texture, "aiGetMaterialTexture");

Any positive advice or explanation will be appreciated.
Roger