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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Ada to C interfacing with access on unconstrained array
Date: Tue, 20 Oct 2009 18:40:37 +0000 (UTC)
Organization: Aioe.org NNTP Server
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Date: 2009-10-20T18:40:37+00:00
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>  type Nut_Array_Type is array (Positive range <>) of Nut_Type;
  C has no concept of an unconstrained array - only pointers to the
start of a length-less array.  The usual way to handle this is to
declare the Ada array constrained, but with a "sufficiently large"
constraint.  You can pass (a pointer to) such an array between C
and Ada.  You lose bounds checking on the Ada side, but you can
fudge that by renaming the actual slice.
So how about:

   type Nut_Array_Type is array (Positive range <>) of Nut_Type;
   subtype C_Nut_Array_Type is Nut_Array_Type(Positive);
   type C_Nut_Array_Access is access C_Nut_Array_Type;

   type Coco_Type is
      record
         X    : Integer;
         Y    : Integer;
         Nuts : C_Nut_Array_Access;
      end record;

   -- This is the procedure I want to be executed from C
   procedure Climb (Coco : in Coco_Type);
   ...
package body Foo is

   procedure Climb (Coco : in Coco_Type) is
     Coco_Nuts : renames Coco.Nuts.all(1 .. actual_length);
   begin