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From: =?ISO-8859-1?Q?Hibou57_=28Yannick_Duch=EAne=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: C interface using a record with discriminant and representation
	clauses
Date: Tue, 30 Jun 2009 16:01:53 -0700 (PDT)
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Date: 2009-06-30T16:01:53-07:00
List-Id: <comp.lang.ada>

Hello,

I wonder about what to think about it, while I could not imagine a
better solution :

Say a C structure is to be interfaced with Ada. The structure has a
"count" member and a variable length array, commonly defined in C as
something like elements[1].

I.e. a C structure like

typedef struct {
   int count;
   my_element_type elements[1];
} my_struct;

I'm tempted to use something like

type Element_Type is <Something>;
for Element_Type'Size use <Something>;

type Array_Type is array (Index_Type range <>) of aliased
Element_Type;
pragma Convention (C, Entity =3D> Array_Type);

type Record_Type (Length : Index_Type) is record
   Elements : Array_Type (1..Length);
end record;

for Record_Type use record
   Length at 0 range 0 .. Something; -- Tell the Ada compiler where
the C
                                                     -- compiler has
placed the =93 discriminant =94
end record;

pragma Convention (C, Entity =3D> Record_Type);

Though the trouble may be that it is not possible to specify the bits
address of Elements, beceause it is not possible to have something
like =93 Elements at 0 range <Something> .. <Something> * Length - 1; =94

What to think about it ?

Is it portable through most compilers ?

** Is it trustable ? **