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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing to C: big structures
Date: Mon, 25 Feb 2008 17:26:00 -0600
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Date: 2008-02-25T17:26:00-06:00
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"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message
news:c48dc7da-6f04-4f0f-9a8f-e0acc371ee3c@o10g2000hsf.googlegroups.com...
> Consider the C API that contains some structure S and a couple of
> functions that operate on the state that is stored in the Struct. A
> typical usage in C might be:
...
> How to interface to this from Ada? I see two options:
>
> 1. Write a simple wrapper that will create S on the heap and use the
> pointer everywhere. This is easy, but imposes the use of dynamic
> memory, which for some reasons I might want to avoid.
> 2. Create an Ada array of basic storage units of "appropriate size"
> and pass its address to the C functions. The advantage of this
> solution is that it does not impose any particular memory management
> scheme, but the disadvantage is that it is potentially non-portable
> (how to get the "appropriate size"?).
>
> Would you suggest some other solution?

Use the Annex B interfacing facilities. The basic idea is to write the C
types in Ada, add the pragma Convention C to them, and let the Ada compiler
handle the rest. Is there some reason this doesn't work in this case?

                                         Randy.