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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: What is the best way to define the Imported C function
Date: Mon, 28 Jan 2008 09:18:17 -0800 (PST)
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Date: 2008-01-28T09:18:17-08:00
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On Jan 26, 5:31 pm, "Jeffrey R. Carter"
<spam.jrcarter....@acm.nospam.org> wrote:

> I can't help you (and really, neither can those who have replied to you) because
> the C specification isn't a specification; it doesn't tell us how the function
> uses its parameters. Without that information, we can't tell how to interface to it.
>
> The problem is that C uses the same construct for many conceptually different
> things. For example:
>
> void f (char* c);
>
> may represent something that is conceptually equivalent to Ada's
>
> procedure F (C : in Character); [unlikely, but possible]
> procedure F (C : in out Character);
> procedure F (C : out Character);
> procedure F (C : in String);
> procedure F (C : in out String);
> procedure F (C : out String);
>
> Given the common practice of using "char" to represent what Ada calls a
> Storage_Element, and "char[]" or "char*" for Storage_Array, this single C
> declaration may mean any of 12 different things.

It's probably worse than that, because even when char * refers to a
structure with multiple characters rather than a single character, you
don't know whether it's supposed to be a null-terminated string, or an
array of characters whose size is given somewhere else, or what.

                               -- Adam