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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Interfaces.C questions
Date: Fri, 17 Mar 2017 23:24:42 +0100
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Date: 2017-03-17T23:24:42+01:00
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On 2017-03-17 22:12, hreba wrote:
> These are my first steps with Interfaces.C:
>
> ----------------------------------------------------------------------
> with Interfaces.C;
>
> package GSL is
>
>    package C renames Interfaces.C;

Renaming packages is a bad idea. Either use fully-qualified names 
"Interfaces.C.size_t" or else do use-clause "size_t". Renaming lacks 
advantages of either approach inheriting their corresponding disadvantages.

>    type size_t is new C.int;

size_t is defined in Interfaces.C.

>    type Real_Function is access function (x: C.double) return C.double;

pragma Convention (C, Real_Function);

>    function Bessel_J0 (x: C.double) return C.double;
>
>    function Integration_QNG
>      (f: Real_Function;
>       a, b, epsabs, epsrel: C.double;
>       result, abserr: out C.double;
>       neval: out size_t)
>      return C.int;

     function Integration_QNG
       (f: Real_Function;
        a, b, epsabs, epsrel: Interfaces.C.double;
        result, abserr: access Interfaces.C.double;
        neval: access Interfaces.C.size_t)
       return Interfaces.C.int;

P.S. For convention C assume this:

1. out T, in out T, access T are equivalent

2. in T and access T are equivalent when T is non-scalar (you can pass 
int, array, or record, the compiler will sort that out)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de