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From: dewar@cs.nyu.edu (Robert Dewar)
Newsgroups: comp.lang.ada
Subject: Re: Importing C Structures
Date: 24 Mar 1995 12:30:09 -0500
Organization: Courant Institute of Mathematical Sciences
Message-ID: <3kuvj1$cro@gnat.cs.nyu.edu>
References: <3kr4q3$jd9@newsflash.concordia.ca>
 <VLADIMIR.95Mar22235527@speedy.intrepid.com>
NNTP-Posting-Host: gnat.cs.nyu.edu
Date: 1995-03-24T12:30:09-05:00
List-Id: <comp.lang.ada>

Vladimir writes:

type A_Struct is
        record
                foo : IC.int;
                bar : IC.char_array (1 .. 10);
                q : access IC.long;
        end record;

that's wrong, you can't use anonymous access types like this (It's always
a good idea to compile code that you put on CLA, to protect against
slipups like this, which can confuse the unwary).

If I were doing this in GNAT, I wouldn't bother with Interfaces.C, since
obviously you are not trying to write code that can be ported to other
Ada 95 compilers. Instead I would just write

type A_Struct is
  record
     foo : Integer;
     bar : String (0 .. 9);
     q   : Access_Long_Integer;
  end record;

it is particularly nice to avoid the To_Ada and To_C stuff for converting
between GNAT Character/String and C char/char*, since these are always
the same in GNAT. Interfaces.C is predicated on the assumption that Ada
and C will use different data structures for basic data. THis assumption
is wrong for GNAT.

Of course if you want to write code that will port to other Ada 95 compilers
that might make less convenient choices, then you can use Interfaces.C