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From: "Adam Beneschan" <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing with C - pointer problem
Date: 31 Jan 2007 10:10:51 -0800
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Date: 2007-01-31T10:10:51-08:00
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On Jan 30, 1:10 pm, tmo...@acm.org wrote:
> >   type LPSTR is access all String;
>
> > This does not work correct. What I found is, that data'Address is 32
> > bit and LPSTR is 64 bit.
>
>    Because LPSTR points to a dynamic size string and thus needs to
> carry along bounds information.  A C LPSTR does not point to a dynamic
> string, but instead points to a single character - the first in the
> string.  So the match is
>    type LPSTR is access Interfaces.C.Char;
>    procedure C_Func (x : LPSTR);  -- expects an address (C-pointer, 32-bit)
> and then
>    data : Interfaces.C.char_array := Interfaces.C.To_C("ABC");
> and
>    C_Func (data(data'first)'unchecked_access);

Or perhaps better:

   procedure C_Func (x : Interfaces.C.Strings.chars_ptr);

   data : aliased Interfaces.C.char_array := Interfaces.C.To_C
("ABC");

   C_Func (Interfaces.C.Strings.To_Chars_Ptr (data'unchecked_access));

May as well use the stuff Ada provides for this exact purpose.

                          -- Adam