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From: Duncan Sands <duncan.sands@math.u-psud.fr>
Newsgroups: comp.lang.ada
Subject: Re: C array to Ada pointer to unconstrained array without copying
	memory
Date: Tue, 7 Oct 2003 23:24:53 +0200
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Date: 2003-10-07T23:24:53+02:00

On Tuesday 07 October 2003 22:53, Chad R. Meiners wrote:
> "Duncan Sands" <baldrick@free.fr> wrote in message
> news:mailman.37.1065537708.25614.comp.lang.ada@ada-france.org...
>
> > The problem is the bounds of course.  For example, GNAT usually uses
> > fat pointers, consisting of two normal pointers where one points to the
> > data, and the other to the bounds.  So the "clever stuff" will need to
> > allocate some memory to hold the bounds and set up the fat pointer
> > appropriately.
> >
> > Does anyone know a good way to do this?  The solution only needs to
> > work with GNAT.  I appreciate that deallocating the pointer may need
> > to be handled specially.
>
> See http://www.adapower.com/lang/accessmem.html method 1c using
> Address_To_Access_Conversions.
>
> Page for strings, but it should work for any array type as long as you have
> the representation correct.

Thanks Chad, but in fact that was not the question :)
The method you refer to makes it easy to get a local
variable with the right bounds, but that is not enough for me!

Here is an example.

Suppose I get the result in a local array X with the right bounds:

type Array_Type is (Positive range <>) of Something;
type Array_Pointer is access Array_Type;

...
get data and length from C
...

X : Array_Type (1 .. length);
for X'Address use data; -- or another method

So far so good.  Now suppose I do:

Y : Array_Pointer := new Array_Type' (X);  -- (*)

The object I want is Y.  What is the problem?  The problem
is that line (*) involves allocating memory and copying the
data from X to that memory.  I would like to end up with Y
without performing the copy (and without reallocating
memory for the array data).

All the best,

Duncan.