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From: "Beard, Frank" <beardf@spawar.navy.mil>
Newsgroups: comp.lang.ada
Subject: RE: Variable length raw-byte data
Date: Mon, 11 Dec 2000 22:30:12 -0500
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Date: 2000-12-11T22:30:12-05:00

Try looking at Interfaces.C and Interfaces.C.Pointers.
If it's string data, look at Interfaces.C.Strings.
I've used this successfully to interface to C.

Or

In your interface routine, receive the pointer as an
address, and then unchecked convert it.

  type Byte is mod 2**8;

  type Byte_Array is array (positive range <>) of Byte;

  type Byte_Array_Pointer is access Byte_Array;

  buffer_Address : System.Address;
  buffer_Pointer : Byte_Array_Pointer;

begin
...
  status := Get_C_Stuff(length         => length,
                        buffer_Address => buffer_Address);

  if (length > 0) then
    declare
      subtype Constrained_Byte_Array is Byte_Array(1..length);
      function To_Buffer_Pointer is
        new Ada.Unchecked_Conversion(System.Address,Constrained_Byte_Array);
    begin
      buffer_Pointer := To_Buffer_Pointer(buffer_Address);
    end;
    ...
  end if;
...

Something like that.  (Constructive corrections only please!)
I haven't done it this way in a while.

Frank

-----Original Message-----
From: Julian Morrison [mailto:julian.morrison@virgin.net]
Sent: Monday, December 11, 2000 2:38 PM
To: comp.lang.ada@ada.eu.org
Subject: Variable length raw-byte data


I'm trying to shim to a C library that returns some data as a length in
bytes and a pointer to the first byte. The length is not known at compile
time. Is there any way I can morph this into an array of mod 2**8? I'm
using the latest Linux GNAT.
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