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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Importing a Unix function call
Date: 1998/12/06
Message-ID: <m33e6t7hqk.fsf@mheaney.ni.net>#1/1
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Sender: matt@mheaney.ni.net
References: <36683FA3.2512DECF@ndirect.co.uk>
NNTP-Posting-Date: Sun, 06 Dec 1998 01:15:53 PDT
Newsgroups: comp.lang.ada
Date: 1998-12-06T00:00:00+00:00
List-Id: <comp.lang.ada>

Steve Crowe <stevecrowe@ndirect.co.uk> writes:

> GNAT AdA compiler running under Unix, the function being imported is a
> Unix 'pipe'.

>From my man page:

       int pipe(int filedes[2]);

       pipe  creates  a  pair  of file descriptors, pointing to a
       pipe inode, and places them in the  array  pointed  to  by
       filedes.   filedes[0]  is  for  reading, filedes[1] is for
       writing.


C doesn't have out parameters: only in parameters that point to the
return data.

How about something like:

with Interfaces.C;  use Interfaces;
package UNIX is

  type File_Descriptor is new C.int;

  type File_Descriptor_Array is
     array (Positive range 1 .. 2) of File_Descriptor;

  pragma Convention (C, File_Descriptor_Array);

  type File_Descriptor_Array_Access is
     access all File_Descriptor_Array;

  pragma Convention (C, File_Descriptor_Array_Access);

  function Pipe
    (Files : in File_Descriptor_Array_Access)
     return C.Int;

  pragma Import (C, Pipe);

end UNIX;


You'd use it like:

declare
  Files  : alised File_Descriptor_Array;
  Status : constant C.Int := Pipe (Files'Access);
begin
...


Is that what you had in mind?