From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <rich@annexia.org>
X-Original-To: caml-list@sympa.inria.fr
Delivered-To: caml-list@sympa.inria.fr
Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104])
	by sympa.inria.fr (Postfix) with ESMTPS id 8C2DB8027D
	for <caml-list@sympa.inria.fr>; Fri, 13 Oct 2017 23:37:43 +0200 (CEST)
Authentication-Results: mail3-smtp-sop.national.inria.fr; spf=None smtp.pra=rich@annexia.org; spf=Pass smtp.mailfrom=rich@annexia.org; spf=Pass smtp.helo=postmaster@annexia.org
Received-SPF: None (mail3-smtp-sop.national.inria.fr: no sender
  authenticity information available from domain of
  rich@annexia.org) identity=pra; client-ip=80.68.91.176;
  receiver=mail3-smtp-sop.national.inria.fr;
  envelope-from="rich@annexia.org";
  x-sender="rich@annexia.org"; x-conformance=sidf_compatible
Received-SPF: Pass (mail3-smtp-sop.national.inria.fr: domain of
  rich@annexia.org designates 80.68.91.176 as permitted sender)
  identity=mailfrom; client-ip=80.68.91.176;
  receiver=mail3-smtp-sop.national.inria.fr;
  envelope-from="rich@annexia.org";
  x-sender="rich@annexia.org"; x-conformance=sidf_compatible;
  x-record-type="v=spf1"
Received-SPF: Pass (mail3-smtp-sop.national.inria.fr: domain of
  postmaster@annexia.org designates 80.68.91.176 as permitted
  sender) identity=helo; client-ip=80.68.91.176;
  receiver=mail3-smtp-sop.national.inria.fr;
  envelope-from="rich@annexia.org";
  x-sender="postmaster@annexia.org";
  x-conformance=sidf_compatible; x-record-type="v=spf1"
IronPort-PHdr: =?us-ascii?q?9a23=3A5RwQChYzIxlN5cNlKXotCkn/LSx+4OfEezUN459i?=
 =?us-ascii?q?sYplN5qZpc27bnLW6fgltlLVR4KTs6sC0LWG9f24EUU7or+/81k6OKRWUBEEjc?=
 =?us-ascii?q?hE1ycBO+WiTXPBEfjxciYhF95DXlI2t1uyMExSBdqsLwaK+i76xXcoFx7+LQt4?=
 =?us-ascii?q?IPjuUs6X1pzvlrP6x5qGRwxVnje7fftOLJSooAPWq9le1Y9rN7w8zAePvntFZe?=
 =?us-ascii?q?lQwn54DVOVhRf1oMmqqs1N6SNV7rgb9sVAWL/2N5t+aPoQLjMgPnt/rJnxtBLD?=
 =?us-ascii?q?ZQKJ4HYMU2xQlQBHVVuWpCrmV4v853Op/tF23zOXaIivFeg5?=
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: =?us-ascii?q?A0AlAgCnMeFZ/7BbRFBcGgEBAQECAQEBA?=
 =?us-ascii?q?QgBAQEBFAEBAQEBAQEBAQEBBwEBAQEBgzSBUp1zPwEBAQEBAQaBK5hDCoU7AoR?=
 =?us-ascii?q?WQxQBAQEBAQEBAQEBAWoogjgFAR4BBYI8AQUyAUYQCxgJExIPLRsGiiMRrj6LM?=
 =?us-ascii?q?gELJoMtggeBCT6BdIMqilkgBaFGApRcgiGJdIcKlW+BOTYhgVmBBwhJgmWEXz+?=
 =?us-ascii?q?JL4FVAQEB?=
X-IPAS-Result: =?us-ascii?q?A0AlAgCnMeFZ/7BbRFBcGgEBAQECAQEBAQgBAQEBFAEBAQE?=
 =?us-ascii?q?BAQEBAQEBBwEBAQEBgzSBUp1zPwEBAQEBAQaBK5hDCoU7AoRWQxQBAQEBAQEBA?=
 =?us-ascii?q?QEBAWoogjgFAR4BBYI8AQUyAUYQCxgJExIPLRsGiiMRrj6LMgELJoMtggeBCT6?=
 =?us-ascii?q?BdIMqilkgBaFGApRcgiGJdIcKlW+BOTYhgVmBBwhJgmWEXz+JL4FVAQEB?=
X-IronPort-AV: E=Sophos;i="5.43,372,1503352800"; 
   d="scan'208";a="240946358"
Received: from annexia.org ([80.68.91.176])
  by mail3-smtp-sop.national.inria.fr with ESMTP/TLS/AES256-GCM-SHA384; 13 Oct 2017 23:37:42 +0200
Received: from rich by annexia.org with local (Exim 4.89)
	(envelope-from <rich@annexia.org>)
	id 1e37eH-0007l1-Gt; Fri, 13 Oct 2017 22:37:41 +0100
Date: Fri, 13 Oct 2017 22:37:41 +0100
From: "Richard W.M. Jones" <rich@annexia.org>
To: Laurent =?iso-8859-1?Q?Th=E9venoux?= <laurent.thevenoux@inria.fr>
Cc: caml-list@inria.fr
Message-ID: <20171013213741.ke5ptnxrq2w3n6oq@annexia.org>
References: <3380AF33-0E0F-46E9-BF03-E61B65E6B838@inria.fr>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <3380AF33-0E0F-46E9-BF03-E61B65E6B838@inria.fr>
User-Agent: NeoMutt/20170113 (1.7.2)
Subject: Re: [Caml-list] Interfacing C with OCaml and file descriptors

On Fri, Oct 13, 2017 at 12:57:33PM +0200, Laurent Thévenoux wrote:
> Hi,
> 
> I have a naive question about file descriptors and C interface (when interfacing C with OCaml).

Firstly, you're confused about the difference between 'FILE *' and a
file descriptor.  They are not the same thing at all.  Read some basic
Unix texts about the difference.

Once you've sorted that out, it turns out that you can (currently)
cast a Unix.file_descr from OCaml directly into a C int file
descriptor using Int_val:

  int fd = Int_val (fdv);
  read (fd, buf, len);

It would be really nice if there was an official C function defined by
OCaml to do this in a portable and future-proof way!

Rich.