From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id VAA07081; Wed, 18 Sep 2002 21:54:53 +0200 (MET DST)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id VAA06559 for <caml-list@pauillac.inria.fr>; Wed, 18 Sep 2002 21:54:52 +0200 (MET DST)
X-SPAM-Warning: Sending machine is listed in blackholes.five-ten-sg.com
Received: from hawk.mail.pas.earthlink.net (hawk.mail.pas.earthlink.net [207.217.120.22])
	by concorde.inria.fr (8.11.1/8.11.1) with ESMTP id g8IJsp117104
	for <caml-list@inria.fr>; Wed, 18 Sep 2002 21:54:51 +0200 (MET DST)
Received: from user-0ccegbj.cable.mindspring.com ([24.199.65.115] helo=cs.cornell.edu)
	by hawk.mail.pas.earthlink.net with esmtp (Exim 3.33 #1)
	id 17rkuQ-0003KA-00
	for caml-list@inria.fr; Wed, 18 Sep 2002 12:54:50 -0700
Message-ID: <3D88DA09.4010906@cs.cornell.edu>
Date: Wed, 18 Sep 2002 15:54:49 -0400
From: "Yaron M. Minsky" <yminsky@CS.Cornell.EDU>
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.1) Gecko/20020826
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: caml-list@inria.fr
Subject: [Caml-list] Bp_val and Data_custom_val
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

I'm wondering if someone can help me out in understanding the difference 
between Bp_val and Data_custom_val.  These are both macros for accessing 
caml values from C.  I lifted and adapted some code from the 
distribution for building a berkeley DB interface.  In that code, Bp_val 
is used to access the contents of finalized blocks.  I adapted that code 
but shifted to custom blocks, which according to the docs have the same 
layout.  The docs also suggest using Data_custom_val for custom blocks. 
  But when I try to do that, I end up with segfaults.  I'm wondering 
what precisely the difference is.  Here's a snippet of my data type 
definitions and the macros I use for accessing the data contained in the 
custom blocks holding that data:


struct camldb {
   DB *db;
   int closed;
};

struct camltxn {
   DB_TXN *txn;
   int closed;
};

#define UW_db(v) (((struct camldb *)Bp_val(v))->db)
#define UW_db_closed(v) (((struct camldb *)Bp_val(v))->closed)

#define UW_txn(v) (((struct camltxn *)Bp_val(v))->txn)
#define UW_txn_closed(v) (((struct camltxn *)Bp_val(v))->closed)

Anything fishy about that?  And any problem with replacing Bp_val with 
Data_custom_val here?

By the way, in a separate post, I put a URL for where you can download 
the entire wrapper in question.  Here it is again:

    http://minsky-primus.homeip.net/ocaml/bdb.tar.gz

y


-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners