From: Joerg Czeranski <jc@joerch.org>
To: malc@pulsesoft.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Troubles with C->Caml
Date: Mon, 5 Nov 2001 18:56:56 +0100 (CET) [thread overview]
Message-ID: <200111051756.SAA24522@kiste.thiemo.net> (raw)
In-Reply-To: <Pine.LNX.4.21.0110211611550.477-100000@oyster>
On Sun, 21 Oct 2001 16:27:08 +0400 (MSD) malc <malc@pulsesoft.com> wrote:
>
> value func (value param)
> {
> CAMLparam1 (param);
> CAMLlocal2 (result, err);
> char *p = String_val (param);
> void *h = af (p);
> err = yaf ();
> if (some_condition) {
> /* raise exception */
> ...
> } else {
> if (Is_exception_result (err)) {
> result = alloc_small (2, 1);
> Field (result, 0) = (value)h;
> Field (result, 1) = Extract_exception (err);
> CAMLreturn (result);
> }
> result = alloc_small (1, 0);
> Field (result, 0) = (value)h;
> CAMLreturn (result);
> }
> }
>
> The decorations are there ditto coredump.
Hi,
I don't remember whether somebody has answered this,
but I think you should never copy an O'Caml pointer into a
variable that's not in CAMLlocal...(), e.g.
"char *p = String_val (param);" copies the pointer param into
the local variable p. When the GC moves param, p points to
garbage. (Same for h.)
On the other hand you can't declare p with CAMLparam..., so
you probably have to write "String_val (param)" wherever you'd
use p.
I'm not sure whether the documentation mentions this, and
I think it's not completely obvious.
regards,
jörch
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prev parent reply other threads:[~2001-11-05 17:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-10-20 23:36 malc
2001-10-21 3:23 ` Daniel de Rauglaudre
2001-10-21 12:27 ` malc
2001-10-21 13:10 ` Dmitry Bely
2001-11-05 17:56 ` Joerg Czeranski [this message]
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