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Date: Tue, 16 Aug 2011 11:04:24 +0300
From: =?ISO-8859-1?Q?T=F6r=F6k_Edwin?= <edwintorok@gmail.com>
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Subject: Re: [Caml-list] Interfacing with C: bad practice

On 08/16/2011 10:37 AM, Dmitry Bely wrote:
> I would like to share my experience of writing bad C bindings. The
> following code is wrong, although no "living in harmony with the
> garbage collector" rule seems to be violated:
> 
> value wrp_ml_cons (value v, value l)
> {
>   CAMLparam2(v, l);
>   CAMLlocal1(cell);
>   cell = caml_alloc_small(2, Tag_cons);
>   Field(cell, 0) = v;
>   Field(cell, 1) = l;
>   CAMLreturn(cell);
> }
> 
> value string_list(const char ** s)
> {
>     CAMLparam0();
>     CAMLlocal1(list);
>     list = Val_emptylist;
>     while (*s != NULL) {
>         list = wrp_ml_cons(caml_copy_string(*s), list); /* bug! */
>     }
>     CAMLreturn(list);
> }
> 
> In the line
> 
>         list = wrp_ml_cons(caml_copy_string(*s), list); /* bug! */
> 
> C compiler first puts "list" pointer on stack and then calls
> caml_copy_string(*s), potentially invalidating "list".

list is a local root though, shouldn't that prevent the invalidation?

Best regards,
--Edwin