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From: Damien Doligez <damien.doligez@inria.fr>
Subject: Re: [Caml-list] C-Interface: CAMLreturn and failwith
Date: Fri, 20 Jan 2006 13:39:33 +0100
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On Jan 20, 2006, at 13:18, Bauer, Christoph wrote:

> Hi,
>
> a question related to CAMLreturn and failwith in C-Stubcode:
>
> Is this code correct:
>
> #include <fail.h>
> ...
>
> CAMLprim value prim( value unit )
> {
>    CAMLparam0();
>    CAMLlocal( result );
>    int error;
>    /* allocate result, error has an errorcode */
>    if( error ) failwith( "error");
>    else CAMLreturn( result );
> }
>
> or should it be
>
> CAMLprim value prim( value unit )
> {
>    CAMLparam0();
>    CAMLlocal( result );
>    int error;
>    /* allocate result, error has an errorcode */
>    if( error ) {
>       caml_local_roots = caml__frame;
>       failwith( "error");
>    }
>    else CAMLreturn( result );
> }

The first one is correct: failwith will take care of deregistering
the local roots (actually, the bytecode interpreter does it when
failwith longjumps to the exception handler).

The second one should work in the current implementation, but it
may break in the future.

-- Damien