C-Interface: CAMLreturn and failwith

C-Interface: CAMLreturn and failwith

[Bauer, Christoph]

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 );
} 

Thanks,

Christoph Bauer
Dipl. Inf.

LMS Deutschland GmbH
Luxemburgerstr. 7
D-67657 Kaiserslautern

T +49 631 303 22 152

mailto:Christoph.Bauer@lms-gmbh.de
http://www.lmsintl.com 

Re: [Caml-list] C-Interface: CAMLreturn and failwith

[Damien Doligez]

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