Re: [Caml-list] Toplevel crashes when trying to call external functions

[Andy Yang <yyu08@yahoo.com>]

Thanks a lot! You are correct about the pointer
representation in Ocaml. However, just now I tried
your codes, it still crashes. 

Actually, SAT_Manager is a pointer to a C++ class
object. In order to use the C++ library in Ocaml,
firstly a C wrapper is added onto the C++ code( this
part has been tested. Calling from the C wrapper,
these  C++ objects work fine.) Then I tried to call
these wrapper functions from Ocaml. 

One questions: Why do you mention C++ codes here? It
seems that currently Ocaml support onlu C interfaces.

Thanks a lot!

Andy

--- John Prevost <j.prevost@gmail.com> wrote:
> You shouldn't have to package up a non-caml managed
> pointer in any
> sort of caml structure at all.  Take a look at
> section 18.6 of the
> manual, specifically the definitions of
> curses_initscr and
> curses_wrefresh.  Any pointer that's outside the
> caml heap (that is,
> pretty much any pointer that you're getting from a
> non-caml function)
> can simply be treated as opaque, and you can use
> Caml's type system to
> make sure it's valid (as long as the C code always
> handles these
> pointers correctly.)
> 
> I'd write your code like the following, based on
> that:
> 
> Caml code:
> type sat_manager
> external zchaff_InitManager : unit -> sat_manager
> external zchall_ReadCnf : sat_manager -> string ->
> unit
> 
> C++ code:
> value zchaff_InitManager(void)
> {
>   CAMLparam0();
>   CAMLreturn((value) SAT_InitManager());
> }
> 
> void zchaff_ReadCnf(value mng, value filename)
> {
>   CAMLparam2(mng, filename);
>   SAT_Manager solver = (void*)mng;
>   cout<<"solver = "<<hex <<solver <<endl;
>   assert(solver != NULL);  
>   char * fn = String_val(filename);  
>   cout<<"file = "<<fn <<endl;
>   read_cnf(solver, fn);
>   CAMLreturn0;
> }
> 
> One thing I wonder about, though, is the line:
> 
>   SAT_Manager solver = (void*)mng;
> 
> shouldn't you be casting to something other than
> (void*) here?  Not
> that I know anything about how the type SAT_Manager
> is represented.
> 
> John.
> 



		
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