Le dimanche 22 août 2010 01:30:28, Jeffrey Barber a écrit :
> Is there a way to get a string from C to OCaml without the caml_copy_string
> function, or is there a version that doesn't copy the string?

an alternative method is to provide a string from ocaml to c then c fills this 
buffer, then you can save allocations by reusing the same buffer, see:

ocamlopt -o test.opt main.ml main_stub.c

$ time ./test.opt 1
44 seconds elapsed

$ time ./test.opt 2
21 seconds elapsed

========================

#include <string.h>
#include <caml/mlvalues.h>
#include <caml/alloc.h>
#include <caml/fail.h>

static const char *str = "the walking camel";
static const int len = 18;

CAMLprim value ml_mystr1(value unit) {
    return caml_copy_string(str);
}

CAMLprim value ml_mystr2(value ml_buf) {
    int buf_len = caml_string_length(ml_buf);
    if (len > buf_len) caml_failwith("buffer overflow");
    memcpy(String_val(ml_buf), str, len);
    return Val_int(len);  /* len chars were written in the buffer */
}

========================

external mystr1: unit -> string = "ml_mystr1"
external mystr2: string -> int = "ml_mystr2" "noalloc"

let n = 1_000_000_000

let test1() =
  for i = 1 to n do
    let _ = mystr1 () in ()
  done

let test2() =
  let buf = String.create 100 in
  for i = 1 to n do
    let _ = mystr2 buf in ()
  done

let () =
  match Sys.argv.(1) with
  | "1" -> test1()
  | "2" -> test2()
  | _ -> assert false

========================

-- 
Regards
Florent