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[Caml-list] interfacing C and OCaml
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Date: -- (:)
From: Mikhail Fedotov <mikhail@k...>
Subject: Re[2]: [Caml-list] interfacing C and OCaml
Hello Jean-Baptiste,

Friday, June 27, 2003, 12:31:44 PM, you wrote:

>> JBR> 1. Should I use
>> JBR> CAMLprim value input(value channel, value buffer, value offset, value
>> JBR> length)
>> JBR> {
>> JBR>   return Val_long (...);
>> JBR> }
>> Yes. This function can be called from other C function or from OCaml.
>> JBR> as in 18.1.2 in the manual, or
>> JBR> void foo (value v1, value v2, value v3)
>> JBR> {
>> JBR> CAMLparam3 (v1, v2, v3);
>> JBR> ...
>> JBR> CAMLreturn0;
>> JBR> }
>> This if for functions called from C only. Not suitable for use from
>> OCaml directly.
>> Should be specified in the manual, I believe, but I've got no response
>> in the list to my comment on this. I hope it will be in the manual for
>> the OCaml 3.07.

JBR> Strange !
JBR> The complete example given in 18.6 contains :

JBR> curses.mli :
JBR> external initscr: unit -> window = "curses_initscr"

JBR> curses.c ("curses.o" in the manual) :
JBR> value curses_initscr(value unit)
JBR> {
JBR> CAMLparam1 (unit);
JBR> CAMLreturn ((value) initscr());
JBR> }

JBR> :
JBR> open Curses
JBR> let main_window = initscr () in

JBR> So functions using CAMLparam and CAMLreturn are called from OCaml directly.
JBR> Or am I completely wrong ?
JBR> I'm worried about the GC (for now, my code seems to run correctly, but use
JBR> perhaps to much memory).

Sorry, I've made a mistake myself. I've been talking mostly about "void" vs "value"
issue in your examples, but this is already addressed in the manual by stating that
the primitive function must return value. The documentation lacks introduction into
the macroses "CAMLprim", "CAMLextern" etc, but they are not strictly required now
if you are not dealing with Windows DLLs.

I'd say that it is a bad style to write code without those macroses,
at least.

Best regards,

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