[Caml-list] Interfacing C++ and Ocaml

[Caml-list] Interfacing C++ and Ocaml

[David Chemouil]

Hi,



I am in the situation where I would like to write an Ocaml program which
makes use of some C++ classes. It seems to me some people had said there
were some problems doing so, but I can't recall what these problems may
be, and didn't find anything precise in the ML archive.

So, I would like to know what may prevent me to reuse C++ code from
Ocaml, if anything may. I am sure some arrangements can be done, as
there exists an Ocaml implementation on BeOS, which is programmed in
C++. 

Moreover, if it is possible, what do you advise me to do? What are the
limitations? Have you got simple examples of such interfacings?


Thanks in advance,

dc



PS: BTW, I would like to thank these happy volunteers who aim at
packaging a Caml Development Kit. IMO, this is truly a good idea, which
may help Caml spread. Just a question to the Caml team: I would like to
know if you intend to include polymorphic I/O and some kind of
overloading in a forthcoming release of Caml. It seems to me Pierre had
written some mails about this, but is is now a long time ago, how is the
situation today?


-- 
David Chemouil    [mailto:David.Chemouil@irit.fr]

Institut de recherche en informatique de Toulouse
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Re: [Caml-list] interfacing C and OCaml

[Jean-Baptiste Rouquier]

> 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.
>


Strange !
The complete example given in 18.6 contains :

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

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

curses.ml :
open Curses
let main_window = initscr () in


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


Thanks,
JBR

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Re: [Caml-list] interfacing C and OCaml

[Jean-Baptiste Rouquier]

> Can anybody explain me if there is anyway that I can pass in
> a (int*int*int*int*int) from a C function to OCaml.

Do you want to call C auxiliary function from Caml, or are you writing your
main programm in C and using some Caml functions ?
Both are very well explained in the manual, though it may take a while to
read it.
Don't hesitate to ask me for a complete example if your main programm is in
Caml (I haven't learn yet how to write the main programm in C).



------------------------------------------------
À propos, I have some questions about the manual :
1. Should I use
CAMLprim value input(value channel, value buffer, value offset, value
length)
{
  return ...
}

as in 18.1.2 in the manual, or

void foo (value v1, value v2, value v3)
{
CAMLparam3 (v1, v2, v3);
...
CAMLreturn0;
}

as in 18.5.1, or both ? I think at least the second.


------------------------------------------------
2.
I use
  alloc(2*n, Double_array_tag.)
to create a float array of size n (then I initialize it), is it correct ?


------------------------------------------------
3. Is it correct to store p in the custom block v by
CAMLlocal(v);
v = alloc_custom(ops, 4, 0, 1);
(my_type *) Data_custom_val(v) = p;
?
When does the parameter "size" (here "4") vary ?

Thanks,
Jean-Baptiste.








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Re: [Caml-list] interfacing C and OCaml

[Lex Stein]

Hi, In the C code allocate a memory block value of size 5 with tag 0.

CAMLparam0 ();
CAMLlocal2 (v, v1);
static value * clos;

v = alloc_tuple (5);
/* assign to the fields using the Store_Field macro */

clos = caml_named_value ("c_function_name")

/* where c_function_name is registered from within the Caml code
   via (Callback.register "c_function_name" function_name)
Then just call the Caml routine via callback like so: */

v1 = callback (*clos, v);

Remember to return from the C function with one of the CAMLreturn
macros to be friendly with the garbage collector.

Let me know if you have any further questions/problems with Caml/C
interaction. I'm happy to help.

Lex

--
Lex Stein                     http://www.eecs.harvard.edu/~stein/
stein@eecs.harvard.edu        TEL: 617-233-0246


On Thu, 26 Jun 2003, Jung Woon Ho wrote:

> Hi,
>
> Can anybody explain me if there is anyway that I can pass in
> a (int*int*int*int*int) from a C function to OCaml.
>
> Thank you.
>
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[Caml-list] interfacing C and OCaml

[Jung Woon Ho]

Hi,

Can anybody explain me if there is anyway that I can pass in
a (int*int*int*int*int) from a C function to OCaml.

Thank you.

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Re: [Caml-list] Interfacing C and Ocaml

[art yerkes]

On Thu, 19 Jun 2003 19:58:16 +0000
"Jung Woon Ho" <unosoft@hotmail.com> wrote:

See: http://lists.suse.com/archive/suse-linux-e/2001-Aug/0476.html

It appears that the name of the curses library on Suse is libncurses.

> Hi, Im trying to implement a simple program that interfaces C and Ocaml.
> Here is what I do:
> 
>         ocamlc -custom -output-obj -o modcaml.o mod.ml
>         ocamlc -c modwrap.c
>         cp /usr/local/lib/ocaml/libcamlrun.a mod.a
>         ar r mod.a modcaml.o modwrap.o
> 	cc -o prog main.c mod.a -lcurses
> 
> and I get the error:
> /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../../i486-suse-linux/bin/ld: 
> cannot find -lcurses
> collect2: ld returned 1 exit status
> 
> I tried cc -o prog main.c mod.a -lcurses -ltermcap and cc -o prog main.c 
> mod.a -ltermcap but i cant get the program to link.
> 
> Does anybody know how to solve this problem?
> 
> Thank you very much.
> 
> 
> 
> 
> ---------------------mod.ml-------------------------------
> (* File mod.ml -- some ``useful'' Caml functions *)
> 
> let rec fib n = if n < 2 then 1 else fib(n-1) + fib(n-2)
> 
> let format_result n = Printf.sprintf "Result is: %d\n" n
> 
> (* Export those two functions to C *)
> 
> let _ = Callback.register "fib" fib
> let _ = Callback.register "format_result" format_result
> ----------------------------------------------------------
> 
> --------------------modwrap.c-----------------------------
> /* File modwrap.c -- wrappers around the Caml functions */
> 
> #include <stdio.h>
> #include <string.h>
> #include <caml/mlvalues.h>
> #include <caml/callback.h>
> 
> int fib(int n)
> {
>   static value * fib_closure = NULL;
>   if (fib_closure == NULL) fib_closure = caml_named_value("fib");
>   return Int_val(callback(*fib_closure, Val_int(n)));
> }
> 
> char * format_result(int n)
> {
>   static value * format_result_closure = NULL;
>   if (format_result_closure == NULL)
>     format_result_closure = caml_named_value("format_result");
>   return strdup(String_val(callback(*format_result_closure, Val_int(n))));
>   /* We copy the C string returned by String_val to the C heap
>      so that it remains valid after garbage collection. */
> }
> ----------------------------------------------------------
> 
> -------------------main.c---------------------------------
> /* File main.c -- a sample client for the Caml functions */
> 
> #include <stdio.h>
> 
> int main(int argc, char ** argv)
> {
>   int result;
> 
>   /* Initialize Caml code */
>   caml_startup(argv);
>   /* Do some computation */
>   result = fib(10);
>   printf("fib(10) = %s\n", format_result(result));
>   return 0;
> }
> ----------------------------------------------------------
> 
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-- 
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Re: [Caml-list] Interfacing C and Ocaml

[Kip Macy]

try sticking in -L<path to libcurses.so> for -lcurses

On Thu, 19 Jun 2003, Jung Woon Ho wrote:

> Hi, Im trying to implement a simple program that interfaces C and Ocaml.
> Here is what I do:
> 
>         ocamlc -custom -output-obj -o modcaml.o mod.ml
>         ocamlc -c modwrap.c
>         cp /usr/local/lib/ocaml/libcamlrun.a mod.a
>         ar r mod.a modcaml.o modwrap.o
> 	cc -o prog main.c mod.a -lcurses
> 
> and I get the error:
> /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../../i486-suse-linux/bin/ld: 
> cannot find -lcurses
> collect2: ld returned 1 exit status
> 
> I tried cc -o prog main.c mod.a -lcurses -ltermcap and cc -o prog main.c 
> mod.a -ltermcap but i cant get the program to link.
> 
> Does anybody know how to solve this problem?
> 
> Thank you very much.
> 
> 
> 
> 
> ---------------------mod.ml-------------------------------
> (* File mod.ml -- some ``useful'' Caml functions *)
> 
> let rec fib n = if n < 2 then 1 else fib(n-1) + fib(n-2)
> 
> let format_result n = Printf.sprintf "Result is: %d\n" n
> 
> (* Export those two functions to C *)
> 
> let _ = Callback.register "fib" fib
> let _ = Callback.register "format_result" format_result
> ----------------------------------------------------------
> 
> --------------------modwrap.c-----------------------------
> /* File modwrap.c -- wrappers around the Caml functions */
> 
> #include <stdio.h>
> #include <string.h>
> #include <caml/mlvalues.h>
> #include <caml/callback.h>
> 
> int fib(int n)
> {
>   static value * fib_closure = NULL;
>   if (fib_closure == NULL) fib_closure = caml_named_value("fib");
>   return Int_val(callback(*fib_closure, Val_int(n)));
> }
> 
> char * format_result(int n)
> {
>   static value * format_result_closure = NULL;
>   if (format_result_closure == NULL)
>     format_result_closure = caml_named_value("format_result");
>   return strdup(String_val(callback(*format_result_closure, Val_int(n))));
>   /* We copy the C string returned by String_val to the C heap
>      so that it remains valid after garbage collection. */
> }
> ----------------------------------------------------------
> 
> -------------------main.c---------------------------------
> /* File main.c -- a sample client for the Caml functions */
> 
> #include <stdio.h>
> 
> int main(int argc, char ** argv)
> {
>   int result;
> 
>   /* Initialize Caml code */
>   caml_startup(argv);
>   /* Do some computation */
>   result = fib(10);
>   printf("fib(10) = %s\n", format_result(result));
>   return 0;
> }
> ----------------------------------------------------------
> 
> _________________________________________________________________
> Help STOP SPAM with the new MSN 8 and get 2 months FREE*  
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[Caml-list] Interfacing C and Ocaml

[Jung Woon Ho]

Hi, Im trying to implement a simple program that interfaces C and Ocaml.
Here is what I do:

        ocamlc -custom -output-obj -o modcaml.o mod.ml
        ocamlc -c modwrap.c
        cp /usr/local/lib/ocaml/libcamlrun.a mod.a
        ar r mod.a modcaml.o modwrap.o
	cc -o prog main.c mod.a -lcurses

and I get the error:
/usr/lib/gcc-lib/i486-suse-linux/3.2/../../../../i486-suse-linux/bin/ld: 
cannot find -lcurses
collect2: ld returned 1 exit status

I tried cc -o prog main.c mod.a -lcurses -ltermcap and cc -o prog main.c 
mod.a -ltermcap but i cant get the program to link.

Does anybody know how to solve this problem?

Thank you very much.




---------------------mod.ml-------------------------------
(* File mod.ml -- some ``useful'' Caml functions *)

let rec fib n = if n < 2 then 1 else fib(n-1) + fib(n-2)

let format_result n = Printf.sprintf "Result is: %d\n" n

(* Export those two functions to C *)

let _ = Callback.register "fib" fib
let _ = Callback.register "format_result" format_result
----------------------------------------------------------

--------------------modwrap.c-----------------------------
/* File modwrap.c -- wrappers around the Caml functions */

#include <stdio.h>
#include <string.h>
#include <caml/mlvalues.h>
#include <caml/callback.h>

int fib(int n)
{
  static value * fib_closure = NULL;
  if (fib_closure == NULL) fib_closure = caml_named_value("fib");
  return Int_val(callback(*fib_closure, Val_int(n)));
}

char * format_result(int n)
{
  static value * format_result_closure = NULL;
  if (format_result_closure == NULL)
    format_result_closure = caml_named_value("format_result");
  return strdup(String_val(callback(*format_result_closure, Val_int(n))));
  /* We copy the C string returned by String_val to the C heap
     so that it remains valid after garbage collection. */
}
----------------------------------------------------------

-------------------main.c---------------------------------
/* File main.c -- a sample client for the Caml functions */

#include <stdio.h>

int main(int argc, char ** argv)
{
  int result;

  /* Initialize Caml code */
  caml_startup(argv);
  /* Do some computation */
  result = fib(10);
  printf("fib(10) = %s\n", format_result(result));
  return 0;
}
----------------------------------------------------------

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Re: [Caml-list] Interfacing C++ and Ocaml

[Fergus Henderson]

On 30-Mar-2001, Bruce Hoult <bruce@hoult.org> wrote:
> I'm no expert on Caml, so maybe the wizards have done something 
> clever, but interfacing other languages to C++ is normally best done 
> by writing an adaptor in C++ that provides a pure C interface to the 
> C++ code (usable by C code, compiled by a C compiler, not C++), and 

In particular defining the C++ functions in your adaptor code
as `extern "C"' so that they can be called from C code.

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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Re: [Caml-list] Interfacing C++ and Ocaml

[Bruce Hoult]

At 10:54 AM +0200 3/30/01, David Chemouil wrote:
>Hi,
>
>
>
>I am in the situation where I would like to write an Ocaml program which
>makes use of some C++ classes. It seems to me some people had said there
>were some problems doing so, but I can't recall what these problems may
>be, and didn't find anything precise in the ML archive.
>
>So, I would like to know what may prevent me to reuse C++ code from
>Ocaml, if anything may. I am sure some arrangements can be done, as
>there exists an Ocaml implementation on BeOS, which is programmed in
>C++.

I'm no expert on Caml, so maybe the wizards have done something 
clever, but interfacing other languages to C++ is normally best done 
by writing an adaptor in C++ that provides a pure C interface to the 
C++ code (usable by C code, compiled by a C compiler, not C++), and 
then call *that* from your favourite language.

-- Bruce
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[Caml-list] Interfacing C++ and Ocaml

[David Chemouil]

Hi,



I am in the situation where I would like to write an Ocaml program which
makes use of some C++ classes. It seems to me some people had said there
were some problems doing so, but I can't recall what these problems may
be, and didn't find anything precise in the ML archive.

So, I would like to know what may prevent me to reuse C++ code from
Ocaml, if anything may. I am sure some arrangements can be done, as
there exists an Ocaml implementation on BeOS, which is programmed in
C++. 

Moreover, if it is possible, what do you advise me to do? What are the
limitations? Have you got simple examples of such interfacings?


Thanks in advance,

dc



PS: BTW, I would like to thank these happy volunteers who aim at
packaging a Caml Development Kit. IMO, this is truly a good idea, which
may help Caml spread. Just a question to the Caml team: I would like to
know if (when?) you intend to include polymorphic I/O and some kind of
overloading in a forthcoming release of Caml. It seems to me Pierre had
written some mails about this, but is is now a long time ago, how is the
situation today?


-- 
David Chemouil    [mailto:David.Chemouil@irit.fr]

Institut de recherche en informatique de Toulouse
-------------------
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