[Caml-list] Re: portable truncate

[Florent Monnier <monnier.florent@gmail.com>]

Hi,

2013/07/26, Florent Monnier wrote:
[...]
> 1) I thought that the module Unix only contains portable things for
> Windows, so it's not true?

This page indeed gives a list of unimplemented functions at the end:
[1] http://caml.inria.fr/pub/docs/manual-ocaml-4.00/manual036.html

but it depends which ocaml variants is used.

This page above says:
"The Cygwin port of OCaml fully implements all functions from the Unix module.
 The native Win32 ports implement a subset of them."

So this page talks about 2 ocaml variants:
- Cygwin ocaml,
- and native Win32 ocaml.

This other page, gives informations for 3 ocanl variants:
[2] http://caml.inria.fr/ocaml/portability.en.html

which are
- native Microsoft
- native MinGW
- and Cygwin

I should probably understand frm this that both
"native Microsoft" and "native MinGW" are native Win32 ocaml.

I made the error to think that native Win32 port only refers to ocaml
compiled with MSVC, while it seems that it also include protz's ocaml
that is a MinGW variant.

I'm still not sure though that compiling with MSVC or MinGW can be
considered equivalent.
And actually they seem not considering this page:
[2] http://caml.inria.fr/ocaml/portability.en.html

And considering the small test (called "MyUnix" below), it shows that
it seems that the function truncate() could work just fine.


[...]
> I tryed to replicate these stubs without the macro that removes these
> functions but I still get the exception from MyUnix.ftruncate: Failure
> "ftruncate"
>
> But if I use MyUnix.truncate instead (the input is then the filename,
> not the Unix.file_descr as I would like), then it works.
>
[...]
>
> /* Xavier Leroy, projet Cristal, INRIA Rocquencourt
>  Copyright 1996 Institut National de Recherche en Informatique et
>  en Automatique.  All rights reserved.  This file is distributed
>  under the terms of the GNU Library General Public License, with
>  the special exception on linking described in the file LICENSE of OCaml.
> */
> #include <sys/types.h>
> #include <fail.h>
> #include <mlvalues.h>
> #include <io.h>
> #include "unixsupport.h"
> #include <unistd.h>
>
> CAMLprim value myunix_ftruncate(value fd, value len)
> {
>   if (ftruncate(Int_val(fd), Long_val(len)) == -1)
>     caml_failwith("ftruncate");
>   return Val_unit;
> }
>
> CAMLprim value myunix_ftruncate_64(value fd, value len)
> {
>   if (ftruncate(Int_val(fd), Int64_val(len)) == -1)
>     caml_failwith("ftruncate64");
>   return Val_unit;
> }
>
> CAMLprim value myunix_truncate(value path, value len)
> {
>   if (truncate(String_val(path), Long_val(len)) == -1)
>     caml_failwith("truncate");
>   return Val_unit;
> }
>
> CAMLprim value myunix_truncate_64(value path, value len)
> {
>   if (truncate(String_val(path), Int64_val(len)) == -1)
>     caml_failwith("truncate64");
>   return Val_unit;
> }
>
>
> $ cat myUnix.ml
>
> (* Xavier Leroy, projet Cristal, INRIA Rocquencourt
>  Copyright 1996 Institut National de Recherche en Informatique et
>  en Automatique.  All rights reserved.  This file is distributed
>  under the terms of the GNU Library General Public License, with
>  the special exception on linking described the file LICENSE of OCaml.
> *)
>
> type file_descr = Unix.file_descr
>
> external ftruncate : file_descr -> int -> unit = "myunix_ftruncate"
> external truncate : string -> int -> unit = "myunix_truncate"
>
> module LargeFile = struct
>   external ftruncate : file_descr -> int64 -> unit = "myunix_ftruncate_64"
>   external truncate : string -> int64 -> unit = "myunix_truncate_64"
> end
>
>
> $ export CC='/bin/i686-w64-mingw32-gcc'
> $ $CC -c -I c:/OCaml/lib/caml ftruncate.c
> $ ocamlc -c myUnix.mli
> $ ocamlc -c myUnix.ml
> $ ocamlmklib -o myunix myUnix.cmo ftruncate.o
>

With this test, the function MyUnix.truncate DOES WORK.

I'm still in hope to find a workaround for ftruncate() that could work
with MinGW's toolchain.

-- 
Cheers