RE: [Caml-list] Re: portable truncate

[David Allsopp <dra-news@metastack.com>]

Florent Monnier wrote:
 
> 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

That page is slightly out of date as it doesn't refer to the 64 bit MinGW port :o)

> 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.

Correct

> 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.

Native in this context means "not Cygwin", indeed.

> 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

I've done some limited Googling, so may be barking up the wrong tree. I believe that in Microsoft C world, the function ftrunctate is called _chsize (http://msdn.microsoft.com/en-gb/library/aa246710(v=vs.60).aspx) in io.h and that MinGW defined a compatible ftruncate in unistd.h a long time ago. I expect that the reason for not implementing ftruncate in win32unix originally was either that whoever wrote it didn't know about _chsize or at the time it didn't work properly (e.g. on Windows 9x). The Windows API functions SetEndOfFile/SetFileValidData (which actually implement this) look comparatively new (Windows XP+), although Microsoft annoyingly altered the "Minimum supported" sections of MSDN a while ago so "minimum" no longer means "introduced".

Altering unix is relatively easy if you've compiled your own OCaml - edit files in otherlibs/win32unix and use make -f Makefile.nt [opt] to recompile. You can simply copy the replacement files into your ocaml lib directory while experimenting. Patches adding missing functionality to win32unix tend to be accepted quite quickly in my experience...


David