Skip site navigation (1) Skip section navigation (2)

Re: Continuing encoding fun....

From: Marc Herbert <Marc(dot)Herbert(at)emicnetworks(dot)com>
To: pgsql-odbc(at)postgresql(dot)org
Subject: Re: Continuing encoding fun....
Date: 2005-09-07 18:16:03
Message-ID: 87acio7nh8.fsf@meije.emic.fr (view raw or flat)
Thread:
Lists: pgsql-odbc
"Dave Page" <dpage(at)vale-housing(dot)co(dot)uk> writes:

> I've been thinking about this whilst getting dragged round the shops
> today, and having read Marko's, Johann's, Hiroshi's and other emails,
> not to mention bits of the ODBC spec, here's where I think we stand.
>
> 1) The current driver works as expected with Unicode apps.
>
> 2) 7 bit ASCII apps work correctly. The driver manager maps the ANSI
> functions to the Unicode ones, and because (as I think Marko pointed
> out) the basic latin chars map directly into the lower Unicode
> characters (see http://www.unicode.org/charts/PDF/U0000.pdf).
>
> 3) Some other single byte LATIN encodings do not work. This is because
> the characters do not map directly into Unicode 80-FF
> (http://www.unicode.org/charts/PDF/U0080.pdf).
>
> 4) Multibyte apps do not work. I believe that in fact they never will
> with a Unicode driver, because multibyte characters simply won't map
> into Unicode in the same way that ASCII does. The user cannot opt to use
> the non-wide functions, because the DM automatically maps them to the
> Unicode versions.
>
> Because the Driver Manager forces the user to use the *W functions if
> they exist, I cannot see any way to make 3 or 4 work with a Unicode
> driver. If we were to try to detect what encoding to use based on the OS
> settings and convert on the fly, we would most likely break any apps
> that try to do the right thing by using Unicode themselves.

In a perfect world there are no "unicode apps", the internal encoding
is set by the system, properly written apps use abstract TCHAR/wchar_t
characters without knowing anything about what encoding they use, and
programs communicating with the outside (such as an database driver),
should query the system encoding using something like "setlocale()",
and perform any appropriate conversion on the fly.

Excerpt from "info libc - Character Set Handling" of GNU libc 2.3.2

<http://www.gnu.org/software/libc/manual/html_node/Character-Set-Handling.html>

  The question remaining is: how to select the character set or
  encoding to use.  The answer: you cannot decide about it yourself,
  it is decided by the developers of the system or the majority of the
  users.  Since the goal is interoperability one has to use whatever
  the other people one works with use.

<http://www.faqs.org/docs/Linux-HOWTO/Unicode-HOWTO.html#s6>
says the same thing:

 "Avoid direct access with Unicode. This is a task of the platform's
 internationalization framework."

Of course those two quotes are targeted at applications
developers. They imply that some driver communicating with the outside
world/database should carry any conversion task.

However, I have no idea how this theory is far from reality, far from
the ODBC API, and far from Windows, sorry :-( I just was woken up by
the "unicode apps" word. I tried to follow the discussions here but
got lost.


My 2 cents.


In response to

Responses

pgsql-odbc by date

Next:From: Adão PaulinoDate: 2005-09-08 00:28:53
Subject: lo type and ODBC
Previous:From: Dave PageDate: 2005-09-07 15:09:10
Subject: Re: notice handler in libpq-based driver

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group