Re: wide_string and assertions

[Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>]

Martin Krischik <krischik@users.sourceforge.net> wrote:
> 
:> (It would be great if someone who know about surrogate characters could
:> check the following. Martin, is this similar to your function?)
: 
: As I said the functions are based on the Unicode part of XML/Ada. Not point
: reinventing the Wheel.

I think I haven't actually, as the wheels are slightly different ;-)
There is also a small difference from how the same functionality
in available in GNAT, see below.
 I want to stay within standard Ada 95 in as many parts of the
program as possible. UTF-8 is so general, shouldn't support be
generally available, as Randy said. (The whole Mac OS X is all UTF-8,
and so was Plan 9, even before the rise of XML.)

 Now there is support for more than one XML library in my program.
Using either library's To_UTF_8 function, if available at all,
might introduce yet another issue to keep track of; they might have
differing semantics (raising exceptions or not, ...).

For example, how does XML/Ada treat Unicode characters in the range
16#D800# .. 16#DFFF#?   AFAICS, they are just treated like the other
Unicode_Char values.
(If I knew the details of current Unicode and ISO 10646 I could 
possibly answer my question: Will this work without surprises
in likely environments now and in the future (Mac, xterm -u8,
cmd.exe /u, ... or Unicode UI-windows)?

:   function To_UTF8 (
:      Str : in Wide_String)
:   return
:      String;

Is this available yet? (I guess it will extend Wide_Character values
into XML/Ada's mod 2**32 Unicode_Char and then pass the result through
the substitution chain?)


:>    function to_UTF8_String
:>      (s: Wide_String; substitute: Character := '#') return String is
: 
: No substitution. An exception is raised if it does not fit. If this is a
: proble you might be better of raising a Utf32_String.

It is a problem as the UTF-8 strings are used in exception messages.
Raising an exception in To_UTF8 when raising another exception via

  Raise_Exception (excpt'Identity, To_UTF8 (msg));

does not seem helpful here?


:>       result: String(1.. 4 * s'length);
:>       --  Unicode has at most 4 bytes for a UTF-8 encoded character
: 
: XML/Ada encodes full 32bit that is up to 6 UTF-8 bytes. In an other
: discussion we allready figured out that this is not realy needed.

Yes.


-- Georg