Re: Unicode question

[Manfred Lotz <manfred.lotz@arcor.de>]

On Thu, 12 Mar 2015 16:41:59 +0100
Ulrike Fischer <news3@nililand.de> wrote:

> Am Thu, 12 Mar 2015 08:48:27 +0100 schrieb Manfred Lotz:
> 
> > Hi all,
> > If I run this minimal example
> > 
> > \starttext
> > 
> > �
> > 
> > \stopluacode
> > 
> > \stoptext
> > 
> > 
> > I get
> > 
> > tex error       > error on line 3 in file /data/tmp/u1.tex: ! String
> > contains an invalid utf-8 sequence
> > 
> > and some more lines.
> > 
> > 
> > The character above is:
> > 
> >   Character: �
> >    Character name: REPLACEMENT CHARACTER
> >         Charblock: Specials
> >          Category: Other symbol
> >           Unicode: U+fffd
> >              UTF8: 0xefbfbd
> > 
> > which is a valid utf8 character.
> > 
> > Questions:
> > 
> > 1. Why is it considered to be invalid?
> 
> This is not a context question/problem but related to the binary
> (you would get the same error with lualatex or plain)
> 

Yes, I know.

> The luatex code contains the lines (in unistring.w)
> 
> if (val == 0xFFFD)
>         utf_error();
>     return (val);
> 
> in a function str2uni. I didn't really try to understand the code
> but it looks as if 0xFFFD is used as "invalid marker": If luatex
> encounters something that isn't valid utf8 it maps val to 0xFFFD and
> then test against 0xFFFD to rise an error.
> 

Took me a while to find the repository but finally I got it.


> > 2. Are there other valid utf8 characters which are considered
> > invalid?
> 
> The comment in the code says 
> 
> /* the 5- and 6-byte UTF-8 sequences generate integers 
> 
> that are outside of the valid UCS range, and therefore
> 
> unsupported 
>          */
> 

Well, it is called REPLACEMENT CHARACTER, and it seems that this
character will be used to replace invalid characters.  Then it causes 
 if (val == 0xFFFD)
        utf_error();

the error message 
    tex_error("String contains an invalid utf-8 sequence", hlp);

to be displayed.

Ok, this answers my question. 

Thanks for the pointer.


-- 
Manfred








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