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Re: Is it valid to use the zero-byte "^@" in regexps?

From: Nicolas Richard
Subject: Re: Is it valid to use the zero-byte "^@" in regexps?
Date: Wed, 18 Jun 2014 12:55:42 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.91 (gnu/linux)

Thorsten Jolitz <address@hidden> writes:
>> I don't see why it wouldn't be valid, but I don't know. If it is
>> desirable is another question : it would be better to search for the
>> beginning, then search for the end with another regexp.
> That what I did initially, and what is of course much easier, but took
> twice (?) as long too ...

I'm surprised but I guess I'm being too naive.

>> Except NUL characters of course.
> i.e. zero-byte "^@"?

Yes, "NUL" is the name you find in most ASCII charts. "zero-byte" less
so, afaict.

> But Emacs can differentiate between NUL characters and the @ character -

Of course. One has ascii code 0, the other is 64.

NUL is represented by ^@ because of

If you hit C-f with point before a NUL, you jump over it ; whereas if
you C-f with point before the two characters ^@ (i.e. not a NUL), cursor
only jumps over the ^.

> Often, but not always, the not matched source-blocks contain @
> characters (but not NUL chars). The strange thing is that the failed
> matching happens with these blocks being part of a really big
> testfile. When I isolate and copy them to a temp buffer and try to match
> them there, it just works.

If you have a reproducible recipe (even with a big file) it would
certainly help.


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