Re: [Flex-help] warning, rule cannot be matched

[Chris v. <che...@gm...>]

I think the default for flex is to understand the full range of 8-bit
characters.  (See the -7 and -8 switches.)

If by "generates an error message" you're talking about the "rule cannot be
matched" message, it makes sense to me.  [^[:alnum;]] will indeed match \n,
so the specific \n pattern is 'redundant' and will never get matched.

-Chris


On Sun, Oct 27, 2013 at 7:04 AM, Arthur Schwarz <asc...@at...>wrote:

> The little code snippet below generates an error message. The reason (I
> think) is that the set [^[:alnum:]] contains a '\n' within it. I had
> assumed that the character set involved was [:print:] = [\x20-\7E], which
> excludes all control characters, [:cntrl:] = [\x00-\x1F\x7F], but
> apparently this is not the case.
>
>
> What is the set of characters recognized by flex when an operation like
> this is performed? Is it[\x00-\x7F], [\x00-\xFF], or ?
>
>
> %option main
>
> %{
> #ifndef DEBUG
>   #define    DEBUG(stmt) stmt
> #else
>   #define    DEBUG(stmt)
> #endif
> %}
>
> %%
>
> [^[:alnum:]]    { DEBUG( ECHO; ) } /* [\x00-\x7F]{-}[:alnum:] ? */
> .               { DEBUG( ECHO; ) }
> \n              { DEBUG( ECHO; ) } /* warning, rule cannot be matched */
> <<EOF>>         { return 1; }
>
>
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