Re: [Flex-help] Where does the longest or first match apply?

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

Your code snippet works fine for me.  Or at least, it behaves the way you
expect, because the message I'm getting from flex is:

:5: warning, rule cannot be matched

Thus, the [[:space:]] rule is indeed winning.  I'm not sure why yours is
unrecognizing and fatally erroring..

I'm using flex 2.5.35 on redhat.

-Chris



On Tue, Oct 29, 2013 at 8:11 AM, Arthur Schwarz <asc...@at...>wrote:

> Section 7 says "When the generated scanner is run, it analyzes its input
> looking for strings which match any of its patterns. If it finds more than
> one match, it takes the one matching the most text (for trailing context
> rules, this includes the length of the trailing part, even though it will
> then be returned to the input). If it finds two or more matches of the same
> length, the rule listed first in the flex input file is chosen."
>
> The following code generates the following errors. Any idea why?
>
> [:space:] natches [ \f\n\r\t\v] and \n is a subset of this pattern. But
> using the 'longest' or the 'first' as a scanning rule the construct should
> be legal and in the case of a '\n' being seen the [[:space:]] rule should
> be chosen (the matches are equal, the first pattern is [[:space:]]).
>
> %option main
>
> %%
> [[:space:]]+
> \n
>
> :5: unrecognized rule
> :5: fatal parse error
>
>
>
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