Flex: unrecognized rule `(?s:.)`-CodePudding

In my flex program, I am unable to use any of these regex. Usage of any of them are generating unrecognized rule error.

%{
#include<stdio.h>
%}

%option nodefault
%option noyywrap
%option outfile="scanner.c"

%%

(?i:a) printf("rule1");

(?s:.) printf("rule2");

(?x:a b) printf("rule3");

(?#foo) printf("rule4");

[a-z]{-}[aeiou] printf("rule5");

%%

All of these are well defined in this docs. I am confused, whether I am using wrong variant of flex! I am using windows machine with GnuWin32 flex v2.5.4.

This is the error being generated:

$flex misc/test_lexer.l
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 11: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 13: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 15: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 17: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule
"misc/test_lexer.l", line 19: unrecognized rule

CodePudding user response：

You need to update your flex installation if you want to use those constructs.

Flex 2.5.4, which was released more than 25 years ago, does not implement {-} nor does it implement any of the (?:...) syntaxes.

The manual you cite, which is also not the current version, specifies:

This edition of The flex Manual documents flex version 2.6.3. It was last updated on 13 January 2017.

Flex v2.5.4 did implement the / trailing context operator, which was in the original version of this question. But note that / cannot be used inside parentheses, and since flex normally adds parentheses around macro expansions, / cannot be used in a macro expansion either.