escaping - Regex clarification on escape sequences with lex -


i'm creating lexer.l file working intended except 1 part. have rule:

[\(\*.*\*\)] {}

which want make when encounter (* test *) in file, nothing it. when run lex lexer.l warning on lines rules \(, \*, , \) stating can never met. guess question why [\(\*.*\*\)] {} interfere \( , others? how can catch (* test *)?

languages comment syntax (*…*) typically allow nested comments, , nested comments cannot recognized (f)lex because nesting requires context-free grammar, , lexical scanner implements regular languages.

if comments not nest (so (* (* else *) comment, rather prefix of longer comment), can use regular expression

[(][*][^*]*[*]+([^*)][^*]*[*]+)*[)]

if require nested comments, can use start conditions , stack (or simulated stack, below):

%x sc_comment  %%   int comment_nesting = 0;  "(*"             { begin(sc_comment); } <sc_comment>{   "(*"           { ++comment_nesting; }   "*"+")"        { if (comment_nesting) --comment_nesting;                    else begin(initial); }   "*"+           ;    [^(*\n]+       ;   [(]            ;    \n             ;  }

that snippet taken this answer, small adjustment because answer recognizes nested /*…*/ comments. fuller explanation of code appears there.


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