Lex reports error because of ambiguous priority -

identifier [\._a-za-z0-9\/]+ comment "//"  <*>{comment}  {     cout<<"comment\n";   char c;   while((c= yyinput()) != '\n')     {     } }  <initial>{s}{e}{t} {    begin(sample_state);    return set; }  <sample_state>{identifier} {     strncpy(yylval.str, yytext,1023);     yylval.str[1023] = '\0';   return identifier; } 

in above lex code, there no error when "// set name" parsed. please notice space after "//" in sentence parsed. however, when "//set name" parsed, there error reported. believe has forward slash appears in both identifier , comment. point going wrong? thanks.

the error caught yyerror

lex matches longest match in context. when input //set, match {identifier} pattern. since never set lex state other sample_state in above code, it's hit problem when in state sample_state, lexer returns identifier, rather matching {comment} rule , skipping rest of line.

there number of ways avoid problem. have {comment} rule match rest of line in pattern:

<*>"//".*   {     cout << "comment\n"; } 

note this, don't need explicit reading of rest of line.

alternately, disallow multiple consecutive / characters in identifer:

identifier (/?[._a-za-z0-9])*/?