Flex not counting lines properly on multiline comments

问题

I`m using the above regex to identify multiline comments in Flex:

[/][*][^*]*[*]+([^*/][^*]*[*]+)*[/]       { /* DO NOTHING */ }

But seems to me that flex/bison is not returning properly the line counter. For example:

Input:

1  ___bqmu7ftc
2 // _qXnFEgQL9Zsyn8Ohtx7zhToLK68xbu3XRrOvRi 
3 /* "{ output 6 = <=W if u7 do nN)T!=$||JN,a9vR)7" 
4  -758939 
5 -31943.6165480 
6 // "RND" 
7  '_' 
8 */
9 [br _int]

Output:

1 TK_IDENT [___bqmu7ftc]
4 [
4 TK_IDENT [br]
4 TK_IDENT [_int]
4 ]

The line should be 9 instead of 4.

Any ideas?

回答1:

I don't know how you generated the test output in your question, but here's an (almost) minimal example of how to use yylineno. It works fine for me:

%{
  #define ID 257
%}

%option yylineno
%option noinput nounput noyywrap

%%

[[:space:]]+                            { /* DO NOTHING */ }
"//".*                                  { /* DO NOTHING */ }
[/][*][^*]*[*]+([^*/][^*]*[*]+)*[/]     { /* DO NOTHING */ }
[[:alpha:]_][[:alnum:]_]*               { return ID; }
.                                       { return *yytext; }

%%

int main(int argc, char** argv) {
  for (;;) {
    int token = yylex();
    switch (token) {
      case 0:   printf("%4d: %s\n",       yylineno, "EOF"); return 0;
      case ID:  printf("%4d: %-4s[%s]\n", yylineno, "ID", yytext); break;
      default:  printf("%4d: %c\n",       yylineno, token); break;
    }
  }
}

回答2:

This is the solution I found on Flex manual

Remember to declare int comment_caller; on your definition scope.

%x comment 
%x foo
%%

"/*" {comment_caller = INITIAL;
    BEGIN(comment);
      }

     <foo>"/*"  {
      comment_caller = foo;
      BEGIN(comment);
      }

     <comment>[^*\n]*    {}
     <comment>"*"+[^*/\n]*   {}
     <comment>\n       {++line_num;}
     <comment>"*"+"/"    BEGIN(comment_caller);

来源：https://stackoverflow.com/questions/25416437/flex-not-counting-lines-properly-on-multiline-comments

标签

compiler-construction

flex-lexer