Processing location information bison c++ parser error

Question

I'm working on a bison c++ parser. Most examples has error method with parameter location& in .y file, but I'm not sure how to get the location_type to call this method.

typedef location location_type;
void
yy::c_parser::error (const location_type& l,
                          const std::string& m)
{
  driver.error (l, m);
}

This is an example excerpt from http://panthema.net/2007/flex-bison-cpp-example/,

if (!driver.calc.existsVariable(*$1)) {
           error(yyloc, std::string("Unknown variable \"") + *$1 + "\"");

However, I got an error that parser.yy:109: error: ‘yyloc’ was not declared in this scope when compiling it.

Answer 1

Your question is slightly unclear: where do you want to call yyerror from?

If you want to call it from the parser, then just use the @n pseudo-variables:

exp: exp "/" exp
  {
    if (!$3)
      {
         yyerror(@3, "division by zero");
         YYERROR;
      }
    else
      {
         $$ = $1 / $3;
      }
  }

If you want to call it from the scanner, then use the variable used there to denote the current location, probably something like yylloc.

If you want to call it from elsewhere (e.g., from an AST traversal, but that would be weird), then find the location there.

But more importantly (sorry, I may state something that you already know): be aware that you typically do not need to call yyerror: you have to provide it, so that parser can raise errors. Typical calls to yyerror are in the generated code, not in code you are expected to write.