Re: don't want to display yyout

[Hans Aberg]

At 10:58 +0200 2005/05/19, Vincent Zweije wrote:
> ||  I think Flex imnplements a default rule
> ||     .  ECHO
> ||  which can be overriden by writing
> ||     .  { /* whatever you like */ }
>
> True.
>
> However, if you hit your default rule, that means that your
> token definitions didn't cover all possible input.  For some
> applications, that's a BAD thing.
>
> If so, find the holes in your token definitions, and plug them.
>
> I like to use %option nodefault precisely for that reason.

The default rule, it seems, is mainly quick hack around proper error 
handling. A proper program should detect the erroneous characters and 
take proper error handling, rather than just outputting them. One 
possibility is an error message from the lexer. Another is to send it 
over to the parser, in the case there is one, and let it generate the 
error message, admitting any eventual error recovery. Also, one could 
output the characters to stderr, which later could be redirected.
--
  Hans Aberg