Re: Bison Error reporting

[Hans Aberg]

At 15:19 +0100 0-12-14, Akim Demaille wrote:
>> - If Bison encounters an undefined token it calls it
>> "$undefined.", usually a sporadic character from the lexer. Is
>> it easy to make the error reporting instead writing out which
>> character this is? (Apart from defining a token for every
>> character.)
>
>Good question.  The problem is you can't really assume you can print
>an unknown token as a char.  Someone might return 424242 in the
>scanner, and then?  What can we do?

Actually, with the Yacc-compatible (non-raw) mode, code numbers start at
257, so it means that 1-256 must be a character code.

So it is possible to always issue an error "unknown character ..." for
codes 1-256.

By the way, it is sort of funny that 0 (= YYEOF) is allowed as
"end-of-lexing", making character code 256 = '\0'. Would it not be better
letting YYEOF = -1, and allow only values < 0 be "end-of-lexing"?

  Hans Aberg