> > cpu% cat t.c
> > void foo (void)
> > {
> > double d = 08.7;
> > USED(d);
> > }
> > cpu% 8c t.c
> > t.c:3 syntax error, last name: 8.7
> > cpu%
> >
> > This came up as I’m making my lexer for C able to scan numbers. I
> > tried to understand ken’s code, but it gets very hairy right around
> > /sys/src/cmd/cc/lex.c:751 — and I think there’s a bug.
>
> you're right, that's wrong. but the question is do you really want
> that to work?
In kencc, maybe not; in a class project designed to implement a C89 compiler,
definitely yes.
> in that case, one could always remove the goto ncu on line 757.
cpu% grep -n 'goto ncu;' /sys/src/cmd/cc/lex.c
778: goto ncu;
788: goto ncu;
801: goto ncu;
808: goto ncu;
cpu%
I think you mean the one on 788. I'm far from comfortable enough with
the code here to suggest a patch, though. Certainly not comfortable
enough to incorporate it into my lexer.
> however, for better or worse, octal constants start with a 0. 08.7
> feels like a syntax error to me. i am a little suprised that gcc
> accepts 08.7. are you sure that that's actually in the standard?
>From the ISO standard (the freely available “draft" C99+TG1+TG2 standard):
6.4.4.2 Floating constants
Syntax
floating-constant:
decimal-floating-constant
hexadecimal-floating-constant
decimal-floating-constant:
fractional-constant exponent-part_{opt} floating-suffix_{opt}
digit-sequence exponent-part floating-suffix_{opt}
…
fractional-constant:
digit-sequence_{opt} . digit-sequence
digit-sequence .
…
digit-sequence:
digit
digit-sequence digit
— no restrictions on the initial digit. You get the same table in
Harbison & Steele, 5th Ed. §2.7.2.
--Joel
