array[-1] -- permitted?

[Every system needs one]

In article <1237 at imagine.PAWL.RPI.EDU>, kyriazis at rpics (George Kyriazis) writes:
> Excuse for the question, but that is the first time I am looking at that
> subject and I don't see any reason why x[-a] can't be permitted, mainly
> for two basic reasons:
>     (a)	x[a] == *(x+a)  therefore  x[-1] == *(x-1), which looks
> 	perfectly ok to me.
> 
>     (b)	yacc uses array[-1].  If it is considered invalid, that will mean
> 	that yacc has to be rewriten for the new standard?
> 
> Am I missing something?

Yes.

The source for who contains the following type of thing:

char *str = "hello world"+6;

where 	printf( "'%c'", str[ -6]);

gives	'h'.

This is is used in the "who am i" command.

It works on most C compilers (with 1 exception still in developement).  The
exception is due to the method of compilation requiring a "fake node" to
make it work.  DMR is quoted as saying it should work by the compiler writer,
even in ANSI C.


| Terry Lambert           UUCP: ...{ decvax, ihnp4 } ...utah-cs!century!terry |
| @ Century Software        OR: ...utah-cs!uplherc!sp7040!obie!wsccs!terry    |
| SLC, Utah                                                                   |
|                   These opinions are not my companies, but if you find them |
|                   useful, send a $20.00 donation to Brisbane Australia...   |
|                   'I have an eight user poetic liscence' - me               |