array[-1] -- permitted?

[Henry Spencer]

In article <69575 at sun.uucp> swilson at sun.UUCP (Scott Wilson) writes:
>I'm not quite sure what is being discussed.  I assume the standard
>says that the -1'th element on an array is not guaranteed to be
>accessible, not that negative array indices are disallowed...

More precisely, what it says is that even *computing* a pointer to the
-1th element of an array can send you off into the Twilight Zone.  This
is not new -- if you read K&R, that's always been the rule.  However,
there is no objection to subtracting 1 from a pointer that already points
to the Nth element of an array, where N > 0.  (&a[1])[-1] is legal.
-- 
NASA is into artificial        |     Henry Spencer at U of Toronto Zoology
stupidity.  - Jerry Pournelle  | uunet!attcan!utzoo!henry henry at zoo.toronto.edu