Re: Commercial C To Ada 95 compiler

[Darren New <dnew@san.rr.com>]

Marin David Condic wrote:
> 
> Unless my intent was to figure out the address of the thing located just
> after X - probably Y in this case. 

You're allowed to go one past the end in either direction. You're not
allowed to go two past the end.

> The thing is that it isn't really an
> error until you are trying to de-reference the thing pointed to by Y.

This is what I'm saying. No, that's theoretically incorrect. It *is* an
error even if you don't try to dereference the thing pointed to by Y. Simply
doing the arithmetic on Y is in theory erroneous.

> Before
> that its just incrementing a counter - which might be done for all sorts of
> reasons none of which may have anything to do with the array X.

Well, no, it's incrementing a pointer into the array X. If you were talking
about using array subscripting, that would be true. But if you're talking
about incrementing pointers rather than integers, the hardware is allowed to
enforce (for example) segments of exactly the right size, such that a
pointer to one chunk of memory is not allowed to point to a different chunk
of memory via incrementing.

> particular case might come under the heading of "No Harm - No Foul" - It may
> be an error in the code, but one that has no impact on the correct operation
> of the program.

Until you port it to a machine that actually checks it, or to a C compiler
or interpreter that actually implements the range checks it's allowed to
implement.

My point is that the C standard says you're *allowed* to implement range
checking on arrays. In practice, very few do, and in my experience, those
that do are specifically low-performance debugging type interpreters.

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.
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