arithmetic on void pointers

[Stephen J. Friedl]

In article <1527 at ncar.ucar.edu>, russ at groucho.ucar.edu (Russ Rew) writes:
> What does the latest dpANS document say?  Is it legal
> to increment a variable of type void* ?

No.

When incrementing a pointer, one multiplies the increment by the
size of the pointed-to object.  Since a `void' has no size, you
can't get to the next one.

The dpANS does not directly say "You can't ++ a void*", so to prove
it you need to string a couple of parts together.

>From the May88 dpANS:  (renditions: ITALICS, /Courier/)

	3.1.2.5 - Types

		"The /void/ type comprises an empty set of values; it
		is an incomplete type that cannot be completed"

### /void/ is an incomplete type

	3.3.3.4 - The /sizeof/ operator

		"The /sizeof/ operator shall not be applied to an
		expression that has function type or an incomplete
		type [...]"

### you can't take the size of /void/

	3.3.2.4 - Postfix increment and decrement operators
and	3.3.3.1 - Prefix increment and decrement operators

		"The operand of the prefix increment or decrement
		operator shall have qualified or unqualified scalar
		type and shall be a modifiable lvalue."

### you can't ++ or -- a /void/



     I would guess that those implementations that permit ++ on
void pointers do so by treating them as char pointers instead.

     Steve, the staggering dpANS (with apologies to Karl)

-- 
Stephen J. Friedl / V-Systems, Inc. / Santa Ana, CA / +1 714 545 6442 
3B2-kind-of-guy   / friedl at vsi.com  / {attmail, uunet, etc}!vsi!friedl

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