andy@cit-vax.Caltech.Edu (Andy Fyfe) (04/21/88)
What does (or should?) the ANSI standard say about const void *?
My intuition says that, so far as conversions without an explicit
cast go, the following should be legal:
any * <--> void *
const any * <--> const void *
any * --> const void *
const any * <-- void *
Or, void * is the generic pointer, and const is treated separately
as an attribute that can be added but not taken away (without an
explicit cast). Is this the way it is supposed to work?
If plain "void *" is to be the generic pointer, is K&R 2 correct
in defining memcmp as
int memcmp(const void *, const void *, size_t)
or fwrite as
size_t fwrite(const void *, size_t, size_t, FILE *)
for example?
Also, should "const any * --> void *" be allowed, since "void *"
is the generic pointer?
--
Andy Fyfe
andy@csvax.caltech.edu
wjafyfe@caltech.bitnet
andy@cit-vax.UUCP (...!ames!elroy!cit-vax!andy)andy@cit-vax.Caltech.Edu (Andy Fyfe) (04/26/88)
In article <6214@cit-vax.Caltech.Edu> andy@cit-vax.UUCP (Andy Fyfe) writes: >What does (or should?) the ANSI standard say about const void *? The reason I wondered about this: Gnu C wants to be follow the rules according to ANSI. The current interpretation says that "void *" is the generic pointer, so it allows any * <--> void * const any * <--> void * and gives warnings for const any * <--> const void * any * <--> const void * ("any" here means any type other than "void".) RMS seems quite willing to make gcc conform to the rules. This has so far given me errors under 2 circumstances. The first occured when trying to compile Henry Spencer's string functions. The second occurs when using function prototypes that use "const void *" (like fwrite, etc.). As an aside, K&R 2 (section 7.8.5) makes it clear that the pointer returned by malloc must explicitly be cast to the correct pointer type. Why is this required, given that malloc returns a "void *"? -- Andy Fyfe andy@csvax.caltech.edu wjafyfe@caltech.bitnet andy@cit-vax.UUCP (...!ames!elroy!cit-vax!andy)
karl@haddock.ISC.COM (Karl Heuer) (04/30/88)
In article <6268@cit-vax.Caltech.Edu> andy@csvax.caltech.edu (Andy Fyfe) writes: >What does (or should?) the ANSI standard say about const void *? Should say: All conversions between (any *) and (void *), with arbitrary type qualifiers on either, are legal operations; but converting from const to non- -const or from (void *) to any pointer type other than (void *) or (char *), except by means of an explicit cast, is a Common Warning. Does say: Something too restrictive, as Dennis has pointed out. Has this been resolved yet, Doug? >As an aside, K&R 2 (section 7.8.5) makes it clear that the pointer returned >by malloc must explicitly be cast to the correct pointer type. Why is this >required, given that malloc returns a "void *"? Probably to avoid the Common Warning. The compiler doesn't know that the result of malloc is maximally aligned; (void *) generally isn't. Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
gwyn@brl-smoke.ARPA (Doug Gwyn ) (04/30/88)
In article <3723@haddock.ISC.COM> karl@haddock.ima.isc.com (Karl Heuer) writes: >Does say: Something too restrictive, as Dennis has pointed out. >Has this been resolved yet, Doug? Yes, the rules for conversion from/to qualified types, particularly by simple assignment, are being changed to reflect the original intent. I haven't seen the final form of the words, but I think they will say something to the effect that qualified and non-qualified types may be freely interconverted and only an attempt to access storage that somewhere along the way was at least temporarily qualified is constrained by the qualifier.