Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!aplcen!jhunix!c08_d103
From: c08_d103@jhunix.HCF.JHU.EDU (Ex-God)
Newsgroups: comp.lang.c
Subject: Re: %p and different pointer representations
Message-ID: <928@jhunix.HCF.JHU.EDU>
Date: 1 Mar 89 21:49:49 GMT
References: <9382@bloom-beacon.MIT.EDU> <1089@vicorp.UUCP> <234@mstan.Morgan.COM> <16112@mimsy.UUCP> <9453@bloom-beacon.MIT.EDU> <1890@dataio.Data-IO.COM>
Reply-To: ins_balb@jhunix.UUCP (Andy Matter)
Organization: The Johns Hopkins University - HCF
Lines: 33

I need a few things clarified; I don't have a copy of the standard,
and a few people have said mutually contradictory things.  So tell me
if the following is right:

Any object or incomplete pointer fits in (void *).
Any object or inconplete pointer fits in (char *).
Any function pointer fits in any other function pointer.
Function pointers do not have to fit into (void *) (or vice-versa).

Also, how's this for a solution:
#if sizeof (void *) > sizeof (void (*)())
#define generic_ptr (void *)
#else
#define generic_ptr (void (*)())
#endif
Then use generic_ptr instead of void *, and any pointer type
(including pointers to functions) will fit (as long as you remember to
cast everything you assign).

I can see one problem with this solution -- if, for example, an
implementation stored functions in one area and objects in another and
there was no pointer type that could point to either.  I suppose you
could use a union or something....

I guess the best solution would have been to continue using char * as
a generic object pointer, to make all function pointer the same size,
and to make void * big enough to hold either.  Someone should have
thought of that earlier, I guess....

     -- Andrew Barnert (Andy Social/Andy Christ/Andy Matter/ex-God)
        ins_balb@jhunix/ins_balb@jhuvms/c08_d103@jhunix
The opinions expressed in this message are yours.
"If you can't stand the Big Chill, burn down the freezer." -- Jello Biafra