Xref: utzoo comp.lang.c++:10966 comp.lang.c:34998
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!rpi!uupsi!glinj.gli.com!bobj
From: bobj@glinj.gli.com (Robert Jacobs)
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: char* vs void*
Keywords: char* vs void* pointer arithmitic
Message-ID: <1991Jan2.171429.11566@glinj.gli.com>
Date: 2 Jan 91 17:14:29 GMT
References: <11745@alice.att.com> <2778A795.6E71@tct.uucp> <17590@paperboy.OSF.ORG> <277BAC53.F2A@tct.uucp>
Organization: General Logistics International, Inc.
Lines: 33


>Pointers of types |char *| and |void *| must both be able to hold the
>address of any object.  The reason why this is so differs for the two
>types.  For |char *| it's existing practice, and for |void *| it's the
>decree of ANSI.

>When ANSI invented |void *|, they made it capable of holding any
>pointer.  Since |void *| can hold any pointer, and |char *| can hold
>any pointer, there would be no point (:-)) in an implementation giving
>them different representations.  So ANSI went that final step and
>_required_ that their representations be identical.

>>Do you mean "can be converted to each other and back without loss of
>>information?"

>Yes, and that's the important point for this discussion.  A portable
>qsort() can cast its |void *| array parameter to |char *| to do
>pointer arithmetic, then cast the results of the pointer arithmetic
>back to |void *| to generate the comparison function's arguments.

What I can't understand is that ANSI decided that one cannot do pointer
arithmitic on a void*, like a char*. Because of this, new work is forced
to use char* as the generic pointer that can do pointer arithmitic.
This continues the existing practice that char* is special. Void*
should be allowed to do pointer arithmitic so that char* does not
have to be used for new work.

But I guess my opinion is too late to be in any version of ANSI C
or C++. Too bad.

Robert Jacobs                                   | 
General Logistics International Inc.            |
bobj@gli.com                                    |