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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.lang.c,news.software.b
Subject: Re: passing NULL to functions
Message-ID: <7974@utzoo.UUCP>
Date: Tue, 28-Apr-87 11:43:54 EDT
Article-I.D.: utzoo.7974
Posted: Tue Apr 28 11:43:54 1987
Date-Received: Tue, 28-Apr-87 11:43:54 EDT
References: <150@sds.UUCP>, <1129@ius2.cs.cmu.edu>
Organization: U of Toronto Zoology
Lines: 18

>   Are you saying that you are not guarenteed sizeof(char *) == sizeof(int *)
> sizeof(long *) == sizeof(whatever *)? ...

Precisely.  The major reason this arises is that on word-addressed machines,
e.g. Data General systems (unless they've changed since I knew them), the
"normal" pointer format points only to a word, and there are no spare bits
in the pointer that could be used to point to a byte within the word.  (The
use of such spare bits is a major reason why the representation of "char *"
can differ from the representation of "int *" even on machines where the
sizes of the two pointers are the same.)  There is just no way to point to
a character except to define a longer kind of pointer to hold the extra
information.

Actually, there is nothing guaranteeing that *any* of those sizes are the
same, but sizeof(char *) is usually the anomalous one in practice.
-- 
"If you want PL/I, you know       Henry Spencer @ U of Toronto Zoology
where to find it." -- DMR         {allegra,ihnp4,decvax,pyramid}!utzoo!henry