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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: pointer alignment when int != char *
Message-ID: <6376@brl-smoke.ARPA>
Date: Mon, 31-Aug-87 21:48:40 EDT
Article-I.D.: brl-smok.6376
Posted: Mon Aug 31 21:48:40 1987
Date-Received: Sat, 5-Sep-87 00:47:04 EDT
References: <493@its63b.ed.ac.uk> <6061@brl-smoke.ARPA> <3812@spool.WISC.EDU> <7939@think.UUCP> <588@murphy.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 15
Xref: mnetor comp.lang.c:4098 comp.unix.wizards:4017

In article <588@murphy.UUCP> dave@murphy.UUCP (Dave Cornutt) writes:
>...  However, I will say this, because I don't
>think the standard has really addressed it: there should be a way to take
>any pointer and generate a byte offset from byte 0 in whatever address
>space the code is running in.  The reason is that you need such a beast
>to feed to lseek if you want to access something through one of the
>/dev/mem devices (or maybe /proc).

The ANSI C standard doesn't address this (pun intended?) because
the process may have incommensurable multiple data address spaces.
It cannot dictate the mapping to be used by UNIX /dev/*mem and
similar facilities; that's not within the scope of the C standard,
which also has to apply to non-UNIX-like environments.  It is up
to the operating system implementation to make things like that
work; it has nothing to do with the C language.