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Path: utzoo!utgpu!water!watmath!orchid!rbutterworth
From: rbutterworth@orchid.UUCP
Newsgroups: comp.lang.c
Subject: Re: Question on external struct declarations in ANSI C
Message-ID: <10112@orchid.waterloo.edu>
Date: Wed, 5-Aug-87 08:32:11 EDT
Article-I.D.: orchid.10112
Posted: Wed Aug  5 08:32:11 1987
Date-Received: Fri, 7-Aug-87 05:41:18 EDT
References: <1429@cullvax.UUCP>
Organization: U of Waterloo, Ontario
Lines: 17

In article <1429@cullvax.UUCP>, drw@cullvax.UUCP (Dale Worley) writes:
> arnold@emory.uucp (Arnold D. Robbins {EUCC}) writes:
> > 	extern struct pte Mbmap[];		/* page tables to map mbutl */
> Well, reading 3.5.2.2 and 3.5.3.2 of the draft suggests that this
> module doesn't need to know the size of Mbmap at all (unless you
> sizeof it or something), and so the size of struct pte doesn't need to
> be known, and so struct pte need not be fully declared.

Which of course implies that either
1) all structs must be aligned on a long double boundary, or
2) all sizeof(struct X*) pointers must be as big as (char *) pointers.

On some machines (e.g. sizeof(char*) = 2*sizeof(int*),
and alignof(long double) = 16), either choice can be fairly
wasteful in terms of both space and cpu, all in the name of
compatibility with old programs written by people too lazy
to declare types when they could get away with it.