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From: brooks@lll-crg.ARPA (Eugene D. Brooks III)
Newsgroups: net.lang.c
Subject: Re: Re: The importance of alignment on a VAX
Message-ID: <478@lll-crg.ARPA>
Date: Tue, 26-Mar-85 20:18:34 EST
Article-I.D.: lll-crg.478
Posted: Tue Mar 26 20:18:34 1985
Date-Received: Fri, 29-Mar-85 01:18:42 EST
References: <466@lll-crg.ARPA> <9339@brl-tgr.ARPA> <1159@reed.UUCP>
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Organization: Lawrence Livermore Labs, CRG group
Lines: 21

> >the hardware will support it easily.  It would be nice to read structures
> >from other machines (like PDP-11's) sometime.
>   So C needs something like the Pascal keyword `packed'. (hee hee)

A packed structure type would only give portability between a few machines.
Although I would never want a machine with a 36 bit word they do exist and
some of them have C compilers.

The portability problem is best handled with a subroutine or macro to read
the structure.  Using a 'packed' structure introduces a speed penalty when
the structure is used elsewhere and a hole host of other troubles just for
the sake of giving limited I/O portability.  I can't see any sense in this.
This is against the philosophy of the language.  The language has no I/O at all.
Lets keep the I/O in routines where it belongs.  If you want to read a structure
from a pdp11 write a routine or a macro.

It appears to me that packed structures are even jumping the gun.  Does the C
language even define the order in which the elements of a structure are placed
in memory? The chapter on structures in K&R only states that the structure is a
grouping of data items and I failed to find any statements about ordering of the
elements.  Am I mistaken about this?