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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: comp.lang.c
Subject: Re: structure enhancements
Message-ID: <6566@brl-smoke.ARPA>
Date: Thu, 15-Oct-87 08:57:37 EDT
Article-I.D.: brl-smok.6566
Posted: Thu Oct 15 08:57:37 1987
Date-Received: Sat, 17-Oct-87 07:33:15 EDT
References: <112@teletron.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 41

In article <112@teletron.UUCP> andrew@teletron.UUCP (Andrew Scott) writes:
>1. structure equality/inequality operators

This has been brought before X3J11 and rejected.  There are several
counterarguments of varying force:
	a. What if the struct contains an array?
		Equality comparison could be extended to aggregates.
	b. What if the struct contains a union?
		The could be made undefined, if we knew how to word it.
	c. Cannot in general use bytewise block comparison (memcmp):
		i. padding may contain garbage
		ii. floating-point representation may not be unique
	d. Simple-looking operation would lead to lots of code, because
		in general the comparison would be done member-by-member.
	e. Facility of limited utility; for instance, a struct member
		is often a pointer to a string, and strcmp() should be
		done on those members, but that is not something the
		compiler is able to determine.
	f. Doesn't help in comparison of "cookies" such as returned by
		fgetpos(), because there's no guarantee that distinct
		cookie encodings will always represent distinct values.
		Such usages should be done via explicit cookiecmp()
		functions.

>2. appropriate bitfield sizing

X3J11 discussed a similar request and decided against it.  I don't have
a record of the reason, but I suspect not a strong enough case was made
for adding this to justify the increased implementation cost.

>It's difficult to use bitfields structures to define "templates" for real world
>data formats as they now stand.

It's difficult in any case!  For example, how to you handle 8-bit byte
oriented data received on a 9-bit byte system?  Bit-fields have limited
utility; they were never intended to be a universal solution to the
problem of externally-imposed data formats.

P.S.  This is not an official X3J11 response.  If you want X3J11 to pay
attention to your ideas, send them to the committee; posting them to
this newsgroup does not guarantee they'll receive a fair hearing.