Path: utzoo!mnetor!uunet!husc6!yale!cmcl2!brl-adm!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: comma operator
Message-ID: <10176@mimsy.UUCP>
Date: 14 Jan 88 04:47:22 GMT
References: <3819@sigi.Colorado.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 34

[More operator drivel :-) ]

In article <3819@sigi.Colorado.EDU> swarbric@tramp.Colorado.EDU
(SWARBRICK FRANCIS JOHN) writes:
>I'd never used the comma operator before (except in for() statements)....
[five examples deleted]
>All five gave the answer "1 0," and (using Turbo C) they all generate the
>same amount of code (OBJ = 223, EXE = 5408).

They should; semantically, they were all the same.

>So, what is the advantage of using the comma operator other than
>to squeeze everything on to one line?

Not `one line', but rather `one expression', such as is required in
`for' statements.  Comma expressions can also be useful in translating
a function to a macro:

	/*
	 * Get the next nybble.  This is an expression rendition of
	 *	if (--pk->pk_1nyb < 0) {
	 *		pk->pk_1nyb = 1;
	 *		pk->pk_c = nextbyte(pk);
	 *		return (pk->pk_c >> 4);
	 *	} else
	 *		return (pk->pk_c & 0xf);
	 */
	#define	nextnyb(f) \
		(--(pk)->pk_1nyb < 0 ? \
		 ((pk)->pk_1nyb = 1, ((pk)->pk_c = nextbyte(pk)) >> 4) : \
		 (pk)->pk_c & 0xf)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris