Path: utzoo!utgpu!water!watmath!clyde!ima!bbn!bbn.com!rsalz
From: rsalz@bbn.com (Rich Salz)
Newsgroups: comp.lang.c
Subject: Re: comma operator
Message-ID: <297@fig.bbn.com>
Date: 14 Jan 88 05:45:20 GMT
References: <3819@sigi.Colorado.EDU>
Reply-To: rsalz@fig.bbn.com (Rich Salz)
Organization: BBN Laboratories, Cambridge MA
Lines: 28

>[what's] the advantage of using the comma operator

One use is in when you are only interested in side-effects, followed shortly
by a test:
	for ( ; ; ) {
	    readorexit();
	    if (satisfied())
		break;
	    ...
	}

	while (readorexit(), !satisfied()) {
	    ...
	}

Or when you want to tie two actions tightly together:
	while (argc--, *++argv)
	    ...

Perhaps the most common use is when you're writing a macro:
	#define SWAP(a, b, temp)  temp=a, a=b, b=temp
You can't write this the "obvious" way:
	#define SWAP(a, b, temp)  {temp=a, a=b, b=temp}
because, someone will write
	if (test(a, b)) SWAP(a, b, temp);
	else abort();
-- 
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