Path: utzoo!utgpu!water!watmath!clyde!rutgers!labrea!decwrl!hplabs!sdcrdcf!ism780c!nobody
From: nobody@ism780c.UUCP (Unprivileged user)
Newsgroups: comp.lang.c
Subject: Re: comma operator
Message-ID: <8599@ism780c.UUCP>
Date: 14 Jan 88 22:46:02 GMT
References: <3819@sigi.Colorado.EDU>
Reply-To: marv@ism780.UUCP (Marvin Rubenstein)
Organization: Interactive Systems Corp., Santa Monica CA
Lines: 20

In article <3819@sigi.Colorado.EDU> swarbric@tramp.Colorado.EDU (SWARBRICK FRANCIS JOHN) writes:

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

At least one use is in a macro, for example:

       #define foo(a,b) ( (x=(a)+(b)) , (y=(a)-(b) )

If the macro were written as:

       #define foo(a,b) { (x=(a)+(b)) ; (y=(a)-(b) }

then it could only be used in the context of a statement.  The first version
is an expression so it can be used where a function reference is allowed.
The value of the first macro is the value assigned to y (which of course may
not be the same as a-b).  The second macro has no value.

     Marv Rubinstein -- Interactive Systems