Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!lll-winken!arisia!quintus!ok
From: ok@quintus.uucp (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: Calling multiple functions in a macro.
Message-ID: <617@quintus.UUCP>
Date: 2 Nov 88 08:35:51 GMT
Article-I.D.: quintus.617
References: <353@marob.MASA.COM> <7462@ihlpl.ATT.COM>
Sender: news@quintus.UUCP
Reply-To: ok@quintus.UUCP (Richard A. O'Keefe)
Organization: Quintus Computer Systems, Inc.
Lines: 17

In article <7462@ihlpl.ATT.COM> knudsen@ihlpl.ATT.COM (Knudsen) writes:
>In article <353@marob.MASA.COM>, daveh@marob.MASA.COM (Dave Hammond) writes:
>> #define FOO()	do { foo1(); foo2(); foo3() foo4(); } while(0)
>Why use the do and while?  C has [compound statements], you can say just plain
>	{foo1(); ... foo4();}

Answer: so you can write if (test) foo(); else baz();
With Hammond's definition, the expansion is
	if (test) do { ... } while (0); else baz();
which is valid.  With Knudsen's definition, the expansion is	
	if (test) { ... } ; else baz();
which is **not** syntactically valid.  

If you want a macro to be usable as an expression, use (...)
If you want a macro to be usable as a statement, use do { ... } while (0)

If C had remained syntactically closer to BCPL and copied less of PL/I's
syntactic arsenic, we'd have been spared a fair bit of irritation.