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From: msb@sq.UUCP
Newsgroups: comp.lang.c
Subject: Re: How can I use #define to make something completely disappear?
Message-ID: <1987Nov6.132634.20906@sq.uucp>
Date: Fri, 6-Nov-87 13:26:34 EST
Article-I.D.: sq.1987Nov6.132634.20906
Posted: Fri Nov  6 13:26:34 1987
Date-Received: Sun, 8-Nov-87 08:39:08 EST
References: <10083@brl-adm.ARPA> <850@tut.cis.ohio-state.edu> <9187@mimsy.UUCP>
Reply-To: msb@sq.UUCP (Mark Brader)
Organization: SoftQuad Inc., Toronto
Lines: 26
Checksum: 43939

Chris Torek (chris@mimsy.UUCP) suggests:

> #define DBPRINT(arglist) if (dflag == 0) /* void */; else printf arglist

As he says, this form lets the macro work correctly inside if-statements.

Personally, though, I prefer to make my macros expression-like no matter
how complicated it makes them; then I know that what looks like an
expression statement really is an expression statement, and again they
work anywhere.

The above can in fact be written about
as simply in expression style, as either of:

#define DBPRINT(arglist) (dflag && printf arglist)
#define DBPRINT(arglist) (dflag? printf arglist: 0)

or other stylistic variations that I don't need to enumerate (and neither
do you, probably).

Of the three forms in this message, I strongly prefer the last, as it is
the only one that expresses the ifness in the conventional sense (as it
would normally be said outside a macro in C).

				"Avoid null THEN" -- Kernighan and Plauger
Mark Brader, SoftQuad Inc., Toronto, utzoo!sq!msb, msb@sq.com