Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!caip!think!nike!ll-xn!cullvax!drw
From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: net.lang.c
Subject: Disappearing function call
Message-ID: <357@cullvax.UUCP>
Date: Wed, 1-Oct-86 16:16:01 EDT
Article-I.D.: cullvax.357
Posted: Wed Oct  1 16:16:01 1986
Date-Received: Fri, 3-Oct-86 10:32:28 EDT
Organization: Cullinet Software, Inc., Westwood, MA
Lines: 53

What I want to do is to write a function call of a variable number of
arguments:

	debug(x, y, z, ...)

that will generate no code when the symbol DEBUG is not defined, but
generate a call of some function (say, debug_()) when it is.  If
debug() always had the same number of arguments, we could use

	#ifdef DEBUG
	#define debug(x, y, z)	debug_(x, y, z)
	#else
	#define debug(x, y, z)	/* null */

but macros aren't allowed to have a variable number of arguments.

The best solutions I've heard so far are:

1) We write

	debug(x Z y Z z)

using "Z" instead of ",".  Using the definitions

	#ifdef DEBUG
	#define debug(x)	debug_(x)
	#define Z		,
	#else
	#define debug(x)	/* null */
	#endif

works, since the "Z"s are turned into "," after the call of debug() is
expanded.  This is ugly because you have to write "Z" instead of ",".

2) We write

	debug(x, y, z))

Using the definitions

	#ifdef DEBUG
	#define debug		(debug_
	#else
	#define	debug		debug1(
	#define	debug1(x)	/* null */

This works when DEBUG is off by replacing the call to debug() to a
call to debug1() with one argument, which is then ignored.  This ugly
because of the mismatched parentheses.

Is there a good way to do this?

Dale