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From: david@sun.uucp (David DiGiacomo)
Newsgroups: comp.lang.c
Subject: Re: #if inside #define -- easy to do, but is it a good idea?
Message-ID: <29339@sun.uucp>
Date: Mon, 28-Sep-87 18:30:43 EDT
Article-I.D.: sun.29339
Posted: Mon Sep 28 18:30:43 1987
Date-Received: Wed, 30-Sep-87 01:11:14 EDT
References: <157@decvax.UUCP>
Organization: Sun Microsystems, Inc. - Mtn View, CA
Lines: 27

In article <157@decvax.UUCP> minow@decvax.UUCP (Martin Minow) writes:
>From time immemorial, C has forbidden # control lines inside a
>macro definition.  When a collegue begged for this capability,
>I discovered it was trivial to add it to Decus CPP (which was posted
>to Usenet mod.sources about 2-3 years ago).  It might be used
>as follows:
>	#define set_bit(bit)				\
>	#if debug					\
>	    printf("setting %04x\n", bit),		\
>	#endif						\
>		(device_register = (bit))

It would be a nice feature to have, but it's not really necessary for your
example:

#if debug
#define	IFDEBUG(x) x
#else
#define IFDEBUG(x)
#endif

#define	set_bit(bit) \
	IFDEBUG(printf("setting %04x\n", bit);) \
	(device_register = (bit))

-- 
David DiGiacomo, Sun Microsystems, Mt. View, CA  sun!david david@sun.com