Path: utzoo!attcan!uunet!virtech!cpcahil
From: cpcahil@virtech.uucp (Conor P. Cahill)
Newsgroups: comp.lang.c
Subject: Re: A question of style
Message-ID: <1989Dec4.032317.29614@virtech.uucp>
Date: 4 Dec 89 03:23:17 GMT
References: <547@mars.Morgan.COM> <1989Nov30.001947.14883@aqdata.uucp> <22139@brunix.UUCP>
Organization: Virtual Technologies Inc.
Lines: 34

In article <22139@brunix.UUCP>, gvr@brunix (George V. Reilly) writes:
> Because of the two uses of the comma as a parameter separator and as a
> sequential-expression separator, you can occasionally get unexpected
> results.  Consider:
> 
> #define single(list) printf list
> #define double(list) printf(list)
> 
> main()
> {
> 	single("%d %d %d", 1, 2, 3);
> 	double("%d %d %d", 1, 2, 3);
> }
> 
> The expansion of |single()| will yield |printf("%d %d %d", 1, 2, 3)|, while
> the expansion of |double()| will yield |printf(("%d %d %d", 1, 2, 3))|.

This is only true if they were called as follows:

  	single(("%d %d %d", 1, 2, 3));
  	double(("%d %d %d", 1, 2, 3));

which is one of the reasons that I dislike cpp not being able to handle 
a variable number of arguments to a macro (because it forces people to 
think up this solution, or to make up different macros for different numbers 
of arguments).



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| Conor P. Cahill     uunet!virtech!cpcahil      	703-430-9247	!
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