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From: kurt@hi.UUCP (Kurt Zeilenga)
Newsgroups: comp.lang.c
Subject: Re: Two dimensional arrays in C (Oops)
Message-ID: <10190@hi.UUCP>
Date: Thu, 2-Jul-87 13:50:26 EDT
Article-I.D.: hi.10190
Posted: Thu Jul  2 13:50:26 1987
Date-Received: Sat, 4-Jul-87 07:41:24 EDT
References: <238@hubcap.UUCP> <245@hubcap.UUCP>
Reply-To: kurt@hi.UUCP (Kurt Zeilenga)
Organization: U. of New Mexico, Albuquerque
Lines: 24

He writes:
>in article <238@hubcap.UUCP>, beede@hubcap.UUCP (Me) says:
>> 
>> #define matrix_el(array,i,j) (array[y*sizeof(double)+j])
>> 
>which of course is completely bogus.  I'm not sure _where_ that
>sizeof(double) popped in, but anyway the correct version is
>
>#define matrix_el(array,i,j) (array[i*y+j]) ,
>

Actually, (I'm being picky) a better version is:

#define matrix_el(array,i,j)	array[(i)*y+(j)]

You should always use '(' and ')' to surround arguments in macros (and the
macro itself if needed) to insure the evaulation order of any expression
in the expanding macro.  Mike's macro, if used like matrix(array,i+1,j),
would return something a bit different then advertised.

-- 
	Kurt Zeilenga	 (zeilenga@hc.dspo.gov)		I want my talk.flame!

	"So long, Mom, I'm off to kill a commie..."