Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!ncar!noao!arizona!dave
From: dave@cs.arizona.edu (Dave P. Schaumann)
Newsgroups: comp.lang.c
Subject: Re: Is #define THING -10 completely safe?
Message-ID: <745@caslon.cs.arizona.edu>
Date: 28 Jan 91 13:50:21 GMT
References: <33@christmas.UUCP> <1991Jan27.233142.28302@watdragon.waterloo.edu> <14999@smoke.brl.mil>
Organization: U of Arizona CS Dept, Tucson
Lines: 37

In article <14999@smoke.brl.mil> gwyn@smoke.brl.mil (Doug Gwyn) writes:
|In article <1991Jan27.233142.28302@watdragon.waterloo.edu> ccplumb@rose.uwaterloo.ca (Colin Plumb) writes:
|-As all loyal followers of the Obfuscated C code contest know,
|-array[i] == *(array+i) == *(i+array) == i[array].  So
|-#define X1 -10
|-#define X2 (-10)
|-[...]
|-printf("%d, %d\n", X1[p], X2[p]);
|-Will print "-35, 15".
|
|No, that's a ludicrous misinterpretation of the situation.  The
|compiler does NOT perform a textual "rewrite" of the [] expression
|then reparse it.


This works as Colin says on my machine (compiling with gcc).  Here is the
full program:

#include <stdio.h>

#define X1  -10
#define X2 (-10)

main(void) {

  int i, a[50], *p = &a[25] ;

  for( i = 0 ; i < 50 ; i++ ) a[i] = i ;

  printf( "X1:%d X2:%d", X1[p], X2[p] ) ;

}

If Colin's interpretation is wrong, what *is* happening?

Dave Schaumann		|  And then -- what then?  Then, future...
dave@cs.arizona.edu	|  		-Weather Report