Another silly question
Byron A Jeff
byron at pyr.gatech.EDU
Fri May 19 23:31:21 AEST 1989
In article <2336 at Portia.Stanford.EDU> mesmo at Portia.Stanford.EDU (Chris Johnson) writes:
-From article <17812 at cup.portal.com>, by Tim_CDC_Roberts at cup.portal.com:
-> Ok, folks. In regards to "a[i] == *(a+i) == *(i+a) == i[a]", let me
-> refer to the oft-used example 2["hello"].
-> I agree that this works and is equivalent to "hello"[2]. I've seen it
-> in books and postings. My simple question is why?
-
- The supposed proof of a[i] == i[a] rests on the faulty
- assumption that (x+y) == (y+x) in all contexts; this is
- not correct.
-
- When "+" denotes simple (ie int/float/etc) arithmetic, the
- operation commutes; when it denotes pointer arithmetic,
- commutation is not legal/meaningful.
-
- The statement that *(a+i) == *(i+a) is therefore invalid.
Try this program on for size:
main()
{
char *p = "Goofy";
printf("%c %c %d %d\n",*(p+2),*(2+p), *(p+2) == *(2+p), 2+p == p+2);
}
and its output:
o o 1 1
Any other assertions you'd like to make?
---
-==============================================================================
- Chris M Johnson === mesmo at portia.stanford.edu === "Grad school sucks rocks"
- "Imitation is the sincerest form of plagiarism" -- ALF
-==============================================================================
--
Another random extraction from the mental bit stream of...
Byron A. Jeff
Georgia Tech, Atlanta GA 30332
Internet: byron at pyr.gatech.edu uucp: ...!gatech!pyr!byron
More information about the Comp.lang.c
mailing list