cc

[rbriber at POLY1.NIST.GOV]

Mike Chapman writes:
	
        I have found a peculiarity in the MIPS C compiler that is more of a 
    curiosity than a problem, but I wonder if someone could shed some light on
    it anyway, just for fun.
	
	    Here is a sample program that exhibits the peculiar behavior:
			#include <stdio.h>
			int a [2];
			main()
			{
				int i;
				a[0] = 5;
				a[1] = 6;
				i = 0;
				printf("%d %d\n", a[i++], a[i++]);
			}
    Depending on the order of evaluation of function arguments, I would expect
    this code to generate "6 5" or "5 6".  But instead it says "5 5", which 
    confuses me a bit.  Do all pre/post increment/decrement operators only
    take effect after the current source line, or what?  I did check the value
    of 'i' on the next line, and it was indeed 2, so that part works.  For C
    reference I only have the ancient K&R, which as far as I can tell does not
    formally specify when these operators are supposed to do their thing.  For
    reference purposes, I ran this code on many platforms (6 different CPUs, 
    8 different compilers), and only the MIPS compiler came out with the "5 5"
    answer.
	
                           (stuff deleted).
====================
Just a note that while cc gives "5 5", GNU's gcc compiler on our Iris 
gives "5 6".

--
 ----------------------------------------------------------------------------
| Adios Amoebas,      | "I've tried and I've tried and I'm still mystified,  |
|   Robert Briber     |  I can't do it anymore and I'm not satisfied."       |
|   224/B210  NIST    |                                 --Elvis              |
|   Gaithersburg, MD  |------------------------------------------------------|
|   20899  USA        | rbriber at poly1.nist.gov   (Internet)                  |
|(301) 975-6775(voice)| rbriber at enh.nist.gov     (Internet)                  |
|(301) 975-2128 (fax) | rbriber at nbsenh           (Bitnet)                    |
 ----------------------------------------------------------------------------