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From: jdp@polstra.UUCP (John Polstra)
Newsgroups: comp.std.c
Subject: Function Argument Evaluation
Message-ID: <7621@polstra.UUCP>
Date: 18 Mar 91 19:29:25 GMT
Organization: Polstra & Co., Inc., Seattle
Lines: 37

Consider the following program:

    #include <stdio.h>

    int x = 100, y = 200, *p;

    main() {
	printf("%d %d\n", *(p = &x), *(p = &y));
    }

Could a conforming compiler translate this in such a way that the output
of the program is "200 200"?

I believe it could, based on this quote from section 3.3.2.2 of the
October 31, 1988 draft:

    The order of evaluation of the function designator, the arguments,
    and subexpressions within the arguments is unspecified, but there is
    a sequence point before the actual call.

If I understand correctly, it would be valid to evaluate in this order:

    "%d %d\n"	/* First argument */
    (p = &x)	/* Subexpression within second argument */
    (p = &y)	/* Subexpression within third argument */
    *p		/* Second argument */
    *p		/* Third argument */

and the resulting output would be "200 200".

Could somebody please support or refute (with accompanying rationale) my
reasoning?
-- 
   John Polstra               polstra!jdp@uunet.uu.net
   Polstra & Co., Inc.           ...!uunet!polstra!jdp
   Seattle, Washington USA              (206) 932-6482
   "Self-knowledge is always bad news."  -- John Barth