Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!mordor!sri-spam!rutgers!uwvax!oddjob!gargoyle!ihnp4!laidbak!daveb
From: daveb@laidbak.UUCP (Dave Burton)
Newsgroups: comp.lang.c
Subject: Re: interesting program
Message-ID: <1330@laidbak.UUCP>
Date: 30 Jan 88 21:00:15 GMT
References: <19@berick.UUCP>
Reply-To: daveb@laidbak.UUCP (Dave Burton)
Organization: is pretty bad/My method of
Lines: 40

In article <19@berick.UUCP> jeffl@berick.UUCP (Jeff Lawhorn) writes:
>What does the following program print?  (I know of at least one
>program that prints the wrong answer).
>
>main()
>{
>	int k = 4;
>	k = k++;
>	printf("and the answer is %d\n", k);
>	exit(0);
>}

Ambiguity warning:
According to K&R, App A, page 187:
"When the postfix ++ is applied to an lvalue the result is the value of the
 object referred to by the lvalue. After the result is noted, the object is
 incremented in the same manner as for the prefix ++ operator."

 The ambiguous word here is "noted".
 This text does not state when assignment is performed.
 "Normal":

 movl	#4,-4(a6)	| k = 4
 addql	#1,-4(a6)	| k = k++

 However, the compiler could note the result, then produce code accordingly:

 movl	#4,-4(a6)	| k = 4
 movl	-8(a6),-4(a6)	| [tmp = k]	noted
 addql	#1,-4(a6)	| k++		incremented
 movl	-4(a6),-8(a6)	| k = tmp	assignment

I think the result is arguably 5, but acknowledge
a result of 4 *could* be considered correct.

Flames to /dev/null, corrections to /dev/lp.
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