Re: c/8030: strange behaviour of side effect operator

Re: c/8030: strange behaviour of side effect operator

[rth]

Synopsis: strange behaviour of side effect operator

State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Thu Sep 26 20:12:43 2002
State-Changed-Why:
    Using -Wall:
    z.c:5: warning: operation on `a' may be undefined
    
    In fact, not "may be" but "is".

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8030

c/8030: strange behaviour of side effect operator

[achille.fouilleul]

>Number:         8030
>Category:       c
>Synopsis:       strange behaviour of side effect operator
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 25 02:46:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     achille.fouilleul@gambro.com
>Release:        gcc-2.95
>Organization:
>Environment:
both Linux and Cygwin
>Description:
Let's consider the following code:

int main() {
	int a = 1;
	int b;

	b = a++ + a;
	printf("%i\n", b);
	return 0;
}

this prints "2" with GCC, whereas it prints "3" with CodeWarrior and Lcc.
Hint: I saw that in the assembler output the incrementation statement occurs AFTER the addition one.
>How-To-Repeat:
Just compile it! "gcc bug.c -o bug"
>Fix:
Dunno. Not a gcc expert!
>Release-Note:
>Audit-Trail:
>Unformatted: