c/2904: printf changes order

c/2904: printf changes order

[guedem]

>Number:         2904
>Category:       c
>Synopsis:       printf changes order
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 22 13:56:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     guedem@uni-freiburg.de
>Release:        unknown-1.0
>Organization:
>Environment:
gcc version 2.95.2 19991024 (release)
i486-suse-linux
>Description:
don't know whether this is realy a bug, but printf (and fprint and fvprintf)
seems to change the order of the ouput. The following little 
programm produces the out put "3, 2, 1". But I've expected to 
receive "1, 2, 3".
>How-To-Repeat:
#include <stdio.h>

int main()
{
	int a[] = {1, 2, 3};
	int* iPtr = a; 

	printf("%d, %d, %d\n", *iPtr++, *iPtr++, *iPtr++);
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: c/2904: printf changes order

[Andreas Jaeger]

The following reply was made to PR c/2904; it has been noted by GNATS.

From: Andreas Jaeger <aj@suse.de>
To: guedem@uni-freiburg.de
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c/2904: printf changes order
Date: 23 May 2001 07:34:51 +0200

 guedem@uni-freiburg.de writes:
 
 > don't know whether this is realy a bug, but printf (and fprint and fvprintf)
 > seems to change the order of the ouput. The following little 
 > programm produces the out put "3, 2, 1". But I've expected to 
 > receive "1, 2, 3".
 > >How-To-Repeat:
 > #include <stdio.h>
 > 
 > int main()
 > {
 > 	int a[] = {1, 2, 3};
 > 	int* iPtr = a; 
 > 
 > 	printf("%d, %d, %d\n", *iPtr++, *iPtr++, *iPtr++);
 > }
 
 The printf output is undefined by ISO C, there's no sequence point
 between the arguments.  It could even be 2,3,1 or something totally
 different.
 
 Andreas
 -- 
  Andreas Jaeger
   SuSE Labs aj@suse.de
    private aj@arthur.inka.de
     http://www.suse.de/~aj

Re: c/2904: printf changes order

[Phil Edwards]

The following reply was made to PR c/2904; it has been noted by GNATS.

From: Phil Edwards <pedwards@disaster.jaj.com>
To: guedem@uni-freiburg.de
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c/2904: printf changes order
Date: Tue, 22 May 2001 17:56:43 -0400

 On Tue, May 22, 2001 at 08:51:36PM -0000, guedem@uni-freiburg.de wrote:
 > 	printf("%d, %d, %d\n", *iPtr++, *iPtr++, *iPtr++);
 
 You are changing a variable more than once within the same statement.  The
 result is undefined behavior.  Not a compiler bug.
 
 -- 
 pedwards at disaster dot jaj dot com  |  pme at sources dot redhat dot com
 devphil at several other less interesting addresses in various dot domains
 The gods do not protect fools.  Fools are protected by more capable fools.