From: keithm at aoeex dot com
Operating system: Linux
PHP version: 5CVS-2004-02-26 (dev)
PHP Bug Type: Scripting Engine problem
Bug description: Comparison order of operations incorrect
Description:
------------
The order of operation for comparisons seems to be incorrect. The
following example script will demonstrate the problem:
Reproduce code:
---------------
<?php
$x=0;
while ($x != ($x=5)){
echo "x is not equal to x";
}
?>
Expected result:
----------------
The screen should display nothing.
I would expect that the $x=5 would execute, and then php would compare $x
!= $x, which of course would be false, and the loop would run.
Actual result:
--------------
x is not equal to x
the loop is executed and that echo statement is displayed.
It seems that php pulls the value of $x, execute the $x=5 statement, and
runs the comparison. So for a split second, you in essence have two $x
variables. One which has the value of 0, and the other with the value of
5.
If you reverse the order of the operands in the condition, then it works
as expected:
<?php
$x=0;
//This works fine, nothing is displayed
while (($x=5) != $x){
echo "x is not equal to x";
}
?>
--
Edit bug report at http://bugs.php.net/?id=27409&edit=1
--
Try a CVS snapshot (php4): http://bugs.php.net/fix.php?id=27409&r=trysnapshot4
Try a CVS snapshot (php5): http://bugs.php.net/fix.php?id=27409&r=trysnapshot5
Fixed in CVS: http://bugs.php.net/fix.php?id=27409&r=fixedcvs
Fixed in release: http://bugs.php.net/fix.php?id=27409&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=27409&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=27409&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=27409&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=27409&r=support
Expected behavior: http://bugs.php.net/fix.php?id=27409&r=notwrong
Not enough info: http://bugs.php.net/fix.php?id=27409&r=notenoughinfo
Submitted twice: http://bugs.php.net/fix.php?id=27409&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=27409&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=27409&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=27409&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=27409&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=27409&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=27409&r=float
