Reference to array not working as expected in PHP

Question

I am confused from the result of the following code: I can't get my expected result:

$arrX = array('a'=>array('val'=>10),'b'=>array('val'=>20), 'c'=>array('val'=>30));
foreach( $arrX as &$DataRow )
{
    $DataRow['val'] = $DataRow['val'] + 20;
}
foreach( $arrX as $DataRow )
{
    echo '<br />val: '.$DataRow['val'].'<br/>';
}

Output: 30, 40, 40

Expected: 30, 40, 50

But again if i make small chage it works fine,

$arrX = array('a'=>array('val'=>10),'b'=>array('val'=>20), 'c'=>array('val'=>30));
foreach( $arrX as &$DataRow )
{
    $DataRow['val'] = $DataRow['val'] + 20;
}
foreach( $arrX as &$DataRow )
{
    echo '<br />val: '.$DataRow['val'].'<br/>';
}

possible duplicate of Strange behaviour after loop by reference - Is this a PHP bug? — John Carter
– John Carter, Commented Nov 22, 2011 at 7:20

codaddict · Accepted Answer · 2010-05-11 11:14:42Z

You need to unset the $DataRow after the loop in which you are making use of it as a reference:

$arrX=array('a'=>array('val'=>10),'b'=>array('val'=>20), 'c'=>array('val'=>30));
foreach( $arrX as &$DataRow ) {
    $DataRow['val'] = $DataRow['val'] + 20;
}

// at this point $DataRow is the reference to the last element of the array.
// ensure that following writes to $DataRow will not modify the last array ele.
unset($DataRow);

foreach( $arrX as $DataRow ) {
    echo '<br />val: '.$DataRow['val'].'<br/>';
}

You can make use of a different variable and avoid the unsetting..although I would not recommend it as $DataRow is still a reference to the last array element and any overwrite of it later on will cause problems.

$arrX=array('a'=>array('val'=>10),'b'=>array('val'=>20), 'c'=>array('val'=>30));
foreach( $arrX as &$DataRow ) {
    $DataRow['val'] = $DataRow['val'] + 20;
}

foreach( $arrX as $foo) { // using a different variable.
    echo '<br />val: '.$foo['val'].'<br/>';
}

ramblex · Accepted Answer · 2010-05-11 11:09:11Z

1

Your question (almost exactly) is addressed on the php foreach manual page :)

http://www.php.net/manual/en/control-structures.foreach.php

http://www.php.net/manual/en/control-structures.foreach.php#92116

answered May 11, 2010 at 11:09

ramblex

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Dan Rosenstark Over a year ago

for the casual/curious reader (and because links do break over time), what's the solution say, basically?

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