1.2.323. Dangling Array References

Always unset a referenced-variable used in a loop.

It is highly recommended to unset blind variables when they are set up as references after a loop. When omitting this step, the next loop that will also require this variable will deal with garbage values, and produce unexpected results.

<?php

$array = array(1,2,3,4);

foreach($array as &$a) {
    $a += 1;
}
// This only unset the reference, not the value
unset($a);


// Dangling array problem
foreach($array as &$a) {
    $a += 1;
}
//$array === array(3,4,5,6);

// This does nothing (apparently)
// $a is already a reference, even if it doesn't show here.
foreach($array as $a) {}
//$array === array(3,4,5,5);

?>

See also No Dangling Reference, PHP foreach pass-by-reference: Do it right, or better not at all, How does PHP ‘foreach’ actually work? and References and foreach.

1.2.323.1. Suggestions

• Avoid using the reference altogether : sometimes, the reference is not needed.

• Add unset() right after the loop, to avoid reusing the reference.

1.2.323.2. Specs

Short name	Structures/DanglingArrayReferences
Rulesets	All, Analyze, CE, CI-checks, PHP recommendations, Top10
Exakat since	0.8.4
PHP Version	All
Severity	Major
Time To Fix	Instant (5 mins)
Precision	Very high
Features	loop
ClearPHP	no-dangling-reference
Examples	Typo3, SugarCrm
Related rule	Altering Foreach Without Reference
Available in	Entreprise Edition, Community Edition, Exakat Cloud