Strange behavior Of foreach

Question

<?php   $a = array('a', 'b', 'c', 'd');    foreach ($a as &$v) { }   foreach ($a as $v) { }    print_r($a); ?> 

I think it's a normal program but this is the output I am getting:

Array (     [0] => a     [1] => b     [2] => c     [3] => c ) 

Can someone please explain this to me?

Answer 1

This is well-documented PHP behaviour See the warning on the foreach page of php.net

Warning

Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset().

$a = array('a', 'b', 'c', 'd');  foreach ($a as &$v) { } unset($v); foreach ($a as $v) { }  print_r($a); 

EDIT

Attempt at a step-by-step guide to what is actually happening here

$a = array('a', 'b', 'c', 'd'); foreach ($a as &$v) { }   // 1st iteration $v is a reference to $a[0] ('a') foreach ($a as &$v) { }   // 2nd iteration $v is a reference to $a[1] ('b') foreach ($a as &$v) { }   // 3rd iteration $v is a reference to $a[2] ('c') foreach ($a as &$v) { }   // 4th iteration $v is a reference to $a[3] ('d')                            // At the end of the foreach loop,                           //    $v is still a reference to $a[3] ('d')  foreach ($a as $v) { }    // 1st iteration $v (still a reference to $a[3])                            //    is set to a value of $a[0] ('a').                           //    Because it is a reference to $a[3],                            //    it sets $a[3] to 'a'. foreach ($a as $v) { }    // 2nd iteration $v (still a reference to $a[3])                            //    is set to a value of $a[1] ('b').                           //    Because it is a reference to $a[3],                            //    it sets $a[3] to 'b'. foreach ($a as $v) { }    // 3rd iteration $v (still a reference to $a[3])                            //    is set to a value of $a[2] ('c').                           //    Because it is a reference to $a[3],                            //    it sets $a[3] to 'c'. foreach ($a as $v) { }    // 4th iteration $v (still a reference to $a[3])                            //    is set to a value of $a[3] ('c' since                            //       the last iteration).                           //    Because it is a reference to $a[3],                            //    it sets $a[3] to 'c'.