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<?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?
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Warning This function has been DEPRECATED as of PHP 7.2. 0. Relying on this function is highly discouraged.
There is no major "performance" difference, because the differences are located inside the logic. You use foreach for array iteration, without integers as keys. You use for for array iteration with integers as keys. etc.
Foreach is a loop statement in the Perl programming language that executes once for each value of a data object. It takes the general form: foreach thing (in object) { do something; do something else; }
The 'foreach' is slow in comparison to the 'for' loop. The foreach copies the array over which the iteration needs to be performed. For improved performance, the concept of references needs to be used.
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'. If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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