array_walk in PHP

Syntax of array_walk

bool array_walk(array input, string callback[, mixed user_data])

Calls the named function for each element in the array. The function is called with the element’s value, key, and optional user data as arguments. To ensure that the function works directly on the values of the array, define the first parameter of the function by reference. Returns true on success, false on failure

Example of array_walk

<?php
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");

function test_alter(&$item1, $key, $prefix)
{
    $item1 = "$prefix: $item1";
}

function test_print($item2, $key)
{
    echo "$key. $item2\n";
}

echo "Before ...:\n";
array_walk($fruits, 'test_print');

array_walk($fruits, 'test_alter', 'fruit');
echo "... and after:\n";

array_walk($fruits, 'test_print');
?>

Before ...:
d. lemon
a. orange
b. banana
c. apple
... and after:
d. fruit: lemon
a. fruit: orange
b. fruit: banana
c. fruit: apple