Using array_walk() with a User-Defined Callback Function to Process Each Array Element

Function Overview

The array_walk() function applies a user‑defined callback to each element of an array. It does not depend on the array's internal pointer and traverses the entire array regardless of pointer position.

Parameters

array – the input array.

funcname – a callable that typically receives the element value as the first argument and the key as the second. The callback may also accept an optional third argument userdata .

userdata – optional data passed to the callback as the third parameter.

Return Value

Returns TRUE on success, or FALSE on failure.

Example

"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');
?>

Output

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