array_walk

    (PHP 4, PHP 5, PHP 7, PHP 8)

    array_walk — Apply a user supplied function to every member of an array

    Description

    array_walk(array|object&$array, callable$callback, mixed$arg = null): bool

    Applies the user-defined callback function to each element of the array array.

    array_walk() is not affected by the internal array pointer of array. array_walk() will walk through the entire array regardless of pointer position.

    Parameters

    array

    The input array.

    callback

    Typically, callback takes on two parameters. The array parameter's value being the first, and the key/index second.

    Note:

    If callback needs to be working with the actual values of the array, specify the first parameter of callback as a reference. Then, any changes made to those elements will be made in the original array itself.

    Note:

    Many internal functions (for example strtolower()) will throw a warning if more than the expected number of argument are passed in and are not usable directly as a callback.

    Only the values of the array may potentially be changed; its structure cannot be altered, i.e., the programmer cannot add, unset or reorder elements. If the callback does not respect this requirement, the behavior of this function is undefined, and unpredictable.

    arg

    If the optional arg parameter is supplied, it will be passed as the third parameter to the callback.

    Return Values

    Returns true.

    Errors/Exceptions

    As of PHP 7.1.0, an ArgumentCountError will be thrown if the callback function requires more than 2 parameters (the value and key of the array member), or more than 3 parameters if the arg is also passed. Previously, in this case an error of level E_WARNING would be generated each time array_walk() calls callback.

    Changelog

    VersionDescription
    8.0.0 If callback expects the second or third parameter to be passed by reference, this function will now emit an E_WARNING.

    Examples

    Example #1 array_walk() example

    <?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');
    ?>

    The above example will output:

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

    Example #2 array_walk() example using anonymous function

    <?php
    $elements     = ['a', 'b', 'c'];

    array_walk($elements, function ($value, $key) {
    echo     "{$key} => {$value}\n";
    });

    ?>

    The above example will output:

    0 => a 1 => b 2 => c

    See Also

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