# array_walk

(PHP 4, PHP 5)

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

### Description

bool array_walk ( array `&$array` , callback `$funcname` [, mixed `$userdata` ] )

Returns `TRUE` on success or `FALSE` on failure.

Applies the user-defined function `funcname` to each element of the `array` array. Typically, `funcname` takes on two parameters. The `array` parameter's value being the first, and the key/index second. If the optional `userdata` parameter is supplied, it will be passed as the third parameter to the callback `funcname` .

If function `funcname` requires more parameters than given to it, an error of level E_WARNING will be generated each time array_walk() calls `funcname` . These warnings may be suppressed by prepending the PHP error operator @ to the array_walk() call, or by using error_reporting().

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

> Note: Passing the key and userdata to `funcname` was added in 4.0.0

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

Users may not change the array itself from the callback function. e.g. Add/delete elements, unset elements, etc. If the array that array_walk() is applied to is changed, the behavior of this function is undefined, and unpredictable.

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. $item2<br />\n";
}
echo "Before ...:\n";
array_walk($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

See also array_walk_recursive(), create_function(), list(), foreach, each(), call_user_func_array(), and array_map(), and information about the callback type.