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(PHP 3>= 3.0.3, PHP 4 )

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


bool array_walk ( array array, callback function [, mixed userdata])

Returns TRUE on success or FALSE on failure.

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

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

Note: If function needs to be working with the actual values of the array, specify the first parameter of function 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 function 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. To reset the pointer, use reset(). In PHP 3, array_walk() resets the pointer.

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

$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 printout of the program above will be:

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 list(), foreach, each(), and call_user_func_array().

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