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Last updated: Tue, 19 Sep 2006


(PHP 3 >= 3.0.3, PHP 4, PHP 5)

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


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

$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.

Last updated: Tue, 19 Sep 2006