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# array_walk

(PHP 3>= 3.0.3, PHP 4 )

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

## Description

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

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
    <?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 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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