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# array_keys

(PHP 4 )

array_keys -- Return all the keys of an array

## Description

array array_keys ( array input [, mixed search_value])

array_keys() returns the keys, numeric and string, from the `input` array.

If the optional `search_value` is specified, then only the keys for that value are returned. Otherwise, all the keys from the `input` are returned.

Example 1. array_keys() example
    $array = array (0 => 100, "color" => "red");
    print_r(array_keys ($array));

    $array = array ("blue", "red", "green", "blue", "blue");
    print_r(array_keys ($array, "blue"));

    $array = array ("color" => array("blue", "red", "green"), "size" => array("small", "medium", "large"));
    print_r(array_keys ($array));
The printout of the program above will be:
    Array
    (
        [0] => 0
        [1] => color
    )
    Array
    (
        [0] => 0
        [1] => 3
        [2] => 4
    )
    Array
    (
        [0] => color
        [1] => size
    )

> Note: This function was added to PHP 4, below is an implementation for those still using PHP 3.

> Example 2. Implementation of array_keys() for PHP 3 users
>     function array_keys ($arr, $term="") {
>         $t = array();
>         while (list($k,$v) = each($arr)) {
>             if ($term && $v != $term) {
>                 continue;
>             }
>             $t[] = $k;
>         }
>         return $t;
>     }

See also array_values().

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