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# array_keys

(PHP 4 >= 4.0.0)

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
    $array = array (0 => 100, "color" => "red");
    array_keys ($array);       // returns array (0, "color")

    $array = array ("blue", "red", "green", "blue", "blue");
    array_keys ($array, "blue");  //  returns array (0, 3, 4)

    $array = array ("color" => array("blue", "red", "green"), "size" => array("small", "medium", "large"));
    array_keys ($array);  //  returns array ("color", "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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