PHP: Manual: array

(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
$array = array (0 => 100, "color" => "red"); array_keys ($array); // returns array (0, "color") $array = array ("blue", "red", "green", "blue", "blue"); array_keys ($array, "blue"); // returns array (0, 3, 4)

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;
}
       