array_keys -- Return all the keys of an array


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")

$array = array(1, 100, 2, 100);
array_keys($array, 100); //  returns array(0, 2) 

See also array_values().

Note: This function was added in PHP 4.0.