PHP array_keys function

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array_keys

(PHP 4, PHP 5)

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.
As of PHP 5, you can use strict parameter for
comparison including type (===).

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 above example will output:

See also array_values() and
array_key_exists().