array_keys

(PHP 4, PHP 5, PHP 7)

Return all the keys or a subset of the keys of an array

array array_keys ( array $array [, mixed $search_value = null [, bool $strict = false ]] )

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

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

Parameters:

array

An array containing keys to return.

search_value

If specified, then only keys containing these values are returned.

strict

Determines if strict comparison (===) should be used during the search.

Returns:

Returns an array of all the keys in array.

Examples:

array_keys() example

<?php
$array = array(0 => 100, "color" => "red");
print_r(array_keys($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:

Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)