array_key_exists
array_map
Array Functions
PHP Manual

# array_keys

(PHP 4, PHP 5)

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

### Description

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.

### Return Values

Returns an array of all the keys in `array`.

### Changelog

Version | Description
--- | ---
5.0.0 | Added the `strict` parameter.

### Examples

Example #1 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
    )

### See Also

- array_values() - Return all the values of an array
- array_key_exists() - Checks if the given key or index exists in the array
- array_search() - Searches the array for a given value and returns the corresponding key if successful

array_key_exists
array_map
Array Functions
PHP Manual