The array_keys() function returns all the keys of an array. It returns an array of all the keys in array.
Syntax
array_keys(arr, value, strict)
Parameters
arr − The array from which the keys will be returned
value − If the values are specified, then only the keys containing these values will be returned.
strict − Determines if strict comparison (===) should be used during the search.
Return
The array_keys() function returns an array of all the keys in array.
Example
<?php
$arr = array("one" => "Pen", "two" => "Pencil", "three" => "Paper", "four" => "Notepad");
print_r(array_keys($arr));
?>Output
Array ( [0] => one [1] => two [2] => three [3] => four )
Example
Let us see another example wherein we will find the key for a specific value “Notepad”.
<?php
$arr = array("one" => "Pen", "two" => "Notepad", "three" => "Paper", "four" => "Notepad");
print_r(array_keys($arr, "Notepad"));
?>Output
Array ( [0] => two [1] => four )