PHP `array_keys()` function returns an array containing all the keys inside the array. array_keys() returns the keys, numerics, and strings from the array.


# Syntax
```
array_keys(array, value, strict)
```
Parameters:

* **`array`**: an array containing keys to return.

* **`search_value`**: if specified, then only keys containing the specified values are returned.

* **`strict`**: determines if strict comparison (===) should be used during the search.




<?php
$a=array("Ahmedabad"=>"AMD","London"=>"LHE","New york"=>"JFK");
print_r(array_keys($a));
?>

What is the array_keys() function?

PHP array_keys() function returns an array of keys from the input array, using optional value and strict parameters.