(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: