PHP Print keys from an object?
If the 'object' is actually an associative array rather than a true object then array_keys() will give you what you need without warnings or errors.
On the other hand, if your object is a true object, then you will get a warning if you try use array_keys() directly.
You can extract the key-value pairs from an object as an associative array with get_object_vars(), you can then get the keys from this with array_keys():
$keysFromObject = array_keys(get_object_vars($anObject));