Description:
------------
If an object is supplied instead of an array, v(s)printf takes the internal object elements as elements despite of its visibility.
This is not only quite annoying but could be a security issue as well.

Reproduce code:
---------------
class foo
{
    private $x = 1;
    private $y = 2;
    
}

$array = new foo;
vprintf('%s < %s',$array);

Expected result:
----------------
An E_WARNING should be triggered.
Alternatively, vprintf could take an object instantiating or extending ArrayObject and behave according to the objects functions.

Actual result:
--------------
vprintf prints:

1 < 2