<?php
error_reporting(E_ALL|E_STRICT);
$a = new stdClass();
$a->str = '';
var_dump((int)'a');
var_dump($a->str['a']);
var_dump($a->str[0]);

int(0)

Notice: Uninitialized string offset:  0 in /t.php on line 6
string(0) ""

Notice: Uninitialized string offset:  0 in /t.php on line 7
string(0) ""