<?phperror_reporting(E_ALL);class stu{    private $a;    private $b = 0;    public $c;    public $d = 0;        //这里的 private 可以用 protected public 替代    private function __get($name) {        return 123;    }        //这里的 private 也可以用 protected public 替代    private function __set($name, $value) {        echo "This is set function";    }} $s = new stu(); var_dump($s->a);  //output: 123var_dump($s->b);  //output: 123var_dump($s->c);  //output: nullvar_dump($s->d);  //output: 0var_dump($s->e);  //output: 123 $s->a = 3;   //output: This is set function$s->c = 3;  //no output$s->f = 3;  //output: This is set function?>