<?php

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();

echo "<pre>";

var_dump($s->a);  //output: 123

var_dump($s->b);  //output: 123

var_dump($s->c);  //output: null

var_dump($s->d);  //output: 0

var_dump($s->e);  //output: 123

$s->a = 3;   //output: This is set function

echo "<br>";

$s->c = 3;  //no output

echo "<br>";

$s->f = 3;  //output: This is set function