php中引用变量2

一、unset只会取消引用，不会销毁内存空间

<?php$a = 1;$b = &$a;unset($b);echo $a; // 1

二、对象本身就是引用传递

三、

<?php/** * 写出如下程序的输出结果 * <?php * * $data = ['a', 'b', 'c']; * * foreach($data as $key => $val) * { *      $val = &$data[$key]; * } * 程序运行时，每一次循环结束后变量$data的值是什么？请解释 * 程序执行完成后，变量$data的值是什么？请解释 */$data = ['a', 'b', 'c'];foreach ($data as $key=>$val){    $val = &$data[$key];    var_dump($data);}var_dump($data);
array (size=3)  0 => &string 'a' (length=1)  1 => string 'b' (length=1)  2 => string 'c' (length=1)
array (size=3)  0 => string 'b' (length=1)  1 => &string 'b' (length=1)  2 => string 'c' (length=1)
array (size=3)  0 => string 'b' (length=1)  1 => string 'c' (length=1)  2 => &string 'c' (length=1)
array (size=3)  0 => string 'b' (length=1)  1 => string 'c' (length=1)  2 => &string 'c' (length=1)