不要光看书，有时手册也比较重要。
https://www.php.net/manual/en/language.basic-syntax.phptags.php

If a file contains only PHP code, it is preferable to omit the PHP closing tag at the end of the file. This prevents accidental whitespace or new lines being added after the PHP closing tag, which may cause unwanted effects because PHP will start output buffering when there is no intention from the programmer to send any output at that point in the script.



https://www.php.net/basic-syntax.instruction-separation

The closing tag of a PHP block at the end of a file is optional, and in some cases omitting it is helpful when using include or require, so unwanted whitespace will not occur at the end of files, and you will still be able to add headers to the response later. It is also handy if you use output buffering, and would not like to see added unwanted whitespace at the end of the parts generated by the included files.

【 在 ludongxing (ludongxing) 的大作中提到: 】
: 在《零基础学PHP》的第214页有这么一段index.php程序，是这样写的：
: <?php
:     //连接MySQL服务器，选择数据库
: ...................
--
修改:world FROM 220.181.41.*
FROM 220.181.41.*