由于我的问题被标记为这个问题的重复，我认为可以发布为什么不省略结束标签?>可能是出于某些原因。

具有完整的处理指令语法(<?php……?>) PHP源代码是有效的SGML文档，可以用SGML解析器毫无问题地解析和处理。在附加的限制下，它也可以是有效的XML/XHTML。

没有什么可以阻止您编写有效的XML/HTML/SGML代码。PHP文档意识到了这一点。摘录:

注意:还要注意，如果要在XML或XHTML中嵌入PHP，则需要使用< ? PHP ?>标记以保持与标准兼容。

当然，PHP语法不是严格的SGML/XML/HTML，您创建的文档不是SGML/XML/HTML，就像您可以将HTML转换为XHTML以符合XML或不符合XML一样。

At some point you may want to concatenate sources. This will be not as easy as simply doing cat source1.php source2.php if you have inconsistency introduced by omitting closing ?> tags. Without ?> it's harder to tell if document was left in PHP escape mode or PHP ignore mode (PI tag <?php may have been opened or not). Life is easier if you consistently leave your documents in PHP ignore mode. It's just like work with well formatted HTML documents compared to documents with unclosed, badly nested tags etc. It seems that some editors like Dreamweaver may have problems with PI left open [1].

这不是标签……

但如果你有了它，你就有可能在它后面留下空白。

如果你把它作为一个包含在文档的顶部，你可能会在你试图发送HTTP头之前插入空白(即内容)，这是不允许的。

如果我正确理解这个问题，它与输出缓冲以及这可能对结束/结束标记的影响有关。我不确定这是一个完全合理的问题。问题是输出缓冲区并不意味着所有内容在发送到客户机之前都保存在内存中。意思是有些内容是。

程序员可以故意刷新缓冲区或输出缓冲区那么PHP中的输出缓冲区选项真的会改变结束标记对编码的影响吗?我认为不是这样的。

也许这就是为什么大多数答案都回到了个人风格和语法。

比正常进程更早地发送头文件可能会产生深远的后果。下面是我当时碰巧想到的其中一些:

While current PHP releases may have output buffering on, the actual production servers you will be deploying your code on are far more important than any development or testing machines. And they do not always tend to follow latest PHP trends immediately. You may have headaches over inexplicable functionality loss. Say, you are implementing some kind payment gateway, and redirect user to a specific URL after successful confirmation by the payment processor. If some kind of PHP error, even a warning, or an excess line ending happens, the payment may remain unprocessed and the user may still seem unbilled. This is also one of the reasons why needless redirection is evil and if redirection is to be used, it must be used with caution. You may get "Page loading canceled" type of errors in Internet Explorer, even in the most recent versions. This is because an AJAX response/json include contains something that it shouldn't contain, because of the excess line endings in some PHP files, just as I've encountered a few days ago. If you have some file downloads in your app, they can break too, because of this. And you may not notice it, even after years, since the specific breaking habit of a download depends on the server, the browser, the type and content of the file (and possibly some other factors I don't want to bore you with). Finally, many PHP frameworks including Symfony, Zend and Laravel (there is no mention of this in the coding guidelines but it follows the suit) and the PSR-2 standard (item 2.2) require omission of the closing tag. PHP manual itself (1,2), Wordpress, Drupal and many other PHP software I guess, advise to do so. If you simply make a habit of following the standard (and setup PHP-CS-Fixer for your code) you can forget the issue. Otherwise you will always need to keep the issue in your mind.

额外的:一些与这两个角色有关的陷阱(实际上目前只有一个):

甚至一些知名的库可能在?>之后包含多余的行尾。一个例子是Smarty，甚至是这两个版本的最新版本。*和3。*分支有这个。因此，与往常一样，要注意第三方代码。额外的奖励:一个用于删除不必要的PHP结尾的正则表达式:在所有包含PHP代码的文件中将(\s*\?>\s*)$替换为空文本。

Pros

像其他语言一样，关闭任何打开的标记是合乎逻辑的。不仅是X(HT)ML标签，还有花括号，括号… 对初学者来说更容易理解。

Cons

避免在结束标记后无意中添加空白，因为它破坏了header()函数的行为…一些编辑器或FTP客户端/服务器也会自动更改文件的结尾(至少，这是它们的默认配置) PHP手册说关闭标记是可选的，Zend甚至禁止它。

结论

我想说，支持省略标记的论点看起来更强(有助于避免header() +它是PHP/Zend的“推荐”)。我承认，就语法一致性而言，这不是我见过的最“漂亮”的解决方案，但还有什么更好的呢?

嗯，我知道原因，但我不能说出来:

对于只包含PHP代码的文件，永远不会出现结束标记(?>) 允许的。PHP并不要求它， 省略它可以防止 意外注入尾白 空格变成响应。

来源:http://framework.zend.com/manual/en/coding-standard.php-file-formatting.html