PHP 标记浅谈

超、凢脫俗 2024-03-26 20:15 68阅读 0赞

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当解析一个文件时，PHP 会寻找起始和结束标记，也就是 <?php 和 ?>，这告诉 PHP 开始和停止解析二者之间的代码。此种解析方式使得 PHP 可以被嵌入到各种不同的文档中去，而任何起始和结束标记之外的部分都会被 PHP 解析器忽略。

PHP 也允许使用短标记 <? 和 ?>，但不鼓励使用。只有通过激活 php.ini 中的 short\_open\_tag 配置指令或者在编译 PHP 时使用了配置选项 --enable-short-tags 时才能使用短标记。

如果文件内容是纯 PHP 代码，最好在文件末尾删除 PHP 结束标记。这可以避免在 PHP 结束标记之后万一意外加入了空格或者换行符，会导致 PHP 开始输出这些空白，而脚本中此时并无输出的意图。

<?php

echo "Hello world";

// ... more code

echo "Last statement";

// 脚本至此结束，并无 PHP 结束标记

<?php\[whitespace\]", not just "<?php"

This is absolutely correct, but the wording may confuse some developers less familiar with the extent of the term "\[whitespace\]".

Whitespace, in this context, would be any character that generated vertical or horizontal space, including [tabs][] ( \\t ), newlines ( \\n ), and carriage returns ( \\r ), as well as a space character ( \\s ). So reusing purkrt's example:

<?php/\*blah\*/ echo "a"?>

would not work, as mentioned, but :

<?php /\*php followed by space\*/ echo "a"?>

will work, as well as :

<?php

/\*php followed by end-of-line\*/ echo "a"?>

and :

<?php

/\*php followed by tab\*/ echo "a"

I just wanted to clarify this to prevent anyone from misreading purkrt's note to mean that a the opening tag --even when being on its own line--required a space ( \\s ) character. The following would work but is not at all necessary or how the earlier comment should be interpreted :

<?php

/\*php followed by a space and end-of-line\*/ echo "a"

<?php

// Code will end here ?> This is output as literal text.

<?php

\# Same with this method of commenting ?> This is output as literal text.

However they do not have an effect in C-style comments:

<?php

/\* Code will not end here ?> as closing tags are ignored inside C-style comments. \*/

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