Home Backend Development PHP Tutorial PHP 的 _FILE_ 恒量

PHP 的 _FILE_ 恒量

Jun 13, 2016 pm 12:25 PM
dirname file nbsp php root

PHP 的 __FILE__ 常量

今天碰到了PHP的常量__FILE__的问题了。

在网上查了一下。总结了以下规律。

dirname(__FILE___) 函数返回的是脚本所在在的路径。

比如文件 b.php 包含如下内容: 

<span style="color: #008080;">1</span> <span style="color: #000000;">php </span><span style="color: #008080;">2</span> <span style="color: #800080;">$basedir</span> = <span style="color: #008080;">dirname</span>(<span style="color: #ff00ff;">__FILE__</span><span style="color: #000000;">); </span><span style="color: #008080;">3</span> ?> 
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如果b.php被其他目录里的a.php文件require 或者 include 去引用的话。

变量$basedir 的内容还是b.php所在的那个文件夹的路径。

而不是变成a.php文件所在的目录。

dirname(__FILE__) 一般会返回文件所的当前目录到系统根目录的一个目录结构。

不会返回当前的文件名称。

dirname(__FILE__) 也可能返回一个 . (当前目录)

[原因是 b.php 文件在 http.conf 或者 PHP 配置开发环境的默认WEB目录下.

比如 WEB_ROOT 为: "C:/root/www/".]

b.php文件路径为: "C:/root/www/b.php".

使用方法提示, 

如果重复一次可以把目录往上提升一个层次:

比如:$d = dirname(dirname(__FILE__));

其实就是把一个目录给dirname()做参数了.因为dirname()返回最后的目录不带\\或者是/

所以重复使用的时候可以认为 dirname() 把最下层的目录当成文件名来处理了.照常返回当前目录的上级目录.

这样重复就得到了它的上一级的目录. 

包含得到上一级目录的文件
include(dirname(__FILE__).'/../filename.php'); 

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