PHP include文件包含路径搜索问题的总结

首先我们来看php官方手册中对的文件搜索原则的描述：

Files for including are first looked for in each include_path entry relative to the current working directory, 
and then in the directory of current script. E.g. if your include_path is libraries , current working directory is  , 
you included  and there is include "b.php"  in that file,   is first looked in   
and then in  . If filename begins with ./  or ../ , it is looked only in the current working directory.

寻找的顺序先是在当前工作目录的相对的 include_path 下寻找，然后是当前运行脚本所在目录相对的 include_path 下寻找。例如 include_path 是 . ，当前工作目录是 ，脚本中要 include 一个 并且在该文件中有一句 include "b.php" ，则寻找 的顺序先是 ，然后是 。如果文件名以 ./ 或者 ../ 开始，则只在当前工作目录相对的 include_path 下寻找。

所以如下所示的文件结构

----a.php

----include/b.php

----include/c.php

其中a.php

<?php
include 'include/b.php';
?>
-----------------------
b.php
<?php
include 'c.php';
include 'include/c.php';
?>

--------------------------

c.php

<?php
echo 'c.php';
?>

--------------------------

都能正确运行，说明b.php中两种不同包含路径都是可行的，根据include寻找包含文件的方式都能找到c.php。

但是最好的方式还是使用绝对路径，如果使用了绝对路径，php内核就直接通过路径去载入文件而不用去include path逐个搜索文件，增加了代码执行效率

<?php
define('ROOT_PATH',dirname(FILE));
include ROOT_PATH.'/c.php';
?>

不同的文件包含方式，程序的执行性能比较具体可以参照此文

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