PHP include檔案包含路徑搜尋問題的總結

首先我們來看php官方手冊中對include的檔案搜尋原則的描述：

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.

尋找包含檔案的順序先是在目前工作目錄的相對的include_path 下尋找，然後是目前執行腳本所在目錄相對的include_path 下尋找。例如 include_path 是 . ，目前工作目錄是  ，腳本中要 include 一個   且在該文件中有一句 include "b.php" ，則尋找   的順序先是  ，然後是  ，然後是  ，然後是  ，然後是  。如果檔案名稱以 ./  或 ../  開始，則只在目前工作目錄相對的 include_path 下尋找。

所以如下圖所示的檔案結構

----a.php

#----include/b.php

----include/c.php

 其中a.php

<?php
include &#39;include/b.php&#39;;
?>
-----------------------
b.php
<?php
include &#39;c.php&#39;;
include &#39;include/c.php&#39;;
?>

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

c.php

<?php
echo &#39;c.php&#39;;
?>

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

都能正確運行，說明b.php中兩種不同包含路徑都是可行的，根據include尋找包含檔案的方式都能找到c.php。

但是最好的方式還是使用絕對路徑，如果使用了絕對路徑，php核心就直接通過路徑去載入文件而不用去include path逐個搜尋文件，增加了程式碼執行效率

<?php
define(&#39;ROOT_PATH&#39;,dirname(FILE));
include ROOT_PATH.&#39;/c.php&#39;;
?>

不同的檔案包含方式，程式的執行效能比較具體可以參考此文

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