Php-PHPini_set ('include _ path') takes effect but include error

The code for the problem is as follows: ini_set (& #39; include_path & #39;, ini_get (& #39; include_path & #39 ;). PATH_SEPARATOR.dirname (_ FILE __). PATH_SEPARATOR. & #39; conf & #39;); echoini_get (& #39; include_path & #39;); if (! File_exists (& #39; confconf. php & #39;) die (& #39; configerror & #39;); php

White question
The code is as follows:

Ini_set ('include _ path', ini_get ('include _ path'). PATH_SEPARATOR. dirname (_ FILE _). PATH_SEPARATOR. '\ Conf ');
Echo ini_get ('include _ path ');
If (! File_exists ('conf/conf. php') die ('config error ');
Include_once ('conf. php ');

Error:
.; D: \ xampp \ php \ PEAR; D: \ web \ bottle; \ conf
Warning: include_once (conf. php) [function. include-once]: failed to open stream: No such file or directory in D: \ web \ bottle \ index. php on line 6

Warning: include_once () [function. include]: Failed opening 'conf. php 'for declaration (include_path = '.; d: \ xampp \ php \ PEAR; D: \ web \ bottle; \ conf ') in D: \ web \ bottle \ index. php on line 6

I don't understand why the environment variable settings have taken effect but cannot be automatically included yet? I don't know how to solve this problem. thank you for your advice.