PHP ini_set('include_path')生效但是include出错

Question

小白的问题
代码如下：

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') ;

报错：
.;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 inclusion (include_path='.;D:\xampp\php\PEAR;D:\web\bottle;\conf') in D:\web\bottle\index.php on line 6

不理解为什么环境变量设置都生效了但是还不能自动包含？不知道怎么去查这个问题了，谢谢指教