我个人理解：getcwd()会随着包含文件的改变而改变，而dirname(__FILE__)不会。即 getcwd() 表示获取当前执行文件的物理路径。

如 getcwd()显示:

/www/project/test/a.php

echo getcwd();

//echo /www/project/test

 

/www/project/b.php

include_once(test/a.php);

//echo /www/project

而dirname(__FILE__):

/www/project/test/a.php

echo dirname(__FILE__);

//echo /www/project/test

/www/project/b.php

include_once(test/a.php);

//echo /www/project/test

 

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a.php include b.php

b.php getcwd -> a所在目录

b.php dirname(__FILE__) -> b所在目录