It's very odd,has anyone ever sum up with a conclusion yet?

Sometimes it checks the directory of the included file,too.

But sometimes not.

D:\test\1.php

<?php

include('sub\2.php');

D:\test\2.php

<?php

include('3.php');

Where 3.php is in the same dir as 2.php.

The above works,but why?The current directory should be D:\test,but it can still find 3.php,which is in D:\test\sub

More story(final)

About a year ago I met this problem,and then I ended up fixed it with the hardcoding like below:

Common.php:

if (file_exists("../../../Common/PHP/Config.inc"))
    include('../../../Common/PHP/Config.inc');

if (file_exists("../../Common/PHP/Config.inc"))
    include('../../Common/PHP/Config.inc');

if (file_exists("../Common/PHP/Config.inc"))
    include('../Common/PHP/Config.inc');

if (file_exists("Common/PHP/Config.inc"))
    include('Common/PHP/Config.inc');

Where Config.inc is in the same directory as Common.php

php include relative-path
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