require_once pit encounter when using ../ and ./

Three documents

r.php   c.php  和 r/d.php

r.php

<?php
require_once 'r/d.php';

echo 'sssss';

?>

d.php

<?php
require_once '../c.php';
echo 'dddddd';
echo '<br />'

?>

c.php

<?php

echo 'cccccc';
echo '<br />'

?>

When performing r.php will error:

Warning: require_once(../c.php): failed to open stream: No such file or directory in D:\phpStudy\PHPTutorial\WWW\php\r\d.php on line 2

Fatal error: require_once(): Failed opening required '../c.php' (include_path='.;C:\php\pear') in D:\phpStudy\PHPTutorial\WWW\php\r\d.php on line 2

But when we direct execution is not being given d.php

Similar r.php here on the practical implementation of this:

? < PHP
 // require_once 'r / d.php'; // here is equivalent to the introduction of such 


require_once '../c.php';     // this is the case is the equivalent of r.php superiors find c.php 
echo 'DDDDDD' ;
 echo '<br />' echo 'sssss' ;
 ?>

You can combine dirname (dirname (__ FILE__)) using an absolute path