相对路径

写一个函数，算出两个文件的相对路径

    <?php
        /** by www.phpddt.com */
        $a = '/a/b/c/d/e.php';
        $b = '/a/b/13/34/c.php';
        echo getRelativePath($a, $b); //"../../12/34/"
        function getRelativePath($a,$b){
            $a2array = explode('/', $a);
            $b2array = explode('/', $b);
            $relativePath   = '';
            for( $i = 1; $i <= count($b2array)-2; $i++ ) {
                $relativePath .= $a2array[$i] == $b2array[$i] ? '../' : $b2array[$i].'/';
            }
            return $relativePath;
        }
    ?>