在看php-openid的源码的时候，发现它实现的创建多级目录的方法的思想很巧妙，特将起代码记录下来：
/** * Create dir_name as a directory if it does not exist. If it
* exists, make sure that it is, in fact, a directory. Returns
* true if the operation succeeded; false if not.
*
* @access private
*/
static function ensureDir($dir_name)
{
if (is_dir($dir_name) || @mkdir($dir_name)) {
return true;
} else {
$parent_dir = dirname($dir_name);
// Terminal case; there is no parent directory to create.
if ($parent_dir == $dir_name) {
return true;
}
return (Auth_OpenID::ensureDir($parent_dir) && @mkdir($dir_name));
}
}