<?php
header('Content-Type:text/html;charset=utf-8');					//设置编码
/*  创建XML格式的字符串  */
$str = <<<XML
<?xml version='1.0' encoding='gb2312'?>
<object>
  <book>
    <computerbook>PHP从入门到精通</computerbook>
  </book>
  <book>
    <computerbook>PHP项目开发全程实录</computerbook>
  </book>
</object>
XML;
/*  **************************  */
$xml = simplexml_load_string($str);							//创建一个simplexml对象
foreach($xml->children() as $layer_one){							//循环输出根节点
  print_r($layer_one);										//查看节点结构
  echo '<br>';
  foreach($layer_one->children() as $layer_two){					//循环输出第二层根节点
    print_r($layer_two);									//查看节点结构
    echo '<br>';
  }
}
?>

运行结果
SimpleXMLElement Object ( [computerbook] => PHP从入门到精通 )
SimpleXMLElement Object ( [0] => PHP从入门到精通 )
SimpleXMLElement Object ( [computerbook] => PHP项目开发全程实录 )
SimpleXMLElement Object ( [0] => PHP项目开发全程实录 )
---------------------

<?php
header('Content-Type:text/html;charset=utf-8');					//设置编码
/*  创建XML格式的字符串  */
$str = <<<XML
<?xml version='1.0' encoding='gb2312'?>
<object name='商品'>
  <book>
    <computerbook>PHP从入门到精通</computerbook>
  </book>
  <book>
    <computerbook name='PHP项目开发全程实录'/>
  </book>
</object>
XML;
/*  **************************  */
$xml = simplexml_load_string($str);								//创建simpleXML对象
echo $xml[name].'<br>';										//输出根元素的属性name
echo $xml->book[0]->computerbook.'<br>';						//输出子元素中computerbook的值
echo $xml->book[1]->computerbook['name'].'<br>';					//输出computerbook的属性值
?>