php simplexml_load_string 返回的对象print_r后，丢失信息？

浏览数：21 / 时间：2015年06月09日

<?php
$content 
= ‘<dblp>
<inproceedings key="conf/aaim/He07" 
mdate="2007-06-28">
<author>Dan He</author>
<title>
<i>BMA</i>
<sup>*</sup>
: An Efficient Algorithm for 
the One-to-Some Shortest Path Problem on Road Maps.
</title>
<pages>346-357</pages>
<year>2007</year>
<crossref>conf/aaim/2007</crossref>
<booktitle>AAIM</booktitle>
<ee>http://dx.doi.org/10.1007/978-3-540-72870-2_33</ee>
<url>db/conf/aaim/aaim2007.html#He07</url>
</inproceedings>
</dblp>‘;
$xml = simplexml_load_string($content);
print_r($xml);

　结果:

SimpleXMLElement Object
(
    [inproceedings] => SimpleXMLElement Object
        (
            [@attributes] => Array
                (
                    [key] => conf/aaim/He07
                    [mdate] => 2007-06-28
                )
 
            [author] => Dan He
            [title] => SimpleXMLElement Object
                (
                    [i] => BMA
                    [sup] => *
                )
 
            [pages] => 346-357
            [year] => 2007
            [crossref] => conf/aaim/2007
            [booktitle] => AAIM
            [ee] => http://dx.doi.org/10.1007/978-3-540-72870-2_33
            [url] => db/conf/aaim/aaim2007.html#He07
        )
 
)