php5中domxml的中文问题

[mysqlmysql]

如以下字符串:

$str = "<a><b>你好</b></a>";

$doc = new DOMDocument();
$doc->loadXML($str);
echo $doc->saveXML();


用php5中的dom中的load_xml($str)报错:Warning: DOMDocument::loadXML() [function.loadXML]: Input is not proper UTF-8, indicate encoding ! in Entity, line: 1 in E:\web\test\xml.php on line 5

应该如何转换编码呢？

[chengsion]

$str = utf8_encode("<a><b>你好</b></a>");

[chengsion]

$str = utf8_encode("<a><b>你好</b></a>");

[chengsion]

$str = utf8_encode("<a><b>你好</b></a>");

[pmaster]

<?
/**
*notes:xml
*/
$str = utf8_decode("<a><b>你好</b></a>");

$doc = new DOMDocument();
$doc->loadXML($str);
echo $doc->saveXML();
?>

这样也不行！！