请教在读childNode时返回失败(指针总返回0)的错误原因? 代码及XML格式如下:代码:------------------------
MSXML2::IXMLDOMDocumentPtr pDoc;          HRESULT hr = pDoc.CreateInstance(__uuidof(MSXML2::DOMDocument30));         if(!SUCCEEDED(hr))          {       
            return ;
         }                hr = pDoc->load("f:\\o0913.xml");         if(FAILED(hr))
 {
 AfxMessageBox("failed to load xml file") ;
 return ;
 }         // 
         MSXML2::IXMLDOMElementPtr  childNode ;         childNode = (MSXML2::IXMLDOMElementPtr)(pDoc->selectSingleNode("//order"));
         childNode = (MSXML2::IXMLDOMElementPtr)pDoc->selectNodes("//orders") ;代码结束-------------------------XML 格式--------------
-<orders>
-<order>
  <name>zhangsan</name>
  <age>26</age>
 </order>
-<order>
  <name>zhangsan222</name>
  <age>2622222</age>
 </order>
</orders>