COM error problems: _com_error and _b_str_t

Christopher <>
Mon, 3 Nov 2008 11:51:16 -0800 (PST)
I am having one hell of a time trying to implement XML parsing,
because of all the COM business that MSXML6 uses. Anyway, my latest
problem is that I tryed to incorperate some error handling. When I
catch a _com_error from a call made on the MSXML smart ptr interfaces
I try to get the error message or description and put it in my own
exception. When I try to assign _com_error::Description() to a
std::string or insert it to a stringstream using <<, I get another
exception of unknown type and the debugger points to assembly.

How can I safely get the error message from a _com_error object and
put it into a std::string in a multibyte project?

Here is my offending code:

void DataManager::ParseGoods(MSXML2::IXMLDOMNodeListPtr &
   BaseException error("Unspecified Error",
DataManager::ParseGoods(MSXML2::IXMLDOMNodeListPtr & goodXMLNodes)",

   for(Good::ID id = 0; id < static_cast<unsigned>(goodXMLNodes-

Getlength()); ++id)

      MSXML2::IXMLDOMNodePtr node = goodXMLNodes->nextNode();

      Good good;
      good.m_ID = id;

      for(node = node->GetfirstChild(); node != NULL; node = node-


         std::string element = node->nodeName;

         if( element == "name" || element == "Name" )
               good.m_name = node->GetnodeTypedValue();
            catch(_com_error & e)
               std::ostringstream errorMsg;
               errorMsg << "Error parsing <good> node #" << id << ".
                        << "Could not get typed value of <name>
                        << "COM error description: " <<

               error.m_msg = errorMsg.str();
               throw error;

I have tryed:

1) << std::string(e.Description());
2) << e.Description.operator const char*();
3) + e.Description

The MSDN documentation on the returned _b_str_t implies that it can be
converted to a regualr const char *, so I do not understand the
problem. Is the damn thing empty? How am I supposed to do this the
right way?

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