Question

I’ve used following code for parsing XML file in c++. http://www.codeproject.com/Articles/176236/Parsing-an-XML-file-in-a-C-C-program.

Now I want to fill data in hashmap. But can’t able to do it. Error says conversion not possible to std::string from BSTR.

Here is part of code…

 MSXML2::IXMLDOMNode *pIParentNode = NULL;
 //Variables to store attribute's name,type and text:    
      BSTR bstrAttrName, bstrAttrType, bstrAttrText;

 typedef std::tr1::unordered_map< std::string, std::string > hashmap;     
      hashmap numbers;

      for(i = 0; i < (NodeListPtr->length); i++)
      {

            if (pIDOMNode) pIDOMNode->Release();            
            NodeListPtr->get_item(i, &pIDOMNode);


            if(pIDOMNode )
            {               

                pIDOMNode->get_nodeTypeString(&bstrNodeType);

                //We process only elements (nodes of "element" type): 
                BSTR temp = L"element";
               pIDOMNode->get_nodeTypeString(&bstrNodeType);

                //We process only elements (nodes of "element" type): 
                BSTR temp = L"element";

                if (lstrcmp((LPCTSTR)bstrNodeType, (LPCTSTR)temp)==0) 
                {


                    pIDOMNode->get_nodeName(&bstrItemNode);                 
                    printf("Node: %ls\n", bstrItemNode);        


                    pIDOMNode->get_text(&bstrItemText);
                    printf("Text: %ls\n", bstrItemText);

numbers[(std::string)bstrItemNode] = (std::string)bstrItemText; // Here error.. need string..

I tried following but it return only one character.

numbers[(char*)bstrItemNode] = (char*)bstrItemText; // return only 1 character..need whole string..

Can anyone tell me that how can I access string from this class to fill in the hashmap??

Error is:

error C2440: 'type cast' : cannot convert from 'BSTR' to 'std::string'
1>        No constructor could take the source type, or constructor overload resolution was ambiguous
1> : error C2440: 'type cast' : cannot convert from 'BSTR' to 'std::string'
1>        No constructor could take the source type, or constructor overload resolution was ambiguous

Please help me, I’m stuck. Any alternative way also appreciate. Thanks…

Answer 1

You can’t cast from a BSTR to a std::string. You have to convert it.

As a side note, BSTR’s support wide character strings, you probably want to consider using std::wstring instead of the narrow string you are currently using. Also, I recommend using _bstr_t instead of the pure BSTR objects you are using here. _bstr_t will take care of managing the memory for you and make the conversions easier (see the above link that uses _bstr_t for the conversions). You can still pass a _bstr_t off to the methods via the GetAddress and GetBSTR methods depending on whether you need a modifiable reference or not (see the docs on _bstr_t for examples).