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Asked: 2026-05-10T21:06:09+00:00

All, this is my code //declare string pointer BSTR markup; //initialize markup to some

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All,

this is my code

//declare string pointer BSTR markup;  //initialize markup to some well formed XML <-  //declare and initialize XML Document MSXML2::IXMLDOMDocument2Ptr pXMLDoc; HRESULT hr; hr = pXMLDoc.CreateInstance(__uuidof(MSXML2::DOMDocument40)); pXMLDoc->async = VARIANT_FALSE; pXMLDoc->validateOnParse = VARIANT_TRUE; pXMLDoc->preserveWhiteSpace = VARIANT_TRUE;      //load markup into XML document vtBoolResult = pXMLDoc->loadXML(markup);  //do some changes to the XML file<-  //get back string from XML doc markup = pXMLDoc->Getxml(); //<-- this retrieves RUBBISH

At this point my string is mangled (just a few chinese characters at the start then rubbish) . Looks like an encoding issue.

I also tried the following:

_bstr_t superMarkup = _bstr_t(markup);  //did my stuff  superMarkup = pXMLDoc->Getxml();  markup = superMarkup;

but still I am getting the same result.

Even if I call GetXML() without changing anything in the xml document I still get rubbish.

At this point if I try to assign the mangled pointer to another pointer it will trow an error:

Attempted to restore write protected memory. this is often an indication that other memory is corrupted.

Any suggestion?

EDIT1:

I found out this is happening in relation to the size of the XML string. If it happens on a given XML string and I reduce the size (keeping the same schema) it will work fine. Looks like MSXML2::DOMDocument40 has a limitation on size? In detail it happens if I have more than 16407 characters. I have one more GetXML will retrieve RUBBISH – if it’s <= 16407 everything works fine.

EDIT2:

Roddy was right – I was missing that _bstr_t is a class …

Rings any bell?

Cheers

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1 Answer

  1. Try replacing

     BSTR Markup;

    with 

     bstr_t Markup;

    BSTR is pretty much a dumb pointer, and I think that the return result of GetXML() is being converted to a temporary which is then destroyed by the time you get to see it. bstr_t wraps that with some smart-pointer goodness…

    Note: Your ‘SuperMarkup’ thing did NOT do what I suggested. Again, BSTR is just a pointer, and doesn’t ‘own’ what it points to. bstr_t, on the other hand does. I think your GetXML() function is returning a bstr_t, which is then being deleted as it goes out of scope, leaving your BSTR pointing to memory that is no longer valid.

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