How can I determine why a call to IXMLDOMDocument::load() fails?

c++, com, xml

Solution

The following code will fetch the specific parser error from the DOM and it's location in the source XML.

CComPtr<IXMLDOMParseError> pError;
CComBSTR sReason, sSource;
long nLine = 0, nColumn = 0;

m_pXmlDoc->get_parseError(&pError);
if(pError)
{
    pError->get_reason(&sReason);
    pError->get_srcText(&sSource);
    pError->get_line(&nLine);
    pError->get_linepos(&nColumn);
}

`sReason` will be filled with the error message. `sSource` will contain the errorneous source line in the XML. `nLine` and `nColumn` should get set to the line number and column of the error, although in practice these two aren't always set reliably (iirc, this is especially true of validation errors, rather than parser/well-formedness ones).

Problem

I am trying to debug what appears to be an XML parsing issue in my code. I have isolated it down to the following code snippet: ``` HRESULT CXmlDocument::Load(IStream* Stream) { CComVariant xmlSource(static_cast<IUnknown*>(Stream)); VARIANT_BOOL isSuccessful; * HRESULT hr = m_pXmlDoc->load(xmlSource, &isSuccessful); return (hr == S_FALSE) ? E_FAIL : hr; } ``` Note: `m_pXmlDoc` is of the type `CComPtr<IXMLDOMDocument>`. It appears that the call to `IXMLDOMDocument::load()` (marked with the *) is failing - IOW, it is returning `S_FALSE`. I am not able to step into `load()` to determine why it is failing, as it is a COM call. The MSDN page for this method doesn't seem to be giving a lot of insight. I have a few hunches: - The XML is not well-formed - The XML file is too large (approximately 120MB) - It is a memory-related issue (the process size gets to > 2GB at the time of failure) - NB: A registry key has been set to allow the process size to be this large, as the largest valid process size for WinXP, AFAIK, is 2GB). Any ideas as to why this call could be failing?

Original source