Xerces XPath causes seg fault when path doesn't exist - c++

Question

I can successfully use Xerces XPath feature to query for information from an XML with the following XML and C++ code.
XML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<root>
<ApplicationSettings>
hello universe
</ApplicationSettings>
</root>
C++
int main()
{
XMLPlatformUtils::Initialize();
// create the DOM parser
XercesDOMParser *parser = new XercesDOMParser;
parser->setValidationScheme(XercesDOMParser::Val_Never);
parser->parse("fake_cmf.xml");
// get the DOM representation
DOMDocument *doc = parser->getDocument();
// get the root element
DOMElement* root = doc->getDocumentElement();
// evaluate the xpath
DOMXPathResult* result=doc->evaluate(
XMLString::transcode("/root/ApplicationSettings"), // <-- HERE IS THE XPATH
root,
NULL,
DOMXPathResult::ORDERED_NODE_SNAPSHOT_TYPE, //DOMXPathResult::ANY_UNORDERED_NODE_TYPE, //DOMXPathResult::STRING_TYPE,
NULL);
// look into the xpart evaluate result
result->snapshotItem(0);
std::cout<<TranscodeToStr(result->getNodeValue()->getFirstChild()->getNodeValue(),"ascii").str()<<std::endl;;
XMLPlatformUtils::Terminate();
return 0;
}
The problem is that sometimes my XML will only have certain fields. But if I remove the ApplicationSettings entry from the XML it will seg fault. How can I properly handle these optional fields? I know that trying to correct from seg faults is risky business.

Answer 1

The seg fault is occurring in this line
std::cout<<TranscodeToStr(result->getNodeValue()->getFirstChild()->getNodeValue(),"ascii").str()<<std::endl;
specifically in get getFirstChild() call because the result of getNodeValue() is NULL.
This is my quick and dirty solution. It's not really ideal but it works. I would prefer a more sophisticated evaluation and response.
if (result->getNodeValue() == NULL)
{
cout << "There is no result for the provided XPath " << endl;
}
else
{
cout<<TranscodeToStr(result->getNodeValue()->getFirstChild()->getNodeValue(),"ascii").str()<<endl;
}