Strange error: doc.setContent(data) returns false

Hi,
I have a problem parsing some xml file from megaupload: my applycation, in short, extract links from a MegaUpload folder url. It works well but sometime I got error; but first of all the code:

Code:

---

void Dialog::parseXml()
{
	muitems.clear();
	if(!internetJob->isRequestAborted() && internetJob->getStatusCode() == 200)
	{
		QByteArray data = internetJob->getData();
		qDebug() << "Checking for data!!\n";
		if(data.isEmpty()) {
			qDebug() << "Megaupload returned an empty result!\n";
			return;
		}
 
		QDomDocument doc;
		if( !doc.setContent( data ) ) {
			qDebug() << "The XML obtained from Megaupload is invalid.";
			return;
		}
 
		QDomElement root = doc.documentElement();
		if( root.tagName() != "FILES" ) {
			qDebug() << "The xml file invalid.";
			return;
		}
 
		QDomNode n = root.firstChild();
		while( !n.isNull() )
		{
			QDomElement e = n.toElement();
			if( !e.isNull() )
			{
				if( e.tagName() == "ROW" )
				{
					MegaUploadItem mui;
					mui.name = e.attribute( "name", "" );
					mui.url = e.attribute( "url", "" );
					muitems.append(mui);
				}
			}
			n = n.nextSibling();
		}
	}
	qSort(muitems);
}

---

Most of the times the code above runs good and my QVector muitems is filled with the needed data (file name and url); some times I got an error at doc.setContent(data) even if I dont' know why; in fact, if I comment line 16 parseXml() continues and data are retrieved correctly; other time I got a error in the same line but it is parsed only the first sibling (hoping I was clear). Below are three different urls: with the first I got no error; whit the second doc.setContent(data) returns false but commenting line 16 the data is retrieved correctly; while the third url gives the error plus only one iteration of while(!n.isNull()) {...}.

http://www.megaupload.com/xml/folder...derid=D4HQHPLJ
http://www.megaupload.com/xml/folder...derid=0JY6SVP1
http://www.megaupload.com/xml/folder...derid=QEKO90W1

You can copy these urls in your browser and take a look at the generated xml file. They are structurally the same...

So my questions are:

1) Why doc.setContent(data) returns false? How get a more verbose output?
2) Why only the first tag is parsed and remaining not?

I was thinking to use QRegExp for parsing, but the captured test is wrong: here a sample row of the xml file:

Quote:

---

<ROW name="VIDEO_TS.part06.rar" name_cut="VIDEO_TS.part06.rar" size="400 MB" url="http://www.megaupload.com/?d=3B1SORP1" downloadid = "3B1SORP1" sizeinbytes="419430400" expired="0"></ROW>

---

and below my pattern:

Code:

---

QRegExp pattern("<ROW\\s((\\w+)\\s*=\\s*(\"[^\"]\"))+></ROW>");

---

Probably the regular expression is wrong; who can review that?


Best regards.

Hello Giuseppe,

I'm not going to comment on the problem you're having with XML, since I haven't used it enough to be knowledgeable in that area. I can comment on your regexp, however.

To start with, using regular expressions for XML is not a good idea. They are far too brittle. If you choose to use one anyway, here is your corrected expression. I use a free program called Regex Coach to proofread mine. I didn't test this in Qt, but it should work.

Code:

---

QRegExp pattern("<ROW\\s+((\\w+)\\s*=\\s*(\"[^\"]*\")\s*)+></ROW>");

---

Quote:

---

Originally Posted by init2null

To start with, using regular expressions for XML is not a good idea. They are far too brittle. If you choose to use one anyway, here is your corrected expression. I use a free program called Regex Coach to proofread mine. I didn't test this in Qt, but it should work.

Code:

---

QRegExp pattern("<ROW\\s+((\\w+)\\s*=\\s*(\"[^\"]*\")\s*)+></ROW>");

---

---

I have tested your pattern but it seems not working; it matches only the last couple of attributeName/attributeValue.

I have used your pattern in the following piece of code:

Code:

---

QTextStream ts(&data);
 
while (!ts.atEnd()) {
	QString line = ts.readLine();
	pattern.indexIn(line);
	int max = pattern.numCaptures() - 1;
	QStringList caps = pattern.capturedTexts();
	for ( int i = 1; i < max; i += 2 )
	{
		QString attributeName = caps.at(i);
		QString attributeValue = caps.at(i + 1);
 
		// do something with that data now
		qDebug() << attributeName + "=" + attributeValue + "\n";
	}
}

---

Thanks

I guess regexps can only capture one value for each set of parenthesis. Since that's the case, either put in this snippet for each key-value pair

Code:

---

(\\w+)\\s*=\\s*(\"[^\"]*\")\s*

---

or parse the XML. I looked a little at your initial questions, and I can answer your question on getting the XML error message. Use the optional arguments for the setContent method:

Code:

---

bool QDomDocument::setContent ( const QString & text, QString * errorMsg = 0, int * errorLine = 0, int * errorColumn = 0 )

---