XML escape

[Vladimir]

Is there any function in QT to escape string for saving it in XML and decode it back after loading from XML ?

[wysota]

Could you give more details on your problem? Have you tried using a CDATA section?

[Vladimir]

I have user-provided string which I want to save into XML file and then read it again. In order to do it I should replace some characters (at least <>&, may be others?) by coresponging XML entities.

Some strings are two short (object names) and there are too many of them to use CDATA. And even for CDATA I should somehow replace "]]>" sequence, shouldn't I ?

May be the problem is not clearly Qt-related, but as Qt has XML parsers I've thought it can also has such a function.

[wysota]

The simplest way is to base64 encode the string you want to store. Or you can do it properly by reencoding xml entities, but I think you'd have to do that manually.

[iw2nhl]

I found 2 possible solutions:

1) encode/decode the text with the static functions
QUrl::toPercentEncoding()
QUrl::fromPercentEncoding()
You can specify what characters must be encoded and what not. You can simply make it encode "<", ">" and "&".

// Original text
QString text = "<text>";
// Encode it
QByteArray encoded = QUrl::toPercentEncoding("<text>", QByteArray(), "<>&");
// --> encoded == "%3Ctext%3E" 
// Decode it
QString decoded = QUrl::fromPercentEncoding(encoded);
// --> decoded == "<text>"

// Original text
QString text = "<text>";
// Encode it
QByteArray encoded = QUrl::toPercentEncoding("<text>", QByteArray(), "<>&");
// --> encoded == "%3Ctext%3E" 
// Decode it
QString decoded = QUrl::fromPercentEncoding(encoded);
// --> decoded == "<text>"

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2) use the new QXmlStreamWriter class which generates XML files, automatically encoding what is needed
See QXmlStreamWriter::writeCharacters() and QXmlStreamWriter::writeCDATA().

[Vladimir]

2) use the new QXmlStreamWriter class which generates XML files, automatically encoding what is needed
See QXmlStreamWriter::writeCharacters() and QXmlStreamWriter::writeCDATA().

This seems to be exactly what I need ! Thanks a lot.

Probably it was overlooked by me and others since it has appeared only in 4.3

[krsmichael]

You do not want to do what the others have suggested. Use these routines for your DomElement, ect values.

QString EncodeXML
(
	const QString& encodeMe
)
{
	QString temp;
 
	for (quint32 index(0); index < encodeMe.size(); index++)
	{
		QChar character(encodeMe.at(index));
 
		switch (character.unicode())
		{
		case '&': 
			temp += "&amp;"; break;
 
		case '\'': 
			temp += "&apos;"; break;
 
		case '"': 
			temp += "&quot;"; break;
 
		case '<': 
			temp += "&lt;"; break;
 
		case '>': 
			temp += "&gt;"; break;
 
		default:
			temp += character;
			break;
		}
	}
 
	return temp;
}
 
QString DecodeXML
(
	const QString& decodeMe
)
{
	QString temp(decodeMe);
 
	temp.replace("&amp;", "&");
	temp.replace("&apos;", "'");
	temp.replace("&quot;", "\"");
	temp.replace("&lt;", "<");
	temp.replace("&gt;", ">");
 
	return temp;
}

QString EncodeXML
(
	const QString& encodeMe
)
{
	QString temp;

	for (quint32 index(0); index < encodeMe.size(); index++)
	{
		QChar character(encodeMe.at(index));

		switch (character.unicode())
		{
		case '&': 
			temp += "&amp;"; break;

		case '\'': 
			temp += "&apos;"; break;

		case '"': 
			temp += "&quot;"; break;

		case '<': 
			temp += "&lt;"; break;

		case '>': 
			temp += "&gt;"; break;

		default:
			temp += character;
			break;
		}
	}

	return temp;
}

QString DecodeXML
(
	const QString& decodeMe
)
{
	QString temp(decodeMe);

	temp.replace("&amp;", "&");
	temp.replace("&apos;", "'");
	temp.replace("&quot;", "\"");
	temp.replace("&lt;", "<");
	temp.replace("&gt;", ">");

	return temp;
}

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If you use toPercentEncoding or...base64 encoding, who can read the xml that you have created? One of the benefits of XML is being able to read it from a text editor. Don't give up that advantage.