why no findXmlElement functions?

fryn3

class MyXmlStreamReader : public QXmlStreamReader
{
public:
    MyXmlStreamReader() : QXmlStreamReader() { }
    MyXmlStreamReader(QIODevice *device) : QXmlStreamReader(device) { }
    MyXmlStreamReader(const QByteArray &data) : QXmlStreamReader(data) { }
    MyXmlStreamReader(const QString &data) : QXmlStreamReader(data) { }
    MyXmlStreamReader(const char * data) : QXmlStreamReader(data) { }
    bool findXmlElement(QStringList path) {
        if (path.isEmpty()) {
            return false;
        }
        QString findName = path.at(0);
        while (!atEnd() && !hasError()) {
            readNextStartElement();
            if (findName == name()) {
                if (path.size() == 1) {
                    return true;
                } else {
                    return findXmlElement(path.mid(1));
                }
            } else {
                skipCurrentElement();
            }
        }
        return false;
    }
    bool findXmlElement(QList<QRegExp> path) { return false; }   // not implemented
};

Example
xml-file

<?xml version="1.0" encoding="UTF-16" ?>
<persons>
    <person id="1">
        <firstname>John</firstname>
        <surname>Doe</surname>
        <email>john.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="2">
        <firstname>Jane</firstname>
        <surname>Doe</surname>
        <email>jane.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="3">
        <firstname>Matti</firstname>
        <surname>Meikäläinen</surname>
        <email>matti.meikalainen@example.com</email>
        <website>http://fi.wikipedia.org/wiki/Matti_Meikäläinen</website>
    </person>
</persons>

code

int main (int argc, char *argv[]) {
    QApplication a(argc, argv);
    QFile f("file.xml");
    f.open(QIODevice::ReadOnly);
    MyXmlStreamReader xml(&f);
    qDebug() << xml.findXmlElement(QStringList() << "persons" << "person" << "email");
    qDebug() << xml.tokenString() << xml.name() << xml.text();
    return 0;
}

JonB

@fryn3 said in why no findXmlElement functions?:

why no findXmlElement functions?

What sort of an answer are you expecting to this? QXmlStreamReader does not provide "find" functions, it's a forward-only fast stream reader. Use https://doc.qt.io/qt-5/qdomdocument.html (e.g. elementsByTagName()) if you want more advanced capabilities after reading in a whole document. Otherwise you are are writing your own findXmlElement() methods, so what's the issue?

fryn3

@JonB said in why no findXmlElement functions?:

Use https://doc.qt.io/qt-5/qdomdocument.html (e.g. elementsByTagName()) if you want more advanced capabilities after reading in a whole document.

The module is not actively maintained anymore. Please use the QXmlStreamReader and QXmlStreamWriter classes in Qt Core instead.

Later, I will prepare a detailed answer.

VRonin

efficiency point:

 bool findXmlElement(QStringList path){return findXmlElement(path.cbegin(),path.cend());}
private:
 bool findXmlElement(QStringList::const_iterator pathBegin,QStringList::const_iterator pathEnd) {
        if (pathBegin==pathEnd)
            return false;
        while (!atEnd() && !hasError()) {
            readNextStartElement();
            if (*pathBegin== name()) {
                if (++pathBegin == pathEnd)
                    return true;
                    return findXmlElement(pathBegin ,pathEnd);
            } else {
                skipCurrentElement();
            }
        }
        return false;
    }

Functionality point:
If you have

<person id="1">
        <firstname>John</firstname>
        <surname>Doe</surname>
        <email>john.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="2">
        <firstname>Jane</firstname>
        <surname>Doe</surname>
       <middlename>James</middlename>
        <email>jane.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>

Your algorithm will not be able to find QStringList{"person","middlename"}

fryn3

This post is deleted!

JonB

@fryn3

The module is not actively maintained anymore. Please use the QXmlStreamReader and QXmlStreamWriter classes in Qt Core instead.

I don't know if this is something aimed at me? Whatever link you put on "The module" in what you wrote doesn't lead anywhere?

ODБOï

@JonB https://doc.qt.io/QT-5/qtxml-module.html

JonB

@LeLev
Oh! You mean that all those QXml... and QDom... classes are being withdrawn? No support for reading your entire XML document into a DOM and searching/editing it from there? Seriously? Seems like a retrograde step, Qt provides loads of useful stuff, does it not need such slightly higher-level support for XML?

Christian Ehrlicher

QtXml is in 'done' state - this doesn't mean it will be removed. It just will not gain any major updates anymore.

VRonin

Just to give you a comparison, bzip2 hasn't received a major update since 2010 and zlib hasn't received any update for more than2 years but they are still the most used compression libraries i can think of. The Qt xml module entered the same stage, it implemented all the features that were considered "in scope" and it woks well as is

JonB

Good to know. In which case, although the OP rejected my suggestion that he could choose to read the whole document in and do things like QDomDocument::elementsByTagName() because "The module is not actively maintained anymore", that is still an acceptable approach going forward, right?

JonB

BTW, I've just searched and am delighted to see that Qt does have XPath/XQuery, https://doc.qt.io/qt-5/xmlprocessing.html. It's up to the OP, but I will say that using XPath queries on your XML documents is an order of magnitude nicer than walking the tree in code.

And for quite separate purposes, I see that also has (at least some) XSLT support, so it gets better & better... :)