Save Configuration Settings to XML file in QT?

Question

I want to Save Configuration Settings to XML file in QT and read it from there ?

What is best approach to do this in QT ?

Any sample/ideas are highly appreciated.

Thanks.

Answer 1

For such things I often use the boost library for C+ and can highly recommend it. It offers serialization for various formats like XML, text, binary etc.

Serialization Tutorial (looks more complicated that it actually is)

Answer 2

You can register your XML file format with QSettings::registerFormat

Here's a sample implementation of the readXmlFile and writeXmlFile

Answer 3

There is Qt examples for XML.

Also you can use QSettings to store your settings.

Answer 4

Here is my code for exporting settings to XML. What you need is to call ExportSettingsToXml() with opened for writing QFile. The exported file can be imported again with ImportSettingsFromXml().

QString Variant2Text( const QVariant &value )
{
    switch (value.type())
    {
    case QVariant::String:
    case QVariant::Int:
    case QVariant::UInt:
    case QVariant::LongLong:
    case QVariant::ULongLong:
    case QVariant::Double:
    case QVariant::Bool:
        return value.toString();
    }

    QByteArray ba;
    value.save(QDataStream(&ba, QIODevice::WriteOnly));

    return QString(ba.toHex());
}

QVariant Text2Variant( const QString &sText, QVariant::Type nType )
{
    switch (nType)
    {
    case QVariant::String:
    case QVariant::Int:
    case QVariant::UInt:
    case QVariant::LongLong:
    case QVariant::ULongLong:
    case QVariant::Double:
    case QVariant::Bool:
        {
            QVariant var(sText);
            if (var.convert(nType))
                return var;

            return QVariant(sText);
        }
        return QVariant::fromValue(sText);
    }

    QVariant value;
    value.load(QDataStream(&QByteArray::fromHex(sText.toLatin1()), QIODevice::ReadOnly));

    return value;
}

void XmlExportSettingsRecursive(QXmlStreamWriter &writer, QSettings &settings, const QStringList &blackList)
{
    QString sGroup = settings.group();

    if (!sGroup.isEmpty())
    {
        writer.writeStartElement("group");  
        writer.writeAttribute(QStringLiteral("name"), sGroup.mid(sGroup.indexOf(QChar('/')) + 1));
    }
    // Write child groups first
    {
        const QStringList &listGroups = settings.childGroups();
        foreach (const QString &group, listGroups)
        {
            settings.beginGroup(group);         
            XmlExportSettingsRecursive(writer, settings, blackList);
            settings.endGroup();
        }
    }

    const QStringList &listKeys = settings.childKeys();
    foreach (const QString &key, listKeys)
    {
        if (blackList.contains(key))
            continue;

        writer.writeStartElement("key");
        writer.writeAttribute(QStringLiteral("name"), key);
        const QVariant &value = settings.value(key);
        writer.writeAttribute(QStringLiteral("type"), value.typeName());
        writer.writeCharacters(Variant2Text(value));
        writer.writeEndElement();
    }

    if (!sGroup.isEmpty())
        writer.writeEndElement();
}

bool XmlImportSettingsRecursive(QXmlStreamReader &reader, QSettings &settings)
{
    while (!reader.atEnd()) {
        reader.readNext();
        if (reader.isStartElement())
        {           
            if (reader.name() == QStringLiteral("group"))
            {
                const QXmlStreamAttributes &attr = reader.attributes();
                QString sGroup = attr.value(QStringLiteral("name")).toString();

                settings.beginGroup(sGroup);
                if (!XmlImportSettingsRecursive(reader, settings))
                    return false;
                settings.endGroup();
            }
            else if (reader.name() == QStringLiteral("key"))
            {
                const QXmlStreamAttributes &attr = reader.attributes();
                const QString &sKey = attr.value(QStringLiteral("name")).toString();
                const QString &sType = attr.value(QStringLiteral("type")).toString();
                if (reader.readNext())
                {
                    if (reader.isCharacters() || reader.isEndElement())
                    {
                        const QString &sValue = reader.text().toString();
                        settings.setValue(sKey, Text2Variant(sValue, QVariant::nameToType(sType.toLatin1())));
                    }
                    else
                        continue;
                }
            }
        }
        else if (reader.isEndElement() && reader.name() == QStringLiteral("group"))
            return true;
    }
    if (reader.hasError()) {
        qDebug()<<reader.errorString();
        return false;
    }

    return true;
}

bool ExportSettingsToXml( QIODevice *device, const QString &settingsGroup = QString(), const QStringList &blackList = QStringList())
{   
    if (!device || !device->isWritable())
        return false;

    QSettings settings;
    settings.beginGroup(settingsGroup);

    QXmlStreamWriter xmlWriter( device );
    xmlWriter.setAutoFormatting( true );
    xmlWriter.writeStartDocument();

    xmlWriter.writeStartElement( QStringLiteral("settings") );

    if (!settingsGroup.isEmpty())
    {   
        xmlWriter.writeStartElement(QStringLiteral("group"));
        xmlWriter.writeAttribute(QStringLiteral("name"), settingsGroup);
    }

    XmlExportSettingsRecursive(xmlWriter, settings, blackList);

    if (!settingsGroup.isEmpty())
        xmlWriter.writeEndElement();

    xmlWriter.writeEndDocument();

    return true;
}

bool ImportSettingsFromXml( QIODevice *device, const QString &settingsGroup = QString())
{
    if (!device || !device->isReadable())
    {
        qDebug()<<"Trying to import XML settings from non-readable device";
        return false;
    }

    QSettings settings;
    settings.beginGroup(settingsGroup);
    QXmlStreamReader xmlReader( device );
    xmlReader.readNext();
    if (!xmlReader.isStartDocument())
    {
        qDebug()<<"Invalid xml document format";
        return false;
    }

    if (!xmlReader.readNextStartElement())
    {
        qDebug()<<"Empty settings xml document";
        return true;
    }

    if (xmlReader.name() == QStringLiteral("settings") )
    {
        if (!XmlImportSettingsRecursive(xmlReader, settings))
            return false;
    }
    else
    {
        qDebug()<<"Unknown settings format.";
        return false;
    }

    return true;
}