Store the QDocument attributes in an ordered way

Lolo67

I am using the following function to write the content from a QDomDocument into a file.

int MyClass::writeFile(const QString outfile,const QDomDocument* XMLContent)
{
    QFile out(outfile);
    if (out.open(QIODevice::ReadWrite|QIODevice::Truncate))
    {
        LOG(INFO) << "Write Out File: " << outfile.toStdString();
        QTextStream stream( &out );
        QString Result_string;
        int ident = 3;
        Result_string = XMLContent->toString(ident);
        stream << Result_string << endl;
        out.close();
        return -1;
    }
    else
    {
        LOG(ERROR) << "ERROR - Cannot write file: " << outfile.toStdString();
        return 0;
    }
}

I am observing that the produced file does not always have the arguments put in the same order within a node.

F.e. sometimes it might be:

<myObject Attribute1="111" Attribute2="222" Attribute3="333">
...
</myObject>

and sometimes it might be:

<myObject Attribute3="333" Attribute1="111" Attribute2="222">
...
</myObject>

I understand that this has no consequence on the generated XML - However it would be convenient if the attributes would always be stored in the same order so that I would able to easily diff two consecutively generated files.

m.sue

Hi @Lolo67

There is an old bug report which shows a workaround: https://bugreports.qt.io/browse/QTBUG-8158

-Michael.

LabanK

Make use of QStreamWriter instead, that solved this issue for me!

QDomElement element = getUserDomElement();

QByteArray byte_array;
QXmlStreamWriter stream(&byte_array);

stream.writeStartDocument();

//(Recursive part)
stream.writeStartElement(element.tagName());

QVector<QString> attribute_names;
const QDomNamedNodeMap attributes = element.attributes();
for(quint32 i = 0; i < attributes.length(); ++i) {
  attribute_names << attributes.item(i).toAttr().name();
}

std::stable_sort(attribute_names.begin(), attribute_names.end());

foreach(QString attr_name, attribute_names) {
  QDomAttr attr = attributes.namedItem(attr_name).toAttr();
  stream.writeAttribute(attr.name(), attr.value());
}

//If has children call recursive function...

stream.writeEndElement();
//(End recursive part)

stream.writeEndDocument();

QFile file("ordered_attributes.xml");
if(file.open(QIODevice::WriteOnly | QIODevice::Text | QIODevice::Truncate)) {
  file.write(byte_array);
  file.flush();
  file.close();
}

This will write one QDomElement on format:

<tag a="value_a" b="value_b" ...></tag>

where attributes are ordered by choice of sorting algorithm.

If QDomElement has children this procedure can be called recursively with stream as argument.