Modify an XML file QXMLStreamReader/Writer

[Arqam]

I am working on something where I am using QXMLStreamReader and QXMLStreamWriter, to read and write to a file.

But am not able to find a way such that I can modify an XML, for example consider this XML :

<?xml version="1.0"?>
<LAMPS>
    <LIGHT1>
        <State>statevalue</State>
        <Room>roomvalue</Room>
        <Potencial>potencialvalue</Potencial>
    </LIGHT1>
</LAMPS>

This is written using the following code :

QFile file(filename);
file.open(QIODevice::WriteOnly);

QXmlStreamWriter xmlWriter(&file);
xmlWriter.setAutoFormatting(true);
xmlWriter.writeStartDocument();

xmlWriter.writeStartElement("LAMPS");

xmlWriter.writeStartElement("LIGHT1");
xmlWriter.writeTextElement("State", "statevalue" );
xmlWriter.writeTextElement("Room", "roomvalue");
xmlWriter.writeTextElement("Potencial", "potencialvalue");
xmlWriter.writeEndElement();
xmlWriter.writeEndElement();
file.close();

Now I want to add one more <LIGHT1> to an EXISTING xml file, then how is possible to do that in QT?

I am doing the following:

//filename = my file path
     QFile file(filename);
     file.open(QIODevice::ReadWrite);
     QXmlStreamWriter xmlWriter(&file);
     QXmlStreamReader xmlReader;
     xmlReader.setDevice(&file);
     xmlWriter.setAutoFormatting(true);
     while(!xmlReader.atEnd()){
         if(xmlReader.isStartDocument())
             xmlWriter.writeStartDocument();
         if(xmlReader.isStartElement()){
             xmlWriter.writeStartElement(xmlReader.name().toString());
             if(xmlReader.name()=="LAMPS"){
                 xmlWriter.writeStartElement("Arqam");
                 xmlWriter.writeTextElement("Arqam","Lucid Dreamer");
                 xmlWriter.writeEndElement();
             }
         }
         if(xmlReader.isEndElement())
             xmlWriter.writeEndElement();
         if(xmlReader.isEndDocument())
             xmlWriter.writeEndDocument();
         xmlReader.readNext();
         file.close();

And I am getting the following errors :

QIODevice::write (QFile, "/Users/arqam/Desktop/XMLGenrator/input/zzzz.xml"): device not open
QIODevice::read (QFile, "/Users/arqam/Desktop/XMLGenrator/input/zzzz.xml"): device not open

[VRonin]

It might be easier to use the xml module to achieve what you are looking for.

[Arqam]

Following worked ::

#include <QTextStream>

int main()
{
    QFile file("test.xml");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        qDebug() << "Failed to open file";
        return 0;
    }
    QDomDocument document;
    if (!document.setContent(&file))
    {
        qDebug() << "failed to parse file";
        file.close();
        return 0;
    }

    file.close();

    QDomElement docEle = document.documentElement();
    QDomNodeList elements = docEle.elementsByTagName("LAMPS");

    QDomElement light1 = document.createElement( "LIGHT1" );
    QDomElement state = document.createElement("State");
    QDomText nextNode = document.createTextNode("State");
    state.appendChild(nextNode);
    light1.appendChild(state);
    docEle.appendChild( light1 );

    QFile outFile( "test-result.xml" );
    if( !outFile.open( QIODevice::WriteOnly | QIODevice::Text ) )
    {
        qDebug( "Failed to open file for writing." );
        return 0;
    }

    QTextStream stream( &outFile );
    stream << document.toString();

    outFile.close();
    return 0;
}