Append nodes to an XML file

Christian Ehrlicher

Try to pass a proper xml - it should start with '<?xml version="1.0"?>'

russjohn834

I tried with a modified xml but the same issue.

This error comes only when I open the file to Append:

QIODevice::ReadWrite | QIODevice::Append | QIODevice::Text

But if it's just for ReadWrite

QIODevice::ReadWrite |  QIODevice::Text

Atleast file is leading. Though I can't change the xml file..

Christian Ehrlicher

Did not notice it - for sure QIODevice::Append will not work. So what's your actual output?

russjohn834

@Christian-Ehrlicher

If I do QIODevice::ReadWrite | QIODevice::Text, file loading ok. But I cant write new nodes to it..

Consol says ReadOnly device

Any idea where I'm wrong?

JonB

@russjohn834
If I understand what you are trying to do correctly, we have gone through this many times in this forum. If your goal is to update XML in a file, you don't open the file for append or read-write or anything like that. You open the file read-only, read it all in, close it. Make your changes to the in-memory document. Then open the file for overwrite, write all content, close file. (Or write to a new file and then delete/rename.) Your code will contain neither QIODevice::ReadWrite nor QIODevice::Append.

mrjj

@russjohn834 said in Append nodes to an XML file:
Hi
......
root.appendChild(newTag);
there is missing a file open here ? ( you call close higher up but i dont see an open for write ?)
QTextStream output(&file);
output << document.toString();
file.close();

Benjamin841

This post is deleted!

russjohn834

Thank you @mrjj @JonB
I can now append a new node to my file, I did as follows:

    if(!file.open(QIODevice::ReadOnly  | QIODevice::Text))
        {
            qDebug () << "Error saving XML file...."; 
            file.close();
        }

        document.setContent(&file);
        QDomElement root = document.documentElement();
        file.close();

        QDomElement newTag = document.createElement(QString("Settings"));
        QDomElement newCurrTag = document.createElement(QString("Current"));
        QDomText newCurrVal = document.createTextNode(QString("45"));
        newCurrTag.appendChild(newCurrVal);
        newTag.appendChild(newCurrTag);
        root.appendChild(newTag);

        file.open(QIODevice::WriteOnly | QIODevice::Text);
        QTextStream output(&file);
        output << document.toString();
        file.close();

JonB

@russjohn834
That's much better!

Now just a minor picky for good code.

    if(!file.open(QIODevice::ReadOnly  | QIODevice::Text))
        {
            qDebug () << "Error saving XML file...."; 
            file.close();
        }
    ...

Don't forget to put some kind of return at the end of that error case so it does not continue into the "opened" code. And (unless you know better for QFile) don't file.close() if you are inside an if (!file.open()), because the file never got opened! Plus, change all that indentation after the if's }, so it doesn't look like it's all still inside the if :)

russjohn834

@JonB Thank you for the feedback :)