Qt C++: QFile won't open *.txt resource in WriteOnly

Question

I am trying to read a line from a .txt file and then write that line back into another .txt. However, I can only open the files in ReadOnly mode. When I try to write back to the second resource .txt it won't open.

In my project I added a resource file and added the two file "Test.txt" and "Ergebnis.txt" to the resource file which now looks like this:

<RCC>
<qresource prefix="/stuff">
    <file>Test.txt</file>
    <file>Ergebnis.txt</file>
</qresource>
<qresource prefix="/things"/>

The actual reading/writing is done in separate functions, which are called like so:

Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);
QString mLine1 = "Success";

mLine = Read(":/stuff/Test.txt");
Write(":/stuff/Ergebnis.txt", mLine1);

}

And which look like so:

QString Dialog::Read(QString filename){
QFile mNewFile(filename);
QString* mText = new QString;
bool check = true;

if(!mNewFile.open(QFile::ReadOnly | QFile::Text)){
            return *mText = "";
}

QTextStream in(&mNewFile);
check = in.readLineInto(mText);

mNewFile.close();

return *mText;
}

void Dialog::Write(QString out, QString Text){
QFile mNewFile(out);
QString errMsg;
QFileDevice::FileError err = QFileDevice::NoError;

if(mNewFile.exists())
    qDebug() << "Ergebnis.txt exists!";

if(!mNewFile.open(QFile::WriteOnly | QFile::Text )){
        errMsg = mNewFile.errorString();
        err = mNewFile.error();
    qDebug() << "Error: " << errMsg <<"Number: " << err;
    return;
}

QTextStream out_str(&mNewFile);
out_str << Text;
mNewFile.flush();
mNewFile.close();
}

Reading works just fine, so I'm confident the paths to the resources are correct. In the Write() function I also checked whether the file exists, which it does. I tried opening the file in ReadOnly, which works as well. The problem seems to be that I can't open the file in WriteOnly or ReadWrite mode. The errMsg outputs "Unknown error" to the command line. The error code is "5", whatever that means...

I also tried opening the file directly from my filesystem using:

Write("/home/js/Dokumente/Cpp/Programme/QT/TestStringSource/Ergebnis.txt", mLine1);

which worked just fine, funnily enough.

Any advice is greatly appreciated!