QString out of range

void okno::on_actionOpen_triggered()
{
    //QString
    QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"),
                                                     "/home",
                                                     tr("Kasia files(*.kas);;Text files (*.txt);;XML files (*.xml);;All files (*.*)"));
    if( !fileName.isNull() )
    {
        fstream plik;
        plik.open("bin/outbase.kas",ios::out | ios::app);
        if( plik.good() == true)
            {
                plik <<fileName.toStdString().c_str()<<"\n";
            }
            else
            {
                Error*o = new Error();
                o->setNapis(QString::fromStdString("Cannot open file"));
                o->show();
            }
        plik.close();
    }
} 

void okno::on_actionOpen_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"),
                                                     "/home",
                                                     tr("Kasia files(*.kas);;Text files (*.txt);;XML files (*.xml);;All files (*.*)"));
    if( !fileName.isNull() ) {
        QFile plik("bin/outbase.kas");
        if(file.open(QIODevice::WriteOnly|QIODevice::Append)) {
            QTextStream text(&plik);
            text <<fileName << endl;
            plik.close();
        } else {
            Error*o = new Error();
            o->setNapis(tr("Cannot open file"));
            o->show();
        }
    }
}