QFile file("proxy_settings.dat");
if(!file.open(QIODevice::WriteOnly)){
    QMessageBox::warning(nullptr, tr("Error"), tr("Cannot write proxy data into file, your settings "
                                                  "of the proxies cannot be saved"));
    return;
}
QDataStream stream(&file);
for(int i = 0; i != ui->tableWidgetPoxyTable->rowCount(); ++i){
    //do something and dump data into file
    stream<<type<<host<<port<<user_name<<password;
}

This naive solution work if everything going right, but it will generate corrupt file if the program exit before the data are written. Do I have an easy way to make sure all of the data can be written? Thanks