@VRonin i before write my code to this method 369 book: void WeatherBalloon::sendDatagram() { QByteArray datagram; QDataStream out(&datagram, QIODevice::WriteOnly); out.setVersion(QDataStream::Qt_4_3); out << QDateTime::currentDateTime() << temperature() << humidity() << altitude(); udpSocket.writeDatagram(datagram, QHostAddress::LocalHost, 5824); } But we want to connect UDP processing data to GUI app, it can not read QDataStream Method and it Crashs. The app is written in C#,So we should try a method that work with VisualStudio. Agian Than kyou for attention best regards stackprogramer