if after connecting to unreachable host we write something to socket it will report this error in infinite loop:

"QNativeSocketEngine::write() was not called in AbstractSocket::ConnectedState
"

sample code:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QTcpSocket socket;
    socket.connectToHost("192.168.1.56",5555);
    socket.write("hello"); 
    return a.exec();
}

socket also emits error(QAbstractSocket::SocketError) in infinite loop.