QProcess again ..

[jacek]

size of the byte array ... i think i cant understand...

I wanted you to check if you actually read something with readStdout():

void ServerMainWindow::readFromStdout(){
   QByteArray data = proc->readStdout();   
   qWarning( "%d", data.size() );
   lineEdit1->setText(QString(data));
   sendToClients(QString(data));
}

void ServerMainWindow::readFromStdout(){
   QByteArray data = proc->readStdout();   
   qWarning( "%d", data.size() );
   lineEdit1->setText(QString(data));
   sendToClients(QString(data));
}

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when should I execute proc->start()

After you connect to readyReadStdout() signal.