@silau It looks good but ldd doesn't always report exactly what is actually happening when you run your exe. It's a good start though. If you really wanted to trace it further you would have to ldd on each of those libs to see what they link. One of them could be using the 5.6 or whatever other version you may have. That being said I find that to be a bit unlikely though. When I get a little bit of time later today I will run your code using Arch linux and 5.11 and see what happens. That will help determine if maybe it's a bug in Qt (which I highly doubt for something that big). If it works for me the next steps for you would be to run it in the debugger and step through the working 5.6 one during socket connections and then the broken 5.11 one and see what is different. Another option is take it down to the simplest form and just use the chat example or something from Qt and see if it works with 5.11 and then try to see what is different. I'll let you know what I find out on my linux/Qt 5.11 in a bit. Edit: Didn't get a chance today, was really busy. I will run a quick test tomorrow some time though.

Hi You are mixing old syntax with lambda which it cannot do. With lambdas you cannot use the SIGNAL() macro. Has to be the new syntax. I used QObject::connect(&but_submit, &QPushButton::clicked, [&]() {... which compiled fine and did show the entered string. But you seems to be using Qt-4.8.5 at and new syntax first came in Qt5 so i guess that is why you get errors. So basically, with that old Qt , you cannot do it in main. You need a QOBJECT based object to send signals to. In that old Qt, its not possible to connect to functions. Only to member slots in a class. You must use that so old Qt ?

Thank you all for helping detect ths error. I will take a close look at the related docs. Regards, Nico

@diredko Qt will output signal/slot problems on the console. Run your application from the console and you should see something like: QObject::connect: No such slot QObject::movePiece(int, int, int, int) Or something similar if there is an issue. Also you can add a qDebug() << "Got here" to your connect() but like @SGaist said, you are connecting in a bad place. qDebugs() will show up on the console as well. If you are in windows you will have to add CONFIG += console to your project file. Linux and OSX should be fine without. And finally add qDebug() messages to your move and movePiece to see if it's getting in there. Or of course you could use the debugger for all this. ;)

@TheBadger I tried to investigate the error, and i found where it is coming from its from this line playList.emplace_back(ui->song->text().toStdString()); which is written before the connect() in the code

@SGaist Yes. That was intensional. I just tested that my installation is still providing the message. Thanks a lot anyway.