Reading from TCP Socket crashes program

[jacek]

and then the client crashes.

And there was only one entry in the backtrace? Did you compile your application in debug mode?

Anyway, you try to read data from the socket before they arrive --- you must wait for readyRead() signal.

[OnionRingOfDoom]

...How do I compile it in debug mode?

[jacek]

...How do I compile it in debug mode?

Add "CONFIG += debug" to your .pro file (and remove "release" if it's there).

[OnionRingOfDoom]

Ok so I changed the connection to do the readSpeed() function whenever readyRead() was emitted. However, now nothing happens when the client connects.

I also added a new connection at the end of the acceptConnection() function, which is as follows: connect(slider, SIGNAL(valueChanged(int)), this, SLOT(sendSpeed()));
so now, whenever I move the slider (and it outputs valueChanged signal), it crashes.

[OnionRingOfDoom]

After further fiddling, it seems that it's not the server's writing to the IO device that's the problem, it's the client's reading from the IO device that's causing the crash. Moving the slider thus causes the server to write data, and the client tries to read it or something, but crashes.

[jacek]

Does it crash if you change MainWindow::readSpeed() to:

void MainWindow::readSpeed()
{
     label->setNum(0);
}

void MainWindow::readSpeed()
{
     label->setNum(0);
}

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?

Did you try to generate that backtrace again?

[OnionRingOfDoom]

yes, it still crashes, oddly enough...
and I'm trying to compile in debug mode, but I have to fix all these errors switching to debug mode seems to have created.

[OnionRingOfDoom]

Oh awesome! It's acting like it can't find the QtNetwork include file anymore...
Any idea why adding that CONFIG thing to the .pro file would make it think it couldn't find QtNetwork, but could still find every other Qt file I included?

[jacek]

yes, it still crashes, oddly enough...

Is that label variable initialized?

It's acting like it can't find the QtNetwork include file anymore...

Can it find "QTcpSocket? Did you compile Qt in debug mode or maybe you have only release version?

[OnionRingOfDoom]

First question: yes, it is initialised
And I fixed the other problem, when I remade the .pro file, it didn't put in the
QT += network thing.

[OnionRingOfDoom]

and now it almost finishes compiling in debug mode... but MinGW comes up with some weird error I'm totally not responsible for:

C:\MinGW\bin\..\lib\gcc\mingw32\3.4.2\..\..\..\..\ mingw32\bin\ld.exe: cannot find -lqtmain

But at least it still compiles in release mode. But it still crashes whenever the client trys to even do anything with the readyRead function.

[OnionRingOfDoom]

Anyone else got any ideas?

[jacek]

but MinGW comes up with some weird error I'm totally not responsible for

Did you compile Qt in debug mode? Do you have the libqtmain.a and libqtmaind.a files in %QTDIR%\lib directory?

But it still crashes whenever the client trys to even do anything with the readyRead function.

Does it crash with empty MainWindow::readSpeed()?

Also add "CONFIG += console" to your .pro file and see whether your program outputs something to the console.

[OnionRingOfDoom]

Does it crash with empty MainWindow::readSpeed()?

Also add "CONFIG += console" to your .pro file and see whether your program outputs something to the console.

No, it does not crash when readSpeed() is empty.
And no, it doesn't write anything to the console.

I'm gonna try to reinstall Qt in debug mode this afternoon, after school

[jacek]

No, it does not crash when readSpeed() is empty.

Could you post the line in which you initialize that label variable?

[OnionRingOfDoom]

As for the label, it's initialized like so:

QLabel *label = new QLabel("change");

QLabel *label = new QLabel("change");

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...............

Wait a sec...... *checks the .h file*

Oh....
I initialised the label variable twice....
**facepalms**
problem solved....

[OnionRingOfDoom]

Heh, thanks for your help through all this! I tend to have other people ask me some question and then I realise a stupid error I made...