Thread problem

Hello,

I can't run all the QThread applications. The problem is the same. Maybe the compiler need some configuration. I have the Qt 4.1.1 open source for windows XP. The problem is the following:

C:\Qt\4.1.1\MyThread>make
mingw32-make -f Makefile.Debug all
mingw32-make[1]: Entering directory `C:/Qt/4.1.1/MyThread'
g++ -c -g -g -frtti -fexceptions -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL
-DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"C:/Qt/4.1.1/
include/QtCore" -I"C:/Qt/4.1.1/include/QtGui" -I"C:/Qt/4.1.1/include" -I"." -I"C
:/Qt/4.1.1/include/ActiveQt" -I"tmp\moc\debug_shared" -I"." -I"C:/Qt/4.1.1/mkspe
cs/win32-g++" -o tmp\obj\debug_shared\main.o main.cpp
main.cpp:26:2: warning: no newline at end of file
g++ -mthreads -Wl,-enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runt
ime-pseudo-reloc -Wl,-subsystem,windows -o "debug\MyThread.exe" tmp\obj\debug_sh
ared\main.o -L"C:\Qt\4.1.1\lib" -L"C:\Qt\4.1.1\lib" -lmingw32 -lqtmaind -lQtGui
d4 -lQtCored4
tmp\obj\debug_shared\main.o(.text$_ZN8MyThreadD1Ev[MyThread::~MyThread()]+0xb):
In function `ZN8MyThreadD1Ev':
C:/Qt/4.1.1/MyThread/main.cpp: undefined reference to `vtable for MyThread'
tmp\obj\debug_shared\main.o(.text$_ZN8MyThreadC1Ev[MyThread::MyThread()]+0x20):C
:/Qt/4.1.1/MyThread/main.cpp: undefined reference to `vtable for MyThread'
collect2: ld returned 1 exit status
mingw32-make[1]: *** [debug\MyThread.exe] Error 1
mingw32-make[1]: Leaving directory `C:/Qt/4.1.1/MyThread'
mingw32-make: *** [debug-all] Error 2

Thanks,
Panos

You have to declare macro Q_OBJECT in the MyThread Body

Code:

---

class MyThread: ....
{
    Q_OBJECT
......
}

---

I have already done that. I don't think that this is the problem.

• Do both MyThread::MyThread() and MyThread::~MyThread() actually have an implementation body?
• Is mythread.h listed in .pro?
• Did you re-run qmake after adding Q_OBJECT?

I have tried all these but the problem remais. I think that the real problem is somewhere here "undefined reference to `vtable for ThreadDialog' ", but I don't know what to do.

Can you post the code?

Quote:

---

Originally Posted by panos

I have tried all these but the problem remais. I think that the real problem is somewhere here "undefined reference to `vtable for ThreadDialog' ", but I don't know what to do.

---

But this is a different error than the one posted above. Repeat the same steps for ThreadDialog.

I am sorry but I have deleted the previous code. So I post here another example that I tried to run:

#include <QApplication>
#include <QThread>

#include <iostream>

using namespace std;

class Producer : public QThread
{
Q_OBJECT
public:
void run();
};

void Producer::run()
{
cout<<"Bye!"<<endl;
}

class Consumer : public QThread
{
Q_OBJECT
public:
void run();
};

void Consumer::run()
{
cout<<"Hello!"<<endl;
}

int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Producer producer;
Consumer consumer;
producer.start();
consumer.start();
producer.wait();
consumer.wait();
return app.exec();
}

By the way I would like to ask you how can I write something in the console (like when using the "cout" in C++)

The problem goes away once you declare classes containing Q_OBJECT macro in header files. Whenever qmake is run, it parses the project's header files and generates make rules to invoke moc for those files that contain a Q_OBJECT macro.

producer.h

Code:

---

class Producer : public QThread
{
    Q_OBJECT
public:
    void run();
};

---

producer.cpp

Code:

---

void Producer::run()
{
    cout<<"Bye!"<<endl;
}

---

This ensures that moc gets run as required. Notice that corresponding files must be listed in .pro file and you must always re-run qmake after adding Q_OBJECT macro to any class. Notice also that you need Q_OBJECT only if you declare custom signals and/or slots, or use other meta object stuff.

Now, if you want to put everything in a .cpp file (which is useful for minimal examples etc.) you must include the moc file by hand (and once again re-run qmake so that qmake detects it and creates proper make rules for moc):

main.cpp

Code:

---

class Producer : public QThread
{
    Q_OBJECT
public:
    void run()
    {
        cout<<"Bye!"<<endl;
    }
};
 
int main(int argc, char *argv[])
{
    ...
}
 
#include "main.moc"

---

For more details about moc, please consult moc docs.

Quote:

---

Originally Posted by panos

By the way I would like to ask you how can I write something in the console (like when using the "cout" in C++)

---

On windows, you must add

Quote:

---

CONFIG += console

---

to the .pro file (and rebuild the project) to be able to output to console. Oh, and there is qDebug() which is aware of most Qt data types, see debugging techniques for more details.

Thank you very much!
That worked for me!