Undefined reference to vtable… Q_OBJECT macro [duplicate]

Answer 1

I had same issue when i decided to add Q_OBJECT into my header file.

• First try run qmake manually.

• If not resolved, so delete build folder and build project again

• If building all of the project is a heavy task, so try following steps:

  1. Add a new temp class with QObject as its base class
  2. Double check your header and source file for any mistake using new temp class
  3. Build your project. It should built successfully
  4. Remove your temp class completely (.h and .cpp file and relative lines on .pro file)

Good luck :)

Answer 2

Q_OBJECT is used by the MOC system to produce the code you need for the signals. My best guess would be that you are not included the MOC generated files in your project (the CPP files which it generates).

How you do this greatly depends on your build system (CMake, QMake, AUtomake, MSVC) but you should refer to the tutorial with QMake first.

That is, the undefined reference to vtable is the error I sometimes get when I forget to update my Cmake files and have a Q_OBJECT.

Also, your ctor for MyApp is wrong, the signature must be:

MyApp( int & argc, char** argv );

The & is important should you ever use command-line parameters.