Yes, every class that inherits from QObject – regardless wheter direct or in an inheritance path – must include the Q_OBJECT macro in the private section of the class definition.

when I do place the Q_OBJECT macro, I get an error indicating ¨error: undefined reference to `vtable for cls_B¨… what does this error imply?

Did you re-run qmake? It must pick up the new header and include some additional build steps for a QObject class with the Q_OBJECT macro in it. You also must add the header file to the HEADERS variable in the .pro file.

Also, if you declare and implement classes in the same file filename, you’ll need a

hi i think i works for me but
try to put the implement of the class constructor and other function in a cpp file not within the class
and put Q_OBJECT for the two classes