Debug: undefined reference to 'vtable for XXXClass'

undefined reference to 'vtable for XXXClass'

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If a class defines virtual methods outside that class, then g++ generates the vtable only in the object file that contains the outside-of-class definition of the virtual method that was declared first: //test.h struct str { virtual void f(); virtual void g(); }; //test1.cpp #include "test.h" void str::f(){} //test2.cpp #include "test.h" void str::g(){} The vtable will be in test1.o, but not in test2.o This is an optimisation g++ implements to avoid having to compile in-class-defined virtual methods that would get pulled in by the vtable. The link error you describe suggests that the definition of a virtual method (str::f in the example above) is missing in your project.