"non-virtual thunk to <method name>", referenced from: Vtable for <classname>in <objectfile.o>

Question

When compiling in debug mode my xcode compilation has these linking errors:

"<method name>", referenced from: 
Vtable for <classname>in <objectfile.o>

"non-virtual thunk to <method name>", referenced from: 
Vtable for <classname>in <objectfile.o>

the strange thing is: It only occurs in one of my build targets (both targets are pretty much the same for that code), plus if these methods are defined in the header file instead of the .cpp it works fine for both targets.

All of those methods are pure virtual. The class where these errors occur inherits from multiple classes but only one of those causes these errors.

Anyone has any idea of what is causing this error?

Answer 1

Got hit by the same issue. It simply happened when we defined a virtual member function (in the .h header file) but not implemented it (in the .cpp file).

In my case, the implementation was inside a #define that prevented to be actually compiled. GCC should have more explicit message for that kind of common mistake such as

virtual function <function> defined but not implemented in class <class>

Answer 2

Encountered this issue when developing with C++/QtCreator, it was caused by including the same file multiple times in the .pro file. Make sure to check each necessary header/source file is only listed under HEADERS += \ and SOURCES += \ once!