error: undefined reference to 'vtable for

A.h:

class ProcessCB

{
public:
virtual ~ProcessCB(){};
virtual void onCallback(int result) = 0;

};

B.h:

class DefogDH: public ProcessCB {
public:
virtual void onCallback(int result);
};

B.cpp:

    DefogDH* mDefogDH;
   mDefogDH = new DefogDH();

编译报错：

error: undefined reference to 'vtable for

解决方法：

添加：

void PrivateDefog::DefogDH::onCallback(int result){}