Undefined reference to vtable?

Question

So, I'm getting the infamously horrible > undefined reference to 'vtable... error for the following code (The class in question is CGameModule.) and I cannot for the life of me understand what the problem is. At first, I thought it was related to forgetting to give a virtual function a body, but as far as I understand, everything is all here. The inheritance chain is a little long, but here is the related source code. I'm not sure what other information I should provide. Note: The constructor is where this error is happening, it'd seem. My code: class CGameModule : public CDasherModule { public: CGameModule(Dasher::CEventHandler *pEventHandler, CSettingsStore *pSettingsStore, CDasherInterfaceBase *pInterface, ModuleID_t iID, const char *szName) : CDasherModule(pEventHandler, pSettingsStore, iID, 0, szName) { g_pLogger->Log("Inside game module constructor");    m_pInterface = pInterface; } virtual ~CGameModule() {}; std::string GetTypedTarget(); std::string GetUntypedTarget(); bool DecorateView(CDasherView *pView) {   //g_pLogger->Log("Decorating the view");   return false; } void SetDasherModel(CDasherModel *pModel) { m_pModel = pModel; } virtual void HandleEvent(Dasher::CEvent *pEvent); private: CDasherNode *pLastTypedNode; CDasherNode *pNextTargetNode;   std::string m_sTargetString; size_t m_stCurrentStringPos; CDasherModel *m_pModel; CDasherInterfaceBase *m_pInterface; }; Inherits from... class CDasherModule; typedef std::vector<CDasherModule*>::size_type ModuleID_t; /// \\ingroup Core /// @{ class CDasherModule : public Dasher::CDasherComponent { public: CDasherModule(Dasher::CEventHandler * pEventHandler, CSettingsStore * pSettingsStore, ModuleID_t iID, int iType, const char *szName); virtual ModuleID_t GetID(); virtual void SetID(ModuleID_t); virtual int GetType(); virtual const char *GetName(); virtual bool GetSettings(SModuleSettings **pSettings, int *iCount) { return false; }; private: ModuleID_t m_iID; int m_iType; const char *m_szName; }; Which inherits from.... namespace Dasher { class CEvent; class CEventHandler; class CDasherComponent; }; /// \\ingroup Core /// @{ class Dasher::CDasherComponent { public: CDasherComponent(Dasher::CEventHandler* pEventHandler, CSettingsStore* pSettingsStore); virtual ~CDasherComponent(); void InsertEvent(Dasher::CEvent * pEvent); virtual void HandleEvent(Dasher::CEvent * pEvent) {}; bool GetBoolParameter(int iParameter) const; void SetBoolParameter(int iParameter, bool bValue) const; long GetLongParameter(int iParameter) const; void SetLongParameter(int iParameter, long lValue) const; std::string GetStringParameter(int iParameter) const; void SetStringParameter(int iParameter, const std::string & sValue) const; ParameterType GetParameterType(int iParameter) const; std::string GetParameterName(int iParameter) const; protected: Dasher::CEventHandler *m_pEventHandler; CSettingsStore *m_pSettingsStore; }; /// @} #endif

Answer 1

Based on only the code from the question, I see CGameModule missing definitions for the following virtual methods:

1. CDasherModule::GetID
2. CDasherModule::SetID
3. CDasherModule::GetType
4. CDasherModule::GetName
5. CDasherComponent::HandleEvent (declared but not defined in CGameModule)

Also note that the virtual keyword is not required on virtual method overrides, and in fact is generally discouraged because it could lead to accidental creation of a new virtual function if the signatures don't perfectly match. Modern C++ (since C++11) prefers use of the override keyword to make this relationship explicit. https://en.cppreference.com/w/cpp/language/override