Member Avatar for clutchkiller

When I declare an event table in a class a.k.a DECLARE_EVENT_TABLE(); then try to compile, i always get this error:
[Linker Error] undefined reference to `vtable for Utility' (utility being my class) What does this mean and how do I fix it? All research on this has turned up dead ends =(. Thanks

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Short answer and context

The linker error "undefined reference to vtable for Utility" happens because the DECLARE_EVENT_TABLE() macro adds event-table-related symbols (effectively the class has extra non-inline virtual machinery) that must be defined in one translation unit. If the corresponding event-table definition or the object file that contains it is missing, the linker complains. and pointed you to the right place: you need the event-table implementation (or to remove the macro if you don't use it). (tool.oschina.net)

Why this error appears (brief)

Compilers normally emit a class's vtable in the translation unit that defines the class's first non-inline "key" virtual function. If that definition is missing (or the .o is not linked) the vtable is unresolved and you get the message you saw. A common practical cause in wxWidgets is using DECLARE_EVENT_TABLE in the header without providing the matching implementation in a compiled .cpp. Another common cause is a missing out‑of‑line definition for a virtual destructor — adding a trivial destructor implementation often exposes the real missing symbol. (stackoverflow.com)

Practical fixes and modern alternative

  • If you want static event tables: make sure the event table implementation is present in exactly one .cpp (use the matching macros and the correct class name) and that .cpp is compiled and linked.

  • If you prefer a cleaner, modern approach, replace the static macros with Bind (or Connect) calls in the constructor; Bind avoids the need for the DECLARE/BEGIN/END macros. Example pattern:

    // in Utility constructor (after creating the button)
Bind(wxEVT_BUTTON, &Utility::OnSend, this, btn_send);

void Utility::OnSend(wxCommandEvent& evt)
{
    // handle send
}

    The wxWidgets project itself recommends using Bind/Connect in new code. (wxwidgets.org)

Quick troubleshooting checklist

  • Confirm the .cpp that contains the event-table implementation is part of the build.
  • Ensure the class name in the implementation matches the header exactly.
  • If the error persists, add an empty out‑of‑line destructor implementation (e.g. Utility::~Utility() {}) to force emission of the vtable and reveal any other missing definitions.
  • Do a full clean rebuild after changes.

Relevant posts: was right to look at the event-table macro, and correctly noted the implementation must exist — that change is exactly what resolves the vtable link error in this scenario. (tool.oschina.net)

Recommended Answers

All 5 Replies

Member Avatar for nucleon

Presumably something needs to be declared as virtual in Utility. Without code, it's hard to say exactly what.

Member Avatar for clutchkiller

Here is my Header file:

#ifndef UTILITY_H
#define UTILITY_H

#include <wx/wx.h>

enum
{
    btn_send = 100,
    btn_main,
    im_box_rec,
    im_box_ent,
    im_box_con,
    im_box_addip,
    im_combo
};

class Utility : public wxFrame
{
    public:
        Utility(const wxString &title, const wxPoint &pos, const wxSize &size);

    private:
       DECLARE_EVENT_TABLE();

};

#endif

And here is my .cpp:

#include "Utility.h"
#include <wx/wx.h>

Utility::Utility(const wxString &title, const wxPoint &pos, const wxSize &size) : wxFrame(NULL, -1, title, pos, size)
{
    /////////////////////////MENU////////////////////////////////


    wxMenu *util_list = new wxMenu;

    util_list -> Append(-1, _T("&"));
    util_list -> Append(-1, _T("&"));
    util_list -> Append(-1, _T("&"));
    util_list -> AppendSeparator();
    util_list -> Append(-1, _T("&About"));
    util_list -> AppendSeparator();
    util_list -> Append(-1, _T("E&xit"));

    wxMenuBar *MENU = new wxMenuBar;

    MENU -> Append(util_list, _T("&Utilities"));

    SetMenuBar(MENU);

    ///////////////////////PANELS/////////////////////////////

    wxPanel *mainPanel = new wxPanel(this, -1, wxPoint(0,0), wxSize(1000,600), wxBORDER_STATIC);
    wxPanel *sideWin = new wxPanel(mainPanel, -1, wxPoint(800,0), wxSize(200,500), wxBORDER_STATIC);

    wxTextCtrl *imBox_rec = new wxTextCtrl(mainPanel, im_box_rec, _T("Recieve text..."), wxPoint(0, 50), wxSize(400,200));
    wxTextCtrl *imBox_ent = new wxTextCtrl(mainPanel, im_box_ent, _T("Enter text..."), wxPoint(0,300), wxSize(400,100));

    wxComboBox *imCombo = new wxComboBox(mainPanel, im_combo, _T("IP List"), wxPoint(100, 25), wxSize(152, 100));

    wxButton *saveTran = new wxButton(mainPanel, -1, _T("Save Transcript"), wxPoint(0, 252), wxSize(400, 20));
    wxButton *addipButton = new wxButton(mainPanel, im_box_addip, _T("Add IP"), wxPoint(100,0), wxSize(150,25));
    wxButton *conButton = new wxButton(mainPanel, im_box_con, _T("Connect to IP"), wxPoint(0,0), wxSize(100,50));
    wxButton *mainButton = new wxButton(mainPanel, btn_main, _T("entr"), wxPoint(300,60), wxSize(100,100));
    wxButton *sendButton = new wxButton(mainPanel, btn_send, _T("Send"), wxPoint(0,400), wxSize(400,50));

    wxBoxSizer *mainSizer = new wxBoxSizer(wxVERTICAL);

    mainSizer -> Add(imBox_rec, 0, wxCENTER, 0);
    mainSizer -> Add(imBox_ent, 0, wxCENTER, 0);
    mainSizer -> Add(mainButton, 0, wxCENTER, 0);
    mainSizer -> Add(sendButton, 0, wxCENTER, 0);

    //mainPanel -> SetAutoLayout(true);
    //mainPanel -> SetSizer(mainSizer);

}
Member Avatar for nucleon

I don't know wxWidgets, so I'm just guessing here. Try making DECLARE_EVENT_TABLE(); public instead of private.

If that doesn't work, try putting this in your code:

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
END_EVENT_TABLE()

Or, if you aren't goint to have any events, remove DECLARE_EVENT_TABLE(); altogether.

Member Avatar for Nick Evan

Try making DECLARE_EVENT_TABLE(); public instead of private.

Nah, don't do that, it's good as is. However this:

try putting this in your code:

BEGIN_EVENT_TABLE(MyFrame, wxFrame)
END_EVENT_TABLE()

Or, if you aren't goint to have any events, remove DECLARE_EVENT_TABLE(); altogether.

is indeed the answer to your problem.

Member Avatar for clutchkiller

Thanks, that solved it =D

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