Question

I have a weird error in my C++ classes at the moment. I have an ActiveX wrapper class (as part of wxWidgets) that i added a new virtual function to. I have another class that inherits from the ActiveX one (wxIEHtmlWin) however the ActiveX class always calls its own function instead of the one in wxIEHtmlWin which overrides it.

I can’t work out why this is happening. I made the function pure virtual and now the program crashes when it does the function call but compiles fine otherwise. Is there any way to disable virtual functions or have I found a bug in Visual Studio?

ActiveX class

protected: virtual FrameSite* getNewFrameSite()=0; 

wxIEHtmlWin class

class wxIEHtmlWin : public wxActiveX { protected:     FrameSite* getNewFrameSite(); }  FrameSite* wxIEHtmlWin::getNewFrameSite() {     return new gcFrameSite(this); } 

Edit: I’ve added another test function (returns an int) and still screws up.

Link to code in question: http://lodle.net/public/iebrowser.rar

Edit:

OK thanks to the answer below i got it to work. What i did was create the activex class in two parts (like suggested) however in wxIEHtmlWin i called the second part in the constructor code. Like so:

wxIEHtmlWin::wxIEHtmlWin(wxWindow * parent, wxWindowID id, const wxPoint& pos,const wxSize& size,long style, const wxString& name) : wxActiveX() {     wxActiveX::Create(parent, PROGID, id, pos, size, style, name);     SetupBrowser(); } 

Now i know why wxWidgets supports two part construction.

Answer 1

You are calling the virtual method from within the class’s constructor (via another call). This will call the method on the current class as the sub-class hasn’t been constructed yet. The fix is to use an init() method and call it after constructing the class.

i.e something like this:

class wxActivex {   wxActivex() {}   virtual void init() {     getNewFrame();   } };    // in the code that uses these classes:   wxActivex *activex = new IEHtmlFrame();   activex->init();