A. Hue A. Hue - 17 days ago 9
C++ Question

Friend class 'has no member named...'

My main frame in a wxWidgets project starts a thread when a button is pushed. I tried to use this example from the documentation of wxThread class, but I get an error compiling it. It says

||=== Build: Debug in WindowsDgpsGUI (compiler: GNU GCC Compiler) ===|
D:\WindowsDgpsGui\NavigationThread.cpp||In destructor 'virtual NavigationThread::~NavigationThread()':|
D:\WindowsDgpsGui\NavigationThread.cpp|82|error: 'class wxFrame' has no member named 'm_navigationThreadCS'|
D:\WindowsDgpsGui\NavigationThread.cpp|84|error: 'class wxFrame' has no member named 'm_navigationThread'|
||=== Build failed: 2 error(s), 0 warning(s) (0 minute(s), 1 second(s)) ===|


Though I can't find what I did wrong...
This is the code of my main frame:

class WindowsDgpsGUIFrame: public wxFrame
{

public:

WindowsDgpsGUIFrame(wxWindow* parent,wxWindowID id = -1);
virtual ~WindowsDgpsGUIFrame();

protected:
wxCriticalSection m_navigationThreadCS; //protects the m_navigationThread pointer

NavigationThread* m_navigationThread;
friend class NavigationThread;
}


This the header of the thread:

class NavigationThread : public wxThread
{

public:
/** \name Constructor */
NavigationThread(wxFrame* parent, navigation_variables usedVariables);

/** \name Destructor */
virtual ~NavigationThread();
private:
virtual ExitCode Entry();
wxFrame* m_parent;
}


and this the destructor of the thread where the error occurs:

NavigationThread::~NavigationThread()
{
wxCriticalSectionLocker enter(m_parent->m_navigationThreadCS);

m_parent->m_navigationThread = NULL;
//dtor
}


Does anyone know what I did wrong? Any help is appreciated.

Answer

As the error says: the class WindowsDgpsGUIFrame owns a member m_navigationThreadCS. The base class wxThread doesn't.

You're trying to access the m_navigationThreadCS member variable through a wxThread pointer

NavigationThread::~NavigationThread()
{
     wxCriticalSectionLocker enter(m_parent->m_navigationThreadCS);
                                   ^^^^^^^^

since m_parent is of type wxFrame*, hence your error.

You can either dynamic_cast your m_parent to the derived class that contains it or just change that type to be WindowsDgpsGUIFrame*