C26434 Function xxx hides a non-virtual function

Take this simple code:

void CRestoreSettingsDlg::OnSize(UINT nType, int cx, int cy)
{
    CResizingDialog::OnSize(nType, cx, cy);

    m_gridBackupLog.ExpandLastColumn();
}

Why is it being flagged?

C26434 Function 'CRestoreSettingsDlg::OnSize' hides a non-virtual function 'CRestoreDialogDlg::OnSize'.

As you can see, I call the base class method.

---

Declarations and Definitions

• CRestoreSettingsDlg:

public:
    afx_msg void OnSize(UINT nType, int cx, int cy);

void CRestoreSettingsDlg::OnSize(UINT nType, int cx, int cy)
{
    CResizingDialog::OnSize(nType, cx, cy);

    m_gridBackupLog.ExpandLastColumn();
}

• CResizingDialog:

public:
    afx_msg void OnSize(UINT nType, int cx, int cy);

void CResizingDialog::OnSize(UINT nType, int cx, int cy)
{
    CDialogEx::OnSize(nType, cx, cy);

    Invalidate(TRUE);
}

• The boilerplate base class (afxwin.h) appears to have:

protected:
    afx_msg void OnSize(UINT nType, int cx, int cy);

_AFXWIN_INLINE void CWnd::OnSize(UINT, int, int)
    { Default(); }

---

Inheritance

1. class CRestoreSettingsDlg : public CResizingDialog
2. class CResizingDialog : public CDialogEx

C26434 warning documentation links to C.128 C++ Core Guidelines Rule. It explains that to enforce correct usage of virtual functions, non-virtual function hiding should produce a warning.

However, with MFC message maps, you have to name your message handler as specified in macro, OnSize in this case, and, since message handlers already dispatched by a virtual function (that is hidden in *_MESSAGE_MAP() macros), message handler by themselves don't have to be virtual.

So it may be seen as a false alarm. Or maybe seen as violation of the above mentioned C.128 rule by MFC itself. No surprise - MFC is decades older than these guidelines.

So I guess you can go ahead and suppress it for all afx_msg functions. Maybe redefine afx_msg to include __pragma(warning(suppress(...))), or just have suppression around afx_msg block.

---

Some options for suppression (Godbolt's compiler explorer demo):

#define afx_msg // this is normally defined by MFC

struct base
{
    afx_msg void OnSize(){}
};


struct derived1 : base
{
    afx_msg void OnSize() {} // produces C26434
};

// Suppression by adding some code:

struct derived2 : base
{
#pragma warning(push)
#pragma warning(disable:26434)
    afx_msg void OnSize() {} 
#pragma warning(pop)
};

struct derived3 : base
{
    [[gsl::suppress(c.128)]] afx_msg void OnSize() {}
};


// Suppression by redefining MFC macro -- dirty but less intrusive:

#undef afx_msg
#define afx_msg __pragma(warning(suppress:26434))


struct derived4 : base
{
    afx_msg void OnSize() {} 
};


#undef afx_msg
#define afx_msg [[gsl::suppress(c.128)]]


struct derived5 : base
{
    afx_msg void OnSize() {}
};