offsetof的意义

#define AFX_NOVTABLE
//#define AFX_NOVTABLE __declspec(novtable)

class AFX_NOVTABLE CNoTrackObject
{
public:
    void* PASCAL operator new(size_t nSize);
    void PASCAL operator delete(void*);
    
    virtual ~CNoTrackObject() { }
};

void* PASCAL CNoTrackObject::operator new(size_t nSize)
{
    void* p = ::LocalAlloc(LPTR, nSize);
//     if (p == NULL)
//         AfxThrowMemoryException();
    return p;
}

void PASCAL CNoTrackObject::operator delete(void* p)
{
    if (p != NULL)
        ::LocalFree(p);
}

struct CThreadData : public CNoTrackObject
{
    CThreadData* pNext; // required to be member of CSimpleList
    int nCount;         // current size of pData
    LPVOID* pData;      // actual thread local data (indexed by nSlot)
};

struct CThreadData2
{
    CThreadData2* pNext;
    int nCount;
    LPVOID* pData;
};


int main(int argc, char* argv[])
{
    int nOffset = offsetof(CThreadData, pNext);
    int nOffset2 = offsetof(CThreadData2, pNext);

    return 0;
}