C / C++ / MFC

class Base
{
protected:
   int x;
};

class Derived : public Base
{
public:
   void Function()
   {
      Base b;
      b.x = 10;
   }
};

class Base
{
protected:
   int x;
};

class DerivedBase : public Base
{
protected:
   double x;
};

class Derived2 : public DerivedBase
{
public:
   void Function()
   {
      Base::x = 10;
      DerivedBase::x = 10.0;
   }
};

class Base
{
protected:
   int x;
};

class Derived : public Base
{
public:
   void Function()
   {
      Base * pBase = new Base;
      pBase->x = 10; // <<A>> Obviously incorrect.
      delete pBase;

      // Just because we use the "this" pointer in the next line of code, doesn't mean we should be able to access the base member.
      // We have taken away our access to the Base protected member, because we have told the compiler that we are now working with
      // a "Base" pointer, instead of a "Derived" pointer.
      // The only "Base" members we have access to, are from the "this" pointer, and once we cast that to a different type of object,
      // in this case "Base", we lose access to those members.
      pBase = (Base*)this;
      pBase->x = 10; // Just as incorrect as the line marked <<A>>
   }
};