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Access to Virtual Functions

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The access control applied to virtual functions is determined by the type used to make the function call. Overriding declarations of the function do not affect the access control for a given type. For example:

class VFuncBase
{
public:
    virtual int GetState() { return _state; }
protected:
    int _state;
};

class VFuncDerived : public VFuncBase
{
private:
    int GetState() { return _state; }
};

...

VFuncDerived vfd;             // Object of derived type.
VFuncBase *pvfb = &vfd;       // Pointer to base type.
VFuncDerived *pvfd = &vfd;    // Pointer to derived type.
int State;

State = pvfb->GetState();     // GetState is public.
State = pvfd->GetState();     // GetState is private; error.

In the preceding example, calling the virtual function GetState using a pointer to type VFuncBase calls VFuncDerived::GetState, and GetState is treated as public. However, calling GetState using a pointer to type VFuncDerived is an access-control violation because GetState is declared private in class VFuncDerived.

! WARNING   The virtual function GetState can be called using a pointer to the base class VFuncBase. This does not mean that the function called is the base-class version of that function.