Access to Virtual Functions
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:
// access_to_virtual_functions.cpp
class VFuncBase
{
public:
virtual int GetState() { return _state; }
protected:
int _state;
};
class VFuncDerived : public VFuncBase
{
private:
int GetState() { return _state; }
};
int main()
{
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(); // C2248 error expected; GetState is private;
}
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.
警告
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.