class DirectInput {
private:
　　int private_member;
protected:
　　void EnumJoystick();
　　static BOOL CALLBACK EnumJoystickCallback(LPDIDEVICEINSTANCE lpddi, LPVOID pvRef);
};

void DirectInput::EnumJoystick() {
　　if (FAILED(m_DI->EnumDevices(DI8DEVCLASS_GAMECTRL, (LPDIENUMDEVICESCALLBACK)EnumJoystickCallback, this, DIEDFL_ATTACHEDONLY))))
}

BOOL CALLBACK DirectInput::EnumJoystickCallback(LPDIDEVICEINSTANCE lpddi, LPVOID pvRef) {
　　((DirectInput *)pvRef)->private_member = 0;
　　return DIENUM_STOP;
}