class Base
{
public:
    virtual void func(int x, float y, unsigned z) = 0;

    void func(int x)
    {
        cout << "func with x only" << endl;
    }
};

class Derived : public Base
{
public:
    void func(int x, float y, unsigned z)
    {
        cout << "func override" << endl;
    }

};

int main()
{
    Derived d;
    d.func(10);     // <<--------- 'COMPILATION ERROR'
    return 0;
}

error: no matching function for call to 'Derived::func(int&)'
note: candidates are: virtual void Derived::func(int, float, unsigned int)

using Base::func;

int main()
{
    Base && b = Derived();
    b.func(10);
    return 0;
}