Private virtual

#include <iostream>

class Base {
    public:
        void doIt() {
            std::cout << "Base::doIt()" << std::endl;
            virtIt();
        }
    private:
        virtual void virtIt() = 0;
};

class Der: public Base {
    public:
        void tryThis() {
            std::cout << "Der::tryThis()" << std::endl;
            virtIt();
        }
    private:
        void virtIt() {
            std::cout << "Der::virtIt()" << std::endl;
        }
};

int main() {
    Der d;
    d.doIt();
    d.tryThis();
    return 0;
}