C ++调用另一个子类的公共方法

Question

is there an elegant version to access a method of an another child class? For a better understanding please watch my c++ code.

Its really important that external functions / classes can access furthermore the addchild() method!!

C++ Code:

class User {
    protected:
        int userid;
        std::string givenname;
        std::string surname;
        std::string birthday;
};

class Child: public User {
    public:
        int addchild() {
            //Doing the required stuff to add a new child
        }
};

class Parent: public User {
    public:
        int addparent() {
            //Here we have to add a new child among others
            addchild();
        }
};


int main() {
    Child child1;
    child1.addchild();

    Parent parent1;
    parent1.addparent();
}

UML:

Answer 1

You could use CRTP for your parent class: https://www.fluentcpp.com/2017/05/12/curiously-recurring-template-pattern/ (more general: https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern )

Because it got no attention I changed the original code sample so that it is using CRTP:

#include <string>

class User {
    protected:
        int userid;
        std::string givenname;
        std::string surname;
        std::string birthday;
};

class Child: public User {
    public:
        int addchild() {
            //Doing the required stuff to add a new child
        }
};

template <typename BASE>
class Parent: public BASE {
    public:
        int addparent() {
            //Here we have to add a new child among others
            this->addchild();
        }
};


int main() {
    Child child1;
    child1.addchild();

    Parent<Child> parent1;
    parent1.addparent();
}

Answer 2

It cannot be done in the current design. You either need to have an object of Child inside Parent class or pass an object of Child as a argument to addparent() function.

class Parent: public User {
    private:
        Child child; //Have an instance of Child class here to be able 
                     //to use addchild() in this class 
    public:            
        int addparent() {
           //Here we have to add a new child among others
           child.addchild();
        }
};

Or passing a argument like this:

class Parent: public User {
    private:
        Child child; //Have an instance of Child class here to be able 
                     //to use addchild() in this class 
    public:            
        int addparent(Child & child) {
             child.addchild(); 
    }
};

I am not sure about how you are structuring your entire class and what you intend to do with them.

Explore design patterns at https://www.tutorialspoint.com/design_pattern/design_pattern_overview.htm

Also, look up the concept of composition in C++ at http://www.learncpp.com/cpp-tutorial/102-composition/

This might help you come up with a better design.