How to propagate changes from one class to another in C ?-CodePudding

Having this code:

#include <iostream>
#include <vector>
#include <string>

class A{
public:
    A(std::string const& name) : name(name) {}
    std::string const& getName() const {
        return name;
    }
private:
    std::string name;
};

class B{
public:
    void add(A const& a){
        //vec.emplace_back(a) does not help either
        vec.push_back(a);
    }
    std::vector<A> const& getVec() const {
        return vec;
    }
private:
    std::vector<A> vec;
};

class C{
public:
    C(B const& b, A const& a) : a(a), b(b) {}
    A const& getA() const {
        return a;
    }
    B& getB() {
        return b;
    }

private:
    A a;
    B b;
};

class D{
public:
    C& add(C& c){
        A const& a = c.getA();
        B& b = c.getB();

        b.add(a);
        vec.push_back(c);
        return c;
    }
private:
    std::vector<C> vec;
};

int main(){
    A a1{"first"};
    A a2{"second"};

    B b;

    C c1{b, a1};
    C c2{b, a2};

    D d;
    d.add(c1);
    d.add(c2);

    for(A const& a : b.getVec()){
        std::cout << a.getName() << ' ';
    }
}

There is no output from the program, but

I would expect output:

first second

Where the B class is holding the vector, and D is trying to modify it (c.getB().add()) via class C. It's just simple example (encountered in a school project), but I wanted to know by this example the flow of changes between classes.

CodePudding user response：

C's members are not reference types. Both c1 and c2 are storing copies of the constructor arguments.

d.add(c1);
d.add(c2);

doesn't affect b in main, only the members of c1 and c2, which are copies of the original b, a1 and a2 in main.