Question

I’ve messed up something.
Here is the code:

#include <iostream>

class connection_c {
  private:
    std::string data_;
    void (*saveCallBack_)();
  public:
    connection_c(std::string &data) : data_(data) { std::cout << "ctor: " << __FUNCTION__ << ":" << data_ << std::endl;}
    void registerCallBack(void(*cb)()) { saveCallBack_ = cb; }
};

class inst_c {
  private:
    static int id;
    connection_c conn;
    static void cb() { std::cout << __FUNCTION__ << " id = " <<  id << std::endl; } 
  public:
    inst_c(connection_c &c, int a) : conn(c),  id(a)  { 
      std::cout << "ctor: " << __FUNCTION__ << " " << id << std::endl;
      conn.registerCallBack(&cb); 
    }
};

class group_inst_c {
  private:
    connection_c conn;
    inst_c i,j,k;
  public:
    group_inst_c(std::string data) : conn(data), i(conn,1), j(conn,2), k(conn,3) {} 
};


int main() {
  group_inst_c gi("asdf");
  return 0;
}

What I want to achieve 😉

• create a group of instances (group_inst_c)
• it should initialize single connection for the group (connection_c)
• each instance (inst_c) should use this connection (it will be serialized)
• .. in addition each instance should register separate callback

For sure I’ve messed up with cloning, but I guess probably not only.
Can someone help me solve this puzzle? thx.

Answer 1

Your code creates a copy of your connection object for each instance. The original connection object is then only accessible by your group_inst_c. Is this what you want? If not, you need to change:

class inst_c {
  private:
    static int id;
    connection_c& conn; // <-- Needs to be a reference.

in addition each instance should register separate callback

I’m not sure what you mean here. Are the callbacks supposed to be member functions? Then you need to use a “pointer to member function” (the ::*, .*, and ->* operators). If the callbacks are supposed to be regular functions, you should be okay with your current code. You’ll just need to add this to class connection_c:

void doCallback(void) { (*saveCallBack_)(); }