Is it possible to send a constructor into ros node subscribe?

Question

I am trying to pass a class constructor into ros subscribe function. Is it possible to have the constructor called when the topic is published to?

      class udpMsg
    {
        public:
        std::string udp;
        size_t posOfDelim;
        std::string token;
        udpMsg(){}; 
        udpMsg(const std_msgs::String::ConstPtr& msg)
        {
        udp = std::string(msg->data);
        posOfDelim = udp.find(delimiter);
        token = udp.substr(0, posOfDelim);
        }
}

    int main(int argc, char **argv)
    {



    ros::init(argc, argv, "listener");
    ros::NodeHandle n;
 A_pub = n.advertise<udpubsub::msgA>("Amsg", 1000);
 B_pub = n.advertise<udpubsub::msgB>("Bmsg", 1000);
udpMsg mainMsg;
ros::Subscriber sub = n.subscribe("chatter", 1000,mainMsg.udpMsg)
 ros::spin();

Answer 1

No, you cannot pass a constructor as a function. udpMsg is the name of the class itself, not the name of a function.

You can write a separate "factory function" that creates objects, and pass that to subscribe, like

udpMsg create_message()
{ return udpMsg(); }