About listener.cpp tutorial. disobey cpp grammar?

edit

 #include "ros/ros.h"
#include "std_msgs/String.h"

void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

    int main(int argc, char **argv)
    {
      ros::init(argc, argv, "listener");

      ros::NodeHandle n;

      ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);

      ros::spin(); 

      return 0;
    }

there is no actual parameter passing to chatterCallback function?