subscribing a node to a topic problem

edit

Hello!,

I'm working with arduino and ros and i'm reading a value of a sensor and, that value is publish in a topic, i'm trying to create a Subscriber who heard the message that the topic is sending, actully i wrote a .cpp file:

#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", 500, chatterCallback);
  ros::spin();

  return 0;
}

but the problem is that the value that i'm reading from the topic of arduino is a float32 value and my listener reads only string values, i try to change the code but when i do make it gives me an error.... If i change the value that the topic gives to me to an string value the listener works ok.

someone could help me???