Publish message to a topic from Callback function

edit

Hi Guys,

This question had been already asked, however I am looking for ways without using C++ classes.

Below is my problem statement.

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

void chatter_callback(const std_msgs::String::ConstPtr& msg)
{
ROS_INFO("Received the message : [%s]", msg->data.c_str());        
    // Here I need to convert this message other datatypes and publish it to topic "X"
    // Can we have while(ros::ok()) here in this callback function

    while(ros::ok())
    {
          chatter_pub.publish(new_msg);
    }
}

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

ros::init(argc, argv, "listener_v1");
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("chatter", 1000, chatter_callback);
ros::Publisher chatter_pub = n.advertise<other data type>("chatter", 1000);
    ros::Rate loop_rate(10);
ros::spin();    

return 0;
}

Also please note that Publisher is defined in main and being used in callback function. I am afraid this is not the right way to use it.

Kindly let me know if the question is not clear and needs more information.

Updating the code :

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

void chatter_callback(const std_msgs::String::ConstPtr& msg)
{
ROS_INFO("Received the message : [%d]", msg->data.c_str());        
   // Convert the msg to the datatype we wanted to 

    chatter_pub.publish(new_msg);

}

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

ros::init(argc, argv, "listener_v1");
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("chatter", 1000, chatter_callback);
ros::Publisher chatter_pub = n.advertise<other data type>("chatter", 1000);
    ros::Rate loop_rate(10);

    while(ros::ok()
   {
        ros::spinOnce();
   }    

return 0;
}

Thank you, KK