ROS Publisher and Subscriber

ROS publisher & subscriber

I just note for the important line of code from the ROS wiki.
The code below is used to define publisher in ROS system.

Publisher

ros::NodeHandle n;
ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 100);

chatter_put is Publisher object.
n.advertise("topicname",numberofMessage);

To publish message, we can use the following code:

msg.data = datatobepublish; // assign message for publish
chatter_put.publish(msg); // Call publish method of Publisher class

Subscriber

A subscriber must define callback function that will get called when a new message have arrived on the chatter topic.

Define callback function:

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

Define nodeHandle and call subscribe function

ros::NodeHandle n;
ros::Subscriber chatter_sub = n.subscribe("chatter", 100, chatterCallback);

The line above means that

nodeObject.subscribe("publisherTopicName",numberOfMsgInQue,callbackFunctionName);


Reference: http://www.ros.org/wiki/ROS/Tutorials/WritingPublisherSubscriber%28c%2B%2B%29