Attempting to publish and subscribe to individual portions of an advertised topic

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Thanks for that, makokal. However, I am still encountering problems in accessing the data. Let me explain my problem more clearly.

I have a certain robot which is producing data under several topics, one of which includes this /XXX/Data. Now /XXX/Data has several members in its definition, for example acc_x, acc_y, acc_z, angle_roll, angle_pitch, angle_yaw etc. What I'm trying to do, is to write a listener that will extract specifically acc_x, which is of int16 type. To access this acc_x, I have tried including the header file, e.g. "information.h" that specifically contains the structure that is publishing /XXX/Data, and this structure contains acc_x, acc_y etc. Then, in my listener, I tried to create an object of the type of the structure I mentioned above. But it's not working.

Let me be even more specific. See this link 'Writing a simple Publisher and Subscriber in C++': http://www.ros.org/wiki/ROS/Tutorials/WritingPublisherSubscriber%28c%2B%2B%29

Now this is part of the code written for the tutorial on how to write a Publisher.

while (ros::ok())

{ /** * This is a message object. You stuff it with data, and then publish it. */ std_msgs::String msg;

std::stringstream ss;
ss << "hello world " << count;
msg.data = ss.str();

ROS_INFO("%s", msg.data.c_str());

Notice how a string object 'ss' is created, and "Hello World" is assigned to 'ss'. Now what I want is, instead of assigning 'Hello World' to this string object, I want to assign information that is being published by the topic /XXX/DATA

I hope my question is clear.