Hi,

You can use boost::bind to add arguments to your callbacks such that you can know from which subscription a specific callback came.  For an example see the ros_tutorial on listener_with_userdata https://code.ros.org/trac/ros/browser/stacks/ros_tutorials/trunk/roscpp_tutorials/listener_with_userdata/listener_with_userdata.cpp

Tully

On Mon, Feb 7, 2011 at 12:20 PM, kadir <kadirfu@gmail.com> wrote:

Hi folks,

Let's say I have two nodes; one is publishing "n" different messages to "n"
different topics and the other one subscribes to all of the topics. But I
know that -more or less- the publisher node publishes new messages to the
topics consecutively(I mean first to topic a, then to topic b, then c, and
so on). All the messages being published have the same sequence_cnt.

What I want from the listener node is that it polls these topics and read
the new incoming message in each topic one by one to ensure that received
messages have the same sequence_cnt to avoid checking each message if they
have same seq_cnt, or synching them.

Do you think it is necessary to create "n" number of callback functions to
make the listener node grab updated data in an event-based fashion or is it
better to use request-response based communication between these nodes? Does
ROS services corresponds to a polling operation?

I'm just wondering how would you approach in this case -of course it depends
on the application, but any suggestions-?
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Tully Foote
Systems Engineer
Willow Garage, Inc.
tfoote@willowgarage.com
(650) 475-2827