Get topic name in callback?

edit

With rospy, you can pass extra argument to a callback function, I think you could pass the topic_name. See this from the Subscriber Class:

class Subscriber Found at: rospy.topics

class Subscriber(Topic):
"""
Class for registering as a subscriber to a specified topic, where
the messages are of a given type.
"""
def __init__(self, name, data_class, callback=None, callback_args=None, 
    queue_size=None, buff_size=DEFAULT_BUFF_SIZE, tcp_nodelay=False):
    """
    [...]

    @param callback_args: additional arguments to pass to the
      callback. This is useful when you wish to reuse the same
      callback for multiple subscriptions.

I think with roscpp something similar exists

I hope somebody comes along with a more elegant solution, but here's the first (ugly, but easy) thing I thought of:

Write one helper function that contains the body of the callback you now have, and whose parameters are the message and a string identifying the source's topic name.

Write separate callback functions for each topic you subscribe to, each of which calls the helper function, passing along the message and adding the appropriate topic name.

EDIT: (assuming roscpp, based on the tags) If you don't know the topics ahead of time, can you define a class with two methods, one of which is the callback, and another that sets the topic? Then, for each topic that's passed in as a parameter, create an instance of your class, set the topic appropriately, and then set its callback function in the subscribe? Here's a tutorial with using class methods in a callback.

(if rospy, then go with gustavo.velascoh's answer - I originally looked, and couldn't quickly find, an equivalent for roscpp)