[ROS2] Is it possible to listen and subscribe to newly created topic in C++?

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How about discovering new topics that are created during run time?

Sure. You can get the list of topics and their types that have been discovered at any time from the API.

See http://docs.ros2.org/latest/api/rclcp... (search for “introspecting the ROS graph”)

But if type is not known in advance, how can we create the subscription? As the message type is needed at the time of subscription creation.

Use the api linked above in the comment to get the list of topics and their types before you call create subscription. Or know through some other means what type you're expecting. The callback must match the type too so you're going to need to have an idea about the type beforehand anyway.

Got it. Thanks!