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I am trying to get a list of all topics (both published and subscribed) to see whether a topic is available or not.
Using method I can get list of all advertised topics but not the ones that are only subscribed to and don't have a publishers yet.
Is there a decent way to do it within a cpp node?
You can find out how many nodes are publishing and listening to a topic.
You'll need to create a subscriber to the topic, wait for a second or so for any publishers to connect then use the getNumPublishers() method to check that it's being published.
You can do the same trick with a subscriber and it's getNumSubscribers() method.
I don't know if there is a more direct approach, but I know this way will work.
You can use the ros_type_introspection package to create generic subscribers. It's a bit trickier for publishers. Why don't you want to make publishers and subscribers in your code? They would only be needed briefly to get the information you want.
Asked: 2019-08-30 05:34:57 -0500
Seen: 830 times
Last updated: Aug 30 '19
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The Master API has a method called
getSystemState(..). That would return all publishers and subscribers. From that you should be able to derive the information you are looking for.that's a python API, I would prefer something in cpp so I can easily add it to my node, but might make a generic node out of it, thanks
That page documents the API, which is an XML-RPC API. It's language agnostic.
You can use any library capable of invoking XML-RPC methods. In ROS 1, xmlrpcpp is used.
There may already be some code that implements this, but I can't link you to a specific example.