What is the best way to look up roscpp apis

Lately, I have been trying to look up the API calls every time I come across a new API call in a demo or example (or just forgot the signature of one I have come across before.)

Is Welcome to the documentation for rclcpp — rclcpp 16.0.5 documentation the best resource? That page seems a bit hard to search and browse…

Instead I typically just google for something like `ROS2 roscpp api create_client’ and see where it takes me.

Is there a better way of doing this?

On a related note:

On a documentation page such as


What does the [in] behind all the parameter names mean?


  • node_name – [in] Name of the node.
  • namespace_ – [in] Namespace of the node.
  • options – [in] Additional options to control creation of the node.



Yes, if you want to look for a list of the client library, that’s where I would check since it comes directly from the code. You can check the actual ROS 2 page though:


I noticed that the humble version is not there but I would always check for the latest version in case something has changed.

As for the [in] in the explanation, it means they are input parameters I believe, which means that you have to provide values to those parameters when you use them.

Thanks for the reply,
I researched a bit more and it seems that everything didn’t completely work with the auto-generated API documentation for a couple of releases.

Things seem to have been straightened out in the Iron release. As of today, I think, the preferred place to find the API documentation is at:

Index of /en/iron/p It is for Iron, but little has changed since humble. The most important part to me is that it is pretty complete.

I am not sure, but it appears that OSRF is trying to shift recent ROS2 release documentation back to docs.ros.org. It seems unnecessarily confusing to me. Probably but part of their long-term branding.

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