How to call ros functions from an external .cpp or .c file?

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Hello rama_bhuyan,

You can have multiples CATKIN_WORKSPACES in your machine, with any name or inside of any directory. However, you won't be able to access the catkin structure if you don't have at least a directory named "src" as something like this: /my_catkin_workspace_in_some_place/src. In your terminal inside of /my_catkin_workspace_in_some_place/ you'll be able to have access to all ROS libraries using a CMakeLists.txt file and a catkin_make command, this tutorial has some steps to do it.

So if you must build projects outside of a CATKIN_WORKSPACES you'll have to do a lot of code in CMakeLists.txt to find all ROS specific environment variables and setup all libs to your code as the catkin tool already does.

My advice is that you consider using a catkin structure even if your circumstances don't allow it, because in this way you won't build the wheel again as the ROS principles say.

I hope it may help you.

Best regards.