Call controller function outer folder

Your error message provides a clue to the problem ... you are linking to c_main inside the cf_folder, where your c_inner_ctrl is.
You should be linking one folder higher.

You have misread/misunderstood the error message, and are drawing an inappropriate conclusion.

If you set up virtual hosting, mapping a local domain to your htdocs/my_project, then your link references could be absolute, i.e. "/cf_folder/c_inner_ctrl" and "/c_main".