What I want to do is add some comments at the function definition and see it as a description when I hover over the function.
Like this:
This is an outstanding enhancement request in CDT. See:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=281437
https://bugs.eclipse.org/bugs/show_bug.cgi?id=251050
https://bugs.eclipse.org/bugs/show_bug.cgi?id=48215
You could try using the plugin mentioned here:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=48215#c4
The plugin is unsupported, but apparently working. I'm planning on trying to install it myself.