How can I convert a list to string so I can call insert or message with it? I need to display c-offsets-alist but I got Wrong type argument: char-or-string-p for insert or Wrong type argument: stringp for message.
I am not sure of what you are trying to achieve, but format converts "stuff" to strings. For instance:
(format "%s" your-list)
will return a representation of your list. message uses format internally, so
(message "%s" your-list)
will print it. Alternatively, use %S instead of %s to print the list in Lisp syntax.