how to print special char in emacs lisp

Question

For example, one line of code in my function

 (message "char %c:%d" character count)

will print the counts for each character. For nonprintable chars, such as newline and tab, I want the output looks like:

 \n:4
 \t:6

instead of printing a newline and tab literally. how can I do that?

Answer 1

You can achieve some of this by let-binding certain variables before printing.

`print-escape-newlines' is a variable defined in `C source code'.
Its value is nil

Documentation:
Non-nil means print newlines in strings as `\n'.
Also print formfeeds as `\f'.

There's also:

print-escape-nonascii
   Non-nil means print unibyte non-ASCII chars in strings as \OOO.

print-escape-multibyte
   Non-nil means print multibyte characters in strings as \xXXXX.

These all work with prin1, so you can use the %S code in format. e.g.:

(let ((print-escape-newlines t))
  (format "%S" "new\nline"))

Answer 2

As suggested by @wvxvw

(defun escaped-print (c)
  (if (and (< c ?z)
           (> c ?A))
      (string c)
    (substring (shell-command-to-string (format "printf \"%%q\" \"%s\"" (string c)))
               2 -1)))

The substring part is to cut out extra stuff from printf's output. I don't have a great deal of knowledge about this command, so it might not be flawless.

Answer 3

There may be some code somewhere in emacs that can do this for you, but one way would be to write a function that converts the special characters to a string:

(defun print-char(c)
  (case c 
    (?\n "\\n")
    (?\t "\\t")
    (t (string c))))

Note that you need to use string format rather than character because you're actually writing multiple characters for each special character.