This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See Printed Representation, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil)) ⇒ (nil) (setcar foo foo) ⇒ (#0)
In the functions below, stream stands for an output stream. (See the previous section for a description of output streams. Also See external-debugging-output, a useful stream value for debugging.) If stream is nil
or omitted, it defaults to the value of standard-output
.
The print
function is a convenient way of printing. It outputs the printed representation of object to stream, printing in addition one newline before object and another after it. Quoting characters are used. print
returns object. For example:
(progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" ⇒ " came back"
This function outputs the printed representation of object to stream. It does not print newlines to separate output as print
does, but it does use quoting characters just like print
. It returns object.
(progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" ⇒ " came back"
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people, not by read
, so it doesn’t insert quoting characters and doesn’t put double-quotes around the contents of strings. It does not add any spacing between calls.
(progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" ⇒ " in the \"hat\""
This function outputs a newline to stream. The name stands for “terminate print”. If ensure is non-nil
no newline is printed if stream is already at the beginning of a line. Note in this case stream can not be a function and an error is signaled if it is. This function returns t
if a newline is printed.
This function outputs character to stream. It returns character.
This function returns a string containing the text that prin1
would have printed for the same argument.
(prin1-to-string 'foo) ⇒ "foo"
(prin1-to-string (mark-marker)) ⇒ "#<marker at 2773 in strings.texi>"
If noescape is non-nil
, that inhibits use of quoting characters in the output. (This argument is supported in Emacs versions 19 and later.)
(prin1-to-string "foo") ⇒ "\"foo\""
(prin1-to-string "foo" t) ⇒ "foo"
See format
, in Formatting Strings, for other ways to obtain the printed representation of a Lisp object as a string.
This macro executes the body forms with standard-output
set up to feed output into a string. Then it returns that string.
For example, if the current buffer name is ‘foo’,
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))
returns "The buffer is foo"
.
This function outputs object to stream, just like prin1
, but does it in a prettier way. That is, it’ll indent and fill the object to make it more readable for humans.
If you need to use binary I/O in batch mode, e.g., use the functions described in this section to write out arbitrary binary data or avoid conversion of newlines on non-POSIX hosts, see set-binary-mode.
Copyright © 1990-1996, 1998-2019 Free Software Foundation, Inc.
Licensed under the GNU GPL license.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Output-Functions.html