2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software
5 @c See the file elisp.texi for copying conditions.
6 @node Strings and Characters
7 @chapter Strings and Characters
9 @cindex character arrays
13 A string in Emacs Lisp is an array that contains an ordered sequence
14 of characters. Strings are used as names of symbols, buffers, and
15 files; to send messages to users; to hold text being copied between
16 buffers; and for many other purposes. Because strings are so important,
17 Emacs Lisp has many functions expressly for manipulating them. Emacs
18 Lisp programs use strings more often than individual characters.
20 @xref{Strings of Events}, for special considerations for strings of
21 keyboard character events.
24 * Basics: String Basics. Basic properties of strings and characters.
25 * Predicates for Strings:: Testing whether an object is a string or char.
26 * Creating Strings:: Functions to allocate new strings.
27 * Modifying Strings:: Altering the contents of an existing string.
28 * Text Comparison:: Comparing characters or strings.
29 * String Conversion:: Converting to and from characters and strings.
30 * Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}.
31 * Case Conversion:: Case conversion functions.
32 * Case Tables:: Customizing case conversion.
36 @section String and Character Basics
38 A character is a Lisp object which represents a single character of
39 text. In Emacs Lisp, characters are simply integers; whether an
40 integer is a character or not is determined only by how it is used.
41 @xref{Character Codes}, for details about character representation in
44 A string is a fixed sequence of characters. It is a type of
45 sequence called a @dfn{array}, meaning that its length is fixed and
46 cannot be altered once it is created (@pxref{Sequences Arrays
47 Vectors}). Unlike in C, Emacs Lisp strings are @emph{not} terminated
48 by a distinguished character code.
50 Since strings are arrays, and therefore sequences as well, you can
51 operate on them with the general array and sequence functions documented
52 in @ref{Sequences Arrays Vectors}. For example, you can access or
53 change individual characters in a string using the functions @code{aref}
54 and @code{aset} (@pxref{Array Functions}). However, note that
55 @code{length} should @emph{not} be used for computing the width of a
56 string on display; use @code{string-width} (@pxref{Size of Displayed
59 There are two text representations for non-@acronym{ASCII}
60 characters in Emacs strings (and in buffers): unibyte and multibyte.
61 For most Lisp programming, you don't need to be concerned with these
62 two representations. @xref{Text Representations}, for details.
64 Sometimes key sequences are represented as unibyte strings. When a
65 unibyte string is a key sequence, string elements in the range 128 to
66 255 represent meta characters (which are large integers) rather than
67 character codes in the range 128 to 255. Strings cannot hold
68 characters that have the hyper, super or alt modifiers; they can hold
69 @acronym{ASCII} control characters, but no other control characters.
70 They do not distinguish case in @acronym{ASCII} control characters.
71 If you want to store such characters in a sequence, such as a key
72 sequence, you must use a vector instead of a string. @xref{Character
73 Type}, for more information about keyboard input characters.
75 Strings are useful for holding regular expressions. You can also
76 match regular expressions against strings with @code{string-match}
77 (@pxref{Regexp Search}). The functions @code{match-string}
78 (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing
79 Match}) are useful for decomposing and modifying strings after
80 matching regular expressions against them.
82 Like a buffer, a string can contain text properties for the characters
83 in it, as well as the characters themselves. @xref{Text Properties}.
84 All the Lisp primitives that copy text from strings to buffers or other
85 strings also copy the properties of the characters being copied.
87 @xref{Text}, for information about functions that display strings or
88 copy them into buffers. @xref{Character Type}, and @ref{String Type},
89 for information about the syntax of characters and strings.
90 @xref{Non-ASCII Characters}, for functions to convert between text
91 representations and to encode and decode character codes.
93 @node Predicates for Strings
94 @section Predicates for Strings
96 For more information about general sequence and array predicates,
97 see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
100 This function returns @code{t} if @var{object} is a string, @code{nil}
104 @defun string-or-null-p object
105 This function returns @code{t} if @var{object} is a string or
106 @code{nil}. It returns @code{nil} otherwise.
109 @defun char-or-string-p object
110 This function returns @code{t} if @var{object} is a string or a
111 character (i.e., an integer), @code{nil} otherwise.
114 @node Creating Strings
115 @section Creating Strings
117 The following functions create strings, either from scratch, or by
118 putting strings together, or by taking them apart.
120 @defun make-string count character
121 This function returns a string made up of @var{count} repetitions of
122 @var{character}. If @var{count} is negative, an error is signaled.
131 Other functions to compare with this one include @code{make-vector}
132 (@pxref{Vectors}) and @code{make-list} (@pxref{Building Lists}).
135 @defun string &rest characters
136 This returns a string containing the characters @var{characters}.
144 @defun substring string start &optional end
145 This function returns a new string which consists of those characters
146 from @var{string} in the range from (and including) the character at the
147 index @var{start} up to (but excluding) the character at the index
148 @var{end}. The first character is at index zero.
152 (substring "abcdefg" 0 3)
158 In the above example, the index for @samp{a} is 0, the index for
159 @samp{b} is 1, and the index for @samp{c} is 2. The index 3---which
160 is the fourth character in the string---marks the character position
161 up to which the substring is copied. Thus, @samp{abc} is copied from
162 the string @code{"abcdefg"}.
164 A negative number counts from the end of the string, so that @minus{}1
165 signifies the index of the last character of the string. For example:
169 (substring "abcdefg" -3 -1)
175 In this example, the index for @samp{e} is @minus{}3, the index for
176 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
177 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
179 When @code{nil} is used for @var{end}, it stands for the length of the
184 (substring "abcdefg" -3 nil)
189 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
190 It follows that @code{(substring @var{string} 0)} returns a copy of all
195 (substring "abcdefg" 0)
201 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
204 If the characters copied from @var{string} have text properties, the
205 properties are copied into the new string also. @xref{Text Properties}.
207 @code{substring} also accepts a vector for the first argument.
211 (substring [a b (c) "d"] 1 3)
215 A @code{wrong-type-argument} error is signaled if @var{start} is not
216 an integer or if @var{end} is neither an integer nor @code{nil}. An
217 @code{args-out-of-range} error is signaled if @var{start} indicates a
218 character following @var{end}, or if either integer is out of range
221 Contrast this function with @code{buffer-substring} (@pxref{Buffer
222 Contents}), which returns a string containing a portion of the text in
223 the current buffer. The beginning of a string is at index 0, but the
224 beginning of a buffer is at index 1.
227 @defun substring-no-properties string &optional start end
228 This works like @code{substring} but discards all text properties from
229 the value. Also, @var{start} may be omitted or @code{nil}, which is
230 equivalent to 0. Thus, @w{@code{(substring-no-properties
231 @var{string})}} returns a copy of @var{string}, with all text
235 @defun concat &rest sequences
236 @cindex copying strings
237 @cindex concatenating strings
238 This function returns a new string consisting of the characters in the
239 arguments passed to it (along with their text properties, if any). The
240 arguments may be strings, lists of numbers, or vectors of numbers; they
241 are not themselves changed. If @code{concat} receives no arguments, it
242 returns an empty string.
245 (concat "abc" "-def")
247 (concat "abc" (list 120 121) [122])
249 ;; @r{@code{nil} is an empty sequence.}
250 (concat "abc" nil "-def")
252 (concat "The " "quick brown " "fox.")
253 @result{} "The quick brown fox."
259 This function always constructs a new string that is not @code{eq} to
260 any existing string, except when the result is the empty string (to
261 save space, Emacs makes only one empty multibyte string).
263 For information about other concatenation functions, see the
264 description of @code{mapconcat} in @ref{Mapping Functions},
265 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
266 Lists}. For concatenating individual command-line arguments into a
267 string to be used as a shell command, see @ref{Shell Arguments,
268 combine-and-quote-strings}.
271 @defun split-string string &optional separators omit-nulls trim
272 This function splits @var{string} into substrings based on the regular
273 expression @var{separators} (@pxref{Regular Expressions}). Each match
274 for @var{separators} defines a splitting point; the substrings between
275 splitting points are made into a list, which is returned.
277 If @var{omit-nulls} is @code{nil} (or omitted), the result contains
278 null strings whenever there are two consecutive matches for
279 @var{separators}, or a match is adjacent to the beginning or end of
280 @var{string}. If @var{omit-nulls} is @code{t}, these null strings are
281 omitted from the result.
283 If @var{separators} is @code{nil} (or omitted), the default is the
284 value of @code{split-string-default-separators}.
286 As a special case, when @var{separators} is @code{nil} (or omitted),
287 null strings are always omitted from the result. Thus:
290 (split-string " two words ")
291 @result{} ("two" "words")
294 The result is not @code{("" "two" "words" "")}, which would rarely be
295 useful. If you need such a result, use an explicit value for
299 (split-string " two words "
300 split-string-default-separators)
301 @result{} ("" "two" "words" "")
307 (split-string "Soup is good food" "o")
308 @result{} ("S" "up is g" "" "d f" "" "d")
309 (split-string "Soup is good food" "o" t)
310 @result{} ("S" "up is g" "d f" "d")
311 (split-string "Soup is good food" "o+")
312 @result{} ("S" "up is g" "d f" "d")
315 Empty matches do count, except that @code{split-string} will not look
316 for a final empty match when it already reached the end of the string
317 using a non-empty match or when @var{string} is empty:
320 (split-string "aooob" "o*")
321 @result{} ("" "a" "" "b" "")
322 (split-string "ooaboo" "o*")
323 @result{} ("" "" "a" "b" "")
328 However, when @var{separators} can match the empty string,
329 @var{omit-nulls} is usually @code{t}, so that the subtleties in the
330 three previous examples are rarely relevant:
333 (split-string "Soup is good food" "o*" t)
334 @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
335 (split-string "Nice doggy!" "" t)
336 @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
337 (split-string "" "" t)
341 Somewhat odd, but predictable, behavior can occur for certain
342 ``non-greedy'' values of @var{separators} that can prefer empty
343 matches over non-empty matches. Again, such values rarely occur in
347 (split-string "ooo" "o*" t)
349 (split-string "ooo" "\\|o+" t)
350 @result{} ("o" "o" "o")
353 If the optional argument @var{trim} is non-@code{nil}, it should be a
354 regular expression to match text to trim from the beginning and end of
355 each substring. If trimming makes the substring empty, it is treated
358 If you need to split a string into a list of individual command-line
359 arguments suitable for @code{call-process} or @code{start-process},
360 see @ref{Shell Arguments, split-string-and-unquote}.
363 @defvar split-string-default-separators
364 The default value of @var{separators} for @code{split-string}. Its
365 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
368 @node Modifying Strings
369 @section Modifying Strings
371 The most basic way to alter the contents of an existing string is with
372 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
373 @var{idx} @var{char})} stores @var{char} into @var{string} at index
374 @var{idx}. Each character occupies one or more bytes, and if @var{char}
375 needs a different number of bytes from the character already present at
376 that index, @code{aset} signals an error.
378 A more powerful function is @code{store-substring}:
380 @defun store-substring string idx obj
381 This function alters part of the contents of the string @var{string}, by
382 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
383 may be either a character or a (smaller) string.
385 Since it is impossible to change the length of an existing string, it is
386 an error if @var{obj} doesn't fit within @var{string}'s actual length,
387 or if any new character requires a different number of bytes from the
388 character currently present at that point in @var{string}.
391 To clear out a string that contained a password, use
394 @defun clear-string string
395 This makes @var{string} a unibyte string and clears its contents to
396 zeros. It may also change @var{string}'s length.
400 @node Text Comparison
401 @section Comparison of Characters and Strings
402 @cindex string equality
404 @defun char-equal character1 character2
405 This function returns @code{t} if the arguments represent the same
406 character, @code{nil} otherwise. This function ignores differences
407 in case if @code{case-fold-search} is non-@code{nil}.
412 (let ((case-fold-search nil))
418 @defun string= string1 string2
419 This function returns @code{t} if the characters of the two strings
420 match exactly. Symbols are also allowed as arguments, in which case
421 the symbol names are used. Case is always significant, regardless of
422 @code{case-fold-search}.
424 This function is equivalent to @code{equal} for comparing two strings
425 (@pxref{Equality Predicates}). In particular, the text properties of
426 the two strings are ignored. But if either argument is not a string
427 or symbol, an error is signaled.
430 (string= "abc" "abc")
432 (string= "abc" "ABC")
438 For technical reasons, a unibyte and a multibyte string are
439 @code{equal} if and only if they contain the same sequence of
440 character codes and all these codes are either in the range 0 through
441 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
442 However, when a unibyte string is converted to a multibyte string, all
443 characters with codes in the range 160 through 255 are converted to
444 characters with higher codes, whereas @acronym{ASCII} characters
445 remain unchanged. Thus, a unibyte string and its conversion to
446 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
447 Character codes 160 through 255 are not entirely proper in multibyte
448 text, even though they can occur. As a consequence, the situation
449 where a unibyte and a multibyte string are @code{equal} without both
450 being all @acronym{ASCII} is a technical oddity that very few Emacs
451 Lisp programmers ever get confronted with. @xref{Text
455 @defun string-equal string1 string2
456 @code{string-equal} is another name for @code{string=}.
459 @cindex lexical comparison
460 @defun string< string1 string2
461 @c (findex string< causes problems for permuted index!!)
462 This function compares two strings a character at a time. It
463 scans both the strings at the same time to find the first pair of corresponding
464 characters that do not match. If the lesser character of these two is
465 the character from @var{string1}, then @var{string1} is less, and this
466 function returns @code{t}. If the lesser character is the one from
467 @var{string2}, then @var{string1} is greater, and this function returns
468 @code{nil}. If the two strings match entirely, the value is @code{nil}.
470 Pairs of characters are compared according to their character codes.
471 Keep in mind that lower case letters have higher numeric values in the
472 @acronym{ASCII} character set than their upper case counterparts; digits and
473 many punctuation characters have a lower numeric value than upper case
474 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
475 character; a unibyte non-@acronym{ASCII} character is always less than any
476 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
480 (string< "abc" "abd")
482 (string< "abd" "abc")
484 (string< "123" "abc")
489 When the strings have different lengths, and they match up to the
490 length of @var{string1}, then the result is @code{t}. If they match up
491 to the length of @var{string2}, the result is @code{nil}. A string of
492 no characters is less than any other string.
509 Symbols are also allowed as arguments, in which case their print names
513 @defun string-lessp string1 string2
514 @code{string-lessp} is another name for @code{string<}.
517 @defun string-prefix-p string1 string2 &optional ignore-case
518 This function returns non-@code{nil} if @var{string1} is a prefix of
519 @var{string2}; i.e., if @var{string2} starts with @var{string1}. If
520 the optional argument @var{ignore-case} is non-@code{nil}, the
521 comparison ignores case differences.
524 @defun string-suffix-p suffix string &optional ignore-case
525 This function returns non-@code{nil} if @var{suffix} is a suffix of
526 @var{string}; i.e., if @var{string} ends with @var{suffix}. If the
527 optional argument @var{ignore-case} is non-@code{nil}, the comparison
528 ignores case differences.
531 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
532 This function compares a specified part of @var{string1} with a
533 specified part of @var{string2}. The specified part of @var{string1}
534 runs from index @var{start1} (inclusive) up to index @var{end1}
535 (exclusive); @code{nil} for @var{start1} means the start of the
536 string, while @code{nil} for @var{end1} means the length of the
537 string. Likewise, the specified part of @var{string2} runs from index
538 @var{start2} up to index @var{end2}.
540 The strings are compared by the numeric values of their characters.
541 For instance, @var{str1} is considered ``smaller than'' @var{str2} if
542 its first differing character has a smaller numeric value. If
543 @var{ignore-case} is non-@code{nil}, characters are converted to
544 lower-case before comparing them. Unibyte strings are converted to
545 multibyte for comparison (@pxref{Text Representations}), so that a
546 unibyte string and its conversion to multibyte are always regarded as
549 If the specified portions of the two strings match, the value is
550 @code{t}. Otherwise, the value is an integer which indicates how many
551 leading characters agree, and which string is less. Its absolute
552 value is one plus the number of characters that agree at the beginning
553 of the two strings. The sign is negative if @var{string1} (or its
554 specified portion) is less.
557 @defun assoc-string key alist &optional case-fold
558 This function works like @code{assoc}, except that @var{key} must be a
559 string or symbol, and comparison is done using @code{compare-strings}.
560 Symbols are converted to strings before testing.
561 If @var{case-fold} is non-@code{nil}, it ignores case differences.
562 Unlike @code{assoc}, this function can also match elements of the alist
563 that are strings or symbols rather than conses. In particular, @var{alist} can
564 be a list of strings or symbols rather than an actual alist.
565 @xref{Association Lists}.
568 See also the function @code{compare-buffer-substrings} in
569 @ref{Comparing Text}, for a way to compare text in buffers. The
570 function @code{string-match}, which matches a regular expression
571 against a string, can be used for a kind of string comparison; see
574 @node String Conversion
575 @section Conversion of Characters and Strings
576 @cindex conversion of strings
578 This section describes functions for converting between characters,
579 strings and integers. @code{format} (@pxref{Formatting Strings}) and
580 @code{prin1-to-string} (@pxref{Output Functions}) can also convert
581 Lisp objects into strings. @code{read-from-string} (@pxref{Input
582 Functions}) can ``convert'' a string representation of a Lisp object
583 into an object. The functions @code{string-to-multibyte} and
584 @code{string-to-unibyte} convert the text representation of a string
585 (@pxref{Converting Representations}).
587 @xref{Documentation}, for functions that produce textual descriptions
588 of text characters and general input events
589 (@code{single-key-description} and @code{text-char-description}). These
590 are used primarily for making help messages.
592 @defun number-to-string number
593 @cindex integer to string
594 @cindex integer to decimal
595 This function returns a string consisting of the printed base-ten
596 representation of @var{number}. The returned value starts with a
597 minus sign if the argument is negative.
600 (number-to-string 256)
603 (number-to-string -23)
606 (number-to-string -23.5)
610 @cindex int-to-string
611 @code{int-to-string} is a semi-obsolete alias for this function.
613 See also the function @code{format} in @ref{Formatting Strings}.
616 @defun string-to-number string &optional base
617 @cindex string to number
618 This function returns the numeric value of the characters in
619 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
620 between 2 and 16 (inclusive), and integers are converted in that base.
621 If @var{base} is @code{nil}, then base ten is used. Floating-point
622 conversion only works in base ten; we have not implemented other
623 radices for floating-point numbers, because that would be much more
624 work and does not seem useful. If @var{string} looks like an integer
625 but its value is too large to fit into a Lisp integer,
626 @code{string-to-number} returns a floating-point result.
628 The parsing skips spaces and tabs at the beginning of @var{string},
629 then reads as much of @var{string} as it can interpret as a number in
630 the given base. (On some systems it ignores other whitespace at the
631 beginning, not just spaces and tabs.) If @var{string} cannot be
632 interpreted as a number, this function returns 0.
635 (string-to-number "256")
637 (string-to-number "25 is a perfect square.")
639 (string-to-number "X256")
641 (string-to-number "-4.5")
643 (string-to-number "1e5")
647 @findex string-to-int
648 @code{string-to-int} is an obsolete alias for this function.
651 @defun char-to-string character
652 @cindex character to string
653 This function returns a new string containing one character,
654 @var{character}. This function is semi-obsolete because the function
655 @code{string} is more general. @xref{Creating Strings}.
658 @defun string-to-char string
659 This function returns the first character in @var{string}. This
660 mostly identical to @code{(aref string 0)}, except that it returns 0
661 if the string is empty. (The value is also 0 when the first character
662 of @var{string} is the null character, @acronym{ASCII} code 0.) This
663 function may be eliminated in the future if it does not seem useful
667 Here are some other functions that can convert to or from a string:
671 This function converts a vector or a list into a string.
672 @xref{Creating Strings}.
675 This function converts a string into a vector. @xref{Vector
679 This function converts a string into a list. @xref{Building Lists}.
682 This function converts a byte of character data into a unibyte string.
683 @xref{Converting Representations}.
686 @node Formatting Strings
687 @section Formatting Strings
688 @cindex formatting strings
689 @cindex strings, formatting them
691 @dfn{Formatting} means constructing a string by substituting
692 computed values at various places in a constant string. This constant
693 string controls how the other values are printed, as well as where
694 they appear; it is called a @dfn{format string}.
696 Formatting is often useful for computing messages to be displayed. In
697 fact, the functions @code{message} and @code{error} provide the same
698 formatting feature described here; they differ from @code{format} only
699 in how they use the result of formatting.
701 @defun format string &rest objects
702 This function returns a new string that is made by copying
703 @var{string} and then replacing any format specification
704 in the copy with encodings of the corresponding @var{objects}. The
705 arguments @var{objects} are the computed values to be formatted.
707 The characters in @var{string}, other than the format specifications,
708 are copied directly into the output, including their text properties,
712 @cindex @samp{%} in format
713 @cindex format specification
714 A format specification is a sequence of characters beginning with a
715 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
716 @code{format} function replaces it with the printed representation of
717 one of the values to be formatted (one of the arguments @var{objects}).
722 (format "The value of fill-column is %d." fill-column)
723 @result{} "The value of fill-column is 72."
727 Since @code{format} interprets @samp{%} characters as format
728 specifications, you should @emph{never} pass an arbitrary string as
729 the first argument. This is particularly true when the string is
730 generated by some Lisp code. Unless the string is @emph{known} to
731 never include any @samp{%} characters, pass @code{"%s"}, described
732 below, as the first argument, and the string as the second, like this:
735 (format "%s" @var{arbitrary-string})
738 If @var{string} contains more than one format specification, the
739 format specifications correspond to successive values from
740 @var{objects}. Thus, the first format specification in @var{string}
741 uses the first such value, the second format specification uses the
742 second such value, and so on. Any extra format specifications (those
743 for which there are no corresponding values) cause an error. Any
744 extra values to be formatted are ignored.
746 Certain format specifications require values of particular types. If
747 you supply a value that doesn't fit the requirements, an error is
750 Here is a table of valid format specifications:
754 Replace the specification with the printed representation of the object,
755 made without quoting (that is, using @code{princ}, not
756 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
757 by their contents alone, with no @samp{"} characters, and symbols appear
758 without @samp{\} characters.
760 If the object is a string, its text properties are
761 copied into the output. The text properties of the @samp{%s} itself
762 are also copied, but those of the object take priority.
765 Replace the specification with the printed representation of the object,
766 made with quoting (that is, using @code{prin1}---@pxref{Output
767 Functions}). Thus, strings are enclosed in @samp{"} characters, and
768 @samp{\} characters appear where necessary before special characters.
771 @cindex integer to octal
772 Replace the specification with the base-eight representation of an
776 Replace the specification with the base-ten representation of an
781 @cindex integer to hexadecimal
782 Replace the specification with the base-sixteen representation of an
783 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
786 Replace the specification with the character which is the value given.
789 Replace the specification with the exponential notation for a
790 floating-point number.
793 Replace the specification with the decimal-point notation for a
794 floating-point number.
797 Replace the specification with notation for a floating-point number,
798 using either exponential notation or decimal-point notation, whichever
802 Replace the specification with a single @samp{%}. This format
803 specification is unusual in that it does not use a value. For example,
804 @code{(format "%% %d" 30)} returns @code{"% 30"}.
807 Any other format character results in an @samp{Invalid format
810 Here are several examples:
814 (format "The name of this buffer is %s." (buffer-name))
815 @result{} "The name of this buffer is strings.texi."
817 (format "The buffer object prints as %s." (current-buffer))
818 @result{} "The buffer object prints as strings.texi."
820 (format "The octal value of %d is %o,
821 and the hex value is %x." 18 18 18)
822 @result{} "The octal value of 18 is 22,
823 and the hex value is 12."
829 A specification can have a @dfn{width}, which is a decimal number
830 between the @samp{%} and the specification character. If the printed
831 representation of the object contains fewer characters than this
832 width, @code{format} extends it with padding. The width specifier is
833 ignored for the @samp{%%} specification. Any padding introduced by
834 the width specifier normally consists of spaces inserted on the left:
837 (format "%5d is padded on the left with spaces" 123)
838 @result{} " 123 is padded on the left with spaces"
842 If the width is too small, @code{format} does not truncate the
843 object's printed representation. Thus, you can use a width to specify
844 a minimum spacing between columns with no risk of losing information.
845 In the following three examples, @samp{%7s} specifies a minimum width
846 of 7. In the first case, the string inserted in place of @samp{%7s}
847 has only 3 letters, and needs 4 blank spaces as padding. In the
848 second case, the string @code{"specification"} is 13 letters wide but
853 (format "The word `%7s' has %d letters in it."
854 "foo" (length "foo"))
855 @result{} "The word ` foo' has 3 letters in it."
856 (format "The word `%7s' has %d letters in it."
857 "specification" (length "specification"))
858 @result{} "The word `specification' has 13 letters in it."
862 @cindex flags in format specifications
863 Immediately after the @samp{%} and before the optional width
864 specifier, you can also put certain @dfn{flag characters}.
866 The flag @samp{+} inserts a plus sign before a positive number, so
867 that it always has a sign. A space character as flag inserts a space
868 before a positive number. (Otherwise, positive numbers start with the
869 first digit.) These flags are useful for ensuring that positive
870 numbers and negative numbers use the same number of columns. They are
871 ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if
872 both flags are used, @samp{+} takes precedence.
874 The flag @samp{#} specifies an ``alternate form'' which depends on
875 the format in use. For @samp{%o}, it ensures that the result begins
876 with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result
877 with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g},
878 the @samp{#} flag means include a decimal point even if the precision
881 The flag @samp{0} ensures that the padding consists of @samp{0}
882 characters instead of spaces. This flag is ignored for non-numerical
883 specification characters like @samp{%s}, @samp{%S} and @samp{%c}.
884 These specification characters accept the @samp{0} flag, but still pad
887 The flag @samp{-} causes the padding inserted by the width
888 specifier, if any, to be inserted on the right rather than the left.
889 If both @samp{-} and @samp{0} are present, the @samp{0} flag is
894 (format "%06d is padded on the left with zeros" 123)
895 @result{} "000123 is padded on the left with zeros"
897 (format "%-6d is padded on the right" 123)
898 @result{} "123 is padded on the right"
900 (format "The word `%-7s' actually has %d letters in it."
901 "foo" (length "foo"))
902 @result{} "The word `foo ' actually has 3 letters in it."
906 @cindex precision in format specifications
907 All the specification characters allow an optional @dfn{precision}
908 before the character (after the width, if present). The precision is
909 a decimal-point @samp{.} followed by a digit-string. For the
910 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
911 precision specifies how many decimal places to show; if zero, the
912 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
913 the precision truncates the string to the given width, so @samp{%.3s}
914 shows only the first three characters of the representation for
915 @var{object}. Precision has no effect for other specification
918 @node Case Conversion
919 @section Case Conversion in Lisp
922 @cindex character case
923 @cindex case conversion in Lisp
925 The character case functions change the case of single characters or
926 of the contents of strings. The functions normally convert only
927 alphabetic characters (the letters @samp{A} through @samp{Z} and
928 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
929 characters are not altered. You can specify a different case
930 conversion mapping by specifying a case table (@pxref{Case Tables}).
932 These functions do not modify the strings that are passed to them as
935 The examples below use the characters @samp{X} and @samp{x} which have
936 @acronym{ASCII} codes 88 and 120 respectively.
938 @defun downcase string-or-char
939 This function converts @var{string-or-char}, which should be either a
940 character or a string, to lower case.
942 When @var{string-or-char} is a string, this function returns a new
943 string in which each letter in the argument that is upper case is
944 converted to lower case. When @var{string-or-char} is a character,
945 this function returns the corresponding lower case character (an
946 integer); if the original character is lower case, or is not a letter,
947 the return value is equal to the original character.
950 (downcase "The cat in the hat")
951 @result{} "the cat in the hat"
958 @defun upcase string-or-char
959 This function converts @var{string-or-char}, which should be either a
960 character or a string, to upper case.
962 When @var{string-or-char} is a string, this function returns a new
963 string in which each letter in the argument that is lower case is
964 converted to upper case. When @var{string-or-char} is a character,
965 this function returns the corresponding upper case character (an
966 integer); if the original character is upper case, or is not a letter,
967 the return value is equal to the original character.
970 (upcase "The cat in the hat")
971 @result{} "THE CAT IN THE HAT"
978 @defun capitalize string-or-char
979 @cindex capitalization
980 This function capitalizes strings or characters. If
981 @var{string-or-char} is a string, the function returns a new string
982 whose contents are a copy of @var{string-or-char} in which each word
983 has been capitalized. This means that the first character of each
984 word is converted to upper case, and the rest are converted to lower
987 The definition of a word is any sequence of consecutive characters that
988 are assigned to the word constituent syntax class in the current syntax
989 table (@pxref{Syntax Class Table}).
991 When @var{string-or-char} is a character, this function does the same
992 thing as @code{upcase}.
996 (capitalize "The cat in the hat")
997 @result{} "The Cat In The Hat"
1001 (capitalize "THE 77TH-HATTED CAT")
1002 @result{} "The 77th-Hatted Cat"
1012 @defun upcase-initials string-or-char
1013 If @var{string-or-char} is a string, this function capitalizes the
1014 initials of the words in @var{string-or-char}, without altering any
1015 letters other than the initials. It returns a new string whose
1016 contents are a copy of @var{string-or-char}, in which each word has
1017 had its initial letter converted to upper case.
1019 The definition of a word is any sequence of consecutive characters that
1020 are assigned to the word constituent syntax class in the current syntax
1021 table (@pxref{Syntax Class Table}).
1023 When the argument to @code{upcase-initials} is a character,
1024 @code{upcase-initials} has the same result as @code{upcase}.
1028 (upcase-initials "The CAT in the hAt")
1029 @result{} "The CAT In The HAt"
1034 @xref{Text Comparison}, for functions that compare strings; some of
1035 them ignore case differences, or can optionally ignore case differences.
1038 @section The Case Table
1040 You can customize case conversion by installing a special @dfn{case
1041 table}. A case table specifies the mapping between upper case and lower
1042 case letters. It affects both the case conversion functions for Lisp
1043 objects (see the previous section) and those that apply to text in the
1044 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1045 also a standard case table which is used to initialize the case table
1048 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1049 @code{case-table}. This char-table maps each character into the
1050 corresponding lower case character. It has three extra slots, which
1051 hold related tables:
1055 The upcase table maps each character into the corresponding upper
1058 The canonicalize table maps all of a set of case-related characters
1059 into a particular member of that set.
1061 The equivalences table maps each one of a set of case-related characters
1062 into the next character in that set.
1065 In simple cases, all you need to specify is the mapping to lower-case;
1066 the three related tables will be calculated automatically from that one.
1068 For some languages, upper and lower case letters are not in one-to-one
1069 correspondence. There may be two different lower case letters with the
1070 same upper case equivalent. In these cases, you need to specify the
1071 maps for both lower case and upper case.
1073 The extra table @var{canonicalize} maps each character to a canonical
1074 equivalent; any two characters that are related by case-conversion have
1075 the same canonical equivalent character. For example, since @samp{a}
1076 and @samp{A} are related by case-conversion, they should have the same
1077 canonical equivalent character (which should be either @samp{a} for both
1078 of them, or @samp{A} for both of them).
1080 The extra table @var{equivalences} is a map that cyclically permutes
1081 each equivalence class (of characters with the same canonical
1082 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1083 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1084 equivalent characters.)
1086 When constructing a case table, you can provide @code{nil} for
1087 @var{canonicalize}; then Emacs fills in this slot from the lower case
1088 and upper case mappings. You can also provide @code{nil} for
1089 @var{equivalences}; then Emacs fills in this slot from
1090 @var{canonicalize}. In a case table that is actually in use, those
1091 components are non-@code{nil}. Do not try to specify
1092 @var{equivalences} without also specifying @var{canonicalize}.
1094 Here are the functions for working with case tables:
1096 @defun case-table-p object
1097 This predicate returns non-@code{nil} if @var{object} is a valid case
1101 @defun set-standard-case-table table
1102 This function makes @var{table} the standard case table, so that it will
1103 be used in any buffers created subsequently.
1106 @defun standard-case-table
1107 This returns the standard case table.
1110 @defun current-case-table
1111 This function returns the current buffer's case table.
1114 @defun set-case-table table
1115 This sets the current buffer's case table to @var{table}.
1118 @defmac with-case-table table body@dots{}
1119 The @code{with-case-table} macro saves the current case table, makes
1120 @var{table} the current case table, evaluates the @var{body} forms,
1121 and finally restores the case table. The return value is the value of
1122 the last form in @var{body}. The case table is restored even in case
1123 of an abnormal exit via @code{throw} or error (@pxref{Nonlocal
1127 Some language environments modify the case conversions of
1128 @acronym{ASCII} characters; for example, in the Turkish language
1129 environment, the @acronym{ASCII} character @samp{I} is downcased into
1130 a Turkish ``dotless i''. This can interfere with code that requires
1131 ordinary @acronym{ASCII} case conversion, such as implementations of
1132 @acronym{ASCII}-based network protocols. In that case, use the
1133 @code{with-case-table} macro with the variable @var{ascii-case-table},
1134 which stores the unmodified case table for the @acronym{ASCII}
1137 @defvar ascii-case-table
1138 The case table for the @acronym{ASCII} character set. This should not be
1139 modified by any language environment settings.
1142 The following three functions are convenient subroutines for packages
1143 that define non-@acronym{ASCII} character sets. They modify the specified
1144 case table @var{case-table}; they also modify the standard syntax table.
1145 @xref{Syntax Tables}. Normally you would use these functions to change
1146 the standard case table.
1148 @defun set-case-syntax-pair uc lc case-table
1149 This function specifies a pair of corresponding letters, one upper case
1153 @defun set-case-syntax-delims l r case-table
1154 This function makes characters @var{l} and @var{r} a matching pair of
1155 case-invariant delimiters.
1158 @defun set-case-syntax char syntax case-table
1159 This function makes @var{char} case-invariant, with syntax
1163 @deffn Command describe-buffer-case-table
1164 This command displays a description of the contents of the current
1165 buffer's case table.