2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2003
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/strings
7 @node Strings and Characters, Lists, Numbers, Top
8 @comment node-name, next, previous, up
9 @chapter Strings and Characters
11 @cindex character arrays
15 A string in Emacs Lisp is an array that contains an ordered sequence
16 of characters. Strings are used as names of symbols, buffers, and
17 files; to send messages to users; to hold text being copied between
18 buffers; and for many other purposes. Because strings are so important,
19 Emacs Lisp has many functions expressly for manipulating them. Emacs
20 Lisp programs use strings more often than individual characters.
22 @xref{Strings of Events}, for special considerations for strings of
23 keyboard character events.
26 * Basics: String Basics. Basic properties of strings and characters.
27 * Predicates for Strings:: Testing whether an object is a string or char.
28 * Creating Strings:: Functions to allocate new strings.
29 * Modifying Strings:: Altering the contents of an existing string.
30 * Text Comparison:: Comparing characters or strings.
31 * String Conversion:: Converting to and from characters and strings.
32 * Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}.
33 * Case Conversion:: Case conversion functions.
34 * Case Tables:: Customizing case conversion.
38 @section String and Character Basics
40 Characters are represented in Emacs Lisp as integers;
41 whether an integer is a character or not is determined only by how it is
42 used. Thus, strings really contain integers.
44 The length of a string (like any array) is fixed, and cannot be
45 altered once the string exists. Strings in Lisp are @emph{not}
46 terminated by a distinguished character code. (By contrast, strings in
47 C are terminated by a character with @sc{ascii} code 0.)
49 Since strings are arrays, and therefore sequences as well, you can
50 operate on them with the general array and sequence functions.
51 (@xref{Sequences Arrays Vectors}.) For example, you can access or
52 change individual characters in a string using the functions @code{aref}
53 and @code{aset} (@pxref{Array Functions}).
55 There are two text representations for non-@sc{ascii} characters in
56 Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
57 Representations}). An @sc{ascii} character always occupies one byte in a
58 string; in fact, when a string is all @sc{ascii}, there is no real
59 difference between the unibyte and multibyte representations.
60 For most Lisp programming, you don't need to be concerned with these two
63 Sometimes key sequences are represented as strings. When a string is
64 a key sequence, string elements in the range 128 to 255 represent meta
65 characters (which are large integers) rather than character
66 codes in the range 128 to 255.
68 Strings cannot hold characters that have the hyper, super or alt
69 modifiers; they can hold @sc{ascii} control characters, but no other
70 control characters. They do not distinguish case in @sc{ascii} control
71 characters. If you want to store such characters in a sequence, such as
72 a key sequence, you must use a vector instead of a string.
73 @xref{Character Type}, for more information about the representation of meta
74 and other modifiers for keyboard input characters.
76 Strings are useful for holding regular expressions. You can also
77 match regular expressions against strings (@pxref{Regexp Search}). The
78 functions @code{match-string} (@pxref{Simple Match Data}) and
79 @code{replace-match} (@pxref{Replacing Match}) are useful for
80 decomposing and modifying strings based on regular expression matching.
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 The 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 char-or-string-p object
105 This function returns @code{t} if @var{object} is a string or a
106 character (i.e., an integer), @code{nil} otherwise.
109 @node Creating Strings
110 @section Creating Strings
112 The following functions create strings, either from scratch, or by
113 putting strings together, or by taking them apart.
115 @defun make-string count character
116 This function returns a string made up of @var{count} repetitions of
117 @var{character}. If @var{count} is negative, an error is signaled.
126 Other functions to compare with this one include @code{char-to-string}
127 (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and
128 @code{make-list} (@pxref{Building Lists}).
131 @defun string &rest characters
132 This returns a string containing the characters @var{characters}.
140 @defun substring string start &optional end
141 This function returns a new string which consists of those characters
142 from @var{string} in the range from (and including) the character at the
143 index @var{start} up to (but excluding) the character at the index
144 @var{end}. The first character is at index zero.
148 (substring "abcdefg" 0 3)
154 Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the
155 index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied
156 from the string @code{"abcdefg"}. The index 3 marks the character
157 position up to which the substring is copied. The character whose index
158 is 3 is actually the fourth character in the string.
160 A negative number counts from the end of the string, so that @minus{}1
161 signifies the index of the last character of the string. For example:
165 (substring "abcdefg" -3 -1)
171 In this example, the index for @samp{e} is @minus{}3, the index for
172 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
173 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
175 When @code{nil} is used for @var{end}, it stands for the length of the
180 (substring "abcdefg" -3 nil)
185 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
186 It follows that @code{(substring @var{string} 0)} returns a copy of all
191 (substring "abcdefg" 0)
197 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
200 If the characters copied from @var{string} have text properties, the
201 properties are copied into the new string also. @xref{Text Properties}.
203 @code{substring} also accepts a vector for the first argument.
207 (substring [a b (c) "d"] 1 3)
211 A @code{wrong-type-argument} error is signaled if @var{start} is not
212 an integer or if @var{end} is neither an integer nor @code{nil}. An
213 @code{args-out-of-range} error is signaled if @var{start} indicates a
214 character following @var{end}, or if either integer is out of range
217 Contrast this function with @code{buffer-substring} (@pxref{Buffer
218 Contents}), which returns a string containing a portion of the text in
219 the current buffer. The beginning of a string is at index 0, but the
220 beginning of a buffer is at index 1.
223 @defun substring-no-properties string &optional start end
224 This works like @code{substring} but discards all text properties from
225 the value. Also, @var{start} may be omitted or @code{nil}, which is
226 equivalent to 0. Thus, @w{@code{(substring-no-properties
227 @var{string})}} returns a copy of @var{string}, with all text
231 @defun concat &rest sequences
232 @cindex copying strings
233 @cindex concatenating strings
234 This function returns a new string consisting of the characters in the
235 arguments passed to it (along with their text properties, if any). The
236 arguments may be strings, lists of numbers, or vectors of numbers; they
237 are not themselves changed. If @code{concat} receives no arguments, it
238 returns an empty string.
241 (concat "abc" "-def")
243 (concat "abc" (list 120 121) [122])
245 ;; @r{@code{nil} is an empty sequence.}
246 (concat "abc" nil "-def")
248 (concat "The " "quick brown " "fox.")
249 @result{} "The quick brown fox."
255 The @code{concat} function always constructs a new string that is
256 not @code{eq} to any existing string.
258 In Emacs versions before 21, when an argument was an integer (not a
259 sequence of integers), it was converted to a string of digits making up
260 the decimal printed representation of the integer. This obsolete usage
261 no longer works. The proper way to convert an integer to its decimal
262 printed form is with @code{format} (@pxref{Formatting Strings}) or
263 @code{number-to-string} (@pxref{String Conversion}).
265 For information about other concatenation functions, see the
266 description of @code{mapconcat} in @ref{Mapping Functions},
267 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
271 @defun split-string string &optional separators omit-nulls
272 This function splits @var{string} into substrings at matches for the
273 regular expression @var{separators}. Each match for @var{separators}
274 defines a splitting point; the substrings between the splitting points
275 are made into a list, which is the value returned by
278 If @var{omit-nulls} is @code{nil}, the result contains null strings
279 whenever there are two consecutive matches for @var{separators}, or a
280 match is adjacent to the beginning or end of @var{string}. If
281 @var{omit-nulls} is @code{t}, these null strings are omitted from the
284 If @var{separators} is @code{nil} (or omitted),
285 the default is the value of @code{split-string-default-separators}.
287 As a special case, when @var{separators} is @code{nil} (or omitted),
288 null strings are always omitted from the result. Thus:
291 (split-string " two words ")
292 @result{} ("two" "words")
295 The result is not @samp{("" "two" "words" "")}, which would rarely be
296 useful. If you need such a result, use an explict value for
300 (split-string " two words " 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")
354 @defvar split-string-default-separators
355 The default value of @var{separators} for @code{split-string}, initially
356 @w{@samp{"[ \f\t\n\r\v]+"}}.
359 @node Modifying Strings
360 @section Modifying Strings
362 The most basic way to alter the contents of an existing string is with
363 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
364 @var{idx} @var{char})} stores @var{char} into @var{string} at index
365 @var{idx}. Each character occupies one or more bytes, and if @var{char}
366 needs a different number of bytes from the character already present at
367 that index, @code{aset} signals an error.
369 A more powerful function is @code{store-substring}:
371 @defun store-substring string idx obj
372 This function alters part of the contents of the string @var{string}, by
373 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
374 may be either a character or a (smaller) string.
376 Since it is impossible to change the length of an existing string, it is
377 an error if @var{obj} doesn't fit within @var{string}'s actual length,
378 or if any new character requires a different number of bytes from the
379 character currently present at that point in @var{string}.
383 @node Text Comparison
384 @section Comparison of Characters and Strings
385 @cindex string equality
387 @defun char-equal character1 character2
388 This function returns @code{t} if the arguments represent the same
389 character, @code{nil} otherwise. This function ignores differences
390 in case if @code{case-fold-search} is non-@code{nil}.
395 (let ((case-fold-search nil))
401 @defun string= string1 string2
402 This function returns @code{t} if the characters of the two strings
403 match exactly. Symbols are also allowed as arguments, in which case
404 their print names are used.
405 Case is always significant, regardless of @code{case-fold-search}.
408 (string= "abc" "abc")
410 (string= "abc" "ABC")
416 The function @code{string=} ignores the text properties of the two
417 strings. When @code{equal} (@pxref{Equality Predicates}) compares two
418 strings, it uses @code{string=}.
420 If the strings contain non-@sc{ascii} characters, and one is unibyte
421 while the other is multibyte, then they cannot be equal. @xref{Text
425 @defun string-equal string1 string2
426 @code{string-equal} is another name for @code{string=}.
429 @cindex lexical comparison
430 @defun string< string1 string2
431 @c (findex string< causes problems for permuted index!!)
432 This function compares two strings a character at a time. It
433 scans both the strings at the same time to find the first pair of corresponding
434 characters that do not match. If the lesser character of these two is
435 the character from @var{string1}, then @var{string1} is less, and this
436 function returns @code{t}. If the lesser character is the one from
437 @var{string2}, then @var{string1} is greater, and this function returns
438 @code{nil}. If the two strings match entirely, the value is @code{nil}.
440 Pairs of characters are compared according to their character codes.
441 Keep in mind that lower case letters have higher numeric values in the
442 @sc{ascii} character set than their upper case counterparts; digits and
443 many punctuation characters have a lower numeric value than upper case
444 letters. An @sc{ascii} character is less than any non-@sc{ascii}
445 character; a unibyte non-@sc{ascii} character is always less than any
446 multibyte non-@sc{ascii} character (@pxref{Text Representations}).
450 (string< "abc" "abd")
452 (string< "abd" "abc")
454 (string< "123" "abc")
459 When the strings have different lengths, and they match up to the
460 length of @var{string1}, then the result is @code{t}. If they match up
461 to the length of @var{string2}, the result is @code{nil}. A string of
462 no characters is less than any other string.
479 Symbols are also allowed as arguments, in which case their print names
483 @defun string-lessp string1 string2
484 @code{string-lessp} is another name for @code{string<}.
487 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
488 This function compares the specified part of @var{string1} with the
489 specified part of @var{string2}. The specified part of @var{string1}
490 runs from index @var{start1} up to index @var{end1} (@code{nil} means
491 the end of the string). The specified part of @var{string2} runs from
492 index @var{start2} up to index @var{end2} (@code{nil} means the end of
495 The strings are both converted to multibyte for the comparison
496 (@pxref{Text Representations}) so that a unibyte string can be equal to
497 a multibyte string. If @var{ignore-case} is non-@code{nil}, then case
498 is ignored, so that upper case letters can be equal to lower case letters.
500 If the specified portions of the two strings match, the value is
501 @code{t}. Otherwise, the value is an integer which indicates how many
502 leading characters agree, and which string is less. Its absolute value
503 is one plus the number of characters that agree at the beginning of the
504 two strings. The sign is negative if @var{string1} (or its specified
508 @defun assoc-ignore-case key alist
509 This function works like @code{assoc}, except that @var{key} must be a
510 string, and comparison is done using @code{compare-strings}, ignoring
511 case differences. @xref{Association Lists}.
514 @defun assoc-ignore-representation key alist
515 This function works like @code{assoc}, except that @var{key} must be a
516 string, and comparison is done using @code{compare-strings}.
517 Case differences are significant.
520 See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
521 a way to compare text in buffers. The function @code{string-match},
522 which matches a regular expression against a string, can be used
523 for a kind of string comparison; see @ref{Regexp Search}.
525 @node String Conversion
526 @comment node-name, next, previous, up
527 @section Conversion of Characters and Strings
528 @cindex conversion of strings
530 This section describes functions for conversions between characters,
531 strings and integers. @code{format} and @code{prin1-to-string}
532 (@pxref{Output Functions}) can also convert Lisp objects into strings.
533 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
534 string representation of a Lisp object into an object. The functions
535 @code{string-make-multibyte} and @code{string-make-unibyte} convert the
536 text representation of a string (@pxref{Converting Representations}).
538 @xref{Documentation}, for functions that produce textual descriptions
539 of text characters and general input events
540 (@code{single-key-description} and @code{text-char-description}). These
541 functions are used primarily for making help messages.
543 @defun char-to-string character
544 @cindex character to string
545 This function returns a new string containing one character,
546 @var{character}. This function is semi-obsolete because the function
547 @code{string} is more general. @xref{Creating Strings}.
550 @defun string-to-char string
551 @cindex string to character
552 This function returns the first character in @var{string}. If the
553 string is empty, the function returns 0. The value is also 0 when the
554 first character of @var{string} is the null character, @sc{ascii} code
558 (string-to-char "ABC")
560 (string-to-char "xyz")
565 (string-to-char "\000")
570 This function may be eliminated in the future if it does not seem useful
574 @defun number-to-string number
575 @cindex integer to string
576 @cindex integer to decimal
577 This function returns a string consisting of the printed base-ten
578 representation of @var{number}, which may be an integer or a floating
579 point number. The returned value starts with a minus sign if the argument is
583 (number-to-string 256)
586 (number-to-string -23)
589 (number-to-string -23.5)
593 @cindex int-to-string
594 @code{int-to-string} is a semi-obsolete alias for this function.
596 See also the function @code{format} in @ref{Formatting Strings}.
599 @defun string-to-number string &optional base
600 @cindex string to number
601 This function returns the numeric value of the characters in
602 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
603 between 2 and 16 (inclusive), and integers are converted in that base.
604 If @var{base} is @code{nil}, then base ten is used. Floating point
605 conversion only works in base ten; we have not implemented other
606 radices for floating point numbers, because that would be much more
607 work and does not seem useful. If @var{string} looks like an integer
608 but its value is too large to fit into a Lisp integer,
609 @code{string-to-number} returns a floating point result.
611 The parsing skips spaces and tabs at the beginning of @var{string},
612 then reads as much of @var{string} as it can interpret as a number in
613 the given base. (On some systems it ignores other whitespace at the
614 beginning, not just spaces and tabs.) If the first character after
615 the ignored whitespace is neither a digit in the given base, nor a
616 plus or minus sign, nor the leading dot of a floating point number,
617 this function returns 0.
620 (string-to-number "256")
622 (string-to-number "25 is a perfect square.")
624 (string-to-number "X256")
626 (string-to-number "-4.5")
628 (string-to-number "1e5")
632 @findex string-to-int
633 @code{string-to-int} is an obsolete alias for this function.
636 Here are some other functions that can convert to or from a string:
640 @code{concat} can convert a vector or a list into a string.
641 @xref{Creating Strings}.
644 @code{vconcat} can convert a string into a vector. @xref{Vector
648 @code{append} can convert a string into a list. @xref{Building Lists}.
651 @node Formatting Strings
652 @comment node-name, next, previous, up
653 @section Formatting Strings
654 @cindex formatting strings
655 @cindex strings, formatting them
657 @dfn{Formatting} means constructing a string by substitution of
658 computed values at various places in a constant string. This constant string
659 controls how the other values are printed, as well as where they appear;
660 it is called a @dfn{format string}.
662 Formatting is often useful for computing messages to be displayed. In
663 fact, the functions @code{message} and @code{error} provide the same
664 formatting feature described here; they differ from @code{format} only
665 in how they use the result of formatting.
667 @defun format string &rest objects
668 This function returns a new string that is made by copying
669 @var{string} and then replacing any format specification
670 in the copy with encodings of the corresponding @var{objects}. The
671 arguments @var{objects} are the computed values to be formatted.
673 The characters in @var{string}, other than the format specifications,
674 are copied directly into the output; starting in Emacs 21, if they have
675 text properties, these are copied into the output also.
678 @cindex @samp{%} in format
679 @cindex format specification
680 A format specification is a sequence of characters beginning with a
681 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
682 @code{format} function replaces it with the printed representation of
683 one of the values to be formatted (one of the arguments @var{objects}).
688 (format "The value of fill-column is %d." fill-column)
689 @result{} "The value of fill-column is 72."
693 If @var{string} contains more than one format specification, the
694 format specifications correspond to successive values from
695 @var{objects}. Thus, the first format specification in @var{string}
696 uses the first such value, the second format specification uses the
697 second such value, and so on. Any extra format specifications (those
698 for which there are no corresponding values) cause unpredictable
699 behavior. Any extra values to be formatted are ignored.
701 Certain format specifications require values of particular types. If
702 you supply a value that doesn't fit the requirements, an error is
705 Here is a table of valid format specifications:
709 Replace the specification with the printed representation of the object,
710 made without quoting (that is, using @code{princ}, not
711 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
712 by their contents alone, with no @samp{"} characters, and symbols appear
713 without @samp{\} characters.
715 Starting in Emacs 21, if the object is a string, its text properties are
716 copied into the output. The text properties of the @samp{%s} itself
717 are also copied, but those of the object take priority.
720 Replace the specification with the printed representation of the object,
721 made with quoting (that is, using @code{prin1}---@pxref{Output
722 Functions}). Thus, strings are enclosed in @samp{"} characters, and
723 @samp{\} characters appear where necessary before special characters.
726 @cindex integer to octal
727 Replace the specification with the base-eight representation of an
731 Replace the specification with the base-ten representation of an
736 @cindex integer to hexadecimal
737 Replace the specification with the base-sixteen representation of an
738 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
741 Replace the specification with the character which is the value given.
744 Replace the specification with the exponential notation for a floating
748 Replace the specification with the decimal-point notation for a floating
752 Replace the specification with notation for a floating point number,
753 using either exponential notation or decimal-point notation, whichever
757 Replace the specification with a single @samp{%}. This format
758 specification is unusual in that it does not use a value. For example,
759 @code{(format "%% %d" 30)} returns @code{"% 30"}.
762 Any other format character results in an @samp{Invalid format
765 Here are several examples:
769 (format "The name of this buffer is %s." (buffer-name))
770 @result{} "The name of this buffer is strings.texi."
772 (format "The buffer object prints as %s." (current-buffer))
773 @result{} "The buffer object prints as strings.texi."
775 (format "The octal value of %d is %o,
776 and the hex value is %x." 18 18 18)
777 @result{} "The octal value of 18 is 22,
778 and the hex value is 12."
782 @cindex numeric prefix
785 All the specification characters allow an optional numeric prefix
786 between the @samp{%} and the character. The optional numeric prefix
787 defines the minimum width for the object. If the printed
788 representation of the object contains fewer characters than this, then
789 it is padded. The padding is on the left if the prefix is positive
790 (or starts with zero) and on the right if the prefix is negative. The
791 padding character is normally a space, but if the numeric prefix
792 starts with a zero, zeros are used for padding. Some of these
793 conventions are ignored for specification characters for which they do
794 not make sense. That is, %s, %S and %c accept a numeric prefix
795 starting with 0, but still pad with @emph{spaces} on the left. Also,
796 %% accepts a numeric prefix, but ignores it. Here are some examples
800 (format "%06d is padded on the left with zeros" 123)
801 @result{} "000123 is padded on the left with zeros"
803 (format "%-6d is padded on the right" 123)
804 @result{} "123 is padded on the right"
807 @code{format} never truncates an object's printed representation, no
808 matter what width you specify. Thus, you can use a numeric prefix to
809 specify a minimum spacing between columns with no risk of losing
812 In the following three examples, @samp{%7s} specifies a minimum width
813 of 7. In the first case, the string inserted in place of @samp{%7s} has
814 only 3 letters, so 4 blank spaces are inserted for padding. In the
815 second case, the string @code{"specification"} is 13 letters wide but is
816 not truncated. In the third case, the padding is on the right.
820 (format "The word `%7s' actually has %d letters in it."
821 "foo" (length "foo"))
822 @result{} "The word ` foo' actually has 3 letters in it."
826 (format "The word `%7s' actually has %d letters in it."
827 "specification" (length "specification"))
828 @result{} "The word `specification' actually has 13 letters in it."
832 (format "The word `%-7s' actually has %d letters in it."
833 "foo" (length "foo"))
834 @result{} "The word `foo ' actually has 3 letters in it."
838 @node Case Conversion
839 @comment node-name, next, previous, up
840 @section Case Conversion in Lisp
843 @cindex character case
844 @cindex case conversion in Lisp
846 The character case functions change the case of single characters or
847 of the contents of strings. The functions normally convert only
848 alphabetic characters (the letters @samp{A} through @samp{Z} and
849 @samp{a} through @samp{z}, as well as non-@sc{ascii} letters); other
850 characters are not altered. You can specify a different case
851 conversion mapping by specifying a case table (@pxref{Case Tables}).
853 These functions do not modify the strings that are passed to them as
856 The examples below use the characters @samp{X} and @samp{x} which have
857 @sc{ascii} codes 88 and 120 respectively.
859 @defun downcase string-or-char
860 This function converts a character or a string to lower case.
862 When the argument to @code{downcase} is a string, the function creates
863 and returns a new string in which each letter in the argument that is
864 upper case is converted to lower case. When the argument to
865 @code{downcase} is a character, @code{downcase} returns the
866 corresponding lower case character. This value is an integer. If the
867 original character is lower case, or is not a letter, then the value
868 equals the original character.
871 (downcase "The cat in the hat")
872 @result{} "the cat in the hat"
879 @defun upcase string-or-char
880 This function converts a character or a string to upper case.
882 When the argument to @code{upcase} is a string, the function creates
883 and returns a new string in which each letter in the argument that is
884 lower case is converted to upper case.
886 When the argument to @code{upcase} is a character, @code{upcase}
887 returns the corresponding upper case character. This value is an integer.
888 If the original character is upper case, or is not a letter, then the
889 value returned equals the original character.
892 (upcase "The cat in the hat")
893 @result{} "THE CAT IN THE HAT"
900 @defun capitalize string-or-char
901 @cindex capitalization
902 This function capitalizes strings or characters. If
903 @var{string-or-char} is a string, the function creates and returns a new
904 string, whose contents are a copy of @var{string-or-char} in which each
905 word has been capitalized. This means that the first character of each
906 word is converted to upper case, and the rest are converted to lower
909 The definition of a word is any sequence of consecutive characters that
910 are assigned to the word constituent syntax class in the current syntax
911 table (@pxref{Syntax Class Table}).
913 When the argument to @code{capitalize} is a character, @code{capitalize}
914 has the same result as @code{upcase}.
918 (capitalize "The cat in the hat")
919 @result{} "The Cat In The Hat"
923 (capitalize "THE 77TH-HATTED CAT")
924 @result{} "The 77th-Hatted Cat"
934 @defun upcase-initials string-or-char
935 If @var{string-or-char} is a string, this function capitalizes the
936 initials of the words in @var{string-or-char}, without altering any
937 letters other than the initials. It returns a new string whose
938 contents are a copy of @var{string-or-char}, in which each word has
939 had its initial letter converted to upper case.
941 The definition of a word is any sequence of consecutive characters that
942 are assigned to the word constituent syntax class in the current syntax
943 table (@pxref{Syntax Class Table}).
945 When the argument to @code{upcase-initials} is a character,
946 @code{upcase-initials} has the same result as @code{upcase}.
950 (upcase-initials "The CAT in the hAt")
951 @result{} "The CAT In The HAt"
956 @xref{Text Comparison}, for functions that compare strings; some of
957 them ignore case differences, or can optionally ignore case differences.
960 @section The Case Table
962 You can customize case conversion by installing a special @dfn{case
963 table}. A case table specifies the mapping between upper case and lower
964 case letters. It affects both the case conversion functions for Lisp
965 objects (see the previous section) and those that apply to text in the
966 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
967 also a standard case table which is used to initialize the case table
970 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
971 @code{case-table}. This char-table maps each character into the
972 corresponding lower case character. It has three extra slots, which
977 The upcase table maps each character into the corresponding upper
980 The canonicalize table maps all of a set of case-related characters
981 into a particular member of that set.
983 The equivalences table maps each one of a set of case-related characters
984 into the next character in that set.
987 In simple cases, all you need to specify is the mapping to lower-case;
988 the three related tables will be calculated automatically from that one.
990 For some languages, upper and lower case letters are not in one-to-one
991 correspondence. There may be two different lower case letters with the
992 same upper case equivalent. In these cases, you need to specify the
993 maps for both lower case and upper case.
995 The extra table @var{canonicalize} maps each character to a canonical
996 equivalent; any two characters that are related by case-conversion have
997 the same canonical equivalent character. For example, since @samp{a}
998 and @samp{A} are related by case-conversion, they should have the same
999 canonical equivalent character (which should be either @samp{a} for both
1000 of them, or @samp{A} for both of them).
1002 The extra table @var{equivalences} is a map that cyclicly permutes
1003 each equivalence class (of characters with the same canonical
1004 equivalent). (For ordinary @sc{ascii}, this would map @samp{a} into
1005 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1006 equivalent characters.)
1008 When you construct a case table, you can provide @code{nil} for
1009 @var{canonicalize}; then Emacs fills in this slot from the lower case
1010 and upper case mappings. You can also provide @code{nil} for
1011 @var{equivalences}; then Emacs fills in this slot from
1012 @var{canonicalize}. In a case table that is actually in use, those
1013 components are non-@code{nil}. Do not try to specify @var{equivalences}
1014 without also specifying @var{canonicalize}.
1016 Here are the functions for working with case tables:
1018 @defun case-table-p object
1019 This predicate returns non-@code{nil} if @var{object} is a valid case
1023 @defun set-standard-case-table table
1024 This function makes @var{table} the standard case table, so that it will
1025 be used in any buffers created subsequently.
1028 @defun standard-case-table
1029 This returns the standard case table.
1032 @defun current-case-table
1033 This function returns the current buffer's case table.
1036 @defun set-case-table table
1037 This sets the current buffer's case table to @var{table}.
1040 The following three functions are convenient subroutines for packages
1041 that define non-@sc{ascii} character sets. They modify the specified
1042 case table @var{case-table}; they also modify the standard syntax table.
1043 @xref{Syntax Tables}. Normally you would use these functions to change
1044 the standard case table.
1046 @defun set-case-syntax-pair uc lc case-table
1047 This function specifies a pair of corresponding letters, one upper case
1051 @defun set-case-syntax-delims l r case-table
1052 This function makes characters @var{l} and @var{r} a matching pair of
1053 case-invariant delimiters.
1056 @defun set-case-syntax char syntax case-table
1057 This function makes @var{char} case-invariant, with syntax
1061 @deffn Command describe-buffer-case-table
1062 This command displays a description of the contents of the current
1063 buffer's case table.
1067 arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4