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 as an index, 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 either @var{start} or
212 @var{end} is not an integer or @code{nil}. An @code{args-out-of-range}
213 error is signaled if @var{start} indicates a character following
214 @var{end}, or if either integer is out of range for @var{string}.
216 Contrast this function with @code{buffer-substring} (@pxref{Buffer
217 Contents}), which returns a string containing a portion of the text in
218 the current buffer. The beginning of a string is at index 0, but the
219 beginning of a buffer is at index 1.
222 @defun concat &rest sequences
223 @cindex copying strings
224 @cindex concatenating strings
225 This function returns a new string consisting of the characters in the
226 arguments passed to it (along with their text properties, if any). The
227 arguments may be strings, lists of numbers, or vectors of numbers; they
228 are not themselves changed. If @code{concat} receives no arguments, it
229 returns an empty string.
232 (concat "abc" "-def")
234 (concat "abc" (list 120 121) [122])
236 ;; @r{@code{nil} is an empty sequence.}
237 (concat "abc" nil "-def")
239 (concat "The " "quick brown " "fox.")
240 @result{} "The quick brown fox."
246 The @code{concat} function always constructs a new string that is
247 not @code{eq} to any existing string.
249 In Emacs versions before 21, when an argument was an integer (not a
250 sequence of integers), it was converted to a string of digits making up
251 the decimal printed representation of the integer. This obsolete usage
252 no longer works. The proper way to convert an integer to its decimal
253 printed form is with @code{format} (@pxref{Formatting Strings}) or
254 @code{number-to-string} (@pxref{String Conversion}).
256 For information about other concatenation functions, see the
257 description of @code{mapconcat} in @ref{Mapping Functions},
258 @code{vconcat} in @ref{Vectors}, and @code{append} in @ref{Building
262 @defun split-string string separators omit-nulls
263 This function splits @var{string} into substrings at matches for the regular
264 expression @var{separators}. Each match for @var{separators} defines a
265 splitting point; the substrings between the splitting points are made
266 into a list, which is the value returned by @code{split-string}. If
267 @var{omit-nulls} is @code{t}, null strings will be removed from the
268 result list. Otherwise, null strings are left in the result.
269 If @var{separators} is @code{nil} (or omitted),
270 the default is the value of @code{split-string-default-separators}.
272 As a special case, when @var{separators} is @code{nil} (or omitted),
273 null strings are always omitted from the result. Thus:
276 (split-string " two words ")
277 @result{} ("two" "words")
280 The result is not @samp{("" "two" "words" "")}, which would rarely be
281 useful. If you need such a result, use an explict value for
285 (split-string " two words " split-string-default-separators)
286 @result{} ("" "two" "words" "")
292 (split-string "Soup is good food" "o")
293 @result{} ("S" "up is g" "" "d f" "" "d")
294 (split-string "Soup is good food" "o" t)
295 @result{} ("S" "up is g" "d f" "d")
296 (split-string "Soup is good food" "o+")
297 @result{} ("S" "up is g" "d f" "d")
300 Empty matches do count, when not adjacent to another match:
303 (split-string "Soup is good food" "o*")
304 @result{}("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
305 (split-string "Nice doggy!" "")
306 @result{}("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
310 @defvar split-string-default-separators
311 The default value of @var{separators} for @code{split-string}, initially
312 @samp{"[ \f\t\n\r\v]+"}.
315 @node Modifying Strings
316 @section Modifying Strings
318 The most basic way to alter the contents of an existing string is with
319 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
320 @var{idx} @var{char})} stores @var{char} into @var{string} at index
321 @var{idx}. Each character occupies one or more bytes, and if @var{char}
322 needs a different number of bytes from the character already present at
323 that index, @code{aset} signals an error.
325 A more powerful function is @code{store-substring}:
327 @defun store-substring string idx obj
328 This function alters part of the contents of the string @var{string}, by
329 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
330 may be either a character or a (smaller) string.
332 Since it is impossible to change the length of an existing string, it is
333 an error if @var{obj} doesn't fit within @var{string}'s actual length,
334 or if any new character requires a different number of bytes from the
335 character currently present at that point in @var{string}.
339 @node Text Comparison
340 @section Comparison of Characters and Strings
341 @cindex string equality
343 @defun char-equal character1 character2
344 This function returns @code{t} if the arguments represent the same
345 character, @code{nil} otherwise. This function ignores differences
346 in case if @code{case-fold-search} is non-@code{nil}.
351 (let ((case-fold-search nil))
357 @defun string= string1 string2
358 This function returns @code{t} if the characters of the two strings
360 Case is always significant, regardless of @code{case-fold-search}.
363 (string= "abc" "abc")
365 (string= "abc" "ABC")
371 The function @code{string=} ignores the text properties of the two
372 strings. When @code{equal} (@pxref{Equality Predicates}) compares two
373 strings, it uses @code{string=}.
375 If the strings contain non-@sc{ascii} characters, and one is unibyte
376 while the other is multibyte, then they cannot be equal. @xref{Text
380 @defun string-equal string1 string2
381 @code{string-equal} is another name for @code{string=}.
384 @cindex lexical comparison
385 @defun string< string1 string2
386 @c (findex string< causes problems for permuted index!!)
387 This function compares two strings a character at a time. It
388 scans both the strings at the same time to find the first pair of corresponding
389 characters that do not match. If the lesser character of these two is
390 the character from @var{string1}, then @var{string1} is less, and this
391 function returns @code{t}. If the lesser character is the one from
392 @var{string2}, then @var{string1} is greater, and this function returns
393 @code{nil}. If the two strings match entirely, the value is @code{nil}.
395 Pairs of characters are compared according to their character codes.
396 Keep in mind that lower case letters have higher numeric values in the
397 @sc{ascii} character set than their upper case counterparts; digits and
398 many punctuation characters have a lower numeric value than upper case
399 letters. An @sc{ascii} character is less than any non-@sc{ascii}
400 character; a unibyte non-@sc{ascii} character is always less than any
401 multibyte non-@sc{ascii} character (@pxref{Text Representations}).
405 (string< "abc" "abd")
407 (string< "abd" "abc")
409 (string< "123" "abc")
414 When the strings have different lengths, and they match up to the
415 length of @var{string1}, then the result is @code{t}. If they match up
416 to the length of @var{string2}, the result is @code{nil}. A string of
417 no characters is less than any other string.
435 @defun string-lessp string1 string2
436 @code{string-lessp} is another name for @code{string<}.
439 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
440 This function compares the specified part of @var{string1} with the
441 specified part of @var{string2}. The specified part of @var{string1}
442 runs from index @var{start1} up to index @var{end1} (@code{nil} means
443 the end of the string). The specified part of @var{string2} runs from
444 index @var{start2} up to index @var{end2} (@code{nil} means the end of
447 The strings are both converted to multibyte for the comparison
448 (@pxref{Text Representations}) so that a unibyte string can be equal to
449 a multibyte string. If @var{ignore-case} is non-@code{nil}, then case
450 is ignored, so that upper case letters can be equal to lower case letters.
452 If the specified portions of the two strings match, the value is
453 @code{t}. Otherwise, the value is an integer which indicates how many
454 leading characters agree, and which string is less. Its absolute value
455 is one plus the number of characters that agree at the beginning of the
456 two strings. The sign is negative if @var{string1} (or its specified
460 @defun assoc-ignore-case key alist
461 This function works like @code{assoc}, except that @var{key} must be a
462 string, and comparison is done using @code{compare-strings}, ignoring
463 case differences. @xref{Association Lists}.
466 @defun assoc-ignore-representation key alist
467 This function works like @code{assoc}, except that @var{key} must be a
468 string, and comparison is done using @code{compare-strings}.
469 Case differences are significant.
472 See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
473 a way to compare text in buffers. The function @code{string-match},
474 which matches a regular expression against a string, can be used
475 for a kind of string comparison; see @ref{Regexp Search}.
477 @node String Conversion
478 @comment node-name, next, previous, up
479 @section Conversion of Characters and Strings
480 @cindex conversion of strings
482 This section describes functions for conversions between characters,
483 strings and integers. @code{format} and @code{prin1-to-string}
484 (@pxref{Output Functions}) can also convert Lisp objects into strings.
485 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
486 string representation of a Lisp object into an object. The functions
487 @code{string-make-multibyte} and @code{string-make-unibyte} convert the
488 text representation of a string (@pxref{Converting Representations}).
490 @xref{Documentation}, for functions that produce textual descriptions
491 of text characters and general input events
492 (@code{single-key-description} and @code{text-char-description}). These
493 functions are used primarily for making help messages.
495 @defun char-to-string character
496 @cindex character to string
497 This function returns a new string containing one character,
498 @var{character}. This function is semi-obsolete because the function
499 @code{string} is more general. @xref{Creating Strings}.
502 @defun string-to-char string
503 @cindex string to character
504 This function returns the first character in @var{string}. If the
505 string is empty, the function returns 0. The value is also 0 when the
506 first character of @var{string} is the null character, @sc{ascii} code
510 (string-to-char "ABC")
512 (string-to-char "xyz")
517 (string-to-char "\000")
522 This function may be eliminated in the future if it does not seem useful
526 @defun number-to-string number
527 @cindex integer to string
528 @cindex integer to decimal
529 This function returns a string consisting of the printed base-ten
530 representation of @var{number}, which may be an integer or a floating
531 point number. The returned value starts with a minus sign if the argument is
535 (number-to-string 256)
537 (number-to-string -23)
539 (number-to-string -23.5)
543 @cindex int-to-string
544 @code{int-to-string} is a semi-obsolete alias for this function.
546 See also the function @code{format} in @ref{Formatting Strings}.
549 @defun string-to-number string &optional base
550 @cindex string to number
551 This function returns the numeric value of the characters in
552 @var{string}. If @var{base} is non-@code{nil}, integers are converted
553 in that base. If @var{base} is @code{nil}, then base ten is used.
554 Floating point conversion always uses base ten; we have not implemented
555 other radices for floating point numbers, because that would be much
556 more work and does not seem useful. If @var{string} looks like an
557 integer but its value is too large to fit into a Lisp integer,
558 @code{string-to-number} returns a floating point result.
560 The parsing skips spaces and tabs at the beginning of @var{string}, then
561 reads as much of @var{string} as it can interpret as a number. (On some
562 systems it ignores other whitespace at the beginning, not just spaces
563 and tabs.) If the first character after the ignored whitespace is
564 neither a digit, nor a plus or minus sign, nor the leading dot of a
565 floating point number, this function returns 0.
568 (string-to-number "256")
570 (string-to-number "25 is a perfect square.")
572 (string-to-number "X256")
574 (string-to-number "-4.5")
576 (string-to-number "1e5")
580 @findex string-to-int
581 @code{string-to-int} is an obsolete alias for this function.
584 Here are some other functions that can convert to or from a string:
588 @code{concat} can convert a vector or a list into a string.
589 @xref{Creating Strings}.
592 @code{vconcat} can convert a string into a vector. @xref{Vector
596 @code{append} can convert a string into a list. @xref{Building Lists}.
599 @node Formatting Strings
600 @comment node-name, next, previous, up
601 @section Formatting Strings
602 @cindex formatting strings
603 @cindex strings, formatting them
605 @dfn{Formatting} means constructing a string by substitution of
606 computed values at various places in a constant string. This constant string
607 controls how the other values are printed, as well as where they appear;
608 it is called a @dfn{format string}.
610 Formatting is often useful for computing messages to be displayed. In
611 fact, the functions @code{message} and @code{error} provide the same
612 formatting feature described here; they differ from @code{format} only
613 in how they use the result of formatting.
615 @defun format string &rest objects
616 This function returns a new string that is made by copying
617 @var{string} and then replacing any format specification
618 in the copy with encodings of the corresponding @var{objects}. The
619 arguments @var{objects} are the computed values to be formatted.
621 The characters in @var{string}, other than the format specifications,
622 are copied directly into the output; starting in Emacs 21, if they have
623 text properties, these are copied into the output also.
626 @cindex @samp{%} in format
627 @cindex format specification
628 A format specification is a sequence of characters beginning with a
629 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
630 @code{format} function replaces it with the printed representation of
631 one of the values to be formatted (one of the arguments @var{objects}).
636 (format "The value of fill-column is %d." fill-column)
637 @result{} "The value of fill-column is 72."
641 If @var{string} contains more than one format specification, the
642 format specifications correspond to successive values from
643 @var{objects}. Thus, the first format specification in @var{string}
644 uses the first such value, the second format specification uses the
645 second such value, and so on. Any extra format specifications (those
646 for which there are no corresponding values) cause unpredictable
647 behavior. Any extra values to be formatted are ignored.
649 Certain format specifications require values of particular types. If
650 you supply a value that doesn't fit the requirements, an error is
653 Here is a table of valid format specifications:
657 Replace the specification with the printed representation of the object,
658 made without quoting (that is, using @code{princ}, not
659 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
660 by their contents alone, with no @samp{"} characters, and symbols appear
661 without @samp{\} characters.
663 Starting in Emacs 21, if the object is a string, its text properties are
664 copied into the output. The text properties of the @samp{%s} itself
665 are also copied, but those of the object take priority.
667 If there is no corresponding object, the empty string is used.
670 Replace the specification with the printed representation of the object,
671 made with quoting (that is, using @code{prin1}---@pxref{Output
672 Functions}). Thus, strings are enclosed in @samp{"} characters, and
673 @samp{\} characters appear where necessary before special characters.
675 If there is no corresponding object, the empty string is used.
678 @cindex integer to octal
679 Replace the specification with the base-eight representation of an
683 Replace the specification with the base-ten representation of an
688 @cindex integer to hexadecimal
689 Replace the specification with the base-sixteen representation of an
690 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
693 Replace the specification with the character which is the value given.
696 Replace the specification with the exponential notation for a floating
700 Replace the specification with the decimal-point notation for a floating
704 Replace the specification with notation for a floating point number,
705 using either exponential notation or decimal-point notation, whichever
709 Replace the specification with a single @samp{%}. This format
710 specification is unusual in that it does not use a value. For example,
711 @code{(format "%% %d" 30)} returns @code{"% 30"}.
714 Any other format character results in an @samp{Invalid format
717 Here are several examples:
721 (format "The name of this buffer is %s." (buffer-name))
722 @result{} "The name of this buffer is strings.texi."
724 (format "The buffer object prints as %s." (current-buffer))
725 @result{} "The buffer object prints as strings.texi."
727 (format "The octal value of %d is %o,
728 and the hex value is %x." 18 18 18)
729 @result{} "The octal value of 18 is 22,
730 and the hex value is 12."
734 @cindex numeric prefix
737 All the specification characters allow an optional numeric prefix
738 between the @samp{%} and the character. The optional numeric prefix
739 defines the minimum width for the object. If the printed representation
740 of the object contains fewer characters than this, then it is padded.
741 The padding is on the left if the prefix is positive (or starts with
742 zero) and on the right if the prefix is negative. The padding character
743 is normally a space, but if the numeric prefix starts with a zero, zeros
744 are used for padding. Here are some examples of padding:
747 (format "%06d is padded on the left with zeros" 123)
748 @result{} "000123 is padded on the left with zeros"
750 (format "%-6d is padded on the right" 123)
751 @result{} "123 is padded on the right"
754 @code{format} never truncates an object's printed representation, no
755 matter what width you specify. Thus, you can use a numeric prefix to
756 specify a minimum spacing between columns with no risk of losing
759 In the following three examples, @samp{%7s} specifies a minimum width
760 of 7. In the first case, the string inserted in place of @samp{%7s} has
761 only 3 letters, so 4 blank spaces are inserted for padding. In the
762 second case, the string @code{"specification"} is 13 letters wide but is
763 not truncated. In the third case, the padding is on the right.
767 (format "The word `%7s' actually has %d letters in it."
768 "foo" (length "foo"))
769 @result{} "The word ` foo' actually has 3 letters in it."
773 (format "The word `%7s' actually has %d letters in it."
774 "specification" (length "specification"))
775 @result{} "The word `specification' actually has 13 letters in it."
779 (format "The word `%-7s' actually has %d letters in it."
780 "foo" (length "foo"))
781 @result{} "The word `foo ' actually has 3 letters in it."
785 @node Case Conversion
786 @comment node-name, next, previous, up
787 @section Case Conversion in Lisp
790 @cindex character case
791 @cindex case conversion in Lisp
793 The character case functions change the case of single characters or
794 of the contents of strings. The functions normally convert only
795 alphabetic characters (the letters @samp{A} through @samp{Z} and
796 @samp{a} through @samp{z}, as well as non-@sc{ascii} letters); other
797 characters are not altered. You can specify a different case
798 conversion mapping by specifying a case table (@pxref{Case Tables}).
800 These functions do not modify the strings that are passed to them as
803 The examples below use the characters @samp{X} and @samp{x} which have
804 @sc{ascii} codes 88 and 120 respectively.
806 @defun downcase string-or-char
807 This function converts a character or a string to lower case.
809 When the argument to @code{downcase} is a string, the function creates
810 and returns a new string in which each letter in the argument that is
811 upper case is converted to lower case. When the argument to
812 @code{downcase} is a character, @code{downcase} returns the
813 corresponding lower case character. This value is an integer. If the
814 original character is lower case, or is not a letter, then the value
815 equals the original character.
818 (downcase "The cat in the hat")
819 @result{} "the cat in the hat"
826 @defun upcase string-or-char
827 This function converts a character or a string to upper case.
829 When the argument to @code{upcase} is a string, the function creates
830 and returns a new string in which each letter in the argument that is
831 lower case is converted to upper case.
833 When the argument to @code{upcase} is a character, @code{upcase}
834 returns the corresponding upper case character. This value is an integer.
835 If the original character is upper case, or is not a letter, then the
836 value returned equals the original character.
839 (upcase "The cat in the hat")
840 @result{} "THE CAT IN THE HAT"
847 @defun capitalize string-or-char
848 @cindex capitalization
849 This function capitalizes strings or characters. If
850 @var{string-or-char} is a string, the function creates and returns a new
851 string, whose contents are a copy of @var{string-or-char} in which each
852 word has been capitalized. This means that the first character of each
853 word is converted to upper case, and the rest are converted to lower
856 The definition of a word is any sequence of consecutive characters that
857 are assigned to the word constituent syntax class in the current syntax
858 table (@pxref{Syntax Class Table}).
860 When the argument to @code{capitalize} is a character, @code{capitalize}
861 has the same result as @code{upcase}.
864 (capitalize "The cat in the hat")
865 @result{} "The Cat In The Hat"
867 (capitalize "THE 77TH-HATTED CAT")
868 @result{} "The 77th-Hatted Cat"
877 @defun upcase-initials string
878 This function capitalizes the initials of the words in @var{string},
879 without altering any letters other than the initials. It returns a new
880 string whose contents are a copy of @var{string}, in which each word has
881 had its initial letter converted to upper case.
883 The definition of a word is any sequence of consecutive characters that
884 are assigned to the word constituent syntax class in the current syntax
885 table (@pxref{Syntax Class Table}).
889 (upcase-initials "The CAT in the hAt")
890 @result{} "The CAT In The HAt"
895 @xref{Text Comparison}, for functions that compare strings; some of
896 them ignore case differences, or can optionally ignore case differences.
899 @section The Case Table
901 You can customize case conversion by installing a special @dfn{case
902 table}. A case table specifies the mapping between upper case and lower
903 case letters. It affects both the case conversion functions for Lisp
904 objects (see the previous section) and those that apply to text in the
905 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
906 also a standard case table which is used to initialize the case table
909 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
910 @code{case-table}. This char-table maps each character into the
911 corresponding lower case character. It has three extra slots, which
916 The upcase table maps each character into the corresponding upper
919 The canonicalize table maps all of a set of case-related characters
920 into a particular member of that set.
922 The equivalences table maps each one of a set of case-related characters
923 into the next character in that set.
926 In simple cases, all you need to specify is the mapping to lower-case;
927 the three related tables will be calculated automatically from that one.
929 For some languages, upper and lower case letters are not in one-to-one
930 correspondence. There may be two different lower case letters with the
931 same upper case equivalent. In these cases, you need to specify the
932 maps for both lower case and upper case.
934 The extra table @var{canonicalize} maps each character to a canonical
935 equivalent; any two characters that are related by case-conversion have
936 the same canonical equivalent character. For example, since @samp{a}
937 and @samp{A} are related by case-conversion, they should have the same
938 canonical equivalent character (which should be either @samp{a} for both
939 of them, or @samp{A} for both of them).
941 The extra table @var{equivalences} is a map that cyclicly permutes
942 each equivalence class (of characters with the same canonical
943 equivalent). (For ordinary @sc{ascii}, this would map @samp{a} into
944 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
945 equivalent characters.)
947 When you construct a case table, you can provide @code{nil} for
948 @var{canonicalize}; then Emacs fills in this slot from the lower case
949 and upper case mappings. You can also provide @code{nil} for
950 @var{equivalences}; then Emacs fills in this slot from
951 @var{canonicalize}. In a case table that is actually in use, those
952 components are non-@code{nil}. Do not try to specify @var{equivalences}
953 without also specifying @var{canonicalize}.
955 Here are the functions for working with case tables:
957 @defun case-table-p object
958 This predicate returns non-@code{nil} if @var{object} is a valid case
962 @defun set-standard-case-table table
963 This function makes @var{table} the standard case table, so that it will
964 be used in any buffers created subsequently.
967 @defun standard-case-table
968 This returns the standard case table.
971 @defun current-case-table
972 This function returns the current buffer's case table.
975 @defun set-case-table table
976 This sets the current buffer's case table to @var{table}.
979 The following three functions are convenient subroutines for packages
980 that define non-@sc{ascii} character sets. They modify the specified
981 case table @var{case-table}; they also modify the standard syntax table.
982 @xref{Syntax Tables}. Normally you would use these functions to change
983 the standard case table.
985 @defun set-case-syntax-pair uc lc case-table
986 This function specifies a pair of corresponding letters, one upper case
990 @defun set-case-syntax-delims l r case-table
991 This function makes characters @var{l} and @var{r} a matching pair of
992 case-invariant delimiters.
995 @defun set-case-syntax char syntax case-table
996 This function makes @var{char} case-invariant, with syntax
1000 @deffn Command describe-buffer-case-table
1001 This command displays a description of the contents of the current
1002 buffer's case table.