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 @acronym{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-@acronym{ASCII} characters in
56 Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
57 Representations}). An @acronym{ASCII} character always occupies one byte in a
58 string; in fact, when a string is all @acronym{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 @acronym{ASCII} control characters, but no other
70 control characters. They do not distinguish case in @acronym{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 explicit 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}.
382 To clear out a string that contained a password, use
385 @defun clear-string string
386 This clears the contents of @var{string} to zeros.
387 It may also change @var{string}'s length and convert it to
392 @node Text Comparison
393 @section Comparison of Characters and Strings
394 @cindex string equality
396 @defun char-equal character1 character2
397 This function returns @code{t} if the arguments represent the same
398 character, @code{nil} otherwise. This function ignores differences
399 in case if @code{case-fold-search} is non-@code{nil}.
404 (let ((case-fold-search nil))
410 @defun string= string1 string2
411 This function returns @code{t} if the characters of the two strings
412 match exactly. Symbols are also allowed as arguments, in which case
413 their print names are used.
414 Case is always significant, regardless of @code{case-fold-search}.
417 (string= "abc" "abc")
419 (string= "abc" "ABC")
425 The function @code{string=} ignores the text properties of the two
426 strings. When @code{equal} (@pxref{Equality Predicates}) compares two
427 strings, it uses @code{string=}.
429 For technical reasons, a unibyte and a multibyte string are
430 @code{equal} if and only if they contain the same sequence of
431 character codes and all these codes are either in the range 0 through
432 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
433 However, when a unibyte string gets converted to a multibyte string,
434 all characters with codes in the range 160 through 255 get converted
435 to characters with higher codes, whereas @acronym{ASCII} characters
436 remain unchanged. Thus, a unibyte string and its conversion to
437 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
438 Character codes 160 through 255 are not entirely proper in multibyte
439 text, even though they can occur. As a consequence, the situation
440 where a unibyte and a multibyte string are @code{equal} without both
441 being all @acronym{ASCII} is a technical oddity that very few Emacs
442 Lisp programmers ever get confronted with. @xref{Text
446 @defun string-equal string1 string2
447 @code{string-equal} is another name for @code{string=}.
450 @cindex lexical comparison
451 @defun string< string1 string2
452 @c (findex string< causes problems for permuted index!!)
453 This function compares two strings a character at a time. It
454 scans both the strings at the same time to find the first pair of corresponding
455 characters that do not match. If the lesser character of these two is
456 the character from @var{string1}, then @var{string1} is less, and this
457 function returns @code{t}. If the lesser character is the one from
458 @var{string2}, then @var{string1} is greater, and this function returns
459 @code{nil}. If the two strings match entirely, the value is @code{nil}.
461 Pairs of characters are compared according to their character codes.
462 Keep in mind that lower case letters have higher numeric values in the
463 @acronym{ASCII} character set than their upper case counterparts; digits and
464 many punctuation characters have a lower numeric value than upper case
465 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
466 character; a unibyte non-@acronym{ASCII} character is always less than any
467 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
471 (string< "abc" "abd")
473 (string< "abd" "abc")
475 (string< "123" "abc")
480 When the strings have different lengths, and they match up to the
481 length of @var{string1}, then the result is @code{t}. If they match up
482 to the length of @var{string2}, the result is @code{nil}. A string of
483 no characters is less than any other string.
500 Symbols are also allowed as arguments, in which case their print names
504 @defun string-lessp string1 string2
505 @code{string-lessp} is another name for @code{string<}.
508 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
509 This function compares the specified part of @var{string1} with the
510 specified part of @var{string2}. The specified part of @var{string1}
511 runs from index @var{start1} up to index @var{end1} (@code{nil} means
512 the end of the string). The specified part of @var{string2} runs from
513 index @var{start2} up to index @var{end2} (@code{nil} means the end of
516 The strings are both converted to multibyte for the comparison
517 (@pxref{Text Representations}) so that a unibyte string and its
518 conversion to multibyte are always regarded as equal. If
519 @var{ignore-case} is non-@code{nil}, then case is ignored, so that
520 upper case letters can be equal to lower case letters.
522 If the specified portions of the two strings match, the value is
523 @code{t}. Otherwise, the value is an integer which indicates how many
524 leading characters agree, and which string is less. Its absolute value
525 is one plus the number of characters that agree at the beginning of the
526 two strings. The sign is negative if @var{string1} (or its specified
530 @defun assoc-string key alist &optional case-fold
531 This function works like @code{assoc}, except that @var{key} must be a
532 string, and comparison is done using @code{compare-strings}. If
533 @var{case-fold} is non-@code{nil}, it ignores case differences.
534 Unlike @code{assoc}, this function can also match elements of the alist
535 that are strings rather than conses. In particular, @var{alist} can
536 be a list of strings rather than an actual alist.
537 @xref{Association Lists}.
540 See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
541 a way to compare text in buffers. The function @code{string-match},
542 which matches a regular expression against a string, can be used
543 for a kind of string comparison; see @ref{Regexp Search}.
545 @node String Conversion
546 @comment node-name, next, previous, up
547 @section Conversion of Characters and Strings
548 @cindex conversion of strings
550 This section describes functions for conversions between characters,
551 strings and integers. @code{format} and @code{prin1-to-string}
552 (@pxref{Output Functions}) can also convert Lisp objects into strings.
553 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
554 string representation of a Lisp object into an object. The functions
555 @code{string-make-multibyte} and @code{string-make-unibyte} convert the
556 text representation of a string (@pxref{Converting Representations}).
558 @xref{Documentation}, for functions that produce textual descriptions
559 of text characters and general input events
560 (@code{single-key-description} and @code{text-char-description}). These
561 functions are used primarily for making help messages.
563 @defun char-to-string character
564 @cindex character to string
565 This function returns a new string containing one character,
566 @var{character}. This function is semi-obsolete because the function
567 @code{string} is more general. @xref{Creating Strings}.
570 @defun string-to-char string
571 @cindex string to character
572 This function returns the first character in @var{string}. If the
573 string is empty, the function returns 0. The value is also 0 when the
574 first character of @var{string} is the null character, @acronym{ASCII} code
578 (string-to-char "ABC")
580 (string-to-char "xyz")
585 (string-to-char "\000")
590 This function may be eliminated in the future if it does not seem useful
594 @defun number-to-string number
595 @cindex integer to string
596 @cindex integer to decimal
597 This function returns a string consisting of the printed base-ten
598 representation of @var{number}, which may be an integer or a floating
599 point number. The returned value starts with a minus sign if the argument is
603 (number-to-string 256)
606 (number-to-string -23)
609 (number-to-string -23.5)
613 @cindex int-to-string
614 @code{int-to-string} is a semi-obsolete alias for this function.
616 See also the function @code{format} in @ref{Formatting Strings}.
619 @defun string-to-number string &optional base
620 @cindex string to number
621 This function returns the numeric value of the characters in
622 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
623 between 2 and 16 (inclusive), and integers are converted in that base.
624 If @var{base} is @code{nil}, then base ten is used. Floating point
625 conversion only works in base ten; we have not implemented other
626 radices for floating point numbers, because that would be much more
627 work and does not seem useful. If @var{string} looks like an integer
628 but its value is too large to fit into a Lisp integer,
629 @code{string-to-number} returns a floating point result.
631 The parsing skips spaces and tabs at the beginning of @var{string},
632 then reads as much of @var{string} as it can interpret as a number in
633 the given base. (On some systems it ignores other whitespace at the
634 beginning, not just spaces and tabs.) If the first character after
635 the ignored whitespace is neither a digit in the given base, nor a
636 plus or minus sign, nor the leading dot of a floating point number,
637 this function returns 0.
640 (string-to-number "256")
642 (string-to-number "25 is a perfect square.")
644 (string-to-number "X256")
646 (string-to-number "-4.5")
648 (string-to-number "1e5")
652 @findex string-to-int
653 @code{string-to-int} is an obsolete alias for this function.
656 Here are some other functions that can convert to or from a string:
660 @code{concat} can convert a vector or a list into a string.
661 @xref{Creating Strings}.
664 @code{vconcat} can convert a string into a vector. @xref{Vector
668 @code{append} can convert a string into a list. @xref{Building Lists}.
671 @node Formatting Strings
672 @comment node-name, next, previous, up
673 @section Formatting Strings
674 @cindex formatting strings
675 @cindex strings, formatting them
677 @dfn{Formatting} means constructing a string by substitution of
678 computed values at various places in a constant string. This constant string
679 controls how the other values are printed, as well as where they appear;
680 it is called a @dfn{format string}.
682 Formatting is often useful for computing messages to be displayed. In
683 fact, the functions @code{message} and @code{error} provide the same
684 formatting feature described here; they differ from @code{format} only
685 in how they use the result of formatting.
687 @defun format string &rest objects
688 This function returns a new string that is made by copying
689 @var{string} and then replacing any format specification
690 in the copy with encodings of the corresponding @var{objects}. The
691 arguments @var{objects} are the computed values to be formatted.
693 The characters in @var{string}, other than the format specifications,
694 are copied directly into the output; starting in Emacs 21, if they have
695 text properties, these are copied into the output also.
698 @cindex @samp{%} in format
699 @cindex format specification
700 A format specification is a sequence of characters beginning with a
701 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
702 @code{format} function replaces it with the printed representation of
703 one of the values to be formatted (one of the arguments @var{objects}).
708 (format "The value of fill-column is %d." fill-column)
709 @result{} "The value of fill-column is 72."
713 If @var{string} contains more than one format specification, the
714 format specifications correspond to successive values from
715 @var{objects}. Thus, the first format specification in @var{string}
716 uses the first such value, the second format specification uses the
717 second such value, and so on. Any extra format specifications (those
718 for which there are no corresponding values) cause an error. Any
719 extra values to be formatted are ignored.
721 Certain format specifications require values of particular types. If
722 you supply a value that doesn't fit the requirements, an error is
725 Here is a table of valid format specifications:
729 Replace the specification with the printed representation of the object,
730 made without quoting (that is, using @code{princ}, not
731 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
732 by their contents alone, with no @samp{"} characters, and symbols appear
733 without @samp{\} characters.
735 Starting in Emacs 21, if the object is a string, its text properties are
736 copied into the output. The text properties of the @samp{%s} itself
737 are also copied, but those of the object take priority.
740 Replace the specification with the printed representation of the object,
741 made with quoting (that is, using @code{prin1}---@pxref{Output
742 Functions}). Thus, strings are enclosed in @samp{"} characters, and
743 @samp{\} characters appear where necessary before special characters.
746 @cindex integer to octal
747 Replace the specification with the base-eight representation of an
751 Replace the specification with the base-ten representation of an
756 @cindex integer to hexadecimal
757 Replace the specification with the base-sixteen representation of an
758 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
761 Replace the specification with the character which is the value given.
764 Replace the specification with the exponential notation for a floating
768 Replace the specification with the decimal-point notation for a floating
772 Replace the specification with notation for a floating point number,
773 using either exponential notation or decimal-point notation, whichever
777 Replace the specification with a single @samp{%}. This format
778 specification is unusual in that it does not use a value. For example,
779 @code{(format "%% %d" 30)} returns @code{"% 30"}.
782 Any other format character results in an @samp{Invalid format
785 Here are several examples:
789 (format "The name of this buffer is %s." (buffer-name))
790 @result{} "The name of this buffer is strings.texi."
792 (format "The buffer object prints as %s." (current-buffer))
793 @result{} "The buffer object prints as strings.texi."
795 (format "The octal value of %d is %o,
796 and the hex value is %x." 18 18 18)
797 @result{} "The octal value of 18 is 22,
798 and the hex value is 12."
804 All the specification characters allow an optional ``width'', which
805 is a digit-string between the @samp{%} and the character. If the
806 printed representation of the object contains fewer characters than
807 this width, then it is padded. The padding is on the left if the
808 width is positive (or starts with zero) and on the right if the
809 width is negative. The padding character is normally a space, but if
810 the width starts with a zero, zeros are used for padding. Some of
811 these conventions are ignored for specification characters for which
812 they do not make sense. That is, @samp{%s}, @samp{%S} and @samp{%c}
813 accept a width starting with 0, but still pad with @emph{spaces} on
814 the left. Also, @samp{%%} accepts a width, but ignores it. Here are
815 some examples of padding:
818 (format "%06d is padded on the left with zeros" 123)
819 @result{} "000123 is padded on the left with zeros"
821 (format "%-6d is padded on the right" 123)
822 @result{} "123 is padded on the right"
825 If the width is too small, @code{format} does not truncate the
826 object's printed representation. Thus, you can use a width to specify
827 a minimum spacing between columns with no risk of losing information.
829 In the following three examples, @samp{%7s} specifies a minimum width
830 of 7. In the first case, the string inserted in place of @samp{%7s} has
831 only 3 letters, so 4 blank spaces are inserted for padding. In the
832 second case, the string @code{"specification"} is 13 letters wide but is
833 not truncated. In the third case, the padding is on the right.
837 (format "The word `%7s' actually has %d letters in it."
838 "foo" (length "foo"))
839 @result{} "The word ` foo' actually has 3 letters in it."
843 (format "The word `%7s' actually has %d letters in it."
844 "specification" (length "specification"))
845 @result{} "The word `specification' actually has 13 letters in it."
849 (format "The word `%-7s' actually has %d letters in it."
850 "foo" (length "foo"))
851 @result{} "The word `foo ' actually has 3 letters in it."
855 @cindex precision in format specifications
856 All the specification characters allow an optional ``precision''
857 before the character (after the width, if present). The precision is
858 a decimal-point @samp{.} followed by a digit-string. For the
859 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
860 precision specifies how many decimal places to show; if zero, the
861 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
862 the precision truncates the string to the given width, so
863 @samp{%.3s} shows only the first three characters of the
864 representation for @var{object}. Precision is ignored for other
865 specification characters.
867 @cindex flags in format specifications
868 Immediately after the @samp{%} and before the optional width and
869 precision, you can put certain ``flag'' characters.
871 A space character inserts a space for positive numbers (otherwise
872 nothing is inserted for positive numbers). This flag is ignored
873 except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}.
875 The flag @samp{#} indicates ``alternate form''. For @samp{%o} it
876 ensures that the result begins with a 0. For @samp{%x} and @samp{%X}
877 the result is prefixed with @samp{0x} or @samp{0X}. For @samp{%e},
878 @samp{%f}, and @samp{%g} a decimal point is always shown even if the
881 @node Case Conversion
882 @comment node-name, next, previous, up
883 @section Case Conversion in Lisp
886 @cindex character case
887 @cindex case conversion in Lisp
889 The character case functions change the case of single characters or
890 of the contents of strings. The functions normally convert only
891 alphabetic characters (the letters @samp{A} through @samp{Z} and
892 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
893 characters are not altered. You can specify a different case
894 conversion mapping by specifying a case table (@pxref{Case Tables}).
896 These functions do not modify the strings that are passed to them as
899 The examples below use the characters @samp{X} and @samp{x} which have
900 @acronym{ASCII} codes 88 and 120 respectively.
902 @defun downcase string-or-char
903 This function converts a character or a string to lower case.
905 When the argument to @code{downcase} is a string, the function creates
906 and returns a new string in which each letter in the argument that is
907 upper case is converted to lower case. When the argument to
908 @code{downcase} is a character, @code{downcase} returns the
909 corresponding lower case character. This value is an integer. If the
910 original character is lower case, or is not a letter, then the value
911 equals the original character.
914 (downcase "The cat in the hat")
915 @result{} "the cat in the hat"
922 @defun upcase string-or-char
923 This function converts a character or a string to upper case.
925 When the argument to @code{upcase} is a string, the function creates
926 and returns a new string in which each letter in the argument that is
927 lower case is converted to upper case.
929 When the argument to @code{upcase} is a character, @code{upcase}
930 returns the corresponding upper case character. This value is an integer.
931 If the original character is upper case, or is not a letter, then the
932 value returned equals the original character.
935 (upcase "The cat in the hat")
936 @result{} "THE CAT IN THE HAT"
943 @defun capitalize string-or-char
944 @cindex capitalization
945 This function capitalizes strings or characters. If
946 @var{string-or-char} is a string, the function creates and returns a new
947 string, whose contents are a copy of @var{string-or-char} in which each
948 word has been capitalized. This means that the first character of each
949 word is converted to upper case, and the rest are converted to lower
952 The definition of a word is any sequence of consecutive characters that
953 are assigned to the word constituent syntax class in the current syntax
954 table (@pxref{Syntax Class Table}).
956 When the argument to @code{capitalize} is a character, @code{capitalize}
957 has the same result as @code{upcase}.
961 (capitalize "The cat in the hat")
962 @result{} "The Cat In The Hat"
966 (capitalize "THE 77TH-HATTED CAT")
967 @result{} "The 77th-Hatted Cat"
977 @defun upcase-initials string-or-char
978 If @var{string-or-char} is a string, this function capitalizes the
979 initials of the words in @var{string-or-char}, without altering any
980 letters other than the initials. It returns a new string whose
981 contents are a copy of @var{string-or-char}, in which each word has
982 had its initial letter converted to upper case.
984 The definition of a word is any sequence of consecutive characters that
985 are assigned to the word constituent syntax class in the current syntax
986 table (@pxref{Syntax Class Table}).
988 When the argument to @code{upcase-initials} is a character,
989 @code{upcase-initials} has the same result as @code{upcase}.
993 (upcase-initials "The CAT in the hAt")
994 @result{} "The CAT In The HAt"
999 @xref{Text Comparison}, for functions that compare strings; some of
1000 them ignore case differences, or can optionally ignore case differences.
1003 @section The Case Table
1005 You can customize case conversion by installing a special @dfn{case
1006 table}. A case table specifies the mapping between upper case and lower
1007 case letters. It affects both the case conversion functions for Lisp
1008 objects (see the previous section) and those that apply to text in the
1009 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1010 also a standard case table which is used to initialize the case table
1013 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1014 @code{case-table}. This char-table maps each character into the
1015 corresponding lower case character. It has three extra slots, which
1016 hold related tables:
1020 The upcase table maps each character into the corresponding upper
1023 The canonicalize table maps all of a set of case-related characters
1024 into a particular member of that set.
1026 The equivalences table maps each one of a set of case-related characters
1027 into the next character in that set.
1030 In simple cases, all you need to specify is the mapping to lower-case;
1031 the three related tables will be calculated automatically from that one.
1033 For some languages, upper and lower case letters are not in one-to-one
1034 correspondence. There may be two different lower case letters with the
1035 same upper case equivalent. In these cases, you need to specify the
1036 maps for both lower case and upper case.
1038 The extra table @var{canonicalize} maps each character to a canonical
1039 equivalent; any two characters that are related by case-conversion have
1040 the same canonical equivalent character. For example, since @samp{a}
1041 and @samp{A} are related by case-conversion, they should have the same
1042 canonical equivalent character (which should be either @samp{a} for both
1043 of them, or @samp{A} for both of them).
1045 The extra table @var{equivalences} is a map that cyclically permutes
1046 each equivalence class (of characters with the same canonical
1047 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1048 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1049 equivalent characters.)
1051 When you construct a case table, you can provide @code{nil} for
1052 @var{canonicalize}; then Emacs fills in this slot from the lower case
1053 and upper case mappings. You can also provide @code{nil} for
1054 @var{equivalences}; then Emacs fills in this slot from
1055 @var{canonicalize}. In a case table that is actually in use, those
1056 components are non-@code{nil}. Do not try to specify @var{equivalences}
1057 without also specifying @var{canonicalize}.
1059 Here are the functions for working with case tables:
1061 @defun case-table-p object
1062 This predicate returns non-@code{nil} if @var{object} is a valid case
1066 @defun set-standard-case-table table
1067 This function makes @var{table} the standard case table, so that it will
1068 be used in any buffers created subsequently.
1071 @defun standard-case-table
1072 This returns the standard case table.
1075 @defun current-case-table
1076 This function returns the current buffer's case table.
1079 @defun set-case-table table
1080 This sets the current buffer's case table to @var{table}.
1083 The following three functions are convenient subroutines for packages
1084 that define non-@acronym{ASCII} character sets. They modify the specified
1085 case table @var{case-table}; they also modify the standard syntax table.
1086 @xref{Syntax Tables}. Normally you would use these functions to change
1087 the standard case table.
1089 @defun set-case-syntax-pair uc lc case-table
1090 This function specifies a pair of corresponding letters, one upper case
1094 @defun set-case-syntax-delims l r case-table
1095 This function makes characters @var{l} and @var{r} a matching pair of
1096 case-invariant delimiters.
1099 @defun set-case-syntax char syntax case-table
1100 This function makes @var{char} case-invariant, with syntax
1104 @deffn Command describe-buffer-case-table
1105 This command displays a description of the contents of the current
1106 buffer's case table.
1110 arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4