2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003,
4 @c 2004, 2005, 2006 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 with @code{string-match}
78 (@pxref{Regexp Search}). The functions @code{match-string}
79 (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing
80 Match}) are useful for decomposing and modifying strings after
81 matching regular expressions against them.
83 Like a buffer, a string can contain text properties for the characters
84 in it, as well as the characters themselves. @xref{Text Properties}.
85 All the Lisp primitives that copy text from strings to buffers or other
86 strings also copy the properties of the characters being copied.
88 @xref{Text}, for information about functions that display strings or
89 copy them into buffers. @xref{Character Type}, and @ref{String Type},
90 for information about the syntax of characters and strings.
91 @xref{Non-ASCII Characters}, for functions to convert between text
92 representations and to encode and decode character codes.
94 @node Predicates for Strings
95 @section The Predicates for Strings
97 For more information about general sequence and array predicates,
98 see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
100 @defun stringp object
101 This function returns @code{t} if @var{object} is a string, @code{nil}
105 @defun char-or-string-p object
106 This function returns @code{t} if @var{object} is a string or a
107 character (i.e., an integer), @code{nil} otherwise.
110 @node Creating Strings
111 @section Creating Strings
113 The following functions create strings, either from scratch, or by
114 putting strings together, or by taking them apart.
116 @defun make-string count character
117 This function returns a string made up of @var{count} repetitions of
118 @var{character}. If @var{count} is negative, an error is signaled.
127 Other functions to compare with this one include @code{char-to-string}
128 (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and
129 @code{make-list} (@pxref{Building Lists}).
132 @defun string &rest characters
133 This returns a string containing the characters @var{characters}.
141 @defun substring string start &optional end
142 This function returns a new string which consists of those characters
143 from @var{string} in the range from (and including) the character at the
144 index @var{start} up to (but excluding) the character at the index
145 @var{end}. The first character is at index zero.
149 (substring "abcdefg" 0 3)
155 Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the
156 index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied
157 from the string @code{"abcdefg"}. The index 3 marks the character
158 position up to which the substring is copied. The character whose index
159 is 3 is actually the fourth character in the string.
161 A negative number counts from the end of the string, so that @minus{}1
162 signifies the index of the last character of the string. For example:
166 (substring "abcdefg" -3 -1)
172 In this example, the index for @samp{e} is @minus{}3, the index for
173 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
174 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
176 When @code{nil} is used for @var{end}, it stands for the length of the
181 (substring "abcdefg" -3 nil)
186 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
187 It follows that @code{(substring @var{string} 0)} returns a copy of all
192 (substring "abcdefg" 0)
198 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
201 If the characters copied from @var{string} have text properties, the
202 properties are copied into the new string also. @xref{Text Properties}.
204 @code{substring} also accepts a vector for the first argument.
208 (substring [a b (c) "d"] 1 3)
212 A @code{wrong-type-argument} error is signaled if @var{start} is not
213 an integer or if @var{end} is neither an integer nor @code{nil}. An
214 @code{args-out-of-range} error is signaled if @var{start} indicates a
215 character following @var{end}, or if either integer is out of range
218 Contrast this function with @code{buffer-substring} (@pxref{Buffer
219 Contents}), which returns a string containing a portion of the text in
220 the current buffer. The beginning of a string is at index 0, but the
221 beginning of a buffer is at index 1.
224 @defun substring-no-properties string &optional start end
225 This works like @code{substring} but discards all text properties from
226 the value. Also, @var{start} may be omitted or @code{nil}, which is
227 equivalent to 0. Thus, @w{@code{(substring-no-properties
228 @var{string})}} returns a copy of @var{string}, with all text
232 @defun concat &rest sequences
233 @cindex copying strings
234 @cindex concatenating strings
235 This function returns a new string consisting of the characters in the
236 arguments passed to it (along with their text properties, if any). The
237 arguments may be strings, lists of numbers, or vectors of numbers; they
238 are not themselves changed. If @code{concat} receives no arguments, it
239 returns an empty string.
242 (concat "abc" "-def")
244 (concat "abc" (list 120 121) [122])
246 ;; @r{@code{nil} is an empty sequence.}
247 (concat "abc" nil "-def")
249 (concat "The " "quick brown " "fox.")
250 @result{} "The quick brown fox."
256 The @code{concat} function always constructs a new string that is
257 not @code{eq} to any existing string.
259 In Emacs versions before 21, when an argument was an integer (not a
260 sequence of integers), it was converted to a string of digits making up
261 the decimal printed representation of the integer. This obsolete usage
262 no longer works. The proper way to convert an integer to its decimal
263 printed form is with @code{format} (@pxref{Formatting Strings}) or
264 @code{number-to-string} (@pxref{String Conversion}).
266 For information about other concatenation functions, see the
267 description of @code{mapconcat} in @ref{Mapping Functions},
268 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
272 @defun split-string string &optional separators omit-nulls
273 This function splits @var{string} into substrings at matches for the
274 regular expression @var{separators}. Each match for @var{separators}
275 defines a splitting point; the substrings between the splitting points
276 are made into a list, which is the value returned by
279 If @var{omit-nulls} is @code{nil}, the result contains null strings
280 whenever there are two consecutive matches for @var{separators}, or a
281 match is adjacent to the beginning or end of @var{string}. If
282 @var{omit-nulls} is @code{t}, these null strings are omitted from the
285 If @var{separators} is @code{nil} (or omitted),
286 the default is the value of @code{split-string-default-separators}.
288 As a special case, when @var{separators} is @code{nil} (or omitted),
289 null strings are always omitted from the result. Thus:
292 (split-string " two words ")
293 @result{} ("two" "words")
296 The result is not @code{("" "two" "words" "")}, which would rarely be
297 useful. If you need such a result, use an explicit value for
301 (split-string " two words "
302 split-string-default-separators)
303 @result{} ("" "two" "words" "")
309 (split-string "Soup is good food" "o")
310 @result{} ("S" "up is g" "" "d f" "" "d")
311 (split-string "Soup is good food" "o" t)
312 @result{} ("S" "up is g" "d f" "d")
313 (split-string "Soup is good food" "o+")
314 @result{} ("S" "up is g" "d f" "d")
317 Empty matches do count, except that @code{split-string} will not look
318 for a final empty match when it already reached the end of the string
319 using a non-empty match or when @var{string} is empty:
322 (split-string "aooob" "o*")
323 @result{} ("" "a" "" "b" "")
324 (split-string "ooaboo" "o*")
325 @result{} ("" "" "a" "b" "")
330 However, when @var{separators} can match the empty string,
331 @var{omit-nulls} is usually @code{t}, so that the subtleties in the
332 three previous examples are rarely relevant:
335 (split-string "Soup is good food" "o*" t)
336 @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
337 (split-string "Nice doggy!" "" t)
338 @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
339 (split-string "" "" t)
343 Somewhat odd, but predictable, behavior can occur for certain
344 ``non-greedy'' values of @var{separators} that can prefer empty
345 matches over non-empty matches. Again, such values rarely occur in
349 (split-string "ooo" "o*" t)
351 (split-string "ooo" "\\|o+" t)
352 @result{} ("o" "o" "o")
356 @defvar split-string-default-separators
357 The default value of @var{separators} for @code{split-string}. Its
358 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
361 @node Modifying Strings
362 @section Modifying Strings
364 The most basic way to alter the contents of an existing string is with
365 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
366 @var{idx} @var{char})} stores @var{char} into @var{string} at index
367 @var{idx}. Each character occupies one or more bytes, and if @var{char}
368 needs a different number of bytes from the character already present at
369 that index, @code{aset} signals an error.
371 A more powerful function is @code{store-substring}:
373 @defun store-substring string idx obj
374 This function alters part of the contents of the string @var{string}, by
375 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
376 may be either a character or a (smaller) string.
378 Since it is impossible to change the length of an existing string, it is
379 an error if @var{obj} doesn't fit within @var{string}'s actual length,
380 or if any new character requires a different number of bytes from the
381 character currently present at that point in @var{string}.
384 To clear out a string that contained a password, use
387 @defun clear-string string
388 This clears the contents of @var{string} to zeros.
389 It may also change @var{string}'s length and convert it to
394 @node Text Comparison
395 @section Comparison of Characters and Strings
396 @cindex string equality
398 @defun char-equal character1 character2
399 This function returns @code{t} if the arguments represent the same
400 character, @code{nil} otherwise. This function ignores differences
401 in case if @code{case-fold-search} is non-@code{nil}.
406 (let ((case-fold-search nil))
412 @defun string= string1 string2
413 This function returns @code{t} if the characters of the two strings
414 match exactly. Symbols are also allowed as arguments, in which case
415 their print names are used.
416 Case is always significant, regardless of @code{case-fold-search}.
419 (string= "abc" "abc")
421 (string= "abc" "ABC")
427 The function @code{string=} ignores the text properties of the two
428 strings. When @code{equal} (@pxref{Equality Predicates}) compares two
429 strings, it uses @code{string=}.
431 For technical reasons, a unibyte and a multibyte string are
432 @code{equal} if and only if they contain the same sequence of
433 character codes and all these codes are either in the range 0 through
434 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
435 However, when a unibyte string gets converted to a multibyte string,
436 all characters with codes in the range 160 through 255 get converted
437 to characters with higher codes, whereas @acronym{ASCII} characters
438 remain unchanged. Thus, a unibyte string and its conversion to
439 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
440 Character codes 160 through 255 are not entirely proper in multibyte
441 text, even though they can occur. As a consequence, the situation
442 where a unibyte and a multibyte string are @code{equal} without both
443 being all @acronym{ASCII} is a technical oddity that very few Emacs
444 Lisp programmers ever get confronted with. @xref{Text
448 @defun string-equal string1 string2
449 @code{string-equal} is another name for @code{string=}.
452 @cindex lexical comparison
453 @defun string< string1 string2
454 @c (findex string< causes problems for permuted index!!)
455 This function compares two strings a character at a time. It
456 scans both the strings at the same time to find the first pair of corresponding
457 characters that do not match. If the lesser character of these two is
458 the character from @var{string1}, then @var{string1} is less, and this
459 function returns @code{t}. If the lesser character is the one from
460 @var{string2}, then @var{string1} is greater, and this function returns
461 @code{nil}. If the two strings match entirely, the value is @code{nil}.
463 Pairs of characters are compared according to their character codes.
464 Keep in mind that lower case letters have higher numeric values in the
465 @acronym{ASCII} character set than their upper case counterparts; digits and
466 many punctuation characters have a lower numeric value than upper case
467 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
468 character; a unibyte non-@acronym{ASCII} character is always less than any
469 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
473 (string< "abc" "abd")
475 (string< "abd" "abc")
477 (string< "123" "abc")
482 When the strings have different lengths, and they match up to the
483 length of @var{string1}, then the result is @code{t}. If they match up
484 to the length of @var{string2}, the result is @code{nil}. A string of
485 no characters is less than any other string.
502 Symbols are also allowed as arguments, in which case their print names
506 @defun string-lessp string1 string2
507 @code{string-lessp} is another name for @code{string<}.
510 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
511 This function compares the specified part of @var{string1} with the
512 specified part of @var{string2}. The specified part of @var{string1}
513 runs from index @var{start1} up to index @var{end1} (@code{nil} means
514 the end of the string). The specified part of @var{string2} runs from
515 index @var{start2} up to index @var{end2} (@code{nil} means the end of
518 The strings are both converted to multibyte for the comparison
519 (@pxref{Text Representations}) so that a unibyte string and its
520 conversion to multibyte are always regarded as equal. If
521 @var{ignore-case} is non-@code{nil}, then case is ignored, so that
522 upper case letters can be equal to lower case letters.
524 If the specified portions of the two strings match, the value is
525 @code{t}. Otherwise, the value is an integer which indicates how many
526 leading characters agree, and which string is less. Its absolute value
527 is one plus the number of characters that agree at the beginning of the
528 two strings. The sign is negative if @var{string1} (or its specified
532 @defun assoc-string key alist &optional case-fold
533 This function works like @code{assoc}, except that @var{key} must be a
534 string, and comparison is done using @code{compare-strings}. If
535 @var{case-fold} is non-@code{nil}, it ignores case differences.
536 Unlike @code{assoc}, this function can also match elements of the alist
537 that are strings rather than conses. In particular, @var{alist} can
538 be a list of strings rather than an actual alist.
539 @xref{Association Lists}.
542 See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for
543 a way to compare text in buffers. The function @code{string-match},
544 which matches a regular expression against a string, can be used
545 for a kind of string comparison; see @ref{Regexp Search}.
547 @node String Conversion
548 @comment node-name, next, previous, up
549 @section Conversion of Characters and Strings
550 @cindex conversion of strings
552 This section describes functions for conversions between characters,
553 strings and integers. @code{format} (@pxref{Formatting Strings})
554 and @code{prin1-to-string}
555 (@pxref{Output Functions}) can also convert Lisp objects into strings.
556 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
557 string representation of a Lisp object into an object. The functions
558 @code{string-make-multibyte} and @code{string-make-unibyte} convert the
559 text representation of a string (@pxref{Converting Representations}).
561 @xref{Documentation}, for functions that produce textual descriptions
562 of text characters and general input events
563 (@code{single-key-description} and @code{text-char-description}). These
564 functions are used primarily for making help messages.
566 @defun char-to-string character
567 @cindex character to string
568 This function returns a new string containing one character,
569 @var{character}. This function is semi-obsolete because the function
570 @code{string} is more general. @xref{Creating Strings}.
573 @defun string-to-char string
574 @cindex string to character
575 This function returns the first character in @var{string}. If the
576 string is empty, the function returns 0. The value is also 0 when the
577 first character of @var{string} is the null character, @acronym{ASCII} code
581 (string-to-char "ABC")
583 (string-to-char "xyz")
588 (string-to-char "\000")
593 This function may be eliminated in the future if it does not seem useful
597 @defun number-to-string number
598 @cindex integer to string
599 @cindex integer to decimal
600 This function returns a string consisting of the printed base-ten
601 representation of @var{number}, which may be an integer or a floating
602 point number. The returned value starts with a minus sign if the argument is
606 (number-to-string 256)
609 (number-to-string -23)
612 (number-to-string -23.5)
616 @cindex int-to-string
617 @code{int-to-string} is a semi-obsolete alias for this function.
619 See also the function @code{format} in @ref{Formatting Strings}.
622 @defun string-to-number string &optional base
623 @cindex string to number
624 This function returns the numeric value of the characters in
625 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
626 between 2 and 16 (inclusive), and integers are converted in that base.
627 If @var{base} is @code{nil}, then base ten is used. Floating point
628 conversion only works in base ten; we have not implemented other
629 radices for floating point numbers, because that would be much more
630 work and does not seem useful. If @var{string} looks like an integer
631 but its value is too large to fit into a Lisp integer,
632 @code{string-to-number} returns a floating point result.
634 The parsing skips spaces and tabs at the beginning of @var{string},
635 then reads as much of @var{string} as it can interpret as a number in
636 the given base. (On some systems it ignores other whitespace at the
637 beginning, not just spaces and tabs.) If the first character after
638 the ignored whitespace is neither a digit in the given base, nor a
639 plus or minus sign, nor the leading dot of a floating point number,
640 this function returns 0.
643 (string-to-number "256")
645 (string-to-number "25 is a perfect square.")
647 (string-to-number "X256")
649 (string-to-number "-4.5")
651 (string-to-number "1e5")
655 @findex string-to-int
656 @code{string-to-int} is an obsolete alias for this function.
659 Here are some other functions that can convert to or from a string:
663 @code{concat} can convert a vector or a list into a string.
664 @xref{Creating Strings}.
667 @code{vconcat} can convert a string into a vector. @xref{Vector
671 @code{append} can convert a string into a list. @xref{Building Lists}.
674 @node Formatting Strings
675 @comment node-name, next, previous, up
676 @section Formatting Strings
677 @cindex formatting strings
678 @cindex strings, formatting them
680 @dfn{Formatting} means constructing a string by substitution of
681 computed values at various places in a constant string. This constant string
682 controls how the other values are printed, as well as where they appear;
683 it is called a @dfn{format string}.
685 Formatting is often useful for computing messages to be displayed. In
686 fact, the functions @code{message} and @code{error} provide the same
687 formatting feature described here; they differ from @code{format} only
688 in how they use the result of formatting.
690 @defun format string &rest objects
691 This function returns a new string that is made by copying
692 @var{string} and then replacing any format specification
693 in the copy with encodings of the corresponding @var{objects}. The
694 arguments @var{objects} are the computed values to be formatted.
696 The characters in @var{string}, other than the format specifications,
697 are copied directly into the output; if they have text properties,
698 these are copied into the output also.
701 @cindex @samp{%} in format
702 @cindex format specification
703 A format specification is a sequence of characters beginning with a
704 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
705 @code{format} function replaces it with the printed representation of
706 one of the values to be formatted (one of the arguments @var{objects}).
711 (format "The value of fill-column is %d." fill-column)
712 @result{} "The value of fill-column is 72."
716 If @var{string} contains more than one format specification, the
717 format specifications correspond to successive values from
718 @var{objects}. Thus, the first format specification in @var{string}
719 uses the first such value, the second format specification uses the
720 second such value, and so on. Any extra format specifications (those
721 for which there are no corresponding values) cause an error. Any
722 extra values to be formatted are ignored.
724 Certain format specifications require values of particular types. If
725 you supply a value that doesn't fit the requirements, an error is
728 Here is a table of valid format specifications:
732 Replace the specification with the printed representation of the object,
733 made without quoting (that is, using @code{princ}, not
734 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
735 by their contents alone, with no @samp{"} characters, and symbols appear
736 without @samp{\} characters.
738 If the object is a string, its text properties are
739 copied into the output. The text properties of the @samp{%s} itself
740 are also copied, but those of the object take priority.
743 Replace the specification with the printed representation of the object,
744 made with quoting (that is, using @code{prin1}---@pxref{Output
745 Functions}). Thus, strings are enclosed in @samp{"} characters, and
746 @samp{\} characters appear where necessary before special characters.
749 @cindex integer to octal
750 Replace the specification with the base-eight representation of an
754 Replace the specification with the base-ten representation of an
759 @cindex integer to hexadecimal
760 Replace the specification with the base-sixteen representation of an
761 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
764 Replace the specification with the character which is the value given.
767 Replace the specification with the exponential notation for a floating
771 Replace the specification with the decimal-point notation for a floating
775 Replace the specification with notation for a floating point number,
776 using either exponential notation or decimal-point notation, whichever
780 Replace the specification with a single @samp{%}. This format
781 specification is unusual in that it does not use a value. For example,
782 @code{(format "%% %d" 30)} returns @code{"% 30"}.
785 Any other format character results in an @samp{Invalid format
788 Here are several examples:
792 (format "The name of this buffer is %s." (buffer-name))
793 @result{} "The name of this buffer is strings.texi."
795 (format "The buffer object prints as %s." (current-buffer))
796 @result{} "The buffer object prints as strings.texi."
798 (format "The octal value of %d is %o,
799 and the hex value is %x." 18 18 18)
800 @result{} "The octal value of 18 is 22,
801 and the hex value is 12."
807 All the specification characters allow an optional ``width'', which
808 is a digit-string between the @samp{%} and the character. If the
809 printed representation of the object contains fewer characters than
810 this width, then it is padded. The padding is on the left if the
811 width is positive (or starts with zero) and on the right if the
812 width is negative. The padding character is normally a space, but if
813 the width starts with a zero, zeros are used for padding. Some of
814 these conventions are ignored for specification characters for which
815 they do not make sense. That is, @samp{%s}, @samp{%S} and @samp{%c}
816 accept a width starting with 0, but still pad with @emph{spaces} on
817 the left. Also, @samp{%%} accepts a width, but ignores it. Here are
818 some examples of padding:
821 (format "%06d is padded on the left with zeros" 123)
822 @result{} "000123 is padded on the left with zeros"
824 (format "%-6d is padded on the right" 123)
825 @result{} "123 is padded on the right"
828 If the width is too small, @code{format} does not truncate the
829 object's printed representation. Thus, you can use a width to specify
830 a minimum spacing between columns with no risk of losing information.
832 In the following three examples, @samp{%7s} specifies a minimum width
833 of 7. In the first case, the string inserted in place of @samp{%7s} has
834 only 3 letters, so 4 blank spaces are inserted for padding. In the
835 second case, the string @code{"specification"} is 13 letters wide but is
836 not truncated. In the third case, the padding is on the right.
840 (format "The word `%7s' actually has %d letters in it."
841 "foo" (length "foo"))
842 @result{} "The word ` foo' actually has 3 letters in it."
846 (format "The word `%7s' actually has %d letters in it."
847 "specification" (length "specification"))
848 @result{} "The word `specification' actually has 13 letters in it."
852 (format "The word `%-7s' actually has %d letters in it."
853 "foo" (length "foo"))
854 @result{} "The word `foo ' actually has 3 letters in it."
858 @cindex precision in format specifications
859 All the specification characters allow an optional ``precision''
860 before the character (after the width, if present). The precision is
861 a decimal-point @samp{.} followed by a digit-string. For the
862 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
863 precision specifies how many decimal places to show; if zero, the
864 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
865 the precision truncates the string to the given width, so
866 @samp{%.3s} shows only the first three characters of the
867 representation for @var{object}. Precision is ignored for other
868 specification characters.
870 @cindex flags in format specifications
871 Immediately after the @samp{%} and before the optional width and
872 precision, you can put certain ``flag'' characters.
874 A space character inserts a space for positive numbers (otherwise
875 nothing is inserted for positive numbers). This flag is ignored
876 except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}.
878 The flag @samp{#} indicates ``alternate form''. For @samp{%o} it
879 ensures that the result begins with a 0. For @samp{%x} and @samp{%X}
880 the result is prefixed with @samp{0x} or @samp{0X}. For @samp{%e},
881 @samp{%f}, and @samp{%g} a decimal point is always shown even if the
884 @node Case Conversion
885 @comment node-name, next, previous, up
886 @section Case Conversion in Lisp
889 @cindex character case
890 @cindex case conversion in Lisp
892 The character case functions change the case of single characters or
893 of the contents of strings. The functions normally convert only
894 alphabetic characters (the letters @samp{A} through @samp{Z} and
895 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
896 characters are not altered. You can specify a different case
897 conversion mapping by specifying a case table (@pxref{Case Tables}).
899 These functions do not modify the strings that are passed to them as
902 The examples below use the characters @samp{X} and @samp{x} which have
903 @acronym{ASCII} codes 88 and 120 respectively.
905 @defun downcase string-or-char
906 This function converts a character or a string to lower case.
908 When the argument to @code{downcase} is a string, the function creates
909 and returns a new string in which each letter in the argument that is
910 upper case is converted to lower case. When the argument to
911 @code{downcase} is a character, @code{downcase} returns the
912 corresponding lower case character. This value is an integer. If the
913 original character is lower case, or is not a letter, then the value
914 equals the original character.
917 (downcase "The cat in the hat")
918 @result{} "the cat in the hat"
925 @defun upcase string-or-char
926 This function converts a character or a string to upper case.
928 When the argument to @code{upcase} is a string, the function creates
929 and returns a new string in which each letter in the argument that is
930 lower case is converted to upper case.
932 When the argument to @code{upcase} is a character, @code{upcase}
933 returns the corresponding upper case character. This value is an integer.
934 If the original character is upper case, or is not a letter, then the
935 value returned equals the original character.
938 (upcase "The cat in the hat")
939 @result{} "THE CAT IN THE HAT"
946 @defun capitalize string-or-char
947 @cindex capitalization
948 This function capitalizes strings or characters. If
949 @var{string-or-char} is a string, the function creates and returns a new
950 string, whose contents are a copy of @var{string-or-char} in which each
951 word has been capitalized. This means that the first character of each
952 word is converted to upper case, and the rest are converted to lower
955 The definition of a word is any sequence of consecutive characters that
956 are assigned to the word constituent syntax class in the current syntax
957 table (@pxref{Syntax Class Table}).
959 When the argument to @code{capitalize} is a character, @code{capitalize}
960 has the same result as @code{upcase}.
964 (capitalize "The cat in the hat")
965 @result{} "The Cat In The Hat"
969 (capitalize "THE 77TH-HATTED CAT")
970 @result{} "The 77th-Hatted Cat"
980 @defun upcase-initials string-or-char
981 If @var{string-or-char} is a string, this function capitalizes the
982 initials of the words in @var{string-or-char}, without altering any
983 letters other than the initials. It returns a new string whose
984 contents are a copy of @var{string-or-char}, in which each word has
985 had its initial letter converted to upper case.
987 The definition of a word is any sequence of consecutive characters that
988 are assigned to the word constituent syntax class in the current syntax
989 table (@pxref{Syntax Class Table}).
991 When the argument to @code{upcase-initials} is a character,
992 @code{upcase-initials} has the same result as @code{upcase}.
996 (upcase-initials "The CAT in the hAt")
997 @result{} "The CAT In The HAt"
1002 @xref{Text Comparison}, for functions that compare strings; some of
1003 them ignore case differences, or can optionally ignore case differences.
1006 @section The Case Table
1008 You can customize case conversion by installing a special @dfn{case
1009 table}. A case table specifies the mapping between upper case and lower
1010 case letters. It affects both the case conversion functions for Lisp
1011 objects (see the previous section) and those that apply to text in the
1012 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1013 also a standard case table which is used to initialize the case table
1016 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1017 @code{case-table}. This char-table maps each character into the
1018 corresponding lower case character. It has three extra slots, which
1019 hold related tables:
1023 The upcase table maps each character into the corresponding upper
1026 The canonicalize table maps all of a set of case-related characters
1027 into a particular member of that set.
1029 The equivalences table maps each one of a set of case-related characters
1030 into the next character in that set.
1033 In simple cases, all you need to specify is the mapping to lower-case;
1034 the three related tables will be calculated automatically from that one.
1036 For some languages, upper and lower case letters are not in one-to-one
1037 correspondence. There may be two different lower case letters with the
1038 same upper case equivalent. In these cases, you need to specify the
1039 maps for both lower case and upper case.
1041 The extra table @var{canonicalize} maps each character to a canonical
1042 equivalent; any two characters that are related by case-conversion have
1043 the same canonical equivalent character. For example, since @samp{a}
1044 and @samp{A} are related by case-conversion, they should have the same
1045 canonical equivalent character (which should be either @samp{a} for both
1046 of them, or @samp{A} for both of them).
1048 The extra table @var{equivalences} is a map that cyclically permutes
1049 each equivalence class (of characters with the same canonical
1050 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1051 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1052 equivalent characters.)
1054 When you construct a case table, you can provide @code{nil} for
1055 @var{canonicalize}; then Emacs fills in this slot from the lower case
1056 and upper case mappings. You can also provide @code{nil} for
1057 @var{equivalences}; then Emacs fills in this slot from
1058 @var{canonicalize}. In a case table that is actually in use, those
1059 components are non-@code{nil}. Do not try to specify @var{equivalences}
1060 without also specifying @var{canonicalize}.
1062 Here are the functions for working with case tables:
1064 @defun case-table-p object
1065 This predicate returns non-@code{nil} if @var{object} is a valid case
1069 @defun set-standard-case-table table
1070 This function makes @var{table} the standard case table, so that it will
1071 be used in any buffers created subsequently.
1074 @defun standard-case-table
1075 This returns the standard case table.
1078 @defun current-case-table
1079 This function returns the current buffer's case table.
1082 @defun set-case-table table
1083 This sets the current buffer's case table to @var{table}.
1086 The following three functions are convenient subroutines for packages
1087 that define non-@acronym{ASCII} character sets. They modify the specified
1088 case table @var{case-table}; they also modify the standard syntax table.
1089 @xref{Syntax Tables}. Normally you would use these functions to change
1090 the standard case table.
1092 @defun set-case-syntax-pair uc lc case-table
1093 This function specifies a pair of corresponding letters, one upper case
1097 @defun set-case-syntax-delims l r case-table
1098 This function makes characters @var{l} and @var{r} a matching pair of
1099 case-invariant delimiters.
1102 @defun set-case-syntax char syntax case-table
1103 This function makes @var{char} case-invariant, with syntax
1107 @deffn Command describe-buffer-case-table
1108 This command displays a description of the contents of the current
1109 buffer's case table.
1113 arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4