2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
4 @c 2002, 2003, 2004, 2005, 2006, 2007, 2008 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. @xref{Character Codes},
43 for details about character representation in Emacs.
45 The length of a string (like any array) is fixed, and cannot be
46 altered once the string exists. Strings in Lisp are @emph{not}
47 terminated by a distinguished character code. (By contrast, strings in
48 C are terminated by a character with @acronym{ASCII} code 0.)
50 Since strings are arrays, and therefore sequences as well, you can
51 operate on them with the general array and sequence functions.
52 (@xref{Sequences Arrays Vectors}.) For example, you can access or
53 change individual characters in a string using the functions @code{aref}
54 and @code{aset} (@pxref{Array Functions}).
56 There are two text representations for non-@acronym{ASCII} characters in
57 Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text
58 Representations}). For most Lisp programming, you don't need to be
59 concerned with these two representations.
61 Sometimes key sequences are represented as unibyte strings. When a
62 unibyte string is a key sequence, string elements in the range 128 to
63 255 represent meta characters (which are large integers) rather than
64 character codes in the range 128 to 255.
66 Strings cannot hold characters that have the hyper, super or alt
67 modifiers; they can hold @acronym{ASCII} control characters, but no other
68 control characters. They do not distinguish case in @acronym{ASCII} control
69 characters. If you want to store such characters in a sequence, such as
70 a key sequence, you must use a vector instead of a string.
71 @xref{Character Type}, for more information about the representation of meta
72 and other modifiers for keyboard input characters.
74 Strings are useful for holding regular expressions. You can also
75 match regular expressions against strings with @code{string-match}
76 (@pxref{Regexp Search}). The functions @code{match-string}
77 (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing
78 Match}) are useful for decomposing and modifying strings after
79 matching regular expressions against them.
81 Like a buffer, a string can contain text properties for the characters
82 in it, as well as the characters themselves. @xref{Text Properties}.
83 All the Lisp primitives that copy text from strings to buffers or other
84 strings also copy the properties of the characters being copied.
86 @xref{Text}, for information about functions that display strings or
87 copy them into buffers. @xref{Character Type}, and @ref{String Type},
88 for information about the syntax of characters and strings.
89 @xref{Non-ASCII Characters}, for functions to convert between text
90 representations and to encode and decode character codes.
92 @node Predicates for Strings
93 @section The Predicates for Strings
95 For more information about general sequence and array predicates,
96 see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
99 This function returns @code{t} if @var{object} is a string, @code{nil}
103 @defun string-or-null-p object
104 This function returns @code{t} if @var{object} is a string or
105 @code{nil}, @code{nil} otherwise.
108 @defun char-or-string-p object
109 This function returns @code{t} if @var{object} is a string or a
110 character (i.e., an integer), @code{nil} otherwise.
113 @node Creating Strings
114 @section Creating Strings
116 The following functions create strings, either from scratch, or by
117 putting strings together, or by taking them apart.
119 @defun make-string count character
120 This function returns a string made up of @var{count} repetitions of
121 @var{character}. If @var{count} is negative, an error is signaled.
130 Other functions to compare with this one include @code{char-to-string}
131 (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and
132 @code{make-list} (@pxref{Building Lists}).
135 @defun string &rest characters
136 This returns a string containing the characters @var{characters}.
144 @defun substring string start &optional end
145 This function returns a new string which consists of those characters
146 from @var{string} in the range from (and including) the character at the
147 index @var{start} up to (but excluding) the character at the index
148 @var{end}. The first character is at index zero.
152 (substring "abcdefg" 0 3)
158 Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the
159 index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied
160 from the string @code{"abcdefg"}. The index 3 marks the character
161 position up to which the substring is copied. The character whose index
162 is 3 is actually the fourth character in the string.
164 A negative number counts from the end of the string, so that @minus{}1
165 signifies the index of the last character of the string. For example:
169 (substring "abcdefg" -3 -1)
175 In this example, the index for @samp{e} is @minus{}3, the index for
176 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
177 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
179 When @code{nil} is used for @var{end}, it stands for the length of the
184 (substring "abcdefg" -3 nil)
189 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
190 It follows that @code{(substring @var{string} 0)} returns a copy of all
195 (substring "abcdefg" 0)
201 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
204 If the characters copied from @var{string} have text properties, the
205 properties are copied into the new string also. @xref{Text Properties}.
207 @code{substring} also accepts a vector for the first argument.
211 (substring [a b (c) "d"] 1 3)
215 A @code{wrong-type-argument} error is signaled if @var{start} is not
216 an integer or if @var{end} is neither an integer nor @code{nil}. An
217 @code{args-out-of-range} error is signaled if @var{start} indicates a
218 character following @var{end}, or if either integer is out of range
221 Contrast this function with @code{buffer-substring} (@pxref{Buffer
222 Contents}), which returns a string containing a portion of the text in
223 the current buffer. The beginning of a string is at index 0, but the
224 beginning of a buffer is at index 1.
227 @defun substring-no-properties string &optional start end
228 This works like @code{substring} but discards all text properties from
229 the value. Also, @var{start} may be omitted or @code{nil}, which is
230 equivalent to 0. Thus, @w{@code{(substring-no-properties
231 @var{string})}} returns a copy of @var{string}, with all text
235 @defun concat &rest sequences
236 @cindex copying strings
237 @cindex concatenating strings
238 This function returns a new string consisting of the characters in the
239 arguments passed to it (along with their text properties, if any). The
240 arguments may be strings, lists of numbers, or vectors of numbers; they
241 are not themselves changed. If @code{concat} receives no arguments, it
242 returns an empty string.
245 (concat "abc" "-def")
247 (concat "abc" (list 120 121) [122])
249 ;; @r{@code{nil} is an empty sequence.}
250 (concat "abc" nil "-def")
252 (concat "The " "quick brown " "fox.")
253 @result{} "The quick brown fox."
259 The @code{concat} function always constructs a new string that is
260 not @code{eq} to any existing string, except when the result is empty
261 (since empty strings are canonicalized to save space).
263 In Emacs versions before 21, when an argument was an integer (not a
264 sequence of integers), it was converted to a string of digits making up
265 the decimal printed representation of the integer. This obsolete usage
266 no longer works. The proper way to convert an integer to its decimal
267 printed form is with @code{format} (@pxref{Formatting Strings}) or
268 @code{number-to-string} (@pxref{String Conversion}).
270 For information about other concatenation functions, see the
271 description of @code{mapconcat} in @ref{Mapping Functions},
272 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
273 Lists}. For concatenating individual command-line arguments into a
274 string to be used as a shell command, see @ref{Shell Arguments,
275 combine-and-quote-strings}.
278 @defun split-string string &optional separators omit-nulls
279 This function splits @var{string} into substrings at matches for the
280 regular expression @var{separators}. Each match for @var{separators}
281 defines a splitting point; the substrings between the splitting points
282 are made into a list, which is the value returned by
285 If @var{omit-nulls} is @code{nil}, the result contains null strings
286 whenever there are two consecutive matches for @var{separators}, or a
287 match is adjacent to the beginning or end of @var{string}. If
288 @var{omit-nulls} is @code{t}, these null strings are omitted from the
291 If @var{separators} is @code{nil} (or omitted),
292 the default is the value of @code{split-string-default-separators}.
294 As a special case, when @var{separators} is @code{nil} (or omitted),
295 null strings are always omitted from the result. Thus:
298 (split-string " two words ")
299 @result{} ("two" "words")
302 The result is not @code{("" "two" "words" "")}, which would rarely be
303 useful. If you need such a result, use an explicit value for
307 (split-string " two words "
308 split-string-default-separators)
309 @result{} ("" "two" "words" "")
315 (split-string "Soup is good food" "o")
316 @result{} ("S" "up is g" "" "d f" "" "d")
317 (split-string "Soup is good food" "o" t)
318 @result{} ("S" "up is g" "d f" "d")
319 (split-string "Soup is good food" "o+")
320 @result{} ("S" "up is g" "d f" "d")
323 Empty matches do count, except that @code{split-string} will not look
324 for a final empty match when it already reached the end of the string
325 using a non-empty match or when @var{string} is empty:
328 (split-string "aooob" "o*")
329 @result{} ("" "a" "" "b" "")
330 (split-string "ooaboo" "o*")
331 @result{} ("" "" "a" "b" "")
336 However, when @var{separators} can match the empty string,
337 @var{omit-nulls} is usually @code{t}, so that the subtleties in the
338 three previous examples are rarely relevant:
341 (split-string "Soup is good food" "o*" t)
342 @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
343 (split-string "Nice doggy!" "" t)
344 @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
345 (split-string "" "" t)
349 Somewhat odd, but predictable, behavior can occur for certain
350 ``non-greedy'' values of @var{separators} that can prefer empty
351 matches over non-empty matches. Again, such values rarely occur in
355 (split-string "ooo" "o*" t)
357 (split-string "ooo" "\\|o+" t)
358 @result{} ("o" "o" "o")
361 If you need to split a string that is a shell command, where
362 individual arguments could be quoted, see @ref{Shell Arguments,
363 split-string-and-unquote}.
366 @defvar split-string-default-separators
367 The default value of @var{separators} for @code{split-string}. Its
368 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
371 @node Modifying Strings
372 @section Modifying Strings
374 The most basic way to alter the contents of an existing string is with
375 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
376 @var{idx} @var{char})} stores @var{char} into @var{string} at index
377 @var{idx}. Each character occupies one or more bytes, and if @var{char}
378 needs a different number of bytes from the character already present at
379 that index, @code{aset} signals an error.
381 A more powerful function is @code{store-substring}:
383 @defun store-substring string idx obj
384 This function alters part of the contents of the string @var{string}, by
385 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
386 may be either a character or a (smaller) string.
388 Since it is impossible to change the length of an existing string, it is
389 an error if @var{obj} doesn't fit within @var{string}'s actual length,
390 or if any new character requires a different number of bytes from the
391 character currently present at that point in @var{string}.
394 To clear out a string that contained a password, use
397 @defun clear-string string
398 This makes @var{string} a unibyte string and clears its contents to
399 zeros. It may also change @var{string}'s length.
403 @node Text Comparison
404 @section Comparison of Characters and Strings
405 @cindex string equality
407 @defun char-equal character1 character2
408 This function returns @code{t} if the arguments represent the same
409 character, @code{nil} otherwise. This function ignores differences
410 in case if @code{case-fold-search} is non-@code{nil}.
415 (let ((case-fold-search nil))
421 @defun string= string1 string2
422 This function returns @code{t} if the characters of the two strings
423 match exactly. Symbols are also allowed as arguments, in which case
424 their print names are used.
425 Case is always significant, regardless of @code{case-fold-search}.
428 (string= "abc" "abc")
430 (string= "abc" "ABC")
436 The function @code{string=} ignores the text properties of the two
437 strings. When @code{equal} (@pxref{Equality Predicates}) compares two
438 strings, it uses @code{string=}.
440 For technical reasons, a unibyte and a multibyte string are
441 @code{equal} if and only if they contain the same sequence of
442 character codes and all these codes are either in the range 0 through
443 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
444 However, when a unibyte string gets converted to a multibyte string,
445 all characters with codes in the range 160 through 255 get converted
446 to characters with higher codes, whereas @acronym{ASCII} characters
447 remain unchanged. Thus, a unibyte string and its conversion to
448 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
449 Character codes 160 through 255 are not entirely proper in multibyte
450 text, even though they can occur. As a consequence, the situation
451 where a unibyte and a multibyte string are @code{equal} without both
452 being all @acronym{ASCII} is a technical oddity that very few Emacs
453 Lisp programmers ever get confronted with. @xref{Text
457 @defun string-equal string1 string2
458 @code{string-equal} is another name for @code{string=}.
461 @cindex lexical comparison
462 @defun string< string1 string2
463 @c (findex string< causes problems for permuted index!!)
464 This function compares two strings a character at a time. It
465 scans both the strings at the same time to find the first pair of corresponding
466 characters that do not match. If the lesser character of these two is
467 the character from @var{string1}, then @var{string1} is less, and this
468 function returns @code{t}. If the lesser character is the one from
469 @var{string2}, then @var{string1} is greater, and this function returns
470 @code{nil}. If the two strings match entirely, the value is @code{nil}.
472 Pairs of characters are compared according to their character codes.
473 Keep in mind that lower case letters have higher numeric values in the
474 @acronym{ASCII} character set than their upper case counterparts; digits and
475 many punctuation characters have a lower numeric value than upper case
476 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
477 character; a unibyte non-@acronym{ASCII} character is always less than any
478 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
482 (string< "abc" "abd")
484 (string< "abd" "abc")
486 (string< "123" "abc")
491 When the strings have different lengths, and they match up to the
492 length of @var{string1}, then the result is @code{t}. If they match up
493 to the length of @var{string2}, the result is @code{nil}. A string of
494 no characters is less than any other string.
511 Symbols are also allowed as arguments, in which case their print names
515 @defun string-lessp string1 string2
516 @code{string-lessp} is another name for @code{string<}.
519 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
520 This function compares the specified part of @var{string1} with the
521 specified part of @var{string2}. The specified part of @var{string1}
522 runs from index @var{start1} up to index @var{end1} (@code{nil} means
523 the end of the string). The specified part of @var{string2} runs from
524 index @var{start2} up to index @var{end2} (@code{nil} means the end of
527 The strings are both converted to multibyte for the comparison
528 (@pxref{Text Representations}) so that a unibyte string and its
529 conversion to multibyte are always regarded as equal. If
530 @var{ignore-case} is non-@code{nil}, then case is ignored, so that
531 upper case letters can be equal to lower case letters.
533 If the specified portions of the two strings match, the value is
534 @code{t}. Otherwise, the value is an integer which indicates how many
535 leading characters agree, and which string is less. Its absolute value
536 is one plus the number of characters that agree at the beginning of the
537 two strings. The sign is negative if @var{string1} (or its specified
541 @defun assoc-string key alist &optional case-fold
542 This function works like @code{assoc}, except that @var{key} must be a
543 string or symbol, and comparison is done using @code{compare-strings}.
544 Symbols are converted to strings before testing.
545 If @var{case-fold} is non-@code{nil}, it ignores case differences.
546 Unlike @code{assoc}, this function can also match elements of the alist
547 that are strings or symbols rather than conses. In particular, @var{alist} can
548 be a list of strings or symbols rather than an actual alist.
549 @xref{Association Lists}.
552 See also the @code{compare-buffer-substrings} function in
553 @ref{Comparing Text}, for a way to compare text in buffers. The
554 function @code{string-match}, which matches a regular expression
555 against a string, can be used for a kind of string comparison; see
558 @node String Conversion
559 @comment node-name, next, previous, up
560 @section Conversion of Characters and Strings
561 @cindex conversion of strings
563 This section describes functions for conversions between characters,
564 strings and integers. @code{format} (@pxref{Formatting Strings})
565 and @code{prin1-to-string}
566 (@pxref{Output Functions}) can also convert Lisp objects into strings.
567 @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a
568 string representation of a Lisp object into an object. The functions
569 @code{string-make-multibyte} and @code{string-make-unibyte} convert the
570 text representation of a string (@pxref{Converting Representations}).
572 @xref{Documentation}, for functions that produce textual descriptions
573 of text characters and general input events
574 (@code{single-key-description} and @code{text-char-description}). These
575 are used primarily for making help messages.
577 @defun char-to-string character
578 @cindex character to string
579 This function returns a new string containing one character,
580 @var{character}. This function is semi-obsolete because the function
581 @code{string} is more general. @xref{Creating Strings}.
584 @defun string-to-char string
585 @cindex string to character
586 This function returns the first character in @var{string}. If the
587 string is empty, the function returns 0. The value is also 0 when the
588 first character of @var{string} is the null character, @acronym{ASCII} code
592 (string-to-char "ABC")
595 (string-to-char "xyz")
600 (string-to-char "\000")
605 This function may be eliminated in the future if it does not seem useful
609 @defun number-to-string number
610 @cindex integer to string
611 @cindex integer to decimal
612 This function returns a string consisting of the printed base-ten
613 representation of @var{number}, which may be an integer or a floating
614 point number. The returned value starts with a minus sign if the argument is
618 (number-to-string 256)
621 (number-to-string -23)
624 (number-to-string -23.5)
628 @cindex int-to-string
629 @code{int-to-string} is a semi-obsolete alias for this function.
631 See also the function @code{format} in @ref{Formatting Strings}.
634 @defun string-to-number string &optional base
635 @cindex string to number
636 This function returns the numeric value of the characters in
637 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
638 between 2 and 16 (inclusive), and integers are converted in that base.
639 If @var{base} is @code{nil}, then base ten is used. Floating point
640 conversion only works in base ten; we have not implemented other
641 radices for floating point numbers, because that would be much more
642 work and does not seem useful. If @var{string} looks like an integer
643 but its value is too large to fit into a Lisp integer,
644 @code{string-to-number} returns a floating point result.
646 The parsing skips spaces and tabs at the beginning of @var{string},
647 then reads as much of @var{string} as it can interpret as a number in
648 the given base. (On some systems it ignores other whitespace at the
649 beginning, not just spaces and tabs.) If the first character after
650 the ignored whitespace is neither a digit in the given base, nor a
651 plus or minus sign, nor the leading dot of a floating point number,
652 this function returns 0.
655 (string-to-number "256")
657 (string-to-number "25 is a perfect square.")
659 (string-to-number "X256")
661 (string-to-number "-4.5")
663 (string-to-number "1e5")
667 @findex string-to-int
668 @code{string-to-int} is an obsolete alias for this function.
671 Here are some other functions that can convert to or from a string:
675 @code{concat} can convert a vector or a list into a string.
676 @xref{Creating Strings}.
679 @code{vconcat} can convert a string into a vector. @xref{Vector
683 @code{append} can convert a string into a list. @xref{Building Lists}.
686 @node Formatting Strings
687 @comment node-name, next, previous, up
688 @section Formatting Strings
689 @cindex formatting strings
690 @cindex strings, formatting them
692 @dfn{Formatting} means constructing a string by substitution of
693 computed values at various places in a constant string. This constant string
694 controls how the other values are printed, as well as where they appear;
695 it is called a @dfn{format string}.
697 Formatting is often useful for computing messages to be displayed. In
698 fact, the functions @code{message} and @code{error} provide the same
699 formatting feature described here; they differ from @code{format} only
700 in how they use the result of formatting.
702 @defun format string &rest objects
703 This function returns a new string that is made by copying
704 @var{string} and then replacing any format specification
705 in the copy with encodings of the corresponding @var{objects}. The
706 arguments @var{objects} are the computed values to be formatted.
708 The characters in @var{string}, other than the format specifications,
709 are copied directly into the output, including their text properties,
713 @cindex @samp{%} in format
714 @cindex format specification
715 A format specification is a sequence of characters beginning with a
716 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
717 @code{format} function replaces it with the printed representation of
718 one of the values to be formatted (one of the arguments @var{objects}).
723 (format "The value of fill-column is %d." fill-column)
724 @result{} "The value of fill-column is 72."
728 Since @code{format} interprets @samp{%} characters as format
729 specifications, you should @emph{never} pass an arbitrary string as
730 the first argument. This is particularly true when the string is
731 generated by some Lisp code. Unless the string is @emph{known} to
732 never include any @samp{%} characters, pass @code{"%s"}, described
733 below, as the first argument, and the string as the second, like this:
736 (format "%s" @var{arbitrary-string})
739 If @var{string} contains more than one format specification, the
740 format specifications correspond to successive values from
741 @var{objects}. Thus, the first format specification in @var{string}
742 uses the first such value, the second format specification uses the
743 second such value, and so on. Any extra format specifications (those
744 for which there are no corresponding values) cause an error. Any
745 extra values to be formatted are ignored.
747 Certain format specifications require values of particular types. If
748 you supply a value that doesn't fit the requirements, an error is
751 Here is a table of valid format specifications:
755 Replace the specification with the printed representation of the object,
756 made without quoting (that is, using @code{princ}, not
757 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
758 by their contents alone, with no @samp{"} characters, and symbols appear
759 without @samp{\} characters.
761 If the object is a string, its text properties are
762 copied into the output. The text properties of the @samp{%s} itself
763 are also copied, but those of the object take priority.
766 Replace the specification with the printed representation of the object,
767 made with quoting (that is, using @code{prin1}---@pxref{Output
768 Functions}). Thus, strings are enclosed in @samp{"} characters, and
769 @samp{\} characters appear where necessary before special characters.
772 @cindex integer to octal
773 Replace the specification with the base-eight representation of an
777 Replace the specification with the base-ten representation of an
782 @cindex integer to hexadecimal
783 Replace the specification with the base-sixteen representation of an
784 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
787 Replace the specification with the character which is the value given.
790 Replace the specification with the exponential notation for a floating
794 Replace the specification with the decimal-point notation for a floating
798 Replace the specification with notation for a floating point number,
799 using either exponential notation or decimal-point notation, whichever
803 Replace the specification with a single @samp{%}. This format
804 specification is unusual in that it does not use a value. For example,
805 @code{(format "%% %d" 30)} returns @code{"% 30"}.
808 Any other format character results in an @samp{Invalid format
811 Here are several examples:
815 (format "The name of this buffer is %s." (buffer-name))
816 @result{} "The name of this buffer is strings.texi."
818 (format "The buffer object prints as %s." (current-buffer))
819 @result{} "The buffer object prints as strings.texi."
821 (format "The octal value of %d is %o,
822 and the hex value is %x." 18 18 18)
823 @result{} "The octal value of 18 is 22,
824 and the hex value is 12."
830 A specification can have a @dfn{width}, which is a decimal number
831 between the @samp{%} and the specification character. If the printed
832 representation of the object contains fewer characters than this
833 width, @code{format} extends it with padding. The width specifier is
834 ignored for the @samp{%%} specification. Any padding introduced by
835 the width specifier normally consists of spaces inserted on the left:
838 (format "%5d is padded on the left with spaces" 123)
839 @result{} " 123 is padded on the left with spaces"
843 If the width is too small, @code{format} does not truncate the
844 object's printed representation. Thus, you can use a width to specify
845 a minimum spacing between columns with no risk of losing information.
846 In the following three examples, @samp{%7s} specifies a minimum width
847 of 7. In the first case, the string inserted in place of @samp{%7s}
848 has only 3 letters, and needs 4 blank spaces as padding. In the
849 second case, the string @code{"specification"} is 13 letters wide but
854 (format "The word `%7s' actually has %d letters in it."
855 "foo" (length "foo"))
856 @result{} "The word ` foo' actually has 3 letters in it."
857 (format "The word `%7s' actually has %d letters in it."
858 "specification" (length "specification"))
859 @result{} "The word `specification' actually has 13 letters in it."
863 @cindex flags in format specifications
864 Immediately after the @samp{%} and before the optional width
865 specifier, you can also put certain @dfn{flag characters}.
867 The flag @samp{+} inserts a plus sign before a positive number, so
868 that it always has a sign. A space character as flag inserts a space
869 before a positive number. (Otherwise, positive numbers start with the
870 first digit.) These flags are useful for ensuring that positive
871 numbers and negative numbers use the same number of columns. They are
872 ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if
873 both flags are used, @samp{+} takes precedence.
875 The flag @samp{#} specifies an ``alternate form'' which depends on
876 the format in use. For @samp{%o}, it ensures that the result begins
877 with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result
878 with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g},
879 the @samp{#} flag means include a decimal point even if the precision
882 The flag @samp{-} causes the padding inserted by the width
883 specifier, if any, to be inserted on the right rather than the left.
884 The flag @samp{0} ensures that the padding consists of @samp{0}
885 characters instead of spaces, inserted on the left. These flags are
886 ignored for specification characters for which they do not make sense:
887 @samp{%s}, @samp{%S} and @samp{%c} accept the @samp{0} flag, but still
888 pad with @emph{spaces} on the left. If both @samp{-} and @samp{0} are
889 present and valid, @samp{-} takes precedence.
893 (format "%06d is padded on the left with zeros" 123)
894 @result{} "000123 is padded on the left with zeros"
896 (format "%-6d is padded on the right" 123)
897 @result{} "123 is padded on the right"
899 (format "The word `%-7s' actually has %d letters in it."
900 "foo" (length "foo"))
901 @result{} "The word `foo ' actually has 3 letters in it."
905 @cindex precision in format specifications
906 All the specification characters allow an optional @dfn{precision}
907 before the character (after the width, if present). The precision is
908 a decimal-point @samp{.} followed by a digit-string. For the
909 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
910 precision specifies how many decimal places to show; if zero, the
911 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
912 the precision truncates the string to the given width, so @samp{%.3s}
913 shows only the first three characters of the representation for
914 @var{object}. Precision has no effect for other specification
917 @node Case Conversion
918 @comment node-name, next, previous, up
919 @section Case Conversion in Lisp
922 @cindex character case
923 @cindex case conversion in Lisp
925 The character case functions change the case of single characters or
926 of the contents of strings. The functions normally convert only
927 alphabetic characters (the letters @samp{A} through @samp{Z} and
928 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
929 characters are not altered. You can specify a different case
930 conversion mapping by specifying a case table (@pxref{Case Tables}).
932 These functions do not modify the strings that are passed to them as
935 The examples below use the characters @samp{X} and @samp{x} which have
936 @acronym{ASCII} codes 88 and 120 respectively.
938 @defun downcase string-or-char
939 This function converts a character or a string to lower case.
941 When the argument to @code{downcase} is a string, the function creates
942 and returns a new string in which each letter in the argument that is
943 upper case is converted to lower case. When the argument to
944 @code{downcase} is a character, @code{downcase} returns the
945 corresponding lower case character. This value is an integer. If the
946 original character is lower case, or is not a letter, then the value
947 equals the original character.
950 (downcase "The cat in the hat")
951 @result{} "the cat in the hat"
958 @defun upcase string-or-char
959 This function converts a character or a string to upper case.
961 When the argument to @code{upcase} is a string, the function creates
962 and returns a new string in which each letter in the argument that is
963 lower case is converted to upper case.
965 When the argument to @code{upcase} is a character, @code{upcase}
966 returns the corresponding upper case character. This value is an integer.
967 If the original character is upper case, or is not a letter, then the
968 value returned equals the original character.
971 (upcase "The cat in the hat")
972 @result{} "THE CAT IN THE HAT"
979 @defun capitalize string-or-char
980 @cindex capitalization
981 This function capitalizes strings or characters. If
982 @var{string-or-char} is a string, the function creates and returns a new
983 string, whose contents are a copy of @var{string-or-char} in which each
984 word has been capitalized. This means that the first character of each
985 word is converted to upper case, and the rest are converted to lower
988 The definition of a word is any sequence of consecutive characters that
989 are assigned to the word constituent syntax class in the current syntax
990 table (@pxref{Syntax Class Table}).
992 When the argument to @code{capitalize} is a character, @code{capitalize}
993 has the same result as @code{upcase}.
997 (capitalize "The cat in the hat")
998 @result{} "The Cat In The Hat"
1002 (capitalize "THE 77TH-HATTED CAT")
1003 @result{} "The 77th-Hatted Cat"
1013 @defun upcase-initials string-or-char
1014 If @var{string-or-char} is a string, this function capitalizes the
1015 initials of the words in @var{string-or-char}, without altering any
1016 letters other than the initials. It returns a new string whose
1017 contents are a copy of @var{string-or-char}, in which each word has
1018 had its initial letter converted to upper case.
1020 The definition of a word is any sequence of consecutive characters that
1021 are assigned to the word constituent syntax class in the current syntax
1022 table (@pxref{Syntax Class Table}).
1024 When the argument to @code{upcase-initials} is a character,
1025 @code{upcase-initials} has the same result as @code{upcase}.
1029 (upcase-initials "The CAT in the hAt")
1030 @result{} "The CAT In The HAt"
1035 @xref{Text Comparison}, for functions that compare strings; some of
1036 them ignore case differences, or can optionally ignore case differences.
1039 @section The Case Table
1041 You can customize case conversion by installing a special @dfn{case
1042 table}. A case table specifies the mapping between upper case and lower
1043 case letters. It affects both the case conversion functions for Lisp
1044 objects (see the previous section) and those that apply to text in the
1045 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1046 also a standard case table which is used to initialize the case table
1049 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1050 @code{case-table}. This char-table maps each character into the
1051 corresponding lower case character. It has three extra slots, which
1052 hold related tables:
1056 The upcase table maps each character into the corresponding upper
1059 The canonicalize table maps all of a set of case-related characters
1060 into a particular member of that set.
1062 The equivalences table maps each one of a set of case-related characters
1063 into the next character in that set.
1066 In simple cases, all you need to specify is the mapping to lower-case;
1067 the three related tables will be calculated automatically from that one.
1069 For some languages, upper and lower case letters are not in one-to-one
1070 correspondence. There may be two different lower case letters with the
1071 same upper case equivalent. In these cases, you need to specify the
1072 maps for both lower case and upper case.
1074 The extra table @var{canonicalize} maps each character to a canonical
1075 equivalent; any two characters that are related by case-conversion have
1076 the same canonical equivalent character. For example, since @samp{a}
1077 and @samp{A} are related by case-conversion, they should have the same
1078 canonical equivalent character (which should be either @samp{a} for both
1079 of them, or @samp{A} for both of them).
1081 The extra table @var{equivalences} is a map that cyclically permutes
1082 each equivalence class (of characters with the same canonical
1083 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1084 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1085 equivalent characters.)
1087 When you construct a case table, you can provide @code{nil} for
1088 @var{canonicalize}; then Emacs fills in this slot from the lower case
1089 and upper case mappings. You can also provide @code{nil} for
1090 @var{equivalences}; then Emacs fills in this slot from
1091 @var{canonicalize}. In a case table that is actually in use, those
1092 components are non-@code{nil}. Do not try to specify @var{equivalences}
1093 without also specifying @var{canonicalize}.
1095 Here are the functions for working with case tables:
1097 @defun case-table-p object
1098 This predicate returns non-@code{nil} if @var{object} is a valid case
1102 @defun set-standard-case-table table
1103 This function makes @var{table} the standard case table, so that it will
1104 be used in any buffers created subsequently.
1107 @defun standard-case-table
1108 This returns the standard case table.
1111 @defun current-case-table
1112 This function returns the current buffer's case table.
1115 @defun set-case-table table
1116 This sets the current buffer's case table to @var{table}.
1119 @defmac with-case-table table body@dots{}
1120 The @code{with-case-table} macro saves the current case table, makes
1121 @var{table} the current case table, evaluates the @var{body} forms,
1122 and finally restores the case table. The return value is the value of
1123 the last form in @var{body}. The case table is restored even in case
1124 of an abnormal exit via @code{throw} or error (@pxref{Nonlocal
1128 Some language environments may modify the case conversions of
1129 @acronym{ASCII} characters; for example, in the Turkish language
1130 environment, the @acronym{ASCII} character @samp{I} is downcased into
1131 a Turkish ``dotless i''. This can interfere with code that requires
1132 ordinary ASCII case conversion, such as implementations of
1133 @acronym{ASCII}-based network protocols. In that case, use the
1134 @code{with-case-table} macro with the variable @var{ascii-case-table},
1135 which stores the unmodified case table for the @acronym{ASCII}
1138 @defvar ascii-case-table
1139 The case table for the @acronym{ASCII} character set. This should not be
1140 modified by any language environment settings.
1143 The following three functions are convenient subroutines for packages
1144 that define non-@acronym{ASCII} character sets. They modify the specified
1145 case table @var{case-table}; they also modify the standard syntax table.
1146 @xref{Syntax Tables}. Normally you would use these functions to change
1147 the standard case table.
1149 @defun set-case-syntax-pair uc lc case-table
1150 This function specifies a pair of corresponding letters, one upper case
1154 @defun set-case-syntax-delims l r case-table
1155 This function makes characters @var{l} and @var{r} a matching pair of
1156 case-invariant delimiters.
1159 @defun set-case-syntax char syntax case-table
1160 This function makes @var{char} case-invariant, with syntax
1164 @deffn Command describe-buffer-case-table
1165 This command displays a description of the contents of the current
1166 buffer's case table.
1170 arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4