2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @node Strings and Characters
7 @chapter Strings and Characters
9 @cindex character arrays
13 A string in Emacs Lisp is an array that contains an ordered sequence
14 of characters. Strings are used as names of symbols, buffers, and
15 files; to send messages to users; to hold text being copied between
16 buffers; and for many other purposes. Because strings are so important,
17 Emacs Lisp has many functions expressly for manipulating them. Emacs
18 Lisp programs use strings more often than individual characters.
20 @xref{Strings of Events}, for special considerations for strings of
21 keyboard character events.
24 * Basics: String Basics. Basic properties of strings and characters.
25 * Predicates for Strings:: Testing whether an object is a string or char.
26 * Creating Strings:: Functions to allocate new strings.
27 * Modifying Strings:: Altering the contents of an existing string.
28 * Text Comparison:: Comparing characters or strings.
29 * String Conversion:: Converting to and from characters and strings.
30 * Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}.
31 * Case Conversion:: Case conversion functions.
32 * Case Tables:: Customizing case conversion.
36 @section String and Character Basics
38 A character is a Lisp object which represents a single character of
39 text. In Emacs Lisp, characters are simply integers; whether an
40 integer is a character or not is determined only by how it is used.
41 @xref{Character Codes}, for details about character representation in
44 A string is a fixed sequence of characters. It is a type of
45 sequence called a @dfn{array}, meaning that its length is fixed and
46 cannot be altered once it is created (@pxref{Sequences Arrays
47 Vectors}). Unlike in C, Emacs Lisp strings are @emph{not} terminated
48 by a distinguished character code.
50 Since strings are arrays, and therefore sequences as well, you can
51 operate on them with the general array and sequence functions
52 documented in @ref{Sequences Arrays Vectors}. For example, you can
53 access or change individual characters in a string using the functions
54 @code{aref} and @code{aset} (@pxref{Array Functions}). However, note
55 that @code{length} should @emph{not} be used for computing the width
56 of a string on display; use @code{string-width} (@pxref{Width})
59 There are two text representations for non-@acronym{ASCII}
60 characters in Emacs strings (and in buffers): unibyte and multibyte.
61 For most Lisp programming, you don't need to be concerned with these
62 two representations. @xref{Text Representations}, for details.
64 Sometimes key sequences are represented as unibyte strings. When a
65 unibyte string is a key sequence, string elements in the range 128 to
66 255 represent meta characters (which are large integers) rather than
67 character codes in the range 128 to 255. Strings cannot hold
68 characters that have the hyper, super or alt modifiers; they can hold
69 @acronym{ASCII} control characters, but no other control characters.
70 They do not distinguish case in @acronym{ASCII} control characters.
71 If you want to store such characters in a sequence, such as a key
72 sequence, you must use a vector instead of a string. @xref{Character
73 Type}, for more information about keyboard input characters.
75 Strings are useful for holding regular expressions. You can also
76 match regular expressions against strings with @code{string-match}
77 (@pxref{Regexp Search}). The functions @code{match-string}
78 (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing
79 Match}) are useful for decomposing and modifying strings after
80 matching regular expressions against them.
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 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 string-or-null-p object
105 This function returns @code{t} if @var{object} is a string or
106 @code{nil}. It returns @code{nil} otherwise.
109 @defun char-or-string-p object
110 This function returns @code{t} if @var{object} is a string or a
111 character (i.e., an integer), @code{nil} otherwise.
114 @node Creating Strings
115 @section Creating Strings
117 The following functions create strings, either from scratch, or by
118 putting strings together, or by taking them apart.
120 @defun make-string count character
121 This function returns a string made up of @var{count} repetitions of
122 @var{character}. If @var{count} is negative, an error is signaled.
131 Other functions to compare with this one include @code{make-vector}
132 (@pxref{Vectors}) and @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 In the above example, the index for @samp{a} is 0, the index for
159 @samp{b} is 1, and the index for @samp{c} is 2. The index 3---which
160 is the fourth character in the string---marks the character position
161 up to which the substring is copied. Thus, @samp{abc} is copied from
162 the string @code{"abcdefg"}.
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 This function always constructs a new string that is not @code{eq} to
260 any existing string, except when the result is the empty string (to
261 save space, Emacs makes only one empty multibyte string).
263 For information about other concatenation functions, see the
264 description of @code{mapconcat} in @ref{Mapping Functions},
265 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
266 Lists}. For concatenating individual command-line arguments into a
267 string to be used as a shell command, see @ref{Shell Arguments,
268 combine-and-quote-strings}.
271 @defun split-string string &optional separators omit-nulls
272 This function splits @var{string} into substrings based on the regular
273 expression @var{separators} (@pxref{Regular Expressions}). Each match
274 for @var{separators} defines a splitting point; the substrings between
275 splitting points are made into a list, which is returned.
277 If @var{omit-nulls} is @code{nil} (or omitted), the result contains
278 null strings whenever there are two consecutive matches for
279 @var{separators}, or a match is adjacent to the beginning or end of
280 @var{string}. If @var{omit-nulls} is @code{t}, these null strings are
281 omitted from the result.
283 If @var{separators} is @code{nil} (or omitted), the default is the
284 value of @code{split-string-default-separators}.
286 As a special case, when @var{separators} is @code{nil} (or omitted),
287 null strings are always omitted from the result. Thus:
290 (split-string " two words ")
291 @result{} ("two" "words")
294 The result is not @code{("" "two" "words" "")}, which would rarely be
295 useful. If you need such a result, use an explicit value for
299 (split-string " two words "
300 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")
353 If you need to split a string into a list of individual command-line
354 arguments suitable for @code{call-process} or @code{start-process},
355 see @ref{Shell Arguments, split-string-and-unquote}.
358 @defvar split-string-default-separators
359 The default value of @var{separators} for @code{split-string}. Its
360 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
363 @node Modifying Strings
364 @section Modifying Strings
366 The most basic way to alter the contents of an existing string is with
367 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
368 @var{idx} @var{char})} stores @var{char} into @var{string} at index
369 @var{idx}. Each character occupies one or more bytes, and if @var{char}
370 needs a different number of bytes from the character already present at
371 that index, @code{aset} signals an error.
373 A more powerful function is @code{store-substring}:
375 @defun store-substring string idx obj
376 This function alters part of the contents of the string @var{string}, by
377 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
378 may be either a character or a (smaller) string.
380 Since it is impossible to change the length of an existing string, it is
381 an error if @var{obj} doesn't fit within @var{string}'s actual length,
382 or if any new character requires a different number of bytes from the
383 character currently present at that point in @var{string}.
386 To clear out a string that contained a password, use
389 @defun clear-string string
390 This makes @var{string} a unibyte string and clears its contents to
391 zeros. It may also change @var{string}'s length.
395 @node Text Comparison
396 @section Comparison of Characters and Strings
397 @cindex string equality
399 @defun char-equal character1 character2
400 This function returns @code{t} if the arguments represent the same
401 character, @code{nil} otherwise. This function ignores differences
402 in case if @code{case-fold-search} is non-@code{nil}.
407 (let ((case-fold-search nil))
413 @defun string= string1 string2
414 This function returns @code{t} if the characters of the two strings
415 match exactly. Symbols are also allowed as arguments, in which case
416 the symbol names are used. Case is always significant, regardless of
417 @code{case-fold-search}.
419 This function is equivalent to @code{equal} for comparing two strings
420 (@pxref{Equality Predicates}). In particular, the text properties of
421 the two strings are ignored. But if either argument is not a string
422 or symbol, an error is signaled.
425 (string= "abc" "abc")
427 (string= "abc" "ABC")
433 For technical reasons, a unibyte and a multibyte string are
434 @code{equal} if and only if they contain the same sequence of
435 character codes and all these codes are either in the range 0 through
436 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
437 However, when a unibyte string is converted to a multibyte string, all
438 characters with codes in the range 160 through 255 are converted to
439 characters with higher codes, whereas @acronym{ASCII} characters
440 remain unchanged. Thus, a unibyte string and its conversion to
441 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
442 Character codes 160 through 255 are not entirely proper in multibyte
443 text, even though they can occur. As a consequence, the situation
444 where a unibyte and a multibyte string are @code{equal} without both
445 being all @acronym{ASCII} is a technical oddity that very few Emacs
446 Lisp programmers ever get confronted with. @xref{Text
450 @defun string-equal string1 string2
451 @code{string-equal} is another name for @code{string=}.
454 @cindex lexical comparison
455 @defun string< string1 string2
456 @c (findex string< causes problems for permuted index!!)
457 This function compares two strings a character at a time. It
458 scans both the strings at the same time to find the first pair of corresponding
459 characters that do not match. If the lesser character of these two is
460 the character from @var{string1}, then @var{string1} is less, and this
461 function returns @code{t}. If the lesser character is the one from
462 @var{string2}, then @var{string1} is greater, and this function returns
463 @code{nil}. If the two strings match entirely, the value is @code{nil}.
465 Pairs of characters are compared according to their character codes.
466 Keep in mind that lower case letters have higher numeric values in the
467 @acronym{ASCII} character set than their upper case counterparts; digits and
468 many punctuation characters have a lower numeric value than upper case
469 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
470 character; a unibyte non-@acronym{ASCII} character is always less than any
471 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
475 (string< "abc" "abd")
477 (string< "abd" "abc")
479 (string< "123" "abc")
484 When the strings have different lengths, and they match up to the
485 length of @var{string1}, then the result is @code{t}. If they match up
486 to the length of @var{string2}, the result is @code{nil}. A string of
487 no characters is less than any other string.
504 Symbols are also allowed as arguments, in which case their print names
508 @defun string-lessp string1 string2
509 @code{string-lessp} is another name for @code{string<}.
512 @defun string-prefix-p string1 string2 &optional ignore-case
513 This function returns non-@code{nil} if @var{string1} is a prefix of
514 @var{string2}; i.e., if @var{string2} starts with @var{string1}. If
515 the optional argument @var{ignore-case} is non-@code{nil}, the
516 comparison ignores case differences.
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 function @code{compare-buffer-substrings} 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 @section Conversion of Characters and Strings
560 @cindex conversion of strings
562 This section describes functions for converting between characters,
563 strings and integers. @code{format} (@pxref{Formatting Strings}) and
564 @code{prin1-to-string} (@pxref{Output Functions}) can also convert
565 Lisp objects into strings. @code{read-from-string} (@pxref{Input
566 Functions}) can ``convert'' a string representation of a Lisp object
567 into an object. The functions @code{string-to-multibyte} and
568 @code{string-to-unibyte} convert the text representation of a string
569 (@pxref{Converting Representations}).
571 @xref{Documentation}, for functions that produce textual descriptions
572 of text characters and general input events
573 (@code{single-key-description} and @code{text-char-description}). These
574 are used primarily for making help messages.
576 @defun number-to-string number
577 @cindex integer to string
578 @cindex integer to decimal
579 This function returns a string consisting of the printed base-ten
580 representation of @var{number}, which may be an integer or a floating
581 point number. The returned value starts with a minus sign if the argument is
585 (number-to-string 256)
588 (number-to-string -23)
591 (number-to-string -23.5)
595 @cindex int-to-string
596 @code{int-to-string} is a semi-obsolete alias for this function.
598 See also the function @code{format} in @ref{Formatting Strings}.
601 @defun string-to-number string &optional base
602 @cindex string to number
603 This function returns the numeric value of the characters in
604 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
605 between 2 and 16 (inclusive), and integers are converted in that base.
606 If @var{base} is @code{nil}, then base ten is used. Floating point
607 conversion only works in base ten; we have not implemented other
608 radices for floating point numbers, because that would be much more
609 work and does not seem useful. If @var{string} looks like an integer
610 but its value is too large to fit into a Lisp integer,
611 @code{string-to-number} returns a floating point result.
613 The parsing skips spaces and tabs at the beginning of @var{string},
614 then reads as much of @var{string} as it can interpret as a number in
615 the given base. (On some systems it ignores other whitespace at the
616 beginning, not just spaces and tabs.) If the first character after
617 the ignored whitespace is neither a digit in the given base, nor a
618 plus or minus sign, nor the leading dot of a floating point number,
619 this function returns 0.
622 (string-to-number "256")
624 (string-to-number "25 is a perfect square.")
626 (string-to-number "X256")
628 (string-to-number "-4.5")
630 (string-to-number "1e5")
634 @findex string-to-int
635 @code{string-to-int} is an obsolete alias for this function.
638 @defun char-to-string character
639 @cindex character to string
640 This function returns a new string containing one character,
641 @var{character}. This function is semi-obsolete because the function
642 @code{string} is more general. @xref{Creating Strings}.
645 @defun string-to-char string
646 This function returns the first character in @var{string}. This
647 mostly identical to @code{(aref string 0)}, except that it returns 0
648 if the string is empty. (The value is also 0 when the first character
649 of @var{string} is the null character, @acronym{ASCII} code 0.) This
650 function may be eliminated in the future if it does not seem useful
654 Here are some other functions that can convert to or from a string:
658 This function converts a vector or a list into a string.
659 @xref{Creating Strings}.
662 This function converts a string into a vector. @xref{Vector
666 This function converts a string into a list. @xref{Building Lists}.
669 This function converts a byte of character data into a unibyte string.
670 @xref{Converting Representations}.
673 @node Formatting Strings
674 @section Formatting Strings
675 @cindex formatting strings
676 @cindex strings, formatting them
678 @dfn{Formatting} means constructing a string by substituting
679 computed values at various places in a constant string. This constant
680 string controls how the other values are printed, as well as where
681 they appear; it is called a @dfn{format string}.
683 Formatting is often useful for computing messages to be displayed. In
684 fact, the functions @code{message} and @code{error} provide the same
685 formatting feature described here; they differ from @code{format} only
686 in how they use the result of formatting.
688 @defun format string &rest objects
689 This function returns a new string that is made by copying
690 @var{string} and then replacing any format specification
691 in the copy with encodings of the corresponding @var{objects}. The
692 arguments @var{objects} are the computed values to be formatted.
694 The characters in @var{string}, other than the format specifications,
695 are copied directly into the output, including their text properties,
699 @cindex @samp{%} in format
700 @cindex format specification
701 A format specification is a sequence of characters beginning with a
702 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
703 @code{format} function replaces it with the printed representation of
704 one of the values to be formatted (one of the arguments @var{objects}).
709 (format "The value of fill-column is %d." fill-column)
710 @result{} "The value of fill-column is 72."
714 Since @code{format} interprets @samp{%} characters as format
715 specifications, you should @emph{never} pass an arbitrary string as
716 the first argument. This is particularly true when the string is
717 generated by some Lisp code. Unless the string is @emph{known} to
718 never include any @samp{%} characters, pass @code{"%s"}, described
719 below, as the first argument, and the string as the second, like this:
722 (format "%s" @var{arbitrary-string})
725 If @var{string} contains more than one format specification, the
726 format specifications correspond to successive values from
727 @var{objects}. Thus, the first format specification in @var{string}
728 uses the first such value, the second format specification uses the
729 second such value, and so on. Any extra format specifications (those
730 for which there are no corresponding values) cause an error. Any
731 extra values to be formatted are ignored.
733 Certain format specifications require values of particular types. If
734 you supply a value that doesn't fit the requirements, an error is
737 Here is a table of valid format specifications:
741 Replace the specification with the printed representation of the object,
742 made without quoting (that is, using @code{princ}, not
743 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
744 by their contents alone, with no @samp{"} characters, and symbols appear
745 without @samp{\} characters.
747 If the object is a string, its text properties are
748 copied into the output. The text properties of the @samp{%s} itself
749 are also copied, but those of the object take priority.
752 Replace the specification with the printed representation of the object,
753 made with quoting (that is, using @code{prin1}---@pxref{Output
754 Functions}). Thus, strings are enclosed in @samp{"} characters, and
755 @samp{\} characters appear where necessary before special characters.
758 @cindex integer to octal
759 Replace the specification with the base-eight representation of an
763 Replace the specification with the base-ten representation of an
768 @cindex integer to hexadecimal
769 Replace the specification with the base-sixteen representation of an
770 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
773 Replace the specification with the character which is the value given.
776 Replace the specification with the exponential notation for a floating
780 Replace the specification with the decimal-point notation for a floating
784 Replace the specification with notation for a floating point number,
785 using either exponential notation or decimal-point notation, whichever
789 Replace the specification with a single @samp{%}. This format
790 specification is unusual in that it does not use a value. For example,
791 @code{(format "%% %d" 30)} returns @code{"% 30"}.
794 Any other format character results in an @samp{Invalid format
797 Here are several examples:
801 (format "The name of this buffer is %s." (buffer-name))
802 @result{} "The name of this buffer is strings.texi."
804 (format "The buffer object prints as %s." (current-buffer))
805 @result{} "The buffer object prints as strings.texi."
807 (format "The octal value of %d is %o,
808 and the hex value is %x." 18 18 18)
809 @result{} "The octal value of 18 is 22,
810 and the hex value is 12."
816 A specification can have a @dfn{width}, which is a decimal number
817 between the @samp{%} and the specification character. If the printed
818 representation of the object contains fewer characters than this
819 width, @code{format} extends it with padding. The width specifier is
820 ignored for the @samp{%%} specification. Any padding introduced by
821 the width specifier normally consists of spaces inserted on the left:
824 (format "%5d is padded on the left with spaces" 123)
825 @result{} " 123 is padded on the left with spaces"
829 If the width is too small, @code{format} does not truncate the
830 object's printed representation. Thus, you can use a width to specify
831 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}
834 has only 3 letters, and needs 4 blank spaces as padding. In the
835 second case, the string @code{"specification"} is 13 letters wide but
840 (format "The word `%7s' has %d letters in it."
841 "foo" (length "foo"))
842 @result{} "The word ` foo' has 3 letters in it."
843 (format "The word `%7s' has %d letters in it."
844 "specification" (length "specification"))
845 @result{} "The word `specification' has 13 letters in it."
849 @cindex flags in format specifications
850 Immediately after the @samp{%} and before the optional width
851 specifier, you can also put certain @dfn{flag characters}.
853 The flag @samp{+} inserts a plus sign before a positive number, so
854 that it always has a sign. A space character as flag inserts a space
855 before a positive number. (Otherwise, positive numbers start with the
856 first digit.) These flags are useful for ensuring that positive
857 numbers and negative numbers use the same number of columns. They are
858 ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if
859 both flags are used, @samp{+} takes precedence.
861 The flag @samp{#} specifies an ``alternate form'' which depends on
862 the format in use. For @samp{%o}, it ensures that the result begins
863 with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result
864 with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g},
865 the @samp{#} flag means include a decimal point even if the precision
868 The flag @samp{0} ensures that the padding consists of @samp{0}
869 characters instead of spaces. This flag is ignored for non-numerical
870 specification characters like @samp{%s}, @samp{%S} and @samp{%c}.
871 These specification characters accept the @samp{0} flag, but still pad
874 The flag @samp{-} causes the padding inserted by the width
875 specifier, if any, to be inserted on the right rather than the left.
876 If both @samp{-} and @samp{0} are present, the @samp{0} flag is
881 (format "%06d is padded on the left with zeros" 123)
882 @result{} "000123 is padded on the left with zeros"
884 (format "%-6d is padded on the right" 123)
885 @result{} "123 is padded on the right"
887 (format "The word `%-7s' actually has %d letters in it."
888 "foo" (length "foo"))
889 @result{} "The word `foo ' actually has 3 letters in it."
893 @cindex precision in format specifications
894 All the specification characters allow an optional @dfn{precision}
895 before the character (after the width, if present). The precision is
896 a decimal-point @samp{.} followed by a digit-string. For the
897 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
898 precision specifies how many decimal places to show; if zero, the
899 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
900 the precision truncates the string to the given width, so @samp{%.3s}
901 shows only the first three characters of the representation for
902 @var{object}. Precision has no effect for other specification
905 @node Case Conversion
906 @section Case Conversion in Lisp
909 @cindex character case
910 @cindex case conversion in Lisp
912 The character case functions change the case of single characters or
913 of the contents of strings. The functions normally convert only
914 alphabetic characters (the letters @samp{A} through @samp{Z} and
915 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
916 characters are not altered. You can specify a different case
917 conversion mapping by specifying a case table (@pxref{Case Tables}).
919 These functions do not modify the strings that are passed to them as
922 The examples below use the characters @samp{X} and @samp{x} which have
923 @acronym{ASCII} codes 88 and 120 respectively.
925 @defun downcase string-or-char
926 This function converts @var{string-or-char}, which should be either a
927 character or a string, to lower case.
929 When @var{string-or-char} is a string, this function returns a new
930 string in which each letter in the argument that is upper case is
931 converted to lower case. When @var{string-or-char} is a character,
932 this function returns the corresponding lower case character (an
933 integer); if the original character is lower case, or is not a letter,
934 the return value is equal to the original character.
937 (downcase "The cat in the hat")
938 @result{} "the cat in the hat"
945 @defun upcase string-or-char
946 This function converts @var{string-or-char}, which should be either a
947 character or a string, to upper case.
949 When @var{string-or-char} is a string, this function returns a new
950 string in which each letter in the argument that is lower case is
951 converted to upper case. When @var{string-or-char} is a character,
952 this function returns the corresponding upper case character (an
953 integer); if the original character is upper case, or is not a letter,
954 the return value is equal to the original character.
957 (upcase "The cat in the hat")
958 @result{} "THE CAT IN THE HAT"
965 @defun capitalize string-or-char
966 @cindex capitalization
967 This function capitalizes strings or characters. If
968 @var{string-or-char} is a string, the function returns a new string
969 whose contents are a copy of @var{string-or-char} in which each word
970 has been capitalized. This means that the first character of each
971 word is converted to upper case, and the rest are converted to lower
974 The definition of a word is any sequence of consecutive characters that
975 are assigned to the word constituent syntax class in the current syntax
976 table (@pxref{Syntax Class Table}).
978 When @var{string-or-char} is a character, this function does the same
979 thing as @code{upcase}.
983 (capitalize "The cat in the hat")
984 @result{} "The Cat In The Hat"
988 (capitalize "THE 77TH-HATTED CAT")
989 @result{} "The 77th-Hatted Cat"
999 @defun upcase-initials string-or-char
1000 If @var{string-or-char} is a string, this function capitalizes the
1001 initials of the words in @var{string-or-char}, without altering any
1002 letters other than the initials. It returns a new string whose
1003 contents are a copy of @var{string-or-char}, in which each word has
1004 had its initial letter converted to upper case.
1006 The definition of a word is any sequence of consecutive characters that
1007 are assigned to the word constituent syntax class in the current syntax
1008 table (@pxref{Syntax Class Table}).
1010 When the argument to @code{upcase-initials} is a character,
1011 @code{upcase-initials} has the same result as @code{upcase}.
1015 (upcase-initials "The CAT in the hAt")
1016 @result{} "The CAT In The HAt"
1021 @xref{Text Comparison}, for functions that compare strings; some of
1022 them ignore case differences, or can optionally ignore case differences.
1025 @section The Case Table
1027 You can customize case conversion by installing a special @dfn{case
1028 table}. A case table specifies the mapping between upper case and lower
1029 case letters. It affects both the case conversion functions for Lisp
1030 objects (see the previous section) and those that apply to text in the
1031 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1032 also a standard case table which is used to initialize the case table
1035 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1036 @code{case-table}. This char-table maps each character into the
1037 corresponding lower case character. It has three extra slots, which
1038 hold related tables:
1042 The upcase table maps each character into the corresponding upper
1045 The canonicalize table maps all of a set of case-related characters
1046 into a particular member of that set.
1048 The equivalences table maps each one of a set of case-related characters
1049 into the next character in that set.
1052 In simple cases, all you need to specify is the mapping to lower-case;
1053 the three related tables will be calculated automatically from that one.
1055 For some languages, upper and lower case letters are not in one-to-one
1056 correspondence. There may be two different lower case letters with the
1057 same upper case equivalent. In these cases, you need to specify the
1058 maps for both lower case and upper case.
1060 The extra table @var{canonicalize} maps each character to a canonical
1061 equivalent; any two characters that are related by case-conversion have
1062 the same canonical equivalent character. For example, since @samp{a}
1063 and @samp{A} are related by case-conversion, they should have the same
1064 canonical equivalent character (which should be either @samp{a} for both
1065 of them, or @samp{A} for both of them).
1067 The extra table @var{equivalences} is a map that cyclically permutes
1068 each equivalence class (of characters with the same canonical
1069 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1070 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1071 equivalent characters.)
1073 When constructing a case table, you can provide @code{nil} for
1074 @var{canonicalize}; then Emacs fills in this slot from the lower case
1075 and upper case mappings. You can also provide @code{nil} for
1076 @var{equivalences}; then Emacs fills in this slot from
1077 @var{canonicalize}. In a case table that is actually in use, those
1078 components are non-@code{nil}. Do not try to specify
1079 @var{equivalences} without also specifying @var{canonicalize}.
1081 Here are the functions for working with case tables:
1083 @defun case-table-p object
1084 This predicate returns non-@code{nil} if @var{object} is a valid case
1088 @defun set-standard-case-table table
1089 This function makes @var{table} the standard case table, so that it will
1090 be used in any buffers created subsequently.
1093 @defun standard-case-table
1094 This returns the standard case table.
1097 @defun current-case-table
1098 This function returns the current buffer's case table.
1101 @defun set-case-table table
1102 This sets the current buffer's case table to @var{table}.
1105 @defmac with-case-table table body@dots{}
1106 The @code{with-case-table} macro saves the current case table, makes
1107 @var{table} the current case table, evaluates the @var{body} forms,
1108 and finally restores the case table. The return value is the value of
1109 the last form in @var{body}. The case table is restored even in case
1110 of an abnormal exit via @code{throw} or error (@pxref{Nonlocal
1114 Some language environments modify the case conversions of
1115 @acronym{ASCII} characters; for example, in the Turkish language
1116 environment, the @acronym{ASCII} character @samp{I} is downcased into
1117 a Turkish ``dotless i''. This can interfere with code that requires
1118 ordinary @acronym{ASCII} case conversion, such as implementations of
1119 @acronym{ASCII}-based network protocols. In that case, use the
1120 @code{with-case-table} macro with the variable @var{ascii-case-table},
1121 which stores the unmodified case table for the @acronym{ASCII}
1124 @defvar ascii-case-table
1125 The case table for the @acronym{ASCII} character set. This should not be
1126 modified by any language environment settings.
1129 The following three functions are convenient subroutines for packages
1130 that define non-@acronym{ASCII} character sets. They modify the specified
1131 case table @var{case-table}; they also modify the standard syntax table.
1132 @xref{Syntax Tables}. Normally you would use these functions to change
1133 the standard case table.
1135 @defun set-case-syntax-pair uc lc case-table
1136 This function specifies a pair of corresponding letters, one upper case
1140 @defun set-case-syntax-delims l r case-table
1141 This function makes characters @var{l} and @var{r} a matching pair of
1142 case-invariant delimiters.
1145 @defun set-case-syntax char syntax case-table
1146 This function makes @var{char} case-invariant, with syntax
1150 @deffn Command describe-buffer-case-table
1151 This command displays a description of the contents of the current
1152 buffer's case table.