2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software
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 documented
52 in @ref{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}). However, note that
55 @code{length} should @emph{not} be used for computing the width of a
56 string on display; use @code{string-width} (@pxref{Size of Displayed
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
95 @cindex predicates for strings
96 @cindex string predicates
98 For more information about general sequence and array predicates,
99 see @ref{Sequences Arrays Vectors}, and @ref{Arrays}.
101 @defun stringp object
102 This function returns @code{t} if @var{object} is a string, @code{nil}
106 @defun string-or-null-p object
107 This function returns @code{t} if @var{object} is a string or
108 @code{nil}. It returns @code{nil} otherwise.
111 @defun char-or-string-p object
112 This function returns @code{t} if @var{object} is a string or a
113 character (i.e., an integer), @code{nil} otherwise.
116 @node Creating Strings
117 @section Creating Strings
118 @cindex creating strings
119 @cindex string creation
121 The following functions create strings, either from scratch, or by
122 putting strings together, or by taking them apart.
124 @defun make-string count character
125 This function returns a string made up of @var{count} repetitions of
126 @var{character}. If @var{count} is negative, an error is signaled.
135 Other functions to compare with this one include @code{make-vector}
136 (@pxref{Vectors}) and @code{make-list} (@pxref{Building Lists}).
139 @defun string &rest characters
140 This returns a string containing the characters @var{characters}.
148 @defun substring string start &optional end
149 This function returns a new string which consists of those characters
150 from @var{string} in the range from (and including) the character at the
151 index @var{start} up to (but excluding) the character at the index
152 @var{end}. The first character is at index zero.
156 (substring "abcdefg" 0 3)
162 In the above example, the index for @samp{a} is 0, the index for
163 @samp{b} is 1, and the index for @samp{c} is 2. The index 3---which
164 is the fourth character in the string---marks the character position
165 up to which the substring is copied. Thus, @samp{abc} is copied from
166 the string @code{"abcdefg"}.
168 A negative number counts from the end of the string, so that @minus{}1
169 signifies the index of the last character of the string. For example:
173 (substring "abcdefg" -3 -1)
179 In this example, the index for @samp{e} is @minus{}3, the index for
180 @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1.
181 Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded.
183 When @code{nil} is used for @var{end}, it stands for the length of the
188 (substring "abcdefg" -3 nil)
193 Omitting the argument @var{end} is equivalent to specifying @code{nil}.
194 It follows that @code{(substring @var{string} 0)} returns a copy of all
199 (substring "abcdefg" 0)
205 But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence
208 If the characters copied from @var{string} have text properties, the
209 properties are copied into the new string also. @xref{Text Properties}.
211 @code{substring} also accepts a vector for the first argument.
215 (substring [a b (c) "d"] 1 3)
219 A @code{wrong-type-argument} error is signaled if @var{start} is not
220 an integer or if @var{end} is neither an integer nor @code{nil}. An
221 @code{args-out-of-range} error is signaled if @var{start} indicates a
222 character following @var{end}, or if either integer is out of range
225 Contrast this function with @code{buffer-substring} (@pxref{Buffer
226 Contents}), which returns a string containing a portion of the text in
227 the current buffer. The beginning of a string is at index 0, but the
228 beginning of a buffer is at index 1.
231 @defun substring-no-properties string &optional start end
232 This works like @code{substring} but discards all text properties from
233 the value. Also, @var{start} may be omitted or @code{nil}, which is
234 equivalent to 0. Thus, @w{@code{(substring-no-properties
235 @var{string})}} returns a copy of @var{string}, with all text
239 @defun concat &rest sequences
240 @cindex copying strings
241 @cindex concatenating strings
242 This function returns a new string consisting of the characters in the
243 arguments passed to it (along with their text properties, if any). The
244 arguments may be strings, lists of numbers, or vectors of numbers; they
245 are not themselves changed. If @code{concat} receives no arguments, it
246 returns an empty string.
249 (concat "abc" "-def")
251 (concat "abc" (list 120 121) [122])
253 ;; @r{@code{nil} is an empty sequence.}
254 (concat "abc" nil "-def")
256 (concat "The " "quick brown " "fox.")
257 @result{} "The quick brown fox."
263 This function always constructs a new string that is not @code{eq} to
264 any existing string, except when the result is the empty string (to
265 save space, Emacs makes only one empty multibyte string).
267 For information about other concatenation functions, see the
268 description of @code{mapconcat} in @ref{Mapping Functions},
269 @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building
270 Lists}. For concatenating individual command-line arguments into a
271 string to be used as a shell command, see @ref{Shell Arguments,
272 combine-and-quote-strings}.
275 @defun split-string string &optional separators omit-nulls trim
276 This function splits @var{string} into substrings based on the regular
277 expression @var{separators} (@pxref{Regular Expressions}). Each match
278 for @var{separators} defines a splitting point; the substrings between
279 splitting points are made into a list, which is returned.
281 If @var{omit-nulls} is @code{nil} (or omitted), the result contains
282 null strings whenever there are two consecutive matches for
283 @var{separators}, or a match is adjacent to the beginning or end of
284 @var{string}. If @var{omit-nulls} is @code{t}, these null strings are
285 omitted from the result.
287 If @var{separators} is @code{nil} (or omitted), the default is the
288 value of @code{split-string-default-separators}.
290 As a special case, when @var{separators} is @code{nil} (or omitted),
291 null strings are always omitted from the result. Thus:
294 (split-string " two words ")
295 @result{} ("two" "words")
298 The result is not @code{("" "two" "words" "")}, which would rarely be
299 useful. If you need such a result, use an explicit value for
303 (split-string " two words "
304 split-string-default-separators)
305 @result{} ("" "two" "words" "")
311 (split-string "Soup is good food" "o")
312 @result{} ("S" "up is g" "" "d f" "" "d")
313 (split-string "Soup is good food" "o" t)
314 @result{} ("S" "up is g" "d f" "d")
315 (split-string "Soup is good food" "o+")
316 @result{} ("S" "up is g" "d f" "d")
319 Empty matches do count, except that @code{split-string} will not look
320 for a final empty match when it already reached the end of the string
321 using a non-empty match or when @var{string} is empty:
324 (split-string "aooob" "o*")
325 @result{} ("" "a" "" "b" "")
326 (split-string "ooaboo" "o*")
327 @result{} ("" "" "a" "b" "")
332 However, when @var{separators} can match the empty string,
333 @var{omit-nulls} is usually @code{t}, so that the subtleties in the
334 three previous examples are rarely relevant:
337 (split-string "Soup is good food" "o*" t)
338 @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
339 (split-string "Nice doggy!" "" t)
340 @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
341 (split-string "" "" t)
345 Somewhat odd, but predictable, behavior can occur for certain
346 ``non-greedy'' values of @var{separators} that can prefer empty
347 matches over non-empty matches. Again, such values rarely occur in
351 (split-string "ooo" "o*" t)
353 (split-string "ooo" "\\|o+" t)
354 @result{} ("o" "o" "o")
357 If the optional argument @var{trim} is non-@code{nil}, it should be a
358 regular expression to match text to trim from the beginning and end of
359 each substring. If trimming makes the substring empty, it is treated
362 If you need to split a string into a list of individual command-line
363 arguments suitable for @code{call-process} or @code{start-process},
364 see @ref{Shell Arguments, split-string-and-unquote}.
367 @defvar split-string-default-separators
368 The default value of @var{separators} for @code{split-string}. Its
369 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
372 @node Modifying Strings
373 @section Modifying Strings
374 @cindex modifying strings
375 @cindex string modification
377 The most basic way to alter the contents of an existing string is with
378 @code{aset} (@pxref{Array Functions}). @code{(aset @var{string}
379 @var{idx} @var{char})} stores @var{char} into @var{string} at index
380 @var{idx}. Each character occupies one or more bytes, and if @var{char}
381 needs a different number of bytes from the character already present at
382 that index, @code{aset} signals an error.
384 A more powerful function is @code{store-substring}:
386 @defun store-substring string idx obj
387 This function alters part of the contents of the string @var{string}, by
388 storing @var{obj} starting at index @var{idx}. The argument @var{obj}
389 may be either a character or a (smaller) string.
391 Since it is impossible to change the length of an existing string, it is
392 an error if @var{obj} doesn't fit within @var{string}'s actual length,
393 or if any new character requires a different number of bytes from the
394 character currently present at that point in @var{string}.
397 To clear out a string that contained a password, use
400 @defun clear-string string
401 This makes @var{string} a unibyte string and clears its contents to
402 zeros. It may also change @var{string}'s length.
406 @node Text Comparison
407 @section Comparison of Characters and Strings
408 @cindex string equality
409 @cindex text comparison
411 @defun char-equal character1 character2
412 This function returns @code{t} if the arguments represent the same
413 character, @code{nil} otherwise. This function ignores differences
414 in case if @code{case-fold-search} is non-@code{nil}.
419 (let ((case-fold-search nil))
425 @defun string= string1 string2
426 This function returns @code{t} if the characters of the two strings
427 match exactly. Symbols are also allowed as arguments, in which case
428 the symbol names are used. Case is always significant, regardless of
429 @code{case-fold-search}.
431 This function is equivalent to @code{equal} for comparing two strings
432 (@pxref{Equality Predicates}). In particular, the text properties of
433 the two strings are ignored; use @code{equal-including-properties} if
434 you need to distinguish between strings that differ only in their text
435 properties. However, unlike @code{equal}, if either argument is not a
436 string or symbol, @code{string=} signals an error.
439 (string= "abc" "abc")
441 (string= "abc" "ABC")
447 For technical reasons, a unibyte and a multibyte string are
448 @code{equal} if and only if they contain the same sequence of
449 character codes and all these codes are either in the range 0 through
450 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
451 However, when a unibyte string is converted to a multibyte string, all
452 characters with codes in the range 160 through 255 are converted to
453 characters with higher codes, whereas @acronym{ASCII} characters
454 remain unchanged. Thus, a unibyte string and its conversion to
455 multibyte are only @code{equal} if the string is all @acronym{ASCII}.
456 Character codes 160 through 255 are not entirely proper in multibyte
457 text, even though they can occur. As a consequence, the situation
458 where a unibyte and a multibyte string are @code{equal} without both
459 being all @acronym{ASCII} is a technical oddity that very few Emacs
460 Lisp programmers ever get confronted with. @xref{Text
464 @defun string-equal string1 string2
465 @code{string-equal} is another name for @code{string=}.
468 @cindex lexical comparison
469 @defun string< string1 string2
470 @c (findex string< causes problems for permuted index!!)
471 This function compares two strings a character at a time. It
472 scans both the strings at the same time to find the first pair of corresponding
473 characters that do not match. If the lesser character of these two is
474 the character from @var{string1}, then @var{string1} is less, and this
475 function returns @code{t}. If the lesser character is the one from
476 @var{string2}, then @var{string1} is greater, and this function returns
477 @code{nil}. If the two strings match entirely, the value is @code{nil}.
479 Pairs of characters are compared according to their character codes.
480 Keep in mind that lower case letters have higher numeric values in the
481 @acronym{ASCII} character set than their upper case counterparts; digits and
482 many punctuation characters have a lower numeric value than upper case
483 letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII}
484 character; a unibyte non-@acronym{ASCII} character is always less than any
485 multibyte non-@acronym{ASCII} character (@pxref{Text Representations}).
489 (string< "abc" "abd")
491 (string< "abd" "abc")
493 (string< "123" "abc")
498 When the strings have different lengths, and they match up to the
499 length of @var{string1}, then the result is @code{t}. If they match up
500 to the length of @var{string2}, the result is @code{nil}. A string of
501 no characters is less than any other string.
518 Symbols are also allowed as arguments, in which case their print names
522 @defun string-lessp string1 string2
523 @code{string-lessp} is another name for @code{string<}.
526 @defun string-prefix-p string1 string2 &optional ignore-case
527 This function returns non-@code{nil} if @var{string1} is a prefix of
528 @var{string2}; i.e., if @var{string2} starts with @var{string1}. If
529 the optional argument @var{ignore-case} is non-@code{nil}, the
530 comparison ignores case differences.
533 @defun string-suffix-p suffix string &optional ignore-case
534 This function returns non-@code{nil} if @var{suffix} is a suffix of
535 @var{string}; i.e., if @var{string} ends with @var{suffix}. If the
536 optional argument @var{ignore-case} is non-@code{nil}, the comparison
537 ignores case differences.
540 @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case
541 This function compares a specified part of @var{string1} with a
542 specified part of @var{string2}. The specified part of @var{string1}
543 runs from index @var{start1} (inclusive) up to index @var{end1}
544 (exclusive); @code{nil} for @var{start1} means the start of the
545 string, while @code{nil} for @var{end1} means the length of the
546 string. Likewise, the specified part of @var{string2} runs from index
547 @var{start2} up to index @var{end2}.
549 The strings are compared by the numeric values of their characters.
550 For instance, @var{str1} is considered ``smaller than'' @var{str2} if
551 its first differing character has a smaller numeric value. If
552 @var{ignore-case} is non-@code{nil}, characters are converted to
553 lower-case before comparing them. Unibyte strings are converted to
554 multibyte for comparison (@pxref{Text Representations}), so that a
555 unibyte string and its conversion to multibyte are always regarded as
558 If the specified portions of the two strings match, the value is
559 @code{t}. Otherwise, the value is an integer which indicates how many
560 leading characters agree, and which string is less. Its absolute
561 value is one plus the number of characters that agree at the beginning
562 of the two strings. The sign is negative if @var{string1} (or its
563 specified portion) is less.
566 @defun assoc-string key alist &optional case-fold
567 This function works like @code{assoc}, except that @var{key} must be a
568 string or symbol, and comparison is done using @code{compare-strings}.
569 Symbols are converted to strings before testing.
570 If @var{case-fold} is non-@code{nil}, it ignores case differences.
571 Unlike @code{assoc}, this function can also match elements of the alist
572 that are strings or symbols rather than conses. In particular, @var{alist} can
573 be a list of strings or symbols rather than an actual alist.
574 @xref{Association Lists}.
577 See also the function @code{compare-buffer-substrings} in
578 @ref{Comparing Text}, for a way to compare text in buffers. The
579 function @code{string-match}, which matches a regular expression
580 against a string, can be used for a kind of string comparison; see
583 @node String Conversion
584 @section Conversion of Characters and Strings
585 @cindex conversion of strings
587 This section describes functions for converting between characters,
588 strings and integers. @code{format} (@pxref{Formatting Strings}) and
589 @code{prin1-to-string} (@pxref{Output Functions}) can also convert
590 Lisp objects into strings. @code{read-from-string} (@pxref{Input
591 Functions}) can ``convert'' a string representation of a Lisp object
592 into an object. The functions @code{string-to-multibyte} and
593 @code{string-to-unibyte} convert the text representation of a string
594 (@pxref{Converting Representations}).
596 @xref{Documentation}, for functions that produce textual descriptions
597 of text characters and general input events
598 (@code{single-key-description} and @code{text-char-description}). These
599 are used primarily for making help messages.
601 @defun number-to-string number
602 @cindex integer to string
603 @cindex integer to decimal
604 This function returns a string consisting of the printed base-ten
605 representation of @var{number}. The returned value starts with a
606 minus sign if the argument is negative.
609 (number-to-string 256)
612 (number-to-string -23)
615 (number-to-string -23.5)
619 @cindex int-to-string
620 @code{int-to-string} is a semi-obsolete alias for this function.
622 See also the function @code{format} in @ref{Formatting Strings}.
625 @defun string-to-number string &optional base
626 @cindex string to number
627 This function returns the numeric value of the characters in
628 @var{string}. If @var{base} is non-@code{nil}, it must be an integer
629 between 2 and 16 (inclusive), and integers are converted in that base.
630 If @var{base} is @code{nil}, then base ten is used. Floating-point
631 conversion only works in base ten; we have not implemented other
632 radices for floating-point numbers, because that would be much more
633 work and does not seem useful. If @var{string} looks like an integer
634 but its value is too large to fit into a Lisp integer,
635 @code{string-to-number} returns a floating-point result.
637 The parsing skips spaces and tabs at the beginning of @var{string},
638 then reads as much of @var{string} as it can interpret as a number in
639 the given base. (On some systems it ignores other whitespace at the
640 beginning, not just spaces and tabs.) If @var{string} cannot be
641 interpreted as a number, this function returns 0.
644 (string-to-number "256")
646 (string-to-number "25 is a perfect square.")
648 (string-to-number "X256")
650 (string-to-number "-4.5")
652 (string-to-number "1e5")
656 @findex string-to-int
657 @code{string-to-int} is an obsolete alias for this function.
660 @defun char-to-string character
661 @cindex character to string
662 This function returns a new string containing one character,
663 @var{character}. This function is semi-obsolete because the function
664 @code{string} is more general. @xref{Creating Strings}.
667 @defun string-to-char string
668 This function returns the first character in @var{string}. This
669 mostly identical to @code{(aref string 0)}, except that it returns 0
670 if the string is empty. (The value is also 0 when the first character
671 of @var{string} is the null character, @acronym{ASCII} code 0.) This
672 function may be eliminated in the future if it does not seem useful
676 Here are some other functions that can convert to or from a string:
680 This function converts a vector or a list into a string.
681 @xref{Creating Strings}.
684 This function converts a string into a vector. @xref{Vector
688 This function converts a string into a list. @xref{Building Lists}.
691 This function converts a byte of character data into a unibyte string.
692 @xref{Converting Representations}.
695 @node Formatting Strings
696 @section Formatting Strings
697 @cindex formatting strings
698 @cindex strings, formatting them
700 @dfn{Formatting} means constructing a string by substituting
701 computed values at various places in a constant string. This constant
702 string controls how the other values are printed, as well as where
703 they appear; it is called a @dfn{format string}.
705 Formatting is often useful for computing messages to be displayed. In
706 fact, the functions @code{message} and @code{error} provide the same
707 formatting feature described here; they differ from @code{format} only
708 in how they use the result of formatting.
710 @defun format string &rest objects
711 This function returns a new string that is made by copying
712 @var{string} and then replacing any format specification
713 in the copy with encodings of the corresponding @var{objects}. The
714 arguments @var{objects} are the computed values to be formatted.
716 The characters in @var{string}, other than the format specifications,
717 are copied directly into the output, including their text properties,
721 @cindex @samp{%} in format
722 @cindex format specification
723 A format specification is a sequence of characters beginning with a
724 @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the
725 @code{format} function replaces it with the printed representation of
726 one of the values to be formatted (one of the arguments @var{objects}).
731 (format "The value of fill-column is %d." fill-column)
732 @result{} "The value of fill-column is 72."
736 Since @code{format} interprets @samp{%} characters as format
737 specifications, you should @emph{never} pass an arbitrary string as
738 the first argument. This is particularly true when the string is
739 generated by some Lisp code. Unless the string is @emph{known} to
740 never include any @samp{%} characters, pass @code{"%s"}, described
741 below, as the first argument, and the string as the second, like this:
744 (format "%s" @var{arbitrary-string})
747 If @var{string} contains more than one format specification, the
748 format specifications correspond to successive values from
749 @var{objects}. Thus, the first format specification in @var{string}
750 uses the first such value, the second format specification uses the
751 second such value, and so on. Any extra format specifications (those
752 for which there are no corresponding values) cause an error. Any
753 extra values to be formatted are ignored.
755 Certain format specifications require values of particular types. If
756 you supply a value that doesn't fit the requirements, an error is
759 Here is a table of valid format specifications:
763 Replace the specification with the printed representation of the object,
764 made without quoting (that is, using @code{princ}, not
765 @code{prin1}---@pxref{Output Functions}). Thus, strings are represented
766 by their contents alone, with no @samp{"} characters, and symbols appear
767 without @samp{\} characters.
769 If the object is a string, its text properties are
770 copied into the output. The text properties of the @samp{%s} itself
771 are also copied, but those of the object take priority.
774 Replace the specification with the printed representation of the object,
775 made with quoting (that is, using @code{prin1}---@pxref{Output
776 Functions}). Thus, strings are enclosed in @samp{"} characters, and
777 @samp{\} characters appear where necessary before special characters.
780 @cindex integer to octal
781 Replace the specification with the base-eight representation of an
785 Replace the specification with the base-ten representation of an
790 @cindex integer to hexadecimal
791 Replace the specification with the base-sixteen representation of an
792 integer. @samp{%x} uses lower case and @samp{%X} uses upper case.
795 Replace the specification with the character which is the value given.
798 Replace the specification with the exponential notation for a
799 floating-point number.
802 Replace the specification with the decimal-point notation for a
803 floating-point number.
806 Replace the specification with notation for a floating-point number,
807 using either exponential notation or decimal-point notation, whichever
811 Replace the specification with a single @samp{%}. This format
812 specification is unusual in that it does not use a value. For example,
813 @code{(format "%% %d" 30)} returns @code{"% 30"}.
816 Any other format character results in an @samp{Invalid format
819 Here are several examples:
823 (format "The name of this buffer is %s." (buffer-name))
824 @result{} "The name of this buffer is strings.texi."
826 (format "The buffer object prints as %s." (current-buffer))
827 @result{} "The buffer object prints as strings.texi."
829 (format "The octal value of %d is %o,
830 and the hex value is %x." 18 18 18)
831 @result{} "The octal value of 18 is 22,
832 and the hex value is 12."
838 A specification can have a @dfn{width}, which is a decimal number
839 between the @samp{%} and the specification character. If the printed
840 representation of the object contains fewer characters than this
841 width, @code{format} extends it with padding. The width specifier is
842 ignored for the @samp{%%} specification. Any padding introduced by
843 the width specifier normally consists of spaces inserted on the left:
846 (format "%5d is padded on the left with spaces" 123)
847 @result{} " 123 is padded on the left with spaces"
851 If the width is too small, @code{format} does not truncate the
852 object's printed representation. Thus, you can use a width to specify
853 a minimum spacing between columns with no risk of losing information.
854 In the following three examples, @samp{%7s} specifies a minimum width
855 of 7. In the first case, the string inserted in place of @samp{%7s}
856 has only 3 letters, and needs 4 blank spaces as padding. In the
857 second case, the string @code{"specification"} is 13 letters wide but
862 (format "The word `%7s' has %d letters in it."
863 "foo" (length "foo"))
864 @result{} "The word ` foo' has 3 letters in it."
865 (format "The word `%7s' has %d letters in it."
866 "specification" (length "specification"))
867 @result{} "The word `specification' has 13 letters in it."
871 @cindex flags in format specifications
872 Immediately after the @samp{%} and before the optional width
873 specifier, you can also put certain @dfn{flag characters}.
875 The flag @samp{+} inserts a plus sign before a positive number, so
876 that it always has a sign. A space character as flag inserts a space
877 before a positive number. (Otherwise, positive numbers start with the
878 first digit.) These flags are useful for ensuring that positive
879 numbers and negative numbers use the same number of columns. They are
880 ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if
881 both flags are used, @samp{+} takes precedence.
883 The flag @samp{#} specifies an ``alternate form'' which depends on
884 the format in use. For @samp{%o}, it ensures that the result begins
885 with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result
886 with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g},
887 the @samp{#} flag means include a decimal point even if the precision
890 The flag @samp{0} ensures that the padding consists of @samp{0}
891 characters instead of spaces. This flag is ignored for non-numerical
892 specification characters like @samp{%s}, @samp{%S} and @samp{%c}.
893 These specification characters accept the @samp{0} flag, but still pad
896 The flag @samp{-} causes the padding inserted by the width
897 specifier, if any, to be inserted on the right rather than the left.
898 If both @samp{-} and @samp{0} are present, the @samp{0} flag is
903 (format "%06d is padded on the left with zeros" 123)
904 @result{} "000123 is padded on the left with zeros"
906 (format "%-6d is padded on the right" 123)
907 @result{} "123 is padded on the right"
909 (format "The word `%-7s' actually has %d letters in it."
910 "foo" (length "foo"))
911 @result{} "The word `foo ' actually has 3 letters in it."
915 @cindex precision in format specifications
916 All the specification characters allow an optional @dfn{precision}
917 before the character (after the width, if present). The precision is
918 a decimal-point @samp{.} followed by a digit-string. For the
919 floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the
920 precision specifies how many decimal places to show; if zero, the
921 decimal-point itself is also omitted. For @samp{%s} and @samp{%S},
922 the precision truncates the string to the given width, so @samp{%.3s}
923 shows only the first three characters of the representation for
924 @var{object}. Precision has no effect for other specification
927 @node Case Conversion
928 @section Case Conversion in Lisp
931 @cindex character case
932 @cindex case conversion in Lisp
934 The character case functions change the case of single characters or
935 of the contents of strings. The functions normally convert only
936 alphabetic characters (the letters @samp{A} through @samp{Z} and
937 @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other
938 characters are not altered. You can specify a different case
939 conversion mapping by specifying a case table (@pxref{Case Tables}).
941 These functions do not modify the strings that are passed to them as
944 The examples below use the characters @samp{X} and @samp{x} which have
945 @acronym{ASCII} codes 88 and 120 respectively.
947 @defun downcase string-or-char
948 This function converts @var{string-or-char}, which should be either a
949 character or a string, to lower case.
951 When @var{string-or-char} is a string, this function returns a new
952 string in which each letter in the argument that is upper case is
953 converted to lower case. When @var{string-or-char} is a character,
954 this function returns the corresponding lower case character (an
955 integer); if the original character is lower case, or is not a letter,
956 the return value is equal to the original character.
959 (downcase "The cat in the hat")
960 @result{} "the cat in the hat"
967 @defun upcase string-or-char
968 This function converts @var{string-or-char}, which should be either a
969 character or a string, to upper case.
971 When @var{string-or-char} is a string, this function returns a new
972 string in which each letter in the argument that is lower case is
973 converted to upper case. When @var{string-or-char} is a character,
974 this function returns the corresponding upper case character (an
975 integer); if the original character is upper case, or is not a letter,
976 the return value is equal to the original character.
979 (upcase "The cat in the hat")
980 @result{} "THE CAT IN THE HAT"
987 @defun capitalize string-or-char
988 @cindex capitalization
989 This function capitalizes strings or characters. If
990 @var{string-or-char} is a string, the function returns a new string
991 whose contents are a copy of @var{string-or-char} in which each word
992 has been capitalized. This means that the first character of each
993 word is converted to upper case, and the rest are converted to lower
996 The definition of a word is any sequence of consecutive characters that
997 are assigned to the word constituent syntax class in the current syntax
998 table (@pxref{Syntax Class Table}).
1000 When @var{string-or-char} is a character, this function does the same
1001 thing as @code{upcase}.
1005 (capitalize "The cat in the hat")
1006 @result{} "The Cat In The Hat"
1010 (capitalize "THE 77TH-HATTED CAT")
1011 @result{} "The 77th-Hatted Cat"
1021 @defun upcase-initials string-or-char
1022 If @var{string-or-char} is a string, this function capitalizes the
1023 initials of the words in @var{string-or-char}, without altering any
1024 letters other than the initials. It returns a new string whose
1025 contents are a copy of @var{string-or-char}, in which each word has
1026 had its initial letter converted to upper case.
1028 The definition of a word is any sequence of consecutive characters that
1029 are assigned to the word constituent syntax class in the current syntax
1030 table (@pxref{Syntax Class Table}).
1032 When the argument to @code{upcase-initials} is a character,
1033 @code{upcase-initials} has the same result as @code{upcase}.
1037 (upcase-initials "The CAT in the hAt")
1038 @result{} "The CAT In The HAt"
1043 @xref{Text Comparison}, for functions that compare strings; some of
1044 them ignore case differences, or can optionally ignore case differences.
1047 @section The Case Table
1049 You can customize case conversion by installing a special @dfn{case
1050 table}. A case table specifies the mapping between upper case and lower
1051 case letters. It affects both the case conversion functions for Lisp
1052 objects (see the previous section) and those that apply to text in the
1053 buffer (@pxref{Case Changes}). Each buffer has a case table; there is
1054 also a standard case table which is used to initialize the case table
1057 A case table is a char-table (@pxref{Char-Tables}) whose subtype is
1058 @code{case-table}. This char-table maps each character into the
1059 corresponding lower case character. It has three extra slots, which
1060 hold related tables:
1064 The upcase table maps each character into the corresponding upper
1067 The canonicalize table maps all of a set of case-related characters
1068 into a particular member of that set.
1070 The equivalences table maps each one of a set of case-related characters
1071 into the next character in that set.
1074 In simple cases, all you need to specify is the mapping to lower-case;
1075 the three related tables will be calculated automatically from that one.
1077 For some languages, upper and lower case letters are not in one-to-one
1078 correspondence. There may be two different lower case letters with the
1079 same upper case equivalent. In these cases, you need to specify the
1080 maps for both lower case and upper case.
1082 The extra table @var{canonicalize} maps each character to a canonical
1083 equivalent; any two characters that are related by case-conversion have
1084 the same canonical equivalent character. For example, since @samp{a}
1085 and @samp{A} are related by case-conversion, they should have the same
1086 canonical equivalent character (which should be either @samp{a} for both
1087 of them, or @samp{A} for both of them).
1089 The extra table @var{equivalences} is a map that cyclically permutes
1090 each equivalence class (of characters with the same canonical
1091 equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into
1092 @samp{A} and @samp{A} into @samp{a}, and likewise for each set of
1093 equivalent characters.)
1095 When constructing a case table, you can provide @code{nil} for
1096 @var{canonicalize}; then Emacs fills in this slot from the lower case
1097 and upper case mappings. You can also provide @code{nil} for
1098 @var{equivalences}; then Emacs fills in this slot from
1099 @var{canonicalize}. In a case table that is actually in use, those
1100 components are non-@code{nil}. Do not try to specify
1101 @var{equivalences} without also specifying @var{canonicalize}.
1103 Here are the functions for working with case tables:
1105 @defun case-table-p object
1106 This predicate returns non-@code{nil} if @var{object} is a valid case
1110 @defun set-standard-case-table table
1111 This function makes @var{table} the standard case table, so that it will
1112 be used in any buffers created subsequently.
1115 @defun standard-case-table
1116 This returns the standard case table.
1119 @defun current-case-table
1120 This function returns the current buffer's case table.
1123 @defun set-case-table table
1124 This sets the current buffer's case table to @var{table}.
1127 @defmac with-case-table table body@dots{}
1128 The @code{with-case-table} macro saves the current case table, makes
1129 @var{table} the current case table, evaluates the @var{body} forms,
1130 and finally restores the case table. The return value is the value of
1131 the last form in @var{body}. The case table is restored even in case
1132 of an abnormal exit via @code{throw} or error (@pxref{Nonlocal
1136 Some language environments modify the case conversions of
1137 @acronym{ASCII} characters; for example, in the Turkish language
1138 environment, the @acronym{ASCII} character @samp{I} is downcased into
1139 a Turkish ``dotless i''. This can interfere with code that requires
1140 ordinary @acronym{ASCII} case conversion, such as implementations of
1141 @acronym{ASCII}-based network protocols. In that case, use the
1142 @code{with-case-table} macro with the variable @var{ascii-case-table},
1143 which stores the unmodified case table for the @acronym{ASCII}
1146 @defvar ascii-case-table
1147 The case table for the @acronym{ASCII} character set. This should not be
1148 modified by any language environment settings.
1151 The following three functions are convenient subroutines for packages
1152 that define non-@acronym{ASCII} character sets. They modify the specified
1153 case table @var{case-table}; they also modify the standard syntax table.
1154 @xref{Syntax Tables}. Normally you would use these functions to change
1155 the standard case table.
1157 @defun set-case-syntax-pair uc lc case-table
1158 This function specifies a pair of corresponding letters, one upper case
1162 @defun set-case-syntax-delims l r case-table
1163 This function makes characters @var{l} and @var{r} a matching pair of
1164 case-invariant delimiters.
1167 @defun set-case-syntax char syntax case-table
1168 This function makes @var{char} case-invariant, with syntax
1172 @deffn Command describe-buffer-case-table
1173 This command displays a description of the contents of the current
1174 buffer's case table.