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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c TTN |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003, |
4 | @c 2004, 2005 Free Software Foundation, Inc. | |
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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 | |
10 | @cindex strings | |
11 | @cindex character arrays | |
12 | @cindex characters | |
13 | @cindex bytes | |
14 | ||
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 | |
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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, | |
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19 | Emacs Lisp has many functions expressly for manipulating them. Emacs |
20 | Lisp programs use strings more often than individual characters. | |
21 | ||
22 | @xref{Strings of Events}, for special considerations for strings of | |
23 | keyboard character events. | |
24 | ||
25 | @menu | |
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. | |
f9f59935 | 29 | * Modifying Strings:: Altering the contents of an existing string. |
869f4785 | 30 | * Text Comparison:: Comparing characters or strings. |
8241495d | 31 | * String Conversion:: Converting to and from characters and strings. |
a9f0a989 | 32 | * Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}. |
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33 | * Case Conversion:: Case conversion functions. |
34 | * Case Tables:: Customizing case conversion. | |
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35 | @end menu |
36 | ||
37 | @node String Basics | |
38 | @section String and Character Basics | |
39 | ||
b6ae404e | 40 | Characters are represented in Emacs Lisp as integers; |
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41 | whether an integer is a character or not is determined only by how it is |
42 | used. Thus, strings really contain integers. | |
869f4785 | 43 | |
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44 | The length of a string (like any array) is fixed, and cannot be |
45 | altered once the string exists. Strings in Lisp are @emph{not} | |
46 | terminated by a distinguished character code. (By contrast, strings in | |
ad800164 | 47 | C are terminated by a character with @acronym{ASCII} code 0.) |
869f4785 | 48 | |
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49 | Since strings are arrays, and therefore sequences as well, you can |
50 | operate on them with the general array and sequence functions. | |
51 | (@xref{Sequences Arrays Vectors}.) For example, you can access or | |
52 | change individual characters in a string using the functions @code{aref} | |
53 | and @code{aset} (@pxref{Array Functions}). | |
869f4785 | 54 | |
ad800164 | 55 | There are two text representations for non-@acronym{ASCII} characters in |
f9f59935 | 56 | Emacs strings (and in buffers): unibyte and multibyte (@pxref{Text |
ad800164 EZ |
57 | Representations}). An @acronym{ASCII} character always occupies one byte in a |
58 | string; in fact, when a string is all @acronym{ASCII}, there is no real | |
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59 | difference between the unibyte and multibyte representations. |
60 | For most Lisp programming, you don't need to be concerned with these two | |
f9f59935 | 61 | representations. |
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62 | |
63 | Sometimes key sequences are represented as strings. When a string is | |
64 | a key sequence, string elements in the range 128 to 255 represent meta | |
8241495d | 65 | characters (which are large integers) rather than character |
969fe9b5 | 66 | codes in the range 128 to 255. |
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67 | |
68 | Strings cannot hold characters that have the hyper, super or alt | |
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69 | modifiers; they can hold @acronym{ASCII} control characters, but no other |
70 | control characters. They do not distinguish case in @acronym{ASCII} control | |
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71 | characters. If you want to store such characters in a sequence, such as |
72 | a key sequence, you must use a vector instead of a string. | |
8241495d | 73 | @xref{Character Type}, for more information about the representation of meta |
f9f59935 | 74 | and other modifiers for keyboard input characters. |
869f4785 | 75 | |
bfe721d1 | 76 | Strings are useful for holding regular expressions. You can also |
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77 | match regular expressions against strings with @code{string-match} |
78 | (@pxref{Regexp Search}). The functions @code{match-string} | |
79 | (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing | |
80 | Match}) are useful for decomposing and modifying strings after | |
81 | matching regular expressions against them. | |
bfe721d1 | 82 | |
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83 | Like a buffer, a string can contain text properties for the characters |
84 | in it, as well as the characters themselves. @xref{Text Properties}. | |
bfe721d1 KH |
85 | All the Lisp primitives that copy text from strings to buffers or other |
86 | strings also copy the properties of the characters being copied. | |
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87 | |
88 | @xref{Text}, for information about functions that display strings or | |
89 | copy them into buffers. @xref{Character Type}, and @ref{String Type}, | |
90 | for information about the syntax of characters and strings. | |
f9f59935 | 91 | @xref{Non-ASCII Characters}, for functions to convert between text |
b6ae404e | 92 | representations and to encode and decode character codes. |
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93 | |
94 | @node Predicates for Strings | |
95 | @section The Predicates for Strings | |
96 | ||
97 | For more information about general sequence and array predicates, | |
98 | see @ref{Sequences Arrays Vectors}, and @ref{Arrays}. | |
99 | ||
100 | @defun stringp object | |
a9f0a989 | 101 | This function returns @code{t} if @var{object} is a string, @code{nil} |
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102 | otherwise. |
103 | @end defun | |
104 | ||
105 | @defun char-or-string-p object | |
a9f0a989 | 106 | This function returns @code{t} if @var{object} is a string or a |
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107 | character (i.e., an integer), @code{nil} otherwise. |
108 | @end defun | |
109 | ||
110 | @node Creating Strings | |
111 | @section Creating Strings | |
112 | ||
113 | The following functions create strings, either from scratch, or by | |
114 | putting strings together, or by taking them apart. | |
115 | ||
116 | @defun make-string count character | |
a9f0a989 | 117 | This function returns a string made up of @var{count} repetitions of |
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118 | @var{character}. If @var{count} is negative, an error is signaled. |
119 | ||
120 | @example | |
121 | (make-string 5 ?x) | |
122 | @result{} "xxxxx" | |
123 | (make-string 0 ?x) | |
124 | @result{} "" | |
125 | @end example | |
126 | ||
127 | Other functions to compare with this one include @code{char-to-string} | |
128 | (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and | |
129 | @code{make-list} (@pxref{Building Lists}). | |
130 | @end defun | |
131 | ||
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132 | @defun string &rest characters |
133 | This returns a string containing the characters @var{characters}. | |
134 | ||
135 | @example | |
136 | (string ?a ?b ?c) | |
137 | @result{} "abc" | |
138 | @end example | |
139 | @end defun | |
140 | ||
869f4785 | 141 | @defun substring string start &optional end |
bfe721d1 | 142 | This function returns a new string which consists of those characters |
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143 | from @var{string} in the range from (and including) the character at the |
144 | index @var{start} up to (but excluding) the character at the index | |
145 | @var{end}. The first character is at index zero. | |
146 | ||
147 | @example | |
148 | @group | |
149 | (substring "abcdefg" 0 3) | |
150 | @result{} "abc" | |
151 | @end group | |
152 | @end example | |
153 | ||
154 | @noindent | |
155 | Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the | |
156 | index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied | |
157 | from the string @code{"abcdefg"}. The index 3 marks the character | |
158 | position up to which the substring is copied. The character whose index | |
159 | is 3 is actually the fourth character in the string. | |
160 | ||
161 | A negative number counts from the end of the string, so that @minus{}1 | |
177c0ea7 | 162 | signifies the index of the last character of the string. For example: |
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163 | |
164 | @example | |
165 | @group | |
166 | (substring "abcdefg" -3 -1) | |
167 | @result{} "ef" | |
168 | @end group | |
169 | @end example | |
170 | ||
171 | @noindent | |
172 | In this example, the index for @samp{e} is @minus{}3, the index for | |
173 | @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. | |
174 | Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. | |
175 | ||
f67b6c12 | 176 | When @code{nil} is used for @var{end}, it stands for the length of the |
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177 | string. Thus, |
178 | ||
179 | @example | |
180 | @group | |
181 | (substring "abcdefg" -3 nil) | |
182 | @result{} "efg" | |
183 | @end group | |
184 | @end example | |
185 | ||
186 | Omitting the argument @var{end} is equivalent to specifying @code{nil}. | |
187 | It follows that @code{(substring @var{string} 0)} returns a copy of all | |
188 | of @var{string}. | |
189 | ||
190 | @example | |
191 | @group | |
192 | (substring "abcdefg" 0) | |
193 | @result{} "abcdefg" | |
194 | @end group | |
195 | @end example | |
196 | ||
197 | @noindent | |
198 | But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence | |
199 | Functions}). | |
200 | ||
bfe721d1 KH |
201 | If the characters copied from @var{string} have text properties, the |
202 | properties are copied into the new string also. @xref{Text Properties}. | |
203 | ||
8241495d | 204 | @code{substring} also accepts a vector for the first argument. |
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205 | For example: |
206 | ||
207 | @example | |
208 | (substring [a b (c) "d"] 1 3) | |
209 | @result{} [b (c)] | |
210 | @end example | |
211 | ||
f67b6c12 LT |
212 | A @code{wrong-type-argument} error is signaled if @var{start} is not |
213 | an integer or if @var{end} is neither an integer nor @code{nil}. An | |
214 | @code{args-out-of-range} error is signaled if @var{start} indicates a | |
215 | character following @var{end}, or if either integer is out of range | |
216 | for @var{string}. | |
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217 | |
218 | Contrast this function with @code{buffer-substring} (@pxref{Buffer | |
219 | Contents}), which returns a string containing a portion of the text in | |
220 | the current buffer. The beginning of a string is at index 0, but the | |
221 | beginning of a buffer is at index 1. | |
222 | @end defun | |
223 | ||
f67b6c12 LT |
224 | @defun substring-no-properties string &optional start end |
225 | This works like @code{substring} but discards all text properties from | |
226 | the value. Also, @var{start} may be omitted or @code{nil}, which is | |
227 | equivalent to 0. Thus, @w{@code{(substring-no-properties | |
228 | @var{string})}} returns a copy of @var{string}, with all text | |
229 | properties removed. | |
1994c2a7 RS |
230 | @end defun |
231 | ||
869f4785 RS |
232 | @defun concat &rest sequences |
233 | @cindex copying strings | |
234 | @cindex concatenating strings | |
235 | This function returns a new string consisting of the characters in the | |
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236 | arguments passed to it (along with their text properties, if any). The |
237 | arguments may be strings, lists of numbers, or vectors of numbers; they | |
238 | are not themselves changed. If @code{concat} receives no arguments, it | |
239 | returns an empty string. | |
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240 | |
241 | @example | |
242 | (concat "abc" "-def") | |
243 | @result{} "abc-def" | |
a9f0a989 | 244 | (concat "abc" (list 120 121) [122]) |
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245 | @result{} "abcxyz" |
246 | ;; @r{@code{nil} is an empty sequence.} | |
247 | (concat "abc" nil "-def") | |
248 | @result{} "abc-def" | |
249 | (concat "The " "quick brown " "fox.") | |
250 | @result{} "The quick brown fox." | |
251 | (concat) | |
252 | @result{} "" | |
253 | @end example | |
254 | ||
255 | @noindent | |
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256 | The @code{concat} function always constructs a new string that is |
257 | not @code{eq} to any existing string. | |
258 | ||
315fe0e9 DL |
259 | In Emacs versions before 21, when an argument was an integer (not a |
260 | sequence of integers), it was converted to a string of digits making up | |
261 | the decimal printed representation of the integer. This obsolete usage | |
262 | no longer works. The proper way to convert an integer to its decimal | |
263 | printed form is with @code{format} (@pxref{Formatting Strings}) or | |
a10f6c69 | 264 | @code{number-to-string} (@pxref{String Conversion}). |
869f4785 | 265 | |
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266 | For information about other concatenation functions, see the |
267 | description of @code{mapconcat} in @ref{Mapping Functions}, | |
ad833e10 | 268 | @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building |
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269 | Lists}. |
270 | @end defun | |
271 | ||
f67b6c12 | 272 | @defun split-string string &optional separators omit-nulls |
a730d07b RS |
273 | This function splits @var{string} into substrings at matches for the |
274 | regular expression @var{separators}. Each match for @var{separators} | |
275 | defines a splitting point; the substrings between the splitting points | |
276 | are made into a list, which is the value returned by | |
277 | @code{split-string}. | |
278 | ||
279 | If @var{omit-nulls} is @code{nil}, the result contains null strings | |
280 | whenever there are two consecutive matches for @var{separators}, or a | |
281 | match is adjacent to the beginning or end of @var{string}. If | |
282 | @var{omit-nulls} is @code{t}, these null strings are omitted from the | |
283 | result list. | |
284 | ||
b6ae404e | 285 | If @var{separators} is @code{nil} (or omitted), |
3aeea9e9 | 286 | the default is the value of @code{split-string-default-separators}. |
f9f59935 | 287 | |
3aeea9e9 JB |
288 | As a special case, when @var{separators} is @code{nil} (or omitted), |
289 | null strings are always omitted from the result. Thus: | |
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290 | |
291 | @example | |
3aeea9e9 | 292 | (split-string " two words ") |
f67b6c12 | 293 | @result{} ("two" "words") |
3aeea9e9 JB |
294 | @end example |
295 | ||
296 | The result is not @samp{("" "two" "words" "")}, which would rarely be | |
d8186297 | 297 | useful. If you need such a result, use an explicit value for |
3aeea9e9 JB |
298 | @var{separators}: |
299 | ||
300 | @example | |
342fd6cd RS |
301 | (split-string " two words " |
302 | split-string-default-separators) | |
f67b6c12 | 303 | @result{} ("" "two" "words" "") |
f9f59935 RS |
304 | @end example |
305 | ||
3aeea9e9 | 306 | More examples: |
f9f59935 RS |
307 | |
308 | @example | |
3aeea9e9 | 309 | (split-string "Soup is good food" "o") |
f67b6c12 | 310 | @result{} ("S" "up is g" "" "d f" "" "d") |
3aeea9e9 | 311 | (split-string "Soup is good food" "o" t) |
f67b6c12 | 312 | @result{} ("S" "up is g" "d f" "d") |
3aeea9e9 | 313 | (split-string "Soup is good food" "o+") |
f67b6c12 | 314 | @result{} ("S" "up is g" "d f" "d") |
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315 | @end example |
316 | ||
f67b6c12 LT |
317 | Empty matches do count, except that @code{split-string} will not look |
318 | for a final empty match when it already reached the end of the string | |
319 | using a non-empty match or when @var{string} is empty: | |
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320 | |
321 | @example | |
f67b6c12 LT |
322 | (split-string "aooob" "o*") |
323 | @result{} ("" "a" "" "b" "") | |
324 | (split-string "ooaboo" "o*") | |
325 | @result{} ("" "" "a" "b" "") | |
326 | (split-string "" "") | |
327 | @result{} ("") | |
328 | @end example | |
329 | ||
330 | However, when @var{separators} can match the empty string, | |
331 | @var{omit-nulls} is usually @code{t}, so that the subtleties in the | |
332 | three previous examples are rarely relevant: | |
333 | ||
334 | @example | |
335 | (split-string "Soup is good food" "o*" t) | |
336 | @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") | |
337 | (split-string "Nice doggy!" "" t) | |
338 | @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") | |
339 | (split-string "" "" t) | |
340 | @result{} nil | |
341 | @end example | |
342 | ||
343 | Somewhat odd, but predictable, behavior can occur for certain | |
344 | ``non-greedy'' values of @var{separators} that can prefer empty | |
345 | matches over non-empty matches. Again, such values rarely occur in | |
346 | practice: | |
347 | ||
348 | @example | |
349 | (split-string "ooo" "o*" t) | |
350 | @result{} nil | |
351 | (split-string "ooo" "\\|o+" t) | |
352 | @result{} ("o" "o" "o") | |
f9f59935 RS |
353 | @end example |
354 | @end defun | |
355 | ||
ac902a01 | 356 | @defvar split-string-default-separators |
342fd6cd RS |
357 | The default value of @var{separators} for @code{split-string}. Its |
358 | usual value is @w{@samp{"[ \f\t\n\r\v]+"}}. | |
ac902a01 MB |
359 | @end defvar |
360 | ||
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361 | @node Modifying Strings |
362 | @section Modifying Strings | |
363 | ||
364 | The most basic way to alter the contents of an existing string is with | |
365 | @code{aset} (@pxref{Array Functions}). @code{(aset @var{string} | |
366 | @var{idx} @var{char})} stores @var{char} into @var{string} at index | |
367 | @var{idx}. Each character occupies one or more bytes, and if @var{char} | |
368 | needs a different number of bytes from the character already present at | |
969fe9b5 | 369 | that index, @code{aset} signals an error. |
f9f59935 RS |
370 | |
371 | A more powerful function is @code{store-substring}: | |
372 | ||
f9f59935 RS |
373 | @defun store-substring string idx obj |
374 | This function alters part of the contents of the string @var{string}, by | |
375 | storing @var{obj} starting at index @var{idx}. The argument @var{obj} | |
376 | may be either a character or a (smaller) string. | |
377 | ||
378 | Since it is impossible to change the length of an existing string, it is | |
379 | an error if @var{obj} doesn't fit within @var{string}'s actual length, | |
b6ae404e | 380 | or if any new character requires a different number of bytes from the |
969fe9b5 | 381 | character currently present at that point in @var{string}. |
81e65dff RS |
382 | @end defun |
383 | ||
384 | To clear out a string that contained a password, use | |
385 | @code{clear-string}: | |
386 | ||
387 | @defun clear-string string | |
376dfc01 RS |
388 | This clears the contents of @var{string} to zeros. |
389 | It may also change @var{string}'s length and convert it to | |
390 | a unibyte string. | |
f9f59935 RS |
391 | @end defun |
392 | ||
bda144f4 | 393 | @need 2000 |
869f4785 RS |
394 | @node Text Comparison |
395 | @section Comparison of Characters and Strings | |
396 | @cindex string equality | |
397 | ||
398 | @defun char-equal character1 character2 | |
399 | This function returns @code{t} if the arguments represent the same | |
400 | character, @code{nil} otherwise. This function ignores differences | |
401 | in case if @code{case-fold-search} is non-@code{nil}. | |
402 | ||
403 | @example | |
404 | (char-equal ?x ?x) | |
405 | @result{} t | |
f9f59935 RS |
406 | (let ((case-fold-search nil)) |
407 | (char-equal ?x ?X)) | |
408 | @result{} nil | |
869f4785 RS |
409 | @end example |
410 | @end defun | |
411 | ||
412 | @defun string= string1 string2 | |
413 | This function returns @code{t} if the characters of the two strings | |
f67b6c12 LT |
414 | match exactly. Symbols are also allowed as arguments, in which case |
415 | their print names are used. | |
b6ae404e | 416 | Case is always significant, regardless of @code{case-fold-search}. |
869f4785 RS |
417 | |
418 | @example | |
419 | (string= "abc" "abc") | |
420 | @result{} t | |
421 | (string= "abc" "ABC") | |
422 | @result{} nil | |
423 | (string= "ab" "ABC") | |
424 | @result{} nil | |
425 | @end example | |
22697dac | 426 | |
f9f59935 RS |
427 | The function @code{string=} ignores the text properties of the two |
428 | strings. When @code{equal} (@pxref{Equality Predicates}) compares two | |
429 | strings, it uses @code{string=}. | |
430 | ||
a62f71e4 LT |
431 | For technical reasons, a unibyte and a multibyte string are |
432 | @code{equal} if and only if they contain the same sequence of | |
433 | character codes and all these codes are either in the range 0 through | |
434 | 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}). | |
435 | However, when a unibyte string gets converted to a multibyte string, | |
436 | all characters with codes in the range 160 through 255 get converted | |
437 | to characters with higher codes, whereas @acronym{ASCII} characters | |
438 | remain unchanged. Thus, a unibyte string and its conversion to | |
439 | multibyte are only @code{equal} if the string is all @acronym{ASCII}. | |
440 | Character codes 160 through 255 are not entirely proper in multibyte | |
441 | text, even though they can occur. As a consequence, the situation | |
442 | where a unibyte and a multibyte string are @code{equal} without both | |
443 | being all @acronym{ASCII} is a technical oddity that very few Emacs | |
444 | Lisp programmers ever get confronted with. @xref{Text | |
f9f59935 | 445 | Representations}. |
869f4785 RS |
446 | @end defun |
447 | ||
448 | @defun string-equal string1 string2 | |
449 | @code{string-equal} is another name for @code{string=}. | |
450 | @end defun | |
451 | ||
452 | @cindex lexical comparison | |
453 | @defun string< string1 string2 | |
454 | @c (findex string< causes problems for permuted index!!) | |
8241495d RS |
455 | This function compares two strings a character at a time. It |
456 | scans both the strings at the same time to find the first pair of corresponding | |
457 | characters that do not match. If the lesser character of these two is | |
869f4785 RS |
458 | the character from @var{string1}, then @var{string1} is less, and this |
459 | function returns @code{t}. If the lesser character is the one from | |
460 | @var{string2}, then @var{string1} is greater, and this function returns | |
461 | @code{nil}. If the two strings match entirely, the value is @code{nil}. | |
462 | ||
969fe9b5 RS |
463 | Pairs of characters are compared according to their character codes. |
464 | Keep in mind that lower case letters have higher numeric values in the | |
ad800164 | 465 | @acronym{ASCII} character set than their upper case counterparts; digits and |
869f4785 | 466 | many punctuation characters have a lower numeric value than upper case |
ad800164 EZ |
467 | letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII} |
468 | character; a unibyte non-@acronym{ASCII} character is always less than any | |
469 | multibyte non-@acronym{ASCII} character (@pxref{Text Representations}). | |
869f4785 RS |
470 | |
471 | @example | |
472 | @group | |
473 | (string< "abc" "abd") | |
474 | @result{} t | |
475 | (string< "abd" "abc") | |
476 | @result{} nil | |
477 | (string< "123" "abc") | |
478 | @result{} t | |
479 | @end group | |
480 | @end example | |
481 | ||
482 | When the strings have different lengths, and they match up to the | |
483 | length of @var{string1}, then the result is @code{t}. If they match up | |
484 | to the length of @var{string2}, the result is @code{nil}. A string of | |
485 | no characters is less than any other string. | |
486 | ||
487 | @example | |
488 | @group | |
489 | (string< "" "abc") | |
490 | @result{} t | |
491 | (string< "ab" "abc") | |
492 | @result{} t | |
493 | (string< "abc" "") | |
494 | @result{} nil | |
495 | (string< "abc" "ab") | |
496 | @result{} nil | |
497 | (string< "" "") | |
177c0ea7 | 498 | @result{} nil |
869f4785 RS |
499 | @end group |
500 | @end example | |
f67b6c12 LT |
501 | |
502 | Symbols are also allowed as arguments, in which case their print names | |
503 | are used. | |
869f4785 RS |
504 | @end defun |
505 | ||
506 | @defun string-lessp string1 string2 | |
507 | @code{string-lessp} is another name for @code{string<}. | |
a9f0a989 RS |
508 | @end defun |
509 | ||
510 | @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case | |
8241495d | 511 | This function compares the specified part of @var{string1} with the |
a9f0a989 | 512 | specified part of @var{string2}. The specified part of @var{string1} |
8241495d RS |
513 | runs from index @var{start1} up to index @var{end1} (@code{nil} means |
514 | the end of the string). The specified part of @var{string2} runs from | |
515 | index @var{start2} up to index @var{end2} (@code{nil} means the end of | |
516 | the string). | |
a9f0a989 RS |
517 | |
518 | The strings are both converted to multibyte for the comparison | |
a62f71e4 LT |
519 | (@pxref{Text Representations}) so that a unibyte string and its |
520 | conversion to multibyte are always regarded as equal. If | |
521 | @var{ignore-case} is non-@code{nil}, then case is ignored, so that | |
522 | upper case letters can be equal to lower case letters. | |
a9f0a989 RS |
523 | |
524 | If the specified portions of the two strings match, the value is | |
525 | @code{t}. Otherwise, the value is an integer which indicates how many | |
526 | leading characters agree, and which string is less. Its absolute value | |
527 | is one plus the number of characters that agree at the beginning of the | |
528 | two strings. The sign is negative if @var{string1} (or its specified | |
529 | portion) is less. | |
530 | @end defun | |
531 | ||
81e65dff RS |
532 | @defun assoc-string key alist &optional case-fold |
533 | This function works like @code{assoc}, except that @var{key} must be a | |
534 | string, and comparison is done using @code{compare-strings}. If | |
535 | @var{case-fold} is non-@code{nil}, it ignores case differences. | |
d8186297 LT |
536 | Unlike @code{assoc}, this function can also match elements of the alist |
537 | that are strings rather than conses. In particular, @var{alist} can | |
538 | be a list of strings rather than an actual alist. | |
a62f71e4 | 539 | @xref{Association Lists}. |
869f4785 RS |
540 | @end defun |
541 | ||
542 | See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for | |
543 | a way to compare text in buffers. The function @code{string-match}, | |
544 | which matches a regular expression against a string, can be used | |
545 | for a kind of string comparison; see @ref{Regexp Search}. | |
546 | ||
547 | @node String Conversion | |
548 | @comment node-name, next, previous, up | |
549 | @section Conversion of Characters and Strings | |
550 | @cindex conversion of strings | |
551 | ||
552 | This section describes functions for conversions between characters, | |
42fc00a4 RS |
553 | strings and integers. @code{format} (@pxref{Formatting Strings}) |
554 | and @code{prin1-to-string} | |
869f4785 RS |
555 | (@pxref{Output Functions}) can also convert Lisp objects into strings. |
556 | @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a | |
f9f59935 RS |
557 | string representation of a Lisp object into an object. The functions |
558 | @code{string-make-multibyte} and @code{string-make-unibyte} convert the | |
559 | text representation of a string (@pxref{Converting Representations}). | |
869f4785 RS |
560 | |
561 | @xref{Documentation}, for functions that produce textual descriptions | |
562 | of text characters and general input events | |
563 | (@code{single-key-description} and @code{text-char-description}). These | |
564 | functions are used primarily for making help messages. | |
565 | ||
566 | @defun char-to-string character | |
567 | @cindex character to string | |
969fe9b5 RS |
568 | This function returns a new string containing one character, |
569 | @var{character}. This function is semi-obsolete because the function | |
570 | @code{string} is more general. @xref{Creating Strings}. | |
869f4785 RS |
571 | @end defun |
572 | ||
573 | @defun string-to-char string | |
574 | @cindex string to character | |
575 | This function returns the first character in @var{string}. If the | |
576 | string is empty, the function returns 0. The value is also 0 when the | |
ad800164 | 577 | first character of @var{string} is the null character, @acronym{ASCII} code |
869f4785 RS |
578 | 0. |
579 | ||
580 | @example | |
581 | (string-to-char "ABC") | |
582 | @result{} 65 | |
583 | (string-to-char "xyz") | |
584 | @result{} 120 | |
585 | (string-to-char "") | |
586 | @result{} 0 | |
8241495d | 587 | @group |
869f4785 RS |
588 | (string-to-char "\000") |
589 | @result{} 0 | |
8241495d | 590 | @end group |
869f4785 RS |
591 | @end example |
592 | ||
593 | This function may be eliminated in the future if it does not seem useful | |
594 | enough to retain. | |
595 | @end defun | |
596 | ||
597 | @defun number-to-string number | |
598 | @cindex integer to string | |
599 | @cindex integer to decimal | |
b6ae404e | 600 | This function returns a string consisting of the printed base-ten |
869f4785 | 601 | representation of @var{number}, which may be an integer or a floating |
8241495d | 602 | point number. The returned value starts with a minus sign if the argument is |
869f4785 RS |
603 | negative. |
604 | ||
605 | @example | |
606 | (number-to-string 256) | |
607 | @result{} "256" | |
f67b6c12 | 608 | @group |
869f4785 RS |
609 | (number-to-string -23) |
610 | @result{} "-23" | |
f67b6c12 | 611 | @end group |
869f4785 RS |
612 | (number-to-string -23.5) |
613 | @result{} "-23.5" | |
614 | @end example | |
615 | ||
616 | @cindex int-to-string | |
617 | @code{int-to-string} is a semi-obsolete alias for this function. | |
618 | ||
619 | See also the function @code{format} in @ref{Formatting Strings}. | |
620 | @end defun | |
621 | ||
a9f0a989 | 622 | @defun string-to-number string &optional base |
869f4785 RS |
623 | @cindex string to number |
624 | This function returns the numeric value of the characters in | |
f67b6c12 LT |
625 | @var{string}. If @var{base} is non-@code{nil}, it must be an integer |
626 | between 2 and 16 (inclusive), and integers are converted in that base. | |
627 | If @var{base} is @code{nil}, then base ten is used. Floating point | |
628 | conversion only works in base ten; we have not implemented other | |
629 | radices for floating point numbers, because that would be much more | |
630 | work and does not seem useful. If @var{string} looks like an integer | |
631 | but its value is too large to fit into a Lisp integer, | |
3afd8c25 | 632 | @code{string-to-number} returns a floating point result. |
f9f59935 | 633 | |
f67b6c12 LT |
634 | The parsing skips spaces and tabs at the beginning of @var{string}, |
635 | then reads as much of @var{string} as it can interpret as a number in | |
636 | the given base. (On some systems it ignores other whitespace at the | |
637 | beginning, not just spaces and tabs.) If the first character after | |
638 | the ignored whitespace is neither a digit in the given base, nor a | |
639 | plus or minus sign, nor the leading dot of a floating point number, | |
640 | this function returns 0. | |
869f4785 RS |
641 | |
642 | @example | |
643 | (string-to-number "256") | |
644 | @result{} 256 | |
645 | (string-to-number "25 is a perfect square.") | |
646 | @result{} 25 | |
647 | (string-to-number "X256") | |
648 | @result{} 0 | |
649 | (string-to-number "-4.5") | |
650 | @result{} -4.5 | |
ea626e87 RS |
651 | (string-to-number "1e5") |
652 | @result{} 100000.0 | |
869f4785 RS |
653 | @end example |
654 | ||
655 | @findex string-to-int | |
656 | @code{string-to-int} is an obsolete alias for this function. | |
657 | @end defun | |
658 | ||
f9f59935 RS |
659 | Here are some other functions that can convert to or from a string: |
660 | ||
661 | @table @code | |
662 | @item concat | |
663 | @code{concat} can convert a vector or a list into a string. | |
664 | @xref{Creating Strings}. | |
665 | ||
666 | @item vconcat | |
667 | @code{vconcat} can convert a string into a vector. @xref{Vector | |
668 | Functions}. | |
669 | ||
670 | @item append | |
671 | @code{append} can convert a string into a list. @xref{Building Lists}. | |
672 | @end table | |
673 | ||
869f4785 RS |
674 | @node Formatting Strings |
675 | @comment node-name, next, previous, up | |
676 | @section Formatting Strings | |
677 | @cindex formatting strings | |
678 | @cindex strings, formatting them | |
679 | ||
680 | @dfn{Formatting} means constructing a string by substitution of | |
b6ae404e KH |
681 | computed values at various places in a constant string. This constant string |
682 | controls how the other values are printed, as well as where they appear; | |
869f4785 RS |
683 | it is called a @dfn{format string}. |
684 | ||
685 | Formatting is often useful for computing messages to be displayed. In | |
686 | fact, the functions @code{message} and @code{error} provide the same | |
687 | formatting feature described here; they differ from @code{format} only | |
688 | in how they use the result of formatting. | |
689 | ||
690 | @defun format string &rest objects | |
969fe9b5 | 691 | This function returns a new string that is made by copying |
177c0ea7 | 692 | @var{string} and then replacing any format specification |
869f4785 RS |
693 | in the copy with encodings of the corresponding @var{objects}. The |
694 | arguments @var{objects} are the computed values to be formatted. | |
8241495d RS |
695 | |
696 | The characters in @var{string}, other than the format specifications, | |
a546cd47 RS |
697 | are copied directly into the output; if they have text properties, |
698 | these are copied into the output also. | |
869f4785 RS |
699 | @end defun |
700 | ||
701 | @cindex @samp{%} in format | |
702 | @cindex format specification | |
703 | A format specification is a sequence of characters beginning with a | |
704 | @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the | |
705 | @code{format} function replaces it with the printed representation of | |
706 | one of the values to be formatted (one of the arguments @var{objects}). | |
707 | For example: | |
708 | ||
709 | @example | |
710 | @group | |
711 | (format "The value of fill-column is %d." fill-column) | |
712 | @result{} "The value of fill-column is 72." | |
713 | @end group | |
714 | @end example | |
715 | ||
716 | If @var{string} contains more than one format specification, the | |
b6ae404e | 717 | format specifications correspond to successive values from |
869f4785 RS |
718 | @var{objects}. Thus, the first format specification in @var{string} |
719 | uses the first such value, the second format specification uses the | |
720 | second such value, and so on. Any extra format specifications (those | |
376dfc01 RS |
721 | for which there are no corresponding values) cause an error. Any |
722 | extra values to be formatted are ignored. | |
869f4785 | 723 | |
a9f0a989 RS |
724 | Certain format specifications require values of particular types. If |
725 | you supply a value that doesn't fit the requirements, an error is | |
726 | signaled. | |
869f4785 RS |
727 | |
728 | Here is a table of valid format specifications: | |
729 | ||
730 | @table @samp | |
731 | @item %s | |
732 | Replace the specification with the printed representation of the object, | |
f9f59935 | 733 | made without quoting (that is, using @code{princ}, not |
969fe9b5 | 734 | @code{prin1}---@pxref{Output Functions}). Thus, strings are represented |
f9f59935 RS |
735 | by their contents alone, with no @samp{"} characters, and symbols appear |
736 | without @samp{\} characters. | |
869f4785 | 737 | |
a546cd47 | 738 | If the object is a string, its text properties are |
8241495d RS |
739 | copied into the output. The text properties of the @samp{%s} itself |
740 | are also copied, but those of the object take priority. | |
741 | ||
869f4785 RS |
742 | @item %S |
743 | Replace the specification with the printed representation of the object, | |
f9f59935 RS |
744 | made with quoting (that is, using @code{prin1}---@pxref{Output |
745 | Functions}). Thus, strings are enclosed in @samp{"} characters, and | |
746 | @samp{\} characters appear where necessary before special characters. | |
869f4785 | 747 | |
869f4785 RS |
748 | @item %o |
749 | @cindex integer to octal | |
750 | Replace the specification with the base-eight representation of an | |
751 | integer. | |
752 | ||
753 | @item %d | |
754 | Replace the specification with the base-ten representation of an | |
755 | integer. | |
756 | ||
757 | @item %x | |
898bb59a | 758 | @itemx %X |
869f4785 RS |
759 | @cindex integer to hexadecimal |
760 | Replace the specification with the base-sixteen representation of an | |
898bb59a | 761 | integer. @samp{%x} uses lower case and @samp{%X} uses upper case. |
869f4785 RS |
762 | |
763 | @item %c | |
764 | Replace the specification with the character which is the value given. | |
765 | ||
766 | @item %e | |
767 | Replace the specification with the exponential notation for a floating | |
394d33a8 | 768 | point number. |
869f4785 RS |
769 | |
770 | @item %f | |
771 | Replace the specification with the decimal-point notation for a floating | |
772 | point number. | |
773 | ||
774 | @item %g | |
775 | Replace the specification with notation for a floating point number, | |
a9f0a989 | 776 | using either exponential notation or decimal-point notation, whichever |
394d33a8 | 777 | is shorter. |
869f4785 RS |
778 | |
779 | @item %% | |
898bb59a DL |
780 | Replace the specification with a single @samp{%}. This format |
781 | specification is unusual in that it does not use a value. For example, | |
782 | @code{(format "%% %d" 30)} returns @code{"% 30"}. | |
869f4785 RS |
783 | @end table |
784 | ||
785 | Any other format character results in an @samp{Invalid format | |
786 | operation} error. | |
787 | ||
788 | Here are several examples: | |
789 | ||
790 | @example | |
791 | @group | |
792 | (format "The name of this buffer is %s." (buffer-name)) | |
793 | @result{} "The name of this buffer is strings.texi." | |
794 | ||
795 | (format "The buffer object prints as %s." (current-buffer)) | |
9feb90da | 796 | @result{} "The buffer object prints as strings.texi." |
869f4785 | 797 | |
177c0ea7 | 798 | (format "The octal value of %d is %o, |
869f4785 | 799 | and the hex value is %x." 18 18 18) |
177c0ea7 | 800 | @result{} "The octal value of 18 is 22, |
869f4785 RS |
801 | and the hex value is 12." |
802 | @end group | |
803 | @end example | |
804 | ||
869f4785 RS |
805 | @cindex field width |
806 | @cindex padding | |
728345f8 JY |
807 | All the specification characters allow an optional ``width'', which |
808 | is a digit-string between the @samp{%} and the character. If the | |
809 | printed representation of the object contains fewer characters than | |
810 | this width, then it is padded. The padding is on the left if the | |
d8186297 LT |
811 | width is positive (or starts with zero) and on the right if the |
812 | width is negative. The padding character is normally a space, but if | |
728345f8 JY |
813 | the width starts with a zero, zeros are used for padding. Some of |
814 | these conventions are ignored for specification characters for which | |
d8186297 LT |
815 | they do not make sense. That is, @samp{%s}, @samp{%S} and @samp{%c} |
816 | accept a width starting with 0, but still pad with @emph{spaces} on | |
817 | the left. Also, @samp{%%} accepts a width, but ignores it. Here are | |
818 | some examples of padding: | |
869f4785 RS |
819 | |
820 | @example | |
821 | (format "%06d is padded on the left with zeros" 123) | |
822 | @result{} "000123 is padded on the left with zeros" | |
823 | ||
824 | (format "%-6d is padded on the right" 123) | |
825 | @result{} "123 is padded on the right" | |
826 | @end example | |
827 | ||
728345f8 JY |
828 | If the width is too small, @code{format} does not truncate the |
829 | object's printed representation. Thus, you can use a width to specify | |
830 | a minimum spacing between columns with no risk of losing information. | |
869f4785 RS |
831 | |
832 | In the following three examples, @samp{%7s} specifies a minimum width | |
833 | of 7. In the first case, the string inserted in place of @samp{%7s} has | |
834 | only 3 letters, so 4 blank spaces are inserted for padding. In the | |
835 | second case, the string @code{"specification"} is 13 letters wide but is | |
836 | not truncated. In the third case, the padding is on the right. | |
837 | ||
177c0ea7 | 838 | @smallexample |
869f4785 RS |
839 | @group |
840 | (format "The word `%7s' actually has %d letters in it." | |
841 | "foo" (length "foo")) | |
177c0ea7 | 842 | @result{} "The word ` foo' actually has 3 letters in it." |
869f4785 RS |
843 | @end group |
844 | ||
845 | @group | |
846 | (format "The word `%7s' actually has %d letters in it." | |
177c0ea7 JB |
847 | "specification" (length "specification")) |
848 | @result{} "The word `specification' actually has 13 letters in it." | |
869f4785 RS |
849 | @end group |
850 | ||
851 | @group | |
852 | (format "The word `%-7s' actually has %d letters in it." | |
853 | "foo" (length "foo")) | |
177c0ea7 | 854 | @result{} "The word `foo ' actually has 3 letters in it." |
869f4785 RS |
855 | @end group |
856 | @end smallexample | |
857 | ||
d8186297 | 858 | @cindex precision in format specifications |
728345f8 JY |
859 | All the specification characters allow an optional ``precision'' |
860 | before the character (after the width, if present). The precision is | |
861 | a decimal-point @samp{.} followed by a digit-string. For the | |
d8186297 LT |
862 | floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the |
863 | precision specifies how many decimal places to show; if zero, the | |
864 | decimal-point itself is also omitted. For @samp{%s} and @samp{%S}, | |
865 | the precision truncates the string to the given width, so | |
866 | @samp{%.3s} shows only the first three characters of the | |
867 | representation for @var{object}. Precision is ignored for other | |
868 | specification characters. | |
869 | ||
870 | @cindex flags in format specifications | |
871 | Immediately after the @samp{%} and before the optional width and | |
872 | precision, you can put certain ``flag'' characters. | |
873 | ||
874 | A space character inserts a space for positive numbers (otherwise | |
728345f8 | 875 | nothing is inserted for positive numbers). This flag is ignored |
d8186297 | 876 | except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}. |
728345f8 | 877 | |
d8186297 LT |
878 | The flag @samp{#} indicates ``alternate form''. For @samp{%o} it |
879 | ensures that the result begins with a 0. For @samp{%x} and @samp{%X} | |
880 | the result is prefixed with @samp{0x} or @samp{0X}. For @samp{%e}, | |
881 | @samp{%f}, and @samp{%g} a decimal point is always shown even if the | |
882 | precision is zero. | |
728345f8 | 883 | |
969fe9b5 | 884 | @node Case Conversion |
177c0ea7 | 885 | @comment node-name, next, previous, up |
969fe9b5 | 886 | @section Case Conversion in Lisp |
177c0ea7 JB |
887 | @cindex upper case |
888 | @cindex lower case | |
889 | @cindex character case | |
969fe9b5 | 890 | @cindex case conversion in Lisp |
869f4785 RS |
891 | |
892 | The character case functions change the case of single characters or | |
a9f0a989 RS |
893 | of the contents of strings. The functions normally convert only |
894 | alphabetic characters (the letters @samp{A} through @samp{Z} and | |
ad800164 | 895 | @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other |
8241495d RS |
896 | characters are not altered. You can specify a different case |
897 | conversion mapping by specifying a case table (@pxref{Case Tables}). | |
a9f0a989 RS |
898 | |
899 | These functions do not modify the strings that are passed to them as | |
900 | arguments. | |
869f4785 RS |
901 | |
902 | The examples below use the characters @samp{X} and @samp{x} which have | |
ad800164 | 903 | @acronym{ASCII} codes 88 and 120 respectively. |
869f4785 RS |
904 | |
905 | @defun downcase string-or-char | |
906 | This function converts a character or a string to lower case. | |
907 | ||
908 | When the argument to @code{downcase} is a string, the function creates | |
909 | and returns a new string in which each letter in the argument that is | |
910 | upper case is converted to lower case. When the argument to | |
911 | @code{downcase} is a character, @code{downcase} returns the | |
912 | corresponding lower case character. This value is an integer. If the | |
913 | original character is lower case, or is not a letter, then the value | |
914 | equals the original character. | |
915 | ||
916 | @example | |
917 | (downcase "The cat in the hat") | |
918 | @result{} "the cat in the hat" | |
919 | ||
920 | (downcase ?X) | |
921 | @result{} 120 | |
922 | @end example | |
923 | @end defun | |
924 | ||
925 | @defun upcase string-or-char | |
926 | This function converts a character or a string to upper case. | |
927 | ||
928 | When the argument to @code{upcase} is a string, the function creates | |
929 | and returns a new string in which each letter in the argument that is | |
930 | lower case is converted to upper case. | |
931 | ||
932 | When the argument to @code{upcase} is a character, @code{upcase} | |
933 | returns the corresponding upper case character. This value is an integer. | |
934 | If the original character is upper case, or is not a letter, then the | |
8241495d | 935 | value returned equals the original character. |
869f4785 RS |
936 | |
937 | @example | |
938 | (upcase "The cat in the hat") | |
939 | @result{} "THE CAT IN THE HAT" | |
940 | ||
941 | (upcase ?x) | |
942 | @result{} 88 | |
943 | @end example | |
944 | @end defun | |
945 | ||
946 | @defun capitalize string-or-char | |
947 | @cindex capitalization | |
948 | This function capitalizes strings or characters. If | |
949 | @var{string-or-char} is a string, the function creates and returns a new | |
950 | string, whose contents are a copy of @var{string-or-char} in which each | |
951 | word has been capitalized. This means that the first character of each | |
952 | word is converted to upper case, and the rest are converted to lower | |
953 | case. | |
954 | ||
955 | The definition of a word is any sequence of consecutive characters that | |
956 | are assigned to the word constituent syntax class in the current syntax | |
15da7853 | 957 | table (@pxref{Syntax Class Table}). |
869f4785 RS |
958 | |
959 | When the argument to @code{capitalize} is a character, @code{capitalize} | |
960 | has the same result as @code{upcase}. | |
961 | ||
962 | @example | |
f67b6c12 | 963 | @group |
869f4785 RS |
964 | (capitalize "The cat in the hat") |
965 | @result{} "The Cat In The Hat" | |
f67b6c12 | 966 | @end group |
869f4785 | 967 | |
f67b6c12 | 968 | @group |
869f4785 RS |
969 | (capitalize "THE 77TH-HATTED CAT") |
970 | @result{} "The 77th-Hatted Cat" | |
f67b6c12 | 971 | @end group |
869f4785 RS |
972 | |
973 | @group | |
974 | (capitalize ?x) | |
975 | @result{} 88 | |
976 | @end group | |
977 | @end example | |
978 | @end defun | |
979 | ||
f67b6c12 LT |
980 | @defun upcase-initials string-or-char |
981 | If @var{string-or-char} is a string, this function capitalizes the | |
982 | initials of the words in @var{string-or-char}, without altering any | |
983 | letters other than the initials. It returns a new string whose | |
984 | contents are a copy of @var{string-or-char}, in which each word has | |
b6ae404e | 985 | had its initial letter converted to upper case. |
969fe9b5 RS |
986 | |
987 | The definition of a word is any sequence of consecutive characters that | |
988 | are assigned to the word constituent syntax class in the current syntax | |
15da7853 | 989 | table (@pxref{Syntax Class Table}). |
969fe9b5 | 990 | |
f67b6c12 LT |
991 | When the argument to @code{upcase-initials} is a character, |
992 | @code{upcase-initials} has the same result as @code{upcase}. | |
993 | ||
969fe9b5 RS |
994 | @example |
995 | @group | |
996 | (upcase-initials "The CAT in the hAt") | |
997 | @result{} "The CAT In The HAt" | |
998 | @end group | |
999 | @end example | |
1000 | @end defun | |
1001 | ||
a9f0a989 RS |
1002 | @xref{Text Comparison}, for functions that compare strings; some of |
1003 | them ignore case differences, or can optionally ignore case differences. | |
1004 | ||
969fe9b5 | 1005 | @node Case Tables |
869f4785 RS |
1006 | @section The Case Table |
1007 | ||
1008 | You can customize case conversion by installing a special @dfn{case | |
1009 | table}. A case table specifies the mapping between upper case and lower | |
969fe9b5 RS |
1010 | case letters. It affects both the case conversion functions for Lisp |
1011 | objects (see the previous section) and those that apply to text in the | |
1012 | buffer (@pxref{Case Changes}). Each buffer has a case table; there is | |
1013 | also a standard case table which is used to initialize the case table | |
1014 | of new buffers. | |
f9f59935 | 1015 | |
969fe9b5 RS |
1016 | A case table is a char-table (@pxref{Char-Tables}) whose subtype is |
1017 | @code{case-table}. This char-table maps each character into the | |
1018 | corresponding lower case character. It has three extra slots, which | |
1019 | hold related tables: | |
f9f59935 RS |
1020 | |
1021 | @table @var | |
1022 | @item upcase | |
1023 | The upcase table maps each character into the corresponding upper | |
1024 | case character. | |
1025 | @item canonicalize | |
1026 | The canonicalize table maps all of a set of case-related characters | |
a9f0a989 | 1027 | into a particular member of that set. |
f9f59935 | 1028 | @item equivalences |
a9f0a989 RS |
1029 | The equivalences table maps each one of a set of case-related characters |
1030 | into the next character in that set. | |
f9f59935 | 1031 | @end table |
869f4785 | 1032 | |
f9f59935 RS |
1033 | In simple cases, all you need to specify is the mapping to lower-case; |
1034 | the three related tables will be calculated automatically from that one. | |
869f4785 RS |
1035 | |
1036 | For some languages, upper and lower case letters are not in one-to-one | |
1037 | correspondence. There may be two different lower case letters with the | |
1038 | same upper case equivalent. In these cases, you need to specify the | |
f9f59935 | 1039 | maps for both lower case and upper case. |
869f4785 | 1040 | |
f9f59935 | 1041 | The extra table @var{canonicalize} maps each character to a canonical |
869f4785 | 1042 | equivalent; any two characters that are related by case-conversion have |
f9f59935 RS |
1043 | the same canonical equivalent character. For example, since @samp{a} |
1044 | and @samp{A} are related by case-conversion, they should have the same | |
1045 | canonical equivalent character (which should be either @samp{a} for both | |
1046 | of them, or @samp{A} for both of them). | |
869f4785 | 1047 | |
d8186297 | 1048 | The extra table @var{equivalences} is a map that cyclically permutes |
f9f59935 | 1049 | each equivalence class (of characters with the same canonical |
ad800164 | 1050 | equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into |
f9f59935 RS |
1051 | @samp{A} and @samp{A} into @samp{a}, and likewise for each set of |
1052 | equivalent characters.) | |
869f4785 | 1053 | |
2778c642 | 1054 | When you construct a case table, you can provide @code{nil} for |
969fe9b5 | 1055 | @var{canonicalize}; then Emacs fills in this slot from the lower case |
f9f59935 | 1056 | and upper case mappings. You can also provide @code{nil} for |
969fe9b5 | 1057 | @var{equivalences}; then Emacs fills in this slot from |
2778c642 RS |
1058 | @var{canonicalize}. In a case table that is actually in use, those |
1059 | components are non-@code{nil}. Do not try to specify @var{equivalences} | |
1060 | without also specifying @var{canonicalize}. | |
869f4785 | 1061 | |
869f4785 RS |
1062 | Here are the functions for working with case tables: |
1063 | ||
1064 | @defun case-table-p object | |
1065 | This predicate returns non-@code{nil} if @var{object} is a valid case | |
1066 | table. | |
1067 | @end defun | |
1068 | ||
1069 | @defun set-standard-case-table table | |
1070 | This function makes @var{table} the standard case table, so that it will | |
969fe9b5 | 1071 | be used in any buffers created subsequently. |
869f4785 RS |
1072 | @end defun |
1073 | ||
1074 | @defun standard-case-table | |
1075 | This returns the standard case table. | |
1076 | @end defun | |
1077 | ||
1078 | @defun current-case-table | |
1079 | This function returns the current buffer's case table. | |
1080 | @end defun | |
1081 | ||
1082 | @defun set-case-table table | |
1083 | This sets the current buffer's case table to @var{table}. | |
1084 | @end defun | |
1085 | ||
1086 | The following three functions are convenient subroutines for packages | |
ad800164 | 1087 | that define non-@acronym{ASCII} character sets. They modify the specified |
f9f59935 | 1088 | case table @var{case-table}; they also modify the standard syntax table. |
969fe9b5 RS |
1089 | @xref{Syntax Tables}. Normally you would use these functions to change |
1090 | the standard case table. | |
869f4785 | 1091 | |
f9f59935 | 1092 | @defun set-case-syntax-pair uc lc case-table |
869f4785 RS |
1093 | This function specifies a pair of corresponding letters, one upper case |
1094 | and one lower case. | |
1095 | @end defun | |
1096 | ||
f9f59935 | 1097 | @defun set-case-syntax-delims l r case-table |
869f4785 RS |
1098 | This function makes characters @var{l} and @var{r} a matching pair of |
1099 | case-invariant delimiters. | |
1100 | @end defun | |
1101 | ||
f9f59935 | 1102 | @defun set-case-syntax char syntax case-table |
869f4785 RS |
1103 | This function makes @var{char} case-invariant, with syntax |
1104 | @var{syntax}. | |
1105 | @end defun | |
1106 | ||
1107 | @deffn Command describe-buffer-case-table | |
1108 | This command displays a description of the contents of the current | |
1109 | buffer's case table. | |
1110 | @end deffn | |
ab5796a9 MB |
1111 | |
1112 | @ignore | |
1113 | arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4 | |
1114 | @end ignore |