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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
b3d90e46 GM |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, |
4 | @c 2002, 2003, 2004, 2005, 2006, 2007 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 | ||
122c3009 RS |
105 | @defun string-or-null-p object |
106 | This function returns @code{t} if @var{object} is a string or nil, | |
107 | @code{nil} otherwise. | |
108 | @end defun | |
109 | ||
869f4785 | 110 | @defun char-or-string-p object |
a9f0a989 | 111 | This function returns @code{t} if @var{object} is a string or a |
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112 | character (i.e., an integer), @code{nil} otherwise. |
113 | @end defun | |
114 | ||
115 | @node Creating Strings | |
116 | @section Creating Strings | |
117 | ||
118 | The following functions create strings, either from scratch, or by | |
119 | putting strings together, or by taking them apart. | |
120 | ||
121 | @defun make-string count character | |
a9f0a989 | 122 | This function returns a string made up of @var{count} repetitions of |
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123 | @var{character}. If @var{count} is negative, an error is signaled. |
124 | ||
125 | @example | |
126 | (make-string 5 ?x) | |
127 | @result{} "xxxxx" | |
128 | (make-string 0 ?x) | |
129 | @result{} "" | |
130 | @end example | |
131 | ||
132 | Other functions to compare with this one include @code{char-to-string} | |
133 | (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and | |
134 | @code{make-list} (@pxref{Building Lists}). | |
135 | @end defun | |
136 | ||
f9f59935 RS |
137 | @defun string &rest characters |
138 | This returns a string containing the characters @var{characters}. | |
139 | ||
140 | @example | |
141 | (string ?a ?b ?c) | |
142 | @result{} "abc" | |
143 | @end example | |
144 | @end defun | |
145 | ||
869f4785 | 146 | @defun substring string start &optional end |
bfe721d1 | 147 | This function returns a new string which consists of those characters |
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148 | from @var{string} in the range from (and including) the character at the |
149 | index @var{start} up to (but excluding) the character at the index | |
150 | @var{end}. The first character is at index zero. | |
151 | ||
152 | @example | |
153 | @group | |
154 | (substring "abcdefg" 0 3) | |
155 | @result{} "abc" | |
156 | @end group | |
157 | @end example | |
158 | ||
159 | @noindent | |
160 | Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the | |
161 | index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied | |
162 | from the string @code{"abcdefg"}. The index 3 marks the character | |
163 | position up to which the substring is copied. The character whose index | |
164 | is 3 is actually the fourth character in the string. | |
165 | ||
166 | A negative number counts from the end of the string, so that @minus{}1 | |
177c0ea7 | 167 | signifies the index of the last character of the string. For example: |
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168 | |
169 | @example | |
170 | @group | |
171 | (substring "abcdefg" -3 -1) | |
172 | @result{} "ef" | |
173 | @end group | |
174 | @end example | |
175 | ||
176 | @noindent | |
177 | In this example, the index for @samp{e} is @minus{}3, the index for | |
178 | @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. | |
179 | Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. | |
180 | ||
f67b6c12 | 181 | When @code{nil} is used for @var{end}, it stands for the length of the |
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182 | string. Thus, |
183 | ||
184 | @example | |
185 | @group | |
186 | (substring "abcdefg" -3 nil) | |
187 | @result{} "efg" | |
188 | @end group | |
189 | @end example | |
190 | ||
191 | Omitting the argument @var{end} is equivalent to specifying @code{nil}. | |
192 | It follows that @code{(substring @var{string} 0)} returns a copy of all | |
193 | of @var{string}. | |
194 | ||
195 | @example | |
196 | @group | |
197 | (substring "abcdefg" 0) | |
198 | @result{} "abcdefg" | |
199 | @end group | |
200 | @end example | |
201 | ||
202 | @noindent | |
203 | But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence | |
204 | Functions}). | |
205 | ||
bfe721d1 KH |
206 | If the characters copied from @var{string} have text properties, the |
207 | properties are copied into the new string also. @xref{Text Properties}. | |
208 | ||
8241495d | 209 | @code{substring} also accepts a vector for the first argument. |
969fe9b5 RS |
210 | For example: |
211 | ||
212 | @example | |
213 | (substring [a b (c) "d"] 1 3) | |
214 | @result{} [b (c)] | |
215 | @end example | |
216 | ||
f67b6c12 LT |
217 | A @code{wrong-type-argument} error is signaled if @var{start} is not |
218 | an integer or if @var{end} is neither an integer nor @code{nil}. An | |
219 | @code{args-out-of-range} error is signaled if @var{start} indicates a | |
220 | character following @var{end}, or if either integer is out of range | |
221 | for @var{string}. | |
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222 | |
223 | Contrast this function with @code{buffer-substring} (@pxref{Buffer | |
224 | Contents}), which returns a string containing a portion of the text in | |
225 | the current buffer. The beginning of a string is at index 0, but the | |
226 | beginning of a buffer is at index 1. | |
227 | @end defun | |
228 | ||
f67b6c12 LT |
229 | @defun substring-no-properties string &optional start end |
230 | This works like @code{substring} but discards all text properties from | |
231 | the value. Also, @var{start} may be omitted or @code{nil}, which is | |
232 | equivalent to 0. Thus, @w{@code{(substring-no-properties | |
233 | @var{string})}} returns a copy of @var{string}, with all text | |
234 | properties removed. | |
1994c2a7 RS |
235 | @end defun |
236 | ||
869f4785 RS |
237 | @defun concat &rest sequences |
238 | @cindex copying strings | |
239 | @cindex concatenating strings | |
240 | This function returns a new string consisting of the characters in the | |
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241 | arguments passed to it (along with their text properties, if any). The |
242 | arguments may be strings, lists of numbers, or vectors of numbers; they | |
243 | are not themselves changed. If @code{concat} receives no arguments, it | |
244 | returns an empty string. | |
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245 | |
246 | @example | |
247 | (concat "abc" "-def") | |
248 | @result{} "abc-def" | |
a9f0a989 | 249 | (concat "abc" (list 120 121) [122]) |
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250 | @result{} "abcxyz" |
251 | ;; @r{@code{nil} is an empty sequence.} | |
252 | (concat "abc" nil "-def") | |
253 | @result{} "abc-def" | |
254 | (concat "The " "quick brown " "fox.") | |
255 | @result{} "The quick brown fox." | |
256 | (concat) | |
257 | @result{} "" | |
258 | @end example | |
259 | ||
260 | @noindent | |
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261 | The @code{concat} function always constructs a new string that is |
262 | not @code{eq} to any existing string. | |
263 | ||
315fe0e9 DL |
264 | In Emacs versions before 21, when an argument was an integer (not a |
265 | sequence of integers), it was converted to a string of digits making up | |
266 | the decimal printed representation of the integer. This obsolete usage | |
267 | no longer works. The proper way to convert an integer to its decimal | |
268 | printed form is with @code{format} (@pxref{Formatting Strings}) or | |
a10f6c69 | 269 | @code{number-to-string} (@pxref{String Conversion}). |
869f4785 | 270 | |
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271 | For information about other concatenation functions, see the |
272 | description of @code{mapconcat} in @ref{Mapping Functions}, | |
ad833e10 | 273 | @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building |
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274 | Lists}. |
275 | @end defun | |
276 | ||
f67b6c12 | 277 | @defun split-string string &optional separators omit-nulls |
a730d07b RS |
278 | This function splits @var{string} into substrings at matches for the |
279 | regular expression @var{separators}. Each match for @var{separators} | |
280 | defines a splitting point; the substrings between the splitting points | |
281 | are made into a list, which is the value returned by | |
282 | @code{split-string}. | |
283 | ||
284 | If @var{omit-nulls} is @code{nil}, the result contains null strings | |
285 | whenever there are two consecutive matches for @var{separators}, or a | |
286 | match is adjacent to the beginning or end of @var{string}. If | |
287 | @var{omit-nulls} is @code{t}, these null strings are omitted from the | |
ece35e15 | 288 | result. |
a730d07b | 289 | |
b6ae404e | 290 | If @var{separators} is @code{nil} (or omitted), |
3aeea9e9 | 291 | the default is the value of @code{split-string-default-separators}. |
f9f59935 | 292 | |
3aeea9e9 JB |
293 | As a special case, when @var{separators} is @code{nil} (or omitted), |
294 | null strings are always omitted from the result. Thus: | |
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295 | |
296 | @example | |
3aeea9e9 | 297 | (split-string " two words ") |
f67b6c12 | 298 | @result{} ("two" "words") |
3aeea9e9 JB |
299 | @end example |
300 | ||
bed0f7b2 | 301 | The result is not @code{("" "two" "words" "")}, which would rarely be |
d8186297 | 302 | useful. If you need such a result, use an explicit value for |
3aeea9e9 JB |
303 | @var{separators}: |
304 | ||
305 | @example | |
342fd6cd RS |
306 | (split-string " two words " |
307 | split-string-default-separators) | |
f67b6c12 | 308 | @result{} ("" "two" "words" "") |
f9f59935 RS |
309 | @end example |
310 | ||
3aeea9e9 | 311 | More examples: |
f9f59935 RS |
312 | |
313 | @example | |
3aeea9e9 | 314 | (split-string "Soup is good food" "o") |
f67b6c12 | 315 | @result{} ("S" "up is g" "" "d f" "" "d") |
3aeea9e9 | 316 | (split-string "Soup is good food" "o" t) |
f67b6c12 | 317 | @result{} ("S" "up is g" "d f" "d") |
3aeea9e9 | 318 | (split-string "Soup is good food" "o+") |
f67b6c12 | 319 | @result{} ("S" "up is g" "d f" "d") |
f9f59935 RS |
320 | @end example |
321 | ||
f67b6c12 LT |
322 | Empty matches do count, except that @code{split-string} will not look |
323 | for a final empty match when it already reached the end of the string | |
324 | using a non-empty match or when @var{string} is empty: | |
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325 | |
326 | @example | |
f67b6c12 LT |
327 | (split-string "aooob" "o*") |
328 | @result{} ("" "a" "" "b" "") | |
329 | (split-string "ooaboo" "o*") | |
330 | @result{} ("" "" "a" "b" "") | |
331 | (split-string "" "") | |
332 | @result{} ("") | |
333 | @end example | |
334 | ||
335 | However, when @var{separators} can match the empty string, | |
336 | @var{omit-nulls} is usually @code{t}, so that the subtleties in the | |
337 | three previous examples are rarely relevant: | |
338 | ||
339 | @example | |
340 | (split-string "Soup is good food" "o*" t) | |
341 | @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") | |
342 | (split-string "Nice doggy!" "" t) | |
343 | @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") | |
344 | (split-string "" "" t) | |
345 | @result{} nil | |
346 | @end example | |
347 | ||
348 | Somewhat odd, but predictable, behavior can occur for certain | |
349 | ``non-greedy'' values of @var{separators} that can prefer empty | |
350 | matches over non-empty matches. Again, such values rarely occur in | |
351 | practice: | |
352 | ||
353 | @example | |
354 | (split-string "ooo" "o*" t) | |
355 | @result{} nil | |
356 | (split-string "ooo" "\\|o+" t) | |
357 | @result{} ("o" "o" "o") | |
f9f59935 RS |
358 | @end example |
359 | @end defun | |
360 | ||
ac902a01 | 361 | @defvar split-string-default-separators |
342fd6cd | 362 | The default value of @var{separators} for @code{split-string}. Its |
bed0f7b2 | 363 | usual value is @w{@code{"[ \f\t\n\r\v]+"}}. |
ac902a01 MB |
364 | @end defvar |
365 | ||
f9f59935 RS |
366 | @node Modifying Strings |
367 | @section Modifying Strings | |
368 | ||
369 | The most basic way to alter the contents of an existing string is with | |
370 | @code{aset} (@pxref{Array Functions}). @code{(aset @var{string} | |
371 | @var{idx} @var{char})} stores @var{char} into @var{string} at index | |
372 | @var{idx}. Each character occupies one or more bytes, and if @var{char} | |
373 | needs a different number of bytes from the character already present at | |
969fe9b5 | 374 | that index, @code{aset} signals an error. |
f9f59935 RS |
375 | |
376 | A more powerful function is @code{store-substring}: | |
377 | ||
f9f59935 RS |
378 | @defun store-substring string idx obj |
379 | This function alters part of the contents of the string @var{string}, by | |
380 | storing @var{obj} starting at index @var{idx}. The argument @var{obj} | |
381 | may be either a character or a (smaller) string. | |
382 | ||
383 | Since it is impossible to change the length of an existing string, it is | |
384 | an error if @var{obj} doesn't fit within @var{string}'s actual length, | |
b6ae404e | 385 | or if any new character requires a different number of bytes from the |
969fe9b5 | 386 | character currently present at that point in @var{string}. |
81e65dff RS |
387 | @end defun |
388 | ||
389 | To clear out a string that contained a password, use | |
390 | @code{clear-string}: | |
391 | ||
392 | @defun clear-string string | |
1f84b630 JB |
393 | This makes @var{string} a unibyte string and clears its contents to |
394 | zeros. It may also change @var{string}'s length. | |
f9f59935 RS |
395 | @end defun |
396 | ||
bda144f4 | 397 | @need 2000 |
869f4785 RS |
398 | @node Text Comparison |
399 | @section Comparison of Characters and Strings | |
400 | @cindex string equality | |
401 | ||
402 | @defun char-equal character1 character2 | |
403 | This function returns @code{t} if the arguments represent the same | |
404 | character, @code{nil} otherwise. This function ignores differences | |
405 | in case if @code{case-fold-search} is non-@code{nil}. | |
406 | ||
407 | @example | |
408 | (char-equal ?x ?x) | |
409 | @result{} t | |
f9f59935 RS |
410 | (let ((case-fold-search nil)) |
411 | (char-equal ?x ?X)) | |
412 | @result{} nil | |
869f4785 RS |
413 | @end example |
414 | @end defun | |
415 | ||
416 | @defun string= string1 string2 | |
417 | This function returns @code{t} if the characters of the two strings | |
f67b6c12 LT |
418 | match exactly. Symbols are also allowed as arguments, in which case |
419 | their print names are used. | |
b6ae404e | 420 | Case is always significant, regardless of @code{case-fold-search}. |
869f4785 RS |
421 | |
422 | @example | |
423 | (string= "abc" "abc") | |
424 | @result{} t | |
425 | (string= "abc" "ABC") | |
426 | @result{} nil | |
427 | (string= "ab" "ABC") | |
428 | @result{} nil | |
429 | @end example | |
22697dac | 430 | |
f9f59935 RS |
431 | The function @code{string=} ignores the text properties of the two |
432 | strings. When @code{equal} (@pxref{Equality Predicates}) compares two | |
433 | strings, it uses @code{string=}. | |
434 | ||
a62f71e4 LT |
435 | For technical reasons, a unibyte and a multibyte string are |
436 | @code{equal} if and only if they contain the same sequence of | |
437 | character codes and all these codes are either in the range 0 through | |
438 | 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}). | |
439 | However, when a unibyte string gets converted to a multibyte string, | |
440 | all characters with codes in the range 160 through 255 get converted | |
441 | to characters with higher codes, whereas @acronym{ASCII} characters | |
442 | remain unchanged. Thus, a unibyte string and its conversion to | |
443 | multibyte are only @code{equal} if the string is all @acronym{ASCII}. | |
444 | Character codes 160 through 255 are not entirely proper in multibyte | |
445 | text, even though they can occur. As a consequence, the situation | |
446 | where a unibyte and a multibyte string are @code{equal} without both | |
447 | being all @acronym{ASCII} is a technical oddity that very few Emacs | |
448 | Lisp programmers ever get confronted with. @xref{Text | |
f9f59935 | 449 | Representations}. |
869f4785 RS |
450 | @end defun |
451 | ||
452 | @defun string-equal string1 string2 | |
453 | @code{string-equal} is another name for @code{string=}. | |
454 | @end defun | |
455 | ||
456 | @cindex lexical comparison | |
457 | @defun string< string1 string2 | |
458 | @c (findex string< causes problems for permuted index!!) | |
8241495d RS |
459 | This function compares two strings a character at a time. It |
460 | scans both the strings at the same time to find the first pair of corresponding | |
461 | characters that do not match. If the lesser character of these two is | |
869f4785 RS |
462 | the character from @var{string1}, then @var{string1} is less, and this |
463 | function returns @code{t}. If the lesser character is the one from | |
464 | @var{string2}, then @var{string1} is greater, and this function returns | |
465 | @code{nil}. If the two strings match entirely, the value is @code{nil}. | |
466 | ||
969fe9b5 RS |
467 | Pairs of characters are compared according to their character codes. |
468 | Keep in mind that lower case letters have higher numeric values in the | |
ad800164 | 469 | @acronym{ASCII} character set than their upper case counterparts; digits and |
869f4785 | 470 | many punctuation characters have a lower numeric value than upper case |
ad800164 EZ |
471 | letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII} |
472 | character; a unibyte non-@acronym{ASCII} character is always less than any | |
473 | multibyte non-@acronym{ASCII} character (@pxref{Text Representations}). | |
869f4785 RS |
474 | |
475 | @example | |
476 | @group | |
477 | (string< "abc" "abd") | |
478 | @result{} t | |
479 | (string< "abd" "abc") | |
480 | @result{} nil | |
481 | (string< "123" "abc") | |
482 | @result{} t | |
483 | @end group | |
484 | @end example | |
485 | ||
486 | When the strings have different lengths, and they match up to the | |
487 | length of @var{string1}, then the result is @code{t}. If they match up | |
488 | to the length of @var{string2}, the result is @code{nil}. A string of | |
489 | no characters is less than any other string. | |
490 | ||
491 | @example | |
492 | @group | |
493 | (string< "" "abc") | |
494 | @result{} t | |
495 | (string< "ab" "abc") | |
496 | @result{} t | |
497 | (string< "abc" "") | |
498 | @result{} nil | |
499 | (string< "abc" "ab") | |
500 | @result{} nil | |
501 | (string< "" "") | |
177c0ea7 | 502 | @result{} nil |
869f4785 RS |
503 | @end group |
504 | @end example | |
f67b6c12 LT |
505 | |
506 | Symbols are also allowed as arguments, in which case their print names | |
507 | are used. | |
869f4785 RS |
508 | @end defun |
509 | ||
510 | @defun string-lessp string1 string2 | |
511 | @code{string-lessp} is another name for @code{string<}. | |
a9f0a989 RS |
512 | @end defun |
513 | ||
514 | @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case | |
8241495d | 515 | This function compares the specified part of @var{string1} with the |
a9f0a989 | 516 | specified part of @var{string2}. The specified part of @var{string1} |
8241495d RS |
517 | runs from index @var{start1} up to index @var{end1} (@code{nil} means |
518 | the end of the string). The specified part of @var{string2} runs from | |
519 | index @var{start2} up to index @var{end2} (@code{nil} means the end of | |
520 | the string). | |
a9f0a989 RS |
521 | |
522 | The strings are both converted to multibyte for the comparison | |
a62f71e4 LT |
523 | (@pxref{Text Representations}) so that a unibyte string and its |
524 | conversion to multibyte are always regarded as equal. If | |
525 | @var{ignore-case} is non-@code{nil}, then case is ignored, so that | |
526 | upper case letters can be equal to lower case letters. | |
a9f0a989 RS |
527 | |
528 | If the specified portions of the two strings match, the value is | |
529 | @code{t}. Otherwise, the value is an integer which indicates how many | |
530 | leading characters agree, and which string is less. Its absolute value | |
531 | is one plus the number of characters that agree at the beginning of the | |
532 | two strings. The sign is negative if @var{string1} (or its specified | |
533 | portion) is less. | |
534 | @end defun | |
535 | ||
81e65dff RS |
536 | @defun assoc-string key alist &optional case-fold |
537 | This function works like @code{assoc}, except that @var{key} must be a | |
0dea6c8b KS |
538 | string or symbol, and comparison is done using @code{compare-strings}. |
539 | Symbols are converted to strings before testing. | |
540 | If @var{case-fold} is non-@code{nil}, it ignores case differences. | |
d8186297 | 541 | Unlike @code{assoc}, this function can also match elements of the alist |
0dea6c8b KS |
542 | that are strings or symbols rather than conses. In particular, @var{alist} can |
543 | be a list of strings or symbols rather than an actual alist. | |
a62f71e4 | 544 | @xref{Association Lists}. |
869f4785 RS |
545 | @end defun |
546 | ||
ece35e15 KB |
547 | See also the @code{compare-buffer-substrings} function in |
548 | @ref{Comparing Text}, for a way to compare text in buffers. The | |
549 | function @code{string-match}, which matches a regular expression | |
550 | against a string, can be used for a kind of string comparison; see | |
551 | @ref{Regexp Search}. | |
869f4785 RS |
552 | |
553 | @node String Conversion | |
554 | @comment node-name, next, previous, up | |
555 | @section Conversion of Characters and Strings | |
556 | @cindex conversion of strings | |
557 | ||
558 | This section describes functions for conversions between characters, | |
42fc00a4 RS |
559 | strings and integers. @code{format} (@pxref{Formatting Strings}) |
560 | and @code{prin1-to-string} | |
869f4785 RS |
561 | (@pxref{Output Functions}) can also convert Lisp objects into strings. |
562 | @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a | |
f9f59935 RS |
563 | string representation of a Lisp object into an object. The functions |
564 | @code{string-make-multibyte} and @code{string-make-unibyte} convert the | |
565 | text representation of a string (@pxref{Converting Representations}). | |
869f4785 RS |
566 | |
567 | @xref{Documentation}, for functions that produce textual descriptions | |
568 | of text characters and general input events | |
569 | (@code{single-key-description} and @code{text-char-description}). These | |
ece35e15 | 570 | are used primarily for making help messages. |
869f4785 RS |
571 | |
572 | @defun char-to-string character | |
573 | @cindex character to string | |
969fe9b5 RS |
574 | This function returns a new string containing one character, |
575 | @var{character}. This function is semi-obsolete because the function | |
576 | @code{string} is more general. @xref{Creating Strings}. | |
869f4785 RS |
577 | @end defun |
578 | ||
579 | @defun string-to-char string | |
580 | @cindex string to character | |
581 | This function returns the first character in @var{string}. If the | |
582 | string is empty, the function returns 0. The value is also 0 when the | |
ad800164 | 583 | first character of @var{string} is the null character, @acronym{ASCII} code |
869f4785 RS |
584 | 0. |
585 | ||
586 | @example | |
587 | (string-to-char "ABC") | |
588 | @result{} 65 | |
a4c5b42a | 589 | |
869f4785 RS |
590 | (string-to-char "xyz") |
591 | @result{} 120 | |
592 | (string-to-char "") | |
593 | @result{} 0 | |
8241495d | 594 | @group |
869f4785 RS |
595 | (string-to-char "\000") |
596 | @result{} 0 | |
8241495d | 597 | @end group |
869f4785 RS |
598 | @end example |
599 | ||
600 | This function may be eliminated in the future if it does not seem useful | |
601 | enough to retain. | |
602 | @end defun | |
603 | ||
604 | @defun number-to-string number | |
605 | @cindex integer to string | |
606 | @cindex integer to decimal | |
b6ae404e | 607 | This function returns a string consisting of the printed base-ten |
869f4785 | 608 | representation of @var{number}, which may be an integer or a floating |
8241495d | 609 | point number. The returned value starts with a minus sign if the argument is |
869f4785 RS |
610 | negative. |
611 | ||
612 | @example | |
613 | (number-to-string 256) | |
614 | @result{} "256" | |
f67b6c12 | 615 | @group |
869f4785 RS |
616 | (number-to-string -23) |
617 | @result{} "-23" | |
f67b6c12 | 618 | @end group |
869f4785 RS |
619 | (number-to-string -23.5) |
620 | @result{} "-23.5" | |
621 | @end example | |
622 | ||
623 | @cindex int-to-string | |
624 | @code{int-to-string} is a semi-obsolete alias for this function. | |
625 | ||
626 | See also the function @code{format} in @ref{Formatting Strings}. | |
627 | @end defun | |
628 | ||
a9f0a989 | 629 | @defun string-to-number string &optional base |
869f4785 RS |
630 | @cindex string to number |
631 | This function returns the numeric value of the characters in | |
f67b6c12 LT |
632 | @var{string}. If @var{base} is non-@code{nil}, it must be an integer |
633 | between 2 and 16 (inclusive), and integers are converted in that base. | |
634 | If @var{base} is @code{nil}, then base ten is used. Floating point | |
635 | conversion only works in base ten; we have not implemented other | |
636 | radices for floating point numbers, because that would be much more | |
637 | work and does not seem useful. If @var{string} looks like an integer | |
638 | but its value is too large to fit into a Lisp integer, | |
3afd8c25 | 639 | @code{string-to-number} returns a floating point result. |
f9f59935 | 640 | |
f67b6c12 LT |
641 | The parsing skips spaces and tabs at the beginning of @var{string}, |
642 | then reads as much of @var{string} as it can interpret as a number in | |
643 | the given base. (On some systems it ignores other whitespace at the | |
644 | beginning, not just spaces and tabs.) If the first character after | |
645 | the ignored whitespace is neither a digit in the given base, nor a | |
646 | plus or minus sign, nor the leading dot of a floating point number, | |
647 | this function returns 0. | |
869f4785 RS |
648 | |
649 | @example | |
650 | (string-to-number "256") | |
651 | @result{} 256 | |
652 | (string-to-number "25 is a perfect square.") | |
653 | @result{} 25 | |
654 | (string-to-number "X256") | |
655 | @result{} 0 | |
656 | (string-to-number "-4.5") | |
657 | @result{} -4.5 | |
ea626e87 RS |
658 | (string-to-number "1e5") |
659 | @result{} 100000.0 | |
869f4785 RS |
660 | @end example |
661 | ||
662 | @findex string-to-int | |
663 | @code{string-to-int} is an obsolete alias for this function. | |
664 | @end defun | |
665 | ||
f9f59935 RS |
666 | Here are some other functions that can convert to or from a string: |
667 | ||
668 | @table @code | |
669 | @item concat | |
670 | @code{concat} can convert a vector or a list into a string. | |
671 | @xref{Creating Strings}. | |
672 | ||
673 | @item vconcat | |
674 | @code{vconcat} can convert a string into a vector. @xref{Vector | |
675 | Functions}. | |
676 | ||
677 | @item append | |
678 | @code{append} can convert a string into a list. @xref{Building Lists}. | |
679 | @end table | |
680 | ||
869f4785 RS |
681 | @node Formatting Strings |
682 | @comment node-name, next, previous, up | |
683 | @section Formatting Strings | |
684 | @cindex formatting strings | |
685 | @cindex strings, formatting them | |
686 | ||
687 | @dfn{Formatting} means constructing a string by substitution of | |
b6ae404e KH |
688 | computed values at various places in a constant string. This constant string |
689 | controls how the other values are printed, as well as where they appear; | |
869f4785 RS |
690 | it is called a @dfn{format string}. |
691 | ||
692 | Formatting is often useful for computing messages to be displayed. In | |
693 | fact, the functions @code{message} and @code{error} provide the same | |
694 | formatting feature described here; they differ from @code{format} only | |
695 | in how they use the result of formatting. | |
696 | ||
697 | @defun format string &rest objects | |
969fe9b5 | 698 | This function returns a new string that is made by copying |
177c0ea7 | 699 | @var{string} and then replacing any format specification |
869f4785 RS |
700 | in the copy with encodings of the corresponding @var{objects}. The |
701 | arguments @var{objects} are the computed values to be formatted. | |
8241495d RS |
702 | |
703 | The characters in @var{string}, other than the format specifications, | |
a1ebfe34 EZ |
704 | are copied directly into the output, including their text properties, |
705 | if any. | |
869f4785 RS |
706 | @end defun |
707 | ||
708 | @cindex @samp{%} in format | |
709 | @cindex format specification | |
710 | A format specification is a sequence of characters beginning with a | |
711 | @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the | |
712 | @code{format} function replaces it with the printed representation of | |
713 | one of the values to be formatted (one of the arguments @var{objects}). | |
714 | For example: | |
715 | ||
716 | @example | |
717 | @group | |
718 | (format "The value of fill-column is %d." fill-column) | |
719 | @result{} "The value of fill-column is 72." | |
720 | @end group | |
721 | @end example | |
722 | ||
65c6c6b6 EZ |
723 | Since @code{format} interprets @samp{%} characters as format |
724 | specifications, you should @emph{never} pass an arbitrary string as | |
725 | the first argument. This is particularly true when the string is | |
726 | generated by some Lisp code. Unless the string is @emph{known} to | |
727 | never include any @samp{%} characters, pass @code{"%s"}, described | |
728 | below, as the first argument, and the string as the second, like this: | |
729 | ||
730 | @example | |
731 | (format "%s" @var{arbitrary-string}) | |
732 | @end example | |
733 | ||
869f4785 | 734 | If @var{string} contains more than one format specification, the |
b6ae404e | 735 | format specifications correspond to successive values from |
869f4785 RS |
736 | @var{objects}. Thus, the first format specification in @var{string} |
737 | uses the first such value, the second format specification uses the | |
738 | second such value, and so on. Any extra format specifications (those | |
376dfc01 RS |
739 | for which there are no corresponding values) cause an error. Any |
740 | extra values to be formatted are ignored. | |
869f4785 | 741 | |
a9f0a989 RS |
742 | Certain format specifications require values of particular types. If |
743 | you supply a value that doesn't fit the requirements, an error is | |
744 | signaled. | |
869f4785 RS |
745 | |
746 | Here is a table of valid format specifications: | |
747 | ||
748 | @table @samp | |
749 | @item %s | |
750 | Replace the specification with the printed representation of the object, | |
f9f59935 | 751 | made without quoting (that is, using @code{princ}, not |
969fe9b5 | 752 | @code{prin1}---@pxref{Output Functions}). Thus, strings are represented |
f9f59935 RS |
753 | by their contents alone, with no @samp{"} characters, and symbols appear |
754 | without @samp{\} characters. | |
869f4785 | 755 | |
a546cd47 | 756 | If the object is a string, its text properties are |
8241495d RS |
757 | copied into the output. The text properties of the @samp{%s} itself |
758 | are also copied, but those of the object take priority. | |
759 | ||
869f4785 RS |
760 | @item %S |
761 | Replace the specification with the printed representation of the object, | |
f9f59935 RS |
762 | made with quoting (that is, using @code{prin1}---@pxref{Output |
763 | Functions}). Thus, strings are enclosed in @samp{"} characters, and | |
764 | @samp{\} characters appear where necessary before special characters. | |
869f4785 | 765 | |
869f4785 RS |
766 | @item %o |
767 | @cindex integer to octal | |
768 | Replace the specification with the base-eight representation of an | |
769 | integer. | |
770 | ||
771 | @item %d | |
772 | Replace the specification with the base-ten representation of an | |
773 | integer. | |
774 | ||
775 | @item %x | |
898bb59a | 776 | @itemx %X |
869f4785 RS |
777 | @cindex integer to hexadecimal |
778 | Replace the specification with the base-sixteen representation of an | |
898bb59a | 779 | integer. @samp{%x} uses lower case and @samp{%X} uses upper case. |
869f4785 RS |
780 | |
781 | @item %c | |
782 | Replace the specification with the character which is the value given. | |
783 | ||
784 | @item %e | |
785 | Replace the specification with the exponential notation for a floating | |
394d33a8 | 786 | point number. |
869f4785 RS |
787 | |
788 | @item %f | |
789 | Replace the specification with the decimal-point notation for a floating | |
790 | point number. | |
791 | ||
792 | @item %g | |
793 | Replace the specification with notation for a floating point number, | |
a9f0a989 | 794 | using either exponential notation or decimal-point notation, whichever |
394d33a8 | 795 | is shorter. |
869f4785 RS |
796 | |
797 | @item %% | |
898bb59a DL |
798 | Replace the specification with a single @samp{%}. This format |
799 | specification is unusual in that it does not use a value. For example, | |
800 | @code{(format "%% %d" 30)} returns @code{"% 30"}. | |
869f4785 RS |
801 | @end table |
802 | ||
803 | Any other format character results in an @samp{Invalid format | |
804 | operation} error. | |
805 | ||
806 | Here are several examples: | |
807 | ||
808 | @example | |
809 | @group | |
810 | (format "The name of this buffer is %s." (buffer-name)) | |
811 | @result{} "The name of this buffer is strings.texi." | |
812 | ||
813 | (format "The buffer object prints as %s." (current-buffer)) | |
9feb90da | 814 | @result{} "The buffer object prints as strings.texi." |
869f4785 | 815 | |
177c0ea7 | 816 | (format "The octal value of %d is %o, |
869f4785 | 817 | and the hex value is %x." 18 18 18) |
177c0ea7 | 818 | @result{} "The octal value of 18 is 22, |
869f4785 RS |
819 | and the hex value is 12." |
820 | @end group | |
821 | @end example | |
822 | ||
869f4785 RS |
823 | @cindex field width |
824 | @cindex padding | |
a48320d9 RS |
825 | A specification can have a @dfn{width}, which is a signed decimal |
826 | number between the @samp{%} and the specification character. If the | |
728345f8 | 827 | printed representation of the object contains fewer characters than |
a48320d9 RS |
828 | this width, @code{format} extends it with padding. The padding goes |
829 | on the left if the width is positive (or starts with zero) and on the | |
830 | right if the width is negative. The padding character is normally a | |
831 | space, but it's @samp{0} if the width starts with a zero. | |
832 | ||
833 | Some of these conventions are ignored for specification characters | |
834 | for which they do not make sense. That is, @samp{%s}, @samp{%S} and | |
835 | @samp{%c} accept a width starting with 0, but still pad with | |
836 | @emph{spaces} on the left. Also, @samp{%%} accepts a width, but | |
837 | ignores it. Here are some examples of padding: | |
869f4785 RS |
838 | |
839 | @example | |
840 | (format "%06d is padded on the left with zeros" 123) | |
841 | @result{} "000123 is padded on the left with zeros" | |
842 | ||
843 | (format "%-6d is padded on the right" 123) | |
844 | @result{} "123 is padded on the right" | |
845 | @end example | |
846 | ||
a48320d9 | 847 | @noindent |
728345f8 JY |
848 | If the width is too small, @code{format} does not truncate the |
849 | object's printed representation. Thus, you can use a width to specify | |
850 | a minimum spacing between columns with no risk of losing information. | |
869f4785 | 851 | |
a48320d9 RS |
852 | In the following three examples, @samp{%7s} specifies a minimum |
853 | width of 7. In the first case, the string inserted in place of | |
854 | @samp{%7s} has only 3 letters, it needs 4 blank spaces as padding. In | |
855 | the second case, the string @code{"specification"} is 13 letters wide | |
856 | but is not truncated. In the third case, the padding is on the right. | |
869f4785 | 857 | |
177c0ea7 | 858 | @smallexample |
869f4785 RS |
859 | @group |
860 | (format "The word `%7s' actually has %d letters in it." | |
861 | "foo" (length "foo")) | |
177c0ea7 | 862 | @result{} "The word ` foo' actually has 3 letters in it." |
869f4785 RS |
863 | @end group |
864 | ||
865 | @group | |
866 | (format "The word `%7s' actually has %d letters in it." | |
177c0ea7 JB |
867 | "specification" (length "specification")) |
868 | @result{} "The word `specification' actually has 13 letters in it." | |
869f4785 RS |
869 | @end group |
870 | ||
871 | @group | |
872 | (format "The word `%-7s' actually has %d letters in it." | |
873 | "foo" (length "foo")) | |
177c0ea7 | 874 | @result{} "The word `foo ' actually has 3 letters in it." |
869f4785 RS |
875 | @end group |
876 | @end smallexample | |
877 | ||
d8186297 | 878 | @cindex precision in format specifications |
a48320d9 | 879 | All the specification characters allow an optional @dfn{precision} |
728345f8 JY |
880 | before the character (after the width, if present). The precision is |
881 | a decimal-point @samp{.} followed by a digit-string. For the | |
d8186297 LT |
882 | floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the |
883 | precision specifies how many decimal places to show; if zero, the | |
884 | decimal-point itself is also omitted. For @samp{%s} and @samp{%S}, | |
a48320d9 RS |
885 | the precision truncates the string to the given width, so @samp{%.3s} |
886 | shows only the first three characters of the representation for | |
887 | @var{object}. Precision has no effect for other specification | |
888 | characters. | |
d8186297 LT |
889 | |
890 | @cindex flags in format specifications | |
a48320d9 | 891 | Immediately after the @samp{%} and before the optional width and |
d8186297 LT |
892 | precision, you can put certain ``flag'' characters. |
893 | ||
a48320d9 RS |
894 | @samp{+} as a flag inserts a plus sign before a positive number, so |
895 | that it always has a sign. A space character as flag inserts a space | |
896 | before a positive number. (Otherwise, positive numbers start with the | |
897 | first digit.) Either of these two flags ensures that positive numbers | |
898 | and negative numbers use the same number of columns. These flags are | |
899 | ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if | |
900 | both flags are used, the @samp{+} takes precedence. | |
901 | ||
902 | The flag @samp{#} specifies an ``alternate form'' which depends on | |
903 | the format in use. For @samp{%o} it ensures that the result begins | |
904 | with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result | |
905 | with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g}, | |
906 | the @samp{#} flag means include a decimal point even if the precision | |
907 | is zero. | |
728345f8 | 908 | |
969fe9b5 | 909 | @node Case Conversion |
177c0ea7 | 910 | @comment node-name, next, previous, up |
969fe9b5 | 911 | @section Case Conversion in Lisp |
177c0ea7 JB |
912 | @cindex upper case |
913 | @cindex lower case | |
914 | @cindex character case | |
969fe9b5 | 915 | @cindex case conversion in Lisp |
869f4785 RS |
916 | |
917 | The character case functions change the case of single characters or | |
a9f0a989 RS |
918 | of the contents of strings. The functions normally convert only |
919 | alphabetic characters (the letters @samp{A} through @samp{Z} and | |
ad800164 | 920 | @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other |
8241495d RS |
921 | characters are not altered. You can specify a different case |
922 | conversion mapping by specifying a case table (@pxref{Case Tables}). | |
a9f0a989 RS |
923 | |
924 | These functions do not modify the strings that are passed to them as | |
925 | arguments. | |
869f4785 RS |
926 | |
927 | The examples below use the characters @samp{X} and @samp{x} which have | |
ad800164 | 928 | @acronym{ASCII} codes 88 and 120 respectively. |
869f4785 RS |
929 | |
930 | @defun downcase string-or-char | |
931 | This function converts a character or a string to lower case. | |
932 | ||
933 | When the argument to @code{downcase} is a string, the function creates | |
934 | and returns a new string in which each letter in the argument that is | |
935 | upper case is converted to lower case. When the argument to | |
936 | @code{downcase} is a character, @code{downcase} returns the | |
937 | corresponding lower case character. This value is an integer. If the | |
938 | original character is lower case, or is not a letter, then the value | |
939 | equals the original character. | |
940 | ||
941 | @example | |
942 | (downcase "The cat in the hat") | |
943 | @result{} "the cat in the hat" | |
944 | ||
945 | (downcase ?X) | |
946 | @result{} 120 | |
947 | @end example | |
948 | @end defun | |
949 | ||
950 | @defun upcase string-or-char | |
951 | This function converts a character or a string to upper case. | |
952 | ||
953 | When the argument to @code{upcase} is a string, the function creates | |
954 | and returns a new string in which each letter in the argument that is | |
955 | lower case is converted to upper case. | |
956 | ||
957 | When the argument to @code{upcase} is a character, @code{upcase} | |
958 | returns the corresponding upper case character. This value is an integer. | |
959 | If the original character is upper case, or is not a letter, then the | |
8241495d | 960 | value returned equals the original character. |
869f4785 RS |
961 | |
962 | @example | |
963 | (upcase "The cat in the hat") | |
964 | @result{} "THE CAT IN THE HAT" | |
965 | ||
966 | (upcase ?x) | |
967 | @result{} 88 | |
968 | @end example | |
969 | @end defun | |
970 | ||
971 | @defun capitalize string-or-char | |
972 | @cindex capitalization | |
973 | This function capitalizes strings or characters. If | |
974 | @var{string-or-char} is a string, the function creates and returns a new | |
975 | string, whose contents are a copy of @var{string-or-char} in which each | |
976 | word has been capitalized. This means that the first character of each | |
977 | word is converted to upper case, and the rest are converted to lower | |
978 | case. | |
979 | ||
980 | The definition of a word is any sequence of consecutive characters that | |
981 | are assigned to the word constituent syntax class in the current syntax | |
15da7853 | 982 | table (@pxref{Syntax Class Table}). |
869f4785 RS |
983 | |
984 | When the argument to @code{capitalize} is a character, @code{capitalize} | |
985 | has the same result as @code{upcase}. | |
986 | ||
987 | @example | |
f67b6c12 | 988 | @group |
869f4785 RS |
989 | (capitalize "The cat in the hat") |
990 | @result{} "The Cat In The Hat" | |
f67b6c12 | 991 | @end group |
869f4785 | 992 | |
f67b6c12 | 993 | @group |
869f4785 RS |
994 | (capitalize "THE 77TH-HATTED CAT") |
995 | @result{} "The 77th-Hatted Cat" | |
f67b6c12 | 996 | @end group |
869f4785 RS |
997 | |
998 | @group | |
999 | (capitalize ?x) | |
1000 | @result{} 88 | |
1001 | @end group | |
1002 | @end example | |
1003 | @end defun | |
1004 | ||
f67b6c12 LT |
1005 | @defun upcase-initials string-or-char |
1006 | If @var{string-or-char} is a string, this function capitalizes the | |
1007 | initials of the words in @var{string-or-char}, without altering any | |
1008 | letters other than the initials. It returns a new string whose | |
1009 | contents are a copy of @var{string-or-char}, in which each word has | |
b6ae404e | 1010 | had its initial letter converted to upper case. |
969fe9b5 RS |
1011 | |
1012 | The definition of a word is any sequence of consecutive characters that | |
1013 | are assigned to the word constituent syntax class in the current syntax | |
15da7853 | 1014 | table (@pxref{Syntax Class Table}). |
969fe9b5 | 1015 | |
f67b6c12 LT |
1016 | When the argument to @code{upcase-initials} is a character, |
1017 | @code{upcase-initials} has the same result as @code{upcase}. | |
1018 | ||
969fe9b5 RS |
1019 | @example |
1020 | @group | |
1021 | (upcase-initials "The CAT in the hAt") | |
1022 | @result{} "The CAT In The HAt" | |
1023 | @end group | |
1024 | @end example | |
1025 | @end defun | |
1026 | ||
a9f0a989 RS |
1027 | @xref{Text Comparison}, for functions that compare strings; some of |
1028 | them ignore case differences, or can optionally ignore case differences. | |
1029 | ||
969fe9b5 | 1030 | @node Case Tables |
869f4785 RS |
1031 | @section The Case Table |
1032 | ||
1033 | You can customize case conversion by installing a special @dfn{case | |
1034 | table}. A case table specifies the mapping between upper case and lower | |
969fe9b5 RS |
1035 | case letters. It affects both the case conversion functions for Lisp |
1036 | objects (see the previous section) and those that apply to text in the | |
1037 | buffer (@pxref{Case Changes}). Each buffer has a case table; there is | |
1038 | also a standard case table which is used to initialize the case table | |
1039 | of new buffers. | |
f9f59935 | 1040 | |
969fe9b5 RS |
1041 | A case table is a char-table (@pxref{Char-Tables}) whose subtype is |
1042 | @code{case-table}. This char-table maps each character into the | |
1043 | corresponding lower case character. It has three extra slots, which | |
1044 | hold related tables: | |
f9f59935 RS |
1045 | |
1046 | @table @var | |
1047 | @item upcase | |
1048 | The upcase table maps each character into the corresponding upper | |
1049 | case character. | |
1050 | @item canonicalize | |
1051 | The canonicalize table maps all of a set of case-related characters | |
a9f0a989 | 1052 | into a particular member of that set. |
f9f59935 | 1053 | @item equivalences |
a9f0a989 RS |
1054 | The equivalences table maps each one of a set of case-related characters |
1055 | into the next character in that set. | |
f9f59935 | 1056 | @end table |
869f4785 | 1057 | |
f9f59935 RS |
1058 | In simple cases, all you need to specify is the mapping to lower-case; |
1059 | the three related tables will be calculated automatically from that one. | |
869f4785 RS |
1060 | |
1061 | For some languages, upper and lower case letters are not in one-to-one | |
1062 | correspondence. There may be two different lower case letters with the | |
1063 | same upper case equivalent. In these cases, you need to specify the | |
f9f59935 | 1064 | maps for both lower case and upper case. |
869f4785 | 1065 | |
f9f59935 | 1066 | The extra table @var{canonicalize} maps each character to a canonical |
869f4785 | 1067 | equivalent; any two characters that are related by case-conversion have |
f9f59935 RS |
1068 | the same canonical equivalent character. For example, since @samp{a} |
1069 | and @samp{A} are related by case-conversion, they should have the same | |
1070 | canonical equivalent character (which should be either @samp{a} for both | |
1071 | of them, or @samp{A} for both of them). | |
869f4785 | 1072 | |
d8186297 | 1073 | The extra table @var{equivalences} is a map that cyclically permutes |
f9f59935 | 1074 | each equivalence class (of characters with the same canonical |
ad800164 | 1075 | equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into |
f9f59935 RS |
1076 | @samp{A} and @samp{A} into @samp{a}, and likewise for each set of |
1077 | equivalent characters.) | |
869f4785 | 1078 | |
2778c642 | 1079 | When you construct a case table, you can provide @code{nil} for |
969fe9b5 | 1080 | @var{canonicalize}; then Emacs fills in this slot from the lower case |
f9f59935 | 1081 | and upper case mappings. You can also provide @code{nil} for |
969fe9b5 | 1082 | @var{equivalences}; then Emacs fills in this slot from |
2778c642 RS |
1083 | @var{canonicalize}. In a case table that is actually in use, those |
1084 | components are non-@code{nil}. Do not try to specify @var{equivalences} | |
1085 | without also specifying @var{canonicalize}. | |
869f4785 | 1086 | |
869f4785 RS |
1087 | Here are the functions for working with case tables: |
1088 | ||
1089 | @defun case-table-p object | |
1090 | This predicate returns non-@code{nil} if @var{object} is a valid case | |
1091 | table. | |
1092 | @end defun | |
1093 | ||
1094 | @defun set-standard-case-table table | |
1095 | This function makes @var{table} the standard case table, so that it will | |
969fe9b5 | 1096 | be used in any buffers created subsequently. |
869f4785 RS |
1097 | @end defun |
1098 | ||
1099 | @defun standard-case-table | |
1100 | This returns the standard case table. | |
1101 | @end defun | |
1102 | ||
1103 | @defun current-case-table | |
1104 | This function returns the current buffer's case table. | |
1105 | @end defun | |
1106 | ||
1107 | @defun set-case-table table | |
1108 | This sets the current buffer's case table to @var{table}. | |
1109 | @end defun | |
1110 | ||
45948ea1 CY |
1111 | @defmac with-case-table table body@dots{} |
1112 | The @code{with-case-table} macro saves the current case table, makes | |
1113 | @var{table} the current case table, evaluates the @var{body} forms, | |
1114 | and finally restores the case table. The return value is the value of | |
1115 | the last form in @var{body}. The case table is restored even in case | |
1116 | of an abnormal exit via @code{throw} or error (@pxref{Nonlocal | |
1117 | Exits}). | |
1118 | @end defmac | |
1119 | ||
1e8f1e2f RS |
1120 | Some language environments may modify the case conversions of |
1121 | @acronym{ASCII} characters; for example, in the Turkish language | |
1122 | environment, the @acronym{ASCII} character @samp{I} is downcased into | |
1123 | a Turkish ``dotless i''. This can interfere with code that requires | |
1124 | ordinary ASCII case conversion, such as implementations of | |
1125 | @acronym{ASCII}-based network protocols. In that case, use the | |
1126 | @code{with-case-table} macro with the variable @var{ascii-case-table}, | |
1127 | which stores the unmodified case table for the @acronym{ASCII} | |
1128 | character set. | |
45948ea1 CY |
1129 | |
1130 | @defvar ascii-case-table | |
1e8f1e2f | 1131 | The case table for the @acronym{ASCII} character set. This should not be |
45948ea1 CY |
1132 | modified by any language environment settings. |
1133 | @end defvar | |
1134 | ||
869f4785 | 1135 | The following three functions are convenient subroutines for packages |
ad800164 | 1136 | that define non-@acronym{ASCII} character sets. They modify the specified |
f9f59935 | 1137 | case table @var{case-table}; they also modify the standard syntax table. |
969fe9b5 RS |
1138 | @xref{Syntax Tables}. Normally you would use these functions to change |
1139 | the standard case table. | |
869f4785 | 1140 | |
f9f59935 | 1141 | @defun set-case-syntax-pair uc lc case-table |
869f4785 RS |
1142 | This function specifies a pair of corresponding letters, one upper case |
1143 | and one lower case. | |
1144 | @end defun | |
1145 | ||
f9f59935 | 1146 | @defun set-case-syntax-delims l r case-table |
869f4785 RS |
1147 | This function makes characters @var{l} and @var{r} a matching pair of |
1148 | case-invariant delimiters. | |
1149 | @end defun | |
1150 | ||
f9f59935 | 1151 | @defun set-case-syntax char syntax case-table |
869f4785 RS |
1152 | This function makes @var{char} case-invariant, with syntax |
1153 | @var{syntax}. | |
1154 | @end defun | |
1155 | ||
1156 | @deffn Command describe-buffer-case-table | |
1157 | This command displays a description of the contents of the current | |
1158 | buffer's case table. | |
1159 | @end deffn | |
ab5796a9 MB |
1160 | |
1161 | @ignore | |
1162 | arch-tag: 700b8e95-7aa5-4b52-9eb3-8f2e1ea152b4 | |
1163 | @end ignore |