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