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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
acaf905b | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 |
d24880de | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 6 | @node Strings and Characters |
b8d4c8d0 GM |
7 | @chapter Strings and Characters |
8 | @cindex strings | |
9 | @cindex character arrays | |
10 | @cindex characters | |
11 | @cindex bytes | |
12 | ||
13 | A string in Emacs Lisp is an array that contains an ordered sequence | |
14 | of characters. Strings are used as names of symbols, buffers, and | |
15 | files; to send messages to users; to hold text being copied between | |
16 | buffers; and for many other purposes. Because strings are so important, | |
17 | Emacs Lisp has many functions expressly for manipulating them. Emacs | |
18 | Lisp programs use strings more often than individual characters. | |
19 | ||
20 | @xref{Strings of Events}, for special considerations for strings of | |
21 | keyboard character events. | |
22 | ||
23 | @menu | |
24 | * Basics: String Basics. Basic properties of strings and characters. | |
25 | * Predicates for Strings:: Testing whether an object is a string or char. | |
26 | * Creating Strings:: Functions to allocate new strings. | |
27 | * Modifying Strings:: Altering the contents of an existing string. | |
28 | * Text Comparison:: Comparing characters or strings. | |
29 | * String Conversion:: Converting to and from characters and strings. | |
30 | * Formatting Strings:: @code{format}: Emacs's analogue of @code{printf}. | |
31 | * Case Conversion:: Case conversion functions. | |
d24880de | 32 | * Case Tables:: Customizing case conversion. |
b8d4c8d0 GM |
33 | @end menu |
34 | ||
35 | @node String Basics | |
36 | @section String and Character Basics | |
37 | ||
48de8b12 CY |
38 | A character is a Lisp object which represents a single character of |
39 | text. In Emacs Lisp, characters are simply integers; whether an | |
40 | integer is a character or not is determined only by how it is used. | |
41 | @xref{Character Codes}, for details about character representation in | |
42 | Emacs. | |
43 | ||
44 | A string is a fixed sequence of characters. It is a type of | |
45 | sequence called a @dfn{array}, meaning that its length is fixed and | |
46 | cannot be altered once it is created (@pxref{Sequences Arrays | |
47 | Vectors}). Unlike in C, Emacs Lisp strings are @emph{not} terminated | |
48 | by a distinguished character code. | |
b8d4c8d0 GM |
49 | |
50 | Since strings are arrays, and therefore sequences as well, you can | |
48de8b12 CY |
51 | operate on them with the general array and sequence functions |
52 | documented in @ref{Sequences Arrays Vectors}. For example, you can | |
53 | access or change individual characters in a string using the functions | |
54 | @code{aref} and @code{aset} (@pxref{Array Functions}). However, note | |
55 | that @code{length} should @emph{not} be used for computing the width | |
56 | of a string on display; use @code{string-width} (@pxref{Width}) | |
57 | instead. | |
58 | ||
59 | There are two text representations for non-@acronym{ASCII} | |
60 | characters in Emacs strings (and in buffers): unibyte and multibyte. | |
61 | For most Lisp programming, you don't need to be concerned with these | |
62 | two representations. @xref{Text Representations}, for details. | |
b8d4c8d0 | 63 | |
5dedd9b5 EZ |
64 | Sometimes key sequences are represented as unibyte strings. When a |
65 | unibyte string is a key sequence, string elements in the range 128 to | |
66 | 255 represent meta characters (which are large integers) rather than | |
8f88eb24 CY |
67 | character codes in the range 128 to 255. Strings cannot hold |
68 | characters that have the hyper, super or alt modifiers; they can hold | |
69 | @acronym{ASCII} control characters, but no other control characters. | |
70 | They do not distinguish case in @acronym{ASCII} control characters. | |
71 | If you want to store such characters in a sequence, such as a key | |
72 | sequence, you must use a vector instead of a string. @xref{Character | |
73 | Type}, for more information about keyboard input characters. | |
b8d4c8d0 GM |
74 | |
75 | Strings are useful for holding regular expressions. You can also | |
76 | match regular expressions against strings with @code{string-match} | |
77 | (@pxref{Regexp Search}). The functions @code{match-string} | |
78 | (@pxref{Simple Match Data}) and @code{replace-match} (@pxref{Replacing | |
79 | Match}) are useful for decomposing and modifying strings after | |
80 | matching regular expressions against them. | |
81 | ||
82 | Like a buffer, a string can contain text properties for the characters | |
83 | in it, as well as the characters themselves. @xref{Text Properties}. | |
84 | All the Lisp primitives that copy text from strings to buffers or other | |
85 | strings also copy the properties of the characters being copied. | |
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. | |
90 | @xref{Non-ASCII Characters}, for functions to convert between text | |
91 | representations and to encode and decode character codes. | |
92 | ||
93 | @node Predicates for Strings | |
48de8b12 | 94 | @section Predicates for Strings |
b8d4c8d0 GM |
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 | |
100 | This function returns @code{t} if @var{object} is a string, @code{nil} | |
101 | otherwise. | |
102 | @end defun | |
103 | ||
104 | @defun string-or-null-p object | |
8c641f06 | 105 | This function returns @code{t} if @var{object} is a string or |
638a2457 | 106 | @code{nil}. It returns @code{nil} otherwise. |
b8d4c8d0 GM |
107 | @end defun |
108 | ||
109 | @defun char-or-string-p object | |
110 | This function returns @code{t} if @var{object} is a string or a | |
111 | character (i.e., an integer), @code{nil} otherwise. | |
112 | @end defun | |
113 | ||
114 | @node Creating Strings | |
115 | @section Creating Strings | |
116 | ||
117 | The following functions create strings, either from scratch, or by | |
118 | putting strings together, or by taking them apart. | |
119 | ||
120 | @defun make-string count character | |
121 | This function returns a string made up of @var{count} repetitions of | |
122 | @var{character}. If @var{count} is negative, an error is signaled. | |
123 | ||
124 | @example | |
125 | (make-string 5 ?x) | |
126 | @result{} "xxxxx" | |
127 | (make-string 0 ?x) | |
128 | @result{} "" | |
129 | @end example | |
130 | ||
3e99b825 CY |
131 | Other functions to compare with this one include @code{make-vector} |
132 | (@pxref{Vectors}) and @code{make-list} (@pxref{Building Lists}). | |
b8d4c8d0 GM |
133 | @end defun |
134 | ||
135 | @defun string &rest characters | |
136 | This returns a string containing the characters @var{characters}. | |
137 | ||
138 | @example | |
139 | (string ?a ?b ?c) | |
140 | @result{} "abc" | |
141 | @end example | |
142 | @end defun | |
143 | ||
144 | @defun substring string start &optional end | |
145 | This function returns a new string which consists of those characters | |
146 | from @var{string} in the range from (and including) the character at the | |
147 | index @var{start} up to (but excluding) the character at the index | |
148 | @var{end}. The first character is at index zero. | |
149 | ||
150 | @example | |
151 | @group | |
152 | (substring "abcdefg" 0 3) | |
153 | @result{} "abc" | |
154 | @end group | |
155 | @end example | |
156 | ||
157 | @noindent | |
8f88eb24 CY |
158 | In the above example, the index for @samp{a} is 0, the index for |
159 | @samp{b} is 1, and the index for @samp{c} is 2. The index 3---which | |
a86cd395 JB |
160 | is the fourth character in the string---marks the character position |
161 | up to which the substring is copied. Thus, @samp{abc} is copied from | |
162 | the string @code{"abcdefg"}. | |
b8d4c8d0 GM |
163 | |
164 | A negative number counts from the end of the string, so that @minus{}1 | |
165 | signifies the index of the last character of the string. For example: | |
166 | ||
167 | @example | |
168 | @group | |
169 | (substring "abcdefg" -3 -1) | |
170 | @result{} "ef" | |
171 | @end group | |
172 | @end example | |
173 | ||
174 | @noindent | |
175 | In this example, the index for @samp{e} is @minus{}3, the index for | |
176 | @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. | |
177 | Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. | |
178 | ||
179 | When @code{nil} is used for @var{end}, it stands for the length of the | |
180 | string. Thus, | |
181 | ||
182 | @example | |
183 | @group | |
184 | (substring "abcdefg" -3 nil) | |
185 | @result{} "efg" | |
186 | @end group | |
187 | @end example | |
188 | ||
189 | Omitting the argument @var{end} is equivalent to specifying @code{nil}. | |
190 | It follows that @code{(substring @var{string} 0)} returns a copy of all | |
191 | of @var{string}. | |
192 | ||
193 | @example | |
194 | @group | |
195 | (substring "abcdefg" 0) | |
196 | @result{} "abcdefg" | |
197 | @end group | |
198 | @end example | |
199 | ||
200 | @noindent | |
201 | But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence | |
202 | Functions}). | |
203 | ||
204 | If the characters copied from @var{string} have text properties, the | |
205 | properties are copied into the new string also. @xref{Text Properties}. | |
206 | ||
207 | @code{substring} also accepts a vector for the first argument. | |
208 | For example: | |
209 | ||
210 | @example | |
211 | (substring [a b (c) "d"] 1 3) | |
212 | @result{} [b (c)] | |
213 | @end example | |
214 | ||
215 | A @code{wrong-type-argument} error is signaled if @var{start} is not | |
216 | an integer or if @var{end} is neither an integer nor @code{nil}. An | |
217 | @code{args-out-of-range} error is signaled if @var{start} indicates a | |
218 | character following @var{end}, or if either integer is out of range | |
219 | for @var{string}. | |
220 | ||
221 | Contrast this function with @code{buffer-substring} (@pxref{Buffer | |
222 | Contents}), which returns a string containing a portion of the text in | |
223 | the current buffer. The beginning of a string is at index 0, but the | |
224 | beginning of a buffer is at index 1. | |
225 | @end defun | |
226 | ||
227 | @defun substring-no-properties string &optional start end | |
228 | This works like @code{substring} but discards all text properties from | |
229 | the value. Also, @var{start} may be omitted or @code{nil}, which is | |
230 | equivalent to 0. Thus, @w{@code{(substring-no-properties | |
231 | @var{string})}} returns a copy of @var{string}, with all text | |
232 | properties removed. | |
233 | @end defun | |
234 | ||
235 | @defun concat &rest sequences | |
236 | @cindex copying strings | |
237 | @cindex concatenating strings | |
238 | This function returns a new string consisting of the characters in the | |
239 | arguments passed to it (along with their text properties, if any). The | |
240 | arguments may be strings, lists of numbers, or vectors of numbers; they | |
241 | are not themselves changed. If @code{concat} receives no arguments, it | |
242 | returns an empty string. | |
243 | ||
244 | @example | |
245 | (concat "abc" "-def") | |
246 | @result{} "abc-def" | |
247 | (concat "abc" (list 120 121) [122]) | |
248 | @result{} "abcxyz" | |
249 | ;; @r{@code{nil} is an empty sequence.} | |
250 | (concat "abc" nil "-def") | |
251 | @result{} "abc-def" | |
252 | (concat "The " "quick brown " "fox.") | |
253 | @result{} "The quick brown fox." | |
254 | (concat) | |
255 | @result{} "" | |
256 | @end example | |
257 | ||
258 | @noindent | |
8f88eb24 CY |
259 | This function always constructs a new string that is not @code{eq} to |
260 | any existing string, except when the result is the empty string (to | |
261 | save space, Emacs makes only one empty multibyte string). | |
b8d4c8d0 GM |
262 | |
263 | For information about other concatenation functions, see the | |
264 | description of @code{mapconcat} in @ref{Mapping Functions}, | |
265 | @code{vconcat} in @ref{Vector Functions}, and @code{append} in @ref{Building | |
fd6f900c EZ |
266 | Lists}. For concatenating individual command-line arguments into a |
267 | string to be used as a shell command, see @ref{Shell Arguments, | |
268 | combine-and-quote-strings}. | |
b8d4c8d0 GM |
269 | @end defun |
270 | ||
271 | @defun split-string string &optional separators omit-nulls | |
8f88eb24 CY |
272 | This function splits @var{string} into substrings based on the regular |
273 | expression @var{separators} (@pxref{Regular Expressions}). Each match | |
274 | for @var{separators} defines a splitting point; the substrings between | |
275 | splitting points are made into a list, which is returned. | |
b8d4c8d0 | 276 | |
8f88eb24 CY |
277 | If @var{omit-nulls} is @code{nil} (or omitted), the result contains |
278 | null strings whenever there are two consecutive matches for | |
279 | @var{separators}, or a match is adjacent to the beginning or end of | |
280 | @var{string}. If @var{omit-nulls} is @code{t}, these null strings are | |
281 | omitted from the result. | |
b8d4c8d0 | 282 | |
8f88eb24 CY |
283 | If @var{separators} is @code{nil} (or omitted), the default is the |
284 | value of @code{split-string-default-separators}. | |
b8d4c8d0 GM |
285 | |
286 | As a special case, when @var{separators} is @code{nil} (or omitted), | |
287 | null strings are always omitted from the result. Thus: | |
288 | ||
289 | @example | |
290 | (split-string " two words ") | |
291 | @result{} ("two" "words") | |
292 | @end example | |
293 | ||
294 | The result is not @code{("" "two" "words" "")}, which would rarely be | |
295 | useful. If you need such a result, use an explicit value for | |
296 | @var{separators}: | |
297 | ||
298 | @example | |
299 | (split-string " two words " | |
300 | split-string-default-separators) | |
301 | @result{} ("" "two" "words" "") | |
302 | @end example | |
303 | ||
304 | More examples: | |
305 | ||
306 | @example | |
307 | (split-string "Soup is good food" "o") | |
308 | @result{} ("S" "up is g" "" "d f" "" "d") | |
309 | (split-string "Soup is good food" "o" t) | |
310 | @result{} ("S" "up is g" "d f" "d") | |
311 | (split-string "Soup is good food" "o+") | |
312 | @result{} ("S" "up is g" "d f" "d") | |
313 | @end example | |
314 | ||
315 | Empty matches do count, except that @code{split-string} will not look | |
316 | for a final empty match when it already reached the end of the string | |
317 | using a non-empty match or when @var{string} is empty: | |
318 | ||
319 | @example | |
320 | (split-string "aooob" "o*") | |
321 | @result{} ("" "a" "" "b" "") | |
322 | (split-string "ooaboo" "o*") | |
323 | @result{} ("" "" "a" "b" "") | |
324 | (split-string "" "") | |
325 | @result{} ("") | |
326 | @end example | |
327 | ||
328 | However, when @var{separators} can match the empty string, | |
329 | @var{omit-nulls} is usually @code{t}, so that the subtleties in the | |
330 | three previous examples are rarely relevant: | |
331 | ||
332 | @example | |
333 | (split-string "Soup is good food" "o*" t) | |
334 | @result{} ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") | |
335 | (split-string "Nice doggy!" "" t) | |
336 | @result{} ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") | |
337 | (split-string "" "" t) | |
338 | @result{} nil | |
339 | @end example | |
340 | ||
341 | Somewhat odd, but predictable, behavior can occur for certain | |
342 | ``non-greedy'' values of @var{separators} that can prefer empty | |
343 | matches over non-empty matches. Again, such values rarely occur in | |
344 | practice: | |
345 | ||
346 | @example | |
347 | (split-string "ooo" "o*" t) | |
348 | @result{} nil | |
349 | (split-string "ooo" "\\|o+" t) | |
350 | @result{} ("o" "o" "o") | |
351 | @end example | |
fd6f900c | 352 | |
4bb49a92 EZ |
353 | If you need to split a string into a list of individual command-line |
354 | arguments suitable for @code{call-process} or @code{start-process}, | |
355 | see @ref{Shell Arguments, split-string-and-unquote}. | |
b8d4c8d0 GM |
356 | @end defun |
357 | ||
358 | @defvar split-string-default-separators | |
359 | The default value of @var{separators} for @code{split-string}. Its | |
360 | usual value is @w{@code{"[ \f\t\n\r\v]+"}}. | |
361 | @end defvar | |
362 | ||
363 | @node Modifying Strings | |
364 | @section Modifying Strings | |
365 | ||
366 | The most basic way to alter the contents of an existing string is with | |
367 | @code{aset} (@pxref{Array Functions}). @code{(aset @var{string} | |
368 | @var{idx} @var{char})} stores @var{char} into @var{string} at index | |
369 | @var{idx}. Each character occupies one or more bytes, and if @var{char} | |
370 | needs a different number of bytes from the character already present at | |
371 | that index, @code{aset} signals an error. | |
372 | ||
373 | A more powerful function is @code{store-substring}: | |
374 | ||
375 | @defun store-substring string idx obj | |
376 | This function alters part of the contents of the string @var{string}, by | |
377 | storing @var{obj} starting at index @var{idx}. The argument @var{obj} | |
378 | may be either a character or a (smaller) string. | |
379 | ||
380 | Since it is impossible to change the length of an existing string, it is | |
381 | an error if @var{obj} doesn't fit within @var{string}'s actual length, | |
382 | or if any new character requires a different number of bytes from the | |
383 | character currently present at that point in @var{string}. | |
384 | @end defun | |
385 | ||
386 | To clear out a string that contained a password, use | |
387 | @code{clear-string}: | |
388 | ||
389 | @defun clear-string string | |
390 | This makes @var{string} a unibyte string and clears its contents to | |
391 | zeros. It may also change @var{string}'s length. | |
392 | @end defun | |
393 | ||
394 | @need 2000 | |
395 | @node Text Comparison | |
396 | @section Comparison of Characters and Strings | |
397 | @cindex string equality | |
398 | ||
399 | @defun char-equal character1 character2 | |
400 | This function returns @code{t} if the arguments represent the same | |
401 | character, @code{nil} otherwise. This function ignores differences | |
402 | in case if @code{case-fold-search} is non-@code{nil}. | |
403 | ||
404 | @example | |
405 | (char-equal ?x ?x) | |
406 | @result{} t | |
407 | (let ((case-fold-search nil)) | |
408 | (char-equal ?x ?X)) | |
409 | @result{} nil | |
410 | @end example | |
411 | @end defun | |
412 | ||
413 | @defun string= string1 string2 | |
414 | This function returns @code{t} if the characters of the two strings | |
415 | match exactly. Symbols are also allowed as arguments, in which case | |
31cbea1d CY |
416 | the symbol names are used. Case is always significant, regardless of |
417 | @code{case-fold-search}. | |
418 | ||
419 | This function is equivalent to @code{equal} for comparing two strings | |
420 | (@pxref{Equality Predicates}). In particular, the text properties of | |
421 | the two strings are ignored. But if either argument is not a string | |
422 | or symbol, an error is signaled. | |
b8d4c8d0 GM |
423 | |
424 | @example | |
425 | (string= "abc" "abc") | |
426 | @result{} t | |
427 | (string= "abc" "ABC") | |
428 | @result{} nil | |
429 | (string= "ab" "ABC") | |
430 | @result{} nil | |
431 | @end example | |
432 | ||
b8d4c8d0 GM |
433 | For technical reasons, a unibyte and a multibyte string are |
434 | @code{equal} if and only if they contain the same sequence of | |
435 | character codes and all these codes are either in the range 0 through | |
436 | 127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}). | |
8f88eb24 CY |
437 | However, when a unibyte string is converted to a multibyte string, all |
438 | characters with codes in the range 160 through 255 are converted to | |
439 | characters with higher codes, whereas @acronym{ASCII} characters | |
b8d4c8d0 GM |
440 | remain unchanged. Thus, a unibyte string and its conversion to |
441 | multibyte are only @code{equal} if the string is all @acronym{ASCII}. | |
442 | Character codes 160 through 255 are not entirely proper in multibyte | |
443 | text, even though they can occur. As a consequence, the situation | |
444 | where a unibyte and a multibyte string are @code{equal} without both | |
445 | being all @acronym{ASCII} is a technical oddity that very few Emacs | |
446 | Lisp programmers ever get confronted with. @xref{Text | |
447 | Representations}. | |
448 | @end defun | |
449 | ||
450 | @defun string-equal string1 string2 | |
451 | @code{string-equal} is another name for @code{string=}. | |
452 | @end defun | |
453 | ||
454 | @cindex lexical comparison | |
455 | @defun string< string1 string2 | |
456 | @c (findex string< causes problems for permuted index!!) | |
457 | This function compares two strings a character at a time. It | |
458 | scans both the strings at the same time to find the first pair of corresponding | |
459 | characters that do not match. If the lesser character of these two is | |
460 | the character from @var{string1}, then @var{string1} is less, and this | |
461 | function returns @code{t}. If the lesser character is the one from | |
462 | @var{string2}, then @var{string1} is greater, and this function returns | |
463 | @code{nil}. If the two strings match entirely, the value is @code{nil}. | |
464 | ||
465 | Pairs of characters are compared according to their character codes. | |
466 | Keep in mind that lower case letters have higher numeric values in the | |
467 | @acronym{ASCII} character set than their upper case counterparts; digits and | |
468 | many punctuation characters have a lower numeric value than upper case | |
469 | letters. An @acronym{ASCII} character is less than any non-@acronym{ASCII} | |
470 | character; a unibyte non-@acronym{ASCII} character is always less than any | |
471 | multibyte non-@acronym{ASCII} character (@pxref{Text Representations}). | |
472 | ||
473 | @example | |
474 | @group | |
475 | (string< "abc" "abd") | |
476 | @result{} t | |
477 | (string< "abd" "abc") | |
478 | @result{} nil | |
479 | (string< "123" "abc") | |
480 | @result{} t | |
481 | @end group | |
482 | @end example | |
483 | ||
484 | When the strings have different lengths, and they match up to the | |
485 | length of @var{string1}, then the result is @code{t}. If they match up | |
486 | to the length of @var{string2}, the result is @code{nil}. A string of | |
487 | no characters is less than any other string. | |
488 | ||
489 | @example | |
490 | @group | |
491 | (string< "" "abc") | |
492 | @result{} t | |
493 | (string< "ab" "abc") | |
494 | @result{} t | |
495 | (string< "abc" "") | |
496 | @result{} nil | |
497 | (string< "abc" "ab") | |
498 | @result{} nil | |
499 | (string< "" "") | |
500 | @result{} nil | |
501 | @end group | |
502 | @end example | |
503 | ||
504 | Symbols are also allowed as arguments, in which case their print names | |
505 | are used. | |
506 | @end defun | |
507 | ||
508 | @defun string-lessp string1 string2 | |
509 | @code{string-lessp} is another name for @code{string<}. | |
510 | @end defun | |
511 | ||
c8f6ec5c GM |
512 | @defun string-prefix-p string1 string2 &optional ignore-case |
513 | This function returns non-@code{nil} if @var{string1} is a prefix of | |
514 | @var{string2}; i.e., if @var{string2} starts with @var{string1}. If | |
515 | the optional argument @var{ignore-case} is non-@code{nil}, the | |
516 | comparison ignores case differences. | |
517 | @end defun | |
518 | ||
b8d4c8d0 GM |
519 | @defun compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case |
520 | This function compares the specified part of @var{string1} with the | |
521 | specified part of @var{string2}. The specified part of @var{string1} | |
522 | runs from index @var{start1} up to index @var{end1} (@code{nil} means | |
523 | the end of the string). The specified part of @var{string2} runs from | |
524 | index @var{start2} up to index @var{end2} (@code{nil} means the end of | |
525 | the string). | |
526 | ||
527 | The strings are both converted to multibyte for the comparison | |
528 | (@pxref{Text Representations}) so that a unibyte string and its | |
529 | conversion to multibyte are always regarded as equal. If | |
530 | @var{ignore-case} is non-@code{nil}, then case is ignored, so that | |
531 | upper case letters can be equal to lower case letters. | |
532 | ||
533 | If the specified portions of the two strings match, the value is | |
534 | @code{t}. Otherwise, the value is an integer which indicates how many | |
535 | leading characters agree, and which string is less. Its absolute value | |
536 | is one plus the number of characters that agree at the beginning of the | |
537 | two strings. The sign is negative if @var{string1} (or its specified | |
538 | portion) is less. | |
539 | @end defun | |
540 | ||
541 | @defun assoc-string key alist &optional case-fold | |
542 | This function works like @code{assoc}, except that @var{key} must be a | |
543 | string or symbol, and comparison is done using @code{compare-strings}. | |
544 | Symbols are converted to strings before testing. | |
545 | If @var{case-fold} is non-@code{nil}, it ignores case differences. | |
546 | Unlike @code{assoc}, this function can also match elements of the alist | |
547 | that are strings or symbols rather than conses. In particular, @var{alist} can | |
548 | be a list of strings or symbols rather than an actual alist. | |
549 | @xref{Association Lists}. | |
550 | @end defun | |
551 | ||
8f88eb24 | 552 | See also the function @code{compare-buffer-substrings} in |
b8d4c8d0 GM |
553 | @ref{Comparing Text}, for a way to compare text in buffers. The |
554 | function @code{string-match}, which matches a regular expression | |
555 | against a string, can be used for a kind of string comparison; see | |
556 | @ref{Regexp Search}. | |
557 | ||
558 | @node String Conversion | |
b8d4c8d0 GM |
559 | @section Conversion of Characters and Strings |
560 | @cindex conversion of strings | |
561 | ||
8f88eb24 CY |
562 | This section describes functions for converting between characters, |
563 | strings and integers. @code{format} (@pxref{Formatting Strings}) and | |
564 | @code{prin1-to-string} (@pxref{Output Functions}) can also convert | |
565 | Lisp objects into strings. @code{read-from-string} (@pxref{Input | |
566 | Functions}) can ``convert'' a string representation of a Lisp object | |
e4021ec1 SM |
567 | into an object. The functions @code{string-to-multibyte} and |
568 | @code{string-to-unibyte} convert the text representation of a string | |
8f88eb24 | 569 | (@pxref{Converting Representations}). |
b8d4c8d0 GM |
570 | |
571 | @xref{Documentation}, for functions that produce textual descriptions | |
572 | of text characters and general input events | |
573 | (@code{single-key-description} and @code{text-char-description}). These | |
574 | are used primarily for making help messages. | |
575 | ||
b8d4c8d0 GM |
576 | @defun number-to-string number |
577 | @cindex integer to string | |
578 | @cindex integer to decimal | |
579 | This function returns a string consisting of the printed base-ten | |
580 | representation of @var{number}, which may be an integer or a floating | |
581 | point number. The returned value starts with a minus sign if the argument is | |
582 | negative. | |
583 | ||
584 | @example | |
585 | (number-to-string 256) | |
586 | @result{} "256" | |
587 | @group | |
588 | (number-to-string -23) | |
589 | @result{} "-23" | |
590 | @end group | |
591 | (number-to-string -23.5) | |
592 | @result{} "-23.5" | |
593 | @end example | |
594 | ||
595 | @cindex int-to-string | |
596 | @code{int-to-string} is a semi-obsolete alias for this function. | |
597 | ||
598 | See also the function @code{format} in @ref{Formatting Strings}. | |
599 | @end defun | |
600 | ||
601 | @defun string-to-number string &optional base | |
602 | @cindex string to number | |
603 | This function returns the numeric value of the characters in | |
604 | @var{string}. If @var{base} is non-@code{nil}, it must be an integer | |
605 | between 2 and 16 (inclusive), and integers are converted in that base. | |
606 | If @var{base} is @code{nil}, then base ten is used. Floating point | |
607 | conversion only works in base ten; we have not implemented other | |
608 | radices for floating point numbers, because that would be much more | |
609 | work and does not seem useful. If @var{string} looks like an integer | |
610 | but its value is too large to fit into a Lisp integer, | |
611 | @code{string-to-number} returns a floating point result. | |
612 | ||
613 | The parsing skips spaces and tabs at the beginning of @var{string}, | |
614 | then reads as much of @var{string} as it can interpret as a number in | |
615 | the given base. (On some systems it ignores other whitespace at the | |
616 | beginning, not just spaces and tabs.) If the first character after | |
617 | the ignored whitespace is neither a digit in the given base, nor a | |
618 | plus or minus sign, nor the leading dot of a floating point number, | |
619 | this function returns 0. | |
620 | ||
621 | @example | |
622 | (string-to-number "256") | |
623 | @result{} 256 | |
624 | (string-to-number "25 is a perfect square.") | |
625 | @result{} 25 | |
626 | (string-to-number "X256") | |
627 | @result{} 0 | |
628 | (string-to-number "-4.5") | |
629 | @result{} -4.5 | |
630 | (string-to-number "1e5") | |
631 | @result{} 100000.0 | |
632 | @end example | |
633 | ||
634 | @findex string-to-int | |
635 | @code{string-to-int} is an obsolete alias for this function. | |
3e99b825 CY |
636 | @end defun |
637 | ||
638 | @defun char-to-string character | |
639 | @cindex character to string | |
640 | This function returns a new string containing one character, | |
641 | @var{character}. This function is semi-obsolete because the function | |
642 | @code{string} is more general. @xref{Creating Strings}. | |
643 | @end defun | |
644 | ||
645 | @defun string-to-char string | |
646 | This function returns the first character in @var{string}. This | |
647 | mostly identical to @code{(aref string 0)}, except that it returns 0 | |
648 | if the string is empty. (The value is also 0 when the first character | |
649 | of @var{string} is the null character, @acronym{ASCII} code 0.) This | |
650 | function may be eliminated in the future if it does not seem useful | |
651 | enough to retain. | |
b8d4c8d0 GM |
652 | @end defun |
653 | ||
654 | Here are some other functions that can convert to or from a string: | |
655 | ||
656 | @table @code | |
657 | @item concat | |
3e99b825 | 658 | This function converts a vector or a list into a string. |
b8d4c8d0 GM |
659 | @xref{Creating Strings}. |
660 | ||
661 | @item vconcat | |
3e99b825 | 662 | This function converts a string into a vector. @xref{Vector |
b8d4c8d0 GM |
663 | Functions}. |
664 | ||
665 | @item append | |
3e99b825 CY |
666 | This function converts a string into a list. @xref{Building Lists}. |
667 | ||
668 | @item byte-to-string | |
669 | This function converts a byte of character data into a unibyte string. | |
670 | @xref{Converting Representations}. | |
b8d4c8d0 GM |
671 | @end table |
672 | ||
673 | @node Formatting Strings | |
b8d4c8d0 GM |
674 | @section Formatting Strings |
675 | @cindex formatting strings | |
676 | @cindex strings, formatting them | |
677 | ||
8f88eb24 CY |
678 | @dfn{Formatting} means constructing a string by substituting |
679 | computed values at various places in a constant string. This constant | |
680 | string controls how the other values are printed, as well as where | |
681 | they appear; it is called a @dfn{format string}. | |
b8d4c8d0 GM |
682 | |
683 | Formatting is often useful for computing messages to be displayed. In | |
684 | fact, the functions @code{message} and @code{error} provide the same | |
685 | formatting feature described here; they differ from @code{format} only | |
686 | in how they use the result of formatting. | |
687 | ||
688 | @defun format string &rest objects | |
689 | This function returns a new string that is made by copying | |
690 | @var{string} and then replacing any format specification | |
691 | in the copy with encodings of the corresponding @var{objects}. The | |
692 | arguments @var{objects} are the computed values to be formatted. | |
693 | ||
694 | The characters in @var{string}, other than the format specifications, | |
695 | are copied directly into the output, including their text properties, | |
696 | if any. | |
697 | @end defun | |
698 | ||
699 | @cindex @samp{%} in format | |
700 | @cindex format specification | |
701 | A format specification is a sequence of characters beginning with a | |
702 | @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the | |
703 | @code{format} function replaces it with the printed representation of | |
704 | one of the values to be formatted (one of the arguments @var{objects}). | |
705 | For example: | |
706 | ||
707 | @example | |
708 | @group | |
709 | (format "The value of fill-column is %d." fill-column) | |
710 | @result{} "The value of fill-column is 72." | |
711 | @end group | |
712 | @end example | |
713 | ||
714 | Since @code{format} interprets @samp{%} characters as format | |
715 | specifications, you should @emph{never} pass an arbitrary string as | |
716 | the first argument. This is particularly true when the string is | |
717 | generated by some Lisp code. Unless the string is @emph{known} to | |
718 | never include any @samp{%} characters, pass @code{"%s"}, described | |
719 | below, as the first argument, and the string as the second, like this: | |
720 | ||
721 | @example | |
722 | (format "%s" @var{arbitrary-string}) | |
723 | @end example | |
724 | ||
725 | If @var{string} contains more than one format specification, the | |
726 | format specifications correspond to successive values from | |
727 | @var{objects}. Thus, the first format specification in @var{string} | |
728 | uses the first such value, the second format specification uses the | |
729 | second such value, and so on. Any extra format specifications (those | |
730 | for which there are no corresponding values) cause an error. Any | |
731 | extra values to be formatted are ignored. | |
732 | ||
733 | Certain format specifications require values of particular types. If | |
734 | you supply a value that doesn't fit the requirements, an error is | |
735 | signaled. | |
736 | ||
737 | Here is a table of valid format specifications: | |
738 | ||
739 | @table @samp | |
740 | @item %s | |
741 | Replace the specification with the printed representation of the object, | |
742 | made without quoting (that is, using @code{princ}, not | |
743 | @code{prin1}---@pxref{Output Functions}). Thus, strings are represented | |
744 | by their contents alone, with no @samp{"} characters, and symbols appear | |
745 | without @samp{\} characters. | |
746 | ||
747 | If the object is a string, its text properties are | |
748 | copied into the output. The text properties of the @samp{%s} itself | |
749 | are also copied, but those of the object take priority. | |
750 | ||
751 | @item %S | |
752 | Replace the specification with the printed representation of the object, | |
753 | made with quoting (that is, using @code{prin1}---@pxref{Output | |
754 | Functions}). Thus, strings are enclosed in @samp{"} characters, and | |
755 | @samp{\} characters appear where necessary before special characters. | |
756 | ||
757 | @item %o | |
758 | @cindex integer to octal | |
759 | Replace the specification with the base-eight representation of an | |
760 | integer. | |
761 | ||
762 | @item %d | |
763 | Replace the specification with the base-ten representation of an | |
764 | integer. | |
765 | ||
766 | @item %x | |
767 | @itemx %X | |
768 | @cindex integer to hexadecimal | |
769 | Replace the specification with the base-sixteen representation of an | |
770 | integer. @samp{%x} uses lower case and @samp{%X} uses upper case. | |
771 | ||
772 | @item %c | |
773 | Replace the specification with the character which is the value given. | |
774 | ||
775 | @item %e | |
776 | Replace the specification with the exponential notation for a floating | |
777 | point number. | |
778 | ||
779 | @item %f | |
780 | Replace the specification with the decimal-point notation for a floating | |
781 | point number. | |
782 | ||
783 | @item %g | |
784 | Replace the specification with notation for a floating point number, | |
785 | using either exponential notation or decimal-point notation, whichever | |
786 | is shorter. | |
787 | ||
788 | @item %% | |
789 | Replace the specification with a single @samp{%}. This format | |
790 | specification is unusual in that it does not use a value. For example, | |
791 | @code{(format "%% %d" 30)} returns @code{"% 30"}. | |
792 | @end table | |
793 | ||
794 | Any other format character results in an @samp{Invalid format | |
795 | operation} error. | |
796 | ||
797 | Here are several examples: | |
798 | ||
799 | @example | |
800 | @group | |
801 | (format "The name of this buffer is %s." (buffer-name)) | |
802 | @result{} "The name of this buffer is strings.texi." | |
803 | ||
804 | (format "The buffer object prints as %s." (current-buffer)) | |
805 | @result{} "The buffer object prints as strings.texi." | |
806 | ||
807 | (format "The octal value of %d is %o, | |
808 | and the hex value is %x." 18 18 18) | |
809 | @result{} "The octal value of 18 is 22, | |
810 | and the hex value is 12." | |
811 | @end group | |
812 | @end example | |
813 | ||
814 | @cindex field width | |
815 | @cindex padding | |
b20e7c7d CY |
816 | A specification can have a @dfn{width}, which is a decimal number |
817 | between the @samp{%} and the specification character. If the printed | |
818 | representation of the object contains fewer characters than this | |
819 | width, @code{format} extends it with padding. The width specifier is | |
820 | ignored for the @samp{%%} specification. Any padding introduced by | |
821 | the width specifier normally consists of spaces inserted on the left: | |
b8d4c8d0 GM |
822 | |
823 | @example | |
b20e7c7d CY |
824 | (format "%5d is padded on the left with spaces" 123) |
825 | @result{} " 123 is padded on the left with spaces" | |
b8d4c8d0 GM |
826 | @end example |
827 | ||
828 | @noindent | |
829 | If the width is too small, @code{format} does not truncate the | |
830 | object's printed representation. Thus, you can use a width to specify | |
831 | a minimum spacing between columns with no risk of losing information. | |
b20e7c7d CY |
832 | In the following three examples, @samp{%7s} specifies a minimum width |
833 | of 7. In the first case, the string inserted in place of @samp{%7s} | |
834 | has only 3 letters, and needs 4 blank spaces as padding. In the | |
835 | second case, the string @code{"specification"} is 13 letters wide but | |
836 | is not truncated. | |
b8d4c8d0 | 837 | |
b20e7c7d | 838 | @example |
b8d4c8d0 | 839 | @group |
049bcbcb | 840 | (format "The word `%7s' has %d letters in it." |
b8d4c8d0 | 841 | "foo" (length "foo")) |
049bcbcb CY |
842 | @result{} "The word ` foo' has 3 letters in it." |
843 | (format "The word `%7s' has %d letters in it." | |
b8d4c8d0 | 844 | "specification" (length "specification")) |
049bcbcb | 845 | @result{} "The word `specification' has 13 letters in it." |
b8d4c8d0 | 846 | @end group |
b20e7c7d CY |
847 | @end example |
848 | ||
849 | @cindex flags in format specifications | |
850 | Immediately after the @samp{%} and before the optional width | |
851 | specifier, you can also put certain @dfn{flag characters}. | |
852 | ||
853 | The flag @samp{+} inserts a plus sign before a positive number, so | |
854 | that it always has a sign. A space character as flag inserts a space | |
855 | before a positive number. (Otherwise, positive numbers start with the | |
856 | first digit.) These flags are useful for ensuring that positive | |
857 | numbers and negative numbers use the same number of columns. They are | |
858 | ignored except for @samp{%d}, @samp{%e}, @samp{%f}, @samp{%g}, and if | |
859 | both flags are used, @samp{+} takes precedence. | |
860 | ||
861 | The flag @samp{#} specifies an ``alternate form'' which depends on | |
862 | the format in use. For @samp{%o}, it ensures that the result begins | |
863 | with a @samp{0}. For @samp{%x} and @samp{%X}, it prefixes the result | |
864 | with @samp{0x} or @samp{0X}. For @samp{%e}, @samp{%f}, and @samp{%g}, | |
865 | the @samp{#} flag means include a decimal point even if the precision | |
866 | is zero. | |
867 | ||
a9ab721e LMI |
868 | The flag @samp{0} ensures that the padding consists of @samp{0} |
869 | characters instead of spaces. This flag is ignored for non-numerical | |
870 | specification characters like @samp{%s}, @samp{%S} and @samp{%c}. | |
871 | These specification characters accept the @samp{0} flag, but still pad | |
872 | with @emph{spaces}. | |
873 | ||
b20e7c7d CY |
874 | The flag @samp{-} causes the padding inserted by the width |
875 | specifier, if any, to be inserted on the right rather than the left. | |
a9ab721e LMI |
876 | If both @samp{-} and @samp{0} are present, the @samp{0} flag is |
877 | ignored. | |
b8d4c8d0 | 878 | |
b20e7c7d | 879 | @example |
b8d4c8d0 | 880 | @group |
b20e7c7d CY |
881 | (format "%06d is padded on the left with zeros" 123) |
882 | @result{} "000123 is padded on the left with zeros" | |
883 | ||
884 | (format "%-6d is padded on the right" 123) | |
885 | @result{} "123 is padded on the right" | |
886 | ||
b8d4c8d0 GM |
887 | (format "The word `%-7s' actually has %d letters in it." |
888 | "foo" (length "foo")) | |
889 | @result{} "The word `foo ' actually has 3 letters in it." | |
890 | @end group | |
b20e7c7d | 891 | @end example |
b8d4c8d0 GM |
892 | |
893 | @cindex precision in format specifications | |
894 | All the specification characters allow an optional @dfn{precision} | |
895 | before the character (after the width, if present). The precision is | |
896 | a decimal-point @samp{.} followed by a digit-string. For the | |
897 | floating-point specifications (@samp{%e}, @samp{%f}, @samp{%g}), the | |
898 | precision specifies how many decimal places to show; if zero, the | |
899 | decimal-point itself is also omitted. For @samp{%s} and @samp{%S}, | |
900 | the precision truncates the string to the given width, so @samp{%.3s} | |
901 | shows only the first three characters of the representation for | |
902 | @var{object}. Precision has no effect for other specification | |
903 | characters. | |
904 | ||
b8d4c8d0 | 905 | @node Case Conversion |
b8d4c8d0 GM |
906 | @section Case Conversion in Lisp |
907 | @cindex upper case | |
908 | @cindex lower case | |
909 | @cindex character case | |
910 | @cindex case conversion in Lisp | |
911 | ||
912 | The character case functions change the case of single characters or | |
913 | of the contents of strings. The functions normally convert only | |
914 | alphabetic characters (the letters @samp{A} through @samp{Z} and | |
915 | @samp{a} through @samp{z}, as well as non-@acronym{ASCII} letters); other | |
916 | characters are not altered. You can specify a different case | |
917 | conversion mapping by specifying a case table (@pxref{Case Tables}). | |
918 | ||
919 | These functions do not modify the strings that are passed to them as | |
920 | arguments. | |
921 | ||
922 | The examples below use the characters @samp{X} and @samp{x} which have | |
923 | @acronym{ASCII} codes 88 and 120 respectively. | |
924 | ||
925 | @defun downcase string-or-char | |
8f88eb24 CY |
926 | This function converts @var{string-or-char}, which should be either a |
927 | character or a string, to lower case. | |
b8d4c8d0 | 928 | |
8f88eb24 CY |
929 | When @var{string-or-char} is a string, this function returns a new |
930 | string in which each letter in the argument that is upper case is | |
931 | converted to lower case. When @var{string-or-char} is a character, | |
932 | this function returns the corresponding lower case character (an | |
933 | integer); if the original character is lower case, or is not a letter, | |
934 | the return value is equal to the original character. | |
b8d4c8d0 GM |
935 | |
936 | @example | |
937 | (downcase "The cat in the hat") | |
938 | @result{} "the cat in the hat" | |
939 | ||
940 | (downcase ?X) | |
941 | @result{} 120 | |
942 | @end example | |
943 | @end defun | |
944 | ||
945 | @defun upcase string-or-char | |
8f88eb24 CY |
946 | This function converts @var{string-or-char}, which should be either a |
947 | character or a string, to upper case. | |
b8d4c8d0 | 948 | |
8f88eb24 CY |
949 | When @var{string-or-char} is a string, this function returns a new |
950 | string in which each letter in the argument that is lower case is | |
951 | converted to upper case. When @var{string-or-char} is a character, | |
a86cd395 | 952 | this function returns the corresponding upper case character (an |
8f88eb24 CY |
953 | integer); if the original character is upper case, or is not a letter, |
954 | the return value is equal to the original character. | |
b8d4c8d0 GM |
955 | |
956 | @example | |
957 | (upcase "The cat in the hat") | |
958 | @result{} "THE CAT IN THE HAT" | |
959 | ||
960 | (upcase ?x) | |
961 | @result{} 88 | |
962 | @end example | |
963 | @end defun | |
964 | ||
965 | @defun capitalize string-or-char | |
966 | @cindex capitalization | |
967 | This function capitalizes strings or characters. If | |
8f88eb24 CY |
968 | @var{string-or-char} is a string, the function returns a new string |
969 | whose contents are a copy of @var{string-or-char} in which each word | |
970 | has been capitalized. This means that the first character of each | |
b8d4c8d0 GM |
971 | word is converted to upper case, and the rest are converted to lower |
972 | case. | |
973 | ||
974 | The definition of a word is any sequence of consecutive characters that | |
975 | are assigned to the word constituent syntax class in the current syntax | |
976 | table (@pxref{Syntax Class Table}). | |
977 | ||
8f88eb24 CY |
978 | When @var{string-or-char} is a character, this function does the same |
979 | thing as @code{upcase}. | |
b8d4c8d0 GM |
980 | |
981 | @example | |
982 | @group | |
983 | (capitalize "The cat in the hat") | |
984 | @result{} "The Cat In The Hat" | |
985 | @end group | |
986 | ||
987 | @group | |
988 | (capitalize "THE 77TH-HATTED CAT") | |
989 | @result{} "The 77th-Hatted Cat" | |
990 | @end group | |
991 | ||
992 | @group | |
993 | (capitalize ?x) | |
994 | @result{} 88 | |
995 | @end group | |
996 | @end example | |
997 | @end defun | |
998 | ||
999 | @defun upcase-initials string-or-char | |
1000 | If @var{string-or-char} is a string, this function capitalizes the | |
1001 | initials of the words in @var{string-or-char}, without altering any | |
1002 | letters other than the initials. It returns a new string whose | |
1003 | contents are a copy of @var{string-or-char}, in which each word has | |
1004 | had its initial letter converted to upper case. | |
1005 | ||
1006 | The definition of a word is any sequence of consecutive characters that | |
1007 | are assigned to the word constituent syntax class in the current syntax | |
1008 | table (@pxref{Syntax Class Table}). | |
1009 | ||
1010 | When the argument to @code{upcase-initials} is a character, | |
1011 | @code{upcase-initials} has the same result as @code{upcase}. | |
1012 | ||
1013 | @example | |
1014 | @group | |
1015 | (upcase-initials "The CAT in the hAt") | |
1016 | @result{} "The CAT In The HAt" | |
1017 | @end group | |
1018 | @end example | |
1019 | @end defun | |
1020 | ||
1021 | @xref{Text Comparison}, for functions that compare strings; some of | |
1022 | them ignore case differences, or can optionally ignore case differences. | |
1023 | ||
1024 | @node Case Tables | |
1025 | @section The Case Table | |
1026 | ||
1027 | You can customize case conversion by installing a special @dfn{case | |
1028 | table}. A case table specifies the mapping between upper case and lower | |
1029 | case letters. It affects both the case conversion functions for Lisp | |
1030 | objects (see the previous section) and those that apply to text in the | |
1031 | buffer (@pxref{Case Changes}). Each buffer has a case table; there is | |
1032 | also a standard case table which is used to initialize the case table | |
1033 | of new buffers. | |
1034 | ||
1035 | A case table is a char-table (@pxref{Char-Tables}) whose subtype is | |
1036 | @code{case-table}. This char-table maps each character into the | |
1037 | corresponding lower case character. It has three extra slots, which | |
1038 | hold related tables: | |
1039 | ||
1040 | @table @var | |
1041 | @item upcase | |
1042 | The upcase table maps each character into the corresponding upper | |
1043 | case character. | |
1044 | @item canonicalize | |
1045 | The canonicalize table maps all of a set of case-related characters | |
1046 | into a particular member of that set. | |
1047 | @item equivalences | |
1048 | The equivalences table maps each one of a set of case-related characters | |
1049 | into the next character in that set. | |
1050 | @end table | |
1051 | ||
1052 | In simple cases, all you need to specify is the mapping to lower-case; | |
1053 | the three related tables will be calculated automatically from that one. | |
1054 | ||
1055 | For some languages, upper and lower case letters are not in one-to-one | |
1056 | correspondence. There may be two different lower case letters with the | |
1057 | same upper case equivalent. In these cases, you need to specify the | |
1058 | maps for both lower case and upper case. | |
1059 | ||
1060 | The extra table @var{canonicalize} maps each character to a canonical | |
1061 | equivalent; any two characters that are related by case-conversion have | |
1062 | the same canonical equivalent character. For example, since @samp{a} | |
1063 | and @samp{A} are related by case-conversion, they should have the same | |
1064 | canonical equivalent character (which should be either @samp{a} for both | |
1065 | of them, or @samp{A} for both of them). | |
1066 | ||
1067 | The extra table @var{equivalences} is a map that cyclically permutes | |
1068 | each equivalence class (of characters with the same canonical | |
1069 | equivalent). (For ordinary @acronym{ASCII}, this would map @samp{a} into | |
1070 | @samp{A} and @samp{A} into @samp{a}, and likewise for each set of | |
1071 | equivalent characters.) | |
1072 | ||
8f88eb24 | 1073 | When constructing a case table, you can provide @code{nil} for |
b8d4c8d0 GM |
1074 | @var{canonicalize}; then Emacs fills in this slot from the lower case |
1075 | and upper case mappings. You can also provide @code{nil} for | |
1076 | @var{equivalences}; then Emacs fills in this slot from | |
1077 | @var{canonicalize}. In a case table that is actually in use, those | |
8f88eb24 CY |
1078 | components are non-@code{nil}. Do not try to specify |
1079 | @var{equivalences} without also specifying @var{canonicalize}. | |
b8d4c8d0 GM |
1080 | |
1081 | Here are the functions for working with case tables: | |
1082 | ||
1083 | @defun case-table-p object | |
1084 | This predicate returns non-@code{nil} if @var{object} is a valid case | |
1085 | table. | |
1086 | @end defun | |
1087 | ||
1088 | @defun set-standard-case-table table | |
1089 | This function makes @var{table} the standard case table, so that it will | |
1090 | be used in any buffers created subsequently. | |
1091 | @end defun | |
1092 | ||
1093 | @defun standard-case-table | |
1094 | This returns the standard case table. | |
1095 | @end defun | |
1096 | ||
1097 | @defun current-case-table | |
1098 | This function returns the current buffer's case table. | |
1099 | @end defun | |
1100 | ||
1101 | @defun set-case-table table | |
1102 | This sets the current buffer's case table to @var{table}. | |
1103 | @end defun | |
1104 | ||
1105 | @defmac with-case-table table body@dots{} | |
1106 | The @code{with-case-table} macro saves the current case table, makes | |
1107 | @var{table} the current case table, evaluates the @var{body} forms, | |
1108 | and finally restores the case table. The return value is the value of | |
1109 | the last form in @var{body}. The case table is restored even in case | |
1110 | of an abnormal exit via @code{throw} or error (@pxref{Nonlocal | |
1111 | Exits}). | |
1112 | @end defmac | |
1113 | ||
8f88eb24 | 1114 | Some language environments modify the case conversions of |
b8d4c8d0 GM |
1115 | @acronym{ASCII} characters; for example, in the Turkish language |
1116 | environment, the @acronym{ASCII} character @samp{I} is downcased into | |
1117 | a Turkish ``dotless i''. This can interfere with code that requires | |
9fce7eda | 1118 | ordinary @acronym{ASCII} case conversion, such as implementations of |
b8d4c8d0 GM |
1119 | @acronym{ASCII}-based network protocols. In that case, use the |
1120 | @code{with-case-table} macro with the variable @var{ascii-case-table}, | |
1121 | which stores the unmodified case table for the @acronym{ASCII} | |
1122 | character set. | |
1123 | ||
1124 | @defvar ascii-case-table | |
1125 | The case table for the @acronym{ASCII} character set. This should not be | |
1126 | modified by any language environment settings. | |
1127 | @end defvar | |
1128 | ||
1129 | The following three functions are convenient subroutines for packages | |
1130 | that define non-@acronym{ASCII} character sets. They modify the specified | |
1131 | case table @var{case-table}; they also modify the standard syntax table. | |
1132 | @xref{Syntax Tables}. Normally you would use these functions to change | |
1133 | the standard case table. | |
1134 | ||
1135 | @defun set-case-syntax-pair uc lc case-table | |
1136 | This function specifies a pair of corresponding letters, one upper case | |
1137 | and one lower case. | |
1138 | @end defun | |
1139 | ||
1140 | @defun set-case-syntax-delims l r case-table | |
1141 | This function makes characters @var{l} and @var{r} a matching pair of | |
1142 | case-invariant delimiters. | |
1143 | @end defun | |
1144 | ||
1145 | @defun set-case-syntax char syntax case-table | |
1146 | This function makes @var{char} case-invariant, with syntax | |
1147 | @var{syntax}. | |
1148 | @end defun | |
1149 | ||
1150 | @deffn Command describe-buffer-case-table | |
1151 | This command displays a description of the contents of the current | |
1152 | buffer's case table. | |
1153 | @end deffn |