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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/strings | |
6 | @node Strings and Characters, Lists, Numbers, Top | |
7 | @comment node-name, next, previous, up | |
8 | @chapter Strings and Characters | |
9 | @cindex strings | |
10 | @cindex character arrays | |
11 | @cindex characters | |
12 | @cindex bytes | |
13 | ||
14 | A string in Emacs Lisp is an array that contains an ordered sequence | |
15 | of characters. Strings are used as names of symbols, buffers, and | |
16 | files, to send messages to users, to hold text being copied between | |
17 | buffers, and for many other purposes. Because strings are so important, | |
18 | Emacs Lisp has many functions expressly for manipulating them. Emacs | |
19 | Lisp programs use strings more often than individual characters. | |
20 | ||
21 | @xref{Strings of Events}, for special considerations for strings of | |
22 | keyboard character events. | |
23 | ||
24 | @menu | |
25 | * Basics: String Basics. Basic properties of strings and characters. | |
26 | * Predicates for Strings:: Testing whether an object is a string or char. | |
27 | * Creating Strings:: Functions to allocate new strings. | |
28 | * Text Comparison:: Comparing characters or strings. | |
29 | * String Conversion:: Converting characters or strings and vice versa. | |
30 | * Formatting Strings:: @code{format}: Emacs's analog of @code{printf}. | |
31 | * Character Case:: Case conversion functions. | |
32 | * Case Table:: Customizing case conversion. | |
33 | @end menu | |
34 | ||
35 | @node String Basics | |
36 | @section String and Character Basics | |
37 | ||
38 | Strings in Emacs Lisp are arrays that contain an ordered sequence of | |
39 | characters. Characters are represented in Emacs Lisp as integers; | |
40 | whether an integer was intended as a character or not is determined only | |
41 | by how it is used. Thus, strings really contain integers. | |
42 | ||
43 | The length of a string (like any array) is fixed and independent of | |
44 | the string contents, and cannot be altered. Strings in Lisp are | |
45 | @emph{not} terminated by a distinguished character code. (By contrast, | |
46 | strings in C are terminated by a character with @sc{ASCII} code 0.) | |
47 | This means that any character, including the null character (@sc{ASCII} | |
48 | code 0), is a valid element of a string.@refill | |
49 | ||
50 | Since strings are considered arrays, you can operate on them with the | |
51 | general array functions. (@xref{Sequences Arrays Vectors}.) For | |
52 | example, you can access or change individual characters in a string | |
53 | using the functions @code{aref} and @code{aset} (@pxref{Array | |
54 | Functions}). | |
55 | ||
56 | Each character in a string is stored in a single byte. Therefore, | |
57 | numbers not in the range 0 to 255 are truncated when stored into a | |
58 | string. This means that a string takes up much less memory than a | |
59 | vector of the same length. | |
60 | ||
61 | Sometimes key sequences are represented as strings. When a string is | |
62 | a key sequence, string elements in the range 128 to 255 represent meta | |
63 | characters (which are extremely large integers) rather than keyboard | |
64 | events in the range 128 to 255. | |
65 | ||
66 | Strings cannot hold characters that have the hyper, super or alt | |
67 | modifiers; they can hold @sc{ASCII} control characters, but no other | |
68 | control characters. They do not distinguish case in @sc{ASCII} control | |
69 | characters. @xref{Character Type}, for more information about | |
70 | representation of meta and other modifiers for keyboard input | |
71 | characters. | |
72 | ||
bfe721d1 KH |
73 | Strings are useful for holding regular expressions. You can also |
74 | match regular expressions against strings (@pxref{Regexp Search}). The | |
75 | functions @code{match-string} (@pxref{Simple Match Data}) and | |
76 | @code{replace-match} (@pxref{Replacing Match}) are useful for | |
77 | decomposing and modifying strings based on regular expression matching. | |
78 | ||
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79 | Like a buffer, a string can contain text properties for the characters |
80 | in it, as well as the characters themselves. @xref{Text Properties}. | |
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81 | All the Lisp primitives that copy text from strings to buffers or other |
82 | strings also copy the properties of the characters being copied. | |
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83 | |
84 | @xref{Text}, for information about functions that display strings or | |
85 | copy them into buffers. @xref{Character Type}, and @ref{String Type}, | |
86 | for information about the syntax of characters and strings. | |
87 | ||
88 | @node Predicates for Strings | |
89 | @section The Predicates for Strings | |
90 | ||
91 | For more information about general sequence and array predicates, | |
92 | see @ref{Sequences Arrays Vectors}, and @ref{Arrays}. | |
93 | ||
94 | @defun stringp object | |
95 | This function returns @code{t} if @var{object} is a string, @code{nil} | |
96 | otherwise. | |
97 | @end defun | |
98 | ||
99 | @defun char-or-string-p object | |
100 | This function returns @code{t} if @var{object} is a string or a | |
101 | character (i.e., an integer), @code{nil} otherwise. | |
102 | @end defun | |
103 | ||
104 | @node Creating Strings | |
105 | @section Creating Strings | |
106 | ||
107 | The following functions create strings, either from scratch, or by | |
108 | putting strings together, or by taking them apart. | |
109 | ||
110 | @defun make-string count character | |
111 | This function returns a string made up of @var{count} repetitions of | |
112 | @var{character}. If @var{count} is negative, an error is signaled. | |
113 | ||
114 | @example | |
115 | (make-string 5 ?x) | |
116 | @result{} "xxxxx" | |
117 | (make-string 0 ?x) | |
118 | @result{} "" | |
119 | @end example | |
120 | ||
121 | Other functions to compare with this one include @code{char-to-string} | |
122 | (@pxref{String Conversion}), @code{make-vector} (@pxref{Vectors}), and | |
123 | @code{make-list} (@pxref{Building Lists}). | |
124 | @end defun | |
125 | ||
126 | @defun substring string start &optional end | |
bfe721d1 | 127 | This function returns a new string which consists of those characters |
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128 | from @var{string} in the range from (and including) the character at the |
129 | index @var{start} up to (but excluding) the character at the index | |
130 | @var{end}. The first character is at index zero. | |
131 | ||
132 | @example | |
133 | @group | |
134 | (substring "abcdefg" 0 3) | |
135 | @result{} "abc" | |
136 | @end group | |
137 | @end example | |
138 | ||
139 | @noindent | |
140 | Here the index for @samp{a} is 0, the index for @samp{b} is 1, and the | |
141 | index for @samp{c} is 2. Thus, three letters, @samp{abc}, are copied | |
142 | from the string @code{"abcdefg"}. The index 3 marks the character | |
143 | position up to which the substring is copied. The character whose index | |
144 | is 3 is actually the fourth character in the string. | |
145 | ||
146 | A negative number counts from the end of the string, so that @minus{}1 | |
147 | signifies the index of the last character of the string. For example: | |
148 | ||
149 | @example | |
150 | @group | |
151 | (substring "abcdefg" -3 -1) | |
152 | @result{} "ef" | |
153 | @end group | |
154 | @end example | |
155 | ||
156 | @noindent | |
157 | In this example, the index for @samp{e} is @minus{}3, the index for | |
158 | @samp{f} is @minus{}2, and the index for @samp{g} is @minus{}1. | |
159 | Therefore, @samp{e} and @samp{f} are included, and @samp{g} is excluded. | |
160 | ||
161 | When @code{nil} is used as an index, it stands for the length of the | |
162 | string. Thus, | |
163 | ||
164 | @example | |
165 | @group | |
166 | (substring "abcdefg" -3 nil) | |
167 | @result{} "efg" | |
168 | @end group | |
169 | @end example | |
170 | ||
171 | Omitting the argument @var{end} is equivalent to specifying @code{nil}. | |
172 | It follows that @code{(substring @var{string} 0)} returns a copy of all | |
173 | of @var{string}. | |
174 | ||
175 | @example | |
176 | @group | |
177 | (substring "abcdefg" 0) | |
178 | @result{} "abcdefg" | |
179 | @end group | |
180 | @end example | |
181 | ||
182 | @noindent | |
183 | But we recommend @code{copy-sequence} for this purpose (@pxref{Sequence | |
184 | Functions}). | |
185 | ||
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186 | If the characters copied from @var{string} have text properties, the |
187 | properties are copied into the new string also. @xref{Text Properties}. | |
188 | ||
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189 | A @code{wrong-type-argument} error is signaled if either @var{start} or |
190 | @var{end} is not an integer or @code{nil}. An @code{args-out-of-range} | |
191 | error is signaled if @var{start} indicates a character following | |
192 | @var{end}, or if either integer is out of range for @var{string}. | |
193 | ||
194 | Contrast this function with @code{buffer-substring} (@pxref{Buffer | |
195 | Contents}), which returns a string containing a portion of the text in | |
196 | the current buffer. The beginning of a string is at index 0, but the | |
197 | beginning of a buffer is at index 1. | |
198 | @end defun | |
199 | ||
200 | @defun concat &rest sequences | |
201 | @cindex copying strings | |
202 | @cindex concatenating strings | |
203 | This function returns a new string consisting of the characters in the | |
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204 | arguments passed to it (along with their text properties, if any). The |
205 | arguments may be strings, lists of numbers, or vectors of numbers; they | |
206 | are not themselves changed. If @code{concat} receives no arguments, it | |
207 | returns an empty string. | |
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208 | |
209 | @example | |
210 | (concat "abc" "-def") | |
211 | @result{} "abc-def" | |
212 | (concat "abc" (list 120 (+ 256 121)) [122]) | |
213 | @result{} "abcxyz" | |
214 | ;; @r{@code{nil} is an empty sequence.} | |
215 | (concat "abc" nil "-def") | |
216 | @result{} "abc-def" | |
217 | (concat "The " "quick brown " "fox.") | |
218 | @result{} "The quick brown fox." | |
219 | (concat) | |
220 | @result{} "" | |
221 | @end example | |
222 | ||
223 | @noindent | |
224 | The second example above shows how characters stored in strings are | |
225 | taken modulo 256. In other words, each character in the string is | |
226 | stored in one byte. | |
227 | ||
228 | The @code{concat} function always constructs a new string that is | |
229 | not @code{eq} to any existing string. | |
230 | ||
231 | When an argument is an integer (not a sequence of integers), it is | |
232 | converted to a string of digits making up the decimal printed | |
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233 | representation of the integer. @strong{Don't use this feature; we plan |
234 | to eliminate it. If you already use this feature, change your programs | |
235 | now!} The proper way to convert an integer to a decimal number in this | |
236 | way is with @code{format} (@pxref{Formatting Strings}) or | |
a10f6c69 | 237 | @code{number-to-string} (@pxref{String Conversion}). |
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238 | |
239 | @example | |
240 | @group | |
241 | (concat 137) | |
242 | @result{} "137" | |
243 | (concat 54 321) | |
244 | @result{} "54321" | |
245 | @end group | |
246 | @end example | |
247 | ||
248 | For information about other concatenation functions, see the | |
249 | description of @code{mapconcat} in @ref{Mapping Functions}, | |
250 | @code{vconcat} in @ref{Vectors}, and @code{append} in @ref{Building | |
251 | Lists}. | |
252 | @end defun | |
253 | ||
bda144f4 | 254 | @need 2000 |
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255 | @node Text Comparison |
256 | @section Comparison of Characters and Strings | |
257 | @cindex string equality | |
258 | ||
259 | @defun char-equal character1 character2 | |
260 | This function returns @code{t} if the arguments represent the same | |
261 | character, @code{nil} otherwise. This function ignores differences | |
262 | in case if @code{case-fold-search} is non-@code{nil}. | |
263 | ||
264 | @example | |
265 | (char-equal ?x ?x) | |
266 | @result{} t | |
267 | (char-to-string (+ 256 ?x)) | |
268 | @result{} "x" | |
269 | (char-equal ?x (+ 256 ?x)) | |
270 | @result{} t | |
271 | @end example | |
272 | @end defun | |
273 | ||
274 | @defun string= string1 string2 | |
275 | This function returns @code{t} if the characters of the two strings | |
276 | match exactly; case is significant. | |
277 | ||
278 | @example | |
279 | (string= "abc" "abc") | |
280 | @result{} t | |
281 | (string= "abc" "ABC") | |
282 | @result{} nil | |
283 | (string= "ab" "ABC") | |
284 | @result{} nil | |
285 | @end example | |
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286 | |
287 | The function @code{string=} ignores the text properties of the | |
288 | two strings. To compare strings in a way that compares their text | |
289 | properties also, use @code{equal} (@pxref{Equality Predicates}). | |
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290 | @end defun |
291 | ||
292 | @defun string-equal string1 string2 | |
293 | @code{string-equal} is another name for @code{string=}. | |
294 | @end defun | |
295 | ||
296 | @cindex lexical comparison | |
297 | @defun string< string1 string2 | |
298 | @c (findex string< causes problems for permuted index!!) | |
299 | This function compares two strings a character at a time. First it | |
300 | scans both the strings at once to find the first pair of corresponding | |
301 | characters that do not match. If the lesser character of those two is | |
302 | the character from @var{string1}, then @var{string1} is less, and this | |
303 | function returns @code{t}. If the lesser character is the one from | |
304 | @var{string2}, then @var{string1} is greater, and this function returns | |
305 | @code{nil}. If the two strings match entirely, the value is @code{nil}. | |
306 | ||
307 | Pairs of characters are compared by their @sc{ASCII} codes. Keep in | |
308 | mind that lower case letters have higher numeric values in the | |
309 | @sc{ASCII} character set than their upper case counterparts; numbers and | |
310 | many punctuation characters have a lower numeric value than upper case | |
311 | letters. | |
312 | ||
313 | @example | |
314 | @group | |
315 | (string< "abc" "abd") | |
316 | @result{} t | |
317 | (string< "abd" "abc") | |
318 | @result{} nil | |
319 | (string< "123" "abc") | |
320 | @result{} t | |
321 | @end group | |
322 | @end example | |
323 | ||
324 | When the strings have different lengths, and they match up to the | |
325 | length of @var{string1}, then the result is @code{t}. If they match up | |
326 | to the length of @var{string2}, the result is @code{nil}. A string of | |
327 | no characters is less than any other string. | |
328 | ||
329 | @example | |
330 | @group | |
331 | (string< "" "abc") | |
332 | @result{} t | |
333 | (string< "ab" "abc") | |
334 | @result{} t | |
335 | (string< "abc" "") | |
336 | @result{} nil | |
337 | (string< "abc" "ab") | |
338 | @result{} nil | |
339 | (string< "" "") | |
340 | @result{} nil | |
341 | @end group | |
342 | @end example | |
343 | @end defun | |
344 | ||
345 | @defun string-lessp string1 string2 | |
346 | @code{string-lessp} is another name for @code{string<}. | |
347 | @end defun | |
348 | ||
349 | See also @code{compare-buffer-substrings} in @ref{Comparing Text}, for | |
350 | a way to compare text in buffers. The function @code{string-match}, | |
351 | which matches a regular expression against a string, can be used | |
352 | for a kind of string comparison; see @ref{Regexp Search}. | |
353 | ||
354 | @node String Conversion | |
355 | @comment node-name, next, previous, up | |
356 | @section Conversion of Characters and Strings | |
357 | @cindex conversion of strings | |
358 | ||
359 | This section describes functions for conversions between characters, | |
360 | strings and integers. @code{format} and @code{prin1-to-string} | |
361 | (@pxref{Output Functions}) can also convert Lisp objects into strings. | |
362 | @code{read-from-string} (@pxref{Input Functions}) can ``convert'' a | |
363 | string representation of a Lisp object into an object. | |
364 | ||
365 | @xref{Documentation}, for functions that produce textual descriptions | |
366 | of text characters and general input events | |
367 | (@code{single-key-description} and @code{text-char-description}). These | |
368 | functions are used primarily for making help messages. | |
369 | ||
370 | @defun char-to-string character | |
371 | @cindex character to string | |
372 | This function returns a new string with a length of one character. | |
373 | The value of @var{character}, modulo 256, is used to initialize the | |
374 | element of the string. | |
375 | ||
376 | This function is similar to @code{make-string} with an integer argument | |
377 | of 1. (@xref{Creating Strings}.) This conversion can also be done with | |
378 | @code{format} using the @samp{%c} format specification. | |
379 | (@xref{Formatting Strings}.) | |
380 | ||
381 | @example | |
382 | (char-to-string ?x) | |
383 | @result{} "x" | |
384 | (char-to-string (+ 256 ?x)) | |
385 | @result{} "x" | |
386 | (make-string 1 ?x) | |
387 | @result{} "x" | |
388 | @end example | |
389 | @end defun | |
390 | ||
391 | @defun string-to-char string | |
392 | @cindex string to character | |
393 | This function returns the first character in @var{string}. If the | |
394 | string is empty, the function returns 0. The value is also 0 when the | |
395 | first character of @var{string} is the null character, @sc{ASCII} code | |
396 | 0. | |
397 | ||
398 | @example | |
399 | (string-to-char "ABC") | |
400 | @result{} 65 | |
401 | (string-to-char "xyz") | |
402 | @result{} 120 | |
403 | (string-to-char "") | |
404 | @result{} 0 | |
405 | (string-to-char "\000") | |
406 | @result{} 0 | |
407 | @end example | |
408 | ||
409 | This function may be eliminated in the future if it does not seem useful | |
410 | enough to retain. | |
411 | @end defun | |
412 | ||
413 | @defun number-to-string number | |
414 | @cindex integer to string | |
415 | @cindex integer to decimal | |
416 | This function returns a string consisting of the printed | |
417 | representation of @var{number}, which may be an integer or a floating | |
418 | point number. The value starts with a sign if the argument is | |
419 | negative. | |
420 | ||
421 | @example | |
422 | (number-to-string 256) | |
423 | @result{} "256" | |
424 | (number-to-string -23) | |
425 | @result{} "-23" | |
426 | (number-to-string -23.5) | |
427 | @result{} "-23.5" | |
428 | @end example | |
429 | ||
430 | @cindex int-to-string | |
431 | @code{int-to-string} is a semi-obsolete alias for this function. | |
432 | ||
433 | See also the function @code{format} in @ref{Formatting Strings}. | |
434 | @end defun | |
435 | ||
436 | @defun string-to-number string | |
437 | @cindex string to number | |
438 | This function returns the numeric value of the characters in | |
439 | @var{string}, read in base ten. It skips spaces and tabs at the | |
440 | beginning of @var{string}, then reads as much of @var{string} as it can | |
441 | interpret as a number. (On some systems it ignores other whitespace at | |
442 | the beginning, not just spaces and tabs.) If the first character after | |
443 | the ignored whitespace is not a digit or a minus sign, this function | |
444 | returns 0. | |
445 | ||
446 | @example | |
447 | (string-to-number "256") | |
448 | @result{} 256 | |
449 | (string-to-number "25 is a perfect square.") | |
450 | @result{} 25 | |
451 | (string-to-number "X256") | |
452 | @result{} 0 | |
453 | (string-to-number "-4.5") | |
454 | @result{} -4.5 | |
455 | @end example | |
456 | ||
457 | @findex string-to-int | |
458 | @code{string-to-int} is an obsolete alias for this function. | |
459 | @end defun | |
460 | ||
461 | @node Formatting Strings | |
462 | @comment node-name, next, previous, up | |
463 | @section Formatting Strings | |
464 | @cindex formatting strings | |
465 | @cindex strings, formatting them | |
466 | ||
467 | @dfn{Formatting} means constructing a string by substitution of | |
468 | computed values at various places in a constant string. This string | |
469 | controls how the other values are printed as well as where they appear; | |
470 | it is called a @dfn{format string}. | |
471 | ||
472 | Formatting is often useful for computing messages to be displayed. In | |
473 | fact, the functions @code{message} and @code{error} provide the same | |
474 | formatting feature described here; they differ from @code{format} only | |
475 | in how they use the result of formatting. | |
476 | ||
477 | @defun format string &rest objects | |
478 | This function returns a new string that is made by copying | |
479 | @var{string} and then replacing any format specification | |
480 | in the copy with encodings of the corresponding @var{objects}. The | |
481 | arguments @var{objects} are the computed values to be formatted. | |
482 | @end defun | |
483 | ||
484 | @cindex @samp{%} in format | |
485 | @cindex format specification | |
486 | A format specification is a sequence of characters beginning with a | |
487 | @samp{%}. Thus, if there is a @samp{%d} in @var{string}, the | |
488 | @code{format} function replaces it with the printed representation of | |
489 | one of the values to be formatted (one of the arguments @var{objects}). | |
490 | For example: | |
491 | ||
492 | @example | |
493 | @group | |
494 | (format "The value of fill-column is %d." fill-column) | |
495 | @result{} "The value of fill-column is 72." | |
496 | @end group | |
497 | @end example | |
498 | ||
499 | If @var{string} contains more than one format specification, the | |
500 | format specifications correspond with successive values from | |
501 | @var{objects}. Thus, the first format specification in @var{string} | |
502 | uses the first such value, the second format specification uses the | |
503 | second such value, and so on. Any extra format specifications (those | |
504 | for which there are no corresponding values) cause unpredictable | |
505 | behavior. Any extra values to be formatted are ignored. | |
506 | ||
507 | Certain format specifications require values of particular types. | |
508 | However, no error is signaled if the value actually supplied fails to | |
509 | have the expected type. Instead, the output is likely to be | |
510 | meaningless. | |
511 | ||
512 | Here is a table of valid format specifications: | |
513 | ||
514 | @table @samp | |
515 | @item %s | |
516 | Replace the specification with the printed representation of the object, | |
517 | made without quoting. Thus, strings are represented by their contents | |
518 | alone, with no @samp{"} characters, and symbols appear without @samp{\} | |
519 | characters. | |
520 | ||
521 | If there is no corresponding object, the empty string is used. | |
522 | ||
523 | @item %S | |
524 | Replace the specification with the printed representation of the object, | |
525 | made with quoting. Thus, strings are enclosed in @samp{"} characters, | |
526 | and @samp{\} characters appear where necessary before special characters. | |
527 | ||
528 | If there is no corresponding object, the empty string is used. | |
529 | ||
530 | @item %o | |
531 | @cindex integer to octal | |
532 | Replace the specification with the base-eight representation of an | |
533 | integer. | |
534 | ||
535 | @item %d | |
536 | Replace the specification with the base-ten representation of an | |
537 | integer. | |
538 | ||
539 | @item %x | |
540 | @cindex integer to hexadecimal | |
541 | Replace the specification with the base-sixteen representation of an | |
542 | integer. | |
543 | ||
544 | @item %c | |
545 | Replace the specification with the character which is the value given. | |
546 | ||
547 | @item %e | |
548 | Replace the specification with the exponential notation for a floating | |
549 | point number. | |
550 | ||
551 | @item %f | |
552 | Replace the specification with the decimal-point notation for a floating | |
553 | point number. | |
554 | ||
555 | @item %g | |
556 | Replace the specification with notation for a floating point number, | |
557 | using either exponential notation or decimal-point notation whichever | |
558 | is shorter. | |
559 | ||
560 | @item %% | |
561 | A single @samp{%} is placed in the string. This format specification is | |
562 | unusual in that it does not use a value. For example, @code{(format "%% | |
563 | %d" 30)} returns @code{"% 30"}. | |
564 | @end table | |
565 | ||
566 | Any other format character results in an @samp{Invalid format | |
567 | operation} error. | |
568 | ||
569 | Here are several examples: | |
570 | ||
571 | @example | |
572 | @group | |
573 | (format "The name of this buffer is %s." (buffer-name)) | |
574 | @result{} "The name of this buffer is strings.texi." | |
575 | ||
576 | (format "The buffer object prints as %s." (current-buffer)) | |
9feb90da | 577 | @result{} "The buffer object prints as strings.texi." |
869f4785 RS |
578 | |
579 | (format "The octal value of %d is %o, | |
580 | and the hex value is %x." 18 18 18) | |
581 | @result{} "The octal value of 18 is 22, | |
582 | and the hex value is 12." | |
583 | @end group | |
584 | @end example | |
585 | ||
586 | @cindex numeric prefix | |
587 | @cindex field width | |
588 | @cindex padding | |
589 | All the specification characters allow an optional numeric prefix | |
590 | between the @samp{%} and the character. The optional numeric prefix | |
591 | defines the minimum width for the object. If the printed representation | |
592 | of the object contains fewer characters than this, then it is padded. | |
593 | The padding is on the left if the prefix is positive (or starts with | |
594 | zero) and on the right if the prefix is negative. The padding character | |
595 | is normally a space, but if the numeric prefix starts with a zero, zeros | |
596 | are used for padding. | |
597 | ||
598 | @example | |
599 | (format "%06d is padded on the left with zeros" 123) | |
600 | @result{} "000123 is padded on the left with zeros" | |
601 | ||
602 | (format "%-6d is padded on the right" 123) | |
603 | @result{} "123 is padded on the right" | |
604 | @end example | |
605 | ||
606 | @code{format} never truncates an object's printed representation, no | |
607 | matter what width you specify. Thus, you can use a numeric prefix to | |
608 | specify a minimum spacing between columns with no risk of losing | |
609 | information. | |
610 | ||
611 | In the following three examples, @samp{%7s} specifies a minimum width | |
612 | of 7. In the first case, the string inserted in place of @samp{%7s} has | |
613 | only 3 letters, so 4 blank spaces are inserted for padding. In the | |
614 | second case, the string @code{"specification"} is 13 letters wide but is | |
615 | not truncated. In the third case, the padding is on the right. | |
616 | ||
617 | @smallexample | |
618 | @group | |
619 | (format "The word `%7s' actually has %d letters in it." | |
620 | "foo" (length "foo")) | |
621 | @result{} "The word ` foo' actually has 3 letters in it." | |
622 | @end group | |
623 | ||
624 | @group | |
625 | (format "The word `%7s' actually has %d letters in it." | |
626 | "specification" (length "specification")) | |
627 | @result{} "The word `specification' actually has 13 letters in it." | |
628 | @end group | |
629 | ||
630 | @group | |
631 | (format "The word `%-7s' actually has %d letters in it." | |
632 | "foo" (length "foo")) | |
633 | @result{} "The word `foo ' actually has 3 letters in it." | |
634 | @end group | |
635 | @end smallexample | |
636 | ||
637 | @node Character Case | |
638 | @comment node-name, next, previous, up | |
639 | @section Character Case | |
640 | @cindex upper case | |
641 | @cindex lower case | |
642 | @cindex character case | |
643 | ||
644 | The character case functions change the case of single characters or | |
645 | of the contents of strings. The functions convert only alphabetic | |
646 | characters (the letters @samp{A} through @samp{Z} and @samp{a} through | |
647 | @samp{z}); other characters are not altered. The functions do not | |
648 | modify the strings that are passed to them as arguments. | |
649 | ||
650 | The examples below use the characters @samp{X} and @samp{x} which have | |
651 | @sc{ASCII} codes 88 and 120 respectively. | |
652 | ||
653 | @defun downcase string-or-char | |
654 | This function converts a character or a string to lower case. | |
655 | ||
656 | When the argument to @code{downcase} is a string, the function creates | |
657 | and returns a new string in which each letter in the argument that is | |
658 | upper case is converted to lower case. When the argument to | |
659 | @code{downcase} is a character, @code{downcase} returns the | |
660 | corresponding lower case character. This value is an integer. If the | |
661 | original character is lower case, or is not a letter, then the value | |
662 | equals the original character. | |
663 | ||
664 | @example | |
665 | (downcase "The cat in the hat") | |
666 | @result{} "the cat in the hat" | |
667 | ||
668 | (downcase ?X) | |
669 | @result{} 120 | |
670 | @end example | |
671 | @end defun | |
672 | ||
673 | @defun upcase string-or-char | |
674 | This function converts a character or a string to upper case. | |
675 | ||
676 | When the argument to @code{upcase} is a string, the function creates | |
677 | and returns a new string in which each letter in the argument that is | |
678 | lower case is converted to upper case. | |
679 | ||
680 | When the argument to @code{upcase} is a character, @code{upcase} | |
681 | returns the corresponding upper case character. This value is an integer. | |
682 | If the original character is upper case, or is not a letter, then the | |
683 | value equals the original character. | |
684 | ||
685 | @example | |
686 | (upcase "The cat in the hat") | |
687 | @result{} "THE CAT IN THE HAT" | |
688 | ||
689 | (upcase ?x) | |
690 | @result{} 88 | |
691 | @end example | |
692 | @end defun | |
693 | ||
694 | @defun capitalize string-or-char | |
695 | @cindex capitalization | |
696 | This function capitalizes strings or characters. If | |
697 | @var{string-or-char} is a string, the function creates and returns a new | |
698 | string, whose contents are a copy of @var{string-or-char} in which each | |
699 | word has been capitalized. This means that the first character of each | |
700 | word is converted to upper case, and the rest are converted to lower | |
701 | case. | |
702 | ||
703 | The definition of a word is any sequence of consecutive characters that | |
704 | are assigned to the word constituent syntax class in the current syntax | |
705 | table (@xref{Syntax Class Table}). | |
706 | ||
707 | When the argument to @code{capitalize} is a character, @code{capitalize} | |
708 | has the same result as @code{upcase}. | |
709 | ||
710 | @example | |
711 | (capitalize "The cat in the hat") | |
712 | @result{} "The Cat In The Hat" | |
713 | ||
714 | (capitalize "THE 77TH-HATTED CAT") | |
715 | @result{} "The 77th-Hatted Cat" | |
716 | ||
717 | @group | |
718 | (capitalize ?x) | |
719 | @result{} 88 | |
720 | @end group | |
721 | @end example | |
722 | @end defun | |
723 | ||
724 | @node Case Table | |
725 | @section The Case Table | |
726 | ||
727 | You can customize case conversion by installing a special @dfn{case | |
728 | table}. A case table specifies the mapping between upper case and lower | |
729 | case letters. It affects both the string and character case conversion | |
730 | functions (see the previous section) and those that apply to text in the | |
731 | buffer (@pxref{Case Changes}). You need a case table if you are using a | |
732 | language which has letters other than the standard @sc{ASCII} letters. | |
733 | ||
734 | A case table is a list of this form: | |
735 | ||
736 | @example | |
737 | (@var{downcase} @var{upcase} @var{canonicalize} @var{equivalences}) | |
738 | @end example | |
739 | ||
740 | @noindent | |
741 | where each element is either @code{nil} or a string of length 256. The | |
742 | element @var{downcase} says how to map each character to its lower-case | |
743 | equivalent. The element @var{upcase} maps each character to its | |
744 | upper-case equivalent. If lower and upper case characters are in | |
745 | one-to-one correspondence, use @code{nil} for @var{upcase}; then Emacs | |
746 | deduces the upcase table from @var{downcase}. | |
747 | ||
748 | For some languages, upper and lower case letters are not in one-to-one | |
749 | correspondence. There may be two different lower case letters with the | |
750 | same upper case equivalent. In these cases, you need to specify the | |
751 | maps for both directions. | |
752 | ||
753 | The element @var{canonicalize} maps each character to a canonical | |
754 | equivalent; any two characters that are related by case-conversion have | |
755 | the same canonical equivalent character. | |
756 | ||
757 | The element @var{equivalences} is a map that cyclicly permutes each | |
758 | equivalence class (of characters with the same canonical equivalent). | |
759 | (For ordinary @sc{ASCII}, this would map @samp{a} into @samp{A} and | |
760 | @samp{A} into @samp{a}, and likewise for each set of equivalent | |
761 | characters.) | |
762 | ||
2778c642 RS |
763 | When you construct a case table, you can provide @code{nil} for |
764 | @var{canonicalize}; then Emacs fills in this string from @var{upcase} | |
765 | and @var{downcase}. You can also provide @code{nil} for | |
766 | @var{equivalences}; then Emacs fills in this string from | |
767 | @var{canonicalize}. In a case table that is actually in use, those | |
768 | components are non-@code{nil}. Do not try to specify @var{equivalences} | |
769 | without also specifying @var{canonicalize}. | |
869f4785 RS |
770 | |
771 | Each buffer has a case table. Emacs also has a @dfn{standard case | |
772 | table} which is copied into each buffer when you create the buffer. | |
773 | Changing the standard case table doesn't affect any existing buffers. | |
774 | ||
775 | Here are the functions for working with case tables: | |
776 | ||
777 | @defun case-table-p object | |
778 | This predicate returns non-@code{nil} if @var{object} is a valid case | |
779 | table. | |
780 | @end defun | |
781 | ||
782 | @defun set-standard-case-table table | |
783 | This function makes @var{table} the standard case table, so that it will | |
784 | apply to any buffers created subsequently. | |
785 | @end defun | |
786 | ||
787 | @defun standard-case-table | |
788 | This returns the standard case table. | |
789 | @end defun | |
790 | ||
791 | @defun current-case-table | |
792 | This function returns the current buffer's case table. | |
793 | @end defun | |
794 | ||
795 | @defun set-case-table table | |
796 | This sets the current buffer's case table to @var{table}. | |
797 | @end defun | |
798 | ||
799 | The following three functions are convenient subroutines for packages | |
800 | that define non-@sc{ASCII} character sets. They modify a string | |
801 | @var{downcase-table} provided as an argument; this should be a string to | |
802 | be used as the @var{downcase} part of a case table. They also modify | |
803 | the standard syntax table. @xref{Syntax Tables}. | |
804 | ||
805 | @defun set-case-syntax-pair uc lc downcase-table | |
806 | This function specifies a pair of corresponding letters, one upper case | |
807 | and one lower case. | |
808 | @end defun | |
809 | ||
810 | @defun set-case-syntax-delims l r downcase-table | |
811 | This function makes characters @var{l} and @var{r} a matching pair of | |
812 | case-invariant delimiters. | |
813 | @end defun | |
814 | ||
815 | @defun set-case-syntax char syntax downcase-table | |
816 | This function makes @var{char} case-invariant, with syntax | |
817 | @var{syntax}. | |
818 | @end defun | |
819 | ||
820 | @deffn Command describe-buffer-case-table | |
821 | This command displays a description of the contents of the current | |
822 | buffer's case table. | |
823 | @end deffn | |
824 | ||
825 | @cindex ISO Latin 1 | |
826 | @pindex iso-syntax | |
827 | You can load the library @file{iso-syntax} to set up the standard syntax | |
0b2f1c85 | 828 | table and define a case table for the 8-bit ISO Latin 1 character set. |