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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, | |
57ebf0be | 4 | @c 2005, 2006, 2007, 2008 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/characters |
b8d4c8d0 GM |
7 | @node Non-ASCII Characters, Searching and Matching, Text, Top |
8 | @chapter Non-@acronym{ASCII} Characters | |
9 | @cindex multibyte characters | |
10 | @cindex characters, multi-byte | |
11 | @cindex non-@acronym{ASCII} characters | |
12 | ||
13 | This chapter covers the special issues relating to non-@acronym{ASCII} | |
14 | characters and how they are stored in strings and buffers. | |
15 | ||
16 | @menu | |
17 | * Text Representations:: Unibyte and multibyte representations | |
18 | * Converting Representations:: Converting unibyte to multibyte and vice versa. | |
19 | * Selecting a Representation:: Treating a byte sequence as unibyte or multi. | |
20 | * Character Codes:: How unibyte and multibyte relate to | |
21 | codes of individual characters. | |
22 | * Character Sets:: The space of possible character codes | |
23 | is divided into various character sets. | |
24 | * Chars and Bytes:: More information about multibyte encodings. | |
25 | * Splitting Characters:: Converting a character to its byte sequence. | |
26 | * Scanning Charsets:: Which character sets are used in a buffer? | |
27 | * Translation of Characters:: Translation tables are used for conversion. | |
28 | * Coding Systems:: Coding systems are conversions for saving files. | |
29 | * Input Methods:: Input methods allow users to enter various | |
30 | non-ASCII characters without special keyboards. | |
31 | * Locales:: Interacting with the POSIX locale. | |
32 | @end menu | |
33 | ||
34 | @node Text Representations | |
35 | @section Text Representations | |
36 | @cindex text representations | |
37 | ||
38 | Emacs has two @dfn{text representations}---two ways to represent text | |
39 | in a string or buffer. These are called @dfn{unibyte} and | |
40 | @dfn{multibyte}. Each string, and each buffer, uses one of these two | |
41 | representations. For most purposes, you can ignore the issue of | |
42 | representations, because Emacs converts text between them as | |
43 | appropriate. Occasionally in Lisp programming you will need to pay | |
44 | attention to the difference. | |
45 | ||
46 | @cindex unibyte text | |
47 | In unibyte representation, each character occupies one byte and | |
48 | therefore the possible character codes range from 0 to 255. Codes 0 | |
49 | through 127 are @acronym{ASCII} characters; the codes from 128 through 255 | |
50 | are used for one non-@acronym{ASCII} character set (you can choose which | |
51 | character set by setting the variable @code{nonascii-insert-offset}). | |
52 | ||
53 | @cindex leading code | |
54 | @cindex multibyte text | |
55 | @cindex trailing codes | |
56 | In multibyte representation, a character may occupy more than one | |
57 | byte, and as a result, the full range of Emacs character codes can be | |
58 | stored. The first byte of a multibyte character is always in the range | |
59 | 128 through 159 (octal 0200 through 0237). These values are called | |
60 | @dfn{leading codes}. The second and subsequent bytes of a multibyte | |
61 | character are always in the range 160 through 255 (octal 0240 through | |
62 | 0377); these values are @dfn{trailing codes}. | |
63 | ||
64 | Some sequences of bytes are not valid in multibyte text: for example, | |
65 | a single isolated byte in the range 128 through 159 is not allowed. But | |
66 | character codes 128 through 159 can appear in multibyte text, | |
67 | represented as two-byte sequences. All the character codes 128 through | |
68 | 255 are possible (though slightly abnormal) in multibyte text; they | |
69 | appear in multibyte buffers and strings when you do explicit encoding | |
70 | and decoding (@pxref{Explicit Encoding}). | |
71 | ||
72 | In a buffer, the buffer-local value of the variable | |
73 | @code{enable-multibyte-characters} specifies the representation used. | |
74 | The representation for a string is determined and recorded in the string | |
75 | when the string is constructed. | |
76 | ||
77 | @defvar enable-multibyte-characters | |
78 | This variable specifies the current buffer's text representation. | |
79 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
80 | it contains unibyte text. | |
81 | ||
82 | You cannot set this variable directly; instead, use the function | |
83 | @code{set-buffer-multibyte} to change a buffer's representation. | |
84 | @end defvar | |
85 | ||
86 | @defvar default-enable-multibyte-characters | |
87 | This variable's value is entirely equivalent to @code{(default-value | |
88 | 'enable-multibyte-characters)}, and setting this variable changes that | |
89 | default value. Setting the local binding of | |
90 | @code{enable-multibyte-characters} in a specific buffer is not allowed, | |
91 | but changing the default value is supported, and it is a reasonable | |
92 | thing to do, because it has no effect on existing buffers. | |
93 | ||
94 | The @samp{--unibyte} command line option does its job by setting the | |
95 | default value to @code{nil} early in startup. | |
96 | @end defvar | |
97 | ||
98 | @defun position-bytes position | |
99 | Return the byte-position corresponding to buffer position | |
100 | @var{position} in the current buffer. This is 1 at the start of the | |
101 | buffer, and counts upward in bytes. If @var{position} is out of | |
102 | range, the value is @code{nil}. | |
103 | @end defun | |
104 | ||
105 | @defun byte-to-position byte-position | |
106 | Return the buffer position corresponding to byte-position | |
107 | @var{byte-position} in the current buffer. If @var{byte-position} is | |
108 | out of range, the value is @code{nil}. | |
109 | @end defun | |
110 | ||
111 | @defun multibyte-string-p string | |
112 | Return @code{t} if @var{string} is a multibyte string. | |
113 | @end defun | |
114 | ||
115 | @defun string-bytes string | |
116 | @cindex string, number of bytes | |
117 | This function returns the number of bytes in @var{string}. | |
118 | If @var{string} is a multibyte string, this can be greater than | |
119 | @code{(length @var{string})}. | |
120 | @end defun | |
121 | ||
122 | @node Converting Representations | |
123 | @section Converting Text Representations | |
124 | ||
125 | Emacs can convert unibyte text to multibyte; it can also convert | |
126 | multibyte text to unibyte, though this conversion loses information. In | |
127 | general these conversions happen when inserting text into a buffer, or | |
128 | when putting text from several strings together in one string. You can | |
129 | also explicitly convert a string's contents to either representation. | |
130 | ||
131 | Emacs chooses the representation for a string based on the text that | |
132 | it is constructed from. The general rule is to convert unibyte text to | |
133 | multibyte text when combining it with other multibyte text, because the | |
134 | multibyte representation is more general and can hold whatever | |
135 | characters the unibyte text has. | |
136 | ||
137 | When inserting text into a buffer, Emacs converts the text to the | |
138 | buffer's representation, as specified by | |
139 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
140 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
141 | to unibyte, even though this conversion cannot in general preserve all | |
142 | the characters that might be in the multibyte text. The other natural | |
143 | alternative, to convert the buffer contents to multibyte, is not | |
144 | acceptable because the buffer's representation is a choice made by the | |
145 | user that cannot be overridden automatically. | |
146 | ||
147 | Converting unibyte text to multibyte text leaves @acronym{ASCII} characters | |
148 | unchanged, and likewise character codes 128 through 159. It converts | |
149 | the non-@acronym{ASCII} codes 160 through 255 by adding the value | |
150 | @code{nonascii-insert-offset} to each character code. By setting this | |
151 | variable, you specify which character set the unibyte characters | |
152 | correspond to (@pxref{Character Sets}). For example, if | |
153 | @code{nonascii-insert-offset} is 2048, which is @code{(- (make-char | |
154 | 'latin-iso8859-1) 128)}, then the unibyte non-@acronym{ASCII} characters | |
155 | correspond to Latin 1. If it is 2688, which is @code{(- (make-char | |
156 | 'greek-iso8859-7) 128)}, then they correspond to Greek letters. | |
157 | ||
158 | Converting multibyte text to unibyte is simpler: it discards all but | |
159 | the low 8 bits of each character code. If @code{nonascii-insert-offset} | |
160 | has a reasonable value, corresponding to the beginning of some character | |
161 | set, this conversion is the inverse of the other: converting unibyte | |
162 | text to multibyte and back to unibyte reproduces the original unibyte | |
163 | text. | |
164 | ||
165 | @defvar nonascii-insert-offset | |
166 | This variable specifies the amount to add to a non-@acronym{ASCII} character | |
167 | when converting unibyte text to multibyte. It also applies when | |
168 | @code{self-insert-command} inserts a character in the unibyte | |
169 | non-@acronym{ASCII} range, 128 through 255. However, the functions | |
170 | @code{insert} and @code{insert-char} do not perform this conversion. | |
171 | ||
172 | The right value to use to select character set @var{cs} is @code{(- | |
173 | (make-char @var{cs}) 128)}. If the value of | |
174 | @code{nonascii-insert-offset} is zero, then conversion actually uses the | |
175 | value for the Latin 1 character set, rather than zero. | |
176 | @end defvar | |
177 | ||
178 | @defvar nonascii-translation-table | |
179 | This variable provides a more general alternative to | |
180 | @code{nonascii-insert-offset}. You can use it to specify independently | |
181 | how to translate each code in the range of 128 through 255 into a | |
182 | multibyte character. The value should be a char-table, or @code{nil}. | |
183 | If this is non-@code{nil}, it overrides @code{nonascii-insert-offset}. | |
184 | @end defvar | |
185 | ||
186 | The next three functions either return the argument @var{string}, or a | |
187 | newly created string with no text properties. | |
188 | ||
189 | @defun string-make-unibyte string | |
190 | This function converts the text of @var{string} to unibyte | |
191 | representation, if it isn't already, and returns the result. If | |
192 | @var{string} is a unibyte string, it is returned unchanged. Multibyte | |
193 | character codes are converted to unibyte according to | |
194 | @code{nonascii-translation-table} or, if that is @code{nil}, using | |
195 | @code{nonascii-insert-offset}. If the lookup in the translation table | |
196 | fails, this function takes just the low 8 bits of each character. | |
197 | @end defun | |
198 | ||
199 | @defun string-make-multibyte string | |
200 | This function converts the text of @var{string} to multibyte | |
201 | representation, if it isn't already, and returns the result. If | |
202 | @var{string} is a multibyte string or consists entirely of | |
203 | @acronym{ASCII} characters, it is returned unchanged. In particular, | |
204 | if @var{string} is unibyte and entirely @acronym{ASCII}, the returned | |
205 | string is unibyte. (When the characters are all @acronym{ASCII}, | |
206 | Emacs primitives will treat the string the same way whether it is | |
207 | unibyte or multibyte.) If @var{string} is unibyte and contains | |
208 | non-@acronym{ASCII} characters, the function | |
209 | @code{unibyte-char-to-multibyte} is used to convert each unibyte | |
210 | character to a multibyte character. | |
211 | @end defun | |
212 | ||
213 | @defun string-to-multibyte string | |
214 | This function returns a multibyte string containing the same sequence | |
215 | of character codes as @var{string}. Unlike | |
216 | @code{string-make-multibyte}, this function unconditionally returns a | |
217 | multibyte string. If @var{string} is a multibyte string, it is | |
218 | returned unchanged. | |
219 | @end defun | |
220 | ||
221 | @defun multibyte-char-to-unibyte char | |
222 | This convert the multibyte character @var{char} to a unibyte | |
223 | character, based on @code{nonascii-translation-table} and | |
224 | @code{nonascii-insert-offset}. | |
225 | @end defun | |
226 | ||
227 | @defun unibyte-char-to-multibyte char | |
228 | This convert the unibyte character @var{char} to a multibyte | |
229 | character, based on @code{nonascii-translation-table} and | |
230 | @code{nonascii-insert-offset}. | |
231 | @end defun | |
232 | ||
233 | @node Selecting a Representation | |
234 | @section Selecting a Representation | |
235 | ||
236 | Sometimes it is useful to examine an existing buffer or string as | |
237 | multibyte when it was unibyte, or vice versa. | |
238 | ||
239 | @defun set-buffer-multibyte multibyte | |
240 | Set the representation type of the current buffer. If @var{multibyte} | |
241 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
242 | is @code{nil}, the buffer becomes unibyte. | |
243 | ||
244 | This function leaves the buffer contents unchanged when viewed as a | |
245 | sequence of bytes. As a consequence, it can change the contents viewed | |
246 | as characters; a sequence of two bytes which is treated as one character | |
247 | in multibyte representation will count as two characters in unibyte | |
248 | representation. Character codes 128 through 159 are an exception. They | |
249 | are represented by one byte in a unibyte buffer, but when the buffer is | |
250 | set to multibyte, they are converted to two-byte sequences, and vice | |
251 | versa. | |
252 | ||
253 | This function sets @code{enable-multibyte-characters} to record which | |
254 | representation is in use. It also adjusts various data in the buffer | |
255 | (including overlays, text properties and markers) so that they cover the | |
256 | same text as they did before. | |
257 | ||
258 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
259 | because indirect buffers always inherit the representation of the | |
260 | base buffer. | |
261 | @end defun | |
262 | ||
263 | @defun string-as-unibyte string | |
264 | This function returns a string with the same bytes as @var{string} but | |
265 | treating each byte as a character. This means that the value may have | |
266 | more characters than @var{string} has. | |
267 | ||
268 | If @var{string} is already a unibyte string, then the value is | |
269 | @var{string} itself. Otherwise it is a newly created string, with no | |
270 | text properties. If @var{string} is multibyte, any characters it | |
271 | contains of charset @code{eight-bit-control} or @code{eight-bit-graphic} | |
272 | are converted to the corresponding single byte. | |
273 | @end defun | |
274 | ||
275 | @defun string-as-multibyte string | |
276 | This function returns a string with the same bytes as @var{string} but | |
277 | treating each multibyte sequence as one character. This means that the | |
278 | value may have fewer characters than @var{string} has. | |
279 | ||
280 | If @var{string} is already a multibyte string, then the value is | |
281 | @var{string} itself. Otherwise it is a newly created string, with no | |
282 | text properties. If @var{string} is unibyte and contains any individual | |
283 | 8-bit bytes (i.e.@: not part of a multibyte form), they are converted to | |
284 | the corresponding multibyte character of charset @code{eight-bit-control} | |
285 | or @code{eight-bit-graphic}. | |
286 | @end defun | |
287 | ||
288 | @node Character Codes | |
289 | @section Character Codes | |
290 | @cindex character codes | |
291 | ||
292 | The unibyte and multibyte text representations use different character | |
293 | codes. The valid character codes for unibyte representation range from | |
294 | 0 to 255---the values that can fit in one byte. The valid character | |
295 | codes for multibyte representation range from 0 to 524287, but not all | |
296 | values in that range are valid. The values 128 through 255 are not | |
297 | entirely proper in multibyte text, but they can occur if you do explicit | |
298 | encoding and decoding (@pxref{Explicit Encoding}). Some other character | |
299 | codes cannot occur at all in multibyte text. Only the @acronym{ASCII} codes | |
300 | 0 through 127 are completely legitimate in both representations. | |
301 | ||
302 | @defun char-valid-p charcode &optional genericp | |
303 | This returns @code{t} if @var{charcode} is valid (either for unibyte | |
304 | text or for multibyte text). | |
305 | ||
306 | @example | |
307 | (char-valid-p 65) | |
308 | @result{} t | |
309 | (char-valid-p 256) | |
310 | @result{} nil | |
311 | (char-valid-p 2248) | |
312 | @result{} t | |
313 | @end example | |
314 | ||
315 | If the optional argument @var{genericp} is non-@code{nil}, this | |
316 | function also returns @code{t} if @var{charcode} is a generic | |
317 | character (@pxref{Splitting Characters}). | |
318 | @end defun | |
319 | ||
320 | @node Character Sets | |
321 | @section Character Sets | |
322 | @cindex character sets | |
323 | ||
324 | Emacs classifies characters into various @dfn{character sets}, each of | |
325 | which has a name which is a symbol. Each character belongs to one and | |
326 | only one character set. | |
327 | ||
328 | In general, there is one character set for each distinct script. For | |
329 | example, @code{latin-iso8859-1} is one character set, | |
330 | @code{greek-iso8859-7} is another, and @code{ascii} is another. An | |
331 | Emacs character set can hold at most 9025 characters; therefore, in some | |
332 | cases, characters that would logically be grouped together are split | |
333 | into several character sets. For example, one set of Chinese | |
334 | characters, generally known as Big 5, is divided into two Emacs | |
335 | character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. | |
336 | ||
337 | @acronym{ASCII} characters are in character set @code{ascii}. The | |
338 | non-@acronym{ASCII} characters 128 through 159 are in character set | |
339 | @code{eight-bit-control}, and codes 160 through 255 are in character set | |
340 | @code{eight-bit-graphic}. | |
341 | ||
342 | @defun charsetp object | |
343 | Returns @code{t} if @var{object} is a symbol that names a character set, | |
344 | @code{nil} otherwise. | |
345 | @end defun | |
346 | ||
347 | @defvar charset-list | |
348 | The value is a list of all defined character set names. | |
349 | @end defvar | |
350 | ||
351 | @defun charset-list | |
352 | This function returns the value of @code{charset-list}. It is only | |
353 | provided for backward compatibility. | |
354 | @end defun | |
355 | ||
356 | @defun char-charset character | |
357 | This function returns the name of the character set that @var{character} | |
358 | belongs to, or the symbol @code{unknown} if @var{character} is not a | |
359 | valid character. | |
360 | @end defun | |
361 | ||
362 | @defun charset-plist charset | |
363 | This function returns the charset property list of the character set | |
364 | @var{charset}. Although @var{charset} is a symbol, this is not the same | |
365 | as the property list of that symbol. Charset properties are used for | |
366 | special purposes within Emacs. | |
367 | @end defun | |
368 | ||
369 | @deffn Command list-charset-chars charset | |
370 | This command displays a list of characters in the character set | |
371 | @var{charset}. | |
372 | @end deffn | |
373 | ||
374 | @node Chars and Bytes | |
375 | @section Characters and Bytes | |
376 | @cindex bytes and characters | |
377 | ||
378 | @cindex introduction sequence (of character) | |
379 | @cindex dimension (of character set) | |
380 | In multibyte representation, each character occupies one or more | |
381 | bytes. Each character set has an @dfn{introduction sequence}, which is | |
382 | normally one or two bytes long. (Exception: the @code{ascii} character | |
383 | set and the @code{eight-bit-graphic} character set have a zero-length | |
384 | introduction sequence.) The introduction sequence is the beginning of | |
385 | the byte sequence for any character in the character set. The rest of | |
386 | the character's bytes distinguish it from the other characters in the | |
387 | same character set. Depending on the character set, there are either | |
388 | one or two distinguishing bytes; the number of such bytes is called the | |
389 | @dfn{dimension} of the character set. | |
390 | ||
391 | @defun charset-dimension charset | |
392 | This function returns the dimension of @var{charset}; at present, the | |
393 | dimension is always 1 or 2. | |
394 | @end defun | |
395 | ||
396 | @defun charset-bytes charset | |
397 | This function returns the number of bytes used to represent a character | |
398 | in character set @var{charset}. | |
399 | @end defun | |
400 | ||
401 | This is the simplest way to determine the byte length of a character | |
402 | set's introduction sequence: | |
403 | ||
404 | @example | |
405 | (- (charset-bytes @var{charset}) | |
406 | (charset-dimension @var{charset})) | |
407 | @end example | |
408 | ||
409 | @node Splitting Characters | |
410 | @section Splitting Characters | |
411 | @cindex character as bytes | |
412 | ||
413 | The functions in this section convert between characters and the byte | |
414 | values used to represent them. For most purposes, there is no need to | |
415 | be concerned with the sequence of bytes used to represent a character, | |
416 | because Emacs translates automatically when necessary. | |
417 | ||
418 | @defun split-char character | |
419 | Return a list containing the name of the character set of | |
420 | @var{character}, followed by one or two byte values (integers) which | |
421 | identify @var{character} within that character set. The number of byte | |
422 | values is the character set's dimension. | |
423 | ||
424 | If @var{character} is invalid as a character code, @code{split-char} | |
425 | returns a list consisting of the symbol @code{unknown} and @var{character}. | |
426 | ||
427 | @example | |
428 | (split-char 2248) | |
429 | @result{} (latin-iso8859-1 72) | |
430 | (split-char 65) | |
431 | @result{} (ascii 65) | |
432 | (split-char 128) | |
433 | @result{} (eight-bit-control 128) | |
434 | @end example | |
435 | @end defun | |
436 | ||
02e99324 | 437 | @c FIXME: update split-char and make-char |
b8d4c8d0 GM |
438 | @cindex generate characters in charsets |
439 | @defun make-char charset &optional code1 code2 | |
440 | This function returns the character in character set @var{charset} whose | |
441 | position codes are @var{code1} and @var{code2}. This is roughly the | |
442 | inverse of @code{split-char}. Normally, you should specify either one | |
443 | or both of @var{code1} and @var{code2} according to the dimension of | |
444 | @var{charset}. For example, | |
445 | ||
446 | @example | |
447 | (make-char 'latin-iso8859-1 72) | |
448 | @result{} 2248 | |
449 | @end example | |
450 | ||
451 | Actually, the eighth bit of both @var{code1} and @var{code2} is zeroed | |
452 | before they are used to index @var{charset}. Thus you may use, for | |
453 | instance, an ISO 8859 character code rather than subtracting 128, as | |
454 | is necessary to index the corresponding Emacs charset. | |
455 | @end defun | |
456 | ||
b8d4c8d0 GM |
457 | @node Scanning Charsets |
458 | @section Scanning for Character Sets | |
459 | ||
460 | Sometimes it is useful to find out which character sets appear in a | |
461 | part of a buffer or a string. One use for this is in determining which | |
462 | coding systems (@pxref{Coding Systems}) are capable of representing all | |
463 | of the text in question. | |
464 | ||
465 | @defun charset-after &optional pos | |
466 | This function return the charset of a character in the current buffer | |
467 | at position @var{pos}. If @var{pos} is omitted or @code{nil}, it | |
468 | defaults to the current value of point. If @var{pos} is out of range, | |
469 | the value is @code{nil}. | |
470 | @end defun | |
471 | ||
472 | @defun find-charset-region beg end &optional translation | |
473 | This function returns a list of the character sets that appear in the | |
474 | current buffer between positions @var{beg} and @var{end}. | |
475 | ||
476 | The optional argument @var{translation} specifies a translation table to | |
477 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
478 | is non-@code{nil}, then each character in the region is translated | |
479 | through this table, and the value returned describes the translated | |
480 | characters instead of the characters actually in the buffer. | |
481 | @end defun | |
482 | ||
483 | @defun find-charset-string string &optional translation | |
484 | This function returns a list of the character sets that appear in the | |
485 | string @var{string}. It is just like @code{find-charset-region}, except | |
486 | that it applies to the contents of @var{string} instead of part of the | |
487 | current buffer. | |
488 | @end defun | |
489 | ||
490 | @node Translation of Characters | |
491 | @section Translation of Characters | |
492 | @cindex character translation tables | |
493 | @cindex translation tables | |
494 | ||
495 | A @dfn{translation table} is a char-table that specifies a mapping | |
496 | of characters into characters. These tables are used in encoding and | |
497 | decoding, and for other purposes. Some coding systems specify their | |
498 | own particular translation tables; there are also default translation | |
499 | tables which apply to all other coding systems. | |
500 | ||
501 | For instance, the coding-system @code{utf-8} has a translation table | |
502 | that maps characters of various charsets (e.g., | |
503 | @code{latin-iso8859-@var{x}}) into Unicode character sets. This way, | |
504 | it can encode Latin-2 characters into UTF-8. Meanwhile, | |
505 | @code{unify-8859-on-decoding-mode} operates by specifying | |
506 | @code{standard-translation-table-for-decode} to translate | |
507 | Latin-@var{x} characters into corresponding Unicode characters. | |
508 | ||
509 | @defun make-translation-table &rest translations | |
510 | This function returns a translation table based on the argument | |
511 | @var{translations}. Each element of @var{translations} should be a | |
512 | list of elements of the form @code{(@var{from} . @var{to})}; this says | |
513 | to translate the character @var{from} into @var{to}. | |
514 | ||
515 | The arguments and the forms in each argument are processed in order, | |
516 | and if a previous form already translates @var{to} to some other | |
517 | character, say @var{to-alt}, @var{from} is also translated to | |
518 | @var{to-alt}. | |
b8d4c8d0 GM |
519 | @end defun |
520 | ||
521 | In decoding, the translation table's translations are applied to the | |
522 | characters that result from ordinary decoding. If a coding system has | |
523 | property @code{translation-table-for-decode}, that specifies the | |
524 | translation table to use. (This is a property of the coding system, | |
525 | as returned by @code{coding-system-get}, not a property of the symbol | |
526 | that is the coding system's name. @xref{Coding System Basics,, Basic | |
527 | Concepts of Coding Systems}.) Otherwise, if | |
528 | @code{standard-translation-table-for-decode} is non-@code{nil}, | |
529 | decoding uses that table. | |
530 | ||
531 | In encoding, the translation table's translations are applied to the | |
532 | characters in the buffer, and the result of translation is actually | |
533 | encoded. If a coding system has property | |
534 | @code{translation-table-for-encode}, that specifies the translation | |
535 | table to use. Otherwise the variable | |
536 | @code{standard-translation-table-for-encode} specifies the translation | |
537 | table. | |
538 | ||
539 | @defvar standard-translation-table-for-decode | |
540 | This is the default translation table for decoding, for | |
541 | coding systems that don't specify any other translation table. | |
542 | @end defvar | |
543 | ||
544 | @defvar standard-translation-table-for-encode | |
545 | This is the default translation table for encoding, for | |
546 | coding systems that don't specify any other translation table. | |
547 | @end defvar | |
548 | ||
b8d4c8d0 GM |
549 | @node Coding Systems |
550 | @section Coding Systems | |
551 | ||
552 | @cindex coding system | |
553 | When Emacs reads or writes a file, and when Emacs sends text to a | |
554 | subprocess or receives text from a subprocess, it normally performs | |
555 | character code conversion and end-of-line conversion as specified | |
556 | by a particular @dfn{coding system}. | |
557 | ||
558 | How to define a coding system is an arcane matter, and is not | |
559 | documented here. | |
560 | ||
561 | @menu | |
562 | * Coding System Basics:: Basic concepts. | |
563 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
564 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
565 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
566 | * Default Coding Systems:: Controlling the default choices. | |
567 | * Specifying Coding Systems:: Requesting a particular coding system | |
568 | for a single file operation. | |
569 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
570 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
571 | * MS-DOS File Types:: How DOS "text" and "binary" files | |
572 | relate to coding systems. | |
573 | @end menu | |
574 | ||
575 | @node Coding System Basics | |
576 | @subsection Basic Concepts of Coding Systems | |
577 | ||
578 | @cindex character code conversion | |
579 | @dfn{Character code conversion} involves conversion between the encoding | |
580 | used inside Emacs and some other encoding. Emacs supports many | |
581 | different encodings, in that it can convert to and from them. For | |
582 | example, it can convert text to or from encodings such as Latin 1, Latin | |
583 | 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some | |
584 | cases, Emacs supports several alternative encodings for the same | |
585 | characters; for example, there are three coding systems for the Cyrillic | |
586 | (Russian) alphabet: ISO, Alternativnyj, and KOI8. | |
587 | ||
588 | Most coding systems specify a particular character code for | |
589 | conversion, but some of them leave the choice unspecified---to be chosen | |
590 | heuristically for each file, based on the data. | |
591 | ||
592 | In general, a coding system doesn't guarantee roundtrip identity: | |
593 | decoding a byte sequence using coding system, then encoding the | |
594 | resulting text in the same coding system, can produce a different byte | |
595 | sequence. However, the following coding systems do guarantee that the | |
596 | byte sequence will be the same as what you originally decoded: | |
597 | ||
598 | @quotation | |
599 | chinese-big5 chinese-iso-8bit cyrillic-iso-8bit emacs-mule | |
600 | greek-iso-8bit hebrew-iso-8bit iso-latin-1 iso-latin-2 iso-latin-3 | |
601 | iso-latin-4 iso-latin-5 iso-latin-8 iso-latin-9 iso-safe | |
602 | japanese-iso-8bit japanese-shift-jis korean-iso-8bit raw-text | |
603 | @end quotation | |
604 | ||
605 | Encoding buffer text and then decoding the result can also fail to | |
606 | reproduce the original text. For instance, if you encode Latin-2 | |
607 | characters with @code{utf-8} and decode the result using the same | |
608 | coding system, you'll get Unicode characters (of charset | |
609 | @code{mule-unicode-0100-24ff}). If you encode Unicode characters with | |
610 | @code{iso-latin-2} and decode the result with the same coding system, | |
611 | you'll get Latin-2 characters. | |
612 | ||
613 | @cindex EOL conversion | |
614 | @cindex end-of-line conversion | |
615 | @cindex line end conversion | |
616 | @dfn{End of line conversion} handles three different conventions used | |
617 | on various systems for representing end of line in files. The Unix | |
618 | convention is to use the linefeed character (also called newline). The | |
619 | DOS convention is to use a carriage-return and a linefeed at the end of | |
620 | a line. The Mac convention is to use just carriage-return. | |
621 | ||
622 | @cindex base coding system | |
623 | @cindex variant coding system | |
624 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
625 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
626 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
627 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
628 | well. Most base coding systems have three corresponding variants whose | |
629 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. | |
630 | ||
631 | The coding system @code{raw-text} is special in that it prevents | |
632 | character code conversion, and causes the buffer visited with that | |
633 | coding system to be a unibyte buffer. It does not specify the | |
634 | end-of-line conversion, allowing that to be determined as usual by the | |
635 | data, and has the usual three variants which specify the end-of-line | |
636 | conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: | |
637 | it specifies no conversion of either character codes or end-of-line. | |
638 | ||
639 | The coding system @code{emacs-mule} specifies that the data is | |
640 | represented in the internal Emacs encoding. This is like | |
641 | @code{raw-text} in that no code conversion happens, but different in | |
642 | that the result is multibyte data. | |
643 | ||
644 | @defun coding-system-get coding-system property | |
645 | This function returns the specified property of the coding system | |
646 | @var{coding-system}. Most coding system properties exist for internal | |
647 | purposes, but one that you might find useful is @code{mime-charset}. | |
648 | That property's value is the name used in MIME for the character coding | |
649 | which this coding system can read and write. Examples: | |
650 | ||
651 | @example | |
652 | (coding-system-get 'iso-latin-1 'mime-charset) | |
653 | @result{} iso-8859-1 | |
654 | (coding-system-get 'iso-2022-cn 'mime-charset) | |
655 | @result{} iso-2022-cn | |
656 | (coding-system-get 'cyrillic-koi8 'mime-charset) | |
657 | @result{} koi8-r | |
658 | @end example | |
659 | ||
660 | The value of the @code{mime-charset} property is also defined | |
661 | as an alias for the coding system. | |
662 | @end defun | |
663 | ||
664 | @node Encoding and I/O | |
665 | @subsection Encoding and I/O | |
666 | ||
667 | The principal purpose of coding systems is for use in reading and | |
668 | writing files. The function @code{insert-file-contents} uses | |
669 | a coding system for decoding the file data, and @code{write-region} | |
670 | uses one to encode the buffer contents. | |
671 | ||
672 | You can specify the coding system to use either explicitly | |
673 | (@pxref{Specifying Coding Systems}), or implicitly using a default | |
674 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
675 | completely specify what to do. For example, they may choose a coding | |
676 | system such as @code{undefined} which leaves the character code | |
677 | conversion to be determined from the data. In these cases, the I/O | |
678 | operation finishes the job of choosing a coding system. Very often | |
679 | you will want to find out afterwards which coding system was chosen. | |
680 | ||
681 | @defvar buffer-file-coding-system | |
e2e3f1d7 MR |
682 | This buffer-local variable records the coding system used for saving the |
683 | buffer and for writing part of the buffer with @code{write-region}. If | |
684 | the text to be written cannot be safely encoded using the coding system | |
685 | specified by this variable, these operations select an alternative | |
686 | encoding by calling the function @code{select-safe-coding-system} | |
687 | (@pxref{User-Chosen Coding Systems}). If selecting a different encoding | |
688 | requires to ask the user to specify a coding system, | |
689 | @code{buffer-file-coding-system} is updated to the newly selected coding | |
690 | system. | |
b8d4c8d0 GM |
691 | |
692 | @code{buffer-file-coding-system} does @emph{not} affect sending text | |
693 | to a subprocess. | |
694 | @end defvar | |
695 | ||
696 | @defvar save-buffer-coding-system | |
697 | This variable specifies the coding system for saving the buffer (by | |
698 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
699 | for @code{write-region}. | |
700 | ||
701 | When a command to save the buffer starts out to use | |
702 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), | |
703 | and that coding system cannot handle | |
704 | the actual text in the buffer, the command asks the user to choose | |
705 | another coding system (by calling @code{select-safe-coding-system}). | |
706 | After that happens, the command also updates | |
707 | @code{buffer-file-coding-system} to represent the coding system that | |
708 | the user specified. | |
709 | @end defvar | |
710 | ||
711 | @defvar last-coding-system-used | |
712 | I/O operations for files and subprocesses set this variable to the | |
713 | coding system name that was used. The explicit encoding and decoding | |
714 | functions (@pxref{Explicit Encoding}) set it too. | |
715 | ||
716 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
717 | it can change whenever Emacs waits; therefore, you should copy the | |
718 | value shortly after the function call that stores the value you are | |
719 | interested in. | |
720 | @end defvar | |
721 | ||
722 | The variable @code{selection-coding-system} specifies how to encode | |
723 | selections for the window system. @xref{Window System Selections}. | |
724 | ||
725 | @defvar file-name-coding-system | |
726 | The variable @code{file-name-coding-system} specifies the coding | |
727 | system to use for encoding file names. Emacs encodes file names using | |
728 | that coding system for all file operations. If | |
729 | @code{file-name-coding-system} is @code{nil}, Emacs uses a default | |
730 | coding system determined by the selected language environment. In the | |
731 | default language environment, any non-@acronym{ASCII} characters in | |
732 | file names are not encoded specially; they appear in the file system | |
733 | using the internal Emacs representation. | |
734 | @end defvar | |
735 | ||
736 | @strong{Warning:} if you change @code{file-name-coding-system} (or | |
737 | the language environment) in the middle of an Emacs session, problems | |
738 | can result if you have already visited files whose names were encoded | |
739 | using the earlier coding system and are handled differently under the | |
740 | new coding system. If you try to save one of these buffers under the | |
741 | visited file name, saving may use the wrong file name, or it may get | |
742 | an error. If such a problem happens, use @kbd{C-x C-w} to specify a | |
743 | new file name for that buffer. | |
744 | ||
745 | @node Lisp and Coding Systems | |
746 | @subsection Coding Systems in Lisp | |
747 | ||
748 | Here are the Lisp facilities for working with coding systems: | |
749 | ||
750 | @defun coding-system-list &optional base-only | |
751 | This function returns a list of all coding system names (symbols). If | |
752 | @var{base-only} is non-@code{nil}, the value includes only the | |
753 | base coding systems. Otherwise, it includes alias and variant coding | |
754 | systems as well. | |
755 | @end defun | |
756 | ||
757 | @defun coding-system-p object | |
758 | This function returns @code{t} if @var{object} is a coding system | |
759 | name or @code{nil}. | |
760 | @end defun | |
761 | ||
762 | @defun check-coding-system coding-system | |
763 | This function checks the validity of @var{coding-system}. | |
764 | If that is valid, it returns @var{coding-system}. | |
765 | Otherwise it signals an error with condition @code{coding-system-error}. | |
766 | @end defun | |
767 | ||
768 | @defun coding-system-eol-type coding-system | |
769 | This function returns the type of end-of-line (a.k.a.@: @dfn{eol}) | |
770 | conversion used by @var{coding-system}. If @var{coding-system} | |
771 | specifies a certain eol conversion, the return value is an integer 0, | |
772 | 1, or 2, standing for @code{unix}, @code{dos}, and @code{mac}, | |
773 | respectively. If @var{coding-system} doesn't specify eol conversion | |
774 | explicitly, the return value is a vector of coding systems, each one | |
775 | with one of the possible eol conversion types, like this: | |
776 | ||
777 | @lisp | |
778 | (coding-system-eol-type 'latin-1) | |
779 | @result{} [latin-1-unix latin-1-dos latin-1-mac] | |
780 | @end lisp | |
781 | ||
782 | @noindent | |
783 | If this function returns a vector, Emacs will decide, as part of the | |
784 | text encoding or decoding process, what eol conversion to use. For | |
785 | decoding, the end-of-line format of the text is auto-detected, and the | |
786 | eol conversion is set to match it (e.g., DOS-style CRLF format will | |
787 | imply @code{dos} eol conversion). For encoding, the eol conversion is | |
788 | taken from the appropriate default coding system (e.g., | |
789 | @code{default-buffer-file-coding-system} for | |
790 | @code{buffer-file-coding-system}), or from the default eol conversion | |
791 | appropriate for the underlying platform. | |
792 | @end defun | |
793 | ||
794 | @defun coding-system-change-eol-conversion coding-system eol-type | |
795 | This function returns a coding system which is like @var{coding-system} | |
796 | except for its eol conversion, which is specified by @code{eol-type}. | |
797 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or | |
798 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
799 | the end-of-line conversion from the data. | |
800 | ||
801 | @var{eol-type} may also be 0, 1 or 2, standing for @code{unix}, | |
802 | @code{dos} and @code{mac}, respectively. | |
803 | @end defun | |
804 | ||
805 | @defun coding-system-change-text-conversion eol-coding text-coding | |
806 | This function returns a coding system which uses the end-of-line | |
807 | conversion of @var{eol-coding}, and the text conversion of | |
808 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
809 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
810 | @end defun | |
811 | ||
812 | @defun find-coding-systems-region from to | |
813 | This function returns a list of coding systems that could be used to | |
814 | encode a text between @var{from} and @var{to}. All coding systems in | |
815 | the list can safely encode any multibyte characters in that portion of | |
816 | the text. | |
817 | ||
818 | If the text contains no multibyte characters, the function returns the | |
819 | list @code{(undecided)}. | |
820 | @end defun | |
821 | ||
822 | @defun find-coding-systems-string string | |
823 | This function returns a list of coding systems that could be used to | |
824 | encode the text of @var{string}. All coding systems in the list can | |
825 | safely encode any multibyte characters in @var{string}. If the text | |
826 | contains no multibyte characters, this returns the list | |
827 | @code{(undecided)}. | |
828 | @end defun | |
829 | ||
830 | @defun find-coding-systems-for-charsets charsets | |
831 | This function returns a list of coding systems that could be used to | |
832 | encode all the character sets in the list @var{charsets}. | |
833 | @end defun | |
834 | ||
835 | @defun detect-coding-region start end &optional highest | |
836 | This function chooses a plausible coding system for decoding the text | |
837 | from @var{start} to @var{end}. This text should be a byte sequence | |
838 | (@pxref{Explicit Encoding}). | |
839 | ||
840 | Normally this function returns a list of coding systems that could | |
841 | handle decoding the text that was scanned. They are listed in order of | |
842 | decreasing priority. But if @var{highest} is non-@code{nil}, then the | |
843 | return value is just one coding system, the one that is highest in | |
844 | priority. | |
845 | ||
846 | If the region contains only @acronym{ASCII} characters except for such | |
847 | ISO-2022 control characters ISO-2022 as @code{ESC}, the value is | |
848 | @code{undecided} or @code{(undecided)}, or a variant specifying | |
849 | end-of-line conversion, if that can be deduced from the text. | |
850 | @end defun | |
851 | ||
852 | @defun detect-coding-string string &optional highest | |
853 | This function is like @code{detect-coding-region} except that it | |
854 | operates on the contents of @var{string} instead of bytes in the buffer. | |
855 | @end defun | |
856 | ||
857 | @xref{Coding systems for a subprocess,, Process Information}, in | |
858 | particular the description of the functions | |
859 | @code{process-coding-system} and @code{set-process-coding-system}, for | |
860 | how to examine or set the coding systems used for I/O to a subprocess. | |
861 | ||
862 | @node User-Chosen Coding Systems | |
863 | @subsection User-Chosen Coding Systems | |
864 | ||
865 | @cindex select safe coding system | |
866 | @defun select-safe-coding-system from to &optional default-coding-system accept-default-p file | |
867 | This function selects a coding system for encoding specified text, | |
868 | asking the user to choose if necessary. Normally the specified text | |
869 | is the text in the current buffer between @var{from} and @var{to}. If | |
870 | @var{from} is a string, the string specifies the text to encode, and | |
871 | @var{to} is ignored. | |
872 | ||
873 | If @var{default-coding-system} is non-@code{nil}, that is the first | |
874 | coding system to try; if that can handle the text, | |
875 | @code{select-safe-coding-system} returns that coding system. It can | |
876 | also be a list of coding systems; then the function tries each of them | |
877 | one by one. After trying all of them, it next tries the current | |
878 | buffer's value of @code{buffer-file-coding-system} (if it is not | |
879 | @code{undecided}), then the value of | |
880 | @code{default-buffer-file-coding-system} and finally the user's most | |
881 | preferred coding system, which the user can set using the command | |
882 | @code{prefer-coding-system} (@pxref{Recognize Coding,, Recognizing | |
883 | Coding Systems, emacs, The GNU Emacs Manual}). | |
884 | ||
885 | If one of those coding systems can safely encode all the specified | |
886 | text, @code{select-safe-coding-system} chooses it and returns it. | |
887 | Otherwise, it asks the user to choose from a list of coding systems | |
888 | which can encode all the text, and returns the user's choice. | |
889 | ||
890 | @var{default-coding-system} can also be a list whose first element is | |
891 | t and whose other elements are coding systems. Then, if no coding | |
892 | system in the list can handle the text, @code{select-safe-coding-system} | |
893 | queries the user immediately, without trying any of the three | |
894 | alternatives described above. | |
895 | ||
896 | The optional argument @var{accept-default-p}, if non-@code{nil}, | |
897 | should be a function to determine whether a coding system selected | |
898 | without user interaction is acceptable. @code{select-safe-coding-system} | |
899 | calls this function with one argument, the base coding system of the | |
900 | selected coding system. If @var{accept-default-p} returns @code{nil}, | |
901 | @code{select-safe-coding-system} rejects the silently selected coding | |
902 | system, and asks the user to select a coding system from a list of | |
903 | possible candidates. | |
904 | ||
905 | @vindex select-safe-coding-system-accept-default-p | |
906 | If the variable @code{select-safe-coding-system-accept-default-p} is | |
907 | non-@code{nil}, its value overrides the value of | |
908 | @var{accept-default-p}. | |
909 | ||
910 | As a final step, before returning the chosen coding system, | |
911 | @code{select-safe-coding-system} checks whether that coding system is | |
912 | consistent with what would be selected if the contents of the region | |
913 | were read from a file. (If not, this could lead to data corruption in | |
914 | a file subsequently re-visited and edited.) Normally, | |
915 | @code{select-safe-coding-system} uses @code{buffer-file-name} as the | |
916 | file for this purpose, but if @var{file} is non-@code{nil}, it uses | |
917 | that file instead (this can be relevant for @code{write-region} and | |
918 | similar functions). If it detects an apparent inconsistency, | |
919 | @code{select-safe-coding-system} queries the user before selecting the | |
920 | coding system. | |
921 | @end defun | |
922 | ||
923 | Here are two functions you can use to let the user specify a coding | |
924 | system, with completion. @xref{Completion}. | |
925 | ||
926 | @defun read-coding-system prompt &optional default | |
927 | This function reads a coding system using the minibuffer, prompting with | |
928 | string @var{prompt}, and returns the coding system name as a symbol. If | |
929 | the user enters null input, @var{default} specifies which coding system | |
930 | to return. It should be a symbol or a string. | |
931 | @end defun | |
932 | ||
933 | @defun read-non-nil-coding-system prompt | |
934 | This function reads a coding system using the minibuffer, prompting with | |
935 | string @var{prompt}, and returns the coding system name as a symbol. If | |
936 | the user tries to enter null input, it asks the user to try again. | |
937 | @xref{Coding Systems}. | |
938 | @end defun | |
939 | ||
940 | @node Default Coding Systems | |
941 | @subsection Default Coding Systems | |
942 | ||
943 | This section describes variables that specify the default coding | |
944 | system for certain files or when running certain subprograms, and the | |
945 | function that I/O operations use to access them. | |
946 | ||
947 | The idea of these variables is that you set them once and for all to the | |
948 | defaults you want, and then do not change them again. To specify a | |
949 | particular coding system for a particular operation in a Lisp program, | |
950 | don't change these variables; instead, override them using | |
951 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
952 | (@pxref{Specifying Coding Systems}). | |
953 | ||
954 | @defvar auto-coding-regexp-alist | |
955 | This variable is an alist of text patterns and corresponding coding | |
956 | systems. Each element has the form @code{(@var{regexp} | |
957 | . @var{coding-system})}; a file whose first few kilobytes match | |
958 | @var{regexp} is decoded with @var{coding-system} when its contents are | |
959 | read into a buffer. The settings in this alist take priority over | |
960 | @code{coding:} tags in the files and the contents of | |
961 | @code{file-coding-system-alist} (see below). The default value is set | |
962 | so that Emacs automatically recognizes mail files in Babyl format and | |
963 | reads them with no code conversions. | |
964 | @end defvar | |
965 | ||
966 | @defvar file-coding-system-alist | |
967 | This variable is an alist that specifies the coding systems to use for | |
968 | reading and writing particular files. Each element has the form | |
969 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
970 | expression that matches certain file names. The element applies to file | |
971 | names that match @var{pattern}. | |
972 | ||
973 | The @sc{cdr} of the element, @var{coding}, should be either a coding | |
974 | system, a cons cell containing two coding systems, or a function name (a | |
975 | symbol with a function definition). If @var{coding} is a coding system, | |
976 | that coding system is used for both reading the file and writing it. If | |
977 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
978 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
979 | coding system for encoding. | |
980 | ||
981 | If @var{coding} is a function name, the function should take one | |
982 | argument, a list of all arguments passed to | |
983 | @code{find-operation-coding-system}. It must return a coding system | |
984 | or a cons cell containing two coding systems. This value has the same | |
985 | meaning as described above. | |
986 | ||
987 | If @var{coding} (or what returned by the above function) is | |
988 | @code{undecided}, the normal code-detection is performed. | |
989 | @end defvar | |
990 | ||
991 | @defvar process-coding-system-alist | |
992 | This variable is an alist specifying which coding systems to use for a | |
993 | subprocess, depending on which program is running in the subprocess. It | |
994 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
995 | matched against the program name used to start the subprocess. The coding | |
996 | system or systems specified in this alist are used to initialize the | |
997 | coding systems used for I/O to the subprocess, but you can specify | |
998 | other coding systems later using @code{set-process-coding-system}. | |
999 | @end defvar | |
1000 | ||
1001 | @strong{Warning:} Coding systems such as @code{undecided}, which | |
1002 | determine the coding system from the data, do not work entirely reliably | |
1003 | with asynchronous subprocess output. This is because Emacs handles | |
1004 | asynchronous subprocess output in batches, as it arrives. If the coding | |
1005 | system leaves the character code conversion unspecified, or leaves the | |
1006 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
1007 | conversion from one batch at a time, and this does not always work. | |
1008 | ||
1009 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
1010 | coding system which determines both the character code conversion and | |
1011 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
1012 | rather than @code{undecided} or @code{latin-1}. | |
1013 | ||
1014 | @defvar network-coding-system-alist | |
1015 | This variable is an alist that specifies the coding system to use for | |
1016 | network streams. It works much like @code{file-coding-system-alist}, | |
1017 | with the difference that the @var{pattern} in an element may be either a | |
1018 | port number or a regular expression. If it is a regular expression, it | |
1019 | is matched against the network service name used to open the network | |
1020 | stream. | |
1021 | @end defvar | |
1022 | ||
1023 | @defvar default-process-coding-system | |
1024 | This variable specifies the coding systems to use for subprocess (and | |
1025 | network stream) input and output, when nothing else specifies what to | |
1026 | do. | |
1027 | ||
1028 | The value should be a cons cell of the form @code{(@var{input-coding} | |
1029 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
1030 | the subprocess, and @var{output-coding} applies to output to it. | |
1031 | @end defvar | |
1032 | ||
1033 | @defvar auto-coding-functions | |
1034 | This variable holds a list of functions that try to determine a | |
1035 | coding system for a file based on its undecoded contents. | |
1036 | ||
1037 | Each function in this list should be written to look at text in the | |
1038 | current buffer, but should not modify it in any way. The buffer will | |
1039 | contain undecoded text of parts of the file. Each function should | |
1040 | take one argument, @var{size}, which tells it how many characters to | |
1041 | look at, starting from point. If the function succeeds in determining | |
1042 | a coding system for the file, it should return that coding system. | |
1043 | Otherwise, it should return @code{nil}. | |
1044 | ||
1045 | If a file has a @samp{coding:} tag, that takes precedence, so these | |
1046 | functions won't be called. | |
1047 | @end defvar | |
1048 | ||
1049 | @defun find-operation-coding-system operation &rest arguments | |
1050 | This function returns the coding system to use (by default) for | |
1051 | performing @var{operation} with @var{arguments}. The value has this | |
1052 | form: | |
1053 | ||
1054 | @example | |
1055 | (@var{decoding-system} . @var{encoding-system}) | |
1056 | @end example | |
1057 | ||
1058 | The first element, @var{decoding-system}, is the coding system to use | |
1059 | for decoding (in case @var{operation} does decoding), and | |
1060 | @var{encoding-system} is the coding system for encoding (in case | |
1061 | @var{operation} does encoding). | |
1062 | ||
1063 | The argument @var{operation} is a symbol, one of @code{write-region}, | |
1064 | @code{start-process}, @code{call-process}, @code{call-process-region}, | |
1065 | @code{insert-file-contents}, or @code{open-network-stream}. These are | |
1066 | the names of the Emacs I/O primitives that can do character code and | |
1067 | eol conversion. | |
1068 | ||
1069 | The remaining arguments should be the same arguments that might be given | |
1070 | to the corresponding I/O primitive. Depending on the primitive, one | |
1071 | of those arguments is selected as the @dfn{target}. For example, if | |
1072 | @var{operation} does file I/O, whichever argument specifies the file | |
1073 | name is the target. For subprocess primitives, the process name is the | |
1074 | target. For @code{open-network-stream}, the target is the service name | |
1075 | or port number. | |
1076 | ||
1077 | Depending on @var{operation}, this function looks up the target in | |
1078 | @code{file-coding-system-alist}, @code{process-coding-system-alist}, | |
1079 | or @code{network-coding-system-alist}. If the target is found in the | |
1080 | alist, @code{find-operation-coding-system} returns its association in | |
1081 | the alist; otherwise it returns @code{nil}. | |
1082 | ||
1083 | If @var{operation} is @code{insert-file-contents}, the argument | |
1084 | corresponding to the target may be a cons cell of the form | |
1085 | @code{(@var{filename} . @var{buffer})}). In that case, @var{filename} | |
1086 | is a file name to look up in @code{file-coding-system-alist}, and | |
1087 | @var{buffer} is a buffer that contains the file's contents (not yet | |
1088 | decoded). If @code{file-coding-system-alist} specifies a function to | |
1089 | call for this file, and that function needs to examine the file's | |
1090 | contents (as it usually does), it should examine the contents of | |
1091 | @var{buffer} instead of reading the file. | |
1092 | @end defun | |
1093 | ||
1094 | @node Specifying Coding Systems | |
1095 | @subsection Specifying a Coding System for One Operation | |
1096 | ||
1097 | You can specify the coding system for a specific operation by binding | |
1098 | the variables @code{coding-system-for-read} and/or | |
1099 | @code{coding-system-for-write}. | |
1100 | ||
1101 | @defvar coding-system-for-read | |
1102 | If this variable is non-@code{nil}, it specifies the coding system to | |
1103 | use for reading a file, or for input from a synchronous subprocess. | |
1104 | ||
1105 | It also applies to any asynchronous subprocess or network stream, but in | |
1106 | a different way: the value of @code{coding-system-for-read} when you | |
1107 | start the subprocess or open the network stream specifies the input | |
1108 | decoding method for that subprocess or network stream. It remains in | |
1109 | use for that subprocess or network stream unless and until overridden. | |
1110 | ||
1111 | The right way to use this variable is to bind it with @code{let} for a | |
1112 | specific I/O operation. Its global value is normally @code{nil}, and | |
1113 | you should not globally set it to any other value. Here is an example | |
1114 | of the right way to use the variable: | |
1115 | ||
1116 | @example | |
1117 | ;; @r{Read the file with no character code conversion.} | |
1118 | ;; @r{Assume @acronym{crlf} represents end-of-line.} | |
1119 | (let ((coding-system-for-read 'emacs-mule-dos)) | |
1120 | (insert-file-contents filename)) | |
1121 | @end example | |
1122 | ||
1123 | When its value is non-@code{nil}, this variable takes precedence over | |
1124 | all other methods of specifying a coding system to use for input, | |
1125 | including @code{file-coding-system-alist}, | |
1126 | @code{process-coding-system-alist} and | |
1127 | @code{network-coding-system-alist}. | |
1128 | @end defvar | |
1129 | ||
1130 | @defvar coding-system-for-write | |
1131 | This works much like @code{coding-system-for-read}, except that it | |
1132 | applies to output rather than input. It affects writing to files, | |
1133 | as well as sending output to subprocesses and net connections. | |
1134 | ||
1135 | When a single operation does both input and output, as do | |
1136 | @code{call-process-region} and @code{start-process}, both | |
1137 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1138 | affect it. | |
1139 | @end defvar | |
1140 | ||
1141 | @defvar inhibit-eol-conversion | |
1142 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
1143 | no matter which coding system is specified. This applies to all the | |
1144 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
1145 | decoding functions (@pxref{Explicit Encoding}). | |
1146 | @end defvar | |
1147 | ||
1148 | @node Explicit Encoding | |
1149 | @subsection Explicit Encoding and Decoding | |
1150 | @cindex encoding in coding systems | |
1151 | @cindex decoding in coding systems | |
1152 | ||
1153 | All the operations that transfer text in and out of Emacs have the | |
1154 | ability to use a coding system to encode or decode the text. | |
1155 | You can also explicitly encode and decode text using the functions | |
1156 | in this section. | |
1157 | ||
1158 | The result of encoding, and the input to decoding, are not ordinary | |
1159 | text. They logically consist of a series of byte values; that is, a | |
1160 | series of characters whose codes are in the range 0 through 255. In a | |
1161 | multibyte buffer or string, character codes 128 through 159 are | |
1162 | represented by multibyte sequences, but this is invisible to Lisp | |
1163 | programs. | |
1164 | ||
1165 | The usual way to read a file into a buffer as a sequence of bytes, so | |
1166 | you can decode the contents explicitly, is with | |
1167 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
1168 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
1169 | visiting a file with @code{find-file-noselect}. These methods result in | |
1170 | a unibyte buffer. | |
1171 | ||
1172 | The usual way to use the byte sequence that results from explicitly | |
1173 | encoding text is to copy it to a file or process---for example, to write | |
1174 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
1175 | encoding by binding @code{coding-system-for-write} to | |
1176 | @code{no-conversion}. | |
1177 | ||
1178 | Here are the functions to perform explicit encoding or decoding. The | |
1179 | encoding functions produce sequences of bytes; the decoding functions | |
1180 | are meant to operate on sequences of bytes. All of these functions | |
1181 | discard text properties. | |
1182 | ||
1183 | @deffn Command encode-coding-region start end coding-system | |
1184 | This command encodes the text from @var{start} to @var{end} according | |
1185 | to coding system @var{coding-system}. The encoded text replaces the | |
1186 | original text in the buffer. The result of encoding is logically a | |
1187 | sequence of bytes, but the buffer remains multibyte if it was multibyte | |
1188 | before. | |
1189 | ||
1190 | This command returns the length of the encoded text. | |
1191 | @end deffn | |
1192 | ||
1193 | @defun encode-coding-string string coding-system &optional nocopy | |
1194 | This function encodes the text in @var{string} according to coding | |
1195 | system @var{coding-system}. It returns a new string containing the | |
1196 | encoded text, except when @var{nocopy} is non-@code{nil}, in which | |
1197 | case the function may return @var{string} itself if the encoding | |
1198 | operation is trivial. The result of encoding is a unibyte string. | |
1199 | @end defun | |
1200 | ||
1201 | @deffn Command decode-coding-region start end coding-system | |
1202 | This command decodes the text from @var{start} to @var{end} according | |
1203 | to coding system @var{coding-system}. The decoded text replaces the | |
1204 | original text in the buffer. To make explicit decoding useful, the text | |
1205 | before decoding ought to be a sequence of byte values, but both | |
1206 | multibyte and unibyte buffers are acceptable. | |
1207 | ||
1208 | This command returns the length of the decoded text. | |
1209 | @end deffn | |
1210 | ||
1211 | @defun decode-coding-string string coding-system &optional nocopy | |
1212 | This function decodes the text in @var{string} according to coding | |
1213 | system @var{coding-system}. It returns a new string containing the | |
1214 | decoded text, except when @var{nocopy} is non-@code{nil}, in which | |
1215 | case the function may return @var{string} itself if the decoding | |
1216 | operation is trivial. To make explicit decoding useful, the contents | |
1217 | of @var{string} ought to be a sequence of byte values, but a multibyte | |
1218 | string is acceptable. | |
1219 | @end defun | |
1220 | ||
1221 | @defun decode-coding-inserted-region from to filename &optional visit beg end replace | |
1222 | This function decodes the text from @var{from} to @var{to} as if | |
1223 | it were being read from file @var{filename} using @code{insert-file-contents} | |
1224 | using the rest of the arguments provided. | |
1225 | ||
1226 | The normal way to use this function is after reading text from a file | |
1227 | without decoding, if you decide you would rather have decoded it. | |
1228 | Instead of deleting the text and reading it again, this time with | |
1229 | decoding, you can call this function. | |
1230 | @end defun | |
1231 | ||
1232 | @node Terminal I/O Encoding | |
1233 | @subsection Terminal I/O Encoding | |
1234 | ||
1235 | Emacs can decode keyboard input using a coding system, and encode | |
1236 | terminal output. This is useful for terminals that transmit or display | |
1237 | text using a particular encoding such as Latin-1. Emacs does not set | |
1238 | @code{last-coding-system-used} for encoding or decoding for the | |
1239 | terminal. | |
1240 | ||
1241 | @defun keyboard-coding-system | |
1242 | This function returns the coding system that is in use for decoding | |
1243 | keyboard input---or @code{nil} if no coding system is to be used. | |
1244 | @end defun | |
1245 | ||
1246 | @deffn Command set-keyboard-coding-system coding-system | |
1247 | This command specifies @var{coding-system} as the coding system to | |
1248 | use for decoding keyboard input. If @var{coding-system} is @code{nil}, | |
1249 | that means do not decode keyboard input. | |
1250 | @end deffn | |
1251 | ||
1252 | @defun terminal-coding-system | |
1253 | This function returns the coding system that is in use for encoding | |
1254 | terminal output---or @code{nil} for no encoding. | |
1255 | @end defun | |
1256 | ||
1257 | @deffn Command set-terminal-coding-system coding-system | |
1258 | This command specifies @var{coding-system} as the coding system to use | |
1259 | for encoding terminal output. If @var{coding-system} is @code{nil}, | |
1260 | that means do not encode terminal output. | |
1261 | @end deffn | |
1262 | ||
1263 | @node MS-DOS File Types | |
1264 | @subsection MS-DOS File Types | |
1265 | @cindex DOS file types | |
1266 | @cindex MS-DOS file types | |
1267 | @cindex Windows file types | |
1268 | @cindex file types on MS-DOS and Windows | |
1269 | @cindex text files and binary files | |
1270 | @cindex binary files and text files | |
1271 | ||
1272 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate | |
1273 | end-of-line conversion for a file by looking at the file's name. This | |
1274 | feature classifies files as @dfn{text files} and @dfn{binary files}. By | |
1275 | ``binary file'' we mean a file of literal byte values that are not | |
1276 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1277 | and no character code conversion for them. On the other hand, the bytes | |
1278 | in a text file are intended to represent characters; when you create a | |
1279 | new file whose name implies that it is a text file, Emacs uses DOS | |
1280 | end-of-line conversion. | |
1281 | ||
1282 | @defvar buffer-file-type | |
1283 | This variable, automatically buffer-local in each buffer, records the | |
1284 | file type of the buffer's visited file. When a buffer does not specify | |
1285 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1286 | used to determine which coding system to use when writing the contents | |
1287 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1288 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1289 | Otherwise, @code{undecided-dos} is used. | |
1290 | ||
1291 | Normally this variable is set by visiting a file; it is set to | |
1292 | @code{nil} if the file was visited without any actual conversion. | |
1293 | @end defvar | |
1294 | ||
1295 | @defopt file-name-buffer-file-type-alist | |
1296 | This variable holds an alist for recognizing text and binary files. | |
1297 | Each element has the form (@var{regexp} . @var{type}), where | |
1298 | @var{regexp} is matched against the file name, and @var{type} may be | |
1299 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1300 | compute which. If it is a function, then it is called with a single | |
1301 | argument (the file name) and should return @code{t} or @code{nil}. | |
1302 | ||
1303 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide | |
1304 | which coding system to use when reading a file. For a text file, | |
1305 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1306 | is used. | |
1307 | ||
1308 | If no element in this alist matches a given file name, then | |
1309 | @code{default-buffer-file-type} says how to treat the file. | |
1310 | @end defopt | |
1311 | ||
1312 | @defopt default-buffer-file-type | |
1313 | This variable says how to handle files for which | |
1314 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1315 | ||
1316 | If this variable is non-@code{nil}, then these files are treated as | |
1317 | binary: the coding system @code{no-conversion} is used. Otherwise, | |
1318 | nothing special is done for them---the coding system is deduced solely | |
1319 | from the file contents, in the usual Emacs fashion. | |
1320 | @end defopt | |
1321 | ||
1322 | @node Input Methods | |
1323 | @section Input Methods | |
1324 | @cindex input methods | |
1325 | ||
1326 | @dfn{Input methods} provide convenient ways of entering non-@acronym{ASCII} | |
1327 | characters from the keyboard. Unlike coding systems, which translate | |
1328 | non-@acronym{ASCII} characters to and from encodings meant to be read by | |
1329 | programs, input methods provide human-friendly commands. (@xref{Input | |
1330 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1331 | use input methods to enter text.) How to define input methods is not | |
1332 | yet documented in this manual, but here we describe how to use them. | |
1333 | ||
1334 | Each input method has a name, which is currently a string; | |
1335 | in the future, symbols may also be usable as input method names. | |
1336 | ||
1337 | @defvar current-input-method | |
1338 | This variable holds the name of the input method now active in the | |
1339 | current buffer. (It automatically becomes local in each buffer when set | |
1340 | in any fashion.) It is @code{nil} if no input method is active in the | |
1341 | buffer now. | |
1342 | @end defvar | |
1343 | ||
1344 | @defopt default-input-method | |
1345 | This variable holds the default input method for commands that choose an | |
1346 | input method. Unlike @code{current-input-method}, this variable is | |
1347 | normally global. | |
1348 | @end defopt | |
1349 | ||
1350 | @deffn Command set-input-method input-method | |
1351 | This command activates input method @var{input-method} for the current | |
1352 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1353 | If @var{input-method} is @code{nil}, this command deactivates any input | |
1354 | method for the current buffer. | |
1355 | @end deffn | |
1356 | ||
1357 | @defun read-input-method-name prompt &optional default inhibit-null | |
1358 | This function reads an input method name with the minibuffer, prompting | |
1359 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1360 | by default, if the user enters empty input. However, if | |
1361 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1362 | ||
1363 | The returned value is a string. | |
1364 | @end defun | |
1365 | ||
1366 | @defvar input-method-alist | |
1367 | This variable defines all the supported input methods. | |
1368 | Each element defines one input method, and should have the form: | |
1369 | ||
1370 | @example | |
1371 | (@var{input-method} @var{language-env} @var{activate-func} | |
1372 | @var{title} @var{description} @var{args}...) | |
1373 | @end example | |
1374 | ||
1375 | Here @var{input-method} is the input method name, a string; | |
1376 | @var{language-env} is another string, the name of the language | |
1377 | environment this input method is recommended for. (That serves only for | |
1378 | documentation purposes.) | |
1379 | ||
1380 | @var{activate-func} is a function to call to activate this method. The | |
1381 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1382 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1383 | the @var{args}. | |
1384 | ||
1385 | @var{title} is a string to display in the mode line while this method is | |
1386 | active. @var{description} is a string describing this method and what | |
1387 | it is good for. | |
1388 | @end defvar | |
1389 | ||
1390 | The fundamental interface to input methods is through the | |
1391 | variable @code{input-method-function}. @xref{Reading One Event}, | |
1392 | and @ref{Invoking the Input Method}. | |
1393 | ||
1394 | @node Locales | |
1395 | @section Locales | |
1396 | @cindex locale | |
1397 | ||
1398 | POSIX defines a concept of ``locales'' which control which language | |
1399 | to use in language-related features. These Emacs variables control | |
1400 | how Emacs interacts with these features. | |
1401 | ||
1402 | @defvar locale-coding-system | |
1403 | @cindex keyboard input decoding on X | |
1404 | This variable specifies the coding system to use for decoding system | |
1405 | error messages and---on X Window system only---keyboard input, for | |
1406 | encoding the format argument to @code{format-time-string}, and for | |
1407 | decoding the return value of @code{format-time-string}. | |
1408 | @end defvar | |
1409 | ||
1410 | @defvar system-messages-locale | |
1411 | This variable specifies the locale to use for generating system error | |
1412 | messages. Changing the locale can cause messages to come out in a | |
1413 | different language or in a different orthography. If the variable is | |
1414 | @code{nil}, the locale is specified by environment variables in the | |
1415 | usual POSIX fashion. | |
1416 | @end defvar | |
1417 | ||
1418 | @defvar system-time-locale | |
1419 | This variable specifies the locale to use for formatting time values. | |
1420 | Changing the locale can cause messages to appear according to the | |
1421 | conventions of a different language. If the variable is @code{nil}, the | |
1422 | locale is specified by environment variables in the usual POSIX fashion. | |
1423 | @end defvar | |
1424 | ||
1425 | @defun locale-info item | |
1426 | This function returns locale data @var{item} for the current POSIX | |
1427 | locale, if available. @var{item} should be one of these symbols: | |
1428 | ||
1429 | @table @code | |
1430 | @item codeset | |
1431 | Return the character set as a string (locale item @code{CODESET}). | |
1432 | ||
1433 | @item days | |
1434 | Return a 7-element vector of day names (locale items | |
1435 | @code{DAY_1} through @code{DAY_7}); | |
1436 | ||
1437 | @item months | |
1438 | Return a 12-element vector of month names (locale items @code{MON_1} | |
1439 | through @code{MON_12}). | |
1440 | ||
1441 | @item paper | |
1442 | Return a list @code{(@var{width} @var{height})} for the default paper | |
1443 | size measured in millimeters (locale items @code{PAPER_WIDTH} and | |
1444 | @code{PAPER_HEIGHT}). | |
1445 | @end table | |
1446 | ||
1447 | If the system can't provide the requested information, or if | |
1448 | @var{item} is not one of those symbols, the value is @code{nil}. All | |
1449 | strings in the return value are decoded using | |
1450 | @code{locale-coding-system}. @xref{Locales,,, libc, The GNU Libc Manual}, | |
1451 | for more information about locales and locale items. | |
1452 | @end defun | |
1453 | ||
1454 | @ignore | |
1455 | arch-tag: be705bf8-941b-4c35-84fc-ad7d20ddb7cb | |
1456 | @end ignore |