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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
fd897522 | 3 | @c Copyright (C) 1998, 1999 Free Software Foundation, Inc. |
cc6d0d2c RS |
4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/characters | |
6 | @node Non-ASCII Characters, Searching and Matching, Text, Top | |
75708135 | 7 | @chapter Non-@sc{ascii} Characters |
cc6d0d2c | 8 | @cindex multibyte characters |
75708135 | 9 | @cindex non-@sc{ascii} characters |
cc6d0d2c | 10 | |
8241495d | 11 | This chapter covers the special issues relating to non-@sc{ascii} |
cc6d0d2c RS |
12 | characters and how they are stored in strings and buffers. |
13 | ||
14 | @menu | |
15 | * Text Representations:: | |
16 | * Converting Representations:: | |
17 | * Selecting a Representation:: | |
18 | * Character Codes:: | |
19 | * Character Sets:: | |
cc6d0d2c | 20 | * Chars and Bytes:: |
a9f0a989 RS |
21 | * Splitting Characters:: |
22 | * Scanning Charsets:: | |
23 | * Translation of Characters:: | |
cc6d0d2c | 24 | * Coding Systems:: |
a9f0a989 | 25 | * Input Methods:: |
2468d0c0 | 26 | * Locales:: Interacting with the POSIX locale. |
cc6d0d2c RS |
27 | @end menu |
28 | ||
29 | @node Text Representations | |
30 | @section Text Representations | |
31 | @cindex text representations | |
32 | ||
33 | Emacs has two @dfn{text representations}---two ways to represent text | |
34 | in a string or buffer. These are called @dfn{unibyte} and | |
35 | @dfn{multibyte}. Each string, and each buffer, uses one of these two | |
36 | representations. For most purposes, you can ignore the issue of | |
37 | representations, because Emacs converts text between them as | |
38 | appropriate. Occasionally in Lisp programming you will need to pay | |
39 | attention to the difference. | |
40 | ||
41 | @cindex unibyte text | |
42 | In unibyte representation, each character occupies one byte and | |
43 | therefore the possible character codes range from 0 to 255. Codes 0 | |
8241495d RS |
44 | through 127 are @sc{ascii} characters; the codes from 128 through 255 |
45 | are used for one non-@sc{ascii} character set (you can choose which | |
969fe9b5 | 46 | character set by setting the variable @code{nonascii-insert-offset}). |
cc6d0d2c RS |
47 | |
48 | @cindex leading code | |
49 | @cindex multibyte text | |
1911e6e5 | 50 | @cindex trailing codes |
cc6d0d2c RS |
51 | In multibyte representation, a character may occupy more than one |
52 | byte, and as a result, the full range of Emacs character codes can be | |
53 | stored. The first byte of a multibyte character is always in the range | |
54 | 128 through 159 (octal 0200 through 0237). These values are called | |
a9f0a989 RS |
55 | @dfn{leading codes}. The second and subsequent bytes of a multibyte |
56 | character are always in the range 160 through 255 (octal 0240 through | |
1911e6e5 | 57 | 0377); these values are @dfn{trailing codes}. |
cc6d0d2c | 58 | |
b6954afd RS |
59 | Some sequences of bytes do not form meaningful multibyte characters: |
60 | for example, a single isolated byte in the range 128 through 255 is | |
61 | never meaningful. Such byte sequences are not entirely valid, and never | |
62 | appear in proper multibyte text (since that consists of a sequence of | |
63 | @emph{characters}); but they can appear as part of ``raw bytes'' | |
64 | (@pxref{Explicit Encoding}). | |
65 | ||
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66 | In a buffer, the buffer-local value of the variable |
67 | @code{enable-multibyte-characters} specifies the representation used. | |
08f0f5e9 KH |
68 | The representation for a string is determined and recorded in the string |
69 | when the string is constructed. | |
cc6d0d2c | 70 | |
cc6d0d2c RS |
71 | @defvar enable-multibyte-characters |
72 | This variable specifies the current buffer's text representation. | |
73 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
74 | it contains unibyte text. | |
75 | ||
969fe9b5 RS |
76 | You cannot set this variable directly; instead, use the function |
77 | @code{set-buffer-multibyte} to change a buffer's representation. | |
cc6d0d2c RS |
78 | @end defvar |
79 | ||
cc6d0d2c | 80 | @defvar default-enable-multibyte-characters |
a9f0a989 | 81 | This variable's value is entirely equivalent to @code{(default-value |
cc6d0d2c | 82 | 'enable-multibyte-characters)}, and setting this variable changes that |
a9f0a989 RS |
83 | default value. Setting the local binding of |
84 | @code{enable-multibyte-characters} in a specific buffer is not allowed, | |
85 | but changing the default value is supported, and it is a reasonable | |
86 | thing to do, because it has no effect on existing buffers. | |
cc6d0d2c RS |
87 | |
88 | The @samp{--unibyte} command line option does its job by setting the | |
89 | default value to @code{nil} early in startup. | |
90 | @end defvar | |
91 | ||
b6954afd RS |
92 | @defun position-bytes position |
93 | @tindex position-bytes | |
94 | Return the byte-position corresponding to buffer position @var{position} | |
95 | in the current buffer. | |
96 | @end defun | |
97 | ||
98 | @defun byte-to-position byte-position | |
99 | @tindex byte-to-position | |
100 | Return the buffer position corresponding to byte-position | |
101 | @var{byte-position} in the current buffer. | |
102 | @end defun | |
103 | ||
cc6d0d2c | 104 | @defun multibyte-string-p string |
b6954afd | 105 | Return @code{t} if @var{string} is a multibyte string. |
cc6d0d2c RS |
106 | @end defun |
107 | ||
108 | @node Converting Representations | |
109 | @section Converting Text Representations | |
110 | ||
111 | Emacs can convert unibyte text to multibyte; it can also convert | |
112 | multibyte text to unibyte, though this conversion loses information. In | |
113 | general these conversions happen when inserting text into a buffer, or | |
114 | when putting text from several strings together in one string. You can | |
115 | also explicitly convert a string's contents to either representation. | |
116 | ||
117 | Emacs chooses the representation for a string based on the text that | |
118 | it is constructed from. The general rule is to convert unibyte text to | |
119 | multibyte text when combining it with other multibyte text, because the | |
120 | multibyte representation is more general and can hold whatever | |
121 | characters the unibyte text has. | |
122 | ||
123 | When inserting text into a buffer, Emacs converts the text to the | |
124 | buffer's representation, as specified by | |
125 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
126 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
127 | to unibyte, even though this conversion cannot in general preserve all | |
128 | the characters that might be in the multibyte text. The other natural | |
129 | alternative, to convert the buffer contents to multibyte, is not | |
130 | acceptable because the buffer's representation is a choice made by the | |
969fe9b5 | 131 | user that cannot be overridden automatically. |
cc6d0d2c | 132 | |
8241495d RS |
133 | Converting unibyte text to multibyte text leaves @sc{ascii} characters |
134 | unchanged, and likewise 128 through 159. It converts the non-@sc{ascii} | |
969fe9b5 RS |
135 | codes 160 through 255 by adding the value @code{nonascii-insert-offset} |
136 | to each character code. By setting this variable, you specify which | |
a9f0a989 RS |
137 | character set the unibyte characters correspond to (@pxref{Character |
138 | Sets}). For example, if @code{nonascii-insert-offset} is 2048, which is | |
139 | @code{(- (make-char 'latin-iso8859-1) 128)}, then the unibyte | |
8241495d | 140 | non-@sc{ascii} characters correspond to Latin 1. If it is 2688, which |
a9f0a989 RS |
141 | is @code{(- (make-char 'greek-iso8859-7) 128)}, then they correspond to |
142 | Greek letters. | |
cc6d0d2c | 143 | |
8241495d RS |
144 | Converting multibyte text to unibyte is simpler: it discards all but |
145 | the low 8 bits of each character code. If @code{nonascii-insert-offset} | |
146 | has a reasonable value, corresponding to the beginning of some character | |
147 | set, this conversion is the inverse of the other: converting unibyte | |
148 | text to multibyte and back to unibyte reproduces the original unibyte | |
149 | text. | |
cc6d0d2c | 150 | |
cc6d0d2c | 151 | @defvar nonascii-insert-offset |
8241495d | 152 | This variable specifies the amount to add to a non-@sc{ascii} character |
cc6d0d2c | 153 | when converting unibyte text to multibyte. It also applies when |
a9f0a989 | 154 | @code{self-insert-command} inserts a character in the unibyte |
8241495d | 155 | non-@sc{ascii} range, 128 through 255. However, the function |
a9f0a989 | 156 | @code{insert-char} does not perform this conversion. |
cc6d0d2c RS |
157 | |
158 | The right value to use to select character set @var{cs} is @code{(- | |
a9f0a989 | 159 | (make-char @var{cs}) 128)}. If the value of |
cc6d0d2c RS |
160 | @code{nonascii-insert-offset} is zero, then conversion actually uses the |
161 | value for the Latin 1 character set, rather than zero. | |
162 | @end defvar | |
163 | ||
a9f0a989 | 164 | @defvar nonascii-translation-table |
cc6d0d2c RS |
165 | This variable provides a more general alternative to |
166 | @code{nonascii-insert-offset}. You can use it to specify independently | |
167 | how to translate each code in the range of 128 through 255 into a | |
168 | multibyte character. The value should be a vector, or @code{nil}. | |
969fe9b5 | 169 | If this is non-@code{nil}, it overrides @code{nonascii-insert-offset}. |
cc6d0d2c RS |
170 | @end defvar |
171 | ||
cc6d0d2c RS |
172 | @defun string-make-unibyte string |
173 | This function converts the text of @var{string} to unibyte | |
1911e6e5 | 174 | representation, if it isn't already, and returns the result. If |
969fe9b5 | 175 | @var{string} is a unibyte string, it is returned unchanged. |
cc6d0d2c RS |
176 | @end defun |
177 | ||
cc6d0d2c RS |
178 | @defun string-make-multibyte string |
179 | This function converts the text of @var{string} to multibyte | |
1911e6e5 | 180 | representation, if it isn't already, and returns the result. If |
969fe9b5 | 181 | @var{string} is a multibyte string, it is returned unchanged. |
cc6d0d2c RS |
182 | @end defun |
183 | ||
184 | @node Selecting a Representation | |
185 | @section Selecting a Representation | |
186 | ||
187 | Sometimes it is useful to examine an existing buffer or string as | |
188 | multibyte when it was unibyte, or vice versa. | |
189 | ||
cc6d0d2c RS |
190 | @defun set-buffer-multibyte multibyte |
191 | Set the representation type of the current buffer. If @var{multibyte} | |
192 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
193 | is @code{nil}, the buffer becomes unibyte. | |
194 | ||
195 | This function leaves the buffer contents unchanged when viewed as a | |
196 | sequence of bytes. As a consequence, it can change the contents viewed | |
197 | as characters; a sequence of two bytes which is treated as one character | |
198 | in multibyte representation will count as two characters in unibyte | |
199 | representation. | |
200 | ||
201 | This function sets @code{enable-multibyte-characters} to record which | |
202 | representation is in use. It also adjusts various data in the buffer | |
969fe9b5 RS |
203 | (including overlays, text properties and markers) so that they cover the |
204 | same text as they did before. | |
b6954afd RS |
205 | |
206 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
207 | because indirect buffers always inherit the representation of the | |
208 | base buffer. | |
cc6d0d2c RS |
209 | @end defun |
210 | ||
cc6d0d2c RS |
211 | @defun string-as-unibyte string |
212 | This function returns a string with the same bytes as @var{string} but | |
213 | treating each byte as a character. This means that the value may have | |
214 | more characters than @var{string} has. | |
215 | ||
b6954afd RS |
216 | If @var{string} is already a unibyte string, then the value is |
217 | @var{string} itself. | |
cc6d0d2c RS |
218 | @end defun |
219 | ||
cc6d0d2c RS |
220 | @defun string-as-multibyte string |
221 | This function returns a string with the same bytes as @var{string} but | |
222 | treating each multibyte sequence as one character. This means that the | |
223 | value may have fewer characters than @var{string} has. | |
224 | ||
b6954afd RS |
225 | If @var{string} is already a multibyte string, then the value is |
226 | @var{string} itself. | |
cc6d0d2c RS |
227 | @end defun |
228 | ||
229 | @node Character Codes | |
230 | @section Character Codes | |
231 | @cindex character codes | |
232 | ||
233 | The unibyte and multibyte text representations use different character | |
234 | codes. The valid character codes for unibyte representation range from | |
235 | 0 to 255---the values that can fit in one byte. The valid character | |
236 | codes for multibyte representation range from 0 to 524287, but not all | |
237 | values in that range are valid. In particular, the values 128 through | |
969fe9b5 | 238 | 255 are not legitimate in multibyte text (though they can occur in ``raw |
8241495d | 239 | bytes''; @pxref{Explicit Encoding}). Only the @sc{ascii} codes 0 |
969fe9b5 | 240 | through 127 are fully legitimate in both representations. |
cc6d0d2c RS |
241 | |
242 | @defun char-valid-p charcode | |
243 | This returns @code{t} if @var{charcode} is valid for either one of the two | |
244 | text representations. | |
245 | ||
246 | @example | |
247 | (char-valid-p 65) | |
248 | @result{} t | |
249 | (char-valid-p 256) | |
250 | @result{} nil | |
251 | (char-valid-p 2248) | |
252 | @result{} t | |
253 | @end example | |
254 | @end defun | |
255 | ||
256 | @node Character Sets | |
257 | @section Character Sets | |
258 | @cindex character sets | |
259 | ||
260 | Emacs classifies characters into various @dfn{character sets}, each of | |
261 | which has a name which is a symbol. Each character belongs to one and | |
262 | only one character set. | |
263 | ||
264 | In general, there is one character set for each distinct script. For | |
265 | example, @code{latin-iso8859-1} is one character set, | |
266 | @code{greek-iso8859-7} is another, and @code{ascii} is another. An | |
969fe9b5 RS |
267 | Emacs character set can hold at most 9025 characters; therefore, in some |
268 | cases, characters that would logically be grouped together are split | |
a9f0a989 RS |
269 | into several character sets. For example, one set of Chinese |
270 | characters, generally known as Big 5, is divided into two Emacs | |
271 | character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. | |
cc6d0d2c | 272 | |
cc6d0d2c | 273 | @defun charsetp object |
8241495d | 274 | Returns @code{t} if @var{object} is a symbol that names a character set, |
cc6d0d2c RS |
275 | @code{nil} otherwise. |
276 | @end defun | |
277 | ||
cc6d0d2c RS |
278 | @defun charset-list |
279 | This function returns a list of all defined character set names. | |
280 | @end defun | |
281 | ||
cc6d0d2c | 282 | @defun char-charset character |
b6954afd RS |
283 | This function returns the name of the character set that @var{character} |
284 | belongs to. | |
cc6d0d2c RS |
285 | @end defun |
286 | ||
8241495d RS |
287 | @defun charset-plist charset |
288 | @tindex charset-plist | |
289 | This function returns the charset property list of the character set | |
290 | @var{charset}. Although @var{charset} is a symbol, this is not the same | |
291 | as the property list of that symbol. Charset properties are used for | |
292 | special purposes within Emacs; for example, @code{x-charset-registry} | |
293 | helps determine which fonts to use (@pxref{Font Selection}). | |
294 | @end defun | |
295 | ||
cc6d0d2c RS |
296 | @node Chars and Bytes |
297 | @section Characters and Bytes | |
298 | @cindex bytes and characters | |
299 | ||
a9f0a989 RS |
300 | @cindex introduction sequence |
301 | @cindex dimension (of character set) | |
cc6d0d2c | 302 | In multibyte representation, each character occupies one or more |
a9f0a989 | 303 | bytes. Each character set has an @dfn{introduction sequence}, which is |
8241495d | 304 | normally one or two bytes long. (Exception: the @sc{ascii} character |
1911e6e5 RS |
305 | set has a zero-length introduction sequence.) The introduction sequence |
306 | is the beginning of the byte sequence for any character in the character | |
307 | set. The rest of the character's bytes distinguish it from the other | |
308 | characters in the same character set. Depending on the character set, | |
309 | there are either one or two distinguishing bytes; the number of such | |
310 | bytes is called the @dfn{dimension} of the character set. | |
a9f0a989 RS |
311 | |
312 | @defun charset-dimension charset | |
b6954afd RS |
313 | This function returns the dimension of @var{charset}; at present, the |
314 | dimension is always 1 or 2. | |
315 | @end defun | |
316 | ||
317 | @defun charset-bytes charset | |
318 | @tindex charset-bytes | |
319 | This function returns the number of bytes used to represent a character | |
320 | in character set @var{charset}. | |
a9f0a989 RS |
321 | @end defun |
322 | ||
323 | This is the simplest way to determine the byte length of a character | |
324 | set's introduction sequence: | |
325 | ||
326 | @example | |
b6954afd | 327 | (- (charset-bytes @var{charset}) |
a9f0a989 RS |
328 | (charset-dimension @var{charset})) |
329 | @end example | |
330 | ||
331 | @node Splitting Characters | |
332 | @section Splitting Characters | |
333 | ||
334 | The functions in this section convert between characters and the byte | |
335 | values used to represent them. For most purposes, there is no need to | |
336 | be concerned with the sequence of bytes used to represent a character, | |
969fe9b5 | 337 | because Emacs translates automatically when necessary. |
cc6d0d2c | 338 | |
cc6d0d2c RS |
339 | @defun split-char character |
340 | Return a list containing the name of the character set of | |
a9f0a989 RS |
341 | @var{character}, followed by one or two byte values (integers) which |
342 | identify @var{character} within that character set. The number of byte | |
343 | values is the character set's dimension. | |
cc6d0d2c RS |
344 | |
345 | @example | |
346 | (split-char 2248) | |
347 | @result{} (latin-iso8859-1 72) | |
348 | (split-char 65) | |
349 | @result{} (ascii 65) | |
350 | @end example | |
351 | ||
8241495d | 352 | Unibyte non-@sc{ascii} characters are considered as part of |
cc6d0d2c RS |
353 | the @code{ascii} character set: |
354 | ||
355 | @example | |
356 | (split-char 192) | |
357 | @result{} (ascii 192) | |
358 | @end example | |
359 | @end defun | |
360 | ||
cc6d0d2c | 361 | @defun make-char charset &rest byte-values |
a9f0a989 RS |
362 | This function returns the character in character set @var{charset} |
363 | identified by @var{byte-values}. This is roughly the inverse of | |
364 | @code{split-char}. Normally, you should specify either one or two | |
365 | @var{byte-values}, according to the dimension of @var{charset}. For | |
366 | example, | |
cc6d0d2c RS |
367 | |
368 | @example | |
369 | (make-char 'latin-iso8859-1 72) | |
370 | @result{} 2248 | |
371 | @end example | |
372 | @end defun | |
373 | ||
a9f0a989 RS |
374 | @cindex generic characters |
375 | If you call @code{make-char} with no @var{byte-values}, the result is | |
376 | a @dfn{generic character} which stands for @var{charset}. A generic | |
377 | character is an integer, but it is @emph{not} valid for insertion in the | |
378 | buffer as a character. It can be used in @code{char-table-range} to | |
379 | refer to the whole character set (@pxref{Char-Tables}). | |
380 | @code{char-valid-p} returns @code{nil} for generic characters. | |
381 | For example: | |
382 | ||
383 | @example | |
384 | (make-char 'latin-iso8859-1) | |
385 | @result{} 2176 | |
386 | (char-valid-p 2176) | |
387 | @result{} nil | |
388 | (split-char 2176) | |
389 | @result{} (latin-iso8859-1 0) | |
390 | @end example | |
391 | ||
392 | @node Scanning Charsets | |
393 | @section Scanning for Character Sets | |
394 | ||
395 | Sometimes it is useful to find out which character sets appear in a | |
396 | part of a buffer or a string. One use for this is in determining which | |
397 | coding systems (@pxref{Coding Systems}) are capable of representing all | |
398 | of the text in question. | |
399 | ||
400 | @defun find-charset-region beg end &optional translation | |
a9f0a989 RS |
401 | This function returns a list of the character sets that appear in the |
402 | current buffer between positions @var{beg} and @var{end}. | |
403 | ||
404 | The optional argument @var{translation} specifies a translation table to | |
405 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
406 | is non-@code{nil}, then each character in the region is translated | |
407 | through this table, and the value returned describes the translated | |
408 | characters instead of the characters actually in the buffer. | |
b6954afd RS |
409 | |
410 | In two peculiar cases, the value includes the symbol @code{unknown}: | |
411 | ||
412 | @itemize @bullet | |
413 | @item | |
8241495d | 414 | When a unibyte buffer contains non-@sc{ascii} characters. |
b6954afd RS |
415 | |
416 | @item | |
417 | When a multibyte buffer contains invalid byte-sequences (raw bytes). | |
418 | @xref{Explicit Encoding}. | |
419 | @end itemize | |
a9f0a989 RS |
420 | @end defun |
421 | ||
422 | @defun find-charset-string string &optional translation | |
b6954afd RS |
423 | This function returns a list of the character sets that appear in the |
424 | string @var{string}. It is just like @code{find-charset-region}, except | |
425 | that it applies to the contents of @var{string} instead of part of the | |
426 | current buffer. | |
a9f0a989 RS |
427 | @end defun |
428 | ||
429 | @node Translation of Characters | |
430 | @section Translation of Characters | |
431 | @cindex character translation tables | |
432 | @cindex translation tables | |
433 | ||
434 | A @dfn{translation table} specifies a mapping of characters | |
435 | into characters. These tables are used in encoding and decoding, and | |
436 | for other purposes. Some coding systems specify their own particular | |
437 | translation tables; there are also default translation tables which | |
438 | apply to all other coding systems. | |
439 | ||
8241495d RS |
440 | @defun make-translation-table &rest translations |
441 | This function returns a translation table based on the argument | |
442 | @var{translations}. Each element of | |
443 | @var{translations} should be a list of the form @code{(@var{from} | |
a9f0a989 RS |
444 | . @var{to})}; this says to translate the character @var{from} into |
445 | @var{to}. | |
446 | ||
447 | You can also map one whole character set into another character set with | |
448 | the same dimension. To do this, you specify a generic character (which | |
449 | designates a character set) for @var{from} (@pxref{Splitting Characters}). | |
450 | In this case, @var{to} should also be a generic character, for another | |
451 | character set of the same dimension. Then the translation table | |
452 | translates each character of @var{from}'s character set into the | |
453 | corresponding character of @var{to}'s character set. | |
454 | @end defun | |
455 | ||
456 | In decoding, the translation table's translations are applied to the | |
457 | characters that result from ordinary decoding. If a coding system has | |
458 | property @code{character-translation-table-for-decode}, that specifies | |
459 | the translation table to use. Otherwise, if | |
b1f687a2 RS |
460 | @code{standard-translation-table-for-decode} is non-@code{nil}, decoding |
461 | uses that table. | |
a9f0a989 RS |
462 | |
463 | In encoding, the translation table's translations are applied to the | |
464 | characters in the buffer, and the result of translation is actually | |
465 | encoded. If a coding system has property | |
466 | @code{character-translation-table-for-encode}, that specifies the | |
467 | translation table to use. Otherwise the variable | |
b1f687a2 RS |
468 | @code{standard-translation-table-for-encode} specifies the translation |
469 | table. | |
a9f0a989 | 470 | |
b1f687a2 | 471 | @defvar standard-translation-table-for-decode |
a9f0a989 RS |
472 | This is the default translation table for decoding, for |
473 | coding systems that don't specify any other translation table. | |
474 | @end defvar | |
475 | ||
b1f687a2 | 476 | @defvar standard-translation-table-for-encode |
a9f0a989 RS |
477 | This is the default translation table for encoding, for |
478 | coding systems that don't specify any other translation table. | |
479 | @end defvar | |
480 | ||
cc6d0d2c RS |
481 | @node Coding Systems |
482 | @section Coding Systems | |
483 | ||
484 | @cindex coding system | |
485 | When Emacs reads or writes a file, and when Emacs sends text to a | |
486 | subprocess or receives text from a subprocess, it normally performs | |
487 | character code conversion and end-of-line conversion as specified | |
488 | by a particular @dfn{coding system}. | |
489 | ||
8241495d RS |
490 | How to define a coding system is an arcane matter, and is not |
491 | documented here. | |
b6954afd | 492 | |
a9f0a989 RS |
493 | @menu |
494 | * Coding System Basics:: | |
495 | * Encoding and I/O:: | |
496 | * Lisp and Coding Systems:: | |
1911e6e5 | 497 | * User-Chosen Coding Systems:: |
a9f0a989 RS |
498 | * Default Coding Systems:: |
499 | * Specifying Coding Systems:: | |
500 | * Explicit Encoding:: | |
501 | * Terminal I/O Encoding:: | |
502 | * MS-DOS File Types:: | |
503 | @end menu | |
504 | ||
505 | @node Coding System Basics | |
506 | @subsection Basic Concepts of Coding Systems | |
507 | ||
cc6d0d2c RS |
508 | @cindex character code conversion |
509 | @dfn{Character code conversion} involves conversion between the encoding | |
510 | used inside Emacs and some other encoding. Emacs supports many | |
511 | different encodings, in that it can convert to and from them. For | |
512 | example, it can convert text to or from encodings such as Latin 1, Latin | |
513 | 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some | |
514 | cases, Emacs supports several alternative encodings for the same | |
515 | characters; for example, there are three coding systems for the Cyrillic | |
516 | (Russian) alphabet: ISO, Alternativnyj, and KOI8. | |
517 | ||
cc6d0d2c | 518 | Most coding systems specify a particular character code for |
8241495d RS |
519 | conversion, but some of them leave the choice unspecified---to be chosen |
520 | heuristically for each file, based on the data. | |
cc6d0d2c | 521 | |
969fe9b5 RS |
522 | @cindex end of line conversion |
523 | @dfn{End of line conversion} handles three different conventions used | |
524 | on various systems for representing end of line in files. The Unix | |
525 | convention is to use the linefeed character (also called newline). The | |
8241495d RS |
526 | DOS convention is to use a carriage-return and a linefeed at the end of |
527 | a line. The Mac convention is to use just carriage-return. | |
969fe9b5 | 528 | |
cc6d0d2c RS |
529 | @cindex base coding system |
530 | @cindex variant coding system | |
531 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
532 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
533 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
534 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
a9f0a989 | 535 | well. Most base coding systems have three corresponding variants whose |
cc6d0d2c RS |
536 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. |
537 | ||
a9f0a989 RS |
538 | The coding system @code{raw-text} is special in that it prevents |
539 | character code conversion, and causes the buffer visited with that | |
540 | coding system to be a unibyte buffer. It does not specify the | |
541 | end-of-line conversion, allowing that to be determined as usual by the | |
542 | data, and has the usual three variants which specify the end-of-line | |
543 | conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: | |
544 | it specifies no conversion of either character codes or end-of-line. | |
545 | ||
546 | The coding system @code{emacs-mule} specifies that the data is | |
547 | represented in the internal Emacs encoding. This is like | |
548 | @code{raw-text} in that no code conversion happens, but different in | |
549 | that the result is multibyte data. | |
550 | ||
551 | @defun coding-system-get coding-system property | |
a9f0a989 RS |
552 | This function returns the specified property of the coding system |
553 | @var{coding-system}. Most coding system properties exist for internal | |
554 | purposes, but one that you might find useful is @code{mime-charset}. | |
555 | That property's value is the name used in MIME for the character coding | |
556 | which this coding system can read and write. Examples: | |
557 | ||
558 | @example | |
559 | (coding-system-get 'iso-latin-1 'mime-charset) | |
560 | @result{} iso-8859-1 | |
561 | (coding-system-get 'iso-2022-cn 'mime-charset) | |
562 | @result{} iso-2022-cn | |
563 | (coding-system-get 'cyrillic-koi8 'mime-charset) | |
564 | @result{} koi8-r | |
565 | @end example | |
566 | ||
567 | The value of the @code{mime-charset} property is also defined | |
568 | as an alias for the coding system. | |
569 | @end defun | |
570 | ||
571 | @node Encoding and I/O | |
572 | @subsection Encoding and I/O | |
573 | ||
1911e6e5 | 574 | The principal purpose of coding systems is for use in reading and |
a9f0a989 RS |
575 | writing files. The function @code{insert-file-contents} uses |
576 | a coding system for decoding the file data, and @code{write-region} | |
577 | uses one to encode the buffer contents. | |
578 | ||
579 | You can specify the coding system to use either explicitly | |
580 | (@pxref{Specifying Coding Systems}), or implicitly using the defaulting | |
581 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
582 | completely specify what to do. For example, they may choose a coding | |
583 | system such as @code{undefined} which leaves the character code | |
584 | conversion to be determined from the data. In these cases, the I/O | |
585 | operation finishes the job of choosing a coding system. Very often | |
586 | you will want to find out afterwards which coding system was chosen. | |
587 | ||
588 | @defvar buffer-file-coding-system | |
a9f0a989 RS |
589 | This variable records the coding system that was used for visiting the |
590 | current buffer. It is used for saving the buffer, and for writing part | |
591 | of the buffer with @code{write-region}. When those operations ask the | |
592 | user to specify a different coding system, | |
593 | @code{buffer-file-coding-system} is updated to the coding system | |
594 | specified. | |
b6954afd RS |
595 | |
596 | However, @code{buffer-file-coding-system} does not affect sending text | |
597 | to a subprocess. | |
a9f0a989 RS |
598 | @end defvar |
599 | ||
600 | @defvar save-buffer-coding-system | |
a9f0a989 | 601 | This variable specifies the coding system for saving the buffer---but it |
8241495d RS |
602 | is not used for @code{write-region}. |
603 | ||
604 | When a command to save the buffer starts out to use | |
605 | @code{save-buffer-coding-system}, and that coding system cannot handle | |
606 | the actual text in the buffer, the command asks the user to choose | |
607 | another coding system. After that happens, the command also updates | |
608 | @code{save-buffer-coding-system} to represent the coding system that the | |
609 | user specified. | |
a9f0a989 RS |
610 | @end defvar |
611 | ||
612 | @defvar last-coding-system-used | |
a9f0a989 RS |
613 | I/O operations for files and subprocesses set this variable to the |
614 | coding system name that was used. The explicit encoding and decoding | |
615 | functions (@pxref{Explicit Encoding}) set it too. | |
616 | ||
617 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
8241495d RS |
618 | it can change whenever Emacs waits; therefore, you should copy the |
619 | value shortly after the function call that stores the value you are | |
a9f0a989 RS |
620 | interested in. |
621 | @end defvar | |
622 | ||
2eb4136f RS |
623 | The variable @code{selection-coding-system} specifies how to encode |
624 | selections for the window system. @xref{Window System Selections}. | |
625 | ||
969fe9b5 RS |
626 | @node Lisp and Coding Systems |
627 | @subsection Coding Systems in Lisp | |
628 | ||
8241495d | 629 | Here are the Lisp facilities for working with coding systems: |
cc6d0d2c | 630 | |
cc6d0d2c RS |
631 | @defun coding-system-list &optional base-only |
632 | This function returns a list of all coding system names (symbols). If | |
633 | @var{base-only} is non-@code{nil}, the value includes only the | |
634 | base coding systems. Otherwise, it includes variant coding systems as well. | |
635 | @end defun | |
636 | ||
cc6d0d2c RS |
637 | @defun coding-system-p object |
638 | This function returns @code{t} if @var{object} is a coding system | |
639 | name. | |
640 | @end defun | |
641 | ||
cc6d0d2c RS |
642 | @defun check-coding-system coding-system |
643 | This function checks the validity of @var{coding-system}. | |
644 | If that is valid, it returns @var{coding-system}. | |
645 | Otherwise it signals an error with condition @code{coding-system-error}. | |
646 | @end defun | |
647 | ||
a9f0a989 | 648 | @defun coding-system-change-eol-conversion coding-system eol-type |
a9f0a989 | 649 | This function returns a coding system which is like @var{coding-system} |
1911e6e5 | 650 | except for its eol conversion, which is specified by @code{eol-type}. |
a9f0a989 RS |
651 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or |
652 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
653 | the end-of-line conversion from the data. | |
654 | @end defun | |
969fe9b5 | 655 | |
a9f0a989 | 656 | @defun coding-system-change-text-conversion eol-coding text-coding |
a9f0a989 RS |
657 | This function returns a coding system which uses the end-of-line |
658 | conversion of @var{eol-coding}, and the text conversion of | |
659 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
660 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
969fe9b5 RS |
661 | @end defun |
662 | ||
a9f0a989 | 663 | @defun find-coding-systems-region from to |
a9f0a989 RS |
664 | This function returns a list of coding systems that could be used to |
665 | encode a text between @var{from} and @var{to}. All coding systems in | |
666 | the list can safely encode any multibyte characters in that portion of | |
667 | the text. | |
668 | ||
669 | If the text contains no multibyte characters, the function returns the | |
670 | list @code{(undecided)}. | |
671 | @end defun | |
672 | ||
673 | @defun find-coding-systems-string string | |
a9f0a989 RS |
674 | This function returns a list of coding systems that could be used to |
675 | encode the text of @var{string}. All coding systems in the list can | |
676 | safely encode any multibyte characters in @var{string}. If the text | |
677 | contains no multibyte characters, this returns the list | |
678 | @code{(undecided)}. | |
679 | @end defun | |
680 | ||
681 | @defun find-coding-systems-for-charsets charsets | |
a9f0a989 RS |
682 | This function returns a list of coding systems that could be used to |
683 | encode all the character sets in the list @var{charsets}. | |
684 | @end defun | |
685 | ||
686 | @defun detect-coding-region start end &optional highest | |
cc6d0d2c RS |
687 | This function chooses a plausible coding system for decoding the text |
688 | from @var{start} to @var{end}. This text should be ``raw bytes'' | |
969fe9b5 | 689 | (@pxref{Explicit Encoding}). |
cc6d0d2c | 690 | |
a9f0a989 | 691 | Normally this function returns a list of coding systems that could |
cc6d0d2c | 692 | handle decoding the text that was scanned. They are listed in order of |
a9f0a989 RS |
693 | decreasing priority. But if @var{highest} is non-@code{nil}, then the |
694 | return value is just one coding system, the one that is highest in | |
695 | priority. | |
696 | ||
8241495d | 697 | If the region contains only @sc{ascii} characters, the value |
a9f0a989 | 698 | is @code{undecided} or @code{(undecided)}. |
cc6d0d2c RS |
699 | @end defun |
700 | ||
a9f0a989 | 701 | @defun detect-coding-string string highest |
cc6d0d2c RS |
702 | This function is like @code{detect-coding-region} except that it |
703 | operates on the contents of @var{string} instead of bytes in the buffer. | |
1911e6e5 RS |
704 | @end defun |
705 | ||
706 | @xref{Process Information}, for how to examine or set the coding | |
707 | systems used for I/O to a subprocess. | |
708 | ||
709 | @node User-Chosen Coding Systems | |
710 | @subsection User-Chosen Coding Systems | |
711 | ||
1911e6e5 | 712 | @defun select-safe-coding-system from to &optional preferred-coding-system |
ebc6903b | 713 | This function selects a coding system for encoding the text between |
1911e6e5 RS |
714 | @var{from} and @var{to}, asking the user to choose if necessary. |
715 | ||
716 | The optional argument @var{preferred-coding-system} specifies a coding | |
ebc6903b RS |
717 | system to try first. If that one can handle the text in the specified |
718 | region, then it is used. If this argument is omitted, the current | |
719 | buffer's value of @code{buffer-file-coding-system} is tried first. | |
1911e6e5 RS |
720 | |
721 | If the region contains some multibyte characters that the preferred | |
722 | coding system cannot encode, this function asks the user to choose from | |
723 | a list of coding systems which can encode the text, and returns the | |
724 | user's choice. | |
725 | ||
726 | One other kludgy feature: if @var{from} is a string, the string is the | |
727 | target text, and @var{to} is ignored. | |
969fe9b5 RS |
728 | @end defun |
729 | ||
730 | Here are two functions you can use to let the user specify a coding | |
731 | system, with completion. @xref{Completion}. | |
732 | ||
a9f0a989 | 733 | @defun read-coding-system prompt &optional default |
969fe9b5 RS |
734 | This function reads a coding system using the minibuffer, prompting with |
735 | string @var{prompt}, and returns the coding system name as a symbol. If | |
736 | the user enters null input, @var{default} specifies which coding system | |
737 | to return. It should be a symbol or a string. | |
738 | @end defun | |
739 | ||
969fe9b5 RS |
740 | @defun read-non-nil-coding-system prompt |
741 | This function reads a coding system using the minibuffer, prompting with | |
a9f0a989 | 742 | string @var{prompt}, and returns the coding system name as a symbol. If |
969fe9b5 RS |
743 | the user tries to enter null input, it asks the user to try again. |
744 | @xref{Coding Systems}. | |
cc6d0d2c RS |
745 | @end defun |
746 | ||
747 | @node Default Coding Systems | |
a9f0a989 | 748 | @subsection Default Coding Systems |
cc6d0d2c | 749 | |
a9f0a989 RS |
750 | This section describes variables that specify the default coding |
751 | system for certain files or when running certain subprograms, and the | |
1911e6e5 | 752 | function that I/O operations use to access them. |
a9f0a989 RS |
753 | |
754 | The idea of these variables is that you set them once and for all to the | |
755 | defaults you want, and then do not change them again. To specify a | |
756 | particular coding system for a particular operation in a Lisp program, | |
757 | don't change these variables; instead, override them using | |
758 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
759 | (@pxref{Specifying Coding Systems}). | |
cc6d0d2c | 760 | |
cc6d0d2c RS |
761 | @defvar file-coding-system-alist |
762 | This variable is an alist that specifies the coding systems to use for | |
763 | reading and writing particular files. Each element has the form | |
764 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
765 | expression that matches certain file names. The element applies to file | |
766 | names that match @var{pattern}. | |
767 | ||
1911e6e5 | 768 | The @sc{cdr} of the element, @var{coding}, should be either a coding |
8241495d RS |
769 | system, a cons cell containing two coding systems, or a function name (a |
770 | symbol with a function definition). If @var{coding} is a coding system, | |
771 | that coding system is used for both reading the file and writing it. If | |
772 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
773 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
774 | coding system for encoding. | |
775 | ||
776 | If @var{coding} is a function name, the function must return a coding | |
cc6d0d2c RS |
777 | system or a cons cell containing two coding systems. This value is used |
778 | as described above. | |
779 | @end defvar | |
780 | ||
cc6d0d2c RS |
781 | @defvar process-coding-system-alist |
782 | This variable is an alist specifying which coding systems to use for a | |
783 | subprocess, depending on which program is running in the subprocess. It | |
784 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
785 | matched against the program name used to start the subprocess. The coding | |
786 | system or systems specified in this alist are used to initialize the | |
787 | coding systems used for I/O to the subprocess, but you can specify | |
788 | other coding systems later using @code{set-process-coding-system}. | |
789 | @end defvar | |
790 | ||
8241495d RS |
791 | @strong{Warning:} Coding systems such as @code{undecided}, which |
792 | determine the coding system from the data, do not work entirely reliably | |
1911e6e5 | 793 | with asynchronous subprocess output. This is because Emacs handles |
a9f0a989 RS |
794 | asynchronous subprocess output in batches, as it arrives. If the coding |
795 | system leaves the character code conversion unspecified, or leaves the | |
796 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
797 | conversion from one batch at a time, and this does not always work. | |
798 | ||
799 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
800 | coding system which determines both the character code conversion and | |
801 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
802 | rather than @code{undecided} or @code{latin-1}. | |
803 | ||
cc6d0d2c RS |
804 | @defvar network-coding-system-alist |
805 | This variable is an alist that specifies the coding system to use for | |
806 | network streams. It works much like @code{file-coding-system-alist}, | |
969fe9b5 | 807 | with the difference that the @var{pattern} in an element may be either a |
cc6d0d2c RS |
808 | port number or a regular expression. If it is a regular expression, it |
809 | is matched against the network service name used to open the network | |
810 | stream. | |
811 | @end defvar | |
812 | ||
cc6d0d2c RS |
813 | @defvar default-process-coding-system |
814 | This variable specifies the coding systems to use for subprocess (and | |
815 | network stream) input and output, when nothing else specifies what to | |
816 | do. | |
817 | ||
a9f0a989 RS |
818 | The value should be a cons cell of the form @code{(@var{input-coding} |
819 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
820 | the subprocess, and @var{output-coding} applies to output to it. | |
cc6d0d2c RS |
821 | @end defvar |
822 | ||
a9f0a989 | 823 | @defun find-operation-coding-system operation &rest arguments |
a9f0a989 RS |
824 | This function returns the coding system to use (by default) for |
825 | performing @var{operation} with @var{arguments}. The value has this | |
826 | form: | |
827 | ||
828 | @example | |
829 | (@var{decoding-system} @var{encoding-system}) | |
830 | @end example | |
831 | ||
832 | The first element, @var{decoding-system}, is the coding system to use | |
833 | for decoding (in case @var{operation} does decoding), and | |
834 | @var{encoding-system} is the coding system for encoding (in case | |
835 | @var{operation} does encoding). | |
836 | ||
8241495d | 837 | The argument @var{operation} should be a symbol, one of |
a9f0a989 RS |
838 | @code{insert-file-contents}, @code{write-region}, @code{call-process}, |
839 | @code{call-process-region}, @code{start-process}, or | |
8241495d RS |
840 | @code{open-network-stream}. These are the names of the Emacs I/O primitives |
841 | that can do coding system conversion. | |
a9f0a989 RS |
842 | |
843 | The remaining arguments should be the same arguments that might be given | |
8241495d | 844 | to that I/O primitive. Depending on the primitive, one of those |
a9f0a989 RS |
845 | arguments is selected as the @dfn{target}. For example, if |
846 | @var{operation} does file I/O, whichever argument specifies the file | |
847 | name is the target. For subprocess primitives, the process name is the | |
848 | target. For @code{open-network-stream}, the target is the service name | |
849 | or port number. | |
850 | ||
851 | This function looks up the target in @code{file-coding-system-alist}, | |
852 | @code{process-coding-system-alist}, or | |
853 | @code{network-coding-system-alist}, depending on @var{operation}. | |
854 | @xref{Default Coding Systems}. | |
855 | @end defun | |
856 | ||
cc6d0d2c | 857 | @node Specifying Coding Systems |
a9f0a989 | 858 | @subsection Specifying a Coding System for One Operation |
cc6d0d2c RS |
859 | |
860 | You can specify the coding system for a specific operation by binding | |
861 | the variables @code{coding-system-for-read} and/or | |
862 | @code{coding-system-for-write}. | |
863 | ||
cc6d0d2c RS |
864 | @defvar coding-system-for-read |
865 | If this variable is non-@code{nil}, it specifies the coding system to | |
866 | use for reading a file, or for input from a synchronous subprocess. | |
867 | ||
868 | It also applies to any asynchronous subprocess or network stream, but in | |
869 | a different way: the value of @code{coding-system-for-read} when you | |
870 | start the subprocess or open the network stream specifies the input | |
871 | decoding method for that subprocess or network stream. It remains in | |
872 | use for that subprocess or network stream unless and until overridden. | |
873 | ||
874 | The right way to use this variable is to bind it with @code{let} for a | |
875 | specific I/O operation. Its global value is normally @code{nil}, and | |
876 | you should not globally set it to any other value. Here is an example | |
877 | of the right way to use the variable: | |
878 | ||
879 | @example | |
880 | ;; @r{Read the file with no character code conversion.} | |
969fe9b5 | 881 | ;; @r{Assume @sc{crlf} represents end-of-line.} |
cc6d0d2c RS |
882 | (let ((coding-system-for-write 'emacs-mule-dos)) |
883 | (insert-file-contents filename)) | |
884 | @end example | |
885 | ||
886 | When its value is non-@code{nil}, @code{coding-system-for-read} takes | |
a9f0a989 | 887 | precedence over all other methods of specifying a coding system to use for |
cc6d0d2c RS |
888 | input, including @code{file-coding-system-alist}, |
889 | @code{process-coding-system-alist} and | |
890 | @code{network-coding-system-alist}. | |
891 | @end defvar | |
892 | ||
cc6d0d2c RS |
893 | @defvar coding-system-for-write |
894 | This works much like @code{coding-system-for-read}, except that it | |
895 | applies to output rather than input. It affects writing to files, | |
b6954afd | 896 | as well as sending output to subprocesses and net connections. |
cc6d0d2c RS |
897 | |
898 | When a single operation does both input and output, as do | |
899 | @code{call-process-region} and @code{start-process}, both | |
900 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
901 | affect it. | |
902 | @end defvar | |
903 | ||
cc6d0d2c RS |
904 | @defvar inhibit-eol-conversion |
905 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
906 | no matter which coding system is specified. This applies to all the | |
907 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
908 | decoding functions (@pxref{Explicit Encoding}). | |
909 | @end defvar | |
910 | ||
cc6d0d2c | 911 | @node Explicit Encoding |
a9f0a989 | 912 | @subsection Explicit Encoding and Decoding |
cc6d0d2c RS |
913 | @cindex encoding text |
914 | @cindex decoding text | |
915 | ||
916 | All the operations that transfer text in and out of Emacs have the | |
917 | ability to use a coding system to encode or decode the text. | |
918 | You can also explicitly encode and decode text using the functions | |
919 | in this section. | |
920 | ||
921 | @cindex raw bytes | |
922 | The result of encoding, and the input to decoding, are not ordinary | |
923 | text. They are ``raw bytes''---bytes that represent text in the same | |
924 | way that an external file would. When a buffer contains raw bytes, it | |
925 | is most natural to mark that buffer as using unibyte representation, | |
926 | using @code{set-buffer-multibyte} (@pxref{Selecting a Representation}), | |
969fe9b5 RS |
927 | but this is not required. If the buffer's contents are only temporarily |
928 | raw, leave the buffer multibyte, which will be correct after you decode | |
929 | them. | |
cc6d0d2c RS |
930 | |
931 | The usual way to get raw bytes in a buffer, for explicit decoding, is | |
969fe9b5 | 932 | to read them from a file with @code{insert-file-contents-literally} |
cc6d0d2c | 933 | (@pxref{Reading from Files}) or specify a non-@code{nil} @var{rawfile} |
969fe9b5 | 934 | argument when visiting a file with @code{find-file-noselect}. |
cc6d0d2c RS |
935 | |
936 | The usual way to use the raw bytes that result from explicitly | |
937 | encoding text is to copy them to a file or process---for example, to | |
969fe9b5 | 938 | write them with @code{write-region} (@pxref{Writing to Files}), and |
cc6d0d2c RS |
939 | suppress encoding for that @code{write-region} call by binding |
940 | @code{coding-system-for-write} to @code{no-conversion}. | |
941 | ||
b6954afd RS |
942 | Raw bytes typically contain stray individual bytes with values in the |
943 | range 128 through 255, that are legitimate only as part of multibyte | |
944 | sequences. Even if the buffer is multibyte, Emacs treats each such | |
945 | individual byte as a character and uses the byte value as its character | |
946 | code. In this way, character codes 128 through 255 can be found in a | |
947 | multibyte buffer, even though they are not legitimate multibyte | |
948 | character codes. | |
949 | ||
1911e6e5 | 950 | Raw bytes sometimes contain overlong byte-sequences that look like a |
b6954afd RS |
951 | proper multibyte character plus extra superfluous trailing codes. For |
952 | most purposes, Emacs treats such a sequence in a buffer or string as a | |
953 | single character, and if you look at its character code, you get the | |
954 | value that corresponds to the multibyte character | |
955 | sequence---disregarding the extra trailing codes. This is not quite | |
956 | clean, but raw bytes are used only in limited ways, so as a practical | |
957 | matter it is not worth the trouble to treat this case differently. | |
958 | ||
959 | When a multibyte buffer contains illegitimate byte sequences, | |
08f0f5e9 | 960 | sometimes insertion or deletion can cause them to coalesce into a |
b6954afd RS |
961 | legitimate multibyte character. For example, suppose the buffer |
962 | contains the sequence 129 68 192, 68 being the character @samp{D}. If | |
963 | you delete the @samp{D}, the bytes 129 and 192 become adjacent, and thus | |
964 | become one multibyte character (Latin-1 A with grave accent). Point | |
965 | moves to one side or the other of the character, since it cannot be | |
966 | within a character. Don't be alarmed by this. | |
967 | ||
968 | Some really peculiar situations prevent proper coalescence. For | |
969 | example, if you narrow the buffer so that the accessible portion begins | |
970 | just before the @samp{D}, then delete the @samp{D}, the two surrounding | |
971 | bytes cannot coalesce because one of them is outside the accessible | |
972 | portion of the buffer. In this case, the deletion cannot be done, so | |
973 | @code{delete-region} signals an error. | |
974 | ||
975 | Here are the functions to perform explicit encoding or decoding. The | |
976 | decoding functions produce ``raw bytes''; the encoding functions are | |
977 | meant to operate on ``raw bytes''. All of these functions discard text | |
978 | properties. | |
1911e6e5 | 979 | |
cc6d0d2c RS |
980 | @defun encode-coding-region start end coding-system |
981 | This function encodes the text from @var{start} to @var{end} according | |
969fe9b5 RS |
982 | to coding system @var{coding-system}. The encoded text replaces the |
983 | original text in the buffer. The result of encoding is ``raw bytes,'' | |
984 | but the buffer remains multibyte if it was multibyte before. | |
cc6d0d2c RS |
985 | @end defun |
986 | ||
cc6d0d2c RS |
987 | @defun encode-coding-string string coding-system |
988 | This function encodes the text in @var{string} according to coding | |
989 | system @var{coding-system}. It returns a new string containing the | |
969fe9b5 | 990 | encoded text. The result of encoding is a unibyte string of ``raw bytes.'' |
cc6d0d2c RS |
991 | @end defun |
992 | ||
cc6d0d2c RS |
993 | @defun decode-coding-region start end coding-system |
994 | This function decodes the text from @var{start} to @var{end} according | |
995 | to coding system @var{coding-system}. The decoded text replaces the | |
996 | original text in the buffer. To make explicit decoding useful, the text | |
997 | before decoding ought to be ``raw bytes.'' | |
998 | @end defun | |
999 | ||
cc6d0d2c RS |
1000 | @defun decode-coding-string string coding-system |
1001 | This function decodes the text in @var{string} according to coding | |
1002 | system @var{coding-system}. It returns a new string containing the | |
1003 | decoded text. To make explicit decoding useful, the contents of | |
1004 | @var{string} ought to be ``raw bytes.'' | |
1005 | @end defun | |
969fe9b5 | 1006 | |
a9f0a989 RS |
1007 | @node Terminal I/O Encoding |
1008 | @subsection Terminal I/O Encoding | |
1009 | ||
1010 | Emacs can decode keyboard input using a coding system, and encode | |
2eb4136f RS |
1011 | terminal output. This is useful for terminals that transmit or display |
1012 | text using a particular encoding such as Latin-1. Emacs does not set | |
1013 | @code{last-coding-system-used} for encoding or decoding for the | |
1014 | terminal. | |
a9f0a989 RS |
1015 | |
1016 | @defun keyboard-coding-system | |
a9f0a989 RS |
1017 | This function returns the coding system that is in use for decoding |
1018 | keyboard input---or @code{nil} if no coding system is to be used. | |
1019 | @end defun | |
1020 | ||
1021 | @defun set-keyboard-coding-system coding-system | |
a9f0a989 RS |
1022 | This function specifies @var{coding-system} as the coding system to |
1023 | use for decoding keyboard input. If @var{coding-system} is @code{nil}, | |
1024 | that means do not decode keyboard input. | |
1025 | @end defun | |
1026 | ||
1027 | @defun terminal-coding-system | |
a9f0a989 RS |
1028 | This function returns the coding system that is in use for encoding |
1029 | terminal output---or @code{nil} for no encoding. | |
1030 | @end defun | |
1031 | ||
1032 | @defun set-terminal-coding-system coding-system | |
a9f0a989 RS |
1033 | This function specifies @var{coding-system} as the coding system to use |
1034 | for encoding terminal output. If @var{coding-system} is @code{nil}, | |
1035 | that means do not encode terminal output. | |
1036 | @end defun | |
1037 | ||
969fe9b5 | 1038 | @node MS-DOS File Types |
a9f0a989 | 1039 | @subsection MS-DOS File Types |
969fe9b5 RS |
1040 | @cindex DOS file types |
1041 | @cindex MS-DOS file types | |
1042 | @cindex Windows file types | |
1043 | @cindex file types on MS-DOS and Windows | |
1044 | @cindex text files and binary files | |
1045 | @cindex binary files and text files | |
1046 | ||
8241495d RS |
1047 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate |
1048 | end-of-line conversion for a file by looking at the file's name. This | |
1049 | feature classifies fils as @dfn{text files} and @dfn{binary files}. By | |
1050 | ``binary file'' we mean a file of literal byte values that are not | |
1051 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1052 | and no character code conversion for them. On the other hand, the bytes | |
1053 | in a text file are intended to represent characters; when you create a | |
1054 | new file whose name implies that it is a text file, Emacs uses DOS | |
1055 | end-of-line conversion. | |
969fe9b5 RS |
1056 | |
1057 | @defvar buffer-file-type | |
1058 | This variable, automatically buffer-local in each buffer, records the | |
a9f0a989 RS |
1059 | file type of the buffer's visited file. When a buffer does not specify |
1060 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1061 | used to determine which coding system to use when writing the contents | |
1062 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1063 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1064 | Otherwise, @code{undecided-dos} is used. | |
1065 | ||
1066 | Normally this variable is set by visiting a file; it is set to | |
1067 | @code{nil} if the file was visited without any actual conversion. | |
969fe9b5 RS |
1068 | @end defvar |
1069 | ||
1070 | @defopt file-name-buffer-file-type-alist | |
1071 | This variable holds an alist for recognizing text and binary files. | |
1072 | Each element has the form (@var{regexp} . @var{type}), where | |
1073 | @var{regexp} is matched against the file name, and @var{type} may be | |
1074 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1075 | compute which. If it is a function, then it is called with a single | |
1076 | argument (the file name) and should return @code{t} or @code{nil}. | |
1077 | ||
8241495d | 1078 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide |
969fe9b5 RS |
1079 | which coding system to use when reading a file. For a text file, |
1080 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1081 | is used. | |
1082 | ||
1083 | If no element in this alist matches a given file name, then | |
1084 | @code{default-buffer-file-type} says how to treat the file. | |
1085 | @end defopt | |
1086 | ||
1087 | @defopt default-buffer-file-type | |
1088 | This variable says how to handle files for which | |
1089 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1090 | ||
1091 | If this variable is non-@code{nil}, then these files are treated as | |
a9f0a989 RS |
1092 | binary: the coding system @code{no-conversion} is used. Otherwise, |
1093 | nothing special is done for them---the coding system is deduced solely | |
1094 | from the file contents, in the usual Emacs fashion. | |
969fe9b5 RS |
1095 | @end defopt |
1096 | ||
a9f0a989 RS |
1097 | @node Input Methods |
1098 | @section Input Methods | |
1099 | @cindex input methods | |
1100 | ||
8241495d | 1101 | @dfn{Input methods} provide convenient ways of entering non-@sc{ascii} |
a9f0a989 | 1102 | characters from the keyboard. Unlike coding systems, which translate |
8241495d | 1103 | non-@sc{ascii} characters to and from encodings meant to be read by |
a9f0a989 RS |
1104 | programs, input methods provide human-friendly commands. (@xref{Input |
1105 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1106 | use input methods to enter text.) How to define input methods is not | |
1107 | yet documented in this manual, but here we describe how to use them. | |
1108 | ||
1109 | Each input method has a name, which is currently a string; | |
1110 | in the future, symbols may also be usable as input method names. | |
1111 | ||
a9f0a989 RS |
1112 | @defvar current-input-method |
1113 | This variable holds the name of the input method now active in the | |
1114 | current buffer. (It automatically becomes local in each buffer when set | |
1115 | in any fashion.) It is @code{nil} if no input method is active in the | |
1116 | buffer now. | |
969fe9b5 RS |
1117 | @end defvar |
1118 | ||
a9f0a989 RS |
1119 | @defvar default-input-method |
1120 | This variable holds the default input method for commands that choose an | |
1121 | input method. Unlike @code{current-input-method}, this variable is | |
1122 | normally global. | |
969fe9b5 | 1123 | @end defvar |
a9f0a989 | 1124 | |
a9f0a989 RS |
1125 | @defun set-input-method input-method |
1126 | This function activates input method @var{input-method} for the current | |
1127 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1128 | If @var{input-method} is @code{nil}, this function deactivates any input | |
1129 | method for the current buffer. | |
1130 | @end defun | |
1131 | ||
a9f0a989 RS |
1132 | @defun read-input-method-name prompt &optional default inhibit-null |
1133 | This function reads an input method name with the minibuffer, prompting | |
1134 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1135 | by default, if the user enters empty input. However, if | |
1136 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1137 | ||
1138 | The returned value is a string. | |
1139 | @end defun | |
1140 | ||
a9f0a989 RS |
1141 | @defvar input-method-alist |
1142 | This variable defines all the supported input methods. | |
1143 | Each element defines one input method, and should have the form: | |
1144 | ||
1145 | @example | |
1911e6e5 RS |
1146 | (@var{input-method} @var{language-env} @var{activate-func} |
1147 | @var{title} @var{description} @var{args}...) | |
a9f0a989 RS |
1148 | @end example |
1149 | ||
1911e6e5 RS |
1150 | Here @var{input-method} is the input method name, a string; |
1151 | @var{language-env} is another string, the name of the language | |
1152 | environment this input method is recommended for. (That serves only for | |
1153 | documentation purposes.) | |
a9f0a989 RS |
1154 | |
1155 | @var{title} is a string to display in the mode line while this method is | |
1156 | active. @var{description} is a string describing this method and what | |
1157 | it is good for. | |
1158 | ||
1159 | @var{activate-func} is a function to call to activate this method. The | |
1160 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1161 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1162 | the @var{args}. | |
1911e6e5 | 1163 | @end defvar |
a9f0a989 | 1164 | |
2eb4136f RS |
1165 | The fundamental interface to input methods is through the |
1166 | variable @code{input-method-function}. @xref{Reading One Event}. | |
2468d0c0 DL |
1167 | |
1168 | @node Locales | |
1169 | @section Locales | |
1170 | @cindex locale | |
1171 | ||
1172 | POSIX defines a concept of ``locales'' which control which language | |
1173 | to use in language-related features. These Emacs variables control | |
1174 | how Emacs interacts with these features. | |
1175 | ||
1176 | @defvar locale-coding-system | |
1177 | @tindex locale-coding-system | |
1178 | This variable specifies the coding system to use for decoding system | |
1179 | error messages, for encoding the format argument to | |
1180 | @code{format-time-string}, and for decoding the return value of | |
1181 | @code{format-time-string}. | |
1182 | @end defvar | |
1183 | ||
1184 | @defvar system-messages-locale | |
1185 | @tindex system-messages-locale | |
1186 | This variable specifies the locale to use for generating system error | |
1187 | messages. Changing the locale can cause messages to come out in a | |
9c17f494 | 1188 | different language or in a different orthography. If the variable is |
2468d0c0 DL |
1189 | @code{nil}, the locale is specified by environment variables in the |
1190 | usual POSIX fashion. | |
1191 | @end defvar | |
1192 | ||
1193 | @defvar system-time-locale | |
1194 | @tindex system-time-locale | |
1195 | This variable specifies the locale to use for formatting time values. | |
1196 | Changing the locale can cause messages to appear according to the | |
1197 | conventions of a different language. If the variable is @code{nil}, the | |
1198 | locale is specified by environment variables in the usual POSIX fashion. | |
1199 | @end defvar |