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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 | |
5557b83b RS |
15 | * Text Representations:: Unibyte and multibyte representations |
16 | * Converting Representations:: Converting unibyte to multibyte and vice versa. | |
17 | * Selecting a Representation:: Treating a byte sequence as unibyte or multi. | |
18 | * Character Codes:: How unibyte and multibyte relate to | |
19 | codes of individual characters. | |
20 | * Character Sets:: The space of possible characters codes | |
21 | is divided into various character sets. | |
22 | * Chars and Bytes:: More information about multibyte encodings. | |
23 | * Splitting Characters:: Converting a character to its byte sequence. | |
24 | * Scanning Charsets:: Which character sets are used in a buffer? | |
25 | * Translation of Characters:: Translation tables are used for conversion. | |
26 | * Coding Systems:: Coding systems are conversions for saving files. | |
27 | * Input Methods:: Input methods allow users to enter various | |
28 | non-ASCII characters without speciak keyboards. | |
29 | * Locales:: Interacting with the POSIX locale. | |
cc6d0d2c RS |
30 | @end menu |
31 | ||
32 | @node Text Representations | |
33 | @section Text Representations | |
34 | @cindex text representations | |
35 | ||
36 | Emacs has two @dfn{text representations}---two ways to represent text | |
37 | in a string or buffer. These are called @dfn{unibyte} and | |
38 | @dfn{multibyte}. Each string, and each buffer, uses one of these two | |
39 | representations. For most purposes, you can ignore the issue of | |
40 | representations, because Emacs converts text between them as | |
41 | appropriate. Occasionally in Lisp programming you will need to pay | |
42 | attention to the difference. | |
43 | ||
44 | @cindex unibyte text | |
45 | In unibyte representation, each character occupies one byte and | |
46 | therefore the possible character codes range from 0 to 255. Codes 0 | |
8241495d RS |
47 | through 127 are @sc{ascii} characters; the codes from 128 through 255 |
48 | are used for one non-@sc{ascii} character set (you can choose which | |
969fe9b5 | 49 | character set by setting the variable @code{nonascii-insert-offset}). |
cc6d0d2c RS |
50 | |
51 | @cindex leading code | |
52 | @cindex multibyte text | |
1911e6e5 | 53 | @cindex trailing codes |
cc6d0d2c RS |
54 | In multibyte representation, a character may occupy more than one |
55 | byte, and as a result, the full range of Emacs character codes can be | |
56 | stored. The first byte of a multibyte character is always in the range | |
57 | 128 through 159 (octal 0200 through 0237). These values are called | |
a9f0a989 RS |
58 | @dfn{leading codes}. The second and subsequent bytes of a multibyte |
59 | character are always in the range 160 through 255 (octal 0240 through | |
1911e6e5 | 60 | 0377); these values are @dfn{trailing codes}. |
cc6d0d2c | 61 | |
0ace421a GM |
62 | Some sequences of bytes are not valid in multibyte text: for example, |
63 | a single isolated byte in the range 128 through 159 is not allowed. | |
64 | But character codes 128 through 159 can appear in multibyte text, | |
65 | represented as two-byte sequences. None of the character codes 128 | |
66 | through 255 normally appear in ordinary multibyte text, but they do | |
67 | appear in multibyte buffers and strings when you do explicit encoding | |
68 | and decoding (@pxref{Explicit Encoding}). | |
b6954afd | 69 | |
cc6d0d2c RS |
70 | In a buffer, the buffer-local value of the variable |
71 | @code{enable-multibyte-characters} specifies the representation used. | |
08f0f5e9 KH |
72 | The representation for a string is determined and recorded in the string |
73 | when the string is constructed. | |
cc6d0d2c | 74 | |
cc6d0d2c RS |
75 | @defvar enable-multibyte-characters |
76 | This variable specifies the current buffer's text representation. | |
77 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
78 | it contains unibyte text. | |
79 | ||
969fe9b5 RS |
80 | You cannot set this variable directly; instead, use the function |
81 | @code{set-buffer-multibyte} to change a buffer's representation. | |
cc6d0d2c RS |
82 | @end defvar |
83 | ||
cc6d0d2c | 84 | @defvar default-enable-multibyte-characters |
a9f0a989 | 85 | This variable's value is entirely equivalent to @code{(default-value |
cc6d0d2c | 86 | 'enable-multibyte-characters)}, and setting this variable changes that |
a9f0a989 RS |
87 | default value. Setting the local binding of |
88 | @code{enable-multibyte-characters} in a specific buffer is not allowed, | |
89 | but changing the default value is supported, and it is a reasonable | |
90 | thing to do, because it has no effect on existing buffers. | |
cc6d0d2c RS |
91 | |
92 | The @samp{--unibyte} command line option does its job by setting the | |
93 | default value to @code{nil} early in startup. | |
94 | @end defvar | |
95 | ||
b6954afd RS |
96 | @defun position-bytes position |
97 | @tindex position-bytes | |
98 | Return the byte-position corresponding to buffer position @var{position} | |
99 | in the current buffer. | |
100 | @end defun | |
101 | ||
102 | @defun byte-to-position byte-position | |
103 | @tindex byte-to-position | |
104 | Return the buffer position corresponding to byte-position | |
105 | @var{byte-position} in the current buffer. | |
106 | @end defun | |
107 | ||
cc6d0d2c | 108 | @defun multibyte-string-p string |
b6954afd | 109 | Return @code{t} if @var{string} is a multibyte string. |
cc6d0d2c RS |
110 | @end defun |
111 | ||
112 | @node Converting Representations | |
113 | @section Converting Text Representations | |
114 | ||
115 | Emacs can convert unibyte text to multibyte; it can also convert | |
116 | multibyte text to unibyte, though this conversion loses information. In | |
117 | general these conversions happen when inserting text into a buffer, or | |
118 | when putting text from several strings together in one string. You can | |
119 | also explicitly convert a string's contents to either representation. | |
120 | ||
121 | Emacs chooses the representation for a string based on the text that | |
122 | it is constructed from. The general rule is to convert unibyte text to | |
123 | multibyte text when combining it with other multibyte text, because the | |
124 | multibyte representation is more general and can hold whatever | |
125 | characters the unibyte text has. | |
126 | ||
127 | When inserting text into a buffer, Emacs converts the text to the | |
128 | buffer's representation, as specified by | |
129 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
130 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
131 | to unibyte, even though this conversion cannot in general preserve all | |
132 | the characters that might be in the multibyte text. The other natural | |
133 | alternative, to convert the buffer contents to multibyte, is not | |
134 | acceptable because the buffer's representation is a choice made by the | |
969fe9b5 | 135 | user that cannot be overridden automatically. |
cc6d0d2c | 136 | |
8241495d RS |
137 | Converting unibyte text to multibyte text leaves @sc{ascii} characters |
138 | unchanged, and likewise 128 through 159. It converts the non-@sc{ascii} | |
969fe9b5 RS |
139 | codes 160 through 255 by adding the value @code{nonascii-insert-offset} |
140 | to each character code. By setting this variable, you specify which | |
a9f0a989 RS |
141 | character set the unibyte characters correspond to (@pxref{Character |
142 | Sets}). For example, if @code{nonascii-insert-offset} is 2048, which is | |
143 | @code{(- (make-char 'latin-iso8859-1) 128)}, then the unibyte | |
8241495d | 144 | non-@sc{ascii} characters correspond to Latin 1. If it is 2688, which |
a9f0a989 RS |
145 | is @code{(- (make-char 'greek-iso8859-7) 128)}, then they correspond to |
146 | Greek letters. | |
cc6d0d2c | 147 | |
8241495d RS |
148 | Converting multibyte text to unibyte is simpler: it discards all but |
149 | the low 8 bits of each character code. If @code{nonascii-insert-offset} | |
150 | has a reasonable value, corresponding to the beginning of some character | |
151 | set, this conversion is the inverse of the other: converting unibyte | |
152 | text to multibyte and back to unibyte reproduces the original unibyte | |
153 | text. | |
cc6d0d2c | 154 | |
cc6d0d2c | 155 | @defvar nonascii-insert-offset |
8241495d | 156 | This variable specifies the amount to add to a non-@sc{ascii} character |
cc6d0d2c | 157 | when converting unibyte text to multibyte. It also applies when |
a9f0a989 | 158 | @code{self-insert-command} inserts a character in the unibyte |
969ac764 | 159 | non-@sc{ascii} range, 128 through 255. However, the functions |
7a063989 | 160 | @code{insert} and @code{insert-char} do not perform this conversion. |
cc6d0d2c RS |
161 | |
162 | The right value to use to select character set @var{cs} is @code{(- | |
a9f0a989 | 163 | (make-char @var{cs}) 128)}. If the value of |
cc6d0d2c RS |
164 | @code{nonascii-insert-offset} is zero, then conversion actually uses the |
165 | value for the Latin 1 character set, rather than zero. | |
166 | @end defvar | |
167 | ||
a9f0a989 | 168 | @defvar nonascii-translation-table |
cc6d0d2c RS |
169 | This variable provides a more general alternative to |
170 | @code{nonascii-insert-offset}. You can use it to specify independently | |
171 | how to translate each code in the range of 128 through 255 into a | |
7a063989 | 172 | multibyte character. The value should be a char-table, or @code{nil}. |
969fe9b5 | 173 | If this is non-@code{nil}, it overrides @code{nonascii-insert-offset}. |
cc6d0d2c RS |
174 | @end defvar |
175 | ||
cc6d0d2c RS |
176 | @defun string-make-unibyte string |
177 | This function converts the text of @var{string} to unibyte | |
1911e6e5 | 178 | representation, if it isn't already, and returns the result. If |
969fe9b5 | 179 | @var{string} is a unibyte string, it is returned unchanged. |
cc6d0d2c RS |
180 | @end defun |
181 | ||
cc6d0d2c RS |
182 | @defun string-make-multibyte string |
183 | This function converts the text of @var{string} to multibyte | |
1911e6e5 | 184 | representation, if it isn't already, and returns the result. If |
969fe9b5 | 185 | @var{string} is a multibyte string, it is returned unchanged. |
cc6d0d2c RS |
186 | @end defun |
187 | ||
188 | @node Selecting a Representation | |
189 | @section Selecting a Representation | |
190 | ||
191 | Sometimes it is useful to examine an existing buffer or string as | |
192 | multibyte when it was unibyte, or vice versa. | |
193 | ||
cc6d0d2c RS |
194 | @defun set-buffer-multibyte multibyte |
195 | Set the representation type of the current buffer. If @var{multibyte} | |
196 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
197 | is @code{nil}, the buffer becomes unibyte. | |
198 | ||
199 | This function leaves the buffer contents unchanged when viewed as a | |
200 | sequence of bytes. As a consequence, it can change the contents viewed | |
201 | as characters; a sequence of two bytes which is treated as one character | |
202 | in multibyte representation will count as two characters in unibyte | |
7a063989 KH |
203 | representation. Character codes 128 through 159 are an exception. They |
204 | are represented by one byte in a unibyte buffer, but when the buffer is | |
205 | set to multibyte, they are converted to two-byte sequences, and vice | |
206 | versa. | |
cc6d0d2c RS |
207 | |
208 | This function sets @code{enable-multibyte-characters} to record which | |
209 | representation is in use. It also adjusts various data in the buffer | |
969fe9b5 RS |
210 | (including overlays, text properties and markers) so that they cover the |
211 | same text as they did before. | |
b6954afd RS |
212 | |
213 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
214 | because indirect buffers always inherit the representation of the | |
215 | base buffer. | |
cc6d0d2c RS |
216 | @end defun |
217 | ||
cc6d0d2c RS |
218 | @defun string-as-unibyte string |
219 | This function returns a string with the same bytes as @var{string} but | |
220 | treating each byte as a character. This means that the value may have | |
221 | more characters than @var{string} has. | |
222 | ||
b6954afd RS |
223 | If @var{string} is already a unibyte string, then the value is |
224 | @var{string} itself. | |
cc6d0d2c RS |
225 | @end defun |
226 | ||
cc6d0d2c RS |
227 | @defun string-as-multibyte string |
228 | This function returns a string with the same bytes as @var{string} but | |
229 | treating each multibyte sequence as one character. This means that the | |
230 | value may have fewer characters than @var{string} has. | |
231 | ||
b6954afd RS |
232 | If @var{string} is already a multibyte string, then the value is |
233 | @var{string} itself. | |
cc6d0d2c RS |
234 | @end defun |
235 | ||
236 | @node Character Codes | |
237 | @section Character Codes | |
238 | @cindex character codes | |
239 | ||
240 | The unibyte and multibyte text representations use different character | |
241 | codes. The valid character codes for unibyte representation range from | |
242 | 0 to 255---the values that can fit in one byte. The valid character | |
243 | codes for multibyte representation range from 0 to 524287, but not all | |
0ace421a GM |
244 | values in that range are valid. The values 128 through 255 are not |
245 | really proper in multibyte text, but they can occur if you do explicit | |
246 | encoding and decoding (@pxref{Explicit Encoding}). Some other character | |
247 | codes cannot occur at all in multibyte text. Only the @sc{ascii} codes | |
248 | 0 through 127 are truly legitimate in both representations. | |
cc6d0d2c | 249 | |
7a063989 | 250 | @defun char-valid-p charcode &optional genericp |
cc6d0d2c RS |
251 | This returns @code{t} if @var{charcode} is valid for either one of the two |
252 | text representations. | |
253 | ||
254 | @example | |
255 | (char-valid-p 65) | |
256 | @result{} t | |
257 | (char-valid-p 256) | |
258 | @result{} nil | |
259 | (char-valid-p 2248) | |
260 | @result{} t | |
261 | @end example | |
7a063989 KH |
262 | |
263 | If the optional argument @var{genericp} is non-nil, this function | |
264 | returns @code{t} if @var{charcode} is a generic character | |
969ac764 | 265 | (@pxref{Splitting Characters}). |
cc6d0d2c RS |
266 | @end defun |
267 | ||
268 | @node Character Sets | |
269 | @section Character Sets | |
270 | @cindex character sets | |
271 | ||
272 | Emacs classifies characters into various @dfn{character sets}, each of | |
273 | which has a name which is a symbol. Each character belongs to one and | |
274 | only one character set. | |
275 | ||
276 | In general, there is one character set for each distinct script. For | |
277 | example, @code{latin-iso8859-1} is one character set, | |
278 | @code{greek-iso8859-7} is another, and @code{ascii} is another. An | |
969fe9b5 RS |
279 | Emacs character set can hold at most 9025 characters; therefore, in some |
280 | cases, characters that would logically be grouped together are split | |
a9f0a989 RS |
281 | into several character sets. For example, one set of Chinese |
282 | characters, generally known as Big 5, is divided into two Emacs | |
283 | character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. | |
cc6d0d2c | 284 | |
4240c779 GM |
285 | @sc{ascii} characters are in character set @code{ascii}. The |
286 | non-@sc{ascii} characters 128 through 159 are in character set | |
287 | @code{eight-bit-control}, and codes 160 through 255 are in character set | |
288 | @code{eight-bit-graphic}. | |
289 | ||
cc6d0d2c | 290 | @defun charsetp object |
8241495d | 291 | Returns @code{t} if @var{object} is a symbol that names a character set, |
cc6d0d2c RS |
292 | @code{nil} otherwise. |
293 | @end defun | |
294 | ||
cc6d0d2c RS |
295 | @defun charset-list |
296 | This function returns a list of all defined character set names. | |
297 | @end defun | |
298 | ||
cc6d0d2c | 299 | @defun char-charset character |
b6954afd RS |
300 | This function returns the name of the character set that @var{character} |
301 | belongs to. | |
cc6d0d2c RS |
302 | @end defun |
303 | ||
8241495d RS |
304 | @defun charset-plist charset |
305 | @tindex charset-plist | |
306 | This function returns the charset property list of the character set | |
307 | @var{charset}. Although @var{charset} is a symbol, this is not the same | |
308 | as the property list of that symbol. Charset properties are used for | |
7a063989 KH |
309 | special purposes within Emacs; for example, |
310 | @code{preferred-coding-system} helps determine which coding system to | |
311 | use to encode characters in a charset. | |
8241495d RS |
312 | @end defun |
313 | ||
cc6d0d2c RS |
314 | @node Chars and Bytes |
315 | @section Characters and Bytes | |
316 | @cindex bytes and characters | |
317 | ||
a9f0a989 RS |
318 | @cindex introduction sequence |
319 | @cindex dimension (of character set) | |
cc6d0d2c | 320 | In multibyte representation, each character occupies one or more |
a9f0a989 | 321 | bytes. Each character set has an @dfn{introduction sequence}, which is |
8241495d | 322 | normally one or two bytes long. (Exception: the @sc{ascii} character |
7a063989 KH |
323 | set and the @sc{eight-bit-graphic} character set have a zero-length |
324 | introduction sequence.) The introduction sequence is the beginning of | |
325 | the byte sequence for any character in the character set. The rest of | |
326 | the character's bytes distinguish it from the other characters in the | |
327 | same character set. Depending on the character set, there are either | |
328 | one or two distinguishing bytes; the number of such bytes is called the | |
329 | @dfn{dimension} of the character set. | |
a9f0a989 RS |
330 | |
331 | @defun charset-dimension charset | |
b6954afd RS |
332 | This function returns the dimension of @var{charset}; at present, the |
333 | dimension is always 1 or 2. | |
334 | @end defun | |
335 | ||
336 | @defun charset-bytes charset | |
337 | @tindex charset-bytes | |
338 | This function returns the number of bytes used to represent a character | |
339 | in character set @var{charset}. | |
a9f0a989 RS |
340 | @end defun |
341 | ||
342 | This is the simplest way to determine the byte length of a character | |
343 | set's introduction sequence: | |
344 | ||
345 | @example | |
b6954afd | 346 | (- (charset-bytes @var{charset}) |
a9f0a989 RS |
347 | (charset-dimension @var{charset})) |
348 | @end example | |
349 | ||
350 | @node Splitting Characters | |
351 | @section Splitting Characters | |
352 | ||
353 | The functions in this section convert between characters and the byte | |
354 | values used to represent them. For most purposes, there is no need to | |
355 | be concerned with the sequence of bytes used to represent a character, | |
969fe9b5 | 356 | because Emacs translates automatically when necessary. |
cc6d0d2c | 357 | |
cc6d0d2c RS |
358 | @defun split-char character |
359 | Return a list containing the name of the character set of | |
a9f0a989 RS |
360 | @var{character}, followed by one or two byte values (integers) which |
361 | identify @var{character} within that character set. The number of byte | |
362 | values is the character set's dimension. | |
cc6d0d2c RS |
363 | |
364 | @example | |
365 | (split-char 2248) | |
366 | @result{} (latin-iso8859-1 72) | |
367 | (split-char 65) | |
368 | @result{} (ascii 65) | |
7a063989 KH |
369 | (split-char 128) |
370 | @result{} (eight-bit-control 128) | |
cc6d0d2c RS |
371 | @end example |
372 | @end defun | |
373 | ||
cc6d0d2c | 374 | @defun make-char charset &rest byte-values |
a9f0a989 RS |
375 | This function returns the character in character set @var{charset} |
376 | identified by @var{byte-values}. This is roughly the inverse of | |
377 | @code{split-char}. Normally, you should specify either one or two | |
378 | @var{byte-values}, according to the dimension of @var{charset}. For | |
379 | example, | |
cc6d0d2c RS |
380 | |
381 | @example | |
382 | (make-char 'latin-iso8859-1 72) | |
383 | @result{} 2248 | |
384 | @end example | |
385 | @end defun | |
386 | ||
a9f0a989 RS |
387 | @cindex generic characters |
388 | If you call @code{make-char} with no @var{byte-values}, the result is | |
389 | a @dfn{generic character} which stands for @var{charset}. A generic | |
390 | character is an integer, but it is @emph{not} valid for insertion in the | |
391 | buffer as a character. It can be used in @code{char-table-range} to | |
392 | refer to the whole character set (@pxref{Char-Tables}). | |
393 | @code{char-valid-p} returns @code{nil} for generic characters. | |
394 | For example: | |
395 | ||
396 | @example | |
397 | (make-char 'latin-iso8859-1) | |
398 | @result{} 2176 | |
399 | (char-valid-p 2176) | |
400 | @result{} nil | |
7a063989 KH |
401 | (char-valid-p 2176 t) |
402 | @result{} t | |
a9f0a989 RS |
403 | (split-char 2176) |
404 | @result{} (latin-iso8859-1 0) | |
405 | @end example | |
406 | ||
7a063989 KH |
407 | The character sets @sc{ascii}, @sc{eight-bit-control}, and |
408 | @sc{eight-bit-graphic} don't have corresponding generic characters. | |
409 | ||
a9f0a989 RS |
410 | @node Scanning Charsets |
411 | @section Scanning for Character Sets | |
412 | ||
413 | Sometimes it is useful to find out which character sets appear in a | |
414 | part of a buffer or a string. One use for this is in determining which | |
415 | coding systems (@pxref{Coding Systems}) are capable of representing all | |
416 | of the text in question. | |
417 | ||
418 | @defun find-charset-region beg end &optional translation | |
a9f0a989 RS |
419 | This function returns a list of the character sets that appear in the |
420 | current buffer between positions @var{beg} and @var{end}. | |
421 | ||
422 | The optional argument @var{translation} specifies a translation table to | |
423 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
424 | is non-@code{nil}, then each character in the region is translated | |
425 | through this table, and the value returned describes the translated | |
426 | characters instead of the characters actually in the buffer. | |
a265079f | 427 | @end defun |
a9f0a989 RS |
428 | |
429 | @defun find-charset-string string &optional translation | |
b6954afd RS |
430 | This function returns a list of the character sets that appear in the |
431 | string @var{string}. It is just like @code{find-charset-region}, except | |
432 | that it applies to the contents of @var{string} instead of part of the | |
433 | current buffer. | |
a9f0a989 RS |
434 | @end defun |
435 | ||
436 | @node Translation of Characters | |
437 | @section Translation of Characters | |
438 | @cindex character translation tables | |
439 | @cindex translation tables | |
440 | ||
441 | A @dfn{translation table} specifies a mapping of characters | |
442 | into characters. These tables are used in encoding and decoding, and | |
443 | for other purposes. Some coding systems specify their own particular | |
444 | translation tables; there are also default translation tables which | |
445 | apply to all other coding systems. | |
446 | ||
8241495d RS |
447 | @defun make-translation-table &rest translations |
448 | This function returns a translation table based on the argument | |
449 | @var{translations}. Each element of | |
450 | @var{translations} should be a list of the form @code{(@var{from} | |
a9f0a989 RS |
451 | . @var{to})}; this says to translate the character @var{from} into |
452 | @var{to}. | |
453 | ||
454 | You can also map one whole character set into another character set with | |
455 | the same dimension. To do this, you specify a generic character (which | |
456 | designates a character set) for @var{from} (@pxref{Splitting Characters}). | |
457 | In this case, @var{to} should also be a generic character, for another | |
458 | character set of the same dimension. Then the translation table | |
459 | translates each character of @var{from}'s character set into the | |
460 | corresponding character of @var{to}'s character set. | |
461 | @end defun | |
462 | ||
463 | In decoding, the translation table's translations are applied to the | |
464 | characters that result from ordinary decoding. If a coding system has | |
465 | property @code{character-translation-table-for-decode}, that specifies | |
466 | the translation table to use. Otherwise, if | |
b1f687a2 RS |
467 | @code{standard-translation-table-for-decode} is non-@code{nil}, decoding |
468 | uses that table. | |
a9f0a989 RS |
469 | |
470 | In encoding, the translation table's translations are applied to the | |
471 | characters in the buffer, and the result of translation is actually | |
472 | encoded. If a coding system has property | |
473 | @code{character-translation-table-for-encode}, that specifies the | |
474 | translation table to use. Otherwise the variable | |
b1f687a2 RS |
475 | @code{standard-translation-table-for-encode} specifies the translation |
476 | table. | |
a9f0a989 | 477 | |
b1f687a2 | 478 | @defvar standard-translation-table-for-decode |
a9f0a989 RS |
479 | This is the default translation table for decoding, for |
480 | coding systems that don't specify any other translation table. | |
481 | @end defvar | |
482 | ||
b1f687a2 | 483 | @defvar standard-translation-table-for-encode |
a9f0a989 RS |
484 | This is the default translation table for encoding, for |
485 | coding systems that don't specify any other translation table. | |
486 | @end defvar | |
487 | ||
cc6d0d2c RS |
488 | @node Coding Systems |
489 | @section Coding Systems | |
490 | ||
491 | @cindex coding system | |
492 | When Emacs reads or writes a file, and when Emacs sends text to a | |
493 | subprocess or receives text from a subprocess, it normally performs | |
494 | character code conversion and end-of-line conversion as specified | |
495 | by a particular @dfn{coding system}. | |
496 | ||
8241495d RS |
497 | How to define a coding system is an arcane matter, and is not |
498 | documented here. | |
b6954afd | 499 | |
a9f0a989 | 500 | @menu |
5557b83b RS |
501 | * Coding System Basics:: Basic concepts. |
502 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
503 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
504 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
505 | * Default Coding Systems:: Controlling the default choices. | |
506 | * Specifying Coding Systems:: Requesting a particular coding system | |
507 | for a single file operation. | |
508 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
509 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
510 | * MS-DOS File Types:: How DOS "text" and "binary" files | |
511 | relate to coding systems. | |
a9f0a989 RS |
512 | @end menu |
513 | ||
514 | @node Coding System Basics | |
515 | @subsection Basic Concepts of Coding Systems | |
516 | ||
cc6d0d2c RS |
517 | @cindex character code conversion |
518 | @dfn{Character code conversion} involves conversion between the encoding | |
519 | used inside Emacs and some other encoding. Emacs supports many | |
520 | different encodings, in that it can convert to and from them. For | |
521 | example, it can convert text to or from encodings such as Latin 1, Latin | |
522 | 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some | |
523 | cases, Emacs supports several alternative encodings for the same | |
524 | characters; for example, there are three coding systems for the Cyrillic | |
525 | (Russian) alphabet: ISO, Alternativnyj, and KOI8. | |
526 | ||
cc6d0d2c | 527 | Most coding systems specify a particular character code for |
8241495d RS |
528 | conversion, but some of them leave the choice unspecified---to be chosen |
529 | heuristically for each file, based on the data. | |
cc6d0d2c | 530 | |
969fe9b5 RS |
531 | @cindex end of line conversion |
532 | @dfn{End of line conversion} handles three different conventions used | |
533 | on various systems for representing end of line in files. The Unix | |
534 | convention is to use the linefeed character (also called newline). The | |
8241495d RS |
535 | DOS convention is to use a carriage-return and a linefeed at the end of |
536 | a line. The Mac convention is to use just carriage-return. | |
969fe9b5 | 537 | |
cc6d0d2c RS |
538 | @cindex base coding system |
539 | @cindex variant coding system | |
540 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
541 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
542 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
543 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
a9f0a989 | 544 | well. Most base coding systems have three corresponding variants whose |
cc6d0d2c RS |
545 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. |
546 | ||
a9f0a989 RS |
547 | The coding system @code{raw-text} is special in that it prevents |
548 | character code conversion, and causes the buffer visited with that | |
549 | coding system to be a unibyte buffer. It does not specify the | |
550 | end-of-line conversion, allowing that to be determined as usual by the | |
551 | data, and has the usual three variants which specify the end-of-line | |
552 | conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: | |
553 | it specifies no conversion of either character codes or end-of-line. | |
554 | ||
555 | The coding system @code{emacs-mule} specifies that the data is | |
556 | represented in the internal Emacs encoding. This is like | |
557 | @code{raw-text} in that no code conversion happens, but different in | |
558 | that the result is multibyte data. | |
559 | ||
560 | @defun coding-system-get coding-system property | |
a9f0a989 RS |
561 | This function returns the specified property of the coding system |
562 | @var{coding-system}. Most coding system properties exist for internal | |
563 | purposes, but one that you might find useful is @code{mime-charset}. | |
564 | That property's value is the name used in MIME for the character coding | |
565 | which this coding system can read and write. Examples: | |
566 | ||
567 | @example | |
568 | (coding-system-get 'iso-latin-1 'mime-charset) | |
569 | @result{} iso-8859-1 | |
570 | (coding-system-get 'iso-2022-cn 'mime-charset) | |
571 | @result{} iso-2022-cn | |
572 | (coding-system-get 'cyrillic-koi8 'mime-charset) | |
573 | @result{} koi8-r | |
574 | @end example | |
575 | ||
576 | The value of the @code{mime-charset} property is also defined | |
577 | as an alias for the coding system. | |
578 | @end defun | |
579 | ||
580 | @node Encoding and I/O | |
581 | @subsection Encoding and I/O | |
582 | ||
1911e6e5 | 583 | The principal purpose of coding systems is for use in reading and |
a9f0a989 RS |
584 | writing files. The function @code{insert-file-contents} uses |
585 | a coding system for decoding the file data, and @code{write-region} | |
586 | uses one to encode the buffer contents. | |
587 | ||
588 | You can specify the coding system to use either explicitly | |
589 | (@pxref{Specifying Coding Systems}), or implicitly using the defaulting | |
590 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
591 | completely specify what to do. For example, they may choose a coding | |
592 | system such as @code{undefined} which leaves the character code | |
593 | conversion to be determined from the data. In these cases, the I/O | |
594 | operation finishes the job of choosing a coding system. Very often | |
595 | you will want to find out afterwards which coding system was chosen. | |
596 | ||
597 | @defvar buffer-file-coding-system | |
a9f0a989 RS |
598 | This variable records the coding system that was used for visiting the |
599 | current buffer. It is used for saving the buffer, and for writing part | |
600 | of the buffer with @code{write-region}. When those operations ask the | |
601 | user to specify a different coding system, | |
602 | @code{buffer-file-coding-system} is updated to the coding system | |
603 | specified. | |
b6954afd RS |
604 | |
605 | However, @code{buffer-file-coding-system} does not affect sending text | |
606 | to a subprocess. | |
a9f0a989 RS |
607 | @end defvar |
608 | ||
609 | @defvar save-buffer-coding-system | |
7a063989 KH |
610 | This variable specifies the coding system for saving the buffer (by |
611 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
612 | for @code{write-region}. | |
8241495d RS |
613 | |
614 | When a command to save the buffer starts out to use | |
7a063989 KH |
615 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), |
616 | and that coding system cannot handle | |
8241495d RS |
617 | the actual text in the buffer, the command asks the user to choose |
618 | another coding system. After that happens, the command also updates | |
7a063989 | 619 | @code{buffer-file-coding-system} to represent the coding system that the |
8241495d | 620 | user specified. |
a9f0a989 RS |
621 | @end defvar |
622 | ||
623 | @defvar last-coding-system-used | |
a9f0a989 RS |
624 | I/O operations for files and subprocesses set this variable to the |
625 | coding system name that was used. The explicit encoding and decoding | |
626 | functions (@pxref{Explicit Encoding}) set it too. | |
627 | ||
628 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
8241495d RS |
629 | it can change whenever Emacs waits; therefore, you should copy the |
630 | value shortly after the function call that stores the value you are | |
a9f0a989 RS |
631 | interested in. |
632 | @end defvar | |
633 | ||
2eb4136f RS |
634 | The variable @code{selection-coding-system} specifies how to encode |
635 | selections for the window system. @xref{Window System Selections}. | |
636 | ||
969fe9b5 RS |
637 | @node Lisp and Coding Systems |
638 | @subsection Coding Systems in Lisp | |
639 | ||
8241495d | 640 | Here are the Lisp facilities for working with coding systems: |
cc6d0d2c | 641 | |
cc6d0d2c RS |
642 | @defun coding-system-list &optional base-only |
643 | This function returns a list of all coding system names (symbols). If | |
644 | @var{base-only} is non-@code{nil}, the value includes only the | |
7a063989 KH |
645 | base coding systems. Otherwise, it includes alias and variant coding |
646 | systems as well. | |
cc6d0d2c RS |
647 | @end defun |
648 | ||
cc6d0d2c RS |
649 | @defun coding-system-p object |
650 | This function returns @code{t} if @var{object} is a coding system | |
651 | name. | |
652 | @end defun | |
653 | ||
cc6d0d2c RS |
654 | @defun check-coding-system coding-system |
655 | This function checks the validity of @var{coding-system}. | |
656 | If that is valid, it returns @var{coding-system}. | |
657 | Otherwise it signals an error with condition @code{coding-system-error}. | |
658 | @end defun | |
659 | ||
a9f0a989 | 660 | @defun coding-system-change-eol-conversion coding-system eol-type |
a9f0a989 | 661 | This function returns a coding system which is like @var{coding-system} |
1911e6e5 | 662 | except for its eol conversion, which is specified by @code{eol-type}. |
a9f0a989 RS |
663 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or |
664 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
665 | the end-of-line conversion from the data. | |
666 | @end defun | |
969fe9b5 | 667 | |
a9f0a989 | 668 | @defun coding-system-change-text-conversion eol-coding text-coding |
a9f0a989 RS |
669 | This function returns a coding system which uses the end-of-line |
670 | conversion of @var{eol-coding}, and the text conversion of | |
671 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
672 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
969fe9b5 RS |
673 | @end defun |
674 | ||
a9f0a989 | 675 | @defun find-coding-systems-region from to |
a9f0a989 RS |
676 | This function returns a list of coding systems that could be used to |
677 | encode a text between @var{from} and @var{to}. All coding systems in | |
678 | the list can safely encode any multibyte characters in that portion of | |
679 | the text. | |
680 | ||
681 | If the text contains no multibyte characters, the function returns the | |
682 | list @code{(undecided)}. | |
683 | @end defun | |
684 | ||
685 | @defun find-coding-systems-string string | |
a9f0a989 RS |
686 | This function returns a list of coding systems that could be used to |
687 | encode the text of @var{string}. All coding systems in the list can | |
688 | safely encode any multibyte characters in @var{string}. If the text | |
689 | contains no multibyte characters, this returns the list | |
690 | @code{(undecided)}. | |
691 | @end defun | |
692 | ||
693 | @defun find-coding-systems-for-charsets charsets | |
a9f0a989 RS |
694 | This function returns a list of coding systems that could be used to |
695 | encode all the character sets in the list @var{charsets}. | |
696 | @end defun | |
697 | ||
698 | @defun detect-coding-region start end &optional highest | |
cc6d0d2c | 699 | This function chooses a plausible coding system for decoding the text |
0ace421a | 700 | from @var{start} to @var{end}. This text should be a byte sequence |
969fe9b5 | 701 | (@pxref{Explicit Encoding}). |
cc6d0d2c | 702 | |
a9f0a989 | 703 | Normally this function returns a list of coding systems that could |
cc6d0d2c | 704 | handle decoding the text that was scanned. They are listed in order of |
a9f0a989 RS |
705 | decreasing priority. But if @var{highest} is non-@code{nil}, then the |
706 | return value is just one coding system, the one that is highest in | |
707 | priority. | |
708 | ||
8241495d | 709 | If the region contains only @sc{ascii} characters, the value |
a9f0a989 | 710 | is @code{undecided} or @code{(undecided)}. |
cc6d0d2c RS |
711 | @end defun |
712 | ||
a9f0a989 | 713 | @defun detect-coding-string string highest |
cc6d0d2c RS |
714 | This function is like @code{detect-coding-region} except that it |
715 | operates on the contents of @var{string} instead of bytes in the buffer. | |
1911e6e5 RS |
716 | @end defun |
717 | ||
718 | @xref{Process Information}, for how to examine or set the coding | |
719 | systems used for I/O to a subprocess. | |
720 | ||
721 | @node User-Chosen Coding Systems | |
722 | @subsection User-Chosen Coding Systems | |
723 | ||
1911e6e5 | 724 | @defun select-safe-coding-system from to &optional preferred-coding-system |
ebc6903b | 725 | This function selects a coding system for encoding the text between |
1911e6e5 RS |
726 | @var{from} and @var{to}, asking the user to choose if necessary. |
727 | ||
728 | The optional argument @var{preferred-coding-system} specifies a coding | |
ebc6903b RS |
729 | system to try first. If that one can handle the text in the specified |
730 | region, then it is used. If this argument is omitted, the current | |
731 | buffer's value of @code{buffer-file-coding-system} is tried first. | |
1911e6e5 RS |
732 | |
733 | If the region contains some multibyte characters that the preferred | |
734 | coding system cannot encode, this function asks the user to choose from | |
735 | a list of coding systems which can encode the text, and returns the | |
736 | user's choice. | |
737 | ||
738 | One other kludgy feature: if @var{from} is a string, the string is the | |
739 | target text, and @var{to} is ignored. | |
969fe9b5 RS |
740 | @end defun |
741 | ||
742 | Here are two functions you can use to let the user specify a coding | |
743 | system, with completion. @xref{Completion}. | |
744 | ||
a9f0a989 | 745 | @defun read-coding-system prompt &optional default |
969fe9b5 RS |
746 | This function reads a coding system using the minibuffer, prompting with |
747 | string @var{prompt}, and returns the coding system name as a symbol. If | |
748 | the user enters null input, @var{default} specifies which coding system | |
749 | to return. It should be a symbol or a string. | |
750 | @end defun | |
751 | ||
969fe9b5 RS |
752 | @defun read-non-nil-coding-system prompt |
753 | This function reads a coding system using the minibuffer, prompting with | |
a9f0a989 | 754 | string @var{prompt}, and returns the coding system name as a symbol. If |
969fe9b5 RS |
755 | the user tries to enter null input, it asks the user to try again. |
756 | @xref{Coding Systems}. | |
cc6d0d2c RS |
757 | @end defun |
758 | ||
759 | @node Default Coding Systems | |
a9f0a989 | 760 | @subsection Default Coding Systems |
cc6d0d2c | 761 | |
a9f0a989 RS |
762 | This section describes variables that specify the default coding |
763 | system for certain files or when running certain subprograms, and the | |
1911e6e5 | 764 | function that I/O operations use to access them. |
a9f0a989 RS |
765 | |
766 | The idea of these variables is that you set them once and for all to the | |
767 | defaults you want, and then do not change them again. To specify a | |
768 | particular coding system for a particular operation in a Lisp program, | |
769 | don't change these variables; instead, override them using | |
770 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
771 | (@pxref{Specifying Coding Systems}). | |
cc6d0d2c | 772 | |
cc6d0d2c RS |
773 | @defvar file-coding-system-alist |
774 | This variable is an alist that specifies the coding systems to use for | |
775 | reading and writing particular files. Each element has the form | |
776 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
777 | expression that matches certain file names. The element applies to file | |
778 | names that match @var{pattern}. | |
779 | ||
1911e6e5 | 780 | The @sc{cdr} of the element, @var{coding}, should be either a coding |
8241495d RS |
781 | system, a cons cell containing two coding systems, or a function name (a |
782 | symbol with a function definition). If @var{coding} is a coding system, | |
783 | that coding system is used for both reading the file and writing it. If | |
784 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
785 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
786 | coding system for encoding. | |
787 | ||
788 | If @var{coding} is a function name, the function must return a coding | |
cc6d0d2c RS |
789 | system or a cons cell containing two coding systems. This value is used |
790 | as described above. | |
791 | @end defvar | |
792 | ||
cc6d0d2c RS |
793 | @defvar process-coding-system-alist |
794 | This variable is an alist specifying which coding systems to use for a | |
795 | subprocess, depending on which program is running in the subprocess. It | |
796 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
797 | matched against the program name used to start the subprocess. The coding | |
798 | system or systems specified in this alist are used to initialize the | |
799 | coding systems used for I/O to the subprocess, but you can specify | |
800 | other coding systems later using @code{set-process-coding-system}. | |
801 | @end defvar | |
802 | ||
8241495d RS |
803 | @strong{Warning:} Coding systems such as @code{undecided}, which |
804 | determine the coding system from the data, do not work entirely reliably | |
1911e6e5 | 805 | with asynchronous subprocess output. This is because Emacs handles |
a9f0a989 RS |
806 | asynchronous subprocess output in batches, as it arrives. If the coding |
807 | system leaves the character code conversion unspecified, or leaves the | |
808 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
809 | conversion from one batch at a time, and this does not always work. | |
810 | ||
811 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
812 | coding system which determines both the character code conversion and | |
813 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
814 | rather than @code{undecided} or @code{latin-1}. | |
815 | ||
cc6d0d2c RS |
816 | @defvar network-coding-system-alist |
817 | This variable is an alist that specifies the coding system to use for | |
818 | network streams. It works much like @code{file-coding-system-alist}, | |
969fe9b5 | 819 | with the difference that the @var{pattern} in an element may be either a |
cc6d0d2c RS |
820 | port number or a regular expression. If it is a regular expression, it |
821 | is matched against the network service name used to open the network | |
822 | stream. | |
823 | @end defvar | |
824 | ||
cc6d0d2c RS |
825 | @defvar default-process-coding-system |
826 | This variable specifies the coding systems to use for subprocess (and | |
827 | network stream) input and output, when nothing else specifies what to | |
828 | do. | |
829 | ||
a9f0a989 RS |
830 | The value should be a cons cell of the form @code{(@var{input-coding} |
831 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
832 | the subprocess, and @var{output-coding} applies to output to it. | |
cc6d0d2c RS |
833 | @end defvar |
834 | ||
a9f0a989 | 835 | @defun find-operation-coding-system operation &rest arguments |
a9f0a989 RS |
836 | This function returns the coding system to use (by default) for |
837 | performing @var{operation} with @var{arguments}. The value has this | |
838 | form: | |
839 | ||
840 | @example | |
841 | (@var{decoding-system} @var{encoding-system}) | |
842 | @end example | |
843 | ||
844 | The first element, @var{decoding-system}, is the coding system to use | |
845 | for decoding (in case @var{operation} does decoding), and | |
846 | @var{encoding-system} is the coding system for encoding (in case | |
847 | @var{operation} does encoding). | |
848 | ||
8241495d | 849 | The argument @var{operation} should be a symbol, one of |
a9f0a989 RS |
850 | @code{insert-file-contents}, @code{write-region}, @code{call-process}, |
851 | @code{call-process-region}, @code{start-process}, or | |
8241495d RS |
852 | @code{open-network-stream}. These are the names of the Emacs I/O primitives |
853 | that can do coding system conversion. | |
a9f0a989 RS |
854 | |
855 | The remaining arguments should be the same arguments that might be given | |
8241495d | 856 | to that I/O primitive. Depending on the primitive, one of those |
a9f0a989 RS |
857 | arguments is selected as the @dfn{target}. For example, if |
858 | @var{operation} does file I/O, whichever argument specifies the file | |
859 | name is the target. For subprocess primitives, the process name is the | |
860 | target. For @code{open-network-stream}, the target is the service name | |
861 | or port number. | |
862 | ||
863 | This function looks up the target in @code{file-coding-system-alist}, | |
864 | @code{process-coding-system-alist}, or | |
865 | @code{network-coding-system-alist}, depending on @var{operation}. | |
866 | @xref{Default Coding Systems}. | |
867 | @end defun | |
868 | ||
cc6d0d2c | 869 | @node Specifying Coding Systems |
a9f0a989 | 870 | @subsection Specifying a Coding System for One Operation |
cc6d0d2c RS |
871 | |
872 | You can specify the coding system for a specific operation by binding | |
873 | the variables @code{coding-system-for-read} and/or | |
874 | @code{coding-system-for-write}. | |
875 | ||
cc6d0d2c RS |
876 | @defvar coding-system-for-read |
877 | If this variable is non-@code{nil}, it specifies the coding system to | |
878 | use for reading a file, or for input from a synchronous subprocess. | |
879 | ||
880 | It also applies to any asynchronous subprocess or network stream, but in | |
881 | a different way: the value of @code{coding-system-for-read} when you | |
882 | start the subprocess or open the network stream specifies the input | |
883 | decoding method for that subprocess or network stream. It remains in | |
884 | use for that subprocess or network stream unless and until overridden. | |
885 | ||
886 | The right way to use this variable is to bind it with @code{let} for a | |
887 | specific I/O operation. Its global value is normally @code{nil}, and | |
888 | you should not globally set it to any other value. Here is an example | |
889 | of the right way to use the variable: | |
890 | ||
891 | @example | |
892 | ;; @r{Read the file with no character code conversion.} | |
969fe9b5 | 893 | ;; @r{Assume @sc{crlf} represents end-of-line.} |
cc6d0d2c RS |
894 | (let ((coding-system-for-write 'emacs-mule-dos)) |
895 | (insert-file-contents filename)) | |
896 | @end example | |
897 | ||
898 | When its value is non-@code{nil}, @code{coding-system-for-read} takes | |
a9f0a989 | 899 | precedence over all other methods of specifying a coding system to use for |
cc6d0d2c RS |
900 | input, including @code{file-coding-system-alist}, |
901 | @code{process-coding-system-alist} and | |
902 | @code{network-coding-system-alist}. | |
903 | @end defvar | |
904 | ||
cc6d0d2c RS |
905 | @defvar coding-system-for-write |
906 | This works much like @code{coding-system-for-read}, except that it | |
907 | applies to output rather than input. It affects writing to files, | |
b6954afd | 908 | as well as sending output to subprocesses and net connections. |
cc6d0d2c RS |
909 | |
910 | When a single operation does both input and output, as do | |
911 | @code{call-process-region} and @code{start-process}, both | |
912 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
913 | affect it. | |
914 | @end defvar | |
915 | ||
cc6d0d2c RS |
916 | @defvar inhibit-eol-conversion |
917 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
918 | no matter which coding system is specified. This applies to all the | |
919 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
920 | decoding functions (@pxref{Explicit Encoding}). | |
921 | @end defvar | |
922 | ||
cc6d0d2c | 923 | @node Explicit Encoding |
a9f0a989 | 924 | @subsection Explicit Encoding and Decoding |
cc6d0d2c RS |
925 | @cindex encoding text |
926 | @cindex decoding text | |
927 | ||
928 | All the operations that transfer text in and out of Emacs have the | |
929 | ability to use a coding system to encode or decode the text. | |
930 | You can also explicitly encode and decode text using the functions | |
931 | in this section. | |
932 | ||
cc6d0d2c | 933 | The result of encoding, and the input to decoding, are not ordinary |
0ace421a GM |
934 | text. They logically consist of a series of byte values; that is, a |
935 | series of characters whose codes are in the range 0 through 255. In a | |
936 | multibyte buffer or string, character codes 128 through 159 are | |
937 | represented by multibyte sequences, but this is invisible to Lisp | |
938 | programs. | |
939 | ||
940 | The usual way to read a file into a buffer as a sequence of bytes, so | |
941 | you can decode the contents explicitly, is with | |
942 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
943 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
944 | visiting a file with @code{find-file-noselect}. These methods result in | |
945 | a unibyte buffer. | |
946 | ||
947 | The usual way to use the byte sequence that results from explicitly | |
948 | encoding text is to copy it to a file or process---for example, to write | |
949 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
950 | encoding by binding @code{coding-system-for-write} to | |
951 | @code{no-conversion}. | |
b6954afd RS |
952 | |
953 | Here are the functions to perform explicit encoding or decoding. The | |
0ace421a GM |
954 | decoding functions produce sequences of bytes; the encoding functions |
955 | are meant to operate on sequences of bytes. All of these functions | |
956 | discard text properties. | |
1911e6e5 | 957 | |
cc6d0d2c RS |
958 | @defun encode-coding-region start end coding-system |
959 | This function encodes the text from @var{start} to @var{end} according | |
969fe9b5 | 960 | to coding system @var{coding-system}. The encoded text replaces the |
0ace421a GM |
961 | original text in the buffer. The result of encoding is logically a |
962 | sequence of bytes, but the buffer remains multibyte if it was multibyte | |
963 | before. | |
cc6d0d2c RS |
964 | @end defun |
965 | ||
cc6d0d2c RS |
966 | @defun encode-coding-string string coding-system |
967 | This function encodes the text in @var{string} according to coding | |
968 | system @var{coding-system}. It returns a new string containing the | |
0ace421a | 969 | encoded text. The result of encoding is a unibyte string. |
cc6d0d2c RS |
970 | @end defun |
971 | ||
cc6d0d2c RS |
972 | @defun decode-coding-region start end coding-system |
973 | This function decodes the text from @var{start} to @var{end} according | |
974 | to coding system @var{coding-system}. The decoded text replaces the | |
975 | original text in the buffer. To make explicit decoding useful, the text | |
0ace421a GM |
976 | before decoding ought to be a sequence of byte values, but both |
977 | multibyte and unibyte buffers are acceptable. | |
cc6d0d2c RS |
978 | @end defun |
979 | ||
cc6d0d2c RS |
980 | @defun decode-coding-string string coding-system |
981 | This function decodes the text in @var{string} according to coding | |
982 | system @var{coding-system}. It returns a new string containing the | |
983 | decoded text. To make explicit decoding useful, the contents of | |
0ace421a GM |
984 | @var{string} ought to be a sequence of byte values, but a multibyte |
985 | string is acceptable. | |
cc6d0d2c | 986 | @end defun |
969fe9b5 | 987 | |
a9f0a989 RS |
988 | @node Terminal I/O Encoding |
989 | @subsection Terminal I/O Encoding | |
990 | ||
991 | Emacs can decode keyboard input using a coding system, and encode | |
2eb4136f RS |
992 | terminal output. This is useful for terminals that transmit or display |
993 | text using a particular encoding such as Latin-1. Emacs does not set | |
994 | @code{last-coding-system-used} for encoding or decoding for the | |
995 | terminal. | |
a9f0a989 RS |
996 | |
997 | @defun keyboard-coding-system | |
a9f0a989 RS |
998 | This function returns the coding system that is in use for decoding |
999 | keyboard input---or @code{nil} if no coding system is to be used. | |
1000 | @end defun | |
1001 | ||
1002 | @defun set-keyboard-coding-system coding-system | |
a9f0a989 RS |
1003 | This function specifies @var{coding-system} as the coding system to |
1004 | use for decoding keyboard input. If @var{coding-system} is @code{nil}, | |
1005 | that means do not decode keyboard input. | |
1006 | @end defun | |
1007 | ||
1008 | @defun terminal-coding-system | |
a9f0a989 RS |
1009 | This function returns the coding system that is in use for encoding |
1010 | terminal output---or @code{nil} for no encoding. | |
1011 | @end defun | |
1012 | ||
1013 | @defun set-terminal-coding-system coding-system | |
a9f0a989 RS |
1014 | This function specifies @var{coding-system} as the coding system to use |
1015 | for encoding terminal output. If @var{coding-system} is @code{nil}, | |
1016 | that means do not encode terminal output. | |
1017 | @end defun | |
1018 | ||
969fe9b5 | 1019 | @node MS-DOS File Types |
a9f0a989 | 1020 | @subsection MS-DOS File Types |
969fe9b5 RS |
1021 | @cindex DOS file types |
1022 | @cindex MS-DOS file types | |
1023 | @cindex Windows file types | |
1024 | @cindex file types on MS-DOS and Windows | |
1025 | @cindex text files and binary files | |
1026 | @cindex binary files and text files | |
1027 | ||
8241495d RS |
1028 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate |
1029 | end-of-line conversion for a file by looking at the file's name. This | |
0ace421a | 1030 | feature classifies files as @dfn{text files} and @dfn{binary files}. By |
8241495d RS |
1031 | ``binary file'' we mean a file of literal byte values that are not |
1032 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1033 | and no character code conversion for them. On the other hand, the bytes | |
1034 | in a text file are intended to represent characters; when you create a | |
1035 | new file whose name implies that it is a text file, Emacs uses DOS | |
1036 | end-of-line conversion. | |
969fe9b5 RS |
1037 | |
1038 | @defvar buffer-file-type | |
1039 | This variable, automatically buffer-local in each buffer, records the | |
a9f0a989 RS |
1040 | file type of the buffer's visited file. When a buffer does not specify |
1041 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1042 | used to determine which coding system to use when writing the contents | |
1043 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1044 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1045 | Otherwise, @code{undecided-dos} is used. | |
1046 | ||
1047 | Normally this variable is set by visiting a file; it is set to | |
1048 | @code{nil} if the file was visited without any actual conversion. | |
969fe9b5 RS |
1049 | @end defvar |
1050 | ||
1051 | @defopt file-name-buffer-file-type-alist | |
1052 | This variable holds an alist for recognizing text and binary files. | |
1053 | Each element has the form (@var{regexp} . @var{type}), where | |
1054 | @var{regexp} is matched against the file name, and @var{type} may be | |
1055 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1056 | compute which. If it is a function, then it is called with a single | |
1057 | argument (the file name) and should return @code{t} or @code{nil}. | |
1058 | ||
8241495d | 1059 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide |
969fe9b5 RS |
1060 | which coding system to use when reading a file. For a text file, |
1061 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1062 | is used. | |
1063 | ||
1064 | If no element in this alist matches a given file name, then | |
1065 | @code{default-buffer-file-type} says how to treat the file. | |
1066 | @end defopt | |
1067 | ||
1068 | @defopt default-buffer-file-type | |
1069 | This variable says how to handle files for which | |
1070 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1071 | ||
1072 | If this variable is non-@code{nil}, then these files are treated as | |
a9f0a989 RS |
1073 | binary: the coding system @code{no-conversion} is used. Otherwise, |
1074 | nothing special is done for them---the coding system is deduced solely | |
1075 | from the file contents, in the usual Emacs fashion. | |
969fe9b5 RS |
1076 | @end defopt |
1077 | ||
a9f0a989 RS |
1078 | @node Input Methods |
1079 | @section Input Methods | |
1080 | @cindex input methods | |
1081 | ||
8241495d | 1082 | @dfn{Input methods} provide convenient ways of entering non-@sc{ascii} |
a9f0a989 | 1083 | characters from the keyboard. Unlike coding systems, which translate |
8241495d | 1084 | non-@sc{ascii} characters to and from encodings meant to be read by |
a9f0a989 RS |
1085 | programs, input methods provide human-friendly commands. (@xref{Input |
1086 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1087 | use input methods to enter text.) How to define input methods is not | |
1088 | yet documented in this manual, but here we describe how to use them. | |
1089 | ||
1090 | Each input method has a name, which is currently a string; | |
1091 | in the future, symbols may also be usable as input method names. | |
1092 | ||
a9f0a989 RS |
1093 | @defvar current-input-method |
1094 | This variable holds the name of the input method now active in the | |
1095 | current buffer. (It automatically becomes local in each buffer when set | |
1096 | in any fashion.) It is @code{nil} if no input method is active in the | |
1097 | buffer now. | |
969fe9b5 RS |
1098 | @end defvar |
1099 | ||
a9f0a989 RS |
1100 | @defvar default-input-method |
1101 | This variable holds the default input method for commands that choose an | |
1102 | input method. Unlike @code{current-input-method}, this variable is | |
1103 | normally global. | |
969fe9b5 | 1104 | @end defvar |
a9f0a989 | 1105 | |
a9f0a989 RS |
1106 | @defun set-input-method input-method |
1107 | This function activates input method @var{input-method} for the current | |
1108 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1109 | If @var{input-method} is @code{nil}, this function deactivates any input | |
1110 | method for the current buffer. | |
1111 | @end defun | |
1112 | ||
a9f0a989 RS |
1113 | @defun read-input-method-name prompt &optional default inhibit-null |
1114 | This function reads an input method name with the minibuffer, prompting | |
1115 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1116 | by default, if the user enters empty input. However, if | |
1117 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1118 | ||
1119 | The returned value is a string. | |
1120 | @end defun | |
1121 | ||
a9f0a989 RS |
1122 | @defvar input-method-alist |
1123 | This variable defines all the supported input methods. | |
1124 | Each element defines one input method, and should have the form: | |
1125 | ||
1126 | @example | |
1911e6e5 RS |
1127 | (@var{input-method} @var{language-env} @var{activate-func} |
1128 | @var{title} @var{description} @var{args}...) | |
a9f0a989 RS |
1129 | @end example |
1130 | ||
1911e6e5 RS |
1131 | Here @var{input-method} is the input method name, a string; |
1132 | @var{language-env} is another string, the name of the language | |
1133 | environment this input method is recommended for. (That serves only for | |
1134 | documentation purposes.) | |
a9f0a989 | 1135 | |
a9f0a989 RS |
1136 | @var{activate-func} is a function to call to activate this method. The |
1137 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1138 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1139 | the @var{args}. | |
0ace421a GM |
1140 | |
1141 | @var{title} is a string to display in the mode line while this method is | |
1142 | active. @var{description} is a string describing this method and what | |
1143 | it is good for. | |
1911e6e5 | 1144 | @end defvar |
a9f0a989 | 1145 | |
2eb4136f RS |
1146 | The fundamental interface to input methods is through the |
1147 | variable @code{input-method-function}. @xref{Reading One Event}. | |
2468d0c0 DL |
1148 | |
1149 | @node Locales | |
1150 | @section Locales | |
1151 | @cindex locale | |
1152 | ||
1153 | POSIX defines a concept of ``locales'' which control which language | |
1154 | to use in language-related features. These Emacs variables control | |
1155 | how Emacs interacts with these features. | |
1156 | ||
1157 | @defvar locale-coding-system | |
1158 | @tindex locale-coding-system | |
1159 | This variable specifies the coding system to use for decoding system | |
1160 | error messages, for encoding the format argument to | |
1161 | @code{format-time-string}, and for decoding the return value of | |
1162 | @code{format-time-string}. | |
1163 | @end defvar | |
1164 | ||
1165 | @defvar system-messages-locale | |
1166 | @tindex system-messages-locale | |
1167 | This variable specifies the locale to use for generating system error | |
1168 | messages. Changing the locale can cause messages to come out in a | |
9c17f494 | 1169 | different language or in a different orthography. If the variable is |
2468d0c0 DL |
1170 | @code{nil}, the locale is specified by environment variables in the |
1171 | usual POSIX fashion. | |
1172 | @end defvar | |
1173 | ||
1174 | @defvar system-time-locale | |
1175 | @tindex system-time-locale | |
1176 | This variable specifies the locale to use for formatting time values. | |
1177 | Changing the locale can cause messages to appear according to the | |
1178 | conventions of a different language. If the variable is @code{nil}, the | |
1179 | locale is specified by environment variables in the usual POSIX fashion. | |
1180 | @end defvar | |
0ace421a | 1181 |