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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
177c0ea7 | 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 | |
8a9e355c | 28 | non-ASCII characters without special keyboards. |
5557b83b | 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 | 62 | Some sequences of bytes are not valid in multibyte text: for example, |
1e4d32f8 GM |
63 | a single isolated byte in the range 128 through 159 is not allowed. But |
64 | character codes 128 through 159 can appear in multibyte text, | |
65 | represented as two-byte sequences. All the character codes 128 through | |
66 | 255 are possible (though slightly abnormal) in multibyte text; they | |
0ace421a GM |
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 | 137 | Converting unibyte text to multibyte text leaves @sc{ascii} characters |
1e4d32f8 GM |
138 | unchanged, and likewise character codes 128 through 159. It converts |
139 | the non-@sc{ascii} codes 160 through 255 by adding the value | |
140 | @code{nonascii-insert-offset} to each character code. By setting this | |
141 | variable, you specify which character set the unibyte characters | |
142 | correspond to (@pxref{Character Sets}). For example, if | |
143 | @code{nonascii-insert-offset} is 2048, which is @code{(- (make-char | |
144 | 'latin-iso8859-1) 128)}, then the unibyte non-@sc{ascii} characters | |
145 | correspond to Latin 1. If it is 2688, which is @code{(- (make-char | |
146 | 'greek-iso8859-7) 128)}, then they correspond to 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 |
38eee91c EZ |
179 | @var{string} is a unibyte string, it is returned unchanged. Multibyte |
180 | character codes are converted to unibyte according to | |
181 | @code{nonascii-translation-table} or, if that is @code{nil}, using | |
182 | @code{nonascii-insert-offset}. If the lookup in the translation table | |
183 | fails, this function takes just the low 8 bits of each character. | |
cc6d0d2c RS |
184 | @end defun |
185 | ||
cc6d0d2c RS |
186 | @defun string-make-multibyte string |
187 | This function converts the text of @var{string} to multibyte | |
1911e6e5 | 188 | representation, if it isn't already, and returns the result. If |
969fe9b5 | 189 | @var{string} is a multibyte string, it is returned unchanged. |
7f84d9ae DL |
190 | The function @code{unibyte-char-to-multibyte} is used to convert |
191 | each unibyte character to a multibyte character. | |
cc6d0d2c RS |
192 | @end defun |
193 | ||
194 | @node Selecting a Representation | |
195 | @section Selecting a Representation | |
196 | ||
197 | Sometimes it is useful to examine an existing buffer or string as | |
198 | multibyte when it was unibyte, or vice versa. | |
199 | ||
cc6d0d2c RS |
200 | @defun set-buffer-multibyte multibyte |
201 | Set the representation type of the current buffer. If @var{multibyte} | |
202 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
203 | is @code{nil}, the buffer becomes unibyte. | |
204 | ||
205 | This function leaves the buffer contents unchanged when viewed as a | |
206 | sequence of bytes. As a consequence, it can change the contents viewed | |
207 | as characters; a sequence of two bytes which is treated as one character | |
208 | in multibyte representation will count as two characters in unibyte | |
7a063989 KH |
209 | representation. Character codes 128 through 159 are an exception. They |
210 | are represented by one byte in a unibyte buffer, but when the buffer is | |
211 | set to multibyte, they are converted to two-byte sequences, and vice | |
212 | versa. | |
cc6d0d2c RS |
213 | |
214 | This function sets @code{enable-multibyte-characters} to record which | |
215 | representation is in use. It also adjusts various data in the buffer | |
969fe9b5 RS |
216 | (including overlays, text properties and markers) so that they cover the |
217 | same text as they did before. | |
b6954afd RS |
218 | |
219 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
220 | because indirect buffers always inherit the representation of the | |
221 | base buffer. | |
cc6d0d2c RS |
222 | @end defun |
223 | ||
cc6d0d2c RS |
224 | @defun string-as-unibyte string |
225 | This function returns a string with the same bytes as @var{string} but | |
226 | treating each byte as a character. This means that the value may have | |
227 | more characters than @var{string} has. | |
228 | ||
b6954afd | 229 | If @var{string} is already a unibyte string, then the value is |
7f84d9ae DL |
230 | @var{string} itself. Otherwise it is a newly created string, with no |
231 | text properties. If @var{string} is multibyte, any characters it | |
232 | contains of charset @var{eight-bit-control} or @var{eight-bit-graphic} | |
233 | are converted to the corresponding single byte. | |
cc6d0d2c RS |
234 | @end defun |
235 | ||
cc6d0d2c RS |
236 | @defun string-as-multibyte string |
237 | This function returns a string with the same bytes as @var{string} but | |
238 | treating each multibyte sequence as one character. This means that the | |
239 | value may have fewer characters than @var{string} has. | |
240 | ||
b6954afd | 241 | If @var{string} is already a multibyte string, then the value is |
7f84d9ae DL |
242 | @var{string} itself. Otherwise it is a newly created string, with no |
243 | text properties. If @var{string} is unibyte and contains any individual | |
244 | 8-bit bytes (i.e.@: not part of a multibyte form), they are converted to | |
245 | the corresponding multibyte character of charset @var{eight-bit-control} | |
246 | or @var{eight-bit-graphic}. | |
cc6d0d2c RS |
247 | @end defun |
248 | ||
249 | @node Character Codes | |
250 | @section Character Codes | |
251 | @cindex character codes | |
252 | ||
253 | The unibyte and multibyte text representations use different character | |
254 | codes. The valid character codes for unibyte representation range from | |
255 | 0 to 255---the values that can fit in one byte. The valid character | |
256 | codes for multibyte representation range from 0 to 524287, but not all | |
0ace421a | 257 | values in that range are valid. The values 128 through 255 are not |
1e4d32f8 | 258 | entirely proper in multibyte text, but they can occur if you do explicit |
0ace421a GM |
259 | encoding and decoding (@pxref{Explicit Encoding}). Some other character |
260 | codes cannot occur at all in multibyte text. Only the @sc{ascii} codes | |
1e4d32f8 | 261 | 0 through 127 are completely legitimate in both representations. |
cc6d0d2c | 262 | |
7a063989 | 263 | @defun char-valid-p charcode &optional genericp |
cc6d0d2c RS |
264 | This returns @code{t} if @var{charcode} is valid for either one of the two |
265 | text representations. | |
266 | ||
267 | @example | |
268 | (char-valid-p 65) | |
269 | @result{} t | |
270 | (char-valid-p 256) | |
271 | @result{} nil | |
272 | (char-valid-p 2248) | |
273 | @result{} t | |
274 | @end example | |
7a063989 KH |
275 | |
276 | If the optional argument @var{genericp} is non-nil, this function | |
277 | returns @code{t} if @var{charcode} is a generic character | |
969ac764 | 278 | (@pxref{Splitting Characters}). |
cc6d0d2c RS |
279 | @end defun |
280 | ||
281 | @node Character Sets | |
282 | @section Character Sets | |
283 | @cindex character sets | |
284 | ||
285 | Emacs classifies characters into various @dfn{character sets}, each of | |
286 | which has a name which is a symbol. Each character belongs to one and | |
287 | only one character set. | |
288 | ||
289 | In general, there is one character set for each distinct script. For | |
290 | example, @code{latin-iso8859-1} is one character set, | |
291 | @code{greek-iso8859-7} is another, and @code{ascii} is another. An | |
969fe9b5 RS |
292 | Emacs character set can hold at most 9025 characters; therefore, in some |
293 | cases, characters that would logically be grouped together are split | |
a9f0a989 RS |
294 | into several character sets. For example, one set of Chinese |
295 | characters, generally known as Big 5, is divided into two Emacs | |
296 | character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. | |
cc6d0d2c | 297 | |
4240c779 GM |
298 | @sc{ascii} characters are in character set @code{ascii}. The |
299 | non-@sc{ascii} characters 128 through 159 are in character set | |
300 | @code{eight-bit-control}, and codes 160 through 255 are in character set | |
301 | @code{eight-bit-graphic}. | |
302 | ||
cc6d0d2c | 303 | @defun charsetp object |
8241495d | 304 | Returns @code{t} if @var{object} is a symbol that names a character set, |
cc6d0d2c RS |
305 | @code{nil} otherwise. |
306 | @end defun | |
307 | ||
cc6d0d2c RS |
308 | @defun charset-list |
309 | This function returns a list of all defined character set names. | |
310 | @end defun | |
311 | ||
cc6d0d2c | 312 | @defun char-charset character |
b6954afd RS |
313 | This function returns the name of the character set that @var{character} |
314 | belongs to. | |
cc6d0d2c RS |
315 | @end defun |
316 | ||
8241495d RS |
317 | @defun charset-plist charset |
318 | @tindex charset-plist | |
319 | This function returns the charset property list of the character set | |
320 | @var{charset}. Although @var{charset} is a symbol, this is not the same | |
321 | as the property list of that symbol. Charset properties are used for | |
7a063989 KH |
322 | special purposes within Emacs; for example, |
323 | @code{preferred-coding-system} helps determine which coding system to | |
324 | use to encode characters in a charset. | |
8241495d RS |
325 | @end defun |
326 | ||
cc6d0d2c RS |
327 | @node Chars and Bytes |
328 | @section Characters and Bytes | |
329 | @cindex bytes and characters | |
330 | ||
a9f0a989 RS |
331 | @cindex introduction sequence |
332 | @cindex dimension (of character set) | |
cc6d0d2c | 333 | In multibyte representation, each character occupies one or more |
a9f0a989 | 334 | bytes. Each character set has an @dfn{introduction sequence}, which is |
8241495d | 335 | normally one or two bytes long. (Exception: the @sc{ascii} character |
7a063989 KH |
336 | set and the @sc{eight-bit-graphic} character set have a zero-length |
337 | introduction sequence.) The introduction sequence is the beginning of | |
338 | the byte sequence for any character in the character set. The rest of | |
339 | the character's bytes distinguish it from the other characters in the | |
340 | same character set. Depending on the character set, there are either | |
341 | one or two distinguishing bytes; the number of such bytes is called the | |
342 | @dfn{dimension} of the character set. | |
a9f0a989 RS |
343 | |
344 | @defun charset-dimension charset | |
b6954afd RS |
345 | This function returns the dimension of @var{charset}; at present, the |
346 | dimension is always 1 or 2. | |
347 | @end defun | |
348 | ||
349 | @defun charset-bytes charset | |
350 | @tindex charset-bytes | |
351 | This function returns the number of bytes used to represent a character | |
352 | in character set @var{charset}. | |
a9f0a989 RS |
353 | @end defun |
354 | ||
355 | This is the simplest way to determine the byte length of a character | |
356 | set's introduction sequence: | |
357 | ||
358 | @example | |
b6954afd | 359 | (- (charset-bytes @var{charset}) |
a9f0a989 RS |
360 | (charset-dimension @var{charset})) |
361 | @end example | |
362 | ||
363 | @node Splitting Characters | |
364 | @section Splitting Characters | |
365 | ||
366 | The functions in this section convert between characters and the byte | |
367 | values used to represent them. For most purposes, there is no need to | |
368 | be concerned with the sequence of bytes used to represent a character, | |
969fe9b5 | 369 | because Emacs translates automatically when necessary. |
cc6d0d2c | 370 | |
cc6d0d2c RS |
371 | @defun split-char character |
372 | Return a list containing the name of the character set of | |
a9f0a989 RS |
373 | @var{character}, followed by one or two byte values (integers) which |
374 | identify @var{character} within that character set. The number of byte | |
375 | values is the character set's dimension. | |
cc6d0d2c RS |
376 | |
377 | @example | |
378 | (split-char 2248) | |
379 | @result{} (latin-iso8859-1 72) | |
380 | (split-char 65) | |
381 | @result{} (ascii 65) | |
7a063989 KH |
382 | (split-char 128) |
383 | @result{} (eight-bit-control 128) | |
cc6d0d2c RS |
384 | @end example |
385 | @end defun | |
386 | ||
e8262f40 DL |
387 | @defun make-char charset &optional code1 code2 |
388 | This function returns the character in character set @var{charset} whose | |
389 | position codes are @var{code1} and @var{code2}. This is roughly the | |
390 | inverse of @code{split-char}. Normally, you should specify either one | |
391 | or both of @var{code1} and @var{code2} according to the dimension of | |
392 | @var{charset}. For example, | |
cc6d0d2c RS |
393 | |
394 | @example | |
395 | (make-char 'latin-iso8859-1 72) | |
396 | @result{} 2248 | |
397 | @end example | |
398 | @end defun | |
399 | ||
a9f0a989 RS |
400 | @cindex generic characters |
401 | If you call @code{make-char} with no @var{byte-values}, the result is | |
402 | a @dfn{generic character} which stands for @var{charset}. A generic | |
403 | character is an integer, but it is @emph{not} valid for insertion in the | |
404 | buffer as a character. It can be used in @code{char-table-range} to | |
405 | refer to the whole character set (@pxref{Char-Tables}). | |
406 | @code{char-valid-p} returns @code{nil} for generic characters. | |
407 | For example: | |
408 | ||
409 | @example | |
410 | (make-char 'latin-iso8859-1) | |
411 | @result{} 2176 | |
412 | (char-valid-p 2176) | |
413 | @result{} nil | |
7a063989 KH |
414 | (char-valid-p 2176 t) |
415 | @result{} t | |
a9f0a989 RS |
416 | (split-char 2176) |
417 | @result{} (latin-iso8859-1 0) | |
418 | @end example | |
419 | ||
7a063989 | 420 | The character sets @sc{ascii}, @sc{eight-bit-control}, and |
e8262f40 DL |
421 | @sc{eight-bit-graphic} don't have corresponding generic characters. If |
422 | @var{charset} is one of them and you don't supply @var{code1}, | |
423 | @code{make-char} returns the character code corresponding to the | |
424 | smallest code in @var{charset}. | |
7a063989 | 425 | |
a9f0a989 RS |
426 | @node Scanning Charsets |
427 | @section Scanning for Character Sets | |
428 | ||
429 | Sometimes it is useful to find out which character sets appear in a | |
430 | part of a buffer or a string. One use for this is in determining which | |
431 | coding systems (@pxref{Coding Systems}) are capable of representing all | |
432 | of the text in question. | |
433 | ||
434 | @defun find-charset-region beg end &optional translation | |
a9f0a989 RS |
435 | This function returns a list of the character sets that appear in the |
436 | current buffer between positions @var{beg} and @var{end}. | |
437 | ||
438 | The optional argument @var{translation} specifies a translation table to | |
439 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
440 | is non-@code{nil}, then each character in the region is translated | |
441 | through this table, and the value returned describes the translated | |
442 | characters instead of the characters actually in the buffer. | |
a265079f | 443 | @end defun |
a9f0a989 RS |
444 | |
445 | @defun find-charset-string string &optional translation | |
b6954afd RS |
446 | This function returns a list of the character sets that appear in the |
447 | string @var{string}. It is just like @code{find-charset-region}, except | |
448 | that it applies to the contents of @var{string} instead of part of the | |
449 | current buffer. | |
a9f0a989 RS |
450 | @end defun |
451 | ||
452 | @node Translation of Characters | |
453 | @section Translation of Characters | |
454 | @cindex character translation tables | |
455 | @cindex translation tables | |
456 | ||
457 | A @dfn{translation table} specifies a mapping of characters | |
458 | into characters. These tables are used in encoding and decoding, and | |
459 | for other purposes. Some coding systems specify their own particular | |
460 | translation tables; there are also default translation tables which | |
461 | apply to all other coding systems. | |
462 | ||
8241495d RS |
463 | @defun make-translation-table &rest translations |
464 | This function returns a translation table based on the argument | |
f57b6e64 DL |
465 | @var{translations}. Each element of @var{translations} should be a |
466 | list of elements of the form @code{(@var{from} . @var{to})}; this says | |
467 | to translate the character @var{from} into @var{to}. | |
a9f0a989 | 468 | |
c04c052b DL |
469 | The arguments and the forms in each argument are processed in order, |
470 | and if a previous form already translates @var{to} to some other | |
471 | character, say @var{to-alt}, @var{from} is also translated to | |
472 | @var{to-alt}. | |
473 | ||
a9f0a989 RS |
474 | You can also map one whole character set into another character set with |
475 | the same dimension. To do this, you specify a generic character (which | |
476 | designates a character set) for @var{from} (@pxref{Splitting Characters}). | |
477 | In this case, @var{to} should also be a generic character, for another | |
478 | character set of the same dimension. Then the translation table | |
479 | translates each character of @var{from}'s character set into the | |
480 | corresponding character of @var{to}'s character set. | |
481 | @end defun | |
482 | ||
483 | In decoding, the translation table's translations are applied to the | |
484 | characters that result from ordinary decoding. If a coding system has | |
485 | property @code{character-translation-table-for-decode}, that specifies | |
486 | the translation table to use. Otherwise, if | |
b1f687a2 RS |
487 | @code{standard-translation-table-for-decode} is non-@code{nil}, decoding |
488 | uses that table. | |
a9f0a989 RS |
489 | |
490 | In encoding, the translation table's translations are applied to the | |
491 | characters in the buffer, and the result of translation is actually | |
492 | encoded. If a coding system has property | |
493 | @code{character-translation-table-for-encode}, that specifies the | |
494 | translation table to use. Otherwise the variable | |
b1f687a2 RS |
495 | @code{standard-translation-table-for-encode} specifies the translation |
496 | table. | |
a9f0a989 | 497 | |
b1f687a2 | 498 | @defvar standard-translation-table-for-decode |
a9f0a989 RS |
499 | This is the default translation table for decoding, for |
500 | coding systems that don't specify any other translation table. | |
501 | @end defvar | |
502 | ||
b1f687a2 | 503 | @defvar standard-translation-table-for-encode |
a9f0a989 RS |
504 | This is the default translation table for encoding, for |
505 | coding systems that don't specify any other translation table. | |
506 | @end defvar | |
507 | ||
cc6d0d2c RS |
508 | @node Coding Systems |
509 | @section Coding Systems | |
510 | ||
511 | @cindex coding system | |
512 | When Emacs reads or writes a file, and when Emacs sends text to a | |
513 | subprocess or receives text from a subprocess, it normally performs | |
514 | character code conversion and end-of-line conversion as specified | |
515 | by a particular @dfn{coding system}. | |
516 | ||
8241495d RS |
517 | How to define a coding system is an arcane matter, and is not |
518 | documented here. | |
b6954afd | 519 | |
a9f0a989 | 520 | @menu |
5557b83b RS |
521 | * Coding System Basics:: Basic concepts. |
522 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
523 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
524 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
525 | * Default Coding Systems:: Controlling the default choices. | |
526 | * Specifying Coding Systems:: Requesting a particular coding system | |
527 | for a single file operation. | |
528 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
529 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
530 | * MS-DOS File Types:: How DOS "text" and "binary" files | |
531 | relate to coding systems. | |
a9f0a989 RS |
532 | @end menu |
533 | ||
534 | @node Coding System Basics | |
535 | @subsection Basic Concepts of Coding Systems | |
536 | ||
cc6d0d2c RS |
537 | @cindex character code conversion |
538 | @dfn{Character code conversion} involves conversion between the encoding | |
539 | used inside Emacs and some other encoding. Emacs supports many | |
540 | different encodings, in that it can convert to and from them. For | |
541 | example, it can convert text to or from encodings such as Latin 1, Latin | |
542 | 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some | |
543 | cases, Emacs supports several alternative encodings for the same | |
544 | characters; for example, there are three coding systems for the Cyrillic | |
545 | (Russian) alphabet: ISO, Alternativnyj, and KOI8. | |
546 | ||
cc6d0d2c | 547 | Most coding systems specify a particular character code for |
8241495d RS |
548 | conversion, but some of them leave the choice unspecified---to be chosen |
549 | heuristically for each file, based on the data. | |
cc6d0d2c | 550 | |
969fe9b5 RS |
551 | @cindex end of line conversion |
552 | @dfn{End of line conversion} handles three different conventions used | |
553 | on various systems for representing end of line in files. The Unix | |
554 | convention is to use the linefeed character (also called newline). The | |
8241495d RS |
555 | DOS convention is to use a carriage-return and a linefeed at the end of |
556 | a line. The Mac convention is to use just carriage-return. | |
969fe9b5 | 557 | |
cc6d0d2c RS |
558 | @cindex base coding system |
559 | @cindex variant coding system | |
560 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
561 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
562 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
563 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
a9f0a989 | 564 | well. Most base coding systems have three corresponding variants whose |
cc6d0d2c RS |
565 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. |
566 | ||
a9f0a989 RS |
567 | The coding system @code{raw-text} is special in that it prevents |
568 | character code conversion, and causes the buffer visited with that | |
569 | coding system to be a unibyte buffer. It does not specify the | |
570 | end-of-line conversion, allowing that to be determined as usual by the | |
571 | data, and has the usual three variants which specify the end-of-line | |
572 | conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: | |
573 | it specifies no conversion of either character codes or end-of-line. | |
574 | ||
575 | The coding system @code{emacs-mule} specifies that the data is | |
576 | represented in the internal Emacs encoding. This is like | |
577 | @code{raw-text} in that no code conversion happens, but different in | |
578 | that the result is multibyte data. | |
579 | ||
580 | @defun coding-system-get coding-system property | |
a9f0a989 RS |
581 | This function returns the specified property of the coding system |
582 | @var{coding-system}. Most coding system properties exist for internal | |
583 | purposes, but one that you might find useful is @code{mime-charset}. | |
584 | That property's value is the name used in MIME for the character coding | |
585 | which this coding system can read and write. Examples: | |
586 | ||
587 | @example | |
588 | (coding-system-get 'iso-latin-1 'mime-charset) | |
589 | @result{} iso-8859-1 | |
590 | (coding-system-get 'iso-2022-cn 'mime-charset) | |
591 | @result{} iso-2022-cn | |
592 | (coding-system-get 'cyrillic-koi8 'mime-charset) | |
593 | @result{} koi8-r | |
594 | @end example | |
595 | ||
596 | The value of the @code{mime-charset} property is also defined | |
597 | as an alias for the coding system. | |
598 | @end defun | |
599 | ||
600 | @node Encoding and I/O | |
601 | @subsection Encoding and I/O | |
602 | ||
1911e6e5 | 603 | The principal purpose of coding systems is for use in reading and |
a9f0a989 RS |
604 | writing files. The function @code{insert-file-contents} uses |
605 | a coding system for decoding the file data, and @code{write-region} | |
606 | uses one to encode the buffer contents. | |
607 | ||
608 | You can specify the coding system to use either explicitly | |
609 | (@pxref{Specifying Coding Systems}), or implicitly using the defaulting | |
610 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
611 | completely specify what to do. For example, they may choose a coding | |
612 | system such as @code{undefined} which leaves the character code | |
613 | conversion to be determined from the data. In these cases, the I/O | |
614 | operation finishes the job of choosing a coding system. Very often | |
615 | you will want to find out afterwards which coding system was chosen. | |
616 | ||
617 | @defvar buffer-file-coding-system | |
a9f0a989 RS |
618 | This variable records the coding system that was used for visiting the |
619 | current buffer. It is used for saving the buffer, and for writing part | |
1b02d12c EZ |
620 | of the buffer with @code{write-region}. If the text to be written |
621 | cannot be safely encoded using the coding system specified by this | |
622 | variable, these operations select an alternative encoding by calling | |
623 | the function @code{select-safe-coding-system} (@pxref{User-Chosen | |
624 | Coding Systems}). If selecting a different encoding requires to ask | |
625 | the user to specify a coding system, @code{buffer-file-coding-system} | |
626 | is updated to the newly selected coding system. | |
627 | ||
628 | @code{buffer-file-coding-system} does @emph{not} affect sending text | |
b6954afd | 629 | to a subprocess. |
a9f0a989 RS |
630 | @end defvar |
631 | ||
632 | @defvar save-buffer-coding-system | |
7a063989 KH |
633 | This variable specifies the coding system for saving the buffer (by |
634 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
635 | for @code{write-region}. | |
8241495d RS |
636 | |
637 | When a command to save the buffer starts out to use | |
7a063989 KH |
638 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), |
639 | and that coding system cannot handle | |
8241495d | 640 | the actual text in the buffer, the command asks the user to choose |
1b02d12c EZ |
641 | another coding system (by calling @code{select-safe-coding-system}). |
642 | After that happens, the command also updates | |
643 | @code{buffer-file-coding-system} to represent the coding system that | |
644 | the user specified. | |
a9f0a989 RS |
645 | @end defvar |
646 | ||
647 | @defvar last-coding-system-used | |
a9f0a989 RS |
648 | I/O operations for files and subprocesses set this variable to the |
649 | coding system name that was used. The explicit encoding and decoding | |
650 | functions (@pxref{Explicit Encoding}) set it too. | |
651 | ||
652 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
8241495d RS |
653 | it can change whenever Emacs waits; therefore, you should copy the |
654 | value shortly after the function call that stores the value you are | |
a9f0a989 RS |
655 | interested in. |
656 | @end defvar | |
657 | ||
2eb4136f RS |
658 | The variable @code{selection-coding-system} specifies how to encode |
659 | selections for the window system. @xref{Window System Selections}. | |
660 | ||
969fe9b5 RS |
661 | @node Lisp and Coding Systems |
662 | @subsection Coding Systems in Lisp | |
663 | ||
8241495d | 664 | Here are the Lisp facilities for working with coding systems: |
cc6d0d2c | 665 | |
cc6d0d2c RS |
666 | @defun coding-system-list &optional base-only |
667 | This function returns a list of all coding system names (symbols). If | |
668 | @var{base-only} is non-@code{nil}, the value includes only the | |
7a063989 KH |
669 | base coding systems. Otherwise, it includes alias and variant coding |
670 | systems as well. | |
cc6d0d2c RS |
671 | @end defun |
672 | ||
cc6d0d2c RS |
673 | @defun coding-system-p object |
674 | This function returns @code{t} if @var{object} is a coding system | |
675 | name. | |
676 | @end defun | |
677 | ||
cc6d0d2c RS |
678 | @defun check-coding-system coding-system |
679 | This function checks the validity of @var{coding-system}. | |
680 | If that is valid, it returns @var{coding-system}. | |
681 | Otherwise it signals an error with condition @code{coding-system-error}. | |
682 | @end defun | |
683 | ||
a9f0a989 | 684 | @defun coding-system-change-eol-conversion coding-system eol-type |
a9f0a989 | 685 | This function returns a coding system which is like @var{coding-system} |
1911e6e5 | 686 | except for its eol conversion, which is specified by @code{eol-type}. |
a9f0a989 RS |
687 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or |
688 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
689 | the end-of-line conversion from the data. | |
690 | @end defun | |
969fe9b5 | 691 | |
a9f0a989 | 692 | @defun coding-system-change-text-conversion eol-coding text-coding |
a9f0a989 RS |
693 | This function returns a coding system which uses the end-of-line |
694 | conversion of @var{eol-coding}, and the text conversion of | |
695 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
696 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
969fe9b5 RS |
697 | @end defun |
698 | ||
a9f0a989 | 699 | @defun find-coding-systems-region from to |
a9f0a989 RS |
700 | This function returns a list of coding systems that could be used to |
701 | encode a text between @var{from} and @var{to}. All coding systems in | |
702 | the list can safely encode any multibyte characters in that portion of | |
703 | the text. | |
704 | ||
705 | If the text contains no multibyte characters, the function returns the | |
706 | list @code{(undecided)}. | |
707 | @end defun | |
708 | ||
709 | @defun find-coding-systems-string string | |
a9f0a989 RS |
710 | This function returns a list of coding systems that could be used to |
711 | encode the text of @var{string}. All coding systems in the list can | |
712 | safely encode any multibyte characters in @var{string}. If the text | |
713 | contains no multibyte characters, this returns the list | |
714 | @code{(undecided)}. | |
715 | @end defun | |
716 | ||
717 | @defun find-coding-systems-for-charsets charsets | |
a9f0a989 RS |
718 | This function returns a list of coding systems that could be used to |
719 | encode all the character sets in the list @var{charsets}. | |
720 | @end defun | |
721 | ||
722 | @defun detect-coding-region start end &optional highest | |
cc6d0d2c | 723 | This function chooses a plausible coding system for decoding the text |
0ace421a | 724 | from @var{start} to @var{end}. This text should be a byte sequence |
969fe9b5 | 725 | (@pxref{Explicit Encoding}). |
cc6d0d2c | 726 | |
a9f0a989 | 727 | Normally this function returns a list of coding systems that could |
cc6d0d2c | 728 | handle decoding the text that was scanned. They are listed in order of |
a9f0a989 RS |
729 | decreasing priority. But if @var{highest} is non-@code{nil}, then the |
730 | return value is just one coding system, the one that is highest in | |
731 | priority. | |
732 | ||
8241495d | 733 | If the region contains only @sc{ascii} characters, the value |
a9f0a989 | 734 | is @code{undecided} or @code{(undecided)}. |
cc6d0d2c RS |
735 | @end defun |
736 | ||
a9f0a989 | 737 | @defun detect-coding-string string highest |
cc6d0d2c RS |
738 | This function is like @code{detect-coding-region} except that it |
739 | operates on the contents of @var{string} instead of bytes in the buffer. | |
1911e6e5 RS |
740 | @end defun |
741 | ||
742 | @xref{Process Information}, for how to examine or set the coding | |
743 | systems used for I/O to a subprocess. | |
744 | ||
745 | @node User-Chosen Coding Systems | |
746 | @subsection User-Chosen Coding Systems | |
747 | ||
1b02d12c | 748 | @cindex select safe coding system |
bf23b477 EZ |
749 | @defun select-safe-coding-system from to &optional default-coding-system accept-default-p |
750 | This function selects a coding system for encoding specified text, | |
751 | asking the user to choose if necessary. Normally the specified text | |
752 | is the text in the current buffer between @var{from} and @var{to}, | |
753 | defaulting to the whole buffer if they are @code{nil}. If @var{from} | |
0d830585 RS |
754 | is a string, the string specifies the text to encode, and @var{to} is |
755 | ignored. | |
bf23b477 EZ |
756 | |
757 | If @var{default-coding-system} is non-@code{nil}, that is the first | |
758 | coding system to try; if that can handle the text, | |
759 | @code{select-safe-coding-system} returns that coding system. It can | |
760 | also be a list of coding systems; then the function tries each of them | |
761 | one by one. After trying all of them, it next tries the user's most | |
762 | preferred coding system (@pxref{Recognize Coding, | |
763 | prefer-coding-system, the description of @code{prefer-coding-system}, | |
764 | emacs, GNU Emacs Manual}), and after that the current buffer's value | |
765 | of @code{buffer-file-coding-system} (if it is not @code{undecided}). | |
766 | ||
767 | If one of those coding systems can safely encode all the specified | |
768 | text, @code{select-safe-coding-system} chooses it and returns it. | |
769 | Otherwise, it asks the user to choose from a list of coding systems | |
770 | which can encode all the text, and returns the user's choice. | |
771 | ||
772 | The optional argument @var{accept-default-p}, if non-@code{nil}, | |
773 | should be a function to determine whether the coding system selected | |
774 | without user interaction is acceptable. If this function returns | |
775 | @code{nil}, the silently selected coding system is rejected, and the | |
776 | user is asked to select a coding system from a list of possible | |
777 | candidates. | |
778 | ||
779 | @vindex select-safe-coding-system-accept-default-p | |
780 | If the variable @code{select-safe-coding-system-accept-default-p} is | |
781 | non-@code{nil}, its value overrides the value of | |
782 | @var{accept-default-p}. | |
969fe9b5 RS |
783 | @end defun |
784 | ||
785 | Here are two functions you can use to let the user specify a coding | |
786 | system, with completion. @xref{Completion}. | |
787 | ||
a9f0a989 | 788 | @defun read-coding-system prompt &optional default |
969fe9b5 RS |
789 | This function reads a coding system using the minibuffer, prompting with |
790 | string @var{prompt}, and returns the coding system name as a symbol. If | |
791 | the user enters null input, @var{default} specifies which coding system | |
792 | to return. It should be a symbol or a string. | |
793 | @end defun | |
794 | ||
969fe9b5 RS |
795 | @defun read-non-nil-coding-system prompt |
796 | This function reads a coding system using the minibuffer, prompting with | |
a9f0a989 | 797 | string @var{prompt}, and returns the coding system name as a symbol. If |
969fe9b5 RS |
798 | the user tries to enter null input, it asks the user to try again. |
799 | @xref{Coding Systems}. | |
cc6d0d2c RS |
800 | @end defun |
801 | ||
802 | @node Default Coding Systems | |
a9f0a989 | 803 | @subsection Default Coding Systems |
cc6d0d2c | 804 | |
a9f0a989 RS |
805 | This section describes variables that specify the default coding |
806 | system for certain files or when running certain subprograms, and the | |
1911e6e5 | 807 | function that I/O operations use to access them. |
a9f0a989 RS |
808 | |
809 | The idea of these variables is that you set them once and for all to the | |
810 | defaults you want, and then do not change them again. To specify a | |
811 | particular coding system for a particular operation in a Lisp program, | |
812 | don't change these variables; instead, override them using | |
813 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
814 | (@pxref{Specifying Coding Systems}). | |
cc6d0d2c | 815 | |
bf23b477 EZ |
816 | @defvar auto-coding-regexp-alist |
817 | This variable is an alist of text patterns and corresponding coding | |
818 | systems. Each element has the form @code{(@var{regexp} | |
819 | . @var{coding-system})}; a file whose first few kilobytes match | |
820 | @var{regexp} is decoded with @var{coding-system} when its contents are | |
821 | read into a buffer. The settings in this alist take priority over | |
822 | @code{coding:} tags in the files and the contents of | |
823 | @code{file-coding-system-alist} (see below). The default value is set | |
824 | so that Emacs automatically recognizes mail files in Babyl format and | |
825 | reads them with no code conversions. | |
826 | @end defvar | |
827 | ||
cc6d0d2c RS |
828 | @defvar file-coding-system-alist |
829 | This variable is an alist that specifies the coding systems to use for | |
830 | reading and writing particular files. Each element has the form | |
831 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
832 | expression that matches certain file names. The element applies to file | |
833 | names that match @var{pattern}. | |
834 | ||
1911e6e5 | 835 | The @sc{cdr} of the element, @var{coding}, should be either a coding |
8241495d RS |
836 | system, a cons cell containing two coding systems, or a function name (a |
837 | symbol with a function definition). If @var{coding} is a coding system, | |
838 | that coding system is used for both reading the file and writing it. If | |
839 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
840 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
841 | coding system for encoding. | |
842 | ||
843 | If @var{coding} is a function name, the function must return a coding | |
cc6d0d2c RS |
844 | system or a cons cell containing two coding systems. This value is used |
845 | as described above. | |
846 | @end defvar | |
847 | ||
cc6d0d2c RS |
848 | @defvar process-coding-system-alist |
849 | This variable is an alist specifying which coding systems to use for a | |
850 | subprocess, depending on which program is running in the subprocess. It | |
851 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
852 | matched against the program name used to start the subprocess. The coding | |
853 | system or systems specified in this alist are used to initialize the | |
854 | coding systems used for I/O to the subprocess, but you can specify | |
855 | other coding systems later using @code{set-process-coding-system}. | |
856 | @end defvar | |
857 | ||
8241495d RS |
858 | @strong{Warning:} Coding systems such as @code{undecided}, which |
859 | determine the coding system from the data, do not work entirely reliably | |
1911e6e5 | 860 | with asynchronous subprocess output. This is because Emacs handles |
a9f0a989 RS |
861 | asynchronous subprocess output in batches, as it arrives. If the coding |
862 | system leaves the character code conversion unspecified, or leaves the | |
863 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
864 | conversion from one batch at a time, and this does not always work. | |
865 | ||
866 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
867 | coding system which determines both the character code conversion and | |
868 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
869 | rather than @code{undecided} or @code{latin-1}. | |
870 | ||
cc6d0d2c RS |
871 | @defvar network-coding-system-alist |
872 | This variable is an alist that specifies the coding system to use for | |
873 | network streams. It works much like @code{file-coding-system-alist}, | |
969fe9b5 | 874 | with the difference that the @var{pattern} in an element may be either a |
cc6d0d2c RS |
875 | port number or a regular expression. If it is a regular expression, it |
876 | is matched against the network service name used to open the network | |
877 | stream. | |
878 | @end defvar | |
879 | ||
cc6d0d2c RS |
880 | @defvar default-process-coding-system |
881 | This variable specifies the coding systems to use for subprocess (and | |
882 | network stream) input and output, when nothing else specifies what to | |
883 | do. | |
884 | ||
a9f0a989 RS |
885 | The value should be a cons cell of the form @code{(@var{input-coding} |
886 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
887 | the subprocess, and @var{output-coding} applies to output to it. | |
cc6d0d2c RS |
888 | @end defvar |
889 | ||
a9f0a989 | 890 | @defun find-operation-coding-system operation &rest arguments |
a9f0a989 RS |
891 | This function returns the coding system to use (by default) for |
892 | performing @var{operation} with @var{arguments}. The value has this | |
893 | form: | |
894 | ||
895 | @example | |
896 | (@var{decoding-system} @var{encoding-system}) | |
897 | @end example | |
898 | ||
899 | The first element, @var{decoding-system}, is the coding system to use | |
900 | for decoding (in case @var{operation} does decoding), and | |
901 | @var{encoding-system} is the coding system for encoding (in case | |
902 | @var{operation} does encoding). | |
903 | ||
8241495d | 904 | The argument @var{operation} should be a symbol, one of |
a9f0a989 RS |
905 | @code{insert-file-contents}, @code{write-region}, @code{call-process}, |
906 | @code{call-process-region}, @code{start-process}, or | |
8241495d RS |
907 | @code{open-network-stream}. These are the names of the Emacs I/O primitives |
908 | that can do coding system conversion. | |
a9f0a989 RS |
909 | |
910 | The remaining arguments should be the same arguments that might be given | |
8241495d | 911 | to that I/O primitive. Depending on the primitive, one of those |
a9f0a989 RS |
912 | arguments is selected as the @dfn{target}. For example, if |
913 | @var{operation} does file I/O, whichever argument specifies the file | |
914 | name is the target. For subprocess primitives, the process name is the | |
915 | target. For @code{open-network-stream}, the target is the service name | |
916 | or port number. | |
917 | ||
918 | This function looks up the target in @code{file-coding-system-alist}, | |
919 | @code{process-coding-system-alist}, or | |
920 | @code{network-coding-system-alist}, depending on @var{operation}. | |
921 | @xref{Default Coding Systems}. | |
922 | @end defun | |
923 | ||
cc6d0d2c | 924 | @node Specifying Coding Systems |
a9f0a989 | 925 | @subsection Specifying a Coding System for One Operation |
cc6d0d2c RS |
926 | |
927 | You can specify the coding system for a specific operation by binding | |
928 | the variables @code{coding-system-for-read} and/or | |
929 | @code{coding-system-for-write}. | |
930 | ||
cc6d0d2c RS |
931 | @defvar coding-system-for-read |
932 | If this variable is non-@code{nil}, it specifies the coding system to | |
933 | use for reading a file, or for input from a synchronous subprocess. | |
934 | ||
935 | It also applies to any asynchronous subprocess or network stream, but in | |
936 | a different way: the value of @code{coding-system-for-read} when you | |
937 | start the subprocess or open the network stream specifies the input | |
938 | decoding method for that subprocess or network stream. It remains in | |
939 | use for that subprocess or network stream unless and until overridden. | |
940 | ||
941 | The right way to use this variable is to bind it with @code{let} for a | |
942 | specific I/O operation. Its global value is normally @code{nil}, and | |
943 | you should not globally set it to any other value. Here is an example | |
944 | of the right way to use the variable: | |
945 | ||
946 | @example | |
947 | ;; @r{Read the file with no character code conversion.} | |
969fe9b5 | 948 | ;; @r{Assume @sc{crlf} represents end-of-line.} |
cc6d0d2c RS |
949 | (let ((coding-system-for-write 'emacs-mule-dos)) |
950 | (insert-file-contents filename)) | |
951 | @end example | |
952 | ||
953 | When its value is non-@code{nil}, @code{coding-system-for-read} takes | |
a9f0a989 | 954 | precedence over all other methods of specifying a coding system to use for |
cc6d0d2c RS |
955 | input, including @code{file-coding-system-alist}, |
956 | @code{process-coding-system-alist} and | |
957 | @code{network-coding-system-alist}. | |
958 | @end defvar | |
959 | ||
cc6d0d2c RS |
960 | @defvar coding-system-for-write |
961 | This works much like @code{coding-system-for-read}, except that it | |
962 | applies to output rather than input. It affects writing to files, | |
b6954afd | 963 | as well as sending output to subprocesses and net connections. |
cc6d0d2c RS |
964 | |
965 | When a single operation does both input and output, as do | |
966 | @code{call-process-region} and @code{start-process}, both | |
967 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
968 | affect it. | |
969 | @end defvar | |
970 | ||
cc6d0d2c RS |
971 | @defvar inhibit-eol-conversion |
972 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
973 | no matter which coding system is specified. This applies to all the | |
974 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
975 | decoding functions (@pxref{Explicit Encoding}). | |
976 | @end defvar | |
977 | ||
cc6d0d2c | 978 | @node Explicit Encoding |
a9f0a989 | 979 | @subsection Explicit Encoding and Decoding |
cc6d0d2c RS |
980 | @cindex encoding text |
981 | @cindex decoding text | |
982 | ||
983 | All the operations that transfer text in and out of Emacs have the | |
984 | ability to use a coding system to encode or decode the text. | |
985 | You can also explicitly encode and decode text using the functions | |
986 | in this section. | |
987 | ||
cc6d0d2c | 988 | The result of encoding, and the input to decoding, are not ordinary |
0ace421a GM |
989 | text. They logically consist of a series of byte values; that is, a |
990 | series of characters whose codes are in the range 0 through 255. In a | |
991 | multibyte buffer or string, character codes 128 through 159 are | |
992 | represented by multibyte sequences, but this is invisible to Lisp | |
993 | programs. | |
994 | ||
995 | The usual way to read a file into a buffer as a sequence of bytes, so | |
996 | you can decode the contents explicitly, is with | |
997 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
998 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
999 | visiting a file with @code{find-file-noselect}. These methods result in | |
1000 | a unibyte buffer. | |
1001 | ||
1002 | The usual way to use the byte sequence that results from explicitly | |
1003 | encoding text is to copy it to a file or process---for example, to write | |
1004 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
1005 | encoding by binding @code{coding-system-for-write} to | |
1006 | @code{no-conversion}. | |
b6954afd RS |
1007 | |
1008 | Here are the functions to perform explicit encoding or decoding. The | |
0ace421a GM |
1009 | decoding functions produce sequences of bytes; the encoding functions |
1010 | are meant to operate on sequences of bytes. All of these functions | |
1011 | discard text properties. | |
1911e6e5 | 1012 | |
cc6d0d2c RS |
1013 | @defun encode-coding-region start end coding-system |
1014 | This function encodes the text from @var{start} to @var{end} according | |
969fe9b5 | 1015 | to coding system @var{coding-system}. The encoded text replaces the |
0ace421a GM |
1016 | original text in the buffer. The result of encoding is logically a |
1017 | sequence of bytes, but the buffer remains multibyte if it was multibyte | |
1018 | before. | |
cc6d0d2c RS |
1019 | @end defun |
1020 | ||
cc6d0d2c RS |
1021 | @defun encode-coding-string string coding-system |
1022 | This function encodes the text in @var{string} according to coding | |
1023 | system @var{coding-system}. It returns a new string containing the | |
0ace421a | 1024 | encoded text. The result of encoding is a unibyte string. |
cc6d0d2c RS |
1025 | @end defun |
1026 | ||
cc6d0d2c RS |
1027 | @defun decode-coding-region start end coding-system |
1028 | This function decodes the text from @var{start} to @var{end} according | |
1029 | to coding system @var{coding-system}. The decoded text replaces the | |
1030 | original text in the buffer. To make explicit decoding useful, the text | |
0ace421a GM |
1031 | before decoding ought to be a sequence of byte values, but both |
1032 | multibyte and unibyte buffers are acceptable. | |
cc6d0d2c RS |
1033 | @end defun |
1034 | ||
cc6d0d2c RS |
1035 | @defun decode-coding-string string coding-system |
1036 | This function decodes the text in @var{string} according to coding | |
1037 | system @var{coding-system}. It returns a new string containing the | |
1038 | decoded text. To make explicit decoding useful, the contents of | |
0ace421a GM |
1039 | @var{string} ought to be a sequence of byte values, but a multibyte |
1040 | string is acceptable. | |
cc6d0d2c | 1041 | @end defun |
969fe9b5 | 1042 | |
a9f0a989 RS |
1043 | @node Terminal I/O Encoding |
1044 | @subsection Terminal I/O Encoding | |
1045 | ||
1046 | Emacs can decode keyboard input using a coding system, and encode | |
2eb4136f RS |
1047 | terminal output. This is useful for terminals that transmit or display |
1048 | text using a particular encoding such as Latin-1. Emacs does not set | |
1049 | @code{last-coding-system-used} for encoding or decoding for the | |
1050 | terminal. | |
a9f0a989 RS |
1051 | |
1052 | @defun keyboard-coding-system | |
a9f0a989 RS |
1053 | This function returns the coding system that is in use for decoding |
1054 | keyboard input---or @code{nil} if no coding system is to be used. | |
1055 | @end defun | |
1056 | ||
1057 | @defun set-keyboard-coding-system coding-system | |
a9f0a989 RS |
1058 | This function specifies @var{coding-system} as the coding system to |
1059 | use for decoding keyboard input. If @var{coding-system} is @code{nil}, | |
1060 | that means do not decode keyboard input. | |
1061 | @end defun | |
1062 | ||
1063 | @defun terminal-coding-system | |
a9f0a989 RS |
1064 | This function returns the coding system that is in use for encoding |
1065 | terminal output---or @code{nil} for no encoding. | |
1066 | @end defun | |
1067 | ||
1068 | @defun set-terminal-coding-system coding-system | |
a9f0a989 RS |
1069 | This function specifies @var{coding-system} as the coding system to use |
1070 | for encoding terminal output. If @var{coding-system} is @code{nil}, | |
1071 | that means do not encode terminal output. | |
1072 | @end defun | |
1073 | ||
969fe9b5 | 1074 | @node MS-DOS File Types |
a9f0a989 | 1075 | @subsection MS-DOS File Types |
969fe9b5 RS |
1076 | @cindex DOS file types |
1077 | @cindex MS-DOS file types | |
1078 | @cindex Windows file types | |
1079 | @cindex file types on MS-DOS and Windows | |
1080 | @cindex text files and binary files | |
1081 | @cindex binary files and text files | |
1082 | ||
8241495d RS |
1083 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate |
1084 | end-of-line conversion for a file by looking at the file's name. This | |
0ace421a | 1085 | feature classifies files as @dfn{text files} and @dfn{binary files}. By |
8241495d RS |
1086 | ``binary file'' we mean a file of literal byte values that are not |
1087 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1088 | and no character code conversion for them. On the other hand, the bytes | |
1089 | in a text file are intended to represent characters; when you create a | |
1090 | new file whose name implies that it is a text file, Emacs uses DOS | |
1091 | end-of-line conversion. | |
969fe9b5 RS |
1092 | |
1093 | @defvar buffer-file-type | |
1094 | This variable, automatically buffer-local in each buffer, records the | |
a9f0a989 RS |
1095 | file type of the buffer's visited file. When a buffer does not specify |
1096 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1097 | used to determine which coding system to use when writing the contents | |
1098 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1099 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1100 | Otherwise, @code{undecided-dos} is used. | |
1101 | ||
1102 | Normally this variable is set by visiting a file; it is set to | |
1103 | @code{nil} if the file was visited without any actual conversion. | |
969fe9b5 RS |
1104 | @end defvar |
1105 | ||
1106 | @defopt file-name-buffer-file-type-alist | |
1107 | This variable holds an alist for recognizing text and binary files. | |
1108 | Each element has the form (@var{regexp} . @var{type}), where | |
1109 | @var{regexp} is matched against the file name, and @var{type} may be | |
1110 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1111 | compute which. If it is a function, then it is called with a single | |
1112 | argument (the file name) and should return @code{t} or @code{nil}. | |
1113 | ||
8241495d | 1114 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide |
969fe9b5 RS |
1115 | which coding system to use when reading a file. For a text file, |
1116 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1117 | is used. | |
1118 | ||
1119 | If no element in this alist matches a given file name, then | |
1120 | @code{default-buffer-file-type} says how to treat the file. | |
1121 | @end defopt | |
1122 | ||
1123 | @defopt default-buffer-file-type | |
1124 | This variable says how to handle files for which | |
1125 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1126 | ||
1127 | If this variable is non-@code{nil}, then these files are treated as | |
a9f0a989 RS |
1128 | binary: the coding system @code{no-conversion} is used. Otherwise, |
1129 | nothing special is done for them---the coding system is deduced solely | |
1130 | from the file contents, in the usual Emacs fashion. | |
969fe9b5 RS |
1131 | @end defopt |
1132 | ||
a9f0a989 RS |
1133 | @node Input Methods |
1134 | @section Input Methods | |
1135 | @cindex input methods | |
1136 | ||
8241495d | 1137 | @dfn{Input methods} provide convenient ways of entering non-@sc{ascii} |
a9f0a989 | 1138 | characters from the keyboard. Unlike coding systems, which translate |
8241495d | 1139 | non-@sc{ascii} characters to and from encodings meant to be read by |
a9f0a989 RS |
1140 | programs, input methods provide human-friendly commands. (@xref{Input |
1141 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1142 | use input methods to enter text.) How to define input methods is not | |
1143 | yet documented in this manual, but here we describe how to use them. | |
1144 | ||
1145 | Each input method has a name, which is currently a string; | |
1146 | in the future, symbols may also be usable as input method names. | |
1147 | ||
a9f0a989 RS |
1148 | @defvar current-input-method |
1149 | This variable holds the name of the input method now active in the | |
1150 | current buffer. (It automatically becomes local in each buffer when set | |
1151 | in any fashion.) It is @code{nil} if no input method is active in the | |
1152 | buffer now. | |
969fe9b5 RS |
1153 | @end defvar |
1154 | ||
a9f0a989 RS |
1155 | @defvar default-input-method |
1156 | This variable holds the default input method for commands that choose an | |
1157 | input method. Unlike @code{current-input-method}, this variable is | |
1158 | normally global. | |
969fe9b5 | 1159 | @end defvar |
a9f0a989 | 1160 | |
a9f0a989 RS |
1161 | @defun set-input-method input-method |
1162 | This function activates input method @var{input-method} for the current | |
1163 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1164 | If @var{input-method} is @code{nil}, this function deactivates any input | |
1165 | method for the current buffer. | |
1166 | @end defun | |
1167 | ||
a9f0a989 RS |
1168 | @defun read-input-method-name prompt &optional default inhibit-null |
1169 | This function reads an input method name with the minibuffer, prompting | |
1170 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1171 | by default, if the user enters empty input. However, if | |
1172 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1173 | ||
1174 | The returned value is a string. | |
1175 | @end defun | |
1176 | ||
a9f0a989 RS |
1177 | @defvar input-method-alist |
1178 | This variable defines all the supported input methods. | |
1179 | Each element defines one input method, and should have the form: | |
1180 | ||
1181 | @example | |
1911e6e5 RS |
1182 | (@var{input-method} @var{language-env} @var{activate-func} |
1183 | @var{title} @var{description} @var{args}...) | |
a9f0a989 RS |
1184 | @end example |
1185 | ||
1911e6e5 RS |
1186 | Here @var{input-method} is the input method name, a string; |
1187 | @var{language-env} is another string, the name of the language | |
1188 | environment this input method is recommended for. (That serves only for | |
1189 | documentation purposes.) | |
a9f0a989 | 1190 | |
a9f0a989 RS |
1191 | @var{activate-func} is a function to call to activate this method. The |
1192 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1193 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1194 | the @var{args}. | |
0ace421a GM |
1195 | |
1196 | @var{title} is a string to display in the mode line while this method is | |
1197 | active. @var{description} is a string describing this method and what | |
1198 | it is good for. | |
1911e6e5 | 1199 | @end defvar |
a9f0a989 | 1200 | |
2eb4136f RS |
1201 | The fundamental interface to input methods is through the |
1202 | variable @code{input-method-function}. @xref{Reading One Event}. | |
2468d0c0 DL |
1203 | |
1204 | @node Locales | |
1205 | @section Locales | |
1206 | @cindex locale | |
1207 | ||
1208 | POSIX defines a concept of ``locales'' which control which language | |
1209 | to use in language-related features. These Emacs variables control | |
1210 | how Emacs interacts with these features. | |
1211 | ||
1212 | @defvar locale-coding-system | |
1213 | @tindex locale-coding-system | |
a007679c | 1214 | @cindex keyboard input decoding on X |
2468d0c0 | 1215 | This variable specifies the coding system to use for decoding system |
a007679c EZ |
1216 | error messages and---on X Window system only---keyboard input, for |
1217 | encoding the format argument to @code{format-time-string}, and for | |
1218 | decoding the return value of @code{format-time-string}. | |
2468d0c0 DL |
1219 | @end defvar |
1220 | ||
1221 | @defvar system-messages-locale | |
1222 | @tindex system-messages-locale | |
1223 | This variable specifies the locale to use for generating system error | |
1224 | messages. Changing the locale can cause messages to come out in a | |
9c17f494 | 1225 | different language or in a different orthography. If the variable is |
2468d0c0 DL |
1226 | @code{nil}, the locale is specified by environment variables in the |
1227 | usual POSIX fashion. | |
1228 | @end defvar | |
1229 | ||
1230 | @defvar system-time-locale | |
1231 | @tindex system-time-locale | |
1232 | This variable specifies the locale to use for formatting time values. | |
1233 | Changing the locale can cause messages to appear according to the | |
1234 | conventions of a different language. If the variable is @code{nil}, the | |
1235 | locale is specified by environment variables in the usual POSIX fashion. | |
1236 | @end defvar | |
0ace421a | 1237 |