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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c | 3 | @c Copyright (C) 1998, 1999, 2002, 2003, 2004, |
ceb4c4d3 | 4 | @c 2005, 2006 Free Software Foundation, Inc. |
cc6d0d2c RS |
5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/characters | |
7 | @node Non-ASCII Characters, Searching and Matching, Text, Top | |
ad800164 | 8 | @chapter Non-@acronym{ASCII} Characters |
cc6d0d2c | 9 | @cindex multibyte characters |
ad800164 | 10 | @cindex non-@acronym{ASCII} characters |
cc6d0d2c | 11 | |
ad800164 | 12 | This chapter covers the special issues relating to non-@acronym{ASCII} |
cc6d0d2c RS |
13 | characters and how they are stored in strings and buffers. |
14 | ||
15 | @menu | |
5557b83b RS |
16 | * Text Representations:: Unibyte and multibyte representations |
17 | * Converting Representations:: Converting unibyte to multibyte and vice versa. | |
18 | * Selecting a Representation:: Treating a byte sequence as unibyte or multi. | |
19 | * Character Codes:: How unibyte and multibyte relate to | |
20 | codes of individual characters. | |
a3d3f60d | 21 | * Character Sets:: The space of possible character codes |
5557b83b RS |
22 | is divided into various character sets. |
23 | * Chars and Bytes:: More information about multibyte encodings. | |
24 | * Splitting Characters:: Converting a character to its byte sequence. | |
25 | * Scanning Charsets:: Which character sets are used in a buffer? | |
26 | * Translation of Characters:: Translation tables are used for conversion. | |
27 | * Coding Systems:: Coding systems are conversions for saving files. | |
28 | * Input Methods:: Input methods allow users to enter various | |
8a9e355c | 29 | non-ASCII characters without special keyboards. |
5557b83b | 30 | * Locales:: Interacting with the POSIX locale. |
cc6d0d2c RS |
31 | @end menu |
32 | ||
33 | @node Text Representations | |
34 | @section Text Representations | |
35 | @cindex text representations | |
36 | ||
37 | Emacs has two @dfn{text representations}---two ways to represent text | |
38 | in a string or buffer. These are called @dfn{unibyte} and | |
39 | @dfn{multibyte}. Each string, and each buffer, uses one of these two | |
40 | representations. For most purposes, you can ignore the issue of | |
41 | representations, because Emacs converts text between them as | |
42 | appropriate. Occasionally in Lisp programming you will need to pay | |
43 | attention to the difference. | |
44 | ||
45 | @cindex unibyte text | |
46 | In unibyte representation, each character occupies one byte and | |
47 | therefore the possible character codes range from 0 to 255. Codes 0 | |
ad800164 EZ |
48 | through 127 are @acronym{ASCII} characters; the codes from 128 through 255 |
49 | are used for one non-@acronym{ASCII} character set (you can choose which | |
969fe9b5 | 50 | character set by setting the variable @code{nonascii-insert-offset}). |
cc6d0d2c RS |
51 | |
52 | @cindex leading code | |
53 | @cindex multibyte text | |
1911e6e5 | 54 | @cindex trailing codes |
cc6d0d2c RS |
55 | In multibyte representation, a character may occupy more than one |
56 | byte, and as a result, the full range of Emacs character codes can be | |
57 | stored. The first byte of a multibyte character is always in the range | |
58 | 128 through 159 (octal 0200 through 0237). These values are called | |
a9f0a989 RS |
59 | @dfn{leading codes}. The second and subsequent bytes of a multibyte |
60 | character are always in the range 160 through 255 (octal 0240 through | |
1911e6e5 | 61 | 0377); these values are @dfn{trailing codes}. |
cc6d0d2c | 62 | |
0ace421a | 63 | Some sequences of bytes are not valid in multibyte text: for example, |
1e4d32f8 GM |
64 | a single isolated byte in the range 128 through 159 is not allowed. But |
65 | character codes 128 through 159 can appear in multibyte text, | |
66 | represented as two-byte sequences. All the character codes 128 through | |
67 | 255 are possible (though slightly abnormal) in multibyte text; they | |
0ace421a GM |
68 | appear in multibyte buffers and strings when you do explicit encoding |
69 | and decoding (@pxref{Explicit Encoding}). | |
b6954afd | 70 | |
cc6d0d2c RS |
71 | In a buffer, the buffer-local value of the variable |
72 | @code{enable-multibyte-characters} specifies the representation used. | |
08f0f5e9 KH |
73 | The representation for a string is determined and recorded in the string |
74 | when the string is constructed. | |
cc6d0d2c | 75 | |
cc6d0d2c RS |
76 | @defvar enable-multibyte-characters |
77 | This variable specifies the current buffer's text representation. | |
78 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
79 | it contains unibyte text. | |
80 | ||
969fe9b5 RS |
81 | You cannot set this variable directly; instead, use the function |
82 | @code{set-buffer-multibyte} to change a buffer's representation. | |
cc6d0d2c RS |
83 | @end defvar |
84 | ||
cc6d0d2c | 85 | @defvar default-enable-multibyte-characters |
a9f0a989 | 86 | This variable's value is entirely equivalent to @code{(default-value |
cc6d0d2c | 87 | 'enable-multibyte-characters)}, and setting this variable changes that |
a9f0a989 RS |
88 | default value. Setting the local binding of |
89 | @code{enable-multibyte-characters} in a specific buffer is not allowed, | |
90 | but changing the default value is supported, and it is a reasonable | |
91 | thing to do, because it has no effect on existing buffers. | |
cc6d0d2c RS |
92 | |
93 | The @samp{--unibyte} command line option does its job by setting the | |
94 | default value to @code{nil} early in startup. | |
95 | @end defvar | |
96 | ||
b6954afd | 97 | @defun position-bytes position |
5ac343ac RS |
98 | Return the byte-position corresponding to buffer position |
99 | @var{position} in the current buffer. This is 1 at the start of the | |
100 | buffer, and counts upward in bytes. If @var{position} is out of | |
101 | range, the value is @code{nil}. | |
b6954afd RS |
102 | @end defun |
103 | ||
104 | @defun byte-to-position byte-position | |
b6954afd | 105 | Return the buffer position corresponding to byte-position |
35864124 LT |
106 | @var{byte-position} in the current buffer. If @var{byte-position} is |
107 | out of range, the value is @code{nil}. | |
b6954afd RS |
108 | @end defun |
109 | ||
cc6d0d2c | 110 | @defun multibyte-string-p string |
b6954afd | 111 | Return @code{t} if @var{string} is a multibyte string. |
cc6d0d2c RS |
112 | @end defun |
113 | ||
114 | @node Converting Representations | |
115 | @section Converting Text Representations | |
116 | ||
117 | Emacs can convert unibyte text to multibyte; it can also convert | |
118 | multibyte text to unibyte, though this conversion loses information. In | |
119 | general these conversions happen when inserting text into a buffer, or | |
120 | when putting text from several strings together in one string. You can | |
121 | also explicitly convert a string's contents to either representation. | |
122 | ||
123 | Emacs chooses the representation for a string based on the text that | |
124 | it is constructed from. The general rule is to convert unibyte text to | |
125 | multibyte text when combining it with other multibyte text, because the | |
126 | multibyte representation is more general and can hold whatever | |
127 | characters the unibyte text has. | |
128 | ||
129 | When inserting text into a buffer, Emacs converts the text to the | |
130 | buffer's representation, as specified by | |
131 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
132 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
133 | to unibyte, even though this conversion cannot in general preserve all | |
134 | the characters that might be in the multibyte text. The other natural | |
135 | alternative, to convert the buffer contents to multibyte, is not | |
136 | acceptable because the buffer's representation is a choice made by the | |
969fe9b5 | 137 | user that cannot be overridden automatically. |
cc6d0d2c | 138 | |
ad800164 | 139 | Converting unibyte text to multibyte text leaves @acronym{ASCII} characters |
1e4d32f8 | 140 | unchanged, and likewise character codes 128 through 159. It converts |
ad800164 | 141 | the non-@acronym{ASCII} codes 160 through 255 by adding the value |
1e4d32f8 GM |
142 | @code{nonascii-insert-offset} to each character code. By setting this |
143 | variable, you specify which character set the unibyte characters | |
144 | correspond to (@pxref{Character Sets}). For example, if | |
145 | @code{nonascii-insert-offset} is 2048, which is @code{(- (make-char | |
ad800164 | 146 | 'latin-iso8859-1) 128)}, then the unibyte non-@acronym{ASCII} characters |
1e4d32f8 GM |
147 | correspond to Latin 1. If it is 2688, which is @code{(- (make-char |
148 | 'greek-iso8859-7) 128)}, then they correspond to Greek letters. | |
cc6d0d2c | 149 | |
8241495d RS |
150 | Converting multibyte text to unibyte is simpler: it discards all but |
151 | the low 8 bits of each character code. If @code{nonascii-insert-offset} | |
152 | has a reasonable value, corresponding to the beginning of some character | |
153 | set, this conversion is the inverse of the other: converting unibyte | |
154 | text to multibyte and back to unibyte reproduces the original unibyte | |
155 | text. | |
cc6d0d2c | 156 | |
cc6d0d2c | 157 | @defvar nonascii-insert-offset |
ad800164 | 158 | This variable specifies the amount to add to a non-@acronym{ASCII} character |
cc6d0d2c | 159 | when converting unibyte text to multibyte. It also applies when |
a9f0a989 | 160 | @code{self-insert-command} inserts a character in the unibyte |
ad800164 | 161 | non-@acronym{ASCII} range, 128 through 255. However, the functions |
7a063989 | 162 | @code{insert} and @code{insert-char} do not perform this conversion. |
cc6d0d2c RS |
163 | |
164 | The right value to use to select character set @var{cs} is @code{(- | |
a9f0a989 | 165 | (make-char @var{cs}) 128)}. If the value of |
cc6d0d2c RS |
166 | @code{nonascii-insert-offset} is zero, then conversion actually uses the |
167 | value for the Latin 1 character set, rather than zero. | |
168 | @end defvar | |
169 | ||
a9f0a989 | 170 | @defvar nonascii-translation-table |
cc6d0d2c RS |
171 | This variable provides a more general alternative to |
172 | @code{nonascii-insert-offset}. You can use it to specify independently | |
173 | how to translate each code in the range of 128 through 255 into a | |
7a063989 | 174 | multibyte character. The value should be a char-table, or @code{nil}. |
969fe9b5 | 175 | If this is non-@code{nil}, it overrides @code{nonascii-insert-offset}. |
cc6d0d2c RS |
176 | @end defvar |
177 | ||
35864124 LT |
178 | The next three functions either return the argument @var{string}, or a |
179 | newly created string with no text properties. | |
180 | ||
cc6d0d2c RS |
181 | @defun string-make-unibyte string |
182 | This function converts the text of @var{string} to unibyte | |
1911e6e5 | 183 | representation, if it isn't already, and returns the result. If |
38eee91c EZ |
184 | @var{string} is a unibyte string, it is returned unchanged. Multibyte |
185 | character codes are converted to unibyte according to | |
186 | @code{nonascii-translation-table} or, if that is @code{nil}, using | |
187 | @code{nonascii-insert-offset}. If the lookup in the translation table | |
188 | fails, this function takes just the low 8 bits of each character. | |
cc6d0d2c RS |
189 | @end defun |
190 | ||
cc6d0d2c RS |
191 | @defun string-make-multibyte string |
192 | This function converts the text of @var{string} to multibyte | |
1911e6e5 | 193 | representation, if it isn't already, and returns the result. If |
35864124 LT |
194 | @var{string} is a multibyte string or consists entirely of |
195 | @acronym{ASCII} characters, it is returned unchanged. In particular, | |
196 | if @var{string} is unibyte and entirely @acronym{ASCII}, the returned | |
197 | string is unibyte. (When the characters are all @acronym{ASCII}, | |
198 | Emacs primitives will treat the string the same way whether it is | |
199 | unibyte or multibyte.) If @var{string} is unibyte and contains | |
200 | non-@acronym{ASCII} characters, the function | |
201 | @code{unibyte-char-to-multibyte} is used to convert each unibyte | |
202 | character to a multibyte character. | |
cc6d0d2c RS |
203 | @end defun |
204 | ||
131bf943 RS |
205 | @defun string-to-multibyte string |
206 | This function returns a multibyte string containing the same sequence | |
35864124 LT |
207 | of character codes as @var{string}. Unlike |
208 | @code{string-make-multibyte}, this function unconditionally returns a | |
209 | multibyte string. If @var{string} is a multibyte string, it is | |
210 | returned unchanged. | |
131bf943 RS |
211 | @end defun |
212 | ||
1ee89891 RS |
213 | @defun multibyte-char-to-unibyte char |
214 | This convert the multibyte character @var{char} to a unibyte | |
215 | character, based on @code{nonascii-translation-table} and | |
216 | @code{nonascii-insert-offset}. | |
217 | @end defun | |
218 | ||
219 | @defun unibyte-char-to-multibyte char | |
220 | This convert the unibyte character @var{char} to a multibyte | |
221 | character, based on @code{nonascii-translation-table} and | |
222 | @code{nonascii-insert-offset}. | |
223 | @end defun | |
224 | ||
cc6d0d2c RS |
225 | @node Selecting a Representation |
226 | @section Selecting a Representation | |
227 | ||
228 | Sometimes it is useful to examine an existing buffer or string as | |
229 | multibyte when it was unibyte, or vice versa. | |
230 | ||
cc6d0d2c RS |
231 | @defun set-buffer-multibyte multibyte |
232 | Set the representation type of the current buffer. If @var{multibyte} | |
233 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
234 | is @code{nil}, the buffer becomes unibyte. | |
235 | ||
236 | This function leaves the buffer contents unchanged when viewed as a | |
237 | sequence of bytes. As a consequence, it can change the contents viewed | |
238 | as characters; a sequence of two bytes which is treated as one character | |
239 | in multibyte representation will count as two characters in unibyte | |
7a063989 KH |
240 | representation. Character codes 128 through 159 are an exception. They |
241 | are represented by one byte in a unibyte buffer, but when the buffer is | |
242 | set to multibyte, they are converted to two-byte sequences, and vice | |
243 | versa. | |
cc6d0d2c RS |
244 | |
245 | This function sets @code{enable-multibyte-characters} to record which | |
246 | representation is in use. It also adjusts various data in the buffer | |
969fe9b5 RS |
247 | (including overlays, text properties and markers) so that they cover the |
248 | same text as they did before. | |
b6954afd RS |
249 | |
250 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
251 | because indirect buffers always inherit the representation of the | |
252 | base buffer. | |
cc6d0d2c RS |
253 | @end defun |
254 | ||
cc6d0d2c RS |
255 | @defun string-as-unibyte string |
256 | This function returns a string with the same bytes as @var{string} but | |
257 | treating each byte as a character. This means that the value may have | |
258 | more characters than @var{string} has. | |
259 | ||
b6954afd | 260 | If @var{string} is already a unibyte string, then the value is |
7f84d9ae DL |
261 | @var{string} itself. Otherwise it is a newly created string, with no |
262 | text properties. If @var{string} is multibyte, any characters it | |
686ffe28 | 263 | contains of charset @code{eight-bit-control} or @code{eight-bit-graphic} |
7f84d9ae | 264 | are converted to the corresponding single byte. |
cc6d0d2c RS |
265 | @end defun |
266 | ||
cc6d0d2c RS |
267 | @defun string-as-multibyte string |
268 | This function returns a string with the same bytes as @var{string} but | |
269 | treating each multibyte sequence as one character. This means that the | |
270 | value may have fewer characters than @var{string} has. | |
271 | ||
b6954afd | 272 | If @var{string} is already a multibyte string, then the value is |
7f84d9ae DL |
273 | @var{string} itself. Otherwise it is a newly created string, with no |
274 | text properties. If @var{string} is unibyte and contains any individual | |
275 | 8-bit bytes (i.e.@: not part of a multibyte form), they are converted to | |
686ffe28 RS |
276 | the corresponding multibyte character of charset @code{eight-bit-control} |
277 | or @code{eight-bit-graphic}. | |
cc6d0d2c RS |
278 | @end defun |
279 | ||
280 | @node Character Codes | |
281 | @section Character Codes | |
282 | @cindex character codes | |
283 | ||
284 | The unibyte and multibyte text representations use different character | |
285 | codes. The valid character codes for unibyte representation range from | |
286 | 0 to 255---the values that can fit in one byte. The valid character | |
287 | codes for multibyte representation range from 0 to 524287, but not all | |
0ace421a | 288 | values in that range are valid. The values 128 through 255 are not |
1e4d32f8 | 289 | entirely proper in multibyte text, but they can occur if you do explicit |
0ace421a | 290 | encoding and decoding (@pxref{Explicit Encoding}). Some other character |
ad800164 | 291 | codes cannot occur at all in multibyte text. Only the @acronym{ASCII} codes |
1e4d32f8 | 292 | 0 through 127 are completely legitimate in both representations. |
cc6d0d2c | 293 | |
7a063989 | 294 | @defun char-valid-p charcode &optional genericp |
0a58afcd RS |
295 | This returns @code{t} if @var{charcode} is valid (either for unibyte |
296 | text or for multibyte text). | |
cc6d0d2c RS |
297 | |
298 | @example | |
299 | (char-valid-p 65) | |
300 | @result{} t | |
301 | (char-valid-p 256) | |
302 | @result{} nil | |
303 | (char-valid-p 2248) | |
304 | @result{} t | |
305 | @end example | |
7a063989 | 306 | |
6fe50867 | 307 | If the optional argument @var{genericp} is non-@code{nil}, this |
35864124 LT |
308 | function also returns @code{t} if @var{charcode} is a generic |
309 | character (@pxref{Splitting Characters}). | |
cc6d0d2c RS |
310 | @end defun |
311 | ||
312 | @node Character Sets | |
313 | @section Character Sets | |
314 | @cindex character sets | |
315 | ||
316 | Emacs classifies characters into various @dfn{character sets}, each of | |
317 | which has a name which is a symbol. Each character belongs to one and | |
318 | only one character set. | |
319 | ||
320 | In general, there is one character set for each distinct script. For | |
321 | example, @code{latin-iso8859-1} is one character set, | |
322 | @code{greek-iso8859-7} is another, and @code{ascii} is another. An | |
969fe9b5 RS |
323 | Emacs character set can hold at most 9025 characters; therefore, in some |
324 | cases, characters that would logically be grouped together are split | |
a9f0a989 RS |
325 | into several character sets. For example, one set of Chinese |
326 | characters, generally known as Big 5, is divided into two Emacs | |
327 | character sets, @code{chinese-big5-1} and @code{chinese-big5-2}. | |
cc6d0d2c | 328 | |
ad800164 EZ |
329 | @acronym{ASCII} characters are in character set @code{ascii}. The |
330 | non-@acronym{ASCII} characters 128 through 159 are in character set | |
4240c779 GM |
331 | @code{eight-bit-control}, and codes 160 through 255 are in character set |
332 | @code{eight-bit-graphic}. | |
333 | ||
cc6d0d2c | 334 | @defun charsetp object |
8241495d | 335 | Returns @code{t} if @var{object} is a symbol that names a character set, |
cc6d0d2c RS |
336 | @code{nil} otherwise. |
337 | @end defun | |
338 | ||
35864124 LT |
339 | @defvar charset-list |
340 | The value is a list of all defined character set names. | |
341 | @end defvar | |
342 | ||
cc6d0d2c | 343 | @defun charset-list |
35864124 LT |
344 | This function returns the value of @code{charset-list}. It is only |
345 | provided for backward compatibility. | |
cc6d0d2c RS |
346 | @end defun |
347 | ||
cc6d0d2c | 348 | @defun char-charset character |
b6954afd | 349 | This function returns the name of the character set that @var{character} |
35864124 LT |
350 | belongs to, or the symbol @code{unknown} if @var{character} is not a |
351 | valid character. | |
cc6d0d2c RS |
352 | @end defun |
353 | ||
8241495d | 354 | @defun charset-plist charset |
8241495d RS |
355 | This function returns the charset property list of the character set |
356 | @var{charset}. Although @var{charset} is a symbol, this is not the same | |
357 | as the property list of that symbol. Charset properties are used for | |
0f4da9ce | 358 | special purposes within Emacs. |
8241495d RS |
359 | @end defun |
360 | ||
5ac343ac RS |
361 | @deffn Command list-charset-chars charset |
362 | This command displays a list of characters in the character set | |
363 | @var{charset}. | |
364 | @end deffn | |
365 | ||
cc6d0d2c RS |
366 | @node Chars and Bytes |
367 | @section Characters and Bytes | |
368 | @cindex bytes and characters | |
369 | ||
a9f0a989 RS |
370 | @cindex introduction sequence |
371 | @cindex dimension (of character set) | |
cc6d0d2c | 372 | In multibyte representation, each character occupies one or more |
a9f0a989 | 373 | bytes. Each character set has an @dfn{introduction sequence}, which is |
ad800164 EZ |
374 | normally one or two bytes long. (Exception: the @code{ascii} character |
375 | set and the @code{eight-bit-graphic} character set have a zero-length | |
7a063989 KH |
376 | introduction sequence.) The introduction sequence is the beginning of |
377 | the byte sequence for any character in the character set. The rest of | |
378 | the character's bytes distinguish it from the other characters in the | |
379 | same character set. Depending on the character set, there are either | |
380 | one or two distinguishing bytes; the number of such bytes is called the | |
381 | @dfn{dimension} of the character set. | |
a9f0a989 RS |
382 | |
383 | @defun charset-dimension charset | |
b6954afd RS |
384 | This function returns the dimension of @var{charset}; at present, the |
385 | dimension is always 1 or 2. | |
386 | @end defun | |
387 | ||
388 | @defun charset-bytes charset | |
b6954afd RS |
389 | This function returns the number of bytes used to represent a character |
390 | in character set @var{charset}. | |
a9f0a989 RS |
391 | @end defun |
392 | ||
393 | This is the simplest way to determine the byte length of a character | |
394 | set's introduction sequence: | |
395 | ||
396 | @example | |
b6954afd | 397 | (- (charset-bytes @var{charset}) |
a9f0a989 RS |
398 | (charset-dimension @var{charset})) |
399 | @end example | |
400 | ||
401 | @node Splitting Characters | |
402 | @section Splitting Characters | |
403 | ||
404 | The functions in this section convert between characters and the byte | |
405 | values used to represent them. For most purposes, there is no need to | |
406 | be concerned with the sequence of bytes used to represent a character, | |
969fe9b5 | 407 | because Emacs translates automatically when necessary. |
cc6d0d2c | 408 | |
cc6d0d2c RS |
409 | @defun split-char character |
410 | Return a list containing the name of the character set of | |
a9f0a989 RS |
411 | @var{character}, followed by one or two byte values (integers) which |
412 | identify @var{character} within that character set. The number of byte | |
413 | values is the character set's dimension. | |
cc6d0d2c | 414 | |
35864124 LT |
415 | If @var{character} is invalid as a character code, @code{split-char} |
416 | returns a list consisting of the symbol @code{unknown} and @var{character}. | |
417 | ||
cc6d0d2c RS |
418 | @example |
419 | (split-char 2248) | |
420 | @result{} (latin-iso8859-1 72) | |
421 | (split-char 65) | |
422 | @result{} (ascii 65) | |
7a063989 KH |
423 | (split-char 128) |
424 | @result{} (eight-bit-control 128) | |
cc6d0d2c RS |
425 | @end example |
426 | @end defun | |
427 | ||
e8262f40 DL |
428 | @defun make-char charset &optional code1 code2 |
429 | This function returns the character in character set @var{charset} whose | |
430 | position codes are @var{code1} and @var{code2}. This is roughly the | |
431 | inverse of @code{split-char}. Normally, you should specify either one | |
432 | or both of @var{code1} and @var{code2} according to the dimension of | |
433 | @var{charset}. For example, | |
cc6d0d2c RS |
434 | |
435 | @example | |
436 | (make-char 'latin-iso8859-1 72) | |
437 | @result{} 2248 | |
438 | @end example | |
0f4da9ce DL |
439 | |
440 | Actually, the eighth bit of both @var{code1} and @var{code2} is zeroed | |
441 | before they are used to index @var{charset}. Thus you may use, for | |
442 | instance, an ISO 8859 character code rather than subtracting 128, as | |
443 | is necessary to index the corresponding Emacs charset. | |
cc6d0d2c RS |
444 | @end defun |
445 | ||
a9f0a989 RS |
446 | @cindex generic characters |
447 | If you call @code{make-char} with no @var{byte-values}, the result is | |
448 | a @dfn{generic character} which stands for @var{charset}. A generic | |
449 | character is an integer, but it is @emph{not} valid for insertion in the | |
450 | buffer as a character. It can be used in @code{char-table-range} to | |
451 | refer to the whole character set (@pxref{Char-Tables}). | |
452 | @code{char-valid-p} returns @code{nil} for generic characters. | |
453 | For example: | |
454 | ||
455 | @example | |
456 | (make-char 'latin-iso8859-1) | |
457 | @result{} 2176 | |
458 | (char-valid-p 2176) | |
459 | @result{} nil | |
7a063989 KH |
460 | (char-valid-p 2176 t) |
461 | @result{} t | |
a9f0a989 RS |
462 | (split-char 2176) |
463 | @result{} (latin-iso8859-1 0) | |
464 | @end example | |
465 | ||
ad800164 EZ |
466 | The character sets @code{ascii}, @code{eight-bit-control}, and |
467 | @code{eight-bit-graphic} don't have corresponding generic characters. If | |
e8262f40 DL |
468 | @var{charset} is one of them and you don't supply @var{code1}, |
469 | @code{make-char} returns the character code corresponding to the | |
470 | smallest code in @var{charset}. | |
7a063989 | 471 | |
a9f0a989 RS |
472 | @node Scanning Charsets |
473 | @section Scanning for Character Sets | |
474 | ||
475 | Sometimes it is useful to find out which character sets appear in a | |
476 | part of a buffer or a string. One use for this is in determining which | |
477 | coding systems (@pxref{Coding Systems}) are capable of representing all | |
478 | of the text in question. | |
479 | ||
5ac343ac RS |
480 | @defun charset-after &optional pos |
481 | This function return the charset of a character in the current buffer | |
482 | at position @var{pos}. If @var{pos} is omitted or @code{nil}, it | |
5a36d834 | 483 | defaults to the current value of point. If @var{pos} is out of range, |
5ac343ac RS |
484 | the value is @code{nil}. |
485 | @end defun | |
486 | ||
a9f0a989 | 487 | @defun find-charset-region beg end &optional translation |
a9f0a989 RS |
488 | This function returns a list of the character sets that appear in the |
489 | current buffer between positions @var{beg} and @var{end}. | |
490 | ||
491 | The optional argument @var{translation} specifies a translation table to | |
492 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
493 | is non-@code{nil}, then each character in the region is translated | |
494 | through this table, and the value returned describes the translated | |
495 | characters instead of the characters actually in the buffer. | |
a265079f | 496 | @end defun |
a9f0a989 RS |
497 | |
498 | @defun find-charset-string string &optional translation | |
b6954afd RS |
499 | This function returns a list of the character sets that appear in the |
500 | string @var{string}. It is just like @code{find-charset-region}, except | |
501 | that it applies to the contents of @var{string} instead of part of the | |
502 | current buffer. | |
a9f0a989 RS |
503 | @end defun |
504 | ||
505 | @node Translation of Characters | |
506 | @section Translation of Characters | |
507 | @cindex character translation tables | |
508 | @cindex translation tables | |
509 | ||
35864124 LT |
510 | A @dfn{translation table} is a char-table that specifies a mapping |
511 | of characters into characters. These tables are used in encoding and | |
512 | decoding, and for other purposes. Some coding systems specify their | |
513 | own particular translation tables; there are also default translation | |
514 | tables which apply to all other coding systems. | |
a9f0a989 | 515 | |
a3d3f60d RS |
516 | For instance, the coding-system @code{utf-8} has a translation table |
517 | that maps characters of various charsets (e.g., | |
518 | @code{latin-iso8859-@var{x}}) into Unicode character sets. This way, | |
519 | it can encode Latin-2 characters into UTF-8. Meanwhile, | |
520 | @code{unify-8859-on-decoding-mode} operates by specifying | |
521 | @code{standard-translation-table-for-decode} to translate | |
522 | Latin-@var{x} characters into corresponding Unicode characters. | |
523 | ||
8241495d RS |
524 | @defun make-translation-table &rest translations |
525 | This function returns a translation table based on the argument | |
f57b6e64 DL |
526 | @var{translations}. Each element of @var{translations} should be a |
527 | list of elements of the form @code{(@var{from} . @var{to})}; this says | |
528 | to translate the character @var{from} into @var{to}. | |
a9f0a989 | 529 | |
c04c052b DL |
530 | The arguments and the forms in each argument are processed in order, |
531 | and if a previous form already translates @var{to} to some other | |
532 | character, say @var{to-alt}, @var{from} is also translated to | |
533 | @var{to-alt}. | |
534 | ||
a9f0a989 RS |
535 | You can also map one whole character set into another character set with |
536 | the same dimension. To do this, you specify a generic character (which | |
537 | designates a character set) for @var{from} (@pxref{Splitting Characters}). | |
35864124 LT |
538 | In this case, if @var{to} is also a generic character, its character |
539 | set should have the same dimension as @var{from}'s. Then the | |
540 | translation table translates each character of @var{from}'s character | |
541 | set into the corresponding character of @var{to}'s character set. If | |
542 | @var{from} is a generic character and @var{to} is an ordinary | |
543 | character, then the translation table translates every character of | |
544 | @var{from}'s character set into @var{to}. | |
a9f0a989 RS |
545 | @end defun |
546 | ||
547 | In decoding, the translation table's translations are applied to the | |
548 | characters that result from ordinary decoding. If a coding system has | |
35864124 LT |
549 | property @code{translation-table-for-decode}, that specifies the |
550 | translation table to use. (This is a property of the coding system, | |
551 | as returned by @code{coding-system-get}, not a property of the symbol | |
552 | that is the coding system's name. @xref{Coding System Basics,, Basic | |
553 | Concepts of Coding Systems}.) Otherwise, if | |
554 | @code{standard-translation-table-for-decode} is non-@code{nil}, | |
555 | decoding uses that table. | |
a9f0a989 RS |
556 | |
557 | In encoding, the translation table's translations are applied to the | |
558 | characters in the buffer, and the result of translation is actually | |
559 | encoded. If a coding system has property | |
35864124 LT |
560 | @code{translation-table-for-encode}, that specifies the translation |
561 | table to use. Otherwise the variable | |
b1f687a2 RS |
562 | @code{standard-translation-table-for-encode} specifies the translation |
563 | table. | |
a9f0a989 | 564 | |
b1f687a2 | 565 | @defvar standard-translation-table-for-decode |
a9f0a989 RS |
566 | This is the default translation table for decoding, for |
567 | coding systems that don't specify any other translation table. | |
568 | @end defvar | |
569 | ||
b1f687a2 | 570 | @defvar standard-translation-table-for-encode |
a9f0a989 RS |
571 | This is the default translation table for encoding, for |
572 | coding systems that don't specify any other translation table. | |
573 | @end defvar | |
574 | ||
131bf943 RS |
575 | @defvar translation-table-for-input |
576 | Self-inserting characters are translated through this translation | |
fa27fb28 RS |
577 | table before they are inserted. Search commands also translate their |
578 | input through this table, so they can compare more reliably with | |
579 | what's in the buffer. | |
a3d3f60d RS |
580 | |
581 | @code{set-buffer-file-coding-system} sets this variable so that your | |
582 | keyboard input gets translated into the character sets that the buffer | |
fa27fb28 RS |
583 | is likely to contain. This variable automatically becomes |
584 | buffer-local when set. | |
131bf943 RS |
585 | @end defvar |
586 | ||
cc6d0d2c RS |
587 | @node Coding Systems |
588 | @section Coding Systems | |
589 | ||
590 | @cindex coding system | |
591 | When Emacs reads or writes a file, and when Emacs sends text to a | |
592 | subprocess or receives text from a subprocess, it normally performs | |
593 | character code conversion and end-of-line conversion as specified | |
594 | by a particular @dfn{coding system}. | |
595 | ||
8241495d RS |
596 | How to define a coding system is an arcane matter, and is not |
597 | documented here. | |
b6954afd | 598 | |
a9f0a989 | 599 | @menu |
5557b83b RS |
600 | * Coding System Basics:: Basic concepts. |
601 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
602 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
603 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
604 | * Default Coding Systems:: Controlling the default choices. | |
605 | * Specifying Coding Systems:: Requesting a particular coding system | |
606 | for a single file operation. | |
607 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
608 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
609 | * MS-DOS File Types:: How DOS "text" and "binary" files | |
610 | relate to coding systems. | |
a9f0a989 RS |
611 | @end menu |
612 | ||
613 | @node Coding System Basics | |
614 | @subsection Basic Concepts of Coding Systems | |
615 | ||
cc6d0d2c RS |
616 | @cindex character code conversion |
617 | @dfn{Character code conversion} involves conversion between the encoding | |
618 | used inside Emacs and some other encoding. Emacs supports many | |
619 | different encodings, in that it can convert to and from them. For | |
620 | example, it can convert text to or from encodings such as Latin 1, Latin | |
621 | 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some | |
622 | cases, Emacs supports several alternative encodings for the same | |
623 | characters; for example, there are three coding systems for the Cyrillic | |
624 | (Russian) alphabet: ISO, Alternativnyj, and KOI8. | |
625 | ||
cc6d0d2c | 626 | Most coding systems specify a particular character code for |
8241495d RS |
627 | conversion, but some of them leave the choice unspecified---to be chosen |
628 | heuristically for each file, based on the data. | |
cc6d0d2c | 629 | |
aa945b59 RS |
630 | In general, a coding system doesn't guarantee roundtrip identity: |
631 | decoding a byte sequence using coding system, then encoding the | |
632 | resulting text in the same coding system, can produce a different byte | |
633 | sequence. However, the following coding systems do guarantee that the | |
634 | byte sequence will be the same as what you originally decoded: | |
6fa88620 KH |
635 | |
636 | @quotation | |
637 | chinese-big5 chinese-iso-8bit cyrillic-iso-8bit emacs-mule | |
638 | greek-iso-8bit hebrew-iso-8bit iso-latin-1 iso-latin-2 iso-latin-3 | |
639 | iso-latin-4 iso-latin-5 iso-latin-8 iso-latin-9 iso-safe | |
640 | japanese-iso-8bit japanese-shift-jis korean-iso-8bit raw-text | |
641 | @end quotation | |
642 | ||
aa945b59 RS |
643 | Encoding buffer text and then decoding the result can also fail to |
644 | reproduce the original text. For instance, if you encode Latin-2 | |
8b918214 RS |
645 | characters with @code{utf-8} and decode the result using the same |
646 | coding system, you'll get Unicode characters (of charset | |
aa945b59 RS |
647 | @code{mule-unicode-0100-24ff}). If you encode Unicode characters with |
648 | @code{iso-latin-2} and decode the result with the same coding system, | |
649 | you'll get Latin-2 characters. | |
6fa88620 | 650 | |
969fe9b5 RS |
651 | @cindex end of line conversion |
652 | @dfn{End of line conversion} handles three different conventions used | |
653 | on various systems for representing end of line in files. The Unix | |
654 | convention is to use the linefeed character (also called newline). The | |
8241495d RS |
655 | DOS convention is to use a carriage-return and a linefeed at the end of |
656 | a line. The Mac convention is to use just carriage-return. | |
969fe9b5 | 657 | |
cc6d0d2c RS |
658 | @cindex base coding system |
659 | @cindex variant coding system | |
660 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
661 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
662 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
663 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
a9f0a989 | 664 | well. Most base coding systems have three corresponding variants whose |
cc6d0d2c RS |
665 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. |
666 | ||
a9f0a989 RS |
667 | The coding system @code{raw-text} is special in that it prevents |
668 | character code conversion, and causes the buffer visited with that | |
669 | coding system to be a unibyte buffer. It does not specify the | |
670 | end-of-line conversion, allowing that to be determined as usual by the | |
671 | data, and has the usual three variants which specify the end-of-line | |
672 | conversion. @code{no-conversion} is equivalent to @code{raw-text-unix}: | |
673 | it specifies no conversion of either character codes or end-of-line. | |
674 | ||
675 | The coding system @code{emacs-mule} specifies that the data is | |
676 | represented in the internal Emacs encoding. This is like | |
677 | @code{raw-text} in that no code conversion happens, but different in | |
678 | that the result is multibyte data. | |
679 | ||
680 | @defun coding-system-get coding-system property | |
a9f0a989 RS |
681 | This function returns the specified property of the coding system |
682 | @var{coding-system}. Most coding system properties exist for internal | |
683 | purposes, but one that you might find useful is @code{mime-charset}. | |
684 | That property's value is the name used in MIME for the character coding | |
685 | which this coding system can read and write. Examples: | |
686 | ||
687 | @example | |
688 | (coding-system-get 'iso-latin-1 'mime-charset) | |
689 | @result{} iso-8859-1 | |
690 | (coding-system-get 'iso-2022-cn 'mime-charset) | |
691 | @result{} iso-2022-cn | |
692 | (coding-system-get 'cyrillic-koi8 'mime-charset) | |
693 | @result{} koi8-r | |
694 | @end example | |
695 | ||
696 | The value of the @code{mime-charset} property is also defined | |
697 | as an alias for the coding system. | |
698 | @end defun | |
699 | ||
700 | @node Encoding and I/O | |
701 | @subsection Encoding and I/O | |
702 | ||
1911e6e5 | 703 | The principal purpose of coding systems is for use in reading and |
a9f0a989 RS |
704 | writing files. The function @code{insert-file-contents} uses |
705 | a coding system for decoding the file data, and @code{write-region} | |
706 | uses one to encode the buffer contents. | |
707 | ||
708 | You can specify the coding system to use either explicitly | |
5ac343ac | 709 | (@pxref{Specifying Coding Systems}), or implicitly using a default |
a9f0a989 RS |
710 | mechanism (@pxref{Default Coding Systems}). But these methods may not |
711 | completely specify what to do. For example, they may choose a coding | |
712 | system such as @code{undefined} which leaves the character code | |
713 | conversion to be determined from the data. In these cases, the I/O | |
714 | operation finishes the job of choosing a coding system. Very often | |
715 | you will want to find out afterwards which coding system was chosen. | |
716 | ||
717 | @defvar buffer-file-coding-system | |
475aab0d CY |
718 | This buffer-local variable records the coding system that was used to visit |
719 | the current buffer. It is used for saving the buffer, and for writing part | |
1b02d12c EZ |
720 | of the buffer with @code{write-region}. If the text to be written |
721 | cannot be safely encoded using the coding system specified by this | |
722 | variable, these operations select an alternative encoding by calling | |
723 | the function @code{select-safe-coding-system} (@pxref{User-Chosen | |
724 | Coding Systems}). If selecting a different encoding requires to ask | |
725 | the user to specify a coding system, @code{buffer-file-coding-system} | |
726 | is updated to the newly selected coding system. | |
727 | ||
728 | @code{buffer-file-coding-system} does @emph{not} affect sending text | |
b6954afd | 729 | to a subprocess. |
a9f0a989 RS |
730 | @end defvar |
731 | ||
732 | @defvar save-buffer-coding-system | |
7a063989 KH |
733 | This variable specifies the coding system for saving the buffer (by |
734 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
735 | for @code{write-region}. | |
8241495d RS |
736 | |
737 | When a command to save the buffer starts out to use | |
7a063989 KH |
738 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), |
739 | and that coding system cannot handle | |
8241495d | 740 | the actual text in the buffer, the command asks the user to choose |
1b02d12c EZ |
741 | another coding system (by calling @code{select-safe-coding-system}). |
742 | After that happens, the command also updates | |
743 | @code{buffer-file-coding-system} to represent the coding system that | |
744 | the user specified. | |
a9f0a989 RS |
745 | @end defvar |
746 | ||
747 | @defvar last-coding-system-used | |
a9f0a989 RS |
748 | I/O operations for files and subprocesses set this variable to the |
749 | coding system name that was used. The explicit encoding and decoding | |
750 | functions (@pxref{Explicit Encoding}) set it too. | |
751 | ||
752 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
8241495d RS |
753 | it can change whenever Emacs waits; therefore, you should copy the |
754 | value shortly after the function call that stores the value you are | |
a9f0a989 RS |
755 | interested in. |
756 | @end defvar | |
757 | ||
2eb4136f RS |
758 | The variable @code{selection-coding-system} specifies how to encode |
759 | selections for the window system. @xref{Window System Selections}. | |
760 | ||
1ee89891 RS |
761 | @defvar file-name-coding-system |
762 | The variable @code{file-name-coding-system} specifies the coding | |
763 | system to use for encoding file names. Emacs encodes file names using | |
764 | that coding system for all file operations. If | |
765 | @code{file-name-coding-system} is @code{nil}, Emacs uses a default | |
766 | coding system determined by the selected language environment. In the | |
767 | default language environment, any non-@acronym{ASCII} characters in | |
768 | file names are not encoded specially; they appear in the file system | |
769 | using the internal Emacs representation. | |
770 | @end defvar | |
771 | ||
772 | @strong{Warning:} if you change @code{file-name-coding-system} (or | |
773 | the language environment) in the middle of an Emacs session, problems | |
774 | can result if you have already visited files whose names were encoded | |
775 | using the earlier coding system and are handled differently under the | |
776 | new coding system. If you try to save one of these buffers under the | |
777 | visited file name, saving may use the wrong file name, or it may get | |
778 | an error. If such a problem happens, use @kbd{C-x C-w} to specify a | |
779 | new file name for that buffer. | |
780 | ||
969fe9b5 RS |
781 | @node Lisp and Coding Systems |
782 | @subsection Coding Systems in Lisp | |
783 | ||
8241495d | 784 | Here are the Lisp facilities for working with coding systems: |
cc6d0d2c | 785 | |
cc6d0d2c RS |
786 | @defun coding-system-list &optional base-only |
787 | This function returns a list of all coding system names (symbols). If | |
788 | @var{base-only} is non-@code{nil}, the value includes only the | |
7a063989 KH |
789 | base coding systems. Otherwise, it includes alias and variant coding |
790 | systems as well. | |
cc6d0d2c RS |
791 | @end defun |
792 | ||
cc6d0d2c RS |
793 | @defun coding-system-p object |
794 | This function returns @code{t} if @var{object} is a coding system | |
35864124 | 795 | name or @code{nil}. |
cc6d0d2c RS |
796 | @end defun |
797 | ||
cc6d0d2c RS |
798 | @defun check-coding-system coding-system |
799 | This function checks the validity of @var{coding-system}. | |
800 | If that is valid, it returns @var{coding-system}. | |
801 | Otherwise it signals an error with condition @code{coding-system-error}. | |
802 | @end defun | |
803 | ||
e1166db9 EZ |
804 | @cindex EOL conversion |
805 | @cindex end-of-line conversion | |
806 | @cindex line end conversion | |
807 | @defun coding-system-eol-type coding-system | |
808 | This function returns the type of end-of-line (a.k.a.@: @dfn{eol}) | |
809 | conversion used by @var{coding-system}. If @var{coding-system} | |
810 | specifies a certain eol conversion, the return value is an integer 0, | |
811 | 1, or 2, standing for @code{unix}, @code{dos}, and @code{mac}, | |
812 | respectively. If @var{coding-system} doesn't specify eol conversion | |
813 | explicitly, the return value is a vector of coding systems, each one | |
814 | with one of the possible eol conversion types, like this: | |
815 | ||
816 | @lisp | |
817 | (coding-system-eol-type 'latin-1) | |
818 | @result{} [latin-1-unix latin-1-dos latin-1-mac] | |
819 | @end lisp | |
820 | ||
821 | @noindent | |
822 | If this function returns a vector, Emacs will decide, as part of the | |
823 | text encoding or decoding process, what eol conversion to use. For | |
824 | decoding, the end-of-line format of the text is auto-detected, and the | |
825 | eol conversion is set to match it (e.g., DOS-style CRLF format will | |
826 | imply @code{dos} eol conversion). For encoding, the eol conversion is | |
827 | taken from the appropriate default coding system (e.g., | |
828 | @code{default-buffer-file-coding-system} for | |
829 | @code{buffer-file-coding-system}), or from the default eol conversion | |
830 | appropriate for the underlying platform. | |
831 | @end defun | |
832 | ||
a9f0a989 | 833 | @defun coding-system-change-eol-conversion coding-system eol-type |
a9f0a989 | 834 | This function returns a coding system which is like @var{coding-system} |
1911e6e5 | 835 | except for its eol conversion, which is specified by @code{eol-type}. |
a9f0a989 RS |
836 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or |
837 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
838 | the end-of-line conversion from the data. | |
35864124 LT |
839 | |
840 | @var{eol-type} may also be 0, 1 or 2, standing for @code{unix}, | |
070b546b | 841 | @code{dos} and @code{mac}, respectively. |
a9f0a989 | 842 | @end defun |
969fe9b5 | 843 | |
a9f0a989 | 844 | @defun coding-system-change-text-conversion eol-coding text-coding |
a9f0a989 RS |
845 | This function returns a coding system which uses the end-of-line |
846 | conversion of @var{eol-coding}, and the text conversion of | |
847 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
848 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
969fe9b5 RS |
849 | @end defun |
850 | ||
a9f0a989 | 851 | @defun find-coding-systems-region from to |
a9f0a989 RS |
852 | This function returns a list of coding systems that could be used to |
853 | encode a text between @var{from} and @var{to}. All coding systems in | |
854 | the list can safely encode any multibyte characters in that portion of | |
855 | the text. | |
856 | ||
857 | If the text contains no multibyte characters, the function returns the | |
858 | list @code{(undecided)}. | |
859 | @end defun | |
860 | ||
861 | @defun find-coding-systems-string string | |
a9f0a989 RS |
862 | This function returns a list of coding systems that could be used to |
863 | encode the text of @var{string}. All coding systems in the list can | |
864 | safely encode any multibyte characters in @var{string}. If the text | |
865 | contains no multibyte characters, this returns the list | |
866 | @code{(undecided)}. | |
867 | @end defun | |
868 | ||
869 | @defun find-coding-systems-for-charsets charsets | |
a9f0a989 RS |
870 | This function returns a list of coding systems that could be used to |
871 | encode all the character sets in the list @var{charsets}. | |
872 | @end defun | |
873 | ||
874 | @defun detect-coding-region start end &optional highest | |
cc6d0d2c | 875 | This function chooses a plausible coding system for decoding the text |
0ace421a | 876 | from @var{start} to @var{end}. This text should be a byte sequence |
969fe9b5 | 877 | (@pxref{Explicit Encoding}). |
cc6d0d2c | 878 | |
a9f0a989 | 879 | Normally this function returns a list of coding systems that could |
cc6d0d2c | 880 | handle decoding the text that was scanned. They are listed in order of |
a9f0a989 RS |
881 | decreasing priority. But if @var{highest} is non-@code{nil}, then the |
882 | return value is just one coding system, the one that is highest in | |
883 | priority. | |
884 | ||
6d05494a KH |
885 | If the region contains only @acronym{ASCII} characters except for such |
886 | ISO-2022 control characters ISO-2022 as @code{ESC}, the value is | |
887 | @code{undecided} or @code{(undecided)}, or a variant specifying | |
35864124 | 888 | end-of-line conversion, if that can be deduced from the text. |
cc6d0d2c RS |
889 | @end defun |
890 | ||
35864124 | 891 | @defun detect-coding-string string &optional highest |
cc6d0d2c RS |
892 | This function is like @code{detect-coding-region} except that it |
893 | operates on the contents of @var{string} instead of bytes in the buffer. | |
1911e6e5 RS |
894 | @end defun |
895 | ||
35864124 LT |
896 | @xref{Coding systems for a subprocess,, Process Information}, in |
897 | particular the description of the functions | |
898 | @code{process-coding-system} and @code{set-process-coding-system}, for | |
899 | how to examine or set the coding systems used for I/O to a subprocess. | |
1911e6e5 RS |
900 | |
901 | @node User-Chosen Coding Systems | |
902 | @subsection User-Chosen Coding Systems | |
903 | ||
1b02d12c | 904 | @cindex select safe coding system |
35864124 | 905 | @defun select-safe-coding-system from to &optional default-coding-system accept-default-p file |
bf23b477 EZ |
906 | This function selects a coding system for encoding specified text, |
907 | asking the user to choose if necessary. Normally the specified text | |
35864124 LT |
908 | is the text in the current buffer between @var{from} and @var{to}. If |
909 | @var{from} is a string, the string specifies the text to encode, and | |
910 | @var{to} is ignored. | |
bf23b477 EZ |
911 | |
912 | If @var{default-coding-system} is non-@code{nil}, that is the first | |
913 | coding system to try; if that can handle the text, | |
914 | @code{select-safe-coding-system} returns that coding system. It can | |
915 | also be a list of coding systems; then the function tries each of them | |
35864124 LT |
916 | one by one. After trying all of them, it next tries the current |
917 | buffer's value of @code{buffer-file-coding-system} (if it is not | |
918 | @code{undecided}), then the value of | |
919 | @code{default-buffer-file-coding-system} and finally the user's most | |
920 | preferred coding system, which the user can set using the command | |
921 | @code{prefer-coding-system} (@pxref{Recognize Coding,, Recognizing | |
922 | Coding Systems, emacs, The GNU Emacs Manual}). | |
bf23b477 EZ |
923 | |
924 | If one of those coding systems can safely encode all the specified | |
925 | text, @code{select-safe-coding-system} chooses it and returns it. | |
926 | Otherwise, it asks the user to choose from a list of coding systems | |
927 | which can encode all the text, and returns the user's choice. | |
928 | ||
35864124 LT |
929 | @var{default-coding-system} can also be a list whose first element is |
930 | t and whose other elements are coding systems. Then, if no coding | |
931 | system in the list can handle the text, @code{select-safe-coding-system} | |
932 | queries the user immediately, without trying any of the three | |
933 | alternatives described above. | |
934 | ||
bf23b477 | 935 | The optional argument @var{accept-default-p}, if non-@code{nil}, |
35864124 LT |
936 | should be a function to determine whether a coding system selected |
937 | without user interaction is acceptable. @code{select-safe-coding-system} | |
938 | calls this function with one argument, the base coding system of the | |
939 | selected coding system. If @var{accept-default-p} returns @code{nil}, | |
940 | @code{select-safe-coding-system} rejects the silently selected coding | |
941 | system, and asks the user to select a coding system from a list of | |
942 | possible candidates. | |
bf23b477 EZ |
943 | |
944 | @vindex select-safe-coding-system-accept-default-p | |
945 | If the variable @code{select-safe-coding-system-accept-default-p} is | |
946 | non-@code{nil}, its value overrides the value of | |
947 | @var{accept-default-p}. | |
35864124 LT |
948 | |
949 | As a final step, before returning the chosen coding system, | |
950 | @code{select-safe-coding-system} checks whether that coding system is | |
951 | consistent with what would be selected if the contents of the region | |
952 | were read from a file. (If not, this could lead to data corruption in | |
953 | a file subsequently re-visited and edited.) Normally, | |
954 | @code{select-safe-coding-system} uses @code{buffer-file-name} as the | |
955 | file for this purpose, but if @var{file} is non-@code{nil}, it uses | |
956 | that file instead (this can be relevant for @code{write-region} and | |
957 | similar functions). If it detects an apparent inconsistency, | |
958 | @code{select-safe-coding-system} queries the user before selecting the | |
959 | coding system. | |
969fe9b5 RS |
960 | @end defun |
961 | ||
962 | Here are two functions you can use to let the user specify a coding | |
963 | system, with completion. @xref{Completion}. | |
964 | ||
a9f0a989 | 965 | @defun read-coding-system prompt &optional default |
969fe9b5 RS |
966 | This function reads a coding system using the minibuffer, prompting with |
967 | string @var{prompt}, and returns the coding system name as a symbol. If | |
968 | the user enters null input, @var{default} specifies which coding system | |
969 | to return. It should be a symbol or a string. | |
970 | @end defun | |
971 | ||
969fe9b5 RS |
972 | @defun read-non-nil-coding-system prompt |
973 | This function reads a coding system using the minibuffer, prompting with | |
a9f0a989 | 974 | string @var{prompt}, and returns the coding system name as a symbol. If |
969fe9b5 RS |
975 | the user tries to enter null input, it asks the user to try again. |
976 | @xref{Coding Systems}. | |
cc6d0d2c RS |
977 | @end defun |
978 | ||
979 | @node Default Coding Systems | |
a9f0a989 | 980 | @subsection Default Coding Systems |
cc6d0d2c | 981 | |
a9f0a989 RS |
982 | This section describes variables that specify the default coding |
983 | system for certain files or when running certain subprograms, and the | |
1911e6e5 | 984 | function that I/O operations use to access them. |
a9f0a989 RS |
985 | |
986 | The idea of these variables is that you set them once and for all to the | |
987 | defaults you want, and then do not change them again. To specify a | |
988 | particular coding system for a particular operation in a Lisp program, | |
989 | don't change these variables; instead, override them using | |
990 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
991 | (@pxref{Specifying Coding Systems}). | |
cc6d0d2c | 992 | |
bf23b477 EZ |
993 | @defvar auto-coding-regexp-alist |
994 | This variable is an alist of text patterns and corresponding coding | |
995 | systems. Each element has the form @code{(@var{regexp} | |
996 | . @var{coding-system})}; a file whose first few kilobytes match | |
997 | @var{regexp} is decoded with @var{coding-system} when its contents are | |
998 | read into a buffer. The settings in this alist take priority over | |
999 | @code{coding:} tags in the files and the contents of | |
1000 | @code{file-coding-system-alist} (see below). The default value is set | |
1001 | so that Emacs automatically recognizes mail files in Babyl format and | |
1002 | reads them with no code conversions. | |
1003 | @end defvar | |
1004 | ||
cc6d0d2c RS |
1005 | @defvar file-coding-system-alist |
1006 | This variable is an alist that specifies the coding systems to use for | |
1007 | reading and writing particular files. Each element has the form | |
1008 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
1009 | expression that matches certain file names. The element applies to file | |
1010 | names that match @var{pattern}. | |
1011 | ||
35864124 | 1012 | The @sc{cdr} of the element, @var{coding}, should be either a coding |
8241495d RS |
1013 | system, a cons cell containing two coding systems, or a function name (a |
1014 | symbol with a function definition). If @var{coding} is a coding system, | |
1015 | that coding system is used for both reading the file and writing it. If | |
35864124 LT |
1016 | @var{coding} is a cons cell containing two coding systems, its @sc{car} |
1017 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
8241495d RS |
1018 | coding system for encoding. |
1019 | ||
35864124 LT |
1020 | If @var{coding} is a function name, the function should take one |
1021 | argument, a list of all arguments passed to | |
1022 | @code{find-operation-coding-system}. It must return a coding system | |
1023 | or a cons cell containing two coding systems. This value has the same | |
1024 | meaning as described above. | |
cc6d0d2c RS |
1025 | @end defvar |
1026 | ||
cc6d0d2c RS |
1027 | @defvar process-coding-system-alist |
1028 | This variable is an alist specifying which coding systems to use for a | |
1029 | subprocess, depending on which program is running in the subprocess. It | |
1030 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
1031 | matched against the program name used to start the subprocess. The coding | |
1032 | system or systems specified in this alist are used to initialize the | |
1033 | coding systems used for I/O to the subprocess, but you can specify | |
1034 | other coding systems later using @code{set-process-coding-system}. | |
1035 | @end defvar | |
1036 | ||
8241495d RS |
1037 | @strong{Warning:} Coding systems such as @code{undecided}, which |
1038 | determine the coding system from the data, do not work entirely reliably | |
1911e6e5 | 1039 | with asynchronous subprocess output. This is because Emacs handles |
a9f0a989 RS |
1040 | asynchronous subprocess output in batches, as it arrives. If the coding |
1041 | system leaves the character code conversion unspecified, or leaves the | |
1042 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
1043 | conversion from one batch at a time, and this does not always work. | |
1044 | ||
1045 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
1046 | coding system which determines both the character code conversion and | |
1047 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
1048 | rather than @code{undecided} or @code{latin-1}. | |
1049 | ||
cc6d0d2c RS |
1050 | @defvar network-coding-system-alist |
1051 | This variable is an alist that specifies the coding system to use for | |
1052 | network streams. It works much like @code{file-coding-system-alist}, | |
969fe9b5 | 1053 | with the difference that the @var{pattern} in an element may be either a |
cc6d0d2c RS |
1054 | port number or a regular expression. If it is a regular expression, it |
1055 | is matched against the network service name used to open the network | |
1056 | stream. | |
1057 | @end defvar | |
1058 | ||
cc6d0d2c RS |
1059 | @defvar default-process-coding-system |
1060 | This variable specifies the coding systems to use for subprocess (and | |
1061 | network stream) input and output, when nothing else specifies what to | |
1062 | do. | |
1063 | ||
a9f0a989 RS |
1064 | The value should be a cons cell of the form @code{(@var{input-coding} |
1065 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
1066 | the subprocess, and @var{output-coding} applies to output to it. | |
cc6d0d2c RS |
1067 | @end defvar |
1068 | ||
131bf943 RS |
1069 | @defvar auto-coding-functions |
1070 | This variable holds a list of functions that try to determine a | |
1071 | coding system for a file based on its undecoded contents. | |
1072 | ||
1073 | Each function in this list should be written to look at text in the | |
1074 | current buffer, but should not modify it in any way. The buffer will | |
1075 | contain undecoded text of parts of the file. Each function should | |
1076 | take one argument, @var{size}, which tells it how many characters to | |
1077 | look at, starting from point. If the function succeeds in determining | |
1078 | a coding system for the file, it should return that coding system. | |
1079 | Otherwise, it should return @code{nil}. | |
1080 | ||
1081 | If a file has a @samp{coding:} tag, that takes precedence, so these | |
1082 | functions won't be called. | |
1083 | @end defvar | |
1084 | ||
a9f0a989 | 1085 | @defun find-operation-coding-system operation &rest arguments |
a9f0a989 RS |
1086 | This function returns the coding system to use (by default) for |
1087 | performing @var{operation} with @var{arguments}. The value has this | |
1088 | form: | |
1089 | ||
1090 | @example | |
35864124 | 1091 | (@var{decoding-system} . @var{encoding-system}) |
a9f0a989 RS |
1092 | @end example |
1093 | ||
1094 | The first element, @var{decoding-system}, is the coding system to use | |
1095 | for decoding (in case @var{operation} does decoding), and | |
1096 | @var{encoding-system} is the coding system for encoding (in case | |
1097 | @var{operation} does encoding). | |
1098 | ||
342fd6cd RS |
1099 | The argument @var{operation} should be a symbol, any one of |
1100 | @code{insert-file-contents}, @code{write-region}, | |
1101 | @code{start-process}, @code{call-process}, @code{call-process-region}, | |
1102 | or @code{open-network-stream}. These are the names of the Emacs I/O | |
e1511d87 | 1103 | primitives that can do character code and eol conversion. |
a9f0a989 RS |
1104 | |
1105 | The remaining arguments should be the same arguments that might be given | |
e1511d87 EZ |
1106 | to the corresponding I/O primitive. Depending on the primitive, one |
1107 | of those arguments is selected as the @dfn{target}. For example, if | |
a9f0a989 RS |
1108 | @var{operation} does file I/O, whichever argument specifies the file |
1109 | name is the target. For subprocess primitives, the process name is the | |
1110 | target. For @code{open-network-stream}, the target is the service name | |
1111 | or port number. | |
1112 | ||
342fd6cd RS |
1113 | Depending on @var{operation}, this function looks up the target in |
1114 | @code{file-coding-system-alist}, @code{process-coding-system-alist}, | |
e1511d87 EZ |
1115 | or @code{network-coding-system-alist}. If the target is found in the |
1116 | alist, @code{find-operation-coding-system} returns its association in | |
1117 | the alist; otherwise it returns @code{nil}. | |
6d3906d5 KH |
1118 | |
1119 | If @var{operation} is @code{insert-file-contents}, the argument | |
1120 | corresponding to the target may be a cons cell of the form | |
b8909e88 | 1121 | @code{(@var{filename} . @var{buffer})}). In that case, @var{filename} |
e1511d87 | 1122 | is a file name to look up in @code{file-coding-system-alist}, and |
749eecf5 RS |
1123 | @var{buffer} is a buffer that contains the file's contents (not yet |
1124 | decoded). If @code{file-coding-system-alist} specifies a function to | |
1125 | call for this file, and that function needs to examine the file's | |
1126 | contents (as it usually does), it should examine the contents of | |
1127 | @var{buffer} instead of reading the file. | |
a9f0a989 RS |
1128 | @end defun |
1129 | ||
cc6d0d2c | 1130 | @node Specifying Coding Systems |
a9f0a989 | 1131 | @subsection Specifying a Coding System for One Operation |
cc6d0d2c RS |
1132 | |
1133 | You can specify the coding system for a specific operation by binding | |
1134 | the variables @code{coding-system-for-read} and/or | |
1135 | @code{coding-system-for-write}. | |
1136 | ||
cc6d0d2c RS |
1137 | @defvar coding-system-for-read |
1138 | If this variable is non-@code{nil}, it specifies the coding system to | |
1139 | use for reading a file, or for input from a synchronous subprocess. | |
1140 | ||
1141 | It also applies to any asynchronous subprocess or network stream, but in | |
1142 | a different way: the value of @code{coding-system-for-read} when you | |
1143 | start the subprocess or open the network stream specifies the input | |
1144 | decoding method for that subprocess or network stream. It remains in | |
1145 | use for that subprocess or network stream unless and until overridden. | |
1146 | ||
1147 | The right way to use this variable is to bind it with @code{let} for a | |
1148 | specific I/O operation. Its global value is normally @code{nil}, and | |
1149 | you should not globally set it to any other value. Here is an example | |
1150 | of the right way to use the variable: | |
1151 | ||
1152 | @example | |
1153 | ;; @r{Read the file with no character code conversion.} | |
ad800164 | 1154 | ;; @r{Assume @acronym{crlf} represents end-of-line.} |
a3d3f60d | 1155 | (let ((coding-system-for-read 'emacs-mule-dos)) |
cc6d0d2c RS |
1156 | (insert-file-contents filename)) |
1157 | @end example | |
1158 | ||
1159 | When its value is non-@code{nil}, @code{coding-system-for-read} takes | |
a9f0a989 | 1160 | precedence over all other methods of specifying a coding system to use for |
cc6d0d2c RS |
1161 | input, including @code{file-coding-system-alist}, |
1162 | @code{process-coding-system-alist} and | |
1163 | @code{network-coding-system-alist}. | |
1164 | @end defvar | |
1165 | ||
cc6d0d2c RS |
1166 | @defvar coding-system-for-write |
1167 | This works much like @code{coding-system-for-read}, except that it | |
1168 | applies to output rather than input. It affects writing to files, | |
b6954afd | 1169 | as well as sending output to subprocesses and net connections. |
cc6d0d2c RS |
1170 | |
1171 | When a single operation does both input and output, as do | |
1172 | @code{call-process-region} and @code{start-process}, both | |
1173 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1174 | affect it. | |
1175 | @end defvar | |
1176 | ||
cc6d0d2c RS |
1177 | @defvar inhibit-eol-conversion |
1178 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
1179 | no matter which coding system is specified. This applies to all the | |
1180 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
1181 | decoding functions (@pxref{Explicit Encoding}). | |
1182 | @end defvar | |
1183 | ||
cc6d0d2c | 1184 | @node Explicit Encoding |
a9f0a989 | 1185 | @subsection Explicit Encoding and Decoding |
cc6d0d2c RS |
1186 | @cindex encoding text |
1187 | @cindex decoding text | |
1188 | ||
1189 | All the operations that transfer text in and out of Emacs have the | |
1190 | ability to use a coding system to encode or decode the text. | |
1191 | You can also explicitly encode and decode text using the functions | |
1192 | in this section. | |
1193 | ||
cc6d0d2c | 1194 | The result of encoding, and the input to decoding, are not ordinary |
0ace421a GM |
1195 | text. They logically consist of a series of byte values; that is, a |
1196 | series of characters whose codes are in the range 0 through 255. In a | |
1197 | multibyte buffer or string, character codes 128 through 159 are | |
1198 | represented by multibyte sequences, but this is invisible to Lisp | |
1199 | programs. | |
1200 | ||
1201 | The usual way to read a file into a buffer as a sequence of bytes, so | |
1202 | you can decode the contents explicitly, is with | |
1203 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
1204 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
1205 | visiting a file with @code{find-file-noselect}. These methods result in | |
1206 | a unibyte buffer. | |
1207 | ||
1208 | The usual way to use the byte sequence that results from explicitly | |
1209 | encoding text is to copy it to a file or process---for example, to write | |
1210 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
1211 | encoding by binding @code{coding-system-for-write} to | |
1212 | @code{no-conversion}. | |
b6954afd RS |
1213 | |
1214 | Here are the functions to perform explicit encoding or decoding. The | |
7f2e71dd | 1215 | encoding functions produce sequences of bytes; the decoding functions |
0ace421a GM |
1216 | are meant to operate on sequences of bytes. All of these functions |
1217 | discard text properties. | |
1911e6e5 | 1218 | |
35864124 LT |
1219 | @deffn Command encode-coding-region start end coding-system |
1220 | This command encodes the text from @var{start} to @var{end} according | |
969fe9b5 | 1221 | to coding system @var{coding-system}. The encoded text replaces the |
0ace421a GM |
1222 | original text in the buffer. The result of encoding is logically a |
1223 | sequence of bytes, but the buffer remains multibyte if it was multibyte | |
1224 | before. | |
cc6d0d2c | 1225 | |
35864124 LT |
1226 | This command returns the length of the encoded text. |
1227 | @end deffn | |
1228 | ||
1229 | @defun encode-coding-string string coding-system &optional nocopy | |
cc6d0d2c RS |
1230 | This function encodes the text in @var{string} according to coding |
1231 | system @var{coding-system}. It returns a new string containing the | |
35864124 LT |
1232 | encoded text, except when @var{nocopy} is non-@code{nil}, in which |
1233 | case the function may return @var{string} itself if the encoding | |
1234 | operation is trivial. The result of encoding is a unibyte string. | |
cc6d0d2c RS |
1235 | @end defun |
1236 | ||
35864124 LT |
1237 | @deffn Command decode-coding-region start end coding-system |
1238 | This command decodes the text from @var{start} to @var{end} according | |
cc6d0d2c RS |
1239 | to coding system @var{coding-system}. The decoded text replaces the |
1240 | original text in the buffer. To make explicit decoding useful, the text | |
0ace421a GM |
1241 | before decoding ought to be a sequence of byte values, but both |
1242 | multibyte and unibyte buffers are acceptable. | |
cc6d0d2c | 1243 | |
35864124 LT |
1244 | This command returns the length of the decoded text. |
1245 | @end deffn | |
1246 | ||
1247 | @defun decode-coding-string string coding-system &optional nocopy | |
cc6d0d2c RS |
1248 | This function decodes the text in @var{string} according to coding |
1249 | system @var{coding-system}. It returns a new string containing the | |
35864124 LT |
1250 | decoded text, except when @var{nocopy} is non-@code{nil}, in which |
1251 | case the function may return @var{string} itself if the decoding | |
1252 | operation is trivial. To make explicit decoding useful, the contents | |
1253 | of @var{string} ought to be a sequence of byte values, but a multibyte | |
0ace421a | 1254 | string is acceptable. |
cc6d0d2c | 1255 | @end defun |
969fe9b5 | 1256 | |
131bf943 RS |
1257 | @defun decode-coding-inserted-region from to filename &optional visit beg end replace |
1258 | This function decodes the text from @var{from} to @var{to} as if | |
1259 | it were being read from file @var{filename} using @code{insert-file-contents} | |
1260 | using the rest of the arguments provided. | |
1261 | ||
1262 | The normal way to use this function is after reading text from a file | |
1263 | without decoding, if you decide you would rather have decoded it. | |
1264 | Instead of deleting the text and reading it again, this time with | |
1265 | decoding, you can call this function. | |
1266 | @end defun | |
1267 | ||
a9f0a989 RS |
1268 | @node Terminal I/O Encoding |
1269 | @subsection Terminal I/O Encoding | |
1270 | ||
1271 | Emacs can decode keyboard input using a coding system, and encode | |
2eb4136f RS |
1272 | terminal output. This is useful for terminals that transmit or display |
1273 | text using a particular encoding such as Latin-1. Emacs does not set | |
1274 | @code{last-coding-system-used} for encoding or decoding for the | |
1275 | terminal. | |
a9f0a989 RS |
1276 | |
1277 | @defun keyboard-coding-system | |
a9f0a989 RS |
1278 | This function returns the coding system that is in use for decoding |
1279 | keyboard input---or @code{nil} if no coding system is to be used. | |
1280 | @end defun | |
1281 | ||
35864124 LT |
1282 | @deffn Command set-keyboard-coding-system coding-system |
1283 | This command specifies @var{coding-system} as the coding system to | |
a9f0a989 RS |
1284 | use for decoding keyboard input. If @var{coding-system} is @code{nil}, |
1285 | that means do not decode keyboard input. | |
35864124 | 1286 | @end deffn |
a9f0a989 RS |
1287 | |
1288 | @defun terminal-coding-system | |
a9f0a989 RS |
1289 | This function returns the coding system that is in use for encoding |
1290 | terminal output---or @code{nil} for no encoding. | |
1291 | @end defun | |
1292 | ||
35864124 LT |
1293 | @deffn Command set-terminal-coding-system coding-system |
1294 | This command specifies @var{coding-system} as the coding system to use | |
a9f0a989 RS |
1295 | for encoding terminal output. If @var{coding-system} is @code{nil}, |
1296 | that means do not encode terminal output. | |
35864124 | 1297 | @end deffn |
a9f0a989 | 1298 | |
969fe9b5 | 1299 | @node MS-DOS File Types |
a9f0a989 | 1300 | @subsection MS-DOS File Types |
969fe9b5 RS |
1301 | @cindex DOS file types |
1302 | @cindex MS-DOS file types | |
1303 | @cindex Windows file types | |
1304 | @cindex file types on MS-DOS and Windows | |
1305 | @cindex text files and binary files | |
1306 | @cindex binary files and text files | |
1307 | ||
8241495d RS |
1308 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate |
1309 | end-of-line conversion for a file by looking at the file's name. This | |
0ace421a | 1310 | feature classifies files as @dfn{text files} and @dfn{binary files}. By |
8241495d RS |
1311 | ``binary file'' we mean a file of literal byte values that are not |
1312 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1313 | and no character code conversion for them. On the other hand, the bytes | |
1314 | in a text file are intended to represent characters; when you create a | |
1315 | new file whose name implies that it is a text file, Emacs uses DOS | |
1316 | end-of-line conversion. | |
969fe9b5 RS |
1317 | |
1318 | @defvar buffer-file-type | |
1319 | This variable, automatically buffer-local in each buffer, records the | |
a9f0a989 RS |
1320 | file type of the buffer's visited file. When a buffer does not specify |
1321 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1322 | used to determine which coding system to use when writing the contents | |
1323 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1324 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1325 | Otherwise, @code{undecided-dos} is used. | |
1326 | ||
1327 | Normally this variable is set by visiting a file; it is set to | |
1328 | @code{nil} if the file was visited without any actual conversion. | |
969fe9b5 RS |
1329 | @end defvar |
1330 | ||
1331 | @defopt file-name-buffer-file-type-alist | |
1332 | This variable holds an alist for recognizing text and binary files. | |
1333 | Each element has the form (@var{regexp} . @var{type}), where | |
1334 | @var{regexp} is matched against the file name, and @var{type} may be | |
1335 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1336 | compute which. If it is a function, then it is called with a single | |
1337 | argument (the file name) and should return @code{t} or @code{nil}. | |
1338 | ||
8241495d | 1339 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide |
969fe9b5 RS |
1340 | which coding system to use when reading a file. For a text file, |
1341 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1342 | is used. | |
1343 | ||
1344 | If no element in this alist matches a given file name, then | |
1345 | @code{default-buffer-file-type} says how to treat the file. | |
1346 | @end defopt | |
1347 | ||
1348 | @defopt default-buffer-file-type | |
1349 | This variable says how to handle files for which | |
1350 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1351 | ||
1352 | If this variable is non-@code{nil}, then these files are treated as | |
a9f0a989 RS |
1353 | binary: the coding system @code{no-conversion} is used. Otherwise, |
1354 | nothing special is done for them---the coding system is deduced solely | |
1355 | from the file contents, in the usual Emacs fashion. | |
969fe9b5 RS |
1356 | @end defopt |
1357 | ||
a9f0a989 RS |
1358 | @node Input Methods |
1359 | @section Input Methods | |
1360 | @cindex input methods | |
1361 | ||
ad800164 | 1362 | @dfn{Input methods} provide convenient ways of entering non-@acronym{ASCII} |
a9f0a989 | 1363 | characters from the keyboard. Unlike coding systems, which translate |
ad800164 | 1364 | non-@acronym{ASCII} characters to and from encodings meant to be read by |
a9f0a989 RS |
1365 | programs, input methods provide human-friendly commands. (@xref{Input |
1366 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1367 | use input methods to enter text.) How to define input methods is not | |
1368 | yet documented in this manual, but here we describe how to use them. | |
1369 | ||
1370 | Each input method has a name, which is currently a string; | |
1371 | in the future, symbols may also be usable as input method names. | |
1372 | ||
a9f0a989 RS |
1373 | @defvar current-input-method |
1374 | This variable holds the name of the input method now active in the | |
1375 | current buffer. (It automatically becomes local in each buffer when set | |
1376 | in any fashion.) It is @code{nil} if no input method is active in the | |
1377 | buffer now. | |
969fe9b5 RS |
1378 | @end defvar |
1379 | ||
35864124 | 1380 | @defopt default-input-method |
a9f0a989 RS |
1381 | This variable holds the default input method for commands that choose an |
1382 | input method. Unlike @code{current-input-method}, this variable is | |
1383 | normally global. | |
35864124 | 1384 | @end defopt |
a9f0a989 | 1385 | |
35864124 LT |
1386 | @deffn Command set-input-method input-method |
1387 | This command activates input method @var{input-method} for the current | |
a9f0a989 | 1388 | buffer. It also sets @code{default-input-method} to @var{input-method}. |
35864124 | 1389 | If @var{input-method} is @code{nil}, this command deactivates any input |
a9f0a989 | 1390 | method for the current buffer. |
35864124 | 1391 | @end deffn |
a9f0a989 | 1392 | |
a9f0a989 RS |
1393 | @defun read-input-method-name prompt &optional default inhibit-null |
1394 | This function reads an input method name with the minibuffer, prompting | |
1395 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1396 | by default, if the user enters empty input. However, if | |
1397 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1398 | ||
1399 | The returned value is a string. | |
1400 | @end defun | |
1401 | ||
a9f0a989 RS |
1402 | @defvar input-method-alist |
1403 | This variable defines all the supported input methods. | |
1404 | Each element defines one input method, and should have the form: | |
1405 | ||
1406 | @example | |
1911e6e5 RS |
1407 | (@var{input-method} @var{language-env} @var{activate-func} |
1408 | @var{title} @var{description} @var{args}...) | |
a9f0a989 RS |
1409 | @end example |
1410 | ||
1911e6e5 RS |
1411 | Here @var{input-method} is the input method name, a string; |
1412 | @var{language-env} is another string, the name of the language | |
1413 | environment this input method is recommended for. (That serves only for | |
1414 | documentation purposes.) | |
a9f0a989 | 1415 | |
a9f0a989 RS |
1416 | @var{activate-func} is a function to call to activate this method. The |
1417 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1418 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1419 | the @var{args}. | |
0ace421a GM |
1420 | |
1421 | @var{title} is a string to display in the mode line while this method is | |
1422 | active. @var{description} is a string describing this method and what | |
1423 | it is good for. | |
1911e6e5 | 1424 | @end defvar |
a9f0a989 | 1425 | |
2eb4136f | 1426 | The fundamental interface to input methods is through the |
35864124 LT |
1427 | variable @code{input-method-function}. @xref{Reading One Event}, |
1428 | and @ref{Invoking the Input Method}. | |
2468d0c0 DL |
1429 | |
1430 | @node Locales | |
1431 | @section Locales | |
1432 | @cindex locale | |
1433 | ||
1434 | POSIX defines a concept of ``locales'' which control which language | |
1435 | to use in language-related features. These Emacs variables control | |
1436 | how Emacs interacts with these features. | |
1437 | ||
1438 | @defvar locale-coding-system | |
a007679c | 1439 | @cindex keyboard input decoding on X |
2468d0c0 | 1440 | This variable specifies the coding system to use for decoding system |
a007679c EZ |
1441 | error messages and---on X Window system only---keyboard input, for |
1442 | encoding the format argument to @code{format-time-string}, and for | |
1443 | decoding the return value of @code{format-time-string}. | |
2468d0c0 DL |
1444 | @end defvar |
1445 | ||
1446 | @defvar system-messages-locale | |
2468d0c0 DL |
1447 | This variable specifies the locale to use for generating system error |
1448 | messages. Changing the locale can cause messages to come out in a | |
9c17f494 | 1449 | different language or in a different orthography. If the variable is |
2468d0c0 DL |
1450 | @code{nil}, the locale is specified by environment variables in the |
1451 | usual POSIX fashion. | |
1452 | @end defvar | |
1453 | ||
1454 | @defvar system-time-locale | |
2468d0c0 DL |
1455 | This variable specifies the locale to use for formatting time values. |
1456 | Changing the locale can cause messages to appear according to the | |
1457 | conventions of a different language. If the variable is @code{nil}, the | |
1458 | locale is specified by environment variables in the usual POSIX fashion. | |
1459 | @end defvar | |
0ace421a | 1460 | |
131bf943 RS |
1461 | @defun locale-info item |
1462 | This function returns locale data @var{item} for the current POSIX | |
1463 | locale, if available. @var{item} should be one of these symbols: | |
1464 | ||
1465 | @table @code | |
1466 | @item codeset | |
1467 | Return the character set as a string (locale item @code{CODESET}). | |
1468 | ||
1469 | @item days | |
1470 | Return a 7-element vector of day names (locale items | |
1471 | @code{DAY_1} through @code{DAY_7}); | |
1472 | ||
1473 | @item months | |
1474 | Return a 12-element vector of month names (locale items @code{MON_1} | |
1475 | through @code{MON_12}). | |
1476 | ||
1477 | @item paper | |
1478 | Return a list @code{(@var{width} @var{height})} for the default paper | |
35864124 | 1479 | size measured in millimeters (locale items @code{PAPER_WIDTH} and |
131bf943 RS |
1480 | @code{PAPER_HEIGHT}). |
1481 | @end table | |
1482 | ||
1483 | If the system can't provide the requested information, or if | |
1484 | @var{item} is not one of those symbols, the value is @code{nil}. All | |
1485 | strings in the return value are decoded using | |
35864124 | 1486 | @code{locale-coding-system}. @xref{Locales,,, libc, The GNU Libc Manual}, |
131bf943 RS |
1487 | for more information about locales and locale items. |
1488 | @end defun | |
ab5796a9 MB |
1489 | |
1490 | @ignore | |
1491 | arch-tag: be705bf8-941b-4c35-84fc-ad7d20ddb7cb | |
1492 | @end ignore |