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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, | |
6ed161e1 | 4 | @c 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/characters |
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7 | @node Non-ASCII Characters, Searching and Matching, Text, Top |
8 | @chapter Non-@acronym{ASCII} Characters | |
9 | @cindex multibyte characters | |
10 | @cindex characters, multi-byte | |
11 | @cindex non-@acronym{ASCII} characters | |
12 | ||
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13 | This chapter covers the special issues relating to characters and |
14 | how they are stored in strings and buffers. | |
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15 | |
16 | @menu | |
c4526e93 | 17 | * Text Representations:: How Emacs represents text. |
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18 | * Converting Representations:: Converting unibyte to multibyte and vice versa. |
19 | * Selecting a Representation:: Treating a byte sequence as unibyte or multi. | |
20 | * Character Codes:: How unibyte and multibyte relate to | |
21 | codes of individual characters. | |
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22 | * Character Properties:: Character attributes that define their |
23 | behavior and handling. | |
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24 | * Character Sets:: The space of possible character codes |
25 | is divided into various character sets. | |
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26 | * Scanning Charsets:: Which character sets are used in a buffer? |
27 | * Translation of Characters:: Translation tables are used for conversion. | |
28 | * Coding Systems:: Coding systems are conversions for saving files. | |
29 | * Input Methods:: Input methods allow users to enter various | |
30 | non-ASCII characters without special keyboards. | |
31 | * Locales:: Interacting with the POSIX locale. | |
32 | @end menu | |
33 | ||
34 | @node Text Representations | |
35 | @section Text Representations | |
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36 | @cindex text representation |
37 | ||
38 | Emacs buffers and strings support a large repertoire of characters | |
39 | from many different scripts. This is so users could type and display | |
40 | text in most any known written language. | |
41 | ||
42 | @cindex character codepoint | |
43 | @cindex codespace | |
44 | @cindex Unicode | |
45 | To support this multitude of characters and scripts, Emacs closely | |
46 | follows the @dfn{Unicode Standard}. The Unicode Standard assigns a | |
47 | unique number, called a @dfn{codepoint}, to each and every character. | |
48 | The range of codepoints defined by Unicode, or the Unicode | |
8b80cdf5 | 49 | @dfn{codespace}, is @code{0..10FFFF} (in hex), inclusive. Emacs |
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50 | extends this range with codepoints in the range @code{110000..3FFFFF}, |
51 | which it uses for representing characters that are not unified with | |
52 | Unicode and raw 8-bit bytes that cannot be interpreted as characters | |
53 | (the latter occupy the range @code{3FFF80..3FFFFF}). Thus, a | |
54 | character codepoint in Emacs is a 22-bit integer number. | |
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55 | |
56 | @cindex internal representation of characters | |
57 | @cindex characters, representation in buffers and strings | |
58 | @cindex multibyte text | |
59 | To conserve memory, Emacs does not hold fixed-length 22-bit numbers | |
60 | that are codepoints of text characters within buffers and strings. | |
61 | Rather, Emacs uses a variable-length internal representation of | |
62 | characters, that stores each character as a sequence of 1 to 5 8-bit | |
63 | bytes, depending on the magnitude of its codepoint@footnote{ | |
64 | This internal representation is based on one of the encodings defined | |
65 | by the Unicode Standard, called @dfn{UTF-8}, for representing any | |
66 | Unicode codepoint, but Emacs extends UTF-8 to represent the additional | |
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67 | codepoints it uses for raw 8-bit bytes and characters not unified with |
68 | Unicode.}. | |
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69 | For example, any @acronym{ASCII} character takes up only 1 byte, a |
70 | Latin-1 character takes up 2 bytes, etc. We call this representation | |
71 | of text @dfn{multibyte}, because it uses several bytes for each | |
72 | character. | |
73 | ||
74 | Outside Emacs, characters can be represented in many different | |
75 | encodings, such as ISO-8859-1, GB-2312, Big-5, etc. Emacs converts | |
76 | between these external encodings and the internal representation, as | |
77 | appropriate, when it reads text into a buffer or a string, or when it | |
78 | writes text to a disk file or passes it to some other process. | |
79 | ||
80 | Occasionally, Emacs needs to hold and manipulate encoded text or | |
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81 | binary non-text data in its buffers or strings. For example, when |
82 | Emacs visits a file, it first reads the file's text verbatim into a | |
83 | buffer, and only then converts it to the internal representation. | |
84 | Before the conversion, the buffer holds encoded text. | |
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85 | |
86 | @cindex unibyte text | |
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87 | Encoded text is not really text, as far as Emacs is concerned, but |
88 | rather a sequence of raw 8-bit bytes. We call buffers and strings | |
89 | that hold encoded text @dfn{unibyte} buffers and strings, because | |
90 | Emacs treats them as a sequence of individual bytes. In particular, | |
91 | Emacs usually displays unibyte buffers and strings as octal codes such | |
92 | as @code{\237}. We recommend that you never use unibyte buffers and | |
93 | strings except for manipulating encoded text or binary non-text data. | |
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94 | |
95 | In a buffer, the buffer-local value of the variable | |
96 | @code{enable-multibyte-characters} specifies the representation used. | |
97 | The representation for a string is determined and recorded in the string | |
98 | when the string is constructed. | |
99 | ||
100 | @defvar enable-multibyte-characters | |
101 | This variable specifies the current buffer's text representation. | |
102 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
c4526e93 | 103 | it contains unibyte encoded text or binary non-text data. |
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104 | |
105 | You cannot set this variable directly; instead, use the function | |
106 | @code{set-buffer-multibyte} to change a buffer's representation. | |
107 | @end defvar | |
108 | ||
109 | @defvar default-enable-multibyte-characters | |
110 | This variable's value is entirely equivalent to @code{(default-value | |
111 | 'enable-multibyte-characters)}, and setting this variable changes that | |
112 | default value. Setting the local binding of | |
113 | @code{enable-multibyte-characters} in a specific buffer is not allowed, | |
114 | but changing the default value is supported, and it is a reasonable | |
115 | thing to do, because it has no effect on existing buffers. | |
116 | ||
117 | The @samp{--unibyte} command line option does its job by setting the | |
118 | default value to @code{nil} early in startup. | |
119 | @end defvar | |
120 | ||
121 | @defun position-bytes position | |
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122 | Buffer positions are measured in character units. This function |
123 | returns the byte-position corresponding to buffer position | |
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124 | @var{position} in the current buffer. This is 1 at the start of the |
125 | buffer, and counts upward in bytes. If @var{position} is out of | |
126 | range, the value is @code{nil}. | |
127 | @end defun | |
128 | ||
129 | @defun byte-to-position byte-position | |
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130 | Return the buffer position, in character units, corresponding to given |
131 | @var{byte-position} in the current buffer. If @var{byte-position} is | |
132 | out of range, the value is @code{nil}. In a multibyte buffer, an | |
133 | arbitrary value of @var{byte-position} can be not at character | |
134 | boundary, but inside a multibyte sequence representing a single | |
135 | character; in this case, this function returns the buffer position of | |
136 | the character whose multibyte sequence includes @var{byte-position}. | |
137 | In other words, the value does not change for all byte positions that | |
138 | belong to the same character. | |
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139 | @end defun |
140 | ||
141 | @defun multibyte-string-p string | |
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142 | Return @code{t} if @var{string} is a multibyte string, @code{nil} |
143 | otherwise. | |
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144 | @end defun |
145 | ||
146 | @defun string-bytes string | |
147 | @cindex string, number of bytes | |
148 | This function returns the number of bytes in @var{string}. | |
149 | If @var{string} is a multibyte string, this can be greater than | |
150 | @code{(length @var{string})}. | |
151 | @end defun | |
152 | ||
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153 | @defun unibyte-string &rest bytes |
154 | This function concatenates all its argument @var{bytes} and makes the | |
155 | result a unibyte string. | |
156 | @end defun | |
157 | ||
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158 | @node Converting Representations |
159 | @section Converting Text Representations | |
160 | ||
161 | Emacs can convert unibyte text to multibyte; it can also convert | |
031c41de | 162 | multibyte text to unibyte, provided that the multibyte text contains |
8b80cdf5 | 163 | only @acronym{ASCII} and 8-bit raw bytes. In general, these |
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164 | conversions happen when inserting text into a buffer, or when putting |
165 | text from several strings together in one string. You can also | |
166 | explicitly convert a string's contents to either representation. | |
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167 | |
168 | Emacs chooses the representation for a string based on the text that | |
169 | it is constructed from. The general rule is to convert unibyte text to | |
170 | multibyte text when combining it with other multibyte text, because the | |
171 | multibyte representation is more general and can hold whatever | |
172 | characters the unibyte text has. | |
173 | ||
174 | When inserting text into a buffer, Emacs converts the text to the | |
175 | buffer's representation, as specified by | |
176 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
177 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
178 | to unibyte, even though this conversion cannot in general preserve all | |
179 | the characters that might be in the multibyte text. The other natural | |
180 | alternative, to convert the buffer contents to multibyte, is not | |
181 | acceptable because the buffer's representation is a choice made by the | |
182 | user that cannot be overridden automatically. | |
183 | ||
184 | Converting unibyte text to multibyte text leaves @acronym{ASCII} characters | |
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185 | unchanged, and converts bytes with codes 128 through 159 to the |
186 | multibyte representation of raw eight-bit bytes. | |
b8d4c8d0 | 187 | |
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188 | Converting multibyte text to unibyte converts all @acronym{ASCII} |
189 | and eight-bit characters to their single-byte form, but loses | |
190 | information for non-@acronym{ASCII} characters by discarding all but | |
191 | the low 8 bits of each character's codepoint. Converting unibyte text | |
192 | to multibyte and back to unibyte reproduces the original unibyte text. | |
b8d4c8d0 | 193 | |
031c41de | 194 | The next two functions either return the argument @var{string}, or a |
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195 | newly created string with no text properties. |
196 | ||
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197 | @defun string-to-multibyte string |
198 | This function returns a multibyte string containing the same sequence | |
031c41de | 199 | of characters as @var{string}. If @var{string} is a multibyte string, |
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200 | it is returned unchanged. The function assumes that @var{string} |
201 | includes only @acronym{ASCII} characters and raw 8-bit bytes; the | |
202 | latter are converted to their multibyte representation corresponding | |
203 | to the codepoints in the @code{3FFF80..3FFFFF} area (@pxref{Text | |
204 | Representations, codepoints}). | |
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205 | @end defun |
206 | ||
207 | @defun string-to-unibyte string | |
208 | This function returns a unibyte string containing the same sequence of | |
209 | characters as @var{string}. It signals an error if @var{string} | |
210 | contains a non-@acronym{ASCII} character. If @var{string} is a | |
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211 | unibyte string, it is returned unchanged. Use this function for |
212 | @var{string} arguments that contain only @acronym{ASCII} and eight-bit | |
213 | characters. | |
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214 | @end defun |
215 | ||
216 | @defun multibyte-char-to-unibyte char | |
217 | This convert the multibyte character @var{char} to a unibyte | |
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218 | character. If @var{char} is a character that is neither |
219 | @acronym{ASCII} nor eight-bit, the value is -1. | |
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220 | @end defun |
221 | ||
222 | @defun unibyte-char-to-multibyte char | |
223 | This convert the unibyte character @var{char} to a multibyte | |
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224 | character, assuming @var{char} is either @acronym{ASCII} or raw 8-bit |
225 | byte. | |
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226 | @end defun |
227 | ||
228 | @node Selecting a Representation | |
229 | @section Selecting a Representation | |
230 | ||
231 | Sometimes it is useful to examine an existing buffer or string as | |
232 | multibyte when it was unibyte, or vice versa. | |
233 | ||
234 | @defun set-buffer-multibyte multibyte | |
235 | Set the representation type of the current buffer. If @var{multibyte} | |
236 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
237 | is @code{nil}, the buffer becomes unibyte. | |
238 | ||
239 | This function leaves the buffer contents unchanged when viewed as a | |
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240 | sequence of bytes. As a consequence, it can change the contents |
241 | viewed as characters; a sequence of three bytes which is treated as | |
242 | one character in multibyte representation will count as three | |
243 | characters in unibyte representation. Eight-bit characters | |
244 | representing raw bytes are an exception. They are represented by one | |
245 | byte in a unibyte buffer, but when the buffer is set to multibyte, | |
246 | they are converted to two-byte sequences, and vice versa. | |
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247 | |
248 | This function sets @code{enable-multibyte-characters} to record which | |
249 | representation is in use. It also adjusts various data in the buffer | |
250 | (including overlays, text properties and markers) so that they cover the | |
251 | same text as they did before. | |
252 | ||
253 | You cannot use @code{set-buffer-multibyte} on an indirect buffer, | |
254 | because indirect buffers always inherit the representation of the | |
255 | base buffer. | |
256 | @end defun | |
257 | ||
258 | @defun string-as-unibyte string | |
259 | This function returns a string with the same bytes as @var{string} but | |
260 | treating each byte as a character. This means that the value may have | |
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261 | more characters than @var{string} has. Eight-bit characters |
262 | representing raw bytes are an exception: each one of them is converted | |
263 | to a single byte. | |
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264 | |
265 | If @var{string} is already a unibyte string, then the value is | |
266 | @var{string} itself. Otherwise it is a newly created string, with no | |
031c41de | 267 | text properties. |
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268 | @end defun |
269 | ||
270 | @defun string-as-multibyte string | |
271 | This function returns a string with the same bytes as @var{string} but | |
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272 | treating each multibyte sequence as one character. This means that |
273 | the value may have fewer characters than @var{string} has. If a byte | |
274 | sequence in @var{string} is invalid as a multibyte representation of a | |
275 | single character, each byte in the sequence is treated as raw 8-bit | |
276 | byte. | |
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277 | |
278 | If @var{string} is already a multibyte string, then the value is | |
279 | @var{string} itself. Otherwise it is a newly created string, with no | |
031c41de | 280 | text properties. |
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281 | @end defun |
282 | ||
283 | @node Character Codes | |
284 | @section Character Codes | |
285 | @cindex character codes | |
286 | ||
ffdbc44b CY |
287 | The unibyte and multibyte text representations use different |
288 | character codes. The valid character codes for unibyte representation | |
289 | range from 0 to 255---the values that can fit in one byte. The valid | |
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290 | character codes for multibyte representation range from 0 to 4194303 |
291 | (#x3FFFFF). In this code space, values 0 through 127 are for | |
292 | @acronym{ASCII} charcters, and values 129 through 4194175 (#x3FFF7F) | |
293 | are for non-@acronym{ASCII} characters. Values 0 through 1114111 | |
294 | (#10FFFF) corresponds to Unicode characters of the same codepoint, | |
295 | while values 4194176 (#x3FFF80) through 4194303 (#x3FFFFF) are for | |
296 | representing eight-bit raw bytes. | |
ffdbc44b CY |
297 | |
298 | @defun characterp charcode | |
299 | This returns @code{t} if @var{charcode} is a valid character, and | |
300 | @code{nil} otherwise. | |
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301 | |
302 | @example | |
80070260 | 303 | @group |
ffdbc44b | 304 | (characterp 65) |
b8d4c8d0 | 305 | @result{} t |
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306 | @end group |
307 | @group | |
ffdbc44b | 308 | (characterp 4194303) |
b8d4c8d0 | 309 | @result{} t |
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310 | @end group |
311 | @group | |
ffdbc44b CY |
312 | (characterp 4194304) |
313 | @result{} nil | |
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314 | @end group |
315 | @end example | |
316 | @end defun | |
317 | ||
318 | @cindex maximum value of character codepoint | |
319 | @cindex codepoint, largest value | |
320 | @defun max-char | |
321 | This function returns the largest value that a valid character | |
322 | codepoint can have. | |
323 | ||
324 | @example | |
325 | @group | |
326 | (characterp (max-char)) | |
327 | @result{} t | |
328 | @end group | |
329 | @group | |
330 | (characterp (1+ (max-char))) | |
331 | @result{} nil | |
332 | @end group | |
b8d4c8d0 | 333 | @end example |
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334 | @end defun |
335 | ||
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336 | @defun get-byte pos &optional string |
337 | This function returns the byte at current buffer's character position | |
338 | @var{pos}. If the current buffer is unibyte, this is literally the | |
339 | byte at that position. If the buffer is multibyte, byte values of | |
340 | @acronym{ASCII} characters are the same as character codepoints, | |
341 | whereas eight-bit raw bytes are converted to their 8-bit codes. The | |
342 | function signals an error if the character at @var{pos} is | |
343 | non-@acronym{ASCII}. | |
344 | ||
345 | The optional argument @var{string} means to get a byte value from that | |
346 | string instead of the current buffer. | |
347 | @end defun | |
348 | ||
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349 | @node Character Properties |
350 | @section Character Properties | |
351 | @cindex character properties | |
352 | A @dfn{character property} is a named attribute of a character that | |
353 | specifies how the character behaves and how it should be handled | |
354 | during text processing and display. Thus, character properties are an | |
355 | important part of specifying the character's semantics. | |
356 | ||
357 | Emacs generally follows the Unicode Standard in its implementation | |
358 | of character properties. In particular, Emacs supports the | |
359 | @uref{http://www.unicode.org/reports/tr23/, Unicode Character Property | |
360 | Model}, and the Emacs character property database is derived from the | |
361 | Unicode Character Database (@acronym{UCD}). See the | |
362 | @uref{http://www.unicode.org/versions/Unicode5.0.0/ch04.pdf, Character | |
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363 | Properties chapter of the Unicode Standard}, for detailed description |
364 | of Unicode character properties and their meaning. This section | |
365 | assumes you are already familiar with that chapter of the Unicode | |
366 | Standard, and want to apply that knowledge to Emacs Lisp programs. | |
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367 | |
368 | The facilities documented in this section are useful for setting and | |
369 | retrieving properties of characters. | |
370 | ||
371 | In Emacs, each property has a name, which is a symbol, and a set of | |
af38459f | 372 | possible values, whose types depend on the property; if a character |
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373 | does not have a certain property, the value is @code{nil}. As a |
374 | general rule, the names of character properties in Emacs are produced | |
375 | from the corresponding Unicode properties by downcasing them and | |
376 | replacing each @samp{_} character with a dash @samp{-}. For example, | |
377 | @code{Canonical_Combining_Class} becomes | |
378 | @code{canonical-combining-class}. However, sometimes we shorten the | |
379 | names to make their use easier. | |
380 | ||
381 | Here's the full list of value types for all the character properties | |
382 | that Emacs knows about: | |
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383 | |
384 | @table @code | |
385 | @item name | |
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386 | This property corresponds to the Unicode @code{Name} property. The |
387 | value is a string consisting of upper-case Latin letters A to Z, | |
388 | digits, spaces, and hyphen @samp{-} characters. | |
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389 | |
390 | @item general-category | |
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391 | This property corresponds to the Unicode @code{General_Category} |
392 | property. The value is a symbol whose name is a 2-letter abbreviation | |
393 | of the character's classification. | |
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394 | |
395 | @item canonical-combining-class | |
af38459f EZ |
396 | Corresponds to the Unicode @code{Canonical_Combining_Class} property. |
397 | The value is an integer number. | |
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398 | |
399 | @item bidi-class | |
af38459f EZ |
400 | Corresponds to the Unicode @code{Bidi_Class} property. The value is a |
401 | symbol whose name is the Unicode @dfn{directional type} of the | |
402 | character. | |
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403 | |
404 | @item decomposition | |
af38459f EZ |
405 | Corresponds to the Unicode @code{Decomposition_Type} and |
406 | @code{Decomposition_Value} properties. The value is a list, whose | |
407 | first element may be a symbol representing a compatibility formatting | |
408 | tag, such as @code{small}@footnote{ | |
c06ea95e EZ |
409 | Note that the Unicode spec writes these tag names inside |
410 | @samp{<..>} brackets. The tag names in Emacs do not include the | |
411 | brackets; e.g., Unicode specifies @samp{<small>} where Emacs uses | |
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412 | @samp{small}. |
413 | }; the other elements are characters that give the compatibility | |
414 | decomposition sequence of this character. | |
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415 | |
416 | @item decimal-digit-value | |
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417 | Corresponds to the Unicode @code{Numeric_Value} property for |
418 | characters whose @code{Numeric_Type} is @samp{Digit}. The value is an | |
419 | integer number. | |
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420 | |
421 | @item digit | |
af38459f EZ |
422 | Corresponds to the Unicode @code{Numeric_Value} property for |
423 | characters whose @code{Numeric_Type} is @samp{Decimal}. The value is | |
424 | an integer number. Examples of such characters include compatibility | |
425 | subscript and superscript digits, for which the value is the | |
426 | corresponding number. | |
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427 | |
428 | @item numeric-value | |
af38459f EZ |
429 | Corresponds to the Unicode @code{Numeric_Value} property for |
430 | characters whose @code{Numeric_Type} is @samp{Numeric}. The value of | |
431 | this property is an integer of a floating-point number. Examples of | |
432 | characters that have this property include fractions, subscripts, | |
91211f07 | 433 | superscripts, Roman numerals, currency numerators, and encircled |
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434 | numbers. For example, the value of this property for the character |
435 | @code{U+2155} (@sc{vulgar fraction one fifth}) is @code{0.2}. | |
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436 | |
437 | @item mirrored | |
af38459f | 438 | Corresponds to the Unicode @code{Bidi_Mirrored} property. The value |
c06ea95e | 439 | of this property is a symbol, either @code{Y} or @code{N}. |
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440 | |
441 | @item old-name | |
af38459f EZ |
442 | Corresponds to the Unicode @code{Unicode_1_Name} property. The value |
443 | is a string. | |
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444 | |
445 | @item iso-10646-comment | |
af38459f EZ |
446 | Corresponds to the Unicode @code{ISO_Comment} property. The value is |
447 | a string. | |
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448 | |
449 | @item uppercase | |
af38459f EZ |
450 | Corresponds to the Unicode @code{Simple_Uppercase_Mapping} property. |
451 | The value of this property is a single character. | |
91211f07 EZ |
452 | |
453 | @item lowercase | |
af38459f EZ |
454 | Corresponds to the Unicode @code{Simple_Lowercase_Mapping} property. |
455 | The value of this property is a single character. | |
91211f07 EZ |
456 | |
457 | @item titlecase | |
af38459f | 458 | Corresponds to the Unicode @code{Simple_Titlecase_Mapping} property. |
91211f07 | 459 | @dfn{Title case} is a special form of a character used when the first |
af38459f EZ |
460 | character of a word needs to be capitalized. The value of this |
461 | property is a single character. | |
91211f07 EZ |
462 | @end table |
463 | ||
464 | @defun get-char-code-property char propname | |
465 | This function returns the value of @var{char}'s @var{propname} property. | |
466 | ||
467 | @example | |
468 | @group | |
469 | (get-char-code-property ? 'general-category) | |
470 | @result{} Zs | |
471 | @end group | |
472 | @group | |
473 | (get-char-code-property ?1 'general-category) | |
474 | @result{} Nd | |
475 | @end group | |
476 | @group | |
477 | (get-char-code-property ?\u2084 'digit-value) ; subscript 4 | |
478 | @result{} 4 | |
479 | @end group | |
480 | @group | |
481 | (get-char-code-property ?\u2155 'numeric-value) ; one fifth | |
482 | @result{} 1/5 | |
483 | @end group | |
484 | @group | |
485 | (get-char-code-property ?\u2163 'numeric-value) ; Roman IV | |
486 | @result{} \4 | |
487 | @end group | |
488 | @end example | |
489 | @end defun | |
490 | ||
491 | @defun char-code-property-description prop value | |
492 | This function returns the description string of property @var{prop}'s | |
493 | @var{value}, or @code{nil} if @var{value} has no description. | |
494 | ||
495 | @example | |
496 | @group | |
497 | (char-code-property-description 'general-category 'Zs) | |
498 | @result{} "Separator, Space" | |
499 | @end group | |
500 | @group | |
501 | (char-code-property-description 'general-category 'Nd) | |
502 | @result{} "Number, Decimal Digit" | |
503 | @end group | |
504 | @group | |
505 | (char-code-property-description 'numeric-value '1/5) | |
506 | @result{} nil | |
507 | @end group | |
508 | @end example | |
509 | @end defun | |
510 | ||
511 | @defun put-char-code-property char propname value | |
512 | This function stores @var{value} as the value of the property | |
513 | @var{propname} for the character @var{char}. | |
514 | @end defun | |
515 | ||
516 | @defvar char-script-table | |
517 | The value of this variable is a char-table (@pxref{Char-Tables}) that | |
518 | specifies, for each character, a symbol whose name is the script to | |
519 | which the character belongs, according to the Unicode Standard | |
520 | classification of the Unicode code space into script-specific blocks. | |
521 | This char-table has a single extra slot whose value is the list of all | |
522 | script symbols. | |
523 | @end defvar | |
524 | ||
525 | @defvar char-width-table | |
526 | The value of this variable is a char-table that specifies the width of | |
527 | each character in columns that it will occupy on the screen. | |
528 | @end defvar | |
529 | ||
530 | @defvar printable-chars | |
531 | The value of this variable is a char-table that specifies, for each | |
532 | character, whether it is printable or not. That is, if evaluating | |
533 | @code{(aref printable-chars char)} results in @code{t}, the character | |
534 | is printable, and if it results in @code{nil}, it is not. | |
535 | @end defvar | |
536 | ||
b8d4c8d0 GM |
537 | @node Character Sets |
538 | @section Character Sets | |
539 | @cindex character sets | |
540 | ||
031c41de EZ |
541 | @cindex charset |
542 | @cindex coded character set | |
543 | An Emacs @dfn{character set}, or @dfn{charset}, is a set of characters | |
544 | in which each character is assigned a numeric code point. (The | |
8b80cdf5 | 545 | Unicode standard calls this a @dfn{coded character set}.) Each Emacs |
031c41de EZ |
546 | charset has a name which is a symbol. A single character can belong |
547 | to any number of different character sets, but it will generally have | |
548 | a different code point in each charset. Examples of character sets | |
549 | include @code{ascii}, @code{iso-8859-1}, @code{greek-iso8859-7}, and | |
550 | @code{windows-1255}. The code point assigned to a character in a | |
551 | charset is usually different from its code point used in Emacs buffers | |
552 | and strings. | |
553 | ||
554 | @cindex @code{emacs}, a charset | |
555 | @cindex @code{unicode}, a charset | |
556 | @cindex @code{eight-bit}, a charset | |
557 | Emacs defines several special character sets. The character set | |
558 | @code{unicode} includes all the characters whose Emacs code points are | |
559 | in the range @code{0..10FFFF}. The character set @code{emacs} | |
560 | includes all @acronym{ASCII} and non-@acronym{ASCII} characters. | |
561 | Finally, the @code{eight-bit} charset includes the 8-bit raw bytes; | |
562 | Emacs uses it to represent raw bytes encountered in text. | |
b8d4c8d0 GM |
563 | |
564 | @defun charsetp object | |
565 | Returns @code{t} if @var{object} is a symbol that names a character set, | |
566 | @code{nil} otherwise. | |
567 | @end defun | |
568 | ||
569 | @defvar charset-list | |
570 | The value is a list of all defined character set names. | |
571 | @end defvar | |
572 | ||
031c41de EZ |
573 | @defun charset-priority-list &optional highestp |
574 | This functions returns a list of all defined character sets ordered by | |
575 | their priority. If @var{highestp} is non-@code{nil}, the function | |
576 | returns a single character set of the highest priority. | |
577 | @end defun | |
578 | ||
579 | @defun set-charset-priority &rest charsets | |
580 | This function makes @var{charsets} the highest priority character sets. | |
b8d4c8d0 GM |
581 | @end defun |
582 | ||
583 | @defun char-charset character | |
031c41de EZ |
584 | This function returns the name of the character set of highest |
585 | priority that @var{character} belongs to. @acronym{ASCII} characters | |
586 | are an exception: for them, this function always returns @code{ascii}. | |
b8d4c8d0 GM |
587 | @end defun |
588 | ||
589 | @defun charset-plist charset | |
031c41de EZ |
590 | This function returns the property list of the character set |
591 | @var{charset}. Although @var{charset} is a symbol, this is not the | |
592 | same as the property list of that symbol. Charset properties include | |
593 | important information about the charset, such as its documentation | |
594 | string, short name, etc. | |
b8d4c8d0 GM |
595 | @end defun |
596 | ||
031c41de EZ |
597 | @defun put-charset-property charset propname value |
598 | This function sets the @var{propname} property of @var{charset} to the | |
599 | given @var{value}. | |
b8d4c8d0 GM |
600 | @end defun |
601 | ||
031c41de EZ |
602 | @defun get-charset-property charset propname |
603 | This function returns the value of @var{charset}s property | |
604 | @var{propname}. | |
b8d4c8d0 GM |
605 | @end defun |
606 | ||
031c41de EZ |
607 | @deffn Command list-charset-chars charset |
608 | This command displays a list of characters in the character set | |
609 | @var{charset}. | |
610 | @end deffn | |
b8d4c8d0 | 611 | |
8b80cdf5 EZ |
612 | Emacs can convert between its internal representation of a character |
613 | and the character's codepoint in a specific charset. The following | |
614 | two functions support these conversions. | |
615 | ||
616 | @c FIXME: decode-char and encode-char accept and ignore an additional | |
617 | @c argument @var{restriction}. When that argument actually makes a | |
618 | @c difference, it should be documented here. | |
031c41de EZ |
619 | @defun decode-char charset code-point |
620 | This function decodes a character that is assigned a @var{code-point} | |
621 | in @var{charset}, to the corresponding Emacs character, and returns | |
8b80cdf5 EZ |
622 | it. If @var{charset} doesn't contain a character of that code point, |
623 | the value is @code{nil}. If @var{code-point} doesn't fit in a Lisp | |
624 | integer (@pxref{Integer Basics, most-positive-fixnum}), it can be | |
625 | specified as a cons cell @code{(@var{high} . @var{low})}, where | |
031c41de EZ |
626 | @var{low} are the lower 16 bits of the value and @var{high} are the |
627 | high 16 bits. | |
b8d4c8d0 GM |
628 | @end defun |
629 | ||
031c41de EZ |
630 | @defun encode-char char charset |
631 | This function returns the code point assigned to the character | |
8b80cdf5 EZ |
632 | @var{char} in @var{charset}. If the result does not fit in a Lisp |
633 | integer, it is returned as a cons cell @code{(@var{high} . @var{low})} | |
634 | that fits the second argument of @code{decode-char} above. If | |
635 | @var{charset} doesn't have a codepoint for @var{char}, the value is | |
636 | @code{nil}. | |
b3f1f4a5 EZ |
637 | @end defun |
638 | ||
639 | The following function comes in handy for applying a certain | |
640 | function to all or part of the characters in a charset: | |
641 | ||
642 | @defun map-charset-chars function charset &optional arg from to | |
643 | Call @var{function} for characters in @var{charset}. @var{function} | |
644 | is called with two arguments. The first one is a cons cell | |
645 | @code{(@var{from} . @var{to})}, where @var{from} and @var{to} | |
646 | indicate a range of characters contained in charset. The second | |
647 | argument is the optional argument @var{arg}. | |
648 | ||
649 | By default, the range of codepoints passed to @var{function} includes | |
650 | all the characters in @var{charset}, but optional arguments @var{from} | |
651 | and @var{to} limit that to the range of characters between these two | |
652 | codepoints. If either of them is @code{nil}, it defaults to the first | |
653 | or last codepoint of @var{charset}, respectively. | |
b8d4c8d0 GM |
654 | @end defun |
655 | ||
b8d4c8d0 GM |
656 | @node Scanning Charsets |
657 | @section Scanning for Character Sets | |
658 | ||
8b80cdf5 EZ |
659 | Sometimes it is useful to find out, for characters that appear in a |
660 | certain part of a buffer or a string, to which character sets they | |
661 | belong. One use for this is in determining which coding systems | |
662 | (@pxref{Coding Systems}) are capable of representing all of the text | |
663 | in question; another is to determine the font(s) for displaying that | |
664 | text. | |
b8d4c8d0 GM |
665 | |
666 | @defun charset-after &optional pos | |
031c41de EZ |
667 | This function returns the charset of highest priority containing the |
668 | character in the current buffer at position @var{pos}. If @var{pos} | |
669 | is omitted or @code{nil}, it defaults to the current value of point. | |
670 | If @var{pos} is out of range, the value is @code{nil}. | |
b8d4c8d0 GM |
671 | @end defun |
672 | ||
673 | @defun find-charset-region beg end &optional translation | |
031c41de | 674 | This function returns a list of the character sets of highest priority |
8b80cdf5 | 675 | that contain characters in the current buffer between positions |
031c41de | 676 | @var{beg} and @var{end}. |
b8d4c8d0 GM |
677 | |
678 | The optional argument @var{translation} specifies a translation table to | |
679 | be used in scanning the text (@pxref{Translation of Characters}). If it | |
680 | is non-@code{nil}, then each character in the region is translated | |
681 | through this table, and the value returned describes the translated | |
682 | characters instead of the characters actually in the buffer. | |
683 | @end defun | |
684 | ||
685 | @defun find-charset-string string &optional translation | |
031c41de EZ |
686 | This function returns a list of the character sets of highest priority |
687 | that contain characters in @var{string}. It is just like | |
688 | @code{find-charset-region}, except that it applies to the contents of | |
689 | @var{string} instead of part of the current buffer. | |
b8d4c8d0 GM |
690 | @end defun |
691 | ||
692 | @node Translation of Characters | |
693 | @section Translation of Characters | |
694 | @cindex character translation tables | |
695 | @cindex translation tables | |
696 | ||
031c41de EZ |
697 | A @dfn{translation table} is a char-table (@pxref{Char-Tables}) that |
698 | specifies a mapping of characters into characters. These tables are | |
699 | used in encoding and decoding, and for other purposes. Some coding | |
700 | systems specify their own particular translation tables; there are | |
701 | also default translation tables which apply to all other coding | |
702 | systems. | |
b8d4c8d0 | 703 | |
031c41de EZ |
704 | A translation table has two extra slots. The first is either |
705 | @code{nil} or a translation table that performs the reverse | |
706 | translation; the second is the maximum number of characters to look up | |
8b80cdf5 EZ |
707 | for translating sequences of characters (see the description of |
708 | @code{make-translation-table-from-alist} below). | |
b8d4c8d0 GM |
709 | |
710 | @defun make-translation-table &rest translations | |
711 | This function returns a translation table based on the argument | |
712 | @var{translations}. Each element of @var{translations} should be a | |
713 | list of elements of the form @code{(@var{from} . @var{to})}; this says | |
714 | to translate the character @var{from} into @var{to}. | |
715 | ||
716 | The arguments and the forms in each argument are processed in order, | |
717 | and if a previous form already translates @var{to} to some other | |
718 | character, say @var{to-alt}, @var{from} is also translated to | |
719 | @var{to-alt}. | |
b8d4c8d0 GM |
720 | @end defun |
721 | ||
031c41de EZ |
722 | During decoding, the translation table's translations are applied to |
723 | the characters that result from ordinary decoding. If a coding system | |
724 | has property @code{:decode-translation-table}, that specifies the | |
725 | translation table to use, or a list of translation tables to apply in | |
726 | sequence. (This is a property of the coding system, as returned by | |
727 | @code{coding-system-get}, not a property of the symbol that is the | |
728 | coding system's name. @xref{Coding System Basics,, Basic Concepts of | |
729 | Coding Systems}.) Finally, if | |
730 | @code{standard-translation-table-for-decode} is non-@code{nil}, the | |
731 | resulting characters are translated by that table. | |
732 | ||
733 | During encoding, the translation table's translations are applied to | |
734 | the characters in the buffer, and the result of translation is | |
735 | actually encoded. If a coding system has property | |
736 | @code{:encode-translation-table}, that specifies the translation table | |
737 | to use, or a list of translation tables to apply in sequence. In | |
738 | addition, if the variable @code{standard-translation-table-for-encode} | |
739 | is non-@code{nil}, it specifies the translation table to use for | |
740 | translating the result. | |
b8d4c8d0 GM |
741 | |
742 | @defvar standard-translation-table-for-decode | |
031c41de EZ |
743 | This is the default translation table for decoding. If a coding |
744 | systems specifies its own translation tables, the table that is the | |
745 | value of this variable, if non-@code{nil}, is applied after them. | |
b8d4c8d0 GM |
746 | @end defvar |
747 | ||
748 | @defvar standard-translation-table-for-encode | |
031c41de EZ |
749 | This is the default translation table for encoding. If a coding |
750 | systems specifies its own translation tables, the table that is the | |
751 | value of this variable, if non-@code{nil}, is applied after them. | |
b8d4c8d0 GM |
752 | @end defvar |
753 | ||
5c9c5c4b EZ |
754 | @defvar translation-table-for-input |
755 | Self-inserting characters are translated through this translation | |
756 | table before they are inserted. Search commands also translate their | |
757 | input through this table, so they can compare more reliably with | |
758 | what's in the buffer. | |
759 | ||
760 | This variable automatically becomes buffer-local when set. | |
761 | @end defvar | |
762 | ||
031c41de EZ |
763 | @defun make-translation-table-from-vector vec |
764 | This function returns a translation table made from @var{vec} that is | |
765 | an array of 256 elements to map byte values 0 through 255 to | |
766 | characters. Elements may be @code{nil} for untranslated bytes. The | |
767 | returned table has a translation table for reverse mapping in the | |
8b80cdf5 | 768 | first extra slot, and the value @code{1} in the second extra slot. |
031c41de EZ |
769 | |
770 | This function provides an easy way to make a private coding system | |
771 | that maps each byte to a specific character. You can specify the | |
772 | returned table and the reverse translation table using the properties | |
773 | @code{:decode-translation-table} and @code{:encode-translation-table} | |
774 | respectively in the @var{props} argument to | |
775 | @code{define-coding-system}. | |
776 | @end defun | |
777 | ||
778 | @defun make-translation-table-from-alist alist | |
779 | This function is similar to @code{make-translation-table} but returns | |
780 | a complex translation table rather than a simple one-to-one mapping. | |
781 | Each element of @var{alist} is of the form @code{(@var{from} | |
782 | . @var{to})}, where @var{from} and @var{to} are either a character or | |
783 | a vector specifying a sequence of characters. If @var{from} is a | |
784 | character, that character is translated to @var{to} (i.e.@: to a | |
785 | character or a character sequence). If @var{from} is a vector of | |
786 | characters, that sequence is translated to @var{to}. The returned | |
787 | table has a translation table for reverse mapping in the first extra | |
8b80cdf5 EZ |
788 | slot, and the maximum length of all the @var{from} character sequences |
789 | in the second extra slot. | |
031c41de EZ |
790 | @end defun |
791 | ||
b8d4c8d0 GM |
792 | @node Coding Systems |
793 | @section Coding Systems | |
794 | ||
795 | @cindex coding system | |
796 | When Emacs reads or writes a file, and when Emacs sends text to a | |
797 | subprocess or receives text from a subprocess, it normally performs | |
798 | character code conversion and end-of-line conversion as specified | |
799 | by a particular @dfn{coding system}. | |
800 | ||
801 | How to define a coding system is an arcane matter, and is not | |
802 | documented here. | |
803 | ||
804 | @menu | |
805 | * Coding System Basics:: Basic concepts. | |
806 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
807 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
808 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
809 | * Default Coding Systems:: Controlling the default choices. | |
810 | * Specifying Coding Systems:: Requesting a particular coding system | |
811 | for a single file operation. | |
812 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
813 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
814 | * MS-DOS File Types:: How DOS "text" and "binary" files | |
815 | relate to coding systems. | |
816 | @end menu | |
817 | ||
818 | @node Coding System Basics | |
819 | @subsection Basic Concepts of Coding Systems | |
820 | ||
821 | @cindex character code conversion | |
80070260 EZ |
822 | @dfn{Character code conversion} involves conversion between the |
823 | internal representation of characters used inside Emacs and some other | |
824 | encoding. Emacs supports many different encodings, in that it can | |
825 | convert to and from them. For example, it can convert text to or from | |
826 | encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and | |
827 | several variants of ISO 2022. In some cases, Emacs supports several | |
828 | alternative encodings for the same characters; for example, there are | |
829 | three coding systems for the Cyrillic (Russian) alphabet: ISO, | |
830 | Alternativnyj, and KOI8. | |
831 | ||
af38459f EZ |
832 | Every coding system specifies a particular set of character code |
833 | conversions, but the coding system @code{undecided} is special: it | |
834 | leaves the choice unspecified, to be chosen heuristically for each | |
835 | file, based on the file's data. | |
b8d4c8d0 GM |
836 | |
837 | In general, a coding system doesn't guarantee roundtrip identity: | |
838 | decoding a byte sequence using coding system, then encoding the | |
839 | resulting text in the same coding system, can produce a different byte | |
80070260 EZ |
840 | sequence. But some coding systems do guarantee that the byte sequence |
841 | will be the same as what you originally decoded. Here are a few | |
842 | examples: | |
b8d4c8d0 GM |
843 | |
844 | @quotation | |
80070260 | 845 | iso-8859-1, utf-8, big5, shift_jis, euc-jp |
b8d4c8d0 GM |
846 | @end quotation |
847 | ||
848 | Encoding buffer text and then decoding the result can also fail to | |
80070260 EZ |
849 | reproduce the original text. For instance, if you encode a character |
850 | with a coding system which does not support that character, the result | |
851 | is unpredictable, and thus decoding it using the same coding system | |
852 | may produce a different text. Currently, Emacs can't report errors | |
853 | that result from encoding unsupported characters. | |
b8d4c8d0 GM |
854 | |
855 | @cindex EOL conversion | |
856 | @cindex end-of-line conversion | |
857 | @cindex line end conversion | |
80070260 EZ |
858 | @dfn{End of line conversion} handles three different conventions |
859 | used on various systems for representing end of line in files. The | |
860 | Unix convention, used on GNU and Unix systems, is to use the linefeed | |
861 | character (also called newline). The DOS convention, used on | |
862 | MS-Windows and MS-DOS systems, is to use a carriage-return and a | |
863 | linefeed at the end of a line. The Mac convention is to use just | |
864 | carriage-return. | |
b8d4c8d0 GM |
865 | |
866 | @cindex base coding system | |
867 | @cindex variant coding system | |
868 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
869 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
870 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
871 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
872 | well. Most base coding systems have three corresponding variants whose | |
873 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. | |
874 | ||
02eccf6b | 875 | @vindex raw-text@r{ coding system} |
b8d4c8d0 | 876 | The coding system @code{raw-text} is special in that it prevents |
02eccf6b EZ |
877 | character code conversion, and causes the buffer visited with this |
878 | coding system to be a unibyte buffer. For historical reasons, you can | |
879 | save both unibyte and multibyte text with this coding system. When | |
880 | you use @code{raw-text} to encode multibyte text, it does perform one | |
881 | character code conversion: it converts eight-bit characters to their | |
882 | single-byte external representation. @code{raw-text} does not specify | |
883 | the end-of-line conversion, allowing that to be determined as usual by | |
884 | the data, and has the usual three variants which specify the | |
885 | end-of-line conversion. | |
886 | ||
887 | @vindex no-conversion@r{ coding system} | |
888 | @vindex binary@r{ coding system} | |
889 | @code{no-conversion} (and its alias @code{binary}) is equivalent to | |
890 | @code{raw-text-unix}: it specifies no conversion of either character | |
891 | codes or end-of-line. | |
b8d4c8d0 | 892 | |
80070260 EZ |
893 | @vindex emacs-internal@r{ coding system} |
894 | The coding system @code{emacs-internal} specifies that the data is | |
b8d4c8d0 GM |
895 | represented in the internal Emacs encoding. This is like |
896 | @code{raw-text} in that no code conversion happens, but different in | |
897 | that the result is multibyte data. | |
898 | ||
899 | @defun coding-system-get coding-system property | |
900 | This function returns the specified property of the coding system | |
901 | @var{coding-system}. Most coding system properties exist for internal | |
80070260 | 902 | purposes, but one that you might find useful is @code{:mime-charset}. |
b8d4c8d0 GM |
903 | That property's value is the name used in MIME for the character coding |
904 | which this coding system can read and write. Examples: | |
905 | ||
906 | @example | |
80070260 | 907 | (coding-system-get 'iso-latin-1 :mime-charset) |
b8d4c8d0 | 908 | @result{} iso-8859-1 |
80070260 | 909 | (coding-system-get 'iso-2022-cn :mime-charset) |
b8d4c8d0 | 910 | @result{} iso-2022-cn |
80070260 | 911 | (coding-system-get 'cyrillic-koi8 :mime-charset) |
b8d4c8d0 GM |
912 | @result{} koi8-r |
913 | @end example | |
914 | ||
80070260 | 915 | The value of the @code{:mime-charset} property is also defined |
b8d4c8d0 GM |
916 | as an alias for the coding system. |
917 | @end defun | |
918 | ||
91211f07 EZ |
919 | @defun coding-system-aliases coding-system |
920 | This function returns the list of aliases of @var{coding-system}. | |
921 | @end defun | |
922 | ||
b8d4c8d0 GM |
923 | @node Encoding and I/O |
924 | @subsection Encoding and I/O | |
925 | ||
926 | The principal purpose of coding systems is for use in reading and | |
927 | writing files. The function @code{insert-file-contents} uses | |
928 | a coding system for decoding the file data, and @code{write-region} | |
929 | uses one to encode the buffer contents. | |
930 | ||
931 | You can specify the coding system to use either explicitly | |
932 | (@pxref{Specifying Coding Systems}), or implicitly using a default | |
933 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
934 | completely specify what to do. For example, they may choose a coding | |
935 | system such as @code{undefined} which leaves the character code | |
936 | conversion to be determined from the data. In these cases, the I/O | |
937 | operation finishes the job of choosing a coding system. Very often | |
938 | you will want to find out afterwards which coding system was chosen. | |
939 | ||
940 | @defvar buffer-file-coding-system | |
e2e3f1d7 MR |
941 | This buffer-local variable records the coding system used for saving the |
942 | buffer and for writing part of the buffer with @code{write-region}. If | |
943 | the text to be written cannot be safely encoded using the coding system | |
944 | specified by this variable, these operations select an alternative | |
945 | encoding by calling the function @code{select-safe-coding-system} | |
946 | (@pxref{User-Chosen Coding Systems}). If selecting a different encoding | |
947 | requires to ask the user to specify a coding system, | |
948 | @code{buffer-file-coding-system} is updated to the newly selected coding | |
949 | system. | |
b8d4c8d0 GM |
950 | |
951 | @code{buffer-file-coding-system} does @emph{not} affect sending text | |
952 | to a subprocess. | |
953 | @end defvar | |
954 | ||
955 | @defvar save-buffer-coding-system | |
956 | This variable specifies the coding system for saving the buffer (by | |
957 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
958 | for @code{write-region}. | |
959 | ||
960 | When a command to save the buffer starts out to use | |
961 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), | |
962 | and that coding system cannot handle | |
963 | the actual text in the buffer, the command asks the user to choose | |
964 | another coding system (by calling @code{select-safe-coding-system}). | |
965 | After that happens, the command also updates | |
966 | @code{buffer-file-coding-system} to represent the coding system that | |
967 | the user specified. | |
968 | @end defvar | |
969 | ||
970 | @defvar last-coding-system-used | |
971 | I/O operations for files and subprocesses set this variable to the | |
972 | coding system name that was used. The explicit encoding and decoding | |
973 | functions (@pxref{Explicit Encoding}) set it too. | |
974 | ||
975 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
976 | it can change whenever Emacs waits; therefore, you should copy the | |
977 | value shortly after the function call that stores the value you are | |
978 | interested in. | |
979 | @end defvar | |
980 | ||
981 | The variable @code{selection-coding-system} specifies how to encode | |
982 | selections for the window system. @xref{Window System Selections}. | |
983 | ||
984 | @defvar file-name-coding-system | |
985 | The variable @code{file-name-coding-system} specifies the coding | |
986 | system to use for encoding file names. Emacs encodes file names using | |
987 | that coding system for all file operations. If | |
988 | @code{file-name-coding-system} is @code{nil}, Emacs uses a default | |
989 | coding system determined by the selected language environment. In the | |
990 | default language environment, any non-@acronym{ASCII} characters in | |
991 | file names are not encoded specially; they appear in the file system | |
992 | using the internal Emacs representation. | |
993 | @end defvar | |
994 | ||
995 | @strong{Warning:} if you change @code{file-name-coding-system} (or | |
996 | the language environment) in the middle of an Emacs session, problems | |
997 | can result if you have already visited files whose names were encoded | |
998 | using the earlier coding system and are handled differently under the | |
999 | new coding system. If you try to save one of these buffers under the | |
1000 | visited file name, saving may use the wrong file name, or it may get | |
1001 | an error. If such a problem happens, use @kbd{C-x C-w} to specify a | |
1002 | new file name for that buffer. | |
1003 | ||
1004 | @node Lisp and Coding Systems | |
1005 | @subsection Coding Systems in Lisp | |
1006 | ||
1007 | Here are the Lisp facilities for working with coding systems: | |
1008 | ||
1009 | @defun coding-system-list &optional base-only | |
1010 | This function returns a list of all coding system names (symbols). If | |
1011 | @var{base-only} is non-@code{nil}, the value includes only the | |
1012 | base coding systems. Otherwise, it includes alias and variant coding | |
1013 | systems as well. | |
1014 | @end defun | |
1015 | ||
1016 | @defun coding-system-p object | |
1017 | This function returns @code{t} if @var{object} is a coding system | |
1018 | name or @code{nil}. | |
1019 | @end defun | |
1020 | ||
1021 | @defun check-coding-system coding-system | |
80070260 EZ |
1022 | This function checks the validity of @var{coding-system}. If that is |
1023 | valid, it returns @var{coding-system}. If @var{coding-system} is | |
1024 | @code{nil}, the function return @code{nil}. For any other values, it | |
1025 | signals an error whose @code{error-symbol} is @code{coding-system-error} | |
1026 | (@pxref{Signaling Errors, signal}). | |
b8d4c8d0 GM |
1027 | @end defun |
1028 | ||
1029 | @defun coding-system-eol-type coding-system | |
1030 | This function returns the type of end-of-line (a.k.a.@: @dfn{eol}) | |
1031 | conversion used by @var{coding-system}. If @var{coding-system} | |
1032 | specifies a certain eol conversion, the return value is an integer 0, | |
1033 | 1, or 2, standing for @code{unix}, @code{dos}, and @code{mac}, | |
1034 | respectively. If @var{coding-system} doesn't specify eol conversion | |
1035 | explicitly, the return value is a vector of coding systems, each one | |
1036 | with one of the possible eol conversion types, like this: | |
1037 | ||
1038 | @lisp | |
1039 | (coding-system-eol-type 'latin-1) | |
1040 | @result{} [latin-1-unix latin-1-dos latin-1-mac] | |
1041 | @end lisp | |
1042 | ||
1043 | @noindent | |
1044 | If this function returns a vector, Emacs will decide, as part of the | |
1045 | text encoding or decoding process, what eol conversion to use. For | |
1046 | decoding, the end-of-line format of the text is auto-detected, and the | |
1047 | eol conversion is set to match it (e.g., DOS-style CRLF format will | |
1048 | imply @code{dos} eol conversion). For encoding, the eol conversion is | |
1049 | taken from the appropriate default coding system (e.g., | |
1050 | @code{default-buffer-file-coding-system} for | |
1051 | @code{buffer-file-coding-system}), or from the default eol conversion | |
1052 | appropriate for the underlying platform. | |
1053 | @end defun | |
1054 | ||
1055 | @defun coding-system-change-eol-conversion coding-system eol-type | |
1056 | This function returns a coding system which is like @var{coding-system} | |
1057 | except for its eol conversion, which is specified by @code{eol-type}. | |
1058 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or | |
1059 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
1060 | the end-of-line conversion from the data. | |
1061 | ||
1062 | @var{eol-type} may also be 0, 1 or 2, standing for @code{unix}, | |
1063 | @code{dos} and @code{mac}, respectively. | |
1064 | @end defun | |
1065 | ||
1066 | @defun coding-system-change-text-conversion eol-coding text-coding | |
1067 | This function returns a coding system which uses the end-of-line | |
1068 | conversion of @var{eol-coding}, and the text conversion of | |
1069 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
1070 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
1071 | @end defun | |
1072 | ||
1073 | @defun find-coding-systems-region from to | |
1074 | This function returns a list of coding systems that could be used to | |
1075 | encode a text between @var{from} and @var{to}. All coding systems in | |
1076 | the list can safely encode any multibyte characters in that portion of | |
1077 | the text. | |
1078 | ||
1079 | If the text contains no multibyte characters, the function returns the | |
1080 | list @code{(undecided)}. | |
1081 | @end defun | |
1082 | ||
1083 | @defun find-coding-systems-string string | |
1084 | This function returns a list of coding systems that could be used to | |
1085 | encode the text of @var{string}. All coding systems in the list can | |
1086 | safely encode any multibyte characters in @var{string}. If the text | |
1087 | contains no multibyte characters, this returns the list | |
1088 | @code{(undecided)}. | |
1089 | @end defun | |
1090 | ||
1091 | @defun find-coding-systems-for-charsets charsets | |
1092 | This function returns a list of coding systems that could be used to | |
1093 | encode all the character sets in the list @var{charsets}. | |
1094 | @end defun | |
1095 | ||
91211f07 EZ |
1096 | @defun check-coding-systems-region start end coding-system-list |
1097 | This function checks whether coding systems in the list | |
1098 | @code{coding-system-list} can encode all the characters in the region | |
1099 | between @var{start} and @var{end}. If all of the coding systems in | |
1100 | the list can encode the specified text, the function returns | |
1101 | @code{nil}. If some coding systems cannot encode some of the | |
1102 | characters, the value is an alist, each element of which has the form | |
1103 | @code{(@var{coding-system1} @var{pos1} @var{pos2} @dots{})}, meaning | |
1104 | that @var{coding-system1} cannot encode characters at buffer positions | |
1105 | @var{pos1}, @var{pos2}, @enddots{}. | |
1106 | ||
1107 | @var{start} may be a string, in which case @var{end} is ignored and | |
1108 | the returned value references string indices instead of buffer | |
1109 | positions. | |
1110 | @end defun | |
1111 | ||
b8d4c8d0 GM |
1112 | @defun detect-coding-region start end &optional highest |
1113 | This function chooses a plausible coding system for decoding the text | |
80070260 EZ |
1114 | from @var{start} to @var{end}. This text should be a byte sequence, |
1115 | i.e.@: unibyte text or multibyte text with only @acronym{ASCII} and | |
1116 | eight-bit characters (@pxref{Explicit Encoding}). | |
b8d4c8d0 GM |
1117 | |
1118 | Normally this function returns a list of coding systems that could | |
1119 | handle decoding the text that was scanned. They are listed in order of | |
1120 | decreasing priority. But if @var{highest} is non-@code{nil}, then the | |
1121 | return value is just one coding system, the one that is highest in | |
1122 | priority. | |
1123 | ||
1124 | If the region contains only @acronym{ASCII} characters except for such | |
1125 | ISO-2022 control characters ISO-2022 as @code{ESC}, the value is | |
1126 | @code{undecided} or @code{(undecided)}, or a variant specifying | |
1127 | end-of-line conversion, if that can be deduced from the text. | |
0b4faef3 EZ |
1128 | |
1129 | If the region contains null bytes, the value is @code{no-conversion}, | |
1130 | even if the region contains text encoded in some coding system. | |
b8d4c8d0 GM |
1131 | @end defun |
1132 | ||
1133 | @defun detect-coding-string string &optional highest | |
1134 | This function is like @code{detect-coding-region} except that it | |
1135 | operates on the contents of @var{string} instead of bytes in the buffer. | |
91211f07 EZ |
1136 | @end defun |
1137 | ||
0b4faef3 EZ |
1138 | @defvar inhibit-null-byte-detection |
1139 | If this variable has a non-@code{nil} value, null bytes are ignored | |
1140 | when detecting the encoding of a region or a string. This allows to | |
1141 | correctly detect the encoding of text that contains null bytes, such | |
1142 | as Info files with Index nodes. | |
1143 | @end defvar | |
1144 | ||
1145 | @defvar inhibit-iso-escape-detection | |
1146 | If this variable has a non-@code{nil} value, ISO-2022 escape sequences | |
1147 | are ignored when detecting the encoding of a region or a string. The | |
1148 | result is that no text is ever detected as encoded in some ISO-2022 | |
1149 | encoding, and all escape sequences become visible in a buffer. | |
1150 | @strong{Warning:} @emph{Use this variable with extreme caution, | |
1151 | because many files in the Emacs distribution use ISO-2022 encoding.} | |
1152 | @end defvar | |
1153 | ||
91211f07 EZ |
1154 | @defun coding-system-charset-list coding-system |
1155 | This function returns the list of character sets (@pxref{Character | |
1156 | Sets}) supported by @var{coding-system}. Some coding systems that | |
1157 | support too many character sets to list them all yield special values: | |
1158 | @itemize @bullet | |
1159 | @item | |
1160 | If @var{coding-system} supports all the ISO-2022 charsets, the value | |
1161 | is @code{iso-2022}. | |
1162 | @item | |
1163 | If @var{coding-system} supports all Emacs characters, the value is | |
1164 | @code{(emacs)}. | |
1165 | @item | |
1166 | If @var{coding-system} supports all emacs-mule characters, the value | |
1167 | is @code{emacs-mule}. | |
1168 | @item | |
1169 | If @var{coding-system} supports all Unicode characters, the value is | |
1170 | @code{(unicode)}. | |
1171 | @end itemize | |
b8d4c8d0 GM |
1172 | @end defun |
1173 | ||
1174 | @xref{Coding systems for a subprocess,, Process Information}, in | |
1175 | particular the description of the functions | |
1176 | @code{process-coding-system} and @code{set-process-coding-system}, for | |
1177 | how to examine or set the coding systems used for I/O to a subprocess. | |
1178 | ||
1179 | @node User-Chosen Coding Systems | |
1180 | @subsection User-Chosen Coding Systems | |
1181 | ||
1182 | @cindex select safe coding system | |
1183 | @defun select-safe-coding-system from to &optional default-coding-system accept-default-p file | |
1184 | This function selects a coding system for encoding specified text, | |
1185 | asking the user to choose if necessary. Normally the specified text | |
1186 | is the text in the current buffer between @var{from} and @var{to}. If | |
1187 | @var{from} is a string, the string specifies the text to encode, and | |
1188 | @var{to} is ignored. | |
1189 | ||
1190 | If @var{default-coding-system} is non-@code{nil}, that is the first | |
1191 | coding system to try; if that can handle the text, | |
1192 | @code{select-safe-coding-system} returns that coding system. It can | |
1193 | also be a list of coding systems; then the function tries each of them | |
1194 | one by one. After trying all of them, it next tries the current | |
1195 | buffer's value of @code{buffer-file-coding-system} (if it is not | |
1196 | @code{undecided}), then the value of | |
1197 | @code{default-buffer-file-coding-system} and finally the user's most | |
1198 | preferred coding system, which the user can set using the command | |
1199 | @code{prefer-coding-system} (@pxref{Recognize Coding,, Recognizing | |
1200 | Coding Systems, emacs, The GNU Emacs Manual}). | |
1201 | ||
1202 | If one of those coding systems can safely encode all the specified | |
1203 | text, @code{select-safe-coding-system} chooses it and returns it. | |
1204 | Otherwise, it asks the user to choose from a list of coding systems | |
1205 | which can encode all the text, and returns the user's choice. | |
1206 | ||
1207 | @var{default-coding-system} can also be a list whose first element is | |
1208 | t and whose other elements are coding systems. Then, if no coding | |
1209 | system in the list can handle the text, @code{select-safe-coding-system} | |
1210 | queries the user immediately, without trying any of the three | |
1211 | alternatives described above. | |
1212 | ||
1213 | The optional argument @var{accept-default-p}, if non-@code{nil}, | |
1214 | should be a function to determine whether a coding system selected | |
1215 | without user interaction is acceptable. @code{select-safe-coding-system} | |
1216 | calls this function with one argument, the base coding system of the | |
1217 | selected coding system. If @var{accept-default-p} returns @code{nil}, | |
1218 | @code{select-safe-coding-system} rejects the silently selected coding | |
1219 | system, and asks the user to select a coding system from a list of | |
1220 | possible candidates. | |
1221 | ||
1222 | @vindex select-safe-coding-system-accept-default-p | |
1223 | If the variable @code{select-safe-coding-system-accept-default-p} is | |
1224 | non-@code{nil}, its value overrides the value of | |
1225 | @var{accept-default-p}. | |
1226 | ||
1227 | As a final step, before returning the chosen coding system, | |
1228 | @code{select-safe-coding-system} checks whether that coding system is | |
1229 | consistent with what would be selected if the contents of the region | |
1230 | were read from a file. (If not, this could lead to data corruption in | |
1231 | a file subsequently re-visited and edited.) Normally, | |
1232 | @code{select-safe-coding-system} uses @code{buffer-file-name} as the | |
1233 | file for this purpose, but if @var{file} is non-@code{nil}, it uses | |
1234 | that file instead (this can be relevant for @code{write-region} and | |
1235 | similar functions). If it detects an apparent inconsistency, | |
1236 | @code{select-safe-coding-system} queries the user before selecting the | |
1237 | coding system. | |
1238 | @end defun | |
1239 | ||
1240 | Here are two functions you can use to let the user specify a coding | |
1241 | system, with completion. @xref{Completion}. | |
1242 | ||
1243 | @defun read-coding-system prompt &optional default | |
1244 | This function reads a coding system using the minibuffer, prompting with | |
1245 | string @var{prompt}, and returns the coding system name as a symbol. If | |
1246 | the user enters null input, @var{default} specifies which coding system | |
1247 | to return. It should be a symbol or a string. | |
1248 | @end defun | |
1249 | ||
1250 | @defun read-non-nil-coding-system prompt | |
1251 | This function reads a coding system using the minibuffer, prompting with | |
1252 | string @var{prompt}, and returns the coding system name as a symbol. If | |
1253 | the user tries to enter null input, it asks the user to try again. | |
1254 | @xref{Coding Systems}. | |
1255 | @end defun | |
1256 | ||
1257 | @node Default Coding Systems | |
1258 | @subsection Default Coding Systems | |
1259 | ||
1260 | This section describes variables that specify the default coding | |
1261 | system for certain files or when running certain subprograms, and the | |
1262 | function that I/O operations use to access them. | |
1263 | ||
1264 | The idea of these variables is that you set them once and for all to the | |
1265 | defaults you want, and then do not change them again. To specify a | |
1266 | particular coding system for a particular operation in a Lisp program, | |
1267 | don't change these variables; instead, override them using | |
1268 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1269 | (@pxref{Specifying Coding Systems}). | |
1270 | ||
1271 | @defvar auto-coding-regexp-alist | |
1272 | This variable is an alist of text patterns and corresponding coding | |
1273 | systems. Each element has the form @code{(@var{regexp} | |
1274 | . @var{coding-system})}; a file whose first few kilobytes match | |
1275 | @var{regexp} is decoded with @var{coding-system} when its contents are | |
1276 | read into a buffer. The settings in this alist take priority over | |
1277 | @code{coding:} tags in the files and the contents of | |
1278 | @code{file-coding-system-alist} (see below). The default value is set | |
1279 | so that Emacs automatically recognizes mail files in Babyl format and | |
1280 | reads them with no code conversions. | |
1281 | @end defvar | |
1282 | ||
1283 | @defvar file-coding-system-alist | |
1284 | This variable is an alist that specifies the coding systems to use for | |
1285 | reading and writing particular files. Each element has the form | |
1286 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
1287 | expression that matches certain file names. The element applies to file | |
1288 | names that match @var{pattern}. | |
1289 | ||
1290 | The @sc{cdr} of the element, @var{coding}, should be either a coding | |
1291 | system, a cons cell containing two coding systems, or a function name (a | |
1292 | symbol with a function definition). If @var{coding} is a coding system, | |
1293 | that coding system is used for both reading the file and writing it. If | |
1294 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
1295 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
1296 | coding system for encoding. | |
1297 | ||
1298 | If @var{coding} is a function name, the function should take one | |
1299 | argument, a list of all arguments passed to | |
1300 | @code{find-operation-coding-system}. It must return a coding system | |
1301 | or a cons cell containing two coding systems. This value has the same | |
1302 | meaning as described above. | |
1303 | ||
1304 | If @var{coding} (or what returned by the above function) is | |
1305 | @code{undecided}, the normal code-detection is performed. | |
1306 | @end defvar | |
1307 | ||
1308 | @defvar process-coding-system-alist | |
1309 | This variable is an alist specifying which coding systems to use for a | |
1310 | subprocess, depending on which program is running in the subprocess. It | |
1311 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
1312 | matched against the program name used to start the subprocess. The coding | |
1313 | system or systems specified in this alist are used to initialize the | |
1314 | coding systems used for I/O to the subprocess, but you can specify | |
1315 | other coding systems later using @code{set-process-coding-system}. | |
1316 | @end defvar | |
1317 | ||
1318 | @strong{Warning:} Coding systems such as @code{undecided}, which | |
1319 | determine the coding system from the data, do not work entirely reliably | |
1320 | with asynchronous subprocess output. This is because Emacs handles | |
1321 | asynchronous subprocess output in batches, as it arrives. If the coding | |
1322 | system leaves the character code conversion unspecified, or leaves the | |
1323 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
1324 | conversion from one batch at a time, and this does not always work. | |
1325 | ||
1326 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
1327 | coding system which determines both the character code conversion and | |
1328 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
1329 | rather than @code{undecided} or @code{latin-1}. | |
1330 | ||
1331 | @defvar network-coding-system-alist | |
1332 | This variable is an alist that specifies the coding system to use for | |
1333 | network streams. It works much like @code{file-coding-system-alist}, | |
1334 | with the difference that the @var{pattern} in an element may be either a | |
1335 | port number or a regular expression. If it is a regular expression, it | |
1336 | is matched against the network service name used to open the network | |
1337 | stream. | |
1338 | @end defvar | |
1339 | ||
1340 | @defvar default-process-coding-system | |
1341 | This variable specifies the coding systems to use for subprocess (and | |
1342 | network stream) input and output, when nothing else specifies what to | |
1343 | do. | |
1344 | ||
1345 | The value should be a cons cell of the form @code{(@var{input-coding} | |
1346 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
1347 | the subprocess, and @var{output-coding} applies to output to it. | |
1348 | @end defvar | |
1349 | ||
1350 | @defvar auto-coding-functions | |
1351 | This variable holds a list of functions that try to determine a | |
1352 | coding system for a file based on its undecoded contents. | |
1353 | ||
1354 | Each function in this list should be written to look at text in the | |
1355 | current buffer, but should not modify it in any way. The buffer will | |
1356 | contain undecoded text of parts of the file. Each function should | |
1357 | take one argument, @var{size}, which tells it how many characters to | |
1358 | look at, starting from point. If the function succeeds in determining | |
1359 | a coding system for the file, it should return that coding system. | |
1360 | Otherwise, it should return @code{nil}. | |
1361 | ||
1362 | If a file has a @samp{coding:} tag, that takes precedence, so these | |
1363 | functions won't be called. | |
1364 | @end defvar | |
1365 | ||
1366 | @defun find-operation-coding-system operation &rest arguments | |
1367 | This function returns the coding system to use (by default) for | |
1368 | performing @var{operation} with @var{arguments}. The value has this | |
1369 | form: | |
1370 | ||
1371 | @example | |
1372 | (@var{decoding-system} . @var{encoding-system}) | |
1373 | @end example | |
1374 | ||
1375 | The first element, @var{decoding-system}, is the coding system to use | |
1376 | for decoding (in case @var{operation} does decoding), and | |
1377 | @var{encoding-system} is the coding system for encoding (in case | |
1378 | @var{operation} does encoding). | |
1379 | ||
1380 | The argument @var{operation} is a symbol, one of @code{write-region}, | |
1381 | @code{start-process}, @code{call-process}, @code{call-process-region}, | |
1382 | @code{insert-file-contents}, or @code{open-network-stream}. These are | |
1383 | the names of the Emacs I/O primitives that can do character code and | |
1384 | eol conversion. | |
1385 | ||
1386 | The remaining arguments should be the same arguments that might be given | |
1387 | to the corresponding I/O primitive. Depending on the primitive, one | |
1388 | of those arguments is selected as the @dfn{target}. For example, if | |
1389 | @var{operation} does file I/O, whichever argument specifies the file | |
1390 | name is the target. For subprocess primitives, the process name is the | |
1391 | target. For @code{open-network-stream}, the target is the service name | |
1392 | or port number. | |
1393 | ||
1394 | Depending on @var{operation}, this function looks up the target in | |
1395 | @code{file-coding-system-alist}, @code{process-coding-system-alist}, | |
1396 | or @code{network-coding-system-alist}. If the target is found in the | |
1397 | alist, @code{find-operation-coding-system} returns its association in | |
1398 | the alist; otherwise it returns @code{nil}. | |
1399 | ||
1400 | If @var{operation} is @code{insert-file-contents}, the argument | |
1401 | corresponding to the target may be a cons cell of the form | |
1402 | @code{(@var{filename} . @var{buffer})}). In that case, @var{filename} | |
1403 | is a file name to look up in @code{file-coding-system-alist}, and | |
1404 | @var{buffer} is a buffer that contains the file's contents (not yet | |
1405 | decoded). If @code{file-coding-system-alist} specifies a function to | |
1406 | call for this file, and that function needs to examine the file's | |
1407 | contents (as it usually does), it should examine the contents of | |
1408 | @var{buffer} instead of reading the file. | |
1409 | @end defun | |
1410 | ||
1411 | @node Specifying Coding Systems | |
1412 | @subsection Specifying a Coding System for One Operation | |
1413 | ||
1414 | You can specify the coding system for a specific operation by binding | |
1415 | the variables @code{coding-system-for-read} and/or | |
1416 | @code{coding-system-for-write}. | |
1417 | ||
1418 | @defvar coding-system-for-read | |
1419 | If this variable is non-@code{nil}, it specifies the coding system to | |
1420 | use for reading a file, or for input from a synchronous subprocess. | |
1421 | ||
1422 | It also applies to any asynchronous subprocess or network stream, but in | |
1423 | a different way: the value of @code{coding-system-for-read} when you | |
1424 | start the subprocess or open the network stream specifies the input | |
1425 | decoding method for that subprocess or network stream. It remains in | |
1426 | use for that subprocess or network stream unless and until overridden. | |
1427 | ||
1428 | The right way to use this variable is to bind it with @code{let} for a | |
1429 | specific I/O operation. Its global value is normally @code{nil}, and | |
1430 | you should not globally set it to any other value. Here is an example | |
1431 | of the right way to use the variable: | |
1432 | ||
1433 | @example | |
1434 | ;; @r{Read the file with no character code conversion.} | |
1435 | ;; @r{Assume @acronym{crlf} represents end-of-line.} | |
1436 | (let ((coding-system-for-read 'emacs-mule-dos)) | |
1437 | (insert-file-contents filename)) | |
1438 | @end example | |
1439 | ||
1440 | When its value is non-@code{nil}, this variable takes precedence over | |
1441 | all other methods of specifying a coding system to use for input, | |
1442 | including @code{file-coding-system-alist}, | |
1443 | @code{process-coding-system-alist} and | |
1444 | @code{network-coding-system-alist}. | |
1445 | @end defvar | |
1446 | ||
1447 | @defvar coding-system-for-write | |
1448 | This works much like @code{coding-system-for-read}, except that it | |
1449 | applies to output rather than input. It affects writing to files, | |
1450 | as well as sending output to subprocesses and net connections. | |
1451 | ||
1452 | When a single operation does both input and output, as do | |
1453 | @code{call-process-region} and @code{start-process}, both | |
1454 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1455 | affect it. | |
1456 | @end defvar | |
1457 | ||
1458 | @defvar inhibit-eol-conversion | |
1459 | When this variable is non-@code{nil}, no end-of-line conversion is done, | |
1460 | no matter which coding system is specified. This applies to all the | |
1461 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
1462 | decoding functions (@pxref{Explicit Encoding}). | |
1463 | @end defvar | |
1464 | ||
91211f07 EZ |
1465 | @cindex priority order of coding systems |
1466 | @cindex coding systems, priority | |
1467 | Sometimes, you need to prefer several coding systems for some | |
1468 | operation, rather than fix a single one. Emacs lets you specify a | |
1469 | priority order for using coding systems. This ordering affects the | |
1470 | sorting of lists of coding sysems returned by functions such as | |
1471 | @code{find-coding-systems-region} (@pxref{Lisp and Coding Systems}). | |
1472 | ||
1473 | @defun coding-system-priority-list &optional highestp | |
1474 | This function returns the list of coding systems in the order of their | |
1475 | current priorities. Optional argument @var{highestp}, if | |
1476 | non-@code{nil}, means return only the highest priority coding system. | |
1477 | @end defun | |
1478 | ||
1479 | @defun set-coding-system-priority &rest coding-systems | |
1480 | This function puts @var{coding-systems} at the beginning of the | |
1481 | priority list for coding systems, thus making their priority higher | |
1482 | than all the rest. | |
1483 | @end defun | |
1484 | ||
1485 | @defmac with-coding-priority coding-systems &rest body@dots{} | |
1486 | This macro execute @var{body}, like @code{progn} does | |
1487 | (@pxref{Sequencing, progn}), with @var{coding-systems} at the front of | |
1488 | the priority list for coding systems. @var{coding-systems} should be | |
1489 | a list of coding systems to prefer during execution of @var{body}. | |
1490 | @end defmac | |
1491 | ||
b8d4c8d0 GM |
1492 | @node Explicit Encoding |
1493 | @subsection Explicit Encoding and Decoding | |
1494 | @cindex encoding in coding systems | |
1495 | @cindex decoding in coding systems | |
1496 | ||
1497 | All the operations that transfer text in and out of Emacs have the | |
1498 | ability to use a coding system to encode or decode the text. | |
1499 | You can also explicitly encode and decode text using the functions | |
1500 | in this section. | |
1501 | ||
1502 | The result of encoding, and the input to decoding, are not ordinary | |
1503 | text. They logically consist of a series of byte values; that is, a | |
80070260 EZ |
1504 | series of @acronym{ASCII} and eight-bit characters. In unibyte |
1505 | buffers and strings, these characters have codes in the range 0 | |
1506 | through 255. In a multibyte buffer or string, eight-bit characters | |
1507 | have character codes higher than 255 (@pxref{Text Representations}), | |
1508 | but Emacs transparently converts them to their single-byte values when | |
1509 | you encode or decode such text. | |
b8d4c8d0 GM |
1510 | |
1511 | The usual way to read a file into a buffer as a sequence of bytes, so | |
1512 | you can decode the contents explicitly, is with | |
1513 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
1514 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
1515 | visiting a file with @code{find-file-noselect}. These methods result in | |
1516 | a unibyte buffer. | |
1517 | ||
1518 | The usual way to use the byte sequence that results from explicitly | |
1519 | encoding text is to copy it to a file or process---for example, to write | |
1520 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
1521 | encoding by binding @code{coding-system-for-write} to | |
1522 | @code{no-conversion}. | |
1523 | ||
1524 | Here are the functions to perform explicit encoding or decoding. The | |
1525 | encoding functions produce sequences of bytes; the decoding functions | |
1526 | are meant to operate on sequences of bytes. All of these functions | |
80070260 EZ |
1527 | discard text properties. They also set @code{last-coding-system-used} |
1528 | to the precise coding system they used. | |
b8d4c8d0 | 1529 | |
80070260 | 1530 | @deffn Command encode-coding-region start end coding-system &optional destination |
b8d4c8d0 | 1531 | This command encodes the text from @var{start} to @var{end} according |
80070260 EZ |
1532 | to coding system @var{coding-system}. Normally, the encoded text |
1533 | replaces the original text in the buffer, but the optional argument | |
1534 | @var{destination} can change that. If @var{destination} is a buffer, | |
1535 | the encoded text is inserted in that buffer after point (point does | |
1536 | not move); if it is @code{t}, the command returns the encoded text as | |
1537 | a unibyte string without inserting it. | |
1538 | ||
1539 | If encoded text is inserted in some buffer, this command returns the | |
1540 | length of the encoded text. | |
1541 | ||
1542 | The result of encoding is logically a sequence of bytes, but the | |
1543 | buffer remains multibyte if it was multibyte before, and any 8-bit | |
1544 | bytes are converted to their multibyte representation (@pxref{Text | |
1545 | Representations}). | |
b8d4c8d0 GM |
1546 | @end deffn |
1547 | ||
80070260 | 1548 | @defun encode-coding-string string coding-system &optional nocopy buffer |
b8d4c8d0 GM |
1549 | This function encodes the text in @var{string} according to coding |
1550 | system @var{coding-system}. It returns a new string containing the | |
1551 | encoded text, except when @var{nocopy} is non-@code{nil}, in which | |
1552 | case the function may return @var{string} itself if the encoding | |
1553 | operation is trivial. The result of encoding is a unibyte string. | |
1554 | @end defun | |
1555 | ||
80070260 | 1556 | @deffn Command decode-coding-region start end coding-system destination |
b8d4c8d0 | 1557 | This command decodes the text from @var{start} to @var{end} according |
80070260 EZ |
1558 | to coding system @var{coding-system}. To make explicit decoding |
1559 | useful, the text before decoding ought to be a sequence of byte | |
1560 | values, but both multibyte and unibyte buffers are acceptable (in the | |
1561 | multibyte case, the raw byte values should be represented as eight-bit | |
1562 | characters). Normally, the decoded text replaces the original text in | |
1563 | the buffer, but the optional argument @var{destination} can change | |
1564 | that. If @var{destination} is a buffer, the decoded text is inserted | |
1565 | in that buffer after point (point does not move); if it is @code{t}, | |
1566 | the command returns the decoded text as a multibyte string without | |
1567 | inserting it. | |
1568 | ||
1569 | If decoded text is inserted in some buffer, this command returns the | |
1570 | length of the decoded text. | |
7d2a859f EZ |
1571 | |
1572 | This command puts a @code{charset} text property on the decoded text. | |
1573 | The value of the property states the character set used to decode the | |
1574 | original text. | |
b8d4c8d0 GM |
1575 | @end deffn |
1576 | ||
80070260 EZ |
1577 | @defun decode-coding-string string coding-system &optional nocopy buffer |
1578 | This function decodes the text in @var{string} according to | |
1579 | @var{coding-system}. It returns a new string containing the decoded | |
1580 | text, except when @var{nocopy} is non-@code{nil}, in which case the | |
1581 | function may return @var{string} itself if the decoding operation is | |
1582 | trivial. To make explicit decoding useful, the contents of | |
1583 | @var{string} ought to be a unibyte string with a sequence of byte | |
1584 | values, but a multibyte string is also acceptable (assuming it | |
1585 | contains 8-bit bytes in their multibyte form). | |
1586 | ||
1587 | If optional argument @var{buffer} specifies a buffer, the decoded text | |
1588 | is inserted in that buffer after point (point does not move). In this | |
1589 | case, the return value is the length of the decoded text. | |
7d2a859f EZ |
1590 | |
1591 | @cindex @code{charset}, text property | |
1592 | This function puts a @code{charset} text property on the decoded text. | |
1593 | The value of the property states the character set used to decode the | |
1594 | original text: | |
1595 | ||
1596 | @example | |
1597 | @group | |
1598 | (decode-coding-string "Gr\374ss Gott" 'latin-1) | |
1599 | @result{} #("Gr@"uss Gott" 0 9 (charset iso-8859-1)) | |
1600 | @end group | |
1601 | @end example | |
b8d4c8d0 GM |
1602 | @end defun |
1603 | ||
1604 | @defun decode-coding-inserted-region from to filename &optional visit beg end replace | |
1605 | This function decodes the text from @var{from} to @var{to} as if | |
1606 | it were being read from file @var{filename} using @code{insert-file-contents} | |
1607 | using the rest of the arguments provided. | |
1608 | ||
1609 | The normal way to use this function is after reading text from a file | |
1610 | without decoding, if you decide you would rather have decoded it. | |
1611 | Instead of deleting the text and reading it again, this time with | |
1612 | decoding, you can call this function. | |
1613 | @end defun | |
1614 | ||
1615 | @node Terminal I/O Encoding | |
1616 | @subsection Terminal I/O Encoding | |
1617 | ||
1618 | Emacs can decode keyboard input using a coding system, and encode | |
80070260 EZ |
1619 | terminal output. This is useful for terminals that transmit or |
1620 | display text using a particular encoding such as Latin-1. Emacs does | |
1621 | not set @code{last-coding-system-used} for encoding or decoding of | |
1622 | terminal I/O. | |
b8d4c8d0 | 1623 | |
3f1d322f | 1624 | @defun keyboard-coding-system &optional terminal |
b8d4c8d0 | 1625 | This function returns the coding system that is in use for decoding |
3f1d322f EZ |
1626 | keyboard input from @var{terminal}---or @code{nil} if no coding system |
1627 | is to be used for that terminal. If @var{terminal} is omitted or | |
1628 | @code{nil}, it means the selected frame's terminal. @xref{Multiple | |
1629 | Terminals}. | |
b8d4c8d0 GM |
1630 | @end defun |
1631 | ||
3f1d322f EZ |
1632 | @deffn Command set-keyboard-coding-system coding-system &optional terminal |
1633 | This command specifies @var{coding-system} as the coding system to use | |
1634 | for decoding keyboard input from @var{terminal}. If | |
1635 | @var{coding-system} is @code{nil}, that means do not decode keyboard | |
1636 | input. If @var{terminal} is a frame, it means that frame's terminal; | |
1637 | if it is @code{nil}, that means the currently selected frame's | |
1638 | terminal. @xref{Multiple Terminals}. | |
b8d4c8d0 GM |
1639 | @end deffn |
1640 | ||
1641 | @defun terminal-coding-system | |
1642 | This function returns the coding system that is in use for encoding | |
1643 | terminal output---or @code{nil} for no encoding. | |
1644 | @end defun | |
1645 | ||
1646 | @deffn Command set-terminal-coding-system coding-system | |
1647 | This command specifies @var{coding-system} as the coding system to use | |
1648 | for encoding terminal output. If @var{coding-system} is @code{nil}, | |
1649 | that means do not encode terminal output. | |
1650 | @end deffn | |
1651 | ||
1652 | @node MS-DOS File Types | |
1653 | @subsection MS-DOS File Types | |
1654 | @cindex DOS file types | |
1655 | @cindex MS-DOS file types | |
1656 | @cindex Windows file types | |
1657 | @cindex file types on MS-DOS and Windows | |
1658 | @cindex text files and binary files | |
1659 | @cindex binary files and text files | |
1660 | ||
1661 | On MS-DOS and Microsoft Windows, Emacs guesses the appropriate | |
1662 | end-of-line conversion for a file by looking at the file's name. This | |
1663 | feature classifies files as @dfn{text files} and @dfn{binary files}. By | |
1664 | ``binary file'' we mean a file of literal byte values that are not | |
1665 | necessarily meant to be characters; Emacs does no end-of-line conversion | |
1666 | and no character code conversion for them. On the other hand, the bytes | |
1667 | in a text file are intended to represent characters; when you create a | |
1668 | new file whose name implies that it is a text file, Emacs uses DOS | |
1669 | end-of-line conversion. | |
1670 | ||
1671 | @defvar buffer-file-type | |
1672 | This variable, automatically buffer-local in each buffer, records the | |
1673 | file type of the buffer's visited file. When a buffer does not specify | |
1674 | a coding system with @code{buffer-file-coding-system}, this variable is | |
1675 | used to determine which coding system to use when writing the contents | |
1676 | of the buffer. It should be @code{nil} for text, @code{t} for binary. | |
1677 | If it is @code{t}, the coding system is @code{no-conversion}. | |
1678 | Otherwise, @code{undecided-dos} is used. | |
1679 | ||
1680 | Normally this variable is set by visiting a file; it is set to | |
1681 | @code{nil} if the file was visited without any actual conversion. | |
1682 | @end defvar | |
1683 | ||
1684 | @defopt file-name-buffer-file-type-alist | |
1685 | This variable holds an alist for recognizing text and binary files. | |
1686 | Each element has the form (@var{regexp} . @var{type}), where | |
1687 | @var{regexp} is matched against the file name, and @var{type} may be | |
1688 | @code{nil} for text, @code{t} for binary, or a function to call to | |
1689 | compute which. If it is a function, then it is called with a single | |
1690 | argument (the file name) and should return @code{t} or @code{nil}. | |
1691 | ||
1692 | When running on MS-DOS or MS-Windows, Emacs checks this alist to decide | |
1693 | which coding system to use when reading a file. For a text file, | |
1694 | @code{undecided-dos} is used. For a binary file, @code{no-conversion} | |
1695 | is used. | |
1696 | ||
1697 | If no element in this alist matches a given file name, then | |
1698 | @code{default-buffer-file-type} says how to treat the file. | |
1699 | @end defopt | |
1700 | ||
1701 | @defopt default-buffer-file-type | |
1702 | This variable says how to handle files for which | |
1703 | @code{file-name-buffer-file-type-alist} says nothing about the type. | |
1704 | ||
1705 | If this variable is non-@code{nil}, then these files are treated as | |
1706 | binary: the coding system @code{no-conversion} is used. Otherwise, | |
1707 | nothing special is done for them---the coding system is deduced solely | |
1708 | from the file contents, in the usual Emacs fashion. | |
1709 | @end defopt | |
1710 | ||
1711 | @node Input Methods | |
1712 | @section Input Methods | |
1713 | @cindex input methods | |
1714 | ||
1715 | @dfn{Input methods} provide convenient ways of entering non-@acronym{ASCII} | |
1716 | characters from the keyboard. Unlike coding systems, which translate | |
1717 | non-@acronym{ASCII} characters to and from encodings meant to be read by | |
1718 | programs, input methods provide human-friendly commands. (@xref{Input | |
1719 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1720 | use input methods to enter text.) How to define input methods is not | |
1721 | yet documented in this manual, but here we describe how to use them. | |
1722 | ||
1723 | Each input method has a name, which is currently a string; | |
1724 | in the future, symbols may also be usable as input method names. | |
1725 | ||
1726 | @defvar current-input-method | |
1727 | This variable holds the name of the input method now active in the | |
1728 | current buffer. (It automatically becomes local in each buffer when set | |
1729 | in any fashion.) It is @code{nil} if no input method is active in the | |
1730 | buffer now. | |
1731 | @end defvar | |
1732 | ||
1733 | @defopt default-input-method | |
1734 | This variable holds the default input method for commands that choose an | |
1735 | input method. Unlike @code{current-input-method}, this variable is | |
1736 | normally global. | |
1737 | @end defopt | |
1738 | ||
1739 | @deffn Command set-input-method input-method | |
1740 | This command activates input method @var{input-method} for the current | |
1741 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1742 | If @var{input-method} is @code{nil}, this command deactivates any input | |
1743 | method for the current buffer. | |
1744 | @end deffn | |
1745 | ||
1746 | @defun read-input-method-name prompt &optional default inhibit-null | |
1747 | This function reads an input method name with the minibuffer, prompting | |
1748 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1749 | by default, if the user enters empty input. However, if | |
1750 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1751 | ||
1752 | The returned value is a string. | |
1753 | @end defun | |
1754 | ||
1755 | @defvar input-method-alist | |
1756 | This variable defines all the supported input methods. | |
1757 | Each element defines one input method, and should have the form: | |
1758 | ||
1759 | @example | |
1760 | (@var{input-method} @var{language-env} @var{activate-func} | |
1761 | @var{title} @var{description} @var{args}...) | |
1762 | @end example | |
1763 | ||
1764 | Here @var{input-method} is the input method name, a string; | |
1765 | @var{language-env} is another string, the name of the language | |
1766 | environment this input method is recommended for. (That serves only for | |
1767 | documentation purposes.) | |
1768 | ||
1769 | @var{activate-func} is a function to call to activate this method. The | |
1770 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1771 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1772 | the @var{args}. | |
1773 | ||
1774 | @var{title} is a string to display in the mode line while this method is | |
1775 | active. @var{description} is a string describing this method and what | |
1776 | it is good for. | |
1777 | @end defvar | |
1778 | ||
1779 | The fundamental interface to input methods is through the | |
1780 | variable @code{input-method-function}. @xref{Reading One Event}, | |
1781 | and @ref{Invoking the Input Method}. | |
1782 | ||
1783 | @node Locales | |
1784 | @section Locales | |
1785 | @cindex locale | |
1786 | ||
1787 | POSIX defines a concept of ``locales'' which control which language | |
1788 | to use in language-related features. These Emacs variables control | |
1789 | how Emacs interacts with these features. | |
1790 | ||
1791 | @defvar locale-coding-system | |
1792 | @cindex keyboard input decoding on X | |
1793 | This variable specifies the coding system to use for decoding system | |
1794 | error messages and---on X Window system only---keyboard input, for | |
1795 | encoding the format argument to @code{format-time-string}, and for | |
1796 | decoding the return value of @code{format-time-string}. | |
1797 | @end defvar | |
1798 | ||
1799 | @defvar system-messages-locale | |
1800 | This variable specifies the locale to use for generating system error | |
1801 | messages. Changing the locale can cause messages to come out in a | |
1802 | different language or in a different orthography. If the variable is | |
1803 | @code{nil}, the locale is specified by environment variables in the | |
1804 | usual POSIX fashion. | |
1805 | @end defvar | |
1806 | ||
1807 | @defvar system-time-locale | |
1808 | This variable specifies the locale to use for formatting time values. | |
1809 | Changing the locale can cause messages to appear according to the | |
1810 | conventions of a different language. If the variable is @code{nil}, the | |
1811 | locale is specified by environment variables in the usual POSIX fashion. | |
1812 | @end defvar | |
1813 | ||
1814 | @defun locale-info item | |
1815 | This function returns locale data @var{item} for the current POSIX | |
1816 | locale, if available. @var{item} should be one of these symbols: | |
1817 | ||
1818 | @table @code | |
1819 | @item codeset | |
1820 | Return the character set as a string (locale item @code{CODESET}). | |
1821 | ||
1822 | @item days | |
1823 | Return a 7-element vector of day names (locale items | |
1824 | @code{DAY_1} through @code{DAY_7}); | |
1825 | ||
1826 | @item months | |
1827 | Return a 12-element vector of month names (locale items @code{MON_1} | |
1828 | through @code{MON_12}). | |
1829 | ||
1830 | @item paper | |
1831 | Return a list @code{(@var{width} @var{height})} for the default paper | |
1832 | size measured in millimeters (locale items @code{PAPER_WIDTH} and | |
1833 | @code{PAPER_HEIGHT}). | |
1834 | @end table | |
1835 | ||
1836 | If the system can't provide the requested information, or if | |
1837 | @var{item} is not one of those symbols, the value is @code{nil}. All | |
1838 | strings in the return value are decoded using | |
1839 | @code{locale-coding-system}. @xref{Locales,,, libc, The GNU Libc Manual}, | |
1840 | for more information about locales and locale items. | |
1841 | @end defun | |
1842 | ||
1843 | @ignore | |
1844 | arch-tag: be705bf8-941b-4c35-84fc-ad7d20ddb7cb | |
1845 | @end ignore |