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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
ab422c4d | 3 | @c Copyright (C) 1998-1999, 2001-2013 Free Software Foundation, Inc. |
b8d4c8d0 | 4 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 5 | @node Non-ASCII Characters |
b8d4c8d0 GM |
6 | @chapter Non-@acronym{ASCII} Characters |
7 | @cindex multibyte characters | |
8 | @cindex characters, multi-byte | |
9 | @cindex non-@acronym{ASCII} characters | |
10 | ||
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11 | This chapter covers the special issues relating to characters and |
12 | how they are stored in strings and buffers. | |
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13 | |
14 | @menu | |
c4526e93 | 15 | * Text Representations:: How Emacs represents text. |
64a695bd | 16 | * Disabling Multibyte:: Controlling whether to use multibyte characters. |
b8d4c8d0 GM |
17 | * Converting Representations:: Converting unibyte to multibyte and vice versa. |
18 | * Selecting a Representation:: Treating a byte sequence as unibyte or multi. | |
19 | * Character Codes:: How unibyte and multibyte relate to | |
20 | codes of individual characters. | |
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21 | * Character Properties:: Character attributes that define their |
22 | behavior and handling. | |
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23 | * Character Sets:: The space of possible character codes |
24 | is divided into various character sets. | |
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25 | * Scanning Charsets:: Which character sets are used in a buffer? |
26 | * Translation of Characters:: Translation tables are used for conversion. | |
27 | * Coding Systems:: Coding systems are conversions for saving files. | |
28 | * Input Methods:: Input methods allow users to enter various | |
29 | non-ASCII characters without special keyboards. | |
30 | * Locales:: Interacting with the POSIX locale. | |
31 | @end menu | |
32 | ||
33 | @node Text Representations | |
34 | @section Text Representations | |
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35 | @cindex text representation |
36 | ||
37 | Emacs buffers and strings support a large repertoire of characters | |
97d8273f | 38 | from many different scripts, allowing users to type and display text |
8cc8cecf | 39 | in almost any known written language. |
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40 | |
41 | @cindex character codepoint | |
42 | @cindex codespace | |
43 | @cindex Unicode | |
44 | To support this multitude of characters and scripts, Emacs closely | |
45 | follows the @dfn{Unicode Standard}. The Unicode Standard assigns a | |
46 | unique number, called a @dfn{codepoint}, to each and every character. | |
47 | The range of codepoints defined by Unicode, or the Unicode | |
85eeac93 CY |
48 | @dfn{codespace}, is @code{0..#x10FFFF} (in hexadecimal notation), |
49 | inclusive. Emacs extends this range with codepoints in the range | |
50 | @code{#x110000..#x3FFFFF}, which it uses for representing characters | |
51 | that are not unified with Unicode and @dfn{raw 8-bit bytes} that | |
52 | cannot be interpreted as characters. Thus, a character codepoint in | |
53 | Emacs is a 22-bit integer number. | |
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54 | |
55 | @cindex internal representation of characters | |
56 | @cindex characters, representation in buffers and strings | |
57 | @cindex multibyte text | |
58 | To conserve memory, Emacs does not hold fixed-length 22-bit numbers | |
59 | that are codepoints of text characters within buffers and strings. | |
60 | Rather, Emacs uses a variable-length internal representation of | |
61 | characters, that stores each character as a sequence of 1 to 5 8-bit | |
62 | bytes, depending on the magnitude of its codepoint@footnote{ | |
63 | This internal representation is based on one of the encodings defined | |
64 | by the Unicode Standard, called @dfn{UTF-8}, for representing any | |
65 | Unicode codepoint, but Emacs extends UTF-8 to represent the additional | |
8b80cdf5 | 66 | codepoints it uses for raw 8-bit bytes and characters not unified with |
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67 | Unicode.}. For example, any @acronym{ASCII} character takes up only 1 |
68 | byte, a Latin-1 character takes up 2 bytes, etc. We call this | |
69 | representation of text @dfn{multibyte}. | |
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70 | |
71 | Outside Emacs, characters can be represented in many different | |
72 | encodings, such as ISO-8859-1, GB-2312, Big-5, etc. Emacs converts | |
97d8273f | 73 | between these external encodings and its internal representation, as |
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74 | appropriate, when it reads text into a buffer or a string, or when it |
75 | writes text to a disk file or passes it to some other process. | |
76 | ||
77 | Occasionally, Emacs needs to hold and manipulate encoded text or | |
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78 | binary non-text data in its buffers or strings. For example, when |
79 | Emacs visits a file, it first reads the file's text verbatim into a | |
80 | buffer, and only then converts it to the internal representation. | |
81 | Before the conversion, the buffer holds encoded text. | |
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82 | |
83 | @cindex unibyte text | |
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84 | Encoded text is not really text, as far as Emacs is concerned, but |
85 | rather a sequence of raw 8-bit bytes. We call buffers and strings | |
86 | that hold encoded text @dfn{unibyte} buffers and strings, because | |
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87 | Emacs treats them as a sequence of individual bytes. Usually, Emacs |
88 | displays unibyte buffers and strings as octal codes such as | |
89 | @code{\237}. We recommend that you never use unibyte buffers and | |
c4526e93 | 90 | strings except for manipulating encoded text or binary non-text data. |
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91 | |
92 | In a buffer, the buffer-local value of the variable | |
93 | @code{enable-multibyte-characters} specifies the representation used. | |
94 | The representation for a string is determined and recorded in the string | |
95 | when the string is constructed. | |
96 | ||
8a14dec7 | 97 | @defvar enable-multibyte-characters |
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98 | This variable specifies the current buffer's text representation. |
99 | If it is non-@code{nil}, the buffer contains multibyte text; otherwise, | |
c4526e93 | 100 | it contains unibyte encoded text or binary non-text data. |
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101 | |
102 | You cannot set this variable directly; instead, use the function | |
103 | @code{set-buffer-multibyte} to change a buffer's representation. | |
8a14dec7 | 104 | @end defvar |
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105 | |
106 | @defun position-bytes position | |
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107 | Buffer positions are measured in character units. This function |
108 | returns the byte-position corresponding to buffer position | |
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109 | @var{position} in the current buffer. This is 1 at the start of the |
110 | buffer, and counts upward in bytes. If @var{position} is out of | |
111 | range, the value is @code{nil}. | |
112 | @end defun | |
113 | ||
114 | @defun byte-to-position byte-position | |
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115 | Return the buffer position, in character units, corresponding to given |
116 | @var{byte-position} in the current buffer. If @var{byte-position} is | |
117 | out of range, the value is @code{nil}. In a multibyte buffer, an | |
118 | arbitrary value of @var{byte-position} can be not at character | |
119 | boundary, but inside a multibyte sequence representing a single | |
120 | character; in this case, this function returns the buffer position of | |
121 | the character whose multibyte sequence includes @var{byte-position}. | |
122 | In other words, the value does not change for all byte positions that | |
123 | belong to the same character. | |
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124 | @end defun |
125 | ||
126 | @defun multibyte-string-p string | |
c4526e93 | 127 | Return @code{t} if @var{string} is a multibyte string, @code{nil} |
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128 | otherwise. This function also returns @code{nil} if @var{string} is |
129 | some object other than a string. | |
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130 | @end defun |
131 | ||
132 | @defun string-bytes string | |
133 | @cindex string, number of bytes | |
134 | This function returns the number of bytes in @var{string}. | |
135 | If @var{string} is a multibyte string, this can be greater than | |
136 | @code{(length @var{string})}. | |
137 | @end defun | |
138 | ||
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139 | @defun unibyte-string &rest bytes |
140 | This function concatenates all its argument @var{bytes} and makes the | |
141 | result a unibyte string. | |
142 | @end defun | |
143 | ||
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144 | @node Disabling Multibyte |
145 | @section Disabling Multibyte Characters | |
146 | @cindex disabling multibyte | |
147 | ||
148 | By default, Emacs starts in multibyte mode: it stores the contents | |
149 | of buffers and strings using an internal encoding that represents | |
150 | non-@acronym{ASCII} characters using multi-byte sequences. Multibyte | |
151 | mode allows you to use all the supported languages and scripts without | |
152 | limitations. | |
153 | ||
154 | @cindex turn multibyte support on or off | |
155 | Under very special circumstances, you may want to disable multibyte | |
156 | character support, for a specific buffer. | |
157 | When multibyte characters are disabled in a buffer, we call | |
158 | that @dfn{unibyte mode}. In unibyte mode, each character in the | |
159 | buffer has a character code ranging from 0 through 255 (0377 octal); 0 | |
160 | through 127 (0177 octal) represent @acronym{ASCII} characters, and 128 | |
161 | (0200 octal) through 255 (0377 octal) represent non-@acronym{ASCII} | |
162 | characters. | |
163 | ||
164 | To edit a particular file in unibyte representation, visit it using | |
165 | @code{find-file-literally}. @xref{Visiting Functions}. You can | |
166 | convert a multibyte buffer to unibyte by saving it to a file, killing | |
167 | the buffer, and visiting the file again with | |
168 | @code{find-file-literally}. Alternatively, you can use @kbd{C-x | |
169 | @key{RET} c} (@code{universal-coding-system-argument}) and specify | |
170 | @samp{raw-text} as the coding system with which to visit or save a | |
171 | file. @xref{Text Coding, , Specifying a Coding System for File Text, | |
172 | emacs, GNU Emacs Manual}. Unlike @code{find-file-literally}, finding | |
173 | a file as @samp{raw-text} doesn't disable format conversion, | |
174 | uncompression, or auto mode selection. | |
175 | ||
176 | @c See http://debbugs.gnu.org/11226 for lack of unibyte tooltip. | |
177 | @vindex enable-multibyte-characters | |
178 | The buffer-local variable @code{enable-multibyte-characters} is | |
179 | non-@code{nil} in multibyte buffers, and @code{nil} in unibyte ones. | |
180 | The mode line also indicates whether a buffer is multibyte or not. | |
181 | With a graphical display, in a multibyte buffer, the portion of the | |
182 | mode line that indicates the character set has a tooltip that (amongst | |
183 | other things) says that the buffer is multibyte. In a unibyte buffer, | |
184 | the character set indicator is absent. Thus, in a unibyte buffer | |
185 | (when using a graphical display) there is normally nothing before the | |
186 | indication of the visited file's end-of-line convention (colon, | |
187 | backslash, etc.), unless you are using an input method. | |
188 | ||
189 | @findex toggle-enable-multibyte-characters | |
190 | You can turn off multibyte support in a specific buffer by invoking the | |
191 | command @code{toggle-enable-multibyte-characters} in that buffer. | |
192 | ||
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193 | @node Converting Representations |
194 | @section Converting Text Representations | |
195 | ||
196 | Emacs can convert unibyte text to multibyte; it can also convert | |
031c41de | 197 | multibyte text to unibyte, provided that the multibyte text contains |
8b80cdf5 | 198 | only @acronym{ASCII} and 8-bit raw bytes. In general, these |
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199 | conversions happen when inserting text into a buffer, or when putting |
200 | text from several strings together in one string. You can also | |
201 | explicitly convert a string's contents to either representation. | |
b8d4c8d0 | 202 | |
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203 | Emacs chooses the representation for a string based on the text from |
204 | which it is constructed. The general rule is to convert unibyte text | |
205 | to multibyte text when combining it with other multibyte text, because | |
206 | the multibyte representation is more general and can hold whatever | |
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207 | characters the unibyte text has. |
208 | ||
209 | When inserting text into a buffer, Emacs converts the text to the | |
210 | buffer's representation, as specified by | |
211 | @code{enable-multibyte-characters} in that buffer. In particular, when | |
212 | you insert multibyte text into a unibyte buffer, Emacs converts the text | |
213 | to unibyte, even though this conversion cannot in general preserve all | |
214 | the characters that might be in the multibyte text. The other natural | |
215 | alternative, to convert the buffer contents to multibyte, is not | |
216 | acceptable because the buffer's representation is a choice made by the | |
217 | user that cannot be overridden automatically. | |
218 | ||
97d8273f | 219 | Converting unibyte text to multibyte text leaves @acronym{ASCII} |
e4021ec1 | 220 | characters unchanged, and converts bytes with codes 128 through 255 to |
97d8273f | 221 | the multibyte representation of raw eight-bit bytes. |
b8d4c8d0 | 222 | |
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223 | Converting multibyte text to unibyte converts all @acronym{ASCII} |
224 | and eight-bit characters to their single-byte form, but loses | |
225 | information for non-@acronym{ASCII} characters by discarding all but | |
226 | the low 8 bits of each character's codepoint. Converting unibyte text | |
227 | to multibyte and back to unibyte reproduces the original unibyte text. | |
b8d4c8d0 | 228 | |
031c41de | 229 | The next two functions either return the argument @var{string}, or a |
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230 | newly created string with no text properties. |
231 | ||
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232 | @defun string-to-multibyte string |
233 | This function returns a multibyte string containing the same sequence | |
031c41de | 234 | of characters as @var{string}. If @var{string} is a multibyte string, |
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235 | it is returned unchanged. The function assumes that @var{string} |
236 | includes only @acronym{ASCII} characters and raw 8-bit bytes; the | |
237 | latter are converted to their multibyte representation corresponding | |
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238 | to the codepoints @code{#x3FFF80} through @code{#x3FFFFF}, inclusive |
239 | (@pxref{Text Representations, codepoints}). | |
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240 | @end defun |
241 | ||
242 | @defun string-to-unibyte string | |
243 | This function returns a unibyte string containing the same sequence of | |
244 | characters as @var{string}. It signals an error if @var{string} | |
245 | contains a non-@acronym{ASCII} character. If @var{string} is a | |
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246 | unibyte string, it is returned unchanged. Use this function for |
247 | @var{string} arguments that contain only @acronym{ASCII} and eight-bit | |
248 | characters. | |
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249 | @end defun |
250 | ||
3e99b825 CY |
251 | @defun byte-to-string byte |
252 | @cindex byte to string | |
253 | This function returns a unibyte string containing a single byte of | |
35a30759 | 254 | character data, @var{character}. It signals an error if |
3e99b825 CY |
255 | @var{character} is not an integer between 0 and 255. |
256 | @end defun | |
b8d4c8d0 GM |
257 | |
258 | @defun multibyte-char-to-unibyte char | |
97d8273f CY |
259 | This converts the multibyte character @var{char} to a unibyte |
260 | character, and returns that character. If @var{char} is neither | |
261 | @acronym{ASCII} nor eight-bit, the function returns -1. | |
b8d4c8d0 GM |
262 | @end defun |
263 | ||
264 | @defun unibyte-char-to-multibyte char | |
265 | This convert the unibyte character @var{char} to a multibyte | |
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266 | character, assuming @var{char} is either @acronym{ASCII} or raw 8-bit |
267 | byte. | |
b8d4c8d0 GM |
268 | @end defun |
269 | ||
270 | @node Selecting a Representation | |
271 | @section Selecting a Representation | |
272 | ||
273 | Sometimes it is useful to examine an existing buffer or string as | |
274 | multibyte when it was unibyte, or vice versa. | |
275 | ||
276 | @defun set-buffer-multibyte multibyte | |
277 | Set the representation type of the current buffer. If @var{multibyte} | |
278 | is non-@code{nil}, the buffer becomes multibyte. If @var{multibyte} | |
279 | is @code{nil}, the buffer becomes unibyte. | |
280 | ||
281 | This function leaves the buffer contents unchanged when viewed as a | |
031c41de | 282 | sequence of bytes. As a consequence, it can change the contents |
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283 | viewed as characters; for instance, a sequence of three bytes which is |
284 | treated as one character in multibyte representation will count as | |
285 | three characters in unibyte representation. Eight-bit characters | |
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286 | representing raw bytes are an exception. They are represented by one |
287 | byte in a unibyte buffer, but when the buffer is set to multibyte, | |
288 | they are converted to two-byte sequences, and vice versa. | |
b8d4c8d0 GM |
289 | |
290 | This function sets @code{enable-multibyte-characters} to record which | |
291 | representation is in use. It also adjusts various data in the buffer | |
292 | (including overlays, text properties and markers) so that they cover the | |
293 | same text as they did before. | |
294 | ||
cd996018 CY |
295 | This function signals an error if the buffer is narrowed, since the |
296 | narrowing might have occurred in the middle of multibyte character | |
297 | sequences. | |
298 | ||
299 | This function also signals an error if the buffer is an indirect | |
300 | buffer. An indirect buffer always inherits the representation of its | |
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301 | base buffer. |
302 | @end defun | |
303 | ||
304 | @defun string-as-unibyte string | |
97d8273f CY |
305 | If @var{string} is already a unibyte string, this function returns |
306 | @var{string} itself. Otherwise, it returns a new string with the same | |
307 | bytes as @var{string}, but treating each byte as a separate character | |
308 | (so that the value may have more characters than @var{string}); as an | |
309 | exception, each eight-bit character representing a raw byte is | |
310 | converted into a single byte. The newly-created string contains no | |
031c41de | 311 | text properties. |
b8d4c8d0 GM |
312 | @end defun |
313 | ||
314 | @defun string-as-multibyte string | |
97d8273f CY |
315 | If @var{string} is a multibyte string, this function returns |
316 | @var{string} itself. Otherwise, it returns a new string with the same | |
317 | bytes as @var{string}, but treating each multibyte sequence as one | |
318 | character. This means that the value may have fewer characters than | |
319 | @var{string} has. If a byte sequence in @var{string} is invalid as a | |
320 | multibyte representation of a single character, each byte in the | |
321 | sequence is treated as a raw 8-bit byte. The newly-created string | |
322 | contains no text properties. | |
b8d4c8d0 GM |
323 | @end defun |
324 | ||
325 | @node Character Codes | |
326 | @section Character Codes | |
327 | @cindex character codes | |
328 | ||
ffdbc44b CY |
329 | The unibyte and multibyte text representations use different |
330 | character codes. The valid character codes for unibyte representation | |
85eeac93 CY |
331 | range from 0 to @code{#xFF} (255)---the values that can fit in one |
332 | byte. The valid character codes for multibyte representation range | |
333 | from 0 to @code{#x3FFFFF}. In this code space, values 0 through | |
334 | @code{#x7F} (127) are for @acronym{ASCII} characters, and values | |
335 | @code{#x80} (128) through @code{#x3FFF7F} (4194175) are for | |
336 | non-@acronym{ASCII} characters. | |
337 | ||
338 | Emacs character codes are a superset of the Unicode standard. | |
339 | Values 0 through @code{#x10FFFF} (1114111) correspond to Unicode | |
340 | characters of the same codepoint; values @code{#x110000} (1114112) | |
341 | through @code{#x3FFF7F} (4194175) represent characters that are not | |
342 | unified with Unicode; and values @code{#x3FFF80} (4194176) through | |
343 | @code{#x3FFFFF} (4194303) represent eight-bit raw bytes. | |
ffdbc44b CY |
344 | |
345 | @defun characterp charcode | |
346 | This returns @code{t} if @var{charcode} is a valid character, and | |
347 | @code{nil} otherwise. | |
b8d4c8d0 GM |
348 | |
349 | @example | |
80070260 | 350 | @group |
ffdbc44b | 351 | (characterp 65) |
b8d4c8d0 | 352 | @result{} t |
80070260 EZ |
353 | @end group |
354 | @group | |
ffdbc44b | 355 | (characterp 4194303) |
b8d4c8d0 | 356 | @result{} t |
80070260 EZ |
357 | @end group |
358 | @group | |
ffdbc44b CY |
359 | (characterp 4194304) |
360 | @result{} nil | |
80070260 EZ |
361 | @end group |
362 | @end example | |
363 | @end defun | |
364 | ||
365 | @cindex maximum value of character codepoint | |
366 | @cindex codepoint, largest value | |
367 | @defun max-char | |
368 | This function returns the largest value that a valid character | |
369 | codepoint can have. | |
370 | ||
371 | @example | |
372 | @group | |
373 | (characterp (max-char)) | |
374 | @result{} t | |
375 | @end group | |
376 | @group | |
377 | (characterp (1+ (max-char))) | |
378 | @result{} nil | |
379 | @end group | |
b8d4c8d0 | 380 | @end example |
b8d4c8d0 GM |
381 | @end defun |
382 | ||
106e6894 | 383 | @defun get-byte &optional pos string |
97d8273f CY |
384 | This function returns the byte at character position @var{pos} in the |
385 | current buffer. If the current buffer is unibyte, this is literally | |
386 | the byte at that position. If the buffer is multibyte, byte values of | |
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387 | @acronym{ASCII} characters are the same as character codepoints, |
388 | whereas eight-bit raw bytes are converted to their 8-bit codes. The | |
389 | function signals an error if the character at @var{pos} is | |
390 | non-@acronym{ASCII}. | |
391 | ||
392 | The optional argument @var{string} means to get a byte value from that | |
393 | string instead of the current buffer. | |
394 | @end defun | |
395 | ||
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396 | @node Character Properties |
397 | @section Character Properties | |
398 | @cindex character properties | |
399 | A @dfn{character property} is a named attribute of a character that | |
400 | specifies how the character behaves and how it should be handled | |
401 | during text processing and display. Thus, character properties are an | |
402 | important part of specifying the character's semantics. | |
403 | ||
434843ec | 404 | On the whole, Emacs follows the Unicode Standard in its implementation |
91211f07 EZ |
405 | of character properties. In particular, Emacs supports the |
406 | @uref{http://www.unicode.org/reports/tr23/, Unicode Character Property | |
407 | Model}, and the Emacs character property database is derived from the | |
408 | Unicode Character Database (@acronym{UCD}). See the | |
409 | @uref{http://www.unicode.org/versions/Unicode5.0.0/ch04.pdf, Character | |
97d8273f CY |
410 | Properties chapter of the Unicode Standard}, for a detailed |
411 | description of Unicode character properties and their meaning. This | |
412 | section assumes you are already familiar with that chapter of the | |
413 | Unicode Standard, and want to apply that knowledge to Emacs Lisp | |
414 | programs. | |
91211f07 EZ |
415 | |
416 | In Emacs, each property has a name, which is a symbol, and a set of | |
af38459f | 417 | possible values, whose types depend on the property; if a character |
c06ea95e EZ |
418 | does not have a certain property, the value is @code{nil}. As a |
419 | general rule, the names of character properties in Emacs are produced | |
420 | from the corresponding Unicode properties by downcasing them and | |
421 | replacing each @samp{_} character with a dash @samp{-}. For example, | |
422 | @code{Canonical_Combining_Class} becomes | |
423 | @code{canonical-combining-class}. However, sometimes we shorten the | |
424 | names to make their use easier. | |
425 | ||
bca633fb EZ |
426 | @cindex unassigned character codepoints |
427 | Some codepoints are left @dfn{unassigned} by the | |
428 | @acronym{UCD}---they don't correspond to any character. The Unicode | |
429 | Standard defines default values of properties for such codepoints; | |
430 | they are mentioned below for each property. | |
431 | ||
97d8273f CY |
432 | Here is the full list of value types for all the character |
433 | properties that Emacs knows about: | |
91211f07 EZ |
434 | |
435 | @table @code | |
436 | @item name | |
049bcbcb CY |
437 | Corresponds to the @code{Name} Unicode property. The value is a |
438 | string consisting of upper-case Latin letters A to Z, digits, spaces, | |
bca633fb EZ |
439 | and hyphen @samp{-} characters. For unassigned codepoints, the value |
440 | is an empty string. | |
91211f07 | 441 | |
f8848423 | 442 | @cindex unicode general category |
91211f07 | 443 | @item general-category |
049bcbcb CY |
444 | Corresponds to the @code{General_Category} Unicode property. The |
445 | value is a symbol whose name is a 2-letter abbreviation of the | |
bca633fb EZ |
446 | character's classification. For unassigned codepoints, the value |
447 | is @code{Cn}. | |
91211f07 EZ |
448 | |
449 | @item canonical-combining-class | |
049bcbcb | 450 | Corresponds to the @code{Canonical_Combining_Class} Unicode property. |
bca633fb EZ |
451 | The value is an integer number. For unassigned codepoints, the value |
452 | is zero. | |
91211f07 | 453 | |
10862873 | 454 | @cindex bidirectional class of characters |
91211f07 | 455 | @item bidi-class |
af38459f EZ |
456 | Corresponds to the Unicode @code{Bidi_Class} property. The value is a |
457 | symbol whose name is the Unicode @dfn{directional type} of the | |
c094bb0c | 458 | character. Emacs uses this property when it reorders bidirectional |
bca633fb EZ |
459 | text for display (@pxref{Bidirectional Display}). For unassigned |
460 | codepoints, the value depends on the code blocks to which the | |
461 | codepoint belongs: most unassigned codepoints get the value of | |
462 | @code{L} (strong L), but some get values of @code{AL} (Arabic letter) | |
463 | or @code{R} (strong R). | |
91211f07 EZ |
464 | |
465 | @item decomposition | |
84f4a531 CY |
466 | Corresponds to the Unicode properties @code{Decomposition_Type} and |
467 | @code{Decomposition_Value}. The value is a list, whose first element | |
468 | may be a symbol representing a compatibility formatting tag, such as | |
469 | @code{small}@footnote{The Unicode specification writes these tag names | |
470 | inside @samp{<..>} brackets, but the tag names in Emacs do not include | |
1df7defd | 471 | the brackets; e.g., Unicode specifies @samp{<small>} where Emacs uses |
84f4a531 CY |
472 | @samp{small}. }; the other elements are characters that give the |
473 | compatibility decomposition sequence of this character. For | |
474 | unassigned codepoints, the value is the character itself. | |
91211f07 EZ |
475 | |
476 | @item decimal-digit-value | |
af38459f EZ |
477 | Corresponds to the Unicode @code{Numeric_Value} property for |
478 | characters whose @code{Numeric_Type} is @samp{Digit}. The value is an | |
bca633fb EZ |
479 | integer number. For unassigned codepoints, the value is @code{nil}, |
480 | which means @acronym{NaN}, or ``not-a-number''. | |
91211f07 | 481 | |
bc039a3b | 482 | @item digit-value |
af38459f EZ |
483 | Corresponds to the Unicode @code{Numeric_Value} property for |
484 | characters whose @code{Numeric_Type} is @samp{Decimal}. The value is | |
485 | an integer number. Examples of such characters include compatibility | |
486 | subscript and superscript digits, for which the value is the | |
bca633fb EZ |
487 | corresponding number. For unassigned codepoints, the value is |
488 | @code{nil}, which means @acronym{NaN}. | |
91211f07 EZ |
489 | |
490 | @item numeric-value | |
af38459f EZ |
491 | Corresponds to the Unicode @code{Numeric_Value} property for |
492 | characters whose @code{Numeric_Type} is @samp{Numeric}. The value of | |
97d8273f | 493 | this property is an integer or a floating-point number. Examples of |
af38459f | 494 | characters that have this property include fractions, subscripts, |
91211f07 | 495 | superscripts, Roman numerals, currency numerators, and encircled |
af38459f | 496 | numbers. For example, the value of this property for the character |
bca633fb EZ |
497 | @code{U+2155} (@sc{vulgar fraction one fifth}) is @code{0.2}. For |
498 | unassigned codepoints, the value is @code{nil}, which means | |
499 | @acronym{NaN}. | |
91211f07 | 500 | |
10862873 | 501 | @cindex mirroring of characters |
91211f07 | 502 | @item mirrored |
af38459f | 503 | Corresponds to the Unicode @code{Bidi_Mirrored} property. The value |
bca633fb EZ |
504 | of this property is a symbol, either @code{Y} or @code{N}. For |
505 | unassigned codepoints, the value is @code{N}. | |
91211f07 | 506 | |
10862873 EZ |
507 | @item mirroring |
508 | Corresponds to the Unicode @code{Bidi_Mirroring_Glyph} property. The | |
509 | value of this property is a character whose glyph represents the | |
510 | mirror image of the character's glyph, or @code{nil} if there's no | |
511 | defined mirroring glyph. All the characters whose @code{mirrored} | |
512 | property is @code{N} have @code{nil} as their @code{mirroring} | |
513 | property; however, some characters whose @code{mirrored} property is | |
514 | @code{Y} also have @code{nil} for @code{mirroring}, because no | |
c094bb0c EZ |
515 | appropriate characters exist with mirrored glyphs. Emacs uses this |
516 | property to display mirror images of characters when appropriate | |
bca633fb EZ |
517 | (@pxref{Bidirectional Display}). For unassigned codepoints, the value |
518 | is @code{nil}. | |
10862873 | 519 | |
91211f07 | 520 | @item old-name |
af38459f | 521 | Corresponds to the Unicode @code{Unicode_1_Name} property. The value |
bca633fb | 522 | is a string. For unassigned codepoints, the value is an empty string. |
91211f07 EZ |
523 | |
524 | @item iso-10646-comment | |
af38459f | 525 | Corresponds to the Unicode @code{ISO_Comment} property. The value is |
bca633fb | 526 | a string. For unassigned codepoints, the value is an empty string. |
91211f07 EZ |
527 | |
528 | @item uppercase | |
af38459f | 529 | Corresponds to the Unicode @code{Simple_Uppercase_Mapping} property. |
bca633fb EZ |
530 | The value of this property is a single character. For unassigned |
531 | codepoints, the value is @code{nil}, which means the character itself. | |
91211f07 EZ |
532 | |
533 | @item lowercase | |
af38459f | 534 | Corresponds to the Unicode @code{Simple_Lowercase_Mapping} property. |
bca633fb EZ |
535 | The value of this property is a single character. For unassigned |
536 | codepoints, the value is @code{nil}, which means the character itself. | |
91211f07 EZ |
537 | |
538 | @item titlecase | |
af38459f | 539 | Corresponds to the Unicode @code{Simple_Titlecase_Mapping} property. |
91211f07 | 540 | @dfn{Title case} is a special form of a character used when the first |
af38459f | 541 | character of a word needs to be capitalized. The value of this |
bca633fb EZ |
542 | property is a single character. For unassigned codepoints, the value |
543 | is @code{nil}, which means the character itself. | |
91211f07 EZ |
544 | @end table |
545 | ||
546 | @defun get-char-code-property char propname | |
547 | This function returns the value of @var{char}'s @var{propname} property. | |
548 | ||
549 | @example | |
550 | @group | |
551 | (get-char-code-property ? 'general-category) | |
552 | @result{} Zs | |
553 | @end group | |
554 | @group | |
555 | (get-char-code-property ?1 'general-category) | |
556 | @result{} Nd | |
557 | @end group | |
558 | @group | |
049bcbcb CY |
559 | ;; subscript 4 |
560 | (get-char-code-property ?\u2084 'digit-value) | |
91211f07 EZ |
561 | @result{} 4 |
562 | @end group | |
563 | @group | |
049bcbcb CY |
564 | ;; one fifth |
565 | (get-char-code-property ?\u2155 'numeric-value) | |
bc039a3b | 566 | @result{} 0.2 |
91211f07 EZ |
567 | @end group |
568 | @group | |
049bcbcb CY |
569 | ;; Roman IV |
570 | (get-char-code-property ?\u2163 'numeric-value) | |
bc039a3b | 571 | @result{} 4 |
91211f07 EZ |
572 | @end group |
573 | @end example | |
574 | @end defun | |
575 | ||
576 | @defun char-code-property-description prop value | |
577 | This function returns the description string of property @var{prop}'s | |
578 | @var{value}, or @code{nil} if @var{value} has no description. | |
579 | ||
580 | @example | |
581 | @group | |
582 | (char-code-property-description 'general-category 'Zs) | |
583 | @result{} "Separator, Space" | |
584 | @end group | |
585 | @group | |
586 | (char-code-property-description 'general-category 'Nd) | |
587 | @result{} "Number, Decimal Digit" | |
588 | @end group | |
589 | @group | |
590 | (char-code-property-description 'numeric-value '1/5) | |
591 | @result{} nil | |
592 | @end group | |
593 | @end example | |
594 | @end defun | |
595 | ||
596 | @defun put-char-code-property char propname value | |
597 | This function stores @var{value} as the value of the property | |
598 | @var{propname} for the character @var{char}. | |
599 | @end defun | |
600 | ||
f8848423 | 601 | @defvar unicode-category-table |
91211f07 | 602 | The value of this variable is a char-table (@pxref{Char-Tables}) that |
f8848423 EZ |
603 | specifies, for each character, its Unicode @code{General_Category} |
604 | property as a symbol. | |
605 | @end defvar | |
606 | ||
607 | @defvar char-script-table | |
608 | The value of this variable is a char-table that specifies, for each | |
609 | character, a symbol whose name is the script to which the character | |
610 | belongs, according to the Unicode Standard classification of the | |
611 | Unicode code space into script-specific blocks. This char-table has a | |
612 | single extra slot whose value is the list of all script symbols. | |
91211f07 EZ |
613 | @end defvar |
614 | ||
615 | @defvar char-width-table | |
616 | The value of this variable is a char-table that specifies the width of | |
617 | each character in columns that it will occupy on the screen. | |
618 | @end defvar | |
619 | ||
620 | @defvar printable-chars | |
621 | The value of this variable is a char-table that specifies, for each | |
622 | character, whether it is printable or not. That is, if evaluating | |
623 | @code{(aref printable-chars char)} results in @code{t}, the character | |
624 | is printable, and if it results in @code{nil}, it is not. | |
625 | @end defvar | |
626 | ||
b8d4c8d0 GM |
627 | @node Character Sets |
628 | @section Character Sets | |
629 | @cindex character sets | |
630 | ||
031c41de EZ |
631 | @cindex charset |
632 | @cindex coded character set | |
633 | An Emacs @dfn{character set}, or @dfn{charset}, is a set of characters | |
634 | in which each character is assigned a numeric code point. (The | |
434843ec | 635 | Unicode Standard calls this a @dfn{coded character set}.) Each Emacs |
031c41de EZ |
636 | charset has a name which is a symbol. A single character can belong |
637 | to any number of different character sets, but it will generally have | |
638 | a different code point in each charset. Examples of character sets | |
639 | include @code{ascii}, @code{iso-8859-1}, @code{greek-iso8859-7}, and | |
640 | @code{windows-1255}. The code point assigned to a character in a | |
641 | charset is usually different from its code point used in Emacs buffers | |
642 | and strings. | |
643 | ||
644 | @cindex @code{emacs}, a charset | |
645 | @cindex @code{unicode}, a charset | |
646 | @cindex @code{eight-bit}, a charset | |
647 | Emacs defines several special character sets. The character set | |
648 | @code{unicode} includes all the characters whose Emacs code points are | |
85eeac93 | 649 | in the range @code{0..#x10FFFF}. The character set @code{emacs} |
031c41de EZ |
650 | includes all @acronym{ASCII} and non-@acronym{ASCII} characters. |
651 | Finally, the @code{eight-bit} charset includes the 8-bit raw bytes; | |
652 | Emacs uses it to represent raw bytes encountered in text. | |
b8d4c8d0 GM |
653 | |
654 | @defun charsetp object | |
655 | Returns @code{t} if @var{object} is a symbol that names a character set, | |
656 | @code{nil} otherwise. | |
657 | @end defun | |
658 | ||
659 | @defvar charset-list | |
660 | The value is a list of all defined character set names. | |
661 | @end defvar | |
662 | ||
031c41de | 663 | @defun charset-priority-list &optional highestp |
73e0cbc0 | 664 | This function returns a list of all defined character sets ordered by |
031c41de EZ |
665 | their priority. If @var{highestp} is non-@code{nil}, the function |
666 | returns a single character set of the highest priority. | |
667 | @end defun | |
668 | ||
669 | @defun set-charset-priority &rest charsets | |
670 | This function makes @var{charsets} the highest priority character sets. | |
b8d4c8d0 GM |
671 | @end defun |
672 | ||
106e6894 | 673 | @defun char-charset character &optional restriction |
031c41de EZ |
674 | This function returns the name of the character set of highest |
675 | priority that @var{character} belongs to. @acronym{ASCII} characters | |
676 | are an exception: for them, this function always returns @code{ascii}. | |
106e6894 CY |
677 | |
678 | If @var{restriction} is non-@code{nil}, it should be a list of | |
679 | charsets to search. Alternatively, it can be a coding system, in | |
680 | which case the returned charset must be supported by that coding | |
681 | system (@pxref{Coding Systems}). | |
b8d4c8d0 GM |
682 | @end defun |
683 | ||
684 | @defun charset-plist charset | |
031c41de EZ |
685 | This function returns the property list of the character set |
686 | @var{charset}. Although @var{charset} is a symbol, this is not the | |
687 | same as the property list of that symbol. Charset properties include | |
688 | important information about the charset, such as its documentation | |
689 | string, short name, etc. | |
b8d4c8d0 GM |
690 | @end defun |
691 | ||
031c41de EZ |
692 | @defun put-charset-property charset propname value |
693 | This function sets the @var{propname} property of @var{charset} to the | |
694 | given @var{value}. | |
b8d4c8d0 GM |
695 | @end defun |
696 | ||
031c41de EZ |
697 | @defun get-charset-property charset propname |
698 | This function returns the value of @var{charset}s property | |
699 | @var{propname}. | |
b8d4c8d0 GM |
700 | @end defun |
701 | ||
031c41de EZ |
702 | @deffn Command list-charset-chars charset |
703 | This command displays a list of characters in the character set | |
704 | @var{charset}. | |
705 | @end deffn | |
b8d4c8d0 | 706 | |
8b80cdf5 EZ |
707 | Emacs can convert between its internal representation of a character |
708 | and the character's codepoint in a specific charset. The following | |
709 | two functions support these conversions. | |
710 | ||
711 | @c FIXME: decode-char and encode-char accept and ignore an additional | |
712 | @c argument @var{restriction}. When that argument actually makes a | |
713 | @c difference, it should be documented here. | |
031c41de EZ |
714 | @defun decode-char charset code-point |
715 | This function decodes a character that is assigned a @var{code-point} | |
716 | in @var{charset}, to the corresponding Emacs character, and returns | |
8b80cdf5 EZ |
717 | it. If @var{charset} doesn't contain a character of that code point, |
718 | the value is @code{nil}. If @var{code-point} doesn't fit in a Lisp | |
719 | integer (@pxref{Integer Basics, most-positive-fixnum}), it can be | |
720 | specified as a cons cell @code{(@var{high} . @var{low})}, where | |
031c41de EZ |
721 | @var{low} are the lower 16 bits of the value and @var{high} are the |
722 | high 16 bits. | |
b8d4c8d0 GM |
723 | @end defun |
724 | ||
031c41de EZ |
725 | @defun encode-char char charset |
726 | This function returns the code point assigned to the character | |
8b80cdf5 EZ |
727 | @var{char} in @var{charset}. If the result does not fit in a Lisp |
728 | integer, it is returned as a cons cell @code{(@var{high} . @var{low})} | |
729 | that fits the second argument of @code{decode-char} above. If | |
730 | @var{charset} doesn't have a codepoint for @var{char}, the value is | |
731 | @code{nil}. | |
b3f1f4a5 EZ |
732 | @end defun |
733 | ||
734 | The following function comes in handy for applying a certain | |
735 | function to all or part of the characters in a charset: | |
736 | ||
85eeac93 | 737 | @defun map-charset-chars function charset &optional arg from-code to-code |
b3f1f4a5 EZ |
738 | Call @var{function} for characters in @var{charset}. @var{function} |
739 | is called with two arguments. The first one is a cons cell | |
740 | @code{(@var{from} . @var{to})}, where @var{from} and @var{to} | |
741 | indicate a range of characters contained in charset. The second | |
85eeac93 | 742 | argument passed to @var{function} is @var{arg}. |
b3f1f4a5 EZ |
743 | |
744 | By default, the range of codepoints passed to @var{function} includes | |
8c9d5f9f KH |
745 | all the characters in @var{charset}, but optional arguments |
746 | @var{from-code} and @var{to-code} limit that to the range of | |
747 | characters between these two codepoints of @var{charset}. If either | |
748 | of them is @code{nil}, it defaults to the first or last codepoint of | |
749 | @var{charset}, respectively. | |
b8d4c8d0 GM |
750 | @end defun |
751 | ||
b8d4c8d0 GM |
752 | @node Scanning Charsets |
753 | @section Scanning for Character Sets | |
754 | ||
97d8273f CY |
755 | Sometimes it is useful to find out which character set a particular |
756 | character belongs to. One use for this is in determining which coding | |
757 | systems (@pxref{Coding Systems}) are capable of representing all of | |
758 | the text in question; another is to determine the font(s) for | |
759 | displaying that text. | |
b8d4c8d0 GM |
760 | |
761 | @defun charset-after &optional pos | |
031c41de | 762 | This function returns the charset of highest priority containing the |
97d8273f | 763 | character at position @var{pos} in the current buffer. If @var{pos} |
031c41de EZ |
764 | is omitted or @code{nil}, it defaults to the current value of point. |
765 | If @var{pos} is out of range, the value is @code{nil}. | |
b8d4c8d0 GM |
766 | @end defun |
767 | ||
768 | @defun find-charset-region beg end &optional translation | |
031c41de | 769 | This function returns a list of the character sets of highest priority |
8b80cdf5 | 770 | that contain characters in the current buffer between positions |
031c41de | 771 | @var{beg} and @var{end}. |
b8d4c8d0 | 772 | |
97d8273f CY |
773 | The optional argument @var{translation} specifies a translation table |
774 | to use for scanning the text (@pxref{Translation of Characters}). If | |
775 | it is non-@code{nil}, then each character in the region is translated | |
b8d4c8d0 GM |
776 | through this table, and the value returned describes the translated |
777 | characters instead of the characters actually in the buffer. | |
778 | @end defun | |
779 | ||
780 | @defun find-charset-string string &optional translation | |
97d8273f | 781 | This function returns a list of character sets of highest priority |
031c41de EZ |
782 | that contain characters in @var{string}. It is just like |
783 | @code{find-charset-region}, except that it applies to the contents of | |
784 | @var{string} instead of part of the current buffer. | |
b8d4c8d0 GM |
785 | @end defun |
786 | ||
787 | @node Translation of Characters | |
788 | @section Translation of Characters | |
789 | @cindex character translation tables | |
790 | @cindex translation tables | |
791 | ||
031c41de EZ |
792 | A @dfn{translation table} is a char-table (@pxref{Char-Tables}) that |
793 | specifies a mapping of characters into characters. These tables are | |
794 | used in encoding and decoding, and for other purposes. Some coding | |
795 | systems specify their own particular translation tables; there are | |
796 | also default translation tables which apply to all other coding | |
797 | systems. | |
b8d4c8d0 | 798 | |
031c41de EZ |
799 | A translation table has two extra slots. The first is either |
800 | @code{nil} or a translation table that performs the reverse | |
801 | translation; the second is the maximum number of characters to look up | |
8b80cdf5 EZ |
802 | for translating sequences of characters (see the description of |
803 | @code{make-translation-table-from-alist} below). | |
b8d4c8d0 GM |
804 | |
805 | @defun make-translation-table &rest translations | |
806 | This function returns a translation table based on the argument | |
807 | @var{translations}. Each element of @var{translations} should be a | |
808 | list of elements of the form @code{(@var{from} . @var{to})}; this says | |
809 | to translate the character @var{from} into @var{to}. | |
810 | ||
811 | The arguments and the forms in each argument are processed in order, | |
812 | and if a previous form already translates @var{to} to some other | |
813 | character, say @var{to-alt}, @var{from} is also translated to | |
814 | @var{to-alt}. | |
b8d4c8d0 GM |
815 | @end defun |
816 | ||
031c41de EZ |
817 | During decoding, the translation table's translations are applied to |
818 | the characters that result from ordinary decoding. If a coding system | |
97d8273f | 819 | has the property @code{:decode-translation-table}, that specifies the |
031c41de EZ |
820 | translation table to use, or a list of translation tables to apply in |
821 | sequence. (This is a property of the coding system, as returned by | |
822 | @code{coding-system-get}, not a property of the symbol that is the | |
823 | coding system's name. @xref{Coding System Basics,, Basic Concepts of | |
824 | Coding Systems}.) Finally, if | |
825 | @code{standard-translation-table-for-decode} is non-@code{nil}, the | |
826 | resulting characters are translated by that table. | |
827 | ||
828 | During encoding, the translation table's translations are applied to | |
829 | the characters in the buffer, and the result of translation is | |
830 | actually encoded. If a coding system has property | |
831 | @code{:encode-translation-table}, that specifies the translation table | |
832 | to use, or a list of translation tables to apply in sequence. In | |
833 | addition, if the variable @code{standard-translation-table-for-encode} | |
834 | is non-@code{nil}, it specifies the translation table to use for | |
835 | translating the result. | |
b8d4c8d0 GM |
836 | |
837 | @defvar standard-translation-table-for-decode | |
031c41de EZ |
838 | This is the default translation table for decoding. If a coding |
839 | systems specifies its own translation tables, the table that is the | |
840 | value of this variable, if non-@code{nil}, is applied after them. | |
b8d4c8d0 GM |
841 | @end defvar |
842 | ||
843 | @defvar standard-translation-table-for-encode | |
031c41de EZ |
844 | This is the default translation table for encoding. If a coding |
845 | systems specifies its own translation tables, the table that is the | |
846 | value of this variable, if non-@code{nil}, is applied after them. | |
b8d4c8d0 GM |
847 | @end defvar |
848 | ||
5c9c5c4b EZ |
849 | @defvar translation-table-for-input |
850 | Self-inserting characters are translated through this translation | |
851 | table before they are inserted. Search commands also translate their | |
852 | input through this table, so they can compare more reliably with | |
853 | what's in the buffer. | |
854 | ||
855 | This variable automatically becomes buffer-local when set. | |
856 | @end defvar | |
857 | ||
031c41de EZ |
858 | @defun make-translation-table-from-vector vec |
859 | This function returns a translation table made from @var{vec} that is | |
85eeac93 | 860 | an array of 256 elements to map bytes (values 0 through #xFF) to |
031c41de EZ |
861 | characters. Elements may be @code{nil} for untranslated bytes. The |
862 | returned table has a translation table for reverse mapping in the | |
8b80cdf5 | 863 | first extra slot, and the value @code{1} in the second extra slot. |
031c41de EZ |
864 | |
865 | This function provides an easy way to make a private coding system | |
866 | that maps each byte to a specific character. You can specify the | |
867 | returned table and the reverse translation table using the properties | |
868 | @code{:decode-translation-table} and @code{:encode-translation-table} | |
869 | respectively in the @var{props} argument to | |
870 | @code{define-coding-system}. | |
871 | @end defun | |
872 | ||
873 | @defun make-translation-table-from-alist alist | |
874 | This function is similar to @code{make-translation-table} but returns | |
875 | a complex translation table rather than a simple one-to-one mapping. | |
876 | Each element of @var{alist} is of the form @code{(@var{from} | |
97d8273f CY |
877 | . @var{to})}, where @var{from} and @var{to} are either characters or |
878 | vectors specifying a sequence of characters. If @var{from} is a | |
1df7defd | 879 | character, that character is translated to @var{to} (i.e., to a |
031c41de EZ |
880 | character or a character sequence). If @var{from} is a vector of |
881 | characters, that sequence is translated to @var{to}. The returned | |
882 | table has a translation table for reverse mapping in the first extra | |
8b80cdf5 EZ |
883 | slot, and the maximum length of all the @var{from} character sequences |
884 | in the second extra slot. | |
031c41de EZ |
885 | @end defun |
886 | ||
b8d4c8d0 GM |
887 | @node Coding Systems |
888 | @section Coding Systems | |
889 | ||
890 | @cindex coding system | |
891 | When Emacs reads or writes a file, and when Emacs sends text to a | |
892 | subprocess or receives text from a subprocess, it normally performs | |
893 | character code conversion and end-of-line conversion as specified | |
894 | by a particular @dfn{coding system}. | |
895 | ||
896 | How to define a coding system is an arcane matter, and is not | |
897 | documented here. | |
898 | ||
899 | @menu | |
900 | * Coding System Basics:: Basic concepts. | |
901 | * Encoding and I/O:: How file I/O functions handle coding systems. | |
902 | * Lisp and Coding Systems:: Functions to operate on coding system names. | |
903 | * User-Chosen Coding Systems:: Asking the user to choose a coding system. | |
904 | * Default Coding Systems:: Controlling the default choices. | |
905 | * Specifying Coding Systems:: Requesting a particular coding system | |
906 | for a single file operation. | |
907 | * Explicit Encoding:: Encoding or decoding text without doing I/O. | |
908 | * Terminal I/O Encoding:: Use of encoding for terminal I/O. | |
b8d4c8d0 GM |
909 | @end menu |
910 | ||
911 | @node Coding System Basics | |
912 | @subsection Basic Concepts of Coding Systems | |
913 | ||
914 | @cindex character code conversion | |
80070260 EZ |
915 | @dfn{Character code conversion} involves conversion between the |
916 | internal representation of characters used inside Emacs and some other | |
917 | encoding. Emacs supports many different encodings, in that it can | |
918 | convert to and from them. For example, it can convert text to or from | |
919 | encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and | |
920 | several variants of ISO 2022. In some cases, Emacs supports several | |
921 | alternative encodings for the same characters; for example, there are | |
922 | three coding systems for the Cyrillic (Russian) alphabet: ISO, | |
923 | Alternativnyj, and KOI8. | |
924 | ||
af38459f EZ |
925 | Every coding system specifies a particular set of character code |
926 | conversions, but the coding system @code{undecided} is special: it | |
927 | leaves the choice unspecified, to be chosen heuristically for each | |
928 | file, based on the file's data. | |
b8d4c8d0 GM |
929 | |
930 | In general, a coding system doesn't guarantee roundtrip identity: | |
931 | decoding a byte sequence using coding system, then encoding the | |
932 | resulting text in the same coding system, can produce a different byte | |
80070260 EZ |
933 | sequence. But some coding systems do guarantee that the byte sequence |
934 | will be the same as what you originally decoded. Here are a few | |
935 | examples: | |
b8d4c8d0 GM |
936 | |
937 | @quotation | |
80070260 | 938 | iso-8859-1, utf-8, big5, shift_jis, euc-jp |
b8d4c8d0 GM |
939 | @end quotation |
940 | ||
941 | Encoding buffer text and then decoding the result can also fail to | |
80070260 EZ |
942 | reproduce the original text. For instance, if you encode a character |
943 | with a coding system which does not support that character, the result | |
944 | is unpredictable, and thus decoding it using the same coding system | |
945 | may produce a different text. Currently, Emacs can't report errors | |
946 | that result from encoding unsupported characters. | |
b8d4c8d0 GM |
947 | |
948 | @cindex EOL conversion | |
949 | @cindex end-of-line conversion | |
950 | @cindex line end conversion | |
80070260 EZ |
951 | @dfn{End of line conversion} handles three different conventions |
952 | used on various systems for representing end of line in files. The | |
953 | Unix convention, used on GNU and Unix systems, is to use the linefeed | |
954 | character (also called newline). The DOS convention, used on | |
955 | MS-Windows and MS-DOS systems, is to use a carriage-return and a | |
956 | linefeed at the end of a line. The Mac convention is to use just | |
957 | carriage-return. | |
b8d4c8d0 GM |
958 | |
959 | @cindex base coding system | |
960 | @cindex variant coding system | |
961 | @dfn{Base coding systems} such as @code{latin-1} leave the end-of-line | |
962 | conversion unspecified, to be chosen based on the data. @dfn{Variant | |
963 | coding systems} such as @code{latin-1-unix}, @code{latin-1-dos} and | |
964 | @code{latin-1-mac} specify the end-of-line conversion explicitly as | |
965 | well. Most base coding systems have three corresponding variants whose | |
966 | names are formed by adding @samp{-unix}, @samp{-dos} and @samp{-mac}. | |
967 | ||
02eccf6b | 968 | @vindex raw-text@r{ coding system} |
b8d4c8d0 | 969 | The coding system @code{raw-text} is special in that it prevents |
02eccf6b EZ |
970 | character code conversion, and causes the buffer visited with this |
971 | coding system to be a unibyte buffer. For historical reasons, you can | |
972 | save both unibyte and multibyte text with this coding system. When | |
973 | you use @code{raw-text} to encode multibyte text, it does perform one | |
974 | character code conversion: it converts eight-bit characters to their | |
975 | single-byte external representation. @code{raw-text} does not specify | |
976 | the end-of-line conversion, allowing that to be determined as usual by | |
977 | the data, and has the usual three variants which specify the | |
978 | end-of-line conversion. | |
979 | ||
980 | @vindex no-conversion@r{ coding system} | |
981 | @vindex binary@r{ coding system} | |
982 | @code{no-conversion} (and its alias @code{binary}) is equivalent to | |
983 | @code{raw-text-unix}: it specifies no conversion of either character | |
984 | codes or end-of-line. | |
b8d4c8d0 | 985 | |
80070260 | 986 | @vindex emacs-internal@r{ coding system} |
97d8273f CY |
987 | @vindex utf-8-emacs@r{ coding system} |
988 | The coding system @code{utf-8-emacs} specifies that the data is | |
989 | represented in the internal Emacs encoding (@pxref{Text | |
990 | Representations}). This is like @code{raw-text} in that no code | |
991 | conversion happens, but different in that the result is multibyte | |
992 | data. The name @code{emacs-internal} is an alias for | |
993 | @code{utf-8-emacs}. | |
b8d4c8d0 GM |
994 | |
995 | @defun coding-system-get coding-system property | |
996 | This function returns the specified property of the coding system | |
997 | @var{coding-system}. Most coding system properties exist for internal | |
80070260 | 998 | purposes, but one that you might find useful is @code{:mime-charset}. |
b8d4c8d0 GM |
999 | That property's value is the name used in MIME for the character coding |
1000 | which this coding system can read and write. Examples: | |
1001 | ||
1002 | @example | |
80070260 | 1003 | (coding-system-get 'iso-latin-1 :mime-charset) |
b8d4c8d0 | 1004 | @result{} iso-8859-1 |
80070260 | 1005 | (coding-system-get 'iso-2022-cn :mime-charset) |
b8d4c8d0 | 1006 | @result{} iso-2022-cn |
80070260 | 1007 | (coding-system-get 'cyrillic-koi8 :mime-charset) |
b8d4c8d0 GM |
1008 | @result{} koi8-r |
1009 | @end example | |
1010 | ||
80070260 | 1011 | The value of the @code{:mime-charset} property is also defined |
b8d4c8d0 GM |
1012 | as an alias for the coding system. |
1013 | @end defun | |
1014 | ||
9097ad86 | 1015 | @cindex alias, for coding systems |
91211f07 EZ |
1016 | @defun coding-system-aliases coding-system |
1017 | This function returns the list of aliases of @var{coding-system}. | |
1018 | @end defun | |
1019 | ||
b8d4c8d0 GM |
1020 | @node Encoding and I/O |
1021 | @subsection Encoding and I/O | |
1022 | ||
1023 | The principal purpose of coding systems is for use in reading and | |
97d8273f CY |
1024 | writing files. The function @code{insert-file-contents} uses a coding |
1025 | system to decode the file data, and @code{write-region} uses one to | |
1026 | encode the buffer contents. | |
b8d4c8d0 GM |
1027 | |
1028 | You can specify the coding system to use either explicitly | |
1029 | (@pxref{Specifying Coding Systems}), or implicitly using a default | |
1030 | mechanism (@pxref{Default Coding Systems}). But these methods may not | |
1031 | completely specify what to do. For example, they may choose a coding | |
1032 | system such as @code{undefined} which leaves the character code | |
1033 | conversion to be determined from the data. In these cases, the I/O | |
1034 | operation finishes the job of choosing a coding system. Very often | |
1035 | you will want to find out afterwards which coding system was chosen. | |
1036 | ||
1037 | @defvar buffer-file-coding-system | |
e2e3f1d7 MR |
1038 | This buffer-local variable records the coding system used for saving the |
1039 | buffer and for writing part of the buffer with @code{write-region}. If | |
1040 | the text to be written cannot be safely encoded using the coding system | |
1041 | specified by this variable, these operations select an alternative | |
1042 | encoding by calling the function @code{select-safe-coding-system} | |
1043 | (@pxref{User-Chosen Coding Systems}). If selecting a different encoding | |
1044 | requires to ask the user to specify a coding system, | |
1045 | @code{buffer-file-coding-system} is updated to the newly selected coding | |
1046 | system. | |
b8d4c8d0 GM |
1047 | |
1048 | @code{buffer-file-coding-system} does @emph{not} affect sending text | |
1049 | to a subprocess. | |
1050 | @end defvar | |
1051 | ||
1052 | @defvar save-buffer-coding-system | |
1053 | This variable specifies the coding system for saving the buffer (by | |
1054 | overriding @code{buffer-file-coding-system}). Note that it is not used | |
1055 | for @code{write-region}. | |
1056 | ||
1057 | When a command to save the buffer starts out to use | |
1058 | @code{buffer-file-coding-system} (or @code{save-buffer-coding-system}), | |
1059 | and that coding system cannot handle | |
1060 | the actual text in the buffer, the command asks the user to choose | |
1061 | another coding system (by calling @code{select-safe-coding-system}). | |
1062 | After that happens, the command also updates | |
1063 | @code{buffer-file-coding-system} to represent the coding system that | |
1064 | the user specified. | |
1065 | @end defvar | |
1066 | ||
1067 | @defvar last-coding-system-used | |
1068 | I/O operations for files and subprocesses set this variable to the | |
1069 | coding system name that was used. The explicit encoding and decoding | |
1070 | functions (@pxref{Explicit Encoding}) set it too. | |
1071 | ||
1072 | @strong{Warning:} Since receiving subprocess output sets this variable, | |
1073 | it can change whenever Emacs waits; therefore, you should copy the | |
1074 | value shortly after the function call that stores the value you are | |
1075 | interested in. | |
1076 | @end defvar | |
1077 | ||
1078 | The variable @code{selection-coding-system} specifies how to encode | |
1079 | selections for the window system. @xref{Window System Selections}. | |
1080 | ||
1081 | @defvar file-name-coding-system | |
1082 | The variable @code{file-name-coding-system} specifies the coding | |
1083 | system to use for encoding file names. Emacs encodes file names using | |
1084 | that coding system for all file operations. If | |
1085 | @code{file-name-coding-system} is @code{nil}, Emacs uses a default | |
1086 | coding system determined by the selected language environment. In the | |
1087 | default language environment, any non-@acronym{ASCII} characters in | |
1088 | file names are not encoded specially; they appear in the file system | |
1089 | using the internal Emacs representation. | |
1090 | @end defvar | |
1091 | ||
1092 | @strong{Warning:} if you change @code{file-name-coding-system} (or | |
1093 | the language environment) in the middle of an Emacs session, problems | |
1094 | can result if you have already visited files whose names were encoded | |
1095 | using the earlier coding system and are handled differently under the | |
1096 | new coding system. If you try to save one of these buffers under the | |
1097 | visited file name, saving may use the wrong file name, or it may get | |
1098 | an error. If such a problem happens, use @kbd{C-x C-w} to specify a | |
1099 | new file name for that buffer. | |
1100 | ||
1101 | @node Lisp and Coding Systems | |
1102 | @subsection Coding Systems in Lisp | |
1103 | ||
1104 | Here are the Lisp facilities for working with coding systems: | |
1105 | ||
0e90e7be | 1106 | @cindex list all coding systems |
b8d4c8d0 GM |
1107 | @defun coding-system-list &optional base-only |
1108 | This function returns a list of all coding system names (symbols). If | |
1109 | @var{base-only} is non-@code{nil}, the value includes only the | |
1110 | base coding systems. Otherwise, it includes alias and variant coding | |
1111 | systems as well. | |
1112 | @end defun | |
1113 | ||
1114 | @defun coding-system-p object | |
1115 | This function returns @code{t} if @var{object} is a coding system | |
1116 | name or @code{nil}. | |
1117 | @end defun | |
1118 | ||
0e90e7be EZ |
1119 | @cindex validity of coding system |
1120 | @cindex coding system, validity check | |
b8d4c8d0 | 1121 | @defun check-coding-system coding-system |
80070260 EZ |
1122 | This function checks the validity of @var{coding-system}. If that is |
1123 | valid, it returns @var{coding-system}. If @var{coding-system} is | |
1124 | @code{nil}, the function return @code{nil}. For any other values, it | |
1125 | signals an error whose @code{error-symbol} is @code{coding-system-error} | |
1126 | (@pxref{Signaling Errors, signal}). | |
b8d4c8d0 GM |
1127 | @end defun |
1128 | ||
0e90e7be | 1129 | @cindex eol type of coding system |
b8d4c8d0 GM |
1130 | @defun coding-system-eol-type coding-system |
1131 | This function returns the type of end-of-line (a.k.a.@: @dfn{eol}) | |
1132 | conversion used by @var{coding-system}. If @var{coding-system} | |
1133 | specifies a certain eol conversion, the return value is an integer 0, | |
1134 | 1, or 2, standing for @code{unix}, @code{dos}, and @code{mac}, | |
1135 | respectively. If @var{coding-system} doesn't specify eol conversion | |
1136 | explicitly, the return value is a vector of coding systems, each one | |
1137 | with one of the possible eol conversion types, like this: | |
1138 | ||
1139 | @lisp | |
1140 | (coding-system-eol-type 'latin-1) | |
1141 | @result{} [latin-1-unix latin-1-dos latin-1-mac] | |
1142 | @end lisp | |
1143 | ||
1144 | @noindent | |
1145 | If this function returns a vector, Emacs will decide, as part of the | |
1146 | text encoding or decoding process, what eol conversion to use. For | |
1147 | decoding, the end-of-line format of the text is auto-detected, and the | |
1148 | eol conversion is set to match it (e.g., DOS-style CRLF format will | |
1149 | imply @code{dos} eol conversion). For encoding, the eol conversion is | |
1150 | taken from the appropriate default coding system (e.g., | |
4e3b4528 | 1151 | default value of @code{buffer-file-coding-system} for |
b8d4c8d0 GM |
1152 | @code{buffer-file-coding-system}), or from the default eol conversion |
1153 | appropriate for the underlying platform. | |
1154 | @end defun | |
1155 | ||
0e90e7be | 1156 | @cindex eol conversion of coding system |
b8d4c8d0 GM |
1157 | @defun coding-system-change-eol-conversion coding-system eol-type |
1158 | This function returns a coding system which is like @var{coding-system} | |
1159 | except for its eol conversion, which is specified by @code{eol-type}. | |
1160 | @var{eol-type} should be @code{unix}, @code{dos}, @code{mac}, or | |
1161 | @code{nil}. If it is @code{nil}, the returned coding system determines | |
1162 | the end-of-line conversion from the data. | |
1163 | ||
1164 | @var{eol-type} may also be 0, 1 or 2, standing for @code{unix}, | |
1165 | @code{dos} and @code{mac}, respectively. | |
1166 | @end defun | |
1167 | ||
0e90e7be | 1168 | @cindex text conversion of coding system |
b8d4c8d0 GM |
1169 | @defun coding-system-change-text-conversion eol-coding text-coding |
1170 | This function returns a coding system which uses the end-of-line | |
1171 | conversion of @var{eol-coding}, and the text conversion of | |
1172 | @var{text-coding}. If @var{text-coding} is @code{nil}, it returns | |
1173 | @code{undecided}, or one of its variants according to @var{eol-coding}. | |
1174 | @end defun | |
1175 | ||
0e90e7be EZ |
1176 | @cindex safely encode region |
1177 | @cindex coding systems for encoding region | |
b8d4c8d0 GM |
1178 | @defun find-coding-systems-region from to |
1179 | This function returns a list of coding systems that could be used to | |
1180 | encode a text between @var{from} and @var{to}. All coding systems in | |
1181 | the list can safely encode any multibyte characters in that portion of | |
1182 | the text. | |
1183 | ||
1184 | If the text contains no multibyte characters, the function returns the | |
1185 | list @code{(undecided)}. | |
1186 | @end defun | |
1187 | ||
0e90e7be EZ |
1188 | @cindex safely encode a string |
1189 | @cindex coding systems for encoding a string | |
b8d4c8d0 GM |
1190 | @defun find-coding-systems-string string |
1191 | This function returns a list of coding systems that could be used to | |
1192 | encode the text of @var{string}. All coding systems in the list can | |
1193 | safely encode any multibyte characters in @var{string}. If the text | |
1194 | contains no multibyte characters, this returns the list | |
1195 | @code{(undecided)}. | |
1196 | @end defun | |
1197 | ||
0e90e7be EZ |
1198 | @cindex charset, coding systems to encode |
1199 | @cindex safely encode characters in a charset | |
b8d4c8d0 GM |
1200 | @defun find-coding-systems-for-charsets charsets |
1201 | This function returns a list of coding systems that could be used to | |
1202 | encode all the character sets in the list @var{charsets}. | |
1203 | @end defun | |
1204 | ||
91211f07 EZ |
1205 | @defun check-coding-systems-region start end coding-system-list |
1206 | This function checks whether coding systems in the list | |
1207 | @code{coding-system-list} can encode all the characters in the region | |
1208 | between @var{start} and @var{end}. If all of the coding systems in | |
1209 | the list can encode the specified text, the function returns | |
1210 | @code{nil}. If some coding systems cannot encode some of the | |
1211 | characters, the value is an alist, each element of which has the form | |
1212 | @code{(@var{coding-system1} @var{pos1} @var{pos2} @dots{})}, meaning | |
1213 | that @var{coding-system1} cannot encode characters at buffer positions | |
1214 | @var{pos1}, @var{pos2}, @enddots{}. | |
1215 | ||
1216 | @var{start} may be a string, in which case @var{end} is ignored and | |
1217 | the returned value references string indices instead of buffer | |
1218 | positions. | |
1219 | @end defun | |
1220 | ||
b8d4c8d0 GM |
1221 | @defun detect-coding-region start end &optional highest |
1222 | This function chooses a plausible coding system for decoding the text | |
80070260 | 1223 | from @var{start} to @var{end}. This text should be a byte sequence, |
1df7defd | 1224 | i.e., unibyte text or multibyte text with only @acronym{ASCII} and |
80070260 | 1225 | eight-bit characters (@pxref{Explicit Encoding}). |
b8d4c8d0 GM |
1226 | |
1227 | Normally this function returns a list of coding systems that could | |
1228 | handle decoding the text that was scanned. They are listed in order of | |
1229 | decreasing priority. But if @var{highest} is non-@code{nil}, then the | |
1230 | return value is just one coding system, the one that is highest in | |
1231 | priority. | |
1232 | ||
1233 | If the region contains only @acronym{ASCII} characters except for such | |
1234 | ISO-2022 control characters ISO-2022 as @code{ESC}, the value is | |
1235 | @code{undecided} or @code{(undecided)}, or a variant specifying | |
1236 | end-of-line conversion, if that can be deduced from the text. | |
0b4faef3 EZ |
1237 | |
1238 | If the region contains null bytes, the value is @code{no-conversion}, | |
1239 | even if the region contains text encoded in some coding system. | |
b8d4c8d0 GM |
1240 | @end defun |
1241 | ||
1242 | @defun detect-coding-string string &optional highest | |
1243 | This function is like @code{detect-coding-region} except that it | |
1244 | operates on the contents of @var{string} instead of bytes in the buffer. | |
91211f07 EZ |
1245 | @end defun |
1246 | ||
0e90e7be | 1247 | @cindex null bytes, and decoding text |
0b4faef3 EZ |
1248 | @defvar inhibit-null-byte-detection |
1249 | If this variable has a non-@code{nil} value, null bytes are ignored | |
1250 | when detecting the encoding of a region or a string. This allows to | |
1251 | correctly detect the encoding of text that contains null bytes, such | |
1252 | as Info files with Index nodes. | |
1253 | @end defvar | |
1254 | ||
1255 | @defvar inhibit-iso-escape-detection | |
1256 | If this variable has a non-@code{nil} value, ISO-2022 escape sequences | |
1257 | are ignored when detecting the encoding of a region or a string. The | |
1258 | result is that no text is ever detected as encoded in some ISO-2022 | |
1259 | encoding, and all escape sequences become visible in a buffer. | |
1260 | @strong{Warning:} @emph{Use this variable with extreme caution, | |
1261 | because many files in the Emacs distribution use ISO-2022 encoding.} | |
1262 | @end defvar | |
1263 | ||
0e90e7be | 1264 | @cindex charsets supported by a coding system |
91211f07 EZ |
1265 | @defun coding-system-charset-list coding-system |
1266 | This function returns the list of character sets (@pxref{Character | |
1267 | Sets}) supported by @var{coding-system}. Some coding systems that | |
1268 | support too many character sets to list them all yield special values: | |
1269 | @itemize @bullet | |
1270 | @item | |
1271 | If @var{coding-system} supports all the ISO-2022 charsets, the value | |
1272 | is @code{iso-2022}. | |
1273 | @item | |
1274 | If @var{coding-system} supports all Emacs characters, the value is | |
1275 | @code{(emacs)}. | |
1276 | @item | |
1277 | If @var{coding-system} supports all emacs-mule characters, the value | |
1278 | is @code{emacs-mule}. | |
1279 | @item | |
1280 | If @var{coding-system} supports all Unicode characters, the value is | |
1281 | @code{(unicode)}. | |
1282 | @end itemize | |
b8d4c8d0 GM |
1283 | @end defun |
1284 | ||
1285 | @xref{Coding systems for a subprocess,, Process Information}, in | |
1286 | particular the description of the functions | |
1287 | @code{process-coding-system} and @code{set-process-coding-system}, for | |
1288 | how to examine or set the coding systems used for I/O to a subprocess. | |
1289 | ||
1290 | @node User-Chosen Coding Systems | |
1291 | @subsection User-Chosen Coding Systems | |
1292 | ||
1293 | @cindex select safe coding system | |
1294 | @defun select-safe-coding-system from to &optional default-coding-system accept-default-p file | |
1295 | This function selects a coding system for encoding specified text, | |
1296 | asking the user to choose if necessary. Normally the specified text | |
1297 | is the text in the current buffer between @var{from} and @var{to}. If | |
1298 | @var{from} is a string, the string specifies the text to encode, and | |
1299 | @var{to} is ignored. | |
1300 | ||
77730170 EZ |
1301 | If the specified text includes raw bytes (@pxref{Text |
1302 | Representations}), @code{select-safe-coding-system} suggests | |
1303 | @code{raw-text} for its encoding. | |
1304 | ||
b8d4c8d0 GM |
1305 | If @var{default-coding-system} is non-@code{nil}, that is the first |
1306 | coding system to try; if that can handle the text, | |
1307 | @code{select-safe-coding-system} returns that coding system. It can | |
1308 | also be a list of coding systems; then the function tries each of them | |
1309 | one by one. After trying all of them, it next tries the current | |
1310 | buffer's value of @code{buffer-file-coding-system} (if it is not | |
4e3b4528 SM |
1311 | @code{undecided}), then the default value of |
1312 | @code{buffer-file-coding-system} and finally the user's most | |
b8d4c8d0 GM |
1313 | preferred coding system, which the user can set using the command |
1314 | @code{prefer-coding-system} (@pxref{Recognize Coding,, Recognizing | |
1315 | Coding Systems, emacs, The GNU Emacs Manual}). | |
1316 | ||
1317 | If one of those coding systems can safely encode all the specified | |
1318 | text, @code{select-safe-coding-system} chooses it and returns it. | |
1319 | Otherwise, it asks the user to choose from a list of coding systems | |
1320 | which can encode all the text, and returns the user's choice. | |
1321 | ||
1322 | @var{default-coding-system} can also be a list whose first element is | |
1323 | t and whose other elements are coding systems. Then, if no coding | |
1324 | system in the list can handle the text, @code{select-safe-coding-system} | |
1325 | queries the user immediately, without trying any of the three | |
1326 | alternatives described above. | |
1327 | ||
1328 | The optional argument @var{accept-default-p}, if non-@code{nil}, | |
1329 | should be a function to determine whether a coding system selected | |
1330 | without user interaction is acceptable. @code{select-safe-coding-system} | |
1331 | calls this function with one argument, the base coding system of the | |
1332 | selected coding system. If @var{accept-default-p} returns @code{nil}, | |
1333 | @code{select-safe-coding-system} rejects the silently selected coding | |
1334 | system, and asks the user to select a coding system from a list of | |
1335 | possible candidates. | |
1336 | ||
1337 | @vindex select-safe-coding-system-accept-default-p | |
1338 | If the variable @code{select-safe-coding-system-accept-default-p} is | |
9bd79893 GM |
1339 | non-@code{nil}, it should be a function taking a single argument. |
1340 | It is used in place of @var{accept-default-p}, overriding any | |
1341 | value supplied for this argument. | |
b8d4c8d0 GM |
1342 | |
1343 | As a final step, before returning the chosen coding system, | |
1344 | @code{select-safe-coding-system} checks whether that coding system is | |
1345 | consistent with what would be selected if the contents of the region | |
1346 | were read from a file. (If not, this could lead to data corruption in | |
1347 | a file subsequently re-visited and edited.) Normally, | |
1348 | @code{select-safe-coding-system} uses @code{buffer-file-name} as the | |
1349 | file for this purpose, but if @var{file} is non-@code{nil}, it uses | |
1350 | that file instead (this can be relevant for @code{write-region} and | |
1351 | similar functions). If it detects an apparent inconsistency, | |
1352 | @code{select-safe-coding-system} queries the user before selecting the | |
1353 | coding system. | |
1354 | @end defun | |
1355 | ||
1356 | Here are two functions you can use to let the user specify a coding | |
1357 | system, with completion. @xref{Completion}. | |
1358 | ||
1359 | @defun read-coding-system prompt &optional default | |
1360 | This function reads a coding system using the minibuffer, prompting with | |
1361 | string @var{prompt}, and returns the coding system name as a symbol. If | |
1362 | the user enters null input, @var{default} specifies which coding system | |
1363 | to return. It should be a symbol or a string. | |
1364 | @end defun | |
1365 | ||
1366 | @defun read-non-nil-coding-system prompt | |
1367 | This function reads a coding system using the minibuffer, prompting with | |
1368 | string @var{prompt}, and returns the coding system name as a symbol. If | |
1369 | the user tries to enter null input, it asks the user to try again. | |
1370 | @xref{Coding Systems}. | |
1371 | @end defun | |
1372 | ||
1373 | @node Default Coding Systems | |
1374 | @subsection Default Coding Systems | |
0e90e7be EZ |
1375 | @cindex default coding system |
1376 | @cindex coding system, automatically determined | |
b8d4c8d0 GM |
1377 | |
1378 | This section describes variables that specify the default coding | |
1379 | system for certain files or when running certain subprograms, and the | |
1380 | function that I/O operations use to access them. | |
1381 | ||
1382 | The idea of these variables is that you set them once and for all to the | |
1383 | defaults you want, and then do not change them again. To specify a | |
1384 | particular coding system for a particular operation in a Lisp program, | |
1385 | don't change these variables; instead, override them using | |
1386 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1387 | (@pxref{Specifying Coding Systems}). | |
1388 | ||
0e90e7be | 1389 | @cindex file contents, and default coding system |
01f17ae2 | 1390 | @defopt auto-coding-regexp-alist |
b8d4c8d0 GM |
1391 | This variable is an alist of text patterns and corresponding coding |
1392 | systems. Each element has the form @code{(@var{regexp} | |
1393 | . @var{coding-system})}; a file whose first few kilobytes match | |
1394 | @var{regexp} is decoded with @var{coding-system} when its contents are | |
1395 | read into a buffer. The settings in this alist take priority over | |
1396 | @code{coding:} tags in the files and the contents of | |
1397 | @code{file-coding-system-alist} (see below). The default value is set | |
1398 | so that Emacs automatically recognizes mail files in Babyl format and | |
1399 | reads them with no code conversions. | |
01f17ae2 | 1400 | @end defopt |
b8d4c8d0 | 1401 | |
0e90e7be | 1402 | @cindex file name, and default coding system |
01f17ae2 | 1403 | @defopt file-coding-system-alist |
b8d4c8d0 GM |
1404 | This variable is an alist that specifies the coding systems to use for |
1405 | reading and writing particular files. Each element has the form | |
1406 | @code{(@var{pattern} . @var{coding})}, where @var{pattern} is a regular | |
1407 | expression that matches certain file names. The element applies to file | |
1408 | names that match @var{pattern}. | |
1409 | ||
1410 | The @sc{cdr} of the element, @var{coding}, should be either a coding | |
1411 | system, a cons cell containing two coding systems, or a function name (a | |
1412 | symbol with a function definition). If @var{coding} is a coding system, | |
1413 | that coding system is used for both reading the file and writing it. If | |
1414 | @var{coding} is a cons cell containing two coding systems, its @sc{car} | |
1415 | specifies the coding system for decoding, and its @sc{cdr} specifies the | |
1416 | coding system for encoding. | |
1417 | ||
1418 | If @var{coding} is a function name, the function should take one | |
1419 | argument, a list of all arguments passed to | |
1420 | @code{find-operation-coding-system}. It must return a coding system | |
1421 | or a cons cell containing two coding systems. This value has the same | |
1422 | meaning as described above. | |
1423 | ||
1424 | If @var{coding} (or what returned by the above function) is | |
1425 | @code{undecided}, the normal code-detection is performed. | |
01f17ae2 | 1426 | @end defopt |
b8d4c8d0 | 1427 | |
01f17ae2 | 1428 | @defopt auto-coding-alist |
0e90e7be EZ |
1429 | This variable is an alist that specifies the coding systems to use for |
1430 | reading and writing particular files. Its form is like that of | |
1431 | @code{file-coding-system-alist}, but, unlike the latter, this variable | |
1432 | takes priority over any @code{coding:} tags in the file. | |
01f17ae2 | 1433 | @end defopt |
0e90e7be EZ |
1434 | |
1435 | @cindex program name, and default coding system | |
b8d4c8d0 GM |
1436 | @defvar process-coding-system-alist |
1437 | This variable is an alist specifying which coding systems to use for a | |
1438 | subprocess, depending on which program is running in the subprocess. It | |
1439 | works like @code{file-coding-system-alist}, except that @var{pattern} is | |
1440 | matched against the program name used to start the subprocess. The coding | |
1441 | system or systems specified in this alist are used to initialize the | |
1442 | coding systems used for I/O to the subprocess, but you can specify | |
1443 | other coding systems later using @code{set-process-coding-system}. | |
1444 | @end defvar | |
1445 | ||
1446 | @strong{Warning:} Coding systems such as @code{undecided}, which | |
1447 | determine the coding system from the data, do not work entirely reliably | |
1448 | with asynchronous subprocess output. This is because Emacs handles | |
1449 | asynchronous subprocess output in batches, as it arrives. If the coding | |
1450 | system leaves the character code conversion unspecified, or leaves the | |
1451 | end-of-line conversion unspecified, Emacs must try to detect the proper | |
1452 | conversion from one batch at a time, and this does not always work. | |
1453 | ||
1454 | Therefore, with an asynchronous subprocess, if at all possible, use a | |
1455 | coding system which determines both the character code conversion and | |
1456 | the end of line conversion---that is, one like @code{latin-1-unix}, | |
1457 | rather than @code{undecided} or @code{latin-1}. | |
1458 | ||
0e90e7be EZ |
1459 | @cindex port number, and default coding system |
1460 | @cindex network service name, and default coding system | |
b8d4c8d0 GM |
1461 | @defvar network-coding-system-alist |
1462 | This variable is an alist that specifies the coding system to use for | |
1463 | network streams. It works much like @code{file-coding-system-alist}, | |
1464 | with the difference that the @var{pattern} in an element may be either a | |
1465 | port number or a regular expression. If it is a regular expression, it | |
1466 | is matched against the network service name used to open the network | |
1467 | stream. | |
1468 | @end defvar | |
1469 | ||
1470 | @defvar default-process-coding-system | |
1471 | This variable specifies the coding systems to use for subprocess (and | |
1472 | network stream) input and output, when nothing else specifies what to | |
1473 | do. | |
1474 | ||
1475 | The value should be a cons cell of the form @code{(@var{input-coding} | |
1476 | . @var{output-coding})}. Here @var{input-coding} applies to input from | |
1477 | the subprocess, and @var{output-coding} applies to output to it. | |
1478 | @end defvar | |
1479 | ||
0e90e7be | 1480 | @cindex default coding system, functions to determine |
01f17ae2 | 1481 | @defopt auto-coding-functions |
b8d4c8d0 GM |
1482 | This variable holds a list of functions that try to determine a |
1483 | coding system for a file based on its undecoded contents. | |
1484 | ||
1485 | Each function in this list should be written to look at text in the | |
1486 | current buffer, but should not modify it in any way. The buffer will | |
1487 | contain undecoded text of parts of the file. Each function should | |
1488 | take one argument, @var{size}, which tells it how many characters to | |
1489 | look at, starting from point. If the function succeeds in determining | |
1490 | a coding system for the file, it should return that coding system. | |
1491 | Otherwise, it should return @code{nil}. | |
1492 | ||
1493 | If a file has a @samp{coding:} tag, that takes precedence, so these | |
1494 | functions won't be called. | |
01f17ae2 | 1495 | @end defopt |
b8d4c8d0 | 1496 | |
0e90e7be EZ |
1497 | @defun find-auto-coding filename size |
1498 | This function tries to determine a suitable coding system for | |
1499 | @var{filename}. It examines the buffer visiting the named file, using | |
1500 | the variables documented above in sequence, until it finds a match for | |
1501 | one of the rules specified by these variables. It then returns a cons | |
1502 | cell of the form @code{(@var{coding} . @var{source})}, where | |
1503 | @var{coding} is the coding system to use and @var{source} is a symbol, | |
1504 | one of @code{auto-coding-alist}, @code{auto-coding-regexp-alist}, | |
1505 | @code{:coding}, or @code{auto-coding-functions}, indicating which one | |
1506 | supplied the matching rule. The value @code{:coding} means the coding | |
1507 | system was specified by the @code{coding:} tag in the file | |
1508 | (@pxref{Specify Coding,, coding tag, emacs, The GNU Emacs Manual}). | |
1509 | The order of looking for a matching rule is @code{auto-coding-alist} | |
1510 | first, then @code{auto-coding-regexp-alist}, then the @code{coding:} | |
1511 | tag, and lastly @code{auto-coding-functions}. If no matching rule was | |
1512 | found, the function returns @code{nil}. | |
1513 | ||
1514 | The second argument @var{size} is the size of text, in characters, | |
1515 | following point. The function examines text only within @var{size} | |
1516 | characters after point. Normally, the buffer should be positioned at | |
1517 | the beginning when this function is called, because one of the places | |
1518 | for the @code{coding:} tag is the first one or two lines of the file; | |
1519 | in that case, @var{size} should be the size of the buffer. | |
1520 | @end defun | |
1521 | ||
1522 | @defun set-auto-coding filename size | |
1523 | This function returns a suitable coding system for file | |
1524 | @var{filename}. It uses @code{find-auto-coding} to find the coding | |
1525 | system. If no coding system could be determined, the function returns | |
1526 | @code{nil}. The meaning of the argument @var{size} is like in | |
1527 | @code{find-auto-coding}. | |
1528 | @end defun | |
1529 | ||
b8d4c8d0 GM |
1530 | @defun find-operation-coding-system operation &rest arguments |
1531 | This function returns the coding system to use (by default) for | |
1532 | performing @var{operation} with @var{arguments}. The value has this | |
1533 | form: | |
1534 | ||
1535 | @example | |
1536 | (@var{decoding-system} . @var{encoding-system}) | |
1537 | @end example | |
1538 | ||
1539 | The first element, @var{decoding-system}, is the coding system to use | |
1540 | for decoding (in case @var{operation} does decoding), and | |
1541 | @var{encoding-system} is the coding system for encoding (in case | |
1542 | @var{operation} does encoding). | |
1543 | ||
049bcbcb CY |
1544 | The argument @var{operation} is a symbol; it should be one of |
1545 | @code{write-region}, @code{start-process}, @code{call-process}, | |
1546 | @code{call-process-region}, @code{insert-file-contents}, or | |
1547 | @code{open-network-stream}. These are the names of the Emacs I/O | |
1548 | primitives that can do character code and eol conversion. | |
b8d4c8d0 GM |
1549 | |
1550 | The remaining arguments should be the same arguments that might be given | |
1551 | to the corresponding I/O primitive. Depending on the primitive, one | |
1552 | of those arguments is selected as the @dfn{target}. For example, if | |
1553 | @var{operation} does file I/O, whichever argument specifies the file | |
1554 | name is the target. For subprocess primitives, the process name is the | |
1555 | target. For @code{open-network-stream}, the target is the service name | |
1556 | or port number. | |
1557 | ||
1558 | Depending on @var{operation}, this function looks up the target in | |
1559 | @code{file-coding-system-alist}, @code{process-coding-system-alist}, | |
1560 | or @code{network-coding-system-alist}. If the target is found in the | |
1561 | alist, @code{find-operation-coding-system} returns its association in | |
1562 | the alist; otherwise it returns @code{nil}. | |
1563 | ||
1564 | If @var{operation} is @code{insert-file-contents}, the argument | |
1565 | corresponding to the target may be a cons cell of the form | |
1566 | @code{(@var{filename} . @var{buffer})}). In that case, @var{filename} | |
1567 | is a file name to look up in @code{file-coding-system-alist}, and | |
1568 | @var{buffer} is a buffer that contains the file's contents (not yet | |
1569 | decoded). If @code{file-coding-system-alist} specifies a function to | |
1570 | call for this file, and that function needs to examine the file's | |
1571 | contents (as it usually does), it should examine the contents of | |
1572 | @var{buffer} instead of reading the file. | |
1573 | @end defun | |
1574 | ||
1575 | @node Specifying Coding Systems | |
1576 | @subsection Specifying a Coding System for One Operation | |
1577 | ||
1578 | You can specify the coding system for a specific operation by binding | |
1579 | the variables @code{coding-system-for-read} and/or | |
1580 | @code{coding-system-for-write}. | |
1581 | ||
1582 | @defvar coding-system-for-read | |
1583 | If this variable is non-@code{nil}, it specifies the coding system to | |
1584 | use for reading a file, or for input from a synchronous subprocess. | |
1585 | ||
1586 | It also applies to any asynchronous subprocess or network stream, but in | |
1587 | a different way: the value of @code{coding-system-for-read} when you | |
1588 | start the subprocess or open the network stream specifies the input | |
1589 | decoding method for that subprocess or network stream. It remains in | |
1590 | use for that subprocess or network stream unless and until overridden. | |
1591 | ||
1592 | The right way to use this variable is to bind it with @code{let} for a | |
1593 | specific I/O operation. Its global value is normally @code{nil}, and | |
1594 | you should not globally set it to any other value. Here is an example | |
1595 | of the right way to use the variable: | |
1596 | ||
1597 | @example | |
1598 | ;; @r{Read the file with no character code conversion.} | |
1599 | ;; @r{Assume @acronym{crlf} represents end-of-line.} | |
1600 | (let ((coding-system-for-read 'emacs-mule-dos)) | |
1601 | (insert-file-contents filename)) | |
1602 | @end example | |
1603 | ||
1604 | When its value is non-@code{nil}, this variable takes precedence over | |
1605 | all other methods of specifying a coding system to use for input, | |
1606 | including @code{file-coding-system-alist}, | |
1607 | @code{process-coding-system-alist} and | |
1608 | @code{network-coding-system-alist}. | |
1609 | @end defvar | |
1610 | ||
1611 | @defvar coding-system-for-write | |
1612 | This works much like @code{coding-system-for-read}, except that it | |
1613 | applies to output rather than input. It affects writing to files, | |
1614 | as well as sending output to subprocesses and net connections. | |
1615 | ||
1616 | When a single operation does both input and output, as do | |
1617 | @code{call-process-region} and @code{start-process}, both | |
1618 | @code{coding-system-for-read} and @code{coding-system-for-write} | |
1619 | affect it. | |
1620 | @end defvar | |
1621 | ||
01f17ae2 | 1622 | @defopt inhibit-eol-conversion |
b8d4c8d0 GM |
1623 | When this variable is non-@code{nil}, no end-of-line conversion is done, |
1624 | no matter which coding system is specified. This applies to all the | |
1625 | Emacs I/O and subprocess primitives, and to the explicit encoding and | |
1626 | decoding functions (@pxref{Explicit Encoding}). | |
01f17ae2 | 1627 | @end defopt |
b8d4c8d0 | 1628 | |
91211f07 EZ |
1629 | @cindex priority order of coding systems |
1630 | @cindex coding systems, priority | |
1631 | Sometimes, you need to prefer several coding systems for some | |
1632 | operation, rather than fix a single one. Emacs lets you specify a | |
1633 | priority order for using coding systems. This ordering affects the | |
333f9019 | 1634 | sorting of lists of coding systems returned by functions such as |
91211f07 EZ |
1635 | @code{find-coding-systems-region} (@pxref{Lisp and Coding Systems}). |
1636 | ||
1637 | @defun coding-system-priority-list &optional highestp | |
1638 | This function returns the list of coding systems in the order of their | |
1639 | current priorities. Optional argument @var{highestp}, if | |
1640 | non-@code{nil}, means return only the highest priority coding system. | |
1641 | @end defun | |
1642 | ||
1643 | @defun set-coding-system-priority &rest coding-systems | |
1644 | This function puts @var{coding-systems} at the beginning of the | |
1645 | priority list for coding systems, thus making their priority higher | |
1646 | than all the rest. | |
1647 | @end defun | |
1648 | ||
1649 | @defmac with-coding-priority coding-systems &rest body@dots{} | |
1650 | This macro execute @var{body}, like @code{progn} does | |
1651 | (@pxref{Sequencing, progn}), with @var{coding-systems} at the front of | |
1652 | the priority list for coding systems. @var{coding-systems} should be | |
1653 | a list of coding systems to prefer during execution of @var{body}. | |
1654 | @end defmac | |
1655 | ||
b8d4c8d0 GM |
1656 | @node Explicit Encoding |
1657 | @subsection Explicit Encoding and Decoding | |
1658 | @cindex encoding in coding systems | |
1659 | @cindex decoding in coding systems | |
1660 | ||
1661 | All the operations that transfer text in and out of Emacs have the | |
1662 | ability to use a coding system to encode or decode the text. | |
1663 | You can also explicitly encode and decode text using the functions | |
1664 | in this section. | |
1665 | ||
1666 | The result of encoding, and the input to decoding, are not ordinary | |
1667 | text. They logically consist of a series of byte values; that is, a | |
80070260 EZ |
1668 | series of @acronym{ASCII} and eight-bit characters. In unibyte |
1669 | buffers and strings, these characters have codes in the range 0 | |
85eeac93 CY |
1670 | through #xFF (255). In a multibyte buffer or string, eight-bit |
1671 | characters have character codes higher than #xFF (@pxref{Text | |
1672 | Representations}), but Emacs transparently converts them to their | |
1673 | single-byte values when you encode or decode such text. | |
b8d4c8d0 GM |
1674 | |
1675 | The usual way to read a file into a buffer as a sequence of bytes, so | |
1676 | you can decode the contents explicitly, is with | |
1677 | @code{insert-file-contents-literally} (@pxref{Reading from Files}); | |
1678 | alternatively, specify a non-@code{nil} @var{rawfile} argument when | |
1679 | visiting a file with @code{find-file-noselect}. These methods result in | |
1680 | a unibyte buffer. | |
1681 | ||
1682 | The usual way to use the byte sequence that results from explicitly | |
1683 | encoding text is to copy it to a file or process---for example, to write | |
1684 | it with @code{write-region} (@pxref{Writing to Files}), and suppress | |
1685 | encoding by binding @code{coding-system-for-write} to | |
1686 | @code{no-conversion}. | |
1687 | ||
1688 | Here are the functions to perform explicit encoding or decoding. The | |
1689 | encoding functions produce sequences of bytes; the decoding functions | |
1690 | are meant to operate on sequences of bytes. All of these functions | |
80070260 EZ |
1691 | discard text properties. They also set @code{last-coding-system-used} |
1692 | to the precise coding system they used. | |
b8d4c8d0 | 1693 | |
80070260 | 1694 | @deffn Command encode-coding-region start end coding-system &optional destination |
b8d4c8d0 | 1695 | This command encodes the text from @var{start} to @var{end} according |
80070260 EZ |
1696 | to coding system @var{coding-system}. Normally, the encoded text |
1697 | replaces the original text in the buffer, but the optional argument | |
1698 | @var{destination} can change that. If @var{destination} is a buffer, | |
1699 | the encoded text is inserted in that buffer after point (point does | |
1700 | not move); if it is @code{t}, the command returns the encoded text as | |
1701 | a unibyte string without inserting it. | |
1702 | ||
1703 | If encoded text is inserted in some buffer, this command returns the | |
1704 | length of the encoded text. | |
1705 | ||
1706 | The result of encoding is logically a sequence of bytes, but the | |
1707 | buffer remains multibyte if it was multibyte before, and any 8-bit | |
1708 | bytes are converted to their multibyte representation (@pxref{Text | |
1709 | Representations}). | |
77730170 EZ |
1710 | |
1711 | @cindex @code{undecided} coding-system, when encoding | |
1712 | Do @emph{not} use @code{undecided} for @var{coding-system} when | |
1713 | encoding text, since that may lead to unexpected results. Instead, | |
1714 | use @code{select-safe-coding-system} (@pxref{User-Chosen Coding | |
1715 | Systems, select-safe-coding-system}) to suggest a suitable encoding, | |
1716 | if there's no obvious pertinent value for @var{coding-system}. | |
b8d4c8d0 GM |
1717 | @end deffn |
1718 | ||
80070260 | 1719 | @defun encode-coding-string string coding-system &optional nocopy buffer |
b8d4c8d0 GM |
1720 | This function encodes the text in @var{string} according to coding |
1721 | system @var{coding-system}. It returns a new string containing the | |
1722 | encoded text, except when @var{nocopy} is non-@code{nil}, in which | |
1723 | case the function may return @var{string} itself if the encoding | |
1724 | operation is trivial. The result of encoding is a unibyte string. | |
1725 | @end defun | |
1726 | ||
106e6894 | 1727 | @deffn Command decode-coding-region start end coding-system &optional destination |
b8d4c8d0 | 1728 | This command decodes the text from @var{start} to @var{end} according |
80070260 EZ |
1729 | to coding system @var{coding-system}. To make explicit decoding |
1730 | useful, the text before decoding ought to be a sequence of byte | |
1731 | values, but both multibyte and unibyte buffers are acceptable (in the | |
1732 | multibyte case, the raw byte values should be represented as eight-bit | |
1733 | characters). Normally, the decoded text replaces the original text in | |
1734 | the buffer, but the optional argument @var{destination} can change | |
1735 | that. If @var{destination} is a buffer, the decoded text is inserted | |
1736 | in that buffer after point (point does not move); if it is @code{t}, | |
1737 | the command returns the decoded text as a multibyte string without | |
1738 | inserting it. | |
1739 | ||
1740 | If decoded text is inserted in some buffer, this command returns the | |
1741 | length of the decoded text. | |
7d2a859f EZ |
1742 | |
1743 | This command puts a @code{charset} text property on the decoded text. | |
1744 | The value of the property states the character set used to decode the | |
1745 | original text. | |
b8d4c8d0 GM |
1746 | @end deffn |
1747 | ||
80070260 EZ |
1748 | @defun decode-coding-string string coding-system &optional nocopy buffer |
1749 | This function decodes the text in @var{string} according to | |
1750 | @var{coding-system}. It returns a new string containing the decoded | |
1751 | text, except when @var{nocopy} is non-@code{nil}, in which case the | |
1752 | function may return @var{string} itself if the decoding operation is | |
1753 | trivial. To make explicit decoding useful, the contents of | |
1754 | @var{string} ought to be a unibyte string with a sequence of byte | |
1755 | values, but a multibyte string is also acceptable (assuming it | |
1756 | contains 8-bit bytes in their multibyte form). | |
1757 | ||
1758 | If optional argument @var{buffer} specifies a buffer, the decoded text | |
1759 | is inserted in that buffer after point (point does not move). In this | |
1760 | case, the return value is the length of the decoded text. | |
7d2a859f EZ |
1761 | |
1762 | @cindex @code{charset}, text property | |
1763 | This function puts a @code{charset} text property on the decoded text. | |
1764 | The value of the property states the character set used to decode the | |
1765 | original text: | |
1766 | ||
1767 | @example | |
1768 | @group | |
1769 | (decode-coding-string "Gr\374ss Gott" 'latin-1) | |
1770 | @result{} #("Gr@"uss Gott" 0 9 (charset iso-8859-1)) | |
1771 | @end group | |
1772 | @end example | |
b8d4c8d0 GM |
1773 | @end defun |
1774 | ||
1775 | @defun decode-coding-inserted-region from to filename &optional visit beg end replace | |
1776 | This function decodes the text from @var{from} to @var{to} as if | |
1777 | it were being read from file @var{filename} using @code{insert-file-contents} | |
1778 | using the rest of the arguments provided. | |
1779 | ||
1780 | The normal way to use this function is after reading text from a file | |
1781 | without decoding, if you decide you would rather have decoded it. | |
1782 | Instead of deleting the text and reading it again, this time with | |
1783 | decoding, you can call this function. | |
1784 | @end defun | |
1785 | ||
1786 | @node Terminal I/O Encoding | |
1787 | @subsection Terminal I/O Encoding | |
1788 | ||
1789 | Emacs can decode keyboard input using a coding system, and encode | |
80070260 EZ |
1790 | terminal output. This is useful for terminals that transmit or |
1791 | display text using a particular encoding such as Latin-1. Emacs does | |
1792 | not set @code{last-coding-system-used} for encoding or decoding of | |
1793 | terminal I/O. | |
b8d4c8d0 | 1794 | |
3f1d322f | 1795 | @defun keyboard-coding-system &optional terminal |
b8d4c8d0 | 1796 | This function returns the coding system that is in use for decoding |
3f1d322f EZ |
1797 | keyboard input from @var{terminal}---or @code{nil} if no coding system |
1798 | is to be used for that terminal. If @var{terminal} is omitted or | |
1799 | @code{nil}, it means the selected frame's terminal. @xref{Multiple | |
1800 | Terminals}. | |
b8d4c8d0 GM |
1801 | @end defun |
1802 | ||
3f1d322f EZ |
1803 | @deffn Command set-keyboard-coding-system coding-system &optional terminal |
1804 | This command specifies @var{coding-system} as the coding system to use | |
1805 | for decoding keyboard input from @var{terminal}. If | |
1806 | @var{coding-system} is @code{nil}, that means do not decode keyboard | |
1807 | input. If @var{terminal} is a frame, it means that frame's terminal; | |
1808 | if it is @code{nil}, that means the currently selected frame's | |
1809 | terminal. @xref{Multiple Terminals}. | |
b8d4c8d0 GM |
1810 | @end deffn |
1811 | ||
106e6894 | 1812 | @defun terminal-coding-system &optional terminal |
b8d4c8d0 | 1813 | This function returns the coding system that is in use for encoding |
106e6894 CY |
1814 | terminal output from @var{terminal}---or @code{nil} if the output is |
1815 | not encoded. If @var{terminal} is a frame, it means that frame's | |
1816 | terminal; if it is @code{nil}, that means the currently selected | |
1817 | frame's terminal. | |
b8d4c8d0 GM |
1818 | @end defun |
1819 | ||
106e6894 | 1820 | @deffn Command set-terminal-coding-system coding-system &optional terminal |
b8d4c8d0 | 1821 | This command specifies @var{coding-system} as the coding system to use |
106e6894 CY |
1822 | for encoding terminal output from @var{terminal}. If |
1823 | @var{coding-system} is @code{nil}, terminal output is not encoded. If | |
1824 | @var{terminal} is a frame, it means that frame's terminal; if it is | |
1825 | @code{nil}, that means the currently selected frame's terminal. | |
b8d4c8d0 GM |
1826 | @end deffn |
1827 | ||
b8d4c8d0 GM |
1828 | @node Input Methods |
1829 | @section Input Methods | |
1830 | @cindex input methods | |
1831 | ||
1832 | @dfn{Input methods} provide convenient ways of entering non-@acronym{ASCII} | |
1833 | characters from the keyboard. Unlike coding systems, which translate | |
1834 | non-@acronym{ASCII} characters to and from encodings meant to be read by | |
1835 | programs, input methods provide human-friendly commands. (@xref{Input | |
1836 | Methods,,, emacs, The GNU Emacs Manual}, for information on how users | |
1837 | use input methods to enter text.) How to define input methods is not | |
1838 | yet documented in this manual, but here we describe how to use them. | |
1839 | ||
1840 | Each input method has a name, which is currently a string; | |
1841 | in the future, symbols may also be usable as input method names. | |
1842 | ||
1843 | @defvar current-input-method | |
1844 | This variable holds the name of the input method now active in the | |
1845 | current buffer. (It automatically becomes local in each buffer when set | |
1846 | in any fashion.) It is @code{nil} if no input method is active in the | |
1847 | buffer now. | |
1848 | @end defvar | |
1849 | ||
1850 | @defopt default-input-method | |
1851 | This variable holds the default input method for commands that choose an | |
1852 | input method. Unlike @code{current-input-method}, this variable is | |
1853 | normally global. | |
1854 | @end defopt | |
1855 | ||
1856 | @deffn Command set-input-method input-method | |
1857 | This command activates input method @var{input-method} for the current | |
1858 | buffer. It also sets @code{default-input-method} to @var{input-method}. | |
1859 | If @var{input-method} is @code{nil}, this command deactivates any input | |
1860 | method for the current buffer. | |
1861 | @end deffn | |
1862 | ||
1863 | @defun read-input-method-name prompt &optional default inhibit-null | |
1864 | This function reads an input method name with the minibuffer, prompting | |
1865 | with @var{prompt}. If @var{default} is non-@code{nil}, that is returned | |
1866 | by default, if the user enters empty input. However, if | |
1867 | @var{inhibit-null} is non-@code{nil}, empty input signals an error. | |
1868 | ||
1869 | The returned value is a string. | |
1870 | @end defun | |
1871 | ||
1872 | @defvar input-method-alist | |
1873 | This variable defines all the supported input methods. | |
1874 | Each element defines one input method, and should have the form: | |
1875 | ||
1876 | @example | |
1877 | (@var{input-method} @var{language-env} @var{activate-func} | |
1878 | @var{title} @var{description} @var{args}...) | |
1879 | @end example | |
1880 | ||
1881 | Here @var{input-method} is the input method name, a string; | |
1882 | @var{language-env} is another string, the name of the language | |
1883 | environment this input method is recommended for. (That serves only for | |
1884 | documentation purposes.) | |
1885 | ||
1886 | @var{activate-func} is a function to call to activate this method. The | |
1887 | @var{args}, if any, are passed as arguments to @var{activate-func}. All | |
1888 | told, the arguments to @var{activate-func} are @var{input-method} and | |
1889 | the @var{args}. | |
1890 | ||
1891 | @var{title} is a string to display in the mode line while this method is | |
1892 | active. @var{description} is a string describing this method and what | |
1893 | it is good for. | |
1894 | @end defvar | |
1895 | ||
1896 | The fundamental interface to input methods is through the | |
1897 | variable @code{input-method-function}. @xref{Reading One Event}, | |
1898 | and @ref{Invoking the Input Method}. | |
1899 | ||
1900 | @node Locales | |
1901 | @section Locales | |
1902 | @cindex locale | |
1903 | ||
1904 | POSIX defines a concept of ``locales'' which control which language | |
1905 | to use in language-related features. These Emacs variables control | |
1906 | how Emacs interacts with these features. | |
1907 | ||
1908 | @defvar locale-coding-system | |
1909 | @cindex keyboard input decoding on X | |
1910 | This variable specifies the coding system to use for decoding system | |
1911 | error messages and---on X Window system only---keyboard input, for | |
1912 | encoding the format argument to @code{format-time-string}, and for | |
1913 | decoding the return value of @code{format-time-string}. | |
1914 | @end defvar | |
1915 | ||
1916 | @defvar system-messages-locale | |
1917 | This variable specifies the locale to use for generating system error | |
1918 | messages. Changing the locale can cause messages to come out in a | |
1919 | different language or in a different orthography. If the variable is | |
1920 | @code{nil}, the locale is specified by environment variables in the | |
1921 | usual POSIX fashion. | |
1922 | @end defvar | |
1923 | ||
1924 | @defvar system-time-locale | |
1925 | This variable specifies the locale to use for formatting time values. | |
1926 | Changing the locale can cause messages to appear according to the | |
1927 | conventions of a different language. If the variable is @code{nil}, the | |
1928 | locale is specified by environment variables in the usual POSIX fashion. | |
1929 | @end defvar | |
1930 | ||
1931 | @defun locale-info item | |
1932 | This function returns locale data @var{item} for the current POSIX | |
1933 | locale, if available. @var{item} should be one of these symbols: | |
1934 | ||
1935 | @table @code | |
1936 | @item codeset | |
1937 | Return the character set as a string (locale item @code{CODESET}). | |
1938 | ||
1939 | @item days | |
1940 | Return a 7-element vector of day names (locale items | |
1941 | @code{DAY_1} through @code{DAY_7}); | |
1942 | ||
1943 | @item months | |
1944 | Return a 12-element vector of month names (locale items @code{MON_1} | |
1945 | through @code{MON_12}). | |
1946 | ||
1947 | @item paper | |
1948 | Return a list @code{(@var{width} @var{height})} for the default paper | |
1949 | size measured in millimeters (locale items @code{PAPER_WIDTH} and | |
1950 | @code{PAPER_HEIGHT}). | |
1951 | @end table | |
1952 | ||
1953 | If the system can't provide the requested information, or if | |
1954 | @var{item} is not one of those symbols, the value is @code{nil}. All | |
1955 | strings in the return value are decoded using | |
1956 | @code{locale-coding-system}. @xref{Locales,,, libc, The GNU Libc Manual}, | |
1957 | for more information about locales and locale items. | |
1958 | @end defun |