1unicode(3) Erlang Module Definition unicode(3)
2
6 unicode - Functions for converting Unicode characters.
7
9 This module contains functions for converting between different charac‐
10 ter representations. It converts between ISO Latin-1 characters and
11 Unicode characters, but it can also convert between different Unicode
12 encodings (like UTF-8, UTF-16, and UTF-32).
13 The default Unicode encoding in Erlang is in binaries UTF-8, which is
15 also the format in which built-in functions and libraries in OTP expect
16 to find binary Unicode data. In lists, Unicode data is encoded as inte‐
17 gers, each integer representing one character and encoded simply as the
18 Unicode code point for the character.
19 Other Unicode encodings than integers representing code points or UTF-8
21 in binaries are referred to as "external encodings". The ISO Latin-1
22 encoding is in binaries and lists referred to as latin1-encoding.
23 It is recommended to only use external encodings for communication with
25 external entities where this is required. When working inside the
26 Erlang/OTP environment, it is recommended to keep binaries in UTF-8
27 when representing Unicode characters. ISO Latin-1 encoding is supported
28 both for backward compatibility and for communication with external
29 entities not supporting Unicode character sets.
30 Programs should always operate on a normalized form and compare canoni‐
32 cal-equivalent Unicode characters as equal. All characters should thus
33 be normalized to one form once on the system borders. One of the fol‐
34 lowing functions can convert characters to their normalized forms char‐
35 acters_to_nfc_list/1, characters_to_nfc_binary/1, charac‐
36 ters_to_nfd_list/1 or characters_to_nfd_binary/1. For general text
37 characters_to_nfc_list/1 or characters_to_nfc_binary/1 is preferred,
38 and for identifiers one of the compatibility normalization functions,
39 such as characters_to_nfkc_list/1, is preferred for security reasons.
40 The normalization functions where introduced in OTP 20. Additional
41 information on normalization can be found in the Unicode FAQ.
42
44 encoding() =
45 latin1 |
46 unicode |
47 utf8 |
48 utf16 |
49 {utf16, endian()} |
50 utf32 |
51 {utf32, endian()}
52 endian() = big | little
54 unicode_binary() = binary()
56 A binary() with characters encoded in the UTF-8 coding standard.
58 chardata() = charlist() | unicode_binary()
60 charlist() =
62 maybe_improper_list(char() | unicode_binary() | charlist(),
63 unicode_binary() | [])
64 external_unicode_binary() = binary()
66 A binary() with characters coded in a user-specified Unicode
68 encoding other than UTF-8 (that is, UTF-16 or UTF-32).
69 external_chardata() =
71 external_charlist() | external_unicode_binary()
72 external_charlist() =
74 maybe_improper_list(char() |
75 external_unicode_binary() |
76 external_charlist(),
77 external_unicode_binary() | [])
78 latin1_binary() = binary()
80 A binary() with characters coded in ISO Latin-1.
82 latin1_char() = byte()
84 An integer() representing a valid ISO Latin-1 character (0-255).
86 latin1_chardata() = latin1_charlist() | latin1_binary()
88 Same as iodata().
90 latin1_charlist() =
92 maybe_improper_list(latin1_char() |
93 latin1_binary() |
94 latin1_charlist(),
95 latin1_binary() | [])
96 Same as iolist().
98
100 bom_to_encoding(Bin) -> {Encoding, Length}
101 Types:
103 Bin = binary()
105 A binary() such that byte_size(Bin) >= 4.
106 Encoding =
107 latin1 | utf8 | {utf16, endian()} | {utf32, endian()}
108 Length = integer() >= 0
109 endian() = big | little
110 Checks for a UTF Byte Order Mark (BOM) in the beginning of a
112 binary. If the supplied binary Bin begins with a valid BOM for
113 either UTF-8, UTF-16, or UTF-32, the function returns the encod‐
114 ing identified along with the BOM length in bytes.
115 If no BOM is found, the function returns {latin1,0}.
117 characters_to_binary(Data) -> Result
119 Types:
121 Data = latin1_chardata() | chardata() | external_chardata()
123 Result =
124 binary() |
125 {error, binary(), RestData} |
126 {incomplete, binary(), binary()}
127 RestData = latin1_chardata() | chardata() | external_char‐
128 data()
129 Same as characters_to_binary(Data, unicode, unicode).
131 characters_to_binary(Data, InEncoding) -> Result
133 Types:
135 Data = latin1_chardata() | chardata() | external_chardata()
137 InEncoding = encoding()
138 Result =
139 binary() |
140 {error, binary(), RestData} |
141 {incomplete, binary(), binary()}
142 RestData = latin1_chardata() | chardata() | external_char‐
143 data()
144 Same as characters_to_binary(Data, InEncoding, unicode).
146 characters_to_binary(Data, InEncoding, OutEncoding) -> Result
148 Types:
150 Data = latin1_chardata() | chardata() | external_chardata()
152 InEncoding = OutEncoding = encoding()
153 Result =
154 binary() |
155 {error, binary(), RestData} |
156 {incomplete, binary(), binary()}
157 RestData = latin1_chardata() | chardata() | external_char‐
158 data()
159 Behaves as characters_to_list/2, but produces a binary instead
161 of a Unicode list.
162 InEncoding defines how input is to be interpreted if binaries
164 are present in Data
165 OutEncoding defines in what format output is to be generated.
167 Options:
169 unicode:
171 An alias for utf8, as this is the preferred encoding for
172 Unicode characters in binaries.
173 utf16:
175 An alias for {utf16,big}.
176 utf32:
178 An alias for {utf32,big}.
179 The atoms big and little denote big- or little-endian encoding.
181 Errors and exceptions occur as in characters_to_list/2, but the
183 second element in tuple error or incomplete is a binary() and
184 not a list().
185 characters_to_list(Data) -> Result
187 Types:
189 Data = latin1_chardata() | chardata() | external_chardata()
191 Result =
192 list() |
193 {error, list(), RestData} |
194 {incomplete, list(), binary()}
195 RestData = latin1_chardata() | chardata() | external_char‐
196 data()
197 Same as characters_to_list(Data, unicode).
199 characters_to_list(Data, InEncoding) -> Result
201 Types:
203 Data = latin1_chardata() | chardata() | external_chardata()
205 InEncoding = encoding()
206 Result =
207 list() |
208 {error, list(), RestData} |
209 {incomplete, list(), binary()}
210 RestData = latin1_chardata() | chardata() | external_char‐
211 data()
212 Converts a possibly deep list of integers and binaries into a
214 list of integers representing Unicode characters. The binaries
215 in the input can have characters encoded as one of the follow‐
216 ing:
217 * ISO Latin-1 (0-255, one character per byte). Here, case
219 parameter InEncoding is to be specified as latin1.
220 * One of the UTF-encodings, which is specified as parameter
222 InEncoding.
223 Note that integers in the list always represent code points
225 regardless of InEncoding passed. If InEncoding latin1 is passed,
226 only code points < 256 are allowed; otherwise, all valid unicode
227 code points are allowed.
228 If InEncoding is latin1, parameter Data corresponds to the
230 iodata() type, but for unicode, parameter Data can contain inte‐
231 gers > 255 (Unicode characters beyond the ISO Latin-1 range),
232 which makes it invalid as iodata().
233 The purpose of the function is mainly to convert combinations of
235 Unicode characters into a pure Unicode string in list represen‐
236 tation for further processing. For writing the data to an exter‐
237 nal entity, the reverse function characters_to_binary/3 comes in
238 handy.
239 Option unicode is an alias for utf8, as this is the preferred
241 encoding for Unicode characters in binaries. utf16 is an alias
242 for {utf16,big} and utf32 is an alias for {utf32,big}. The atoms
243 big and little denote big- or little-endian encoding.
244 If the data cannot be converted, either because of illegal Uni‐
246 code/ISO Latin-1 characters in the list, or because of invalid
247 UTF encoding in any binaries, an error tuple is returned. The
248 error tuple contains the tag error, a list representing the
249 characters that could be converted before the error occurred and
250 a representation of the characters including and after the
251 offending integer/bytes. The last part is mostly for debugging,
252 as it still constitutes a possibly deep or mixed list, or both,
253 not necessarily of the same depth as the original data. The
254 error occurs when traversing the list and whatever is left to
255 decode is returned "as is".
256 However, if the input Data is a pure binary, the third part of
258 the error tuple is guaranteed to be a binary as well.
259 Errors occur for the following reasons:
261 * Integers out of range.
263 If InEncoding is latin1, an error occurs whenever an integer
265 > 255 is found in the lists.
266 If InEncoding is of a Unicode type, an error occurs whenever
268 either of the following is found:
269 * An integer > 16#10FFFF (the maximum Unicode character)
271 * An integer in the range 16#D800 to 16#DFFF (invalid range
273 reserved for UTF-16 surrogate pairs)
274 * Incorrect UTF encoding.
276 If InEncoding is one of the UTF types, the bytes in any
278 binaries must be valid in that encoding.
279 Errors can occur for various reasons, including the follow‐
281 ing:
282 * "Pure" decoding errors (like the upper bits of the bytes
284 being wrong).
285 * The bytes are decoded to a too large number.
287 * The bytes are decoded to a code point in the invalid Uni‐
289 code range.
290 * Encoding is "overlong", meaning that a number should have
292 been encoded in fewer bytes.
293 The case of a truncated UTF is handled specially, see the
295 paragraph about incomplete binaries below.
296 If InEncoding is latin1, binaries are always valid as long
298 as they contain whole bytes, as each byte falls into the
299 valid ISO Latin-1 range.
300 A special type of error is when no actual invalid integers or
302 bytes are found, but a trailing binary() consists of too few
303 bytes to decode the last character. This error can occur if
304 bytes are read from a file in chunks or if binaries in other
305 ways are split on non-UTF character boundaries. An incomplete
306 tuple is then returned instead of the error tuple. It consists
307 of the same parts as the error tuple, but the tag is incomplete
308 instead of error and the last element is always guaranteed to be
309 a binary consisting of the first part of a (so far) valid UTF
310 character.
311 If one UTF character is split over two consecutive binaries in
313 the Data, the conversion succeeds. This means that a character
314 can be decoded from a range of binaries as long as the whole
315 range is specified as input without errors occurring.
316 Example:
318 decode_data(Data) ->
320 case unicode:characters_to_list(Data,unicode) of
321 {incomplete,Encoded, Rest} ->
322 More = get_some_more_data(),
323 Encoded ++ decode_data([Rest, More]);
324 {error,Encoded,Rest} ->
325 handle_error(Encoded,Rest);
326 List ->
327 List
328 end.
329 However, bit strings that are not whole bytes are not allowed,
331 so a UTF character must be split along 8-bit boundaries to ever
332 be decoded.
333 A badarg exception is thrown for the following cases:
335 * Any parameters are of the wrong type.
337 * The list structure is invalid (a number as tail).
339 * The binaries do not contain whole bytes (bit strings).
341 characters_to_nfc_list(CD :: chardata()) ->
343 [char()] | {error, [char()], chardata()}
344 Converts a possibly deep list of characters and binaries into a
346 Normalized Form of canonical equivalent Composed characters
347 according to the Unicode standard.
348 Any binaries in the input must be encoded with utf8 encoding.
350 The result is a list of characters.
352 3> unicode:characters_to_nfc_list([<<"abc..a">>,[778],$a,[776],$o,[776]]).
354 "abc..åäö"
355 characters_to_nfc_binary(CD :: chardata()) ->
358 unicode_binary() |
359 {error, unicode_binary(), chardata()}
360 Converts a possibly deep list of characters and binaries into a
362 Normalized Form of canonical equivalent Composed characters
363 according to the Unicode standard.
364 Any binaries in the input must be encoded with utf8 encoding.
366 The result is an utf8 encoded binary.
368 4> unicode:characters_to_nfc_binary([<<"abc..a">>,[778],$a,[776],$o,[776]]).
370 <<"abc..åäö"/utf8>>
371 characters_to_nfd_list(CD :: chardata()) ->
374 [char()] | {error, [char()], chardata()}
375 Converts a possibly deep list of characters and binaries into a
377 Normalized Form of canonical equivalent Decomposed characters
378 according to the Unicode standard.
379 Any binaries in the input must be encoded with utf8 encoding.
381 The result is a list of characters.
383 1> unicode:characters_to_nfd_list("abc..åäö").
385 [97,98,99,46,46,97,778,97,776,111,776]
386 characters_to_nfd_binary(CD :: chardata()) ->
389 unicode_binary() |
390 {error, unicode_binary(), chardata()}
391 Converts a possibly deep list of characters and binaries into a
393 Normalized Form of canonical equivalent Decomposed characters
394 according to the Unicode standard.
395 Any binaries in the input must be encoded with utf8 encoding.
397 The result is an utf8 encoded binary.
399 2> unicode:characters_to_nfd_binary("abc..åäö").
401 <<97,98,99,46,46,97,204,138,97,204,136,111,204,136>>
402 characters_to_nfkc_list(CD :: chardata()) ->
405 [char()] |
406 {error, [char()], chardata()}
407 Converts a possibly deep list of characters and binaries into a
409 Normalized Form of compatibly equivalent Composed characters
410 according to the Unicode standard.
411 Any binaries in the input must be encoded with utf8 encoding.
413 The result is a list of characters.
415 3> unicode:characters_to_nfkc_list([<<"abc..a">>,[778],$a,[776],$o,[776],[65299,65298]]).
417 "abc..åäö32"
418 characters_to_nfkc_binary(CD :: chardata()) ->
421 unicode_binary() |
422 {error, unicode_binary(), chardata()}
423 Converts a possibly deep list of characters and binaries into a
425 Normalized Form of compatibly equivalent Composed characters
426 according to the Unicode standard.
427 Any binaries in the input must be encoded with utf8 encoding.
429 The result is an utf8 encoded binary.
431 4> unicode:characters_to_nfkc_binary([<<"abc..a">>,[778],$a,[776],$o,[776],[65299,65298]]).
433 <<"abc..åäö32"/utf8>>
434 characters_to_nfkd_list(CD :: chardata()) ->
437 [char()] |
438 {error, [char()], chardata()}
439 Converts a possibly deep list of characters and binaries into a
441 Normalized Form of compatibly equivalent Decomposed characters
442 according to the Unicode standard.
443 Any binaries in the input must be encoded with utf8 encoding.
445 The result is a list of characters.
447 1> unicode:characters_to_nfkd_list(["abc..åäö",[65299,65298]]).
449 [97,98,99,46,46,97,778,97,776,111,776,51,50]
450 characters_to_nfkd_binary(CD :: chardata()) ->
453 unicode_binary() |
454 {error, unicode_binary(), chardata()}
455 Converts a possibly deep list of characters and binaries into a
457 Normalized Form of compatibly equivalent Decomposed characters
458 according to the Unicode standard.
459 Any binaries in the input must be encoded with utf8 encoding.
461 The result is an utf8 encoded binary.
463 2> unicode:characters_to_nfkd_binary(["abc..åäö",[65299,65298]]).
465 <<97,98,99,46,46,97,204,138,97,204,136,111,204,136,51,50>>
466 encoding_to_bom(InEncoding) -> Bin
469 Types:
471 Bin = binary()
473 A binary() such that byte_size(Bin) >= 4.
474 InEncoding = encoding()
475 Creates a UTF Byte Order Mark (BOM) as a binary from the sup‐
477 plied InEncoding. The BOM is, if supported at all, expected to
478 be placed first in UTF encoded files or messages.
479 The function returns <<>> for latin1 encoding, as there is no
481 BOM for ISO Latin-1.
482 Notice that the BOM for UTF-8 is seldom used, and it is really
484 not a byte order mark. There are obviously no byte order issues
485 with UTF-8, so the BOM is only there to differentiate UTF-8
486 encoding from other UTF formats.
487Ericsson AB stdlib 3.4.5.1 unicode(3)