| blob | 2d8133d4741d3d876842dac679d05f0b24431e61 |
1 Q: Why does libiconv support encoding XXX? Why does libiconv not support
2 encoding ZZZ?
4 A: libiconv, as an internationalization library, supports those character
5 sets and encodings which are in wide-spread use in at least one territory
6 of the world.
8 Hint1: On http://www.w3c.org/International/O-charset-lang.html you find a
9 page "Languages, countries, and the charsets typically used for them".
10 From this table, we can conclude that the following are in active use:
12 ISO-8859-1, CP1252 Afrikaans, Albanian, Basque, Catalan, Danish, Dutch,
13 English, Faroese, Finnish, French, Galician, German,
14 Icelandic, Irish, Italian, Norwegian, Portuguese,
15 Scottish, Spanish, Swedish
16 ISO-8859-2 Croatian, Czech, Hungarian, Polish, Romanian, Slovak,
17 Slovenian
18 ISO-8859-3 Esperanto, Maltese
19 ISO-8859-5 Bulgarian, Byelorussian, Macedonian, Russian,
20 Serbian, Ukrainian
21 ISO-8859-6 Arabic
22 ISO-8859-7 Greek
23 ISO-8859-8 Hebrew
24 ISO-8859-9, CP1254 Turkish
25 ISO-8859-10 Inuit, Lapp
26 ISO-8859-13 Latvian, Lithuanian
27 ISO-8859-15 Estonian
28 KOI8-R Russian
29 SHIFT_JIS Japanese
30 ISO-2022-JP Japanese
31 EUC-JP Japanese
33 Ordered by frequency on the web (1997):
34 ISO-8859-1, CP1252 96%
35 SHIFT_JIS 1.6%
36 ISO-2022-JP 1.2%
37 EUC-JP 0.4%
38 CP1250 0.3%
39 CP1251 0.2%
40 CP850 0.1%
41 MACINTOSH 0.1%
42 ISO-8859-5 0.1%
43 ISO-8859-2 0.0%
45 Hint2: The character sets mentioned in the XFree86 4.0 locale.alias file.
47 ISO-8859-1 Afrikaans, Basque, Breton, Catalan, Danish, Dutch,
48 English, Estonian, Faroese, Finnish, French,
49 Galician, German, Greenlandic, Icelandic,
50 Indonesian, Irish, Italian, Lithuanian, Norwegian,
51 Occitan, Portuguese, Scottish, Spanish, Swedish,
52 Walloon, Welsh
53 ISO-8859-2 Albanian, Croatian, Czech, Hungarian, Polish,
54 Romanian, Serbian, Slovak, Slovenian
55 ISO-8859-3 Esperanto
56 ISO-8859-4 Estonian, Latvian, Lithuanian
57 ISO-8859-5 Bulgarian, Byelorussian, Macedonian, Russian,
58 Serbian, Ukrainian
59 ISO-8859-6 Arabic
60 ISO-8859-7 Greek
61 ISO-8859-8 Hebrew
62 ISO-8859-9 Turkish
63 ISO-8859-14 Breton, Irish, Scottish, Welsh
64 ISO-8859-15 Basque, Breton, Catalan, Danish, Dutch, Estonian,
65 Faroese, Finnish, French, Galician, German,
66 Greenlandic, Icelandic, Irish, Italian, Lithuanian,
67 Norwegian, Occitan, Portuguese, Scottish, Spanish,
68 Swedish, Walloon, Welsh
69 KOI8-R Russian
70 KOI8-U Russian, Ukrainian
71 EUC-JP (alias eucJP) Japanese
72 ISO-2022-JP (alias JIS7) Japanese
73 SHIFT_JIS (alias SJIS) Japanese
74 U90 Japanese
75 S90 Japanese
76 EUC-CN (alias eucCN) Chinese
77 EUC-TW (alias eucTW) Chinese
78 BIG5 Chinese
79 EUC-KR (alias eucKR) Korean
80 ARMSCII-8 Armenian
81 GEORGIAN-ACADEMY Georgian
82 GEORGIAN-PS Georgian
83 TIS-620 (alias TACTIS) Thai
84 MULELAO-1 Laothian
85 IBM-CP1133 Laothian
86 VISCII Vietnamese
87 TCVN Vietnamese
88 NUNACOM-8 Inuktitut
90 Hint3: The character sets supported by Netscape Communicator 4.
92 Where is this documented? For the complete picture, I had to use
93 "strings netscape" and then a lot of guesswork. For a quick take,
94 look at the "View - Character set" menu of Netscape Communicator 4.6:
96 ISO-8859-{1,2,5,7,9,15}
97 WINDOWS-{1250,1251,1253}
98 KOI8-R Cyrillic
99 CP866 Cyrillic
100 Autodetect Japanese (EUC-JP, ISO-2022-JP, ISO-2022-JP-2, SJIS)
101 EUC-JP Japanese
102 SHIFT_JIS Japanese
103 GB2312 Chinese
104 BIG5 Chinese
105 EUC-TW Chinese
106 Autodetect Korean (EUC-KR, ISO-2022-KR, but not JOHAB)
108 UTF-8
109 UTF-7
111 Hint4: The character sets supported by Microsoft Internet Explorer 4.
113 ISO-8859-{1,2,3,4,5,6,7,8,9}
114 WINDOWS-{1250,1251,1252,1253,1254,1255,1256,1257}
115 KOI8-R Cyrillic
116 KOI8-RU Ukrainian
117 ASMO-708 Arabic
118 EUC-JP Japanese
119 ISO-2022-JP Japanese
120 SHIFT_JIS Japanese
121 GB2312 Chinese
122 HZ-GB-2312 Chinese
123 BIG5 Chinese
124 EUC-KR Korean
125 ISO-2022-KR Korean
126 WINDOWS-874 Thai
127 WINDOWS-1258 Vietnamese
129 UTF-8
130 UTF-7
131 UNICODE actually UNICODE-LITTLE
132 UNICODEFEFF actually UNICODE-BIG
134 and various DOS character sets: DOS-720, DOS-862, IBM852, CP866.
136 We take the union of all these four sets. The result is:
138 European and Semitic languages
139 * ASCII.
140 We implement this because it is occasionally useful to know or to
141 check whether some text is entirely ASCII (i.e. if the conversion
142 ISO-8859-x -> UTF-8 is trivial).
143 * ISO-8859-{1,2,3,4,5,6,7,8,9,10}
144 We implement this because they are widely used. Except ISO-8859-4
145 which appears to have been superseded by ISO-8859-13 in the baltic
146 countries. But it's an ISO standard anyway.
147 * ISO-8859-13
148 We implement this because it's a standard in Lithuania and Latvia.
149 * ISO-8859-14
150 We implement this because it's an ISO standard.
151 * ISO-8859-15
152 We implement this because it's increasingly used in Europe, because
153 of the Euro symbol.
154 * ISO-8859-16
155 We implement this because it's an ISO standard.
156 * KOI8-R, KOI8-U
157 We implement this because it appears to be the predominant encoding
158 on Unix in Russia and Ukraine, respectively.
159 * KOI8-RU
160 We implement this because MSIE4 supports it.
161 * CP{1250,1251,1252,1253,1254,1255,1256,1257}
162 We implement these because they are the predominant Windows encodings
163 in Europe.
164 * CP850
165 We implement this because it is mentioned as occurring in the web
166 in the aforementioned statistics.
167 * CP862
168 We implement this because Ron Aaron says it is sometimes used in web
169 pages and emails.
170 * CP866
171 We implement this because Netscape Communicator does.
172 * Mac{Roman,CentralEurope,Croatian,Romania,Cyrillic,Greek,Turkish} and
173 Mac{Hebrew,Arabic}
174 We implement these because the Sun JDK does, and because Mac users
175 don't deserve to be punished.
176 * Macintosh
177 We implement this because it is mentioned as occurring in the web
178 in the aforementioned statistics.
179 Japanese
180 * EUC-JP, SHIFT-JIS, ISO-2022-JP
181 We implement these because they are widely used. EUC-JP and SHIFT-JIS
182 are more used for files, whereas ISO-2022-JP is recommended for email.
183 * CP932
184 We implement this because it is the Microsoft variant of SHIFT-JIS,
185 used on Windows.
186 * ISO-2022-JP-2
187 We implement this because it's the common way to represent mails which
188 make use of JIS X 0212 characters.
189 * ISO-2022-JP-1
190 We implement this because it's in the RFCs, but I don't think it is
191 really used.
192 * U90, S90
193 We DON'T implement this because I have no informations about what it
194 is or who uses it.
195 Simplified Chinese
196 * EUC-CN = GB2312
197 We implement this because it is the widely used representation
198 of simplified Chinese.
199 * GBK
200 We implement this because it appears to be used on Solaris and Windows.
201 * GB18030
202 We implement this because it is an official requirement in the
203 People's Republic of China.
204 * ISO-2022-CN
205 We implement this because it is in the RFCs, but I have no idea
206 whether it is really used.
207 * ISO-2022-CN-EXT
208 We implement this because it's in the RFCs, but I don't think it is
209 really used.
210 * HZ = HZ-GB-2312
211 We implement this because the RFCs recommend it for Usenet postings,
212 and because MSIE4 supports it.
213 Traditional Chinese
214 * EUC-TW
215 We implement it because it appears to be used on Unix.
216 * BIG5
217 We implement it because it is the de-facto standard for traditional
218 Chinese.
219 * CP950
220 We implement this because it is the Microsoft variant of BIG5, used
221 on Windows.
222 * BIG5+
223 We DON'T implement this because it doesn't appear to be in wide use.
224 Only the CWEX fonts use this encoding. Furthermore, the conversion
225 tables in the big5p package are not coherent: If you convert directly,
226 you get different results than when you convert via GBK.
227 * BIG5HKSCS
228 We implement it because it is the de-facto standard for traditional
229 Chinese in Hongkong.
230 Korean
231 * EUC-KR
232 We implement these because they appear to be the widely used
233 representations for Korean.
234 * CP949
235 We implement this because it is the Microsoft variant of EUC-KR, used
236 on Windows.
237 * ISO-2022-KR
238 We implement it because it is in the RFCs and because MSIE4 supports
239 it, but I have no idea whether it's really used.
240 * JOHAB
241 We implement this because it is apparently used on Windows as a locale
242 encoding (codepage 1361).
243 * ISO-646-KR
244 We DON'T implement this because although an old ASCII variant, its
245 glyph for 0x7E is not clear: RFC 1345 and unicode.org's JOHAB.TXT
246 say it's a tilde, but Ken Lunde's "CJKV information processing" says
247 it's an overline. And it is not ISO-IR registered.
248 Armenian
249 * ARMSCII-8
250 We implement it because XFree86 supports it.
251 Georgian
252 * Georgian-Academy, Georgian-PS
253 We implement these because they appear to be both used for Georgian;
254 Xfree86 supports them.
255 Thai
256 * TIS-620
257 We implement this because it seems to be standard for Thai.
258 * CP874
259 We implement this because MSIE4 supports it.
260 * MacThai
261 We implement this because the Sun JDK does, and because Mac users
262 don't deserve to be punished.
263 Laotian
264 * MuleLao-1, CP1133
265 We implement these because XFree86 supports them. I have no idea which
266 one is used more widely.
267 Vietnamese
268 * VISCII, TCVN
269 We implement these because XFree86 supports them.
270 * CP1258
271 We implement this because MSIE4 supports it.
272 Other languages
273 * NUNACOM-8 (Inuktitut)
274 We DON'T implement this because it isn't part of Unicode yet, and
275 therefore doesn't convert to anything except itself.
276 Platform specifics
277 * HP-ROMAN8, NEXTSTEP
278 We implement these because they were the native character set on HPs
279 and NeXTs for a long time, and libiconv is intended to be usable on
280 these old machines.
281 Full Unicode
282 * UTF-8, UCS-2, UCS-4
283 We implement these. Obviously.
284 * UCS-2BE, UCS-2LE, UCS-4BE, UCS-4LE
285 We implement these because they are the preferred internal
286 representation of strings in Unicode aware applications. These are
287 non-ambiguous names, known to glibc. (glibc doesn't have
288 UCS-2-INTERNAL and UCS-4-INTERNAL.)
289 * UTF-16, UTF-16BE, UTF-16LE
290 We implement these, because UTF-16 is still the favourite encoding of
291 the president of the Unicode Consortium (for political reasons), and
292 because they appear in RFC 2781.
293 * UTF-7
294 We implement this because it is essential functionality for mail
295 applications.
296 * JAVA
297 We implement it because it's used for Java programs and because it's
298 a nice encoding for debugging.
299 * UNICODE (big endian), UNICODEFEFF (little endian)
300 We DON'T implement these because they are stupid and not standardized.
301 Full Unicode, in terms of `uint16_t' or `uint32_t'
302 (with machine dependent endianness and alignment)
303 * UCS-2-INTERNAL, UCS-4-INTERNAL
304 We implement these because they are the preferred internal
305 representation of strings in Unicode aware applications.
307 Q: Support encodings mentioned in RFC 1345 ?
308 A: No, they are not in use any more. Supporting ISO-646 variants is pointless
309 since ISO-8859-* have been adopted.
311 Q: Support EBCDIC ?
312 A: No!
314 Q: How do I add a new character set?
315 A: 1. Explain the "why" in this file, above.
316 2. You need to have a conversion table from/to Unicode. Transform it into
317 the format used by the mapping tables found on ftp.unicode.org: each line
318 contains the character code, in hex, with 0x prefix, then whitespace,
319 then the Unicode code point, in hex, 4 hex digits, with 0x prefix. '#'
320 counts as a comment delimiter until end of line.
321 Please also send your table to Mark Leisher <mleisher@crl.nmsu.edu> so he
322 can include it in his collection.
323 3. If it's an 8-bit character set, use the '8bit_tab_to_h' program in the
324 tools directory to generate the C code for the conversion. You may tweak
325 the resulting C code if you are not satisfied with its quality, but this
326 is rarely needed.
327 If it's a two-dimensional character set (with rows and columns), use the
328 'cjk_tab_to_h' program in the tools directory to generate the C code for
329 the conversion. You will need to modify the main() function to recognize
330 the new character set name, with the proper dimensions, but that shouldn't
331 be too hard. This yields the CCS. The CES you have to write by hand.
332 4. Store the resulting C code file in the lib directory. Add a #include
333 directive to converters.h, and add an entry to the encodings.def file.
334 5. Compile the package, and test your new encoding using a program like
335 iconv(1) or clisp(1).
336 6. Augment the testsuite: Add a line to each of tests/Makefile.in,
337 tests/Makefile.msvc and tests/Makefile.os2. For a stateless encoding,
338 create the complete table as a TXT file. For a stateful encoding,
339 provide a text snippet encoded using your new encoding and its UTF-8
340 equivalent.
341 7. Update the README and man/iconv_open.3, to mention the new encoding.
342 Add a note in the NEWS file.
344 Q: What about bidirectional text? Should it be tagged or reversed when
345 converting from ISO-8859-8 or ISO-8859-6 to Unicode? Qt appears to do
346 this, see qt-2.0.1/src/tools/qrtlcodec.cpp.
347 A: After reading RFC 1556: I don't think so. Support for ISO-8859-8-I and
348 ISO-8859-E remains to be implemented.
349 On the other hand, a page on www.w3c.org says that ISO-8859-8 in *email*
350 is visually encoded, ISO-8859-8 in *HTML* is logically encoded, i.e.
351 the same as ISO-8859-8-I. I'm confused.
353 Other character sets not implemented:
354 "MNEMONIC" = "csMnemonic"
355 "MNEM" = "csMnem"
356 "ISO-10646-UCS-Basic" = "csUnicodeASCII"
357 "ISO-10646-Unicode-Latin1" = "csUnicodeLatin1" = "ISO-10646"
358 "ISO-10646-J-1"
359 "UNICODE-1-1" = "csUnicode11"
360 "csWindows31Latin5"
362 Other aliases not implemented (and not implemented in glibc-2.1 either):
363 From MSIE4:
364 ISO-8859-1: alias ISO8859-1
365 ISO-8859-2: alias ISO8859-2
366 KSC_5601: alias KS_C_5601
367 UTF-8: aliases UNICODE-1-1-UTF-8 UNICODE-2-0-UTF-8
370 Q: How can I integrate libiconv into my package?
371 A: Just copy the entire libiconv package into a subdirectory of your package.
372 At configuration time, call libiconv's configure script with the
373 appropriate --srcdir option and maybe --enable-static or --disable-shared.
374 Then "cd libiconv && make && make install-lib libdir=... includedir=...".
375 'install-lib' is a special (not GNU standardized) target which installs
376 only the include file - in $(includedir) - and the library - in $(libdir) -
377 and does not use other directory variables. After "installing" libiconv
378 in your package's build directory, building of your package can proceed.
380 Q: Why is the testsuite so big?
381 A: Because some of the tests are very comprehensive.
382 If you don't feel like using the testsuite, you can simply remove the
383 tests/ directory.