405 lines
17 KiB
Plaintext
405 lines
17 KiB
Plaintext
Q: Why does libiconv support encoding XXX? Why does libiconv not support
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encoding ZZZ?
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A: libiconv, as an internationalization library, supports those character
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sets and encodings which are in wide-spread use in at least one territory
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of the world.
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Hint1: On http://www.w3c.org/International/O-charset-lang.html you find a
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page "Languages, countries, and the charsets typically used for them".
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From this table, we can conclude that the following are in active use:
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ISO-8859-1, CP1252 Afrikaans, Albanian, Basque, Catalan, Danish, Dutch,
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English, Faroese, Finnish, French, Galician, German,
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Icelandic, Irish, Italian, Norwegian, Portuguese,
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Scottish, Spanish, Swedish
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ISO-8859-2 Croatian, Czech, Hungarian, Polish, Romanian, Slovak,
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Slovenian
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ISO-8859-3 Esperanto, Maltese
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ISO-8859-5 Bulgarian, Byelorussian, Macedonian, Russian,
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Serbian, Ukrainian
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ISO-8859-6 Arabic
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ISO-8859-7 Greek
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ISO-8859-8 Hebrew
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ISO-8859-9, CP1254 Turkish
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ISO-8859-10 Inuit, Lapp
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ISO-8859-13 Latvian, Lithuanian
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ISO-8859-15 Estonian
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KOI8-R Russian
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SHIFT_JIS Japanese
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ISO-2022-JP Japanese
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EUC-JP Japanese
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Ordered by frequency on the web (1997):
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ISO-8859-1, CP1252 96%
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SHIFT_JIS 1.6%
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ISO-2022-JP 1.2%
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EUC-JP 0.4%
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CP1250 0.3%
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CP1251 0.2%
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CP850 0.1%
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MACINTOSH 0.1%
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ISO-8859-5 0.1%
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ISO-8859-2 0.0%
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Hint2: The character sets mentioned in the XFree86 4.0 locale.alias file.
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ISO-8859-1 Afrikaans, Basque, Breton, Catalan, Danish, Dutch,
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English, Estonian, Faroese, Finnish, French,
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Galician, German, Greenlandic, Icelandic,
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Indonesian, Irish, Italian, Lithuanian, Norwegian,
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Occitan, Portuguese, Scottish, Spanish, Swedish,
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Walloon, Welsh
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ISO-8859-2 Albanian, Croatian, Czech, Hungarian, Polish,
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Romanian, Serbian, Slovak, Slovenian
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ISO-8859-3 Esperanto
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ISO-8859-4 Estonian, Latvian, Lithuanian
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ISO-8859-5 Bulgarian, Byelorussian, Macedonian, Russian,
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Serbian, Ukrainian
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ISO-8859-6 Arabic
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ISO-8859-7 Greek
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ISO-8859-8 Hebrew
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ISO-8859-9 Turkish
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ISO-8859-14 Breton, Irish, Scottish, Welsh
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ISO-8859-15 Basque, Breton, Catalan, Danish, Dutch, Estonian,
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Faroese, Finnish, French, Galician, German,
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Greenlandic, Icelandic, Irish, Italian, Lithuanian,
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Norwegian, Occitan, Portuguese, Scottish, Spanish,
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Swedish, Walloon, Welsh
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KOI8-R Russian
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KOI8-U Russian, Ukrainian
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EUC-JP (alias eucJP) Japanese
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ISO-2022-JP (alias JIS7) Japanese
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SHIFT_JIS (alias SJIS) Japanese
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U90 Japanese
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S90 Japanese
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EUC-CN (alias eucCN) Chinese
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EUC-TW (alias eucTW) Chinese
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BIG5 Chinese
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EUC-KR (alias eucKR) Korean
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ARMSCII-8 Armenian
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GEORGIAN-ACADEMY Georgian
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GEORGIAN-PS Georgian
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TIS-620 (alias TACTIS) Thai
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MULELAO-1 Laothian
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IBM-CP1133 Laothian
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VISCII Vietnamese
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TCVN Vietnamese
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NUNACOM-8 Inuktitut
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Hint3: The character sets supported by Netscape Communicator 4.
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Where is this documented? For the complete picture, I had to use
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"strings netscape" and then a lot of guesswork. For a quick take,
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look at the "View - Character set" menu of Netscape Communicator 4.6:
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ISO-8859-{1,2,5,7,9,15}
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WINDOWS-{1250,1251,1253}
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KOI8-R Cyrillic
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CP866 Cyrillic
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Autodetect Japanese (EUC-JP, ISO-2022-JP, ISO-2022-JP-2, SJIS)
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EUC-JP Japanese
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SHIFT_JIS Japanese
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GB2312 Chinese
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BIG5 Chinese
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EUC-TW Chinese
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Autodetect Korean (EUC-KR, ISO-2022-KR, but not JOHAB)
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UTF-8
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UTF-7
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Hint4: The character sets supported by Microsoft Internet Explorer 4.
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ISO-8859-{1,2,3,4,5,6,7,8,9}
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WINDOWS-{1250,1251,1252,1253,1254,1255,1256,1257}
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KOI8-R Cyrillic
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KOI8-RU Ukrainian
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ASMO-708 Arabic
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EUC-JP Japanese
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ISO-2022-JP Japanese
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SHIFT_JIS Japanese
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GB2312 Chinese
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HZ-GB-2312 Chinese
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BIG5 Chinese
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EUC-KR Korean
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ISO-2022-KR Korean
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WINDOWS-874 Thai
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WINDOWS-1258 Vietnamese
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UTF-8
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UTF-7
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UNICODE actually UNICODE-LITTLE
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UNICODEFEFF actually UNICODE-BIG
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and various DOS character sets: DOS-720, DOS-862, IBM852, CP866.
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We take the union of all these four sets. The result is:
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European and Semitic languages
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* ASCII.
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We implement this because it is occasionally useful to know or to
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check whether some text is entirely ASCII (i.e. if the conversion
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ISO-8859-x -> UTF-8 is trivial).
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* ISO-8859-{1,2,3,4,5,6,7,8,9,10}
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We implement this because they are widely used. Except ISO-8859-4
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which appears to have been superseded by ISO-8859-13 in the baltic
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countries. But it's an ISO standard anyway.
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* ISO-8859-13
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We implement this because it's a standard in Lithuania and Latvia.
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* ISO-8859-14
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We implement this because it's an ISO standard.
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* ISO-8859-15
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We implement this because it's increasingly used in Europe, because
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of the Euro symbol.
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* ISO-8859-16
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We implement this because it's an ISO standard.
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* KOI8-R, KOI8-U
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We implement this because it appears to be the predominant encoding
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on Unix in Russia and Ukraine, respectively.
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* KOI8-RU
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We implement this because MSIE4 supports it.
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* KOI8-T
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We implement this because it is the locale encoding in glibc's Tajik
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locale.
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* PT154
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We implement this because it is the locale encoding in glibc's Kazakh
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locale.
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* RK1048
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We implement this because it's a standard in Kazakhstan.
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* CP{1250,1251,1252,1253,1254,1255,1256,1257}
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We implement these because they are the predominant Windows encodings
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in Europe.
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* CP850
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We implement this because it is mentioned as occurring in the web
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in the aforementioned statistics.
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* CP862
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We implement this because Ron Aaron says it is sometimes used in web
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pages and emails.
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* CP866
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We implement this because Netscape Communicator does.
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* CP1131
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We implement this because it is the locale encoding of a Belorusian
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locale in FreeBSD and MacOS X.
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* Mac{Roman,CentralEurope,Croatian,Romania,Cyrillic,Greek,Turkish} and
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Mac{Hebrew,Arabic}
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We implement these because the Sun JDK does, and because Mac users
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don't deserve to be punished.
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* Macintosh
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We implement this because it is mentioned as occurring in the web
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in the aforementioned statistics.
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Japanese
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* EUC-JP, SHIFT_JIS, ISO-2022-JP
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We implement these because they are widely used. EUC-JP and SHIFT_JIS
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are more used for files, whereas ISO-2022-JP is recommended for email.
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* CP932
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We implement this because it is the Microsoft variant of SHIFT_JIS,
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used on Windows.
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* ISO-2022-JP-2
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We implement this because it's the common way to represent mails which
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make use of JIS X 0212 characters.
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* ISO-2022-JP-1
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We implement this because it's in the RFCs, but I don't think it is
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really used.
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* ISO-2022-JP-MS
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We implement this because Microsoft Outlook Express / Microsoft MimeOLE
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sends emails in this encoding.
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* U90, S90
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We DON'T implement this because I have no informations about what it
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is or who uses it.
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Simplified Chinese
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* EUC-CN = GB2312
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We implement this because it is the widely used representation
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of simplified Chinese.
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* GBK
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We implement this because it appears to be used on Solaris and Windows.
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* GB18030
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We implement this because it is an official requirement in the
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People's Republic of China.
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* ISO-2022-CN
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We implement this because it is in the RFCs, but I have no idea
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whether it is really used.
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* ISO-2022-CN-EXT
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We implement this because it's in the RFCs, but I don't think it is
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really used.
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* HZ = HZ-GB-2312
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We implement this because the RFCs recommend it for Usenet postings,
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and because MSIE4 supports it.
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Traditional Chinese
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* EUC-TW
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We implement it because it appears to be used on Unix.
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* BIG5
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We implement it because it is the de-facto standard for traditional
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Chinese.
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* CP950
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We implement this because it is the Microsoft variant of BIG5, used
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on Windows.
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* BIG5+
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We DON'T implement this because it doesn't appear to be in wide use.
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Only the CWEX fonts use this encoding. Furthermore, the conversion
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tables in the big5p package are not coherent: If you convert directly,
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you get different results than when you convert via GBK.
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* BIG5-HKSCS
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We implement it because it is the de-facto standard for traditional
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Chinese in Hongkong.
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Korean
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* EUC-KR
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We implement these because they appear to be the widely used
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representations for Korean.
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* CP949
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We implement this because it is the Microsoft variant of EUC-KR, used
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on Windows.
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* ISO-2022-KR
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We implement it because it is in the RFCs and because MSIE4 supports
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it, but I have no idea whether it's really used.
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* JOHAB
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We implement this because it is apparently used on Windows as a locale
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encoding (codepage 1361).
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* ISO-646-KR
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We DON'T implement this because although an old ASCII variant, its
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glyph for 0x7E is not clear: RFC 1345 and unicode.org's JOHAB.TXT
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say it's a tilde, but Ken Lunde's "CJKV information processing" says
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it's an overline. And it is not ISO-IR registered.
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Armenian
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* ARMSCII-8
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We implement it because XFree86 supports it.
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Georgian
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* Georgian-Academy, Georgian-PS
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We implement these because they appear to be both used for Georgian;
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Xfree86 supports them.
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Thai
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* ISO-8859-11, TIS-620
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We implement these because it seems to be standard for Thai.
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* CP874
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We implement this because MSIE4 supports it.
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* MacThai
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We implement this because the Sun JDK does, and because Mac users
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don't deserve to be punished.
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Laotian
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* MuleLao-1, CP1133
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We implement these because XFree86 supports them. I have no idea which
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one is used more widely.
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Vietnamese
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* VISCII, TCVN
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We implement these because XFree86 supports them.
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* CP1258
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We implement this because MSIE4 supports it.
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Other languages
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* NUNACOM-8 (Inuktitut)
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We DON'T implement this because it isn't part of Unicode yet, and
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therefore doesn't convert to anything except itself.
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Platform specifics
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* HP-ROMAN8, NEXTSTEP
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We implement these because they were the native character set on HPs
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and NeXTs for a long time, and libiconv is intended to be usable on
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these old machines.
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Full Unicode
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* UTF-8, UCS-2, UCS-4
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We implement these. Obviously.
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* UCS-2BE, UCS-2LE, UCS-4BE, UCS-4LE
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We implement these because they are the preferred internal
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representation of strings in Unicode aware applications. These are
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non-ambiguous names, known to glibc. (glibc doesn't have
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UCS-2-INTERNAL and UCS-4-INTERNAL.)
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* UTF-16, UTF-16BE, UTF-16LE
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We implement these, because UTF-16 is still the favourite encoding of
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the president of the Unicode Consortium (for political reasons), and
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because they appear in RFC 2781.
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* UTF-32, UTF-32BE, UTF-32LE
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We implement these because they are part of Unicode 3.1.
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* UTF-7
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We implement this because it is essential functionality for mail
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applications.
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* C99
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We implement it because it's used for C and C++ programs and because
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it's a nice encoding for debugging.
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* JAVA
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We implement it because it's used for Java programs and because it's
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a nice encoding for debugging.
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* UNICODE (big endian), UNICODEFEFF (little endian)
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We DON'T implement these because they are stupid and not standardized.
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Full Unicode, in terms of 'uint16_t' or 'uint32_t'
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(with machine dependent endianness and alignment)
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* UCS-2-INTERNAL, UCS-4-INTERNAL
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We implement these because they are the preferred internal
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representation of strings in Unicode aware applications.
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Q: Support encodings mentioned in RFC 1345 ?
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A: No, they are not in use any more. Supporting ISO-646 variants is pointless
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since ISO-8859-* have been adopted.
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Q: Support EBCDIC ?
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A: Available through --enable-extra-encodings.
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Why? Because several people (Ulrich Schwab, Calvin Buckley) have shown
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interest in these encodings, by preparing forks of GNU libiconv.
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Q: How do I add a new character set?
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A: 1. Explain the "why" in this file, above.
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2. You need to have a conversion table from/to Unicode. Transform it into
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the format used by the mapping tables found on ftp.unicode.org: each line
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contains the character code, in hex, with 0x prefix, then whitespace,
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then the Unicode code point, in hex, 4 hex digits, with 0x prefix. '#'
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counts as a comment delimiter until end of line.
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Please also send your table to Mark Leisher <mleisher@crl.nmsu.edu> so he
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can include it in his collection.
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3. If it's an 8-bit character set, use the '8bit_tab_to_h' program in the
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tools directory to generate the C code for the conversion. You may tweak
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the resulting C code if you are not satisfied with its quality, but this
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is rarely needed.
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If it's a two-dimensional character set (with rows and columns), use the
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'cjk_tab_to_h' program in the tools directory to generate the C code for
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the conversion. You will need to modify the main() function to recognize
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the new character set name, with the proper dimensions, but that shouldn't
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be too hard. This yields the CCS. The CES you have to write by hand.
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4. Store the resulting C code file in the lib directory. Add a #include
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directive to converters.h, and add an entry to the encodings.def file.
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5. Compile the package, and test your new encoding using a program like
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iconv(1) or clisp(1).
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6. Augment the testsuite: Add a line to tests/Makefile.in. For a stateless
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encoding, create the complete table as a TXT file. For a stateful encoding,
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provide a text snippet encoded using your new encoding and its UTF-8
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equivalent.
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7. Update the README and man/iconv_open.3, to mention the new encoding.
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Add a note in the NEWS file.
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Q: What about bidirectional text? Should it be tagged or reversed when
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converting from ISO-8859-8 or ISO-8859-6 to Unicode? Qt appears to do
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this, see qt-2.0.1/src/tools/qrtlcodec.cpp.
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A: After reading RFC 1556: I don't think so. Support for ISO-8859-8-I and
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ISO-8859-E remains to be implemented.
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On the other hand, a page on www.w3c.org says that ISO-8859-8 in *email*
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is visually encoded, ISO-8859-8 in *HTML* is logically encoded, i.e.
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the same as ISO-8859-8-I. I'm confused.
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Other character sets not implemented:
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"MNEMONIC" = "csMnemonic"
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"MNEM" = "csMnem"
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"ISO-10646-UCS-Basic" = "csUnicodeASCII"
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"ISO-10646-Unicode-Latin1" = "csUnicodeLatin1" = "ISO-10646"
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"ISO-10646-J-1"
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"UNICODE-1-1" = "csUnicode11"
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"csWindows31Latin5"
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Other aliases not implemented (and not implemented in glibc-2.1 either):
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From MSIE4:
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ISO-8859-1: alias ISO8859-1
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ISO-8859-2: alias ISO8859-2
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KSC_5601: alias KS_C_5601
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UTF-8: aliases UNICODE-1-1-UTF-8 UNICODE-2-0-UTF-8
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Q: How can I integrate libiconv into my package?
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A: Just copy the entire libiconv package into a subdirectory of your package.
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At configuration time, call libiconv's configure script with the
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appropriate --srcdir option and maybe --enable-static or --disable-shared.
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Then "cd libiconv && make && make install-lib libdir=... includedir=...".
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'install-lib' is a special (not GNU standardized) target which installs
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only the include file - in $(includedir) - and the library - in $(libdir) -
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and does not use other directory variables. After "installing" libiconv
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in your package's build directory, building of your package can proceed.
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Q: Why is the testsuite so big?
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A: Because some of the tests are very comprehensive.
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If you don't feel like using the testsuite, you can simply remove the
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tests/ directory.
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