notes

libiconv是一个很不错的字符集转换库。程序接口也很简单

Q: Why does libiconv support encoding XXX? Why does libiconv not support
   encoding ZZZ?

A: libiconv, as an internationalization library, supports those character
   sets and encodings which are in wide-spread use in at least one territory
   of the world.

   Hint1: On http://www.w3c.org/International/O-charset-lang.html you find a
   page "Languages, countries, and the charsets typically used for them".
   From this table, we can conclude that the following are in active use:

     ISO-8859-1, CP1252   Afrikaans, Albanian, Basque, Catalan, Danish, Dutch,
                          English, Faroese, Finnish, French, Galician, German,
                          Icelandic, Irish, Italian, Norwegian, Portuguese,
                          Scottish, Spanish, Swedish
     ISO-8859-2           Croatian, Czech, Hungarian, Polish, Romanian, Slovak,
                          Slovenian
     ISO-8859-3           Esperanto, Maltese
     ISO-8859-5           Bulgarian, Byelorussian, Macedonian, Russian,
                          Serbian, Ukrainian
     ISO-8859-6           Arabic
     ISO-8859-7           Greek
     ISO-8859-8           Hebrew
     ISO-8859-9, CP1254   Turkish
     ISO-8859-10          Inuit, Lapp
     ISO-8859-13          Latvian, Lithuanian
     ISO-8859-15          Estonian
     KOI8-R               Russian
     SHIFT_JIS            Japanese
     ISO-2022-JP          Japanese
     EUC-JP               Japanese

   Ordered by frequency on the web (1997):
     ISO-8859-1, CP1252   96%
     SHIFT_JIS             1.6%
     ISO-2022-JP           1.2%
     EUC-JP                0.4%
     CP1250                0.3%
     CP1251                0.2%
     CP850                 0.1%
     MACINTOSH             0.1%
     ISO-8859-5            0.1%
     ISO-8859-2            0.0%

   Hint2: The character sets mentioned in the XFree86 4.0 locale.alias file.

     ISO-8859-1           Afrikaans, Basque, Breton, Catalan, Danish, Dutch,
                          English, Estonian, Faroese, Finnish, French,
                          Galician, German, Greenlandic, Icelandic,
                          Indonesian, Irish, Italian, Lithuanian, Norwegian,
                          Occitan, Portuguese, Scottish, Spanish, Swedish,
                          Walloon, Welsh
     ISO-8859-2           Albanian, Croatian, Czech, Hungarian, Polish,
                          Romanian, Serbian, Slovak, Slovenian
     ISO-8859-3           Esperanto
     ISO-8859-4           Estonian, Latvian, Lithuanian
     ISO-8859-5           Bulgarian, Byelorussian, Macedonian, Russian,
                          Serbian, Ukrainian
     ISO-8859-6           Arabic
     ISO-8859-7           Greek
     ISO-8859-8           Hebrew
     ISO-8859-9           Turkish
     ISO-8859-14          Breton, Irish, Scottish, Welsh
     ISO-8859-15          Basque, Breton, Catalan, Danish, Dutch, Estonian,
                          Faroese, Finnish, French, Galician, German,
                          Greenlandic, Icelandic, Irish, Italian, Lithuanian,
                          Norwegian, Occitan, Portuguese, Scottish, Spanish,
                          Swedish, Walloon, Welsh
     KOI8-R               Russian
     KOI8-U               Russian, Ukrainian
     EUC-JP (alias eucJP)      Japanese
     ISO-2022-JP (alias JIS7)  Japanese
     SHIFT_JIS (alias SJIS)    Japanese
     U90                       Japanese
     S90                       Japanese
     EUC-CN (alias eucCN)      Chinese
     EUC-TW (alias eucTW)      Chinese
     BIG5                      Chinese
     EUC-KR (alias eucKR)      Korean
     ARMSCII-8                 Armenian
     GEORGIAN-ACADEMY          Georgian
     GEORGIAN-PS               Georgian
     TIS-620 (alias TACTIS)    Thai
     MULELAO-1                 Laothian
     IBM-CP1133                Laothian
     VISCII                    Vietnamese
     TCVN                      Vietnamese
     NUNACOM-8                 Inuktitut

   Hint3: The character sets supported by Netscape Communicator 4.

     Where is this documented? For the complete picture, I had to use
     "strings netscape" and then a lot of guesswork. For a quick take,
     look at the "View - Character set" menu of Netscape Communicator 4.6:

     ISO-8859-{1,2,5,7,9,15}
     WINDOWS-{1250,1251,1253}
     KOI8-R               Cyrillic
     CP866                Cyrillic
     Autodetect           Japanese  (EUC-JP, ISO-2022-JP, ISO-2022-JP-2, SJIS)
     EUC-JP               Japanese
     SHIFT_JIS            Japanese
     GB2312               Chinese
     BIG5                 Chinese
     EUC-TW               Chinese
     Autodetect           Korean    (EUC-KR, ISO-2022-KR, but not JOHAB)

     UTF-8
     UTF-7

   Hint4: The character sets supported by Microsoft Internet Explorer 4.

     ISO-8859-{1,2,3,4,5,6,7,8,9}
     WINDOWS-{1250,1251,1252,1253,1254,1255,1256,1257}
     KOI8-R               Cyrillic
     KOI8-RU              Ukrainian
     ASMO-708             Arabic
     EUC-JP               Japanese
     ISO-2022-JP          Japanese
     SHIFT_JIS            Japanese
     GB2312               Chinese
     HZ-GB-2312           Chinese
     BIG5                 Chinese
     EUC-KR               Korean
     ISO-2022-KR          Korean
     WINDOWS-874          Thai
     WINDOWS-1258         Vietnamese

     UTF-8
     UTF-7
     UNICODE             actually UNICODE-LITTLE
     UNICODEFEFF         actually UNICODE-BIG

     and various DOS character sets: DOS-720, DOS-862, IBM852, CP866.

   We take the union of all these four sets. The result is:

   European and Semitic languages
     * ASCII.
       We implement this because it is occasionally useful to know or to
       check whether some text is entirely ASCII (i.e. if the conversion
       ISO-8859-x -> UTF-8 is trivial).
     * ISO-8859-{1,2,3,4,5,6,7,8,9,10}
       We implement this because they are widely used. Except ISO-8859-4
       which appears to have been superseded by ISO-8859-13 in the baltic
       countries. But it's an ISO standard anyway.
     * ISO-8859-13
       We implement this because it's a standard in Lithuania and Latvia.
     * ISO-8859-14
       We implement this because it's an ISO standard.
     * ISO-8859-15
       We implement this because it's increasingly used in Europe, because
       of the Euro symbol.
     * ISO-8859-16
       We implement this because it's an ISO standard.
     * KOI8-R, KOI8-U
       We implement this because it appears to be the predominant encoding
       on Unix in Russia and Ukraine, respectively.
     * KOI8-RU
       We implement this because MSIE4 supports it.
     * KOI8-T
       We implement this because it is the locale encoding in glibc's Tajik
       locale.
     * CP{1250,1251,1252,1253,1254,1255,1256,1257}
       We implement these because they are the predominant Windows encodings
       in Europe.
     * CP850
       We implement this because it is mentioned as occurring in the web
       in the aforementioned statistics.
     * CP862
       We implement this because Ron Aaron says it is sometimes used in web
       pages and emails.
     * CP866
       We implement this because Netscape Communicator does.
     * Mac{Roman,CentralEurope,Croatian,Romania,Cyrillic,Greek,Turkish} and
       Mac{Hebrew,Arabic}
       We implement these because the Sun JDK does, and because Mac users
       don't deserve to be punished.
     * Macintosh
       We implement this because it is mentioned as occurring in the web
       in the aforementioned statistics.
   Japanese
     * EUC-JP, SHIFT_JIS, ISO-2022-JP
       We implement these because they are widely used. EUC-JP and SHIFT_JIS
       are more used for files, whereas ISO-2022-JP is recommended for email.
     * CP932
       We implement this because it is the Microsoft variant of SHIFT_JIS,
       used on Windows.
     * ISO-2022-JP-2
       We implement this because it's the common way to represent mails which
       make use of JIS X 0212 characters.
     * ISO-2022-JP-1
       We implement this because it's in the RFCs, but I don't think it is
       really used.
     * U90, S90
       We DON'T implement this because I have no informations about what it
       is or who uses it.