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402 lines
17 KiB
402 lines
17 KiB
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: No! |
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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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