libiconv

Introduction to libiconv

International text is mostly encoded in Unicode. For historical reasons, however, it is sometimes still encoded using a language or country dependent character encoding. With the advent of the internet and the frequent exchange of text across countries - even the viewing of a web page from a foreign country is a "text exchange" in this context -, conversions between these encodings have become a necessity.

In particular, computers with the Windows operating system still operate in locale with a traditional (limited) character encoding. Some programs, like mailers and web browsers, must be able to convert between a given text encoding and the user's encoding. Other programs internally store strings in Unicode, to facilitate internal processing, and need to convert between internal string representation (Unicode) and external string representation (a traditional encoding) when they are doing I/O. GNU libiconv is a conversion library for both kinds of applications.

Details

This library provides an iconv() implementation, for use on systems which don't have one, or whose implementation cannot convert from/to Unicode.

It provides support for the encodings:

European languages: ASCII, ISO-8859-{1,2,3,4,5,7,9,10,13,14,15,16}, KOI8-R, KOI8-U, KOI8-RU, CP{1250,1251,1252,1253,1254,1257}, CP{850,866,1131}, Mac{Roman,CentralEurope,Iceland,Croatian,Romania}, Mac{Cyrillic,Ukraine,Greek,Turkish}, Macintosh
Semitic languages: ISO-8859-{6,8}, CP{1255,1256}, CP862, Mac{Hebrew,Arabic}
Japanese: EUC-JP, SHIFT_JIS, CP932, ISO-2022-JP, ISO-2022-JP-2, ISO-2022-JP-1, ISO-2022-JP-MS
Chinese: EUC-CN, HZ, GBK, CP936, GB18030, EUC-TW, BIG5, CP950, BIG5-HKSCS, BIG5-HKSCS:2004, BIG5-HKSCS:2001, BIG5-HKSCS:1999, ISO-2022-CN, ISO-2022-CN-EXT
Korean: EUC-KR, CP949, ISO-2022-KR, JOHAB
Armenian: ARMSCII-8
Georgian: Georgian-Academy, Georgian-PS
Tajik: KOI8-T
Kazakh: PT154, RK1048
Thai: ISO-8859-11, TIS-620, CP874, MacThai
Laotian: MuleLao-1, CP1133
Vietnamese: VISCII, TCVN, CP1258
Platform specifics: HP-ROMAN8, NEXTSTEP
Full Unicode: UTF-8
UCS-2, UCS-2BE, UCS-2LE
UCS-4, UCS-4BE, UCS-4LE
UTF-16, UTF-16BE, UTF-16LE
UTF-32, UTF-32BE, UTF-32LE
UTF-7
C99, JAVA
Full Unicode, in terms of uint16_t or uint32_t (with machine dependent endianness and alignment): UCS-2-INTERNAL, UCS-4-INTERNAL
Locale dependent, in terms of `char' or `wchar_t' (with machine dependent endianness and alignment, and with OS and locale dependent semantics): char, wchar_t
The empty encoding name "" is equivalent to "char": it denotes the locale dependent character encoding.

When configured with the option --enable-extra-encodings, it also provides support for a few extra encodings:

European languages: CP{437,737,775,852,853,855,857,858,860,861,863,865,869,1125}
Semitic languages: CP864
Japanese: EUC-JISX0213, Shift_JISX0213, ISO-2022-JP-3
Chinese: BIG5-2003 (experimental)
Turkmen: TDS565
Platform specifics: ATARIST, RISCOS-LATIN1

It can convert from any of these encodings to any other, through Unicode conversion.

It has also some limited support for transliteration, i.e. when a character cannot be represented in the target character set, it can be approximated through one or several similarly looking characters. Transliteration is activated when "//TRANSLIT" is appended to the target encoding name.

libiconv is for you if your application needs to support multiple character encodings, but that support lacks from your system.

Installation

As usual for GNU packages:

$ ./configure --prefix=/usr/local
$ make
$ make install

After installing GNU libiconv for the first time, it is recommended to recompile and reinstall GNU gettext, so that it can take advantage of libiconv.

On systems other than GNU/Linux, the iconv program will be internationalized only if GNU gettext has been built and installed before GNU libiconv. This means that the first time GNU libiconv is installed, we have a circular dependency between the GNU libiconv and GNU gettext packages, which can be resolved by building and installing either

first libiconv, then gettext, then libiconv again,

or (on systems supporting shared libraries, excluding AIX)

first gettext, then libiconv, then gettext again.

Recall that before building a package for the second time, you need to erase the traces of the first build by running "make distclean".

This library can be built and installed in two variants:

The library mode. This works on all systems, and uses a library libiconv.so and a header file <iconv.h>. (Both are installed through "make install".)
To use it, simply #include <iconv.h> and use the functions.
To use it in an autoconfiguring package:
- If you don't use automake, append m4/iconv.m4 to your aclocal.m4 file.
- If you do use automake, add m4/iconv.m4 to your m4 macro repository.
- Add to the link command line of libraries and executables that use the functions the placeholder @LIBICONV@ (or, if using libtool for the link, @LTLIBICONV@). If you use automake, the right place for these additions are the *_LDADD variables.
Note that iconv.m4 is also part of the GNU gettext package, which installs it in /usr/local/share/aclocal/iconv.m4.
The libc plug/override mode. This works on GNU/Linux, Solaris and OSF/1 systems only. It is a way to get good iconv support without having glibc-2.1. It installs a library preloadable_libiconv.so. This library can be used with LD_PRELOAD, to override the iconv* functions present in the C library.
- On GNU/Linux and Solaris:
```
$ export LD_PRELOAD=/usr/local/lib/preloadable_libiconv.so
```
- On OSF/1:
```
$ export _RLD_LIST=/usr/local/lib/preloadable_libiconv.so:DEFAULT
```
A program's source need not be modified, the program need not even be recompiled. Just set the LD_PRELOAD environment variable, that's it!

Copyright

The libiconv and libcharset libraries and their header files are under LGPL.

The iconv program is under GPL.

Downloading libiconv

libiconv can be downloaded from https://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.17.tar.gz. For other ways to obtain libiconv, please read How to get GNU Software.

The latest development sources can be obtained through the savannah project.

Documentation

Below are the links for the online documentation.

The iconv program: iconv.1.html

The library functions: iconv_open.3.html
iconv.3.html
iconv_close.3.html
iconvctl.3.html
iconv_open_into.3.html

Bug reports

Bug reports should be sent to <bug-gnu-libiconv@gnu.org>.

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Please send general FSF & GNU inquiries to <gnu@gnu.org>. There are also other ways to contact the FSF.
Please send broken links and other corrections or suggestions to <bug-gnu-libiconv-antispam@antispam.gnu.org>.

Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.

Last updated: $Date: 2022/05/15 20:38:31 $ $Author: haible $