NAME
unac - remove accents from string or character
SYNOPSIS
#include <unac.h>
const char* unac_version();
int unac_string(const char* charset,
const char* in, int in_length,
char** out, int* out_length);
int unac_string_utf16(const char* in, int in_length,
char** out, int* out_length);
/* MACRO: side effect on unaccented and length arguments */
unac_char_utf16(unsigned short c,
unsigned short* unaccented,
int length);
const char* unac_version()
/*
* The level argument can be one of:
* UNAC_DEBUG_NONE UNAC_DEBUG_LOW UNAC_DEBUG_HIGH
*/
void unac_debug(int level)
typedef void (*unac_debug_print_t)(const char* message, void* data);
void unac_debug_callback(int level, unac_debug_print_t function, void* data)
DESCRIPTION
unac is a C library that removes accents from characters, regardless of
the character set (ISO-8859-15, ISO-CELTIC, KOI8-RU...) as long as
iconv(3) is able to convert it into UTF-16 (Unicode).
The unac_string function is given a charset (ISO-8859-15 for instance)
and a string. It converts the string into UTF-16 and calls the
unac_string_utf16 function to remove all accents from the UTF-16
version. The unaccented string is then converted into the original
charset (ISO-8859-15 for instance) and returned to the caller of
unac_string.
unac does a little more than removing accents: every character that is
made of two character such as æ (ISO-8859-15 octal code 346) will be
expanded in two characters a and e. Should a character be made of
three characters, it would be decomposed in the same way.
The conversion from and to UTF-16 is done with iconv(3). The iconv -l
command will list all available charsets. Using UTF-16 as a pivot
implies an overhead but ensures that accents can be removed from all
character for which there is an equivalent character in Unicode.
unac_char_utf16 is a CPP macro that returns a pointer to the unaccented
equivalent of a given UTF-16 character. It is the basic building block
of unac.
unac_string_utf16 repeatidly applies the unac_char_utf16 macro to each
character of an UTF-16 string.
FUNCTIONS
int unac_string(const char* charset, const char* in, size_t in_length,
char** out, size_t* out_length)
Returns the unaccented equivalent of the string ’in’ of length
’in_length’ bytes. The returned string is stored in the pointer
pointed by the ’out’ argument and the length of the ’out’
string, in bytes, is stored in the integer pointed by the
’out_length ’ argument. If the ’*out’ pointer is not null, it
must point to an area allocated by malloc(3) and the length of
the array must be specified in the ’*out_length’ argument. Both
arguments ’*out’ and ’*out_length’ will be replaced with the
return values when the function returns on success. The ’*out’
pointer may point to a memory location that has been reallocated
(using realloc(3)) by the unac_string function. There is no
guarantee that ’*out’ is identical to the value given by the
caller. The pointer provided as ’*out’ by the caller may not be
useable when the function returns (either error or success). If
the ’*out’ pointer is null, the unac_string function allocates a
new memory block using malloc(3). It is the responsibility of
the caller to deallocate the area returned in the ’*out’
pointer.
The return value of unac_string is 0 on success and -1 on error,
in which case the errno variable is set to the corresponding
error code. See the ERROR section below for more information.
The iconv(3) manual page may also help.
int unac_string_utf16(const char* in, int in_length, char** out, int*
out_length)
Has the same effect as unac_string("UTF-16", in, in_length, out,
out_length). Since the unac_string_utf16 is the backend
function of the unac_string function it is more efficient
because no charset conversion of the input string (from and to
UTF-16) is necessary.
unac_char_utf16(const unsigned short c, unsigned short* p, int l)
Warning: this is a macro, each argument may be evaluated more
than once. Returns the unaccented equivalent of the UTF-16
character ’c’ in the pointer ’p’. The length of the unsigned
short array pointed by ’p’ is returned in the ’l’ argument.
const char* unac_version()
Return the version number of unac.
void unac_debug(int level)
Set the debug level of the unac library to ’level’. Possible
values are: UNAC_DEBUG_NONE for no debug at all, UNAC_DEBUG_LOW
for terse human readable information, UNAC_DEBUG_HIGH for very
detailed information only usable when translating a few strings.
unac_debug_callback with anything but UNAC_DEBUG_NONE is not
thread safe.
void unac_debug_callback(int level, unac_debug_print_t function, void*
data)
Set the debug level and define a printing function callback.
The ’level’ is the same as in unac_debug. The ’function’ is in
charge of dealing with the debug messages, presumably to print
them to the user. The ’data’ is an opaque pointer that is
passed along to function, should it need to manage a persistent
context.
The prototype of ’function’ accepts two arguments. The first is
the debug message (const char*), the second is the opaque
pointer given as ’data’ argument to unac_debug_callback.
If ’function’ is NULL, messages are printed on the standard
error output using fprintf(stderr...).
unac_debug_callback with anything but UNAC_DEBUG_NONE is not
thread safe.
ERRORS
EINVAL the requested conversion pair is not available. For instance,
when specifying the ISO-0000 charset (imaginary), it means it is
not possible to convert from ISO-0000 to UTF-16.
EXAMPLES
Convert the été string into ete.
#include <unac.h>
char* out = 0;
int out_length = 0;
if(unac_string("ISO-8859-1", "été", strlen("été"), &out, &out_length)) {
perror("unac_string");
} else {
printf("%.*s0, out_length, out);
free(out);
}
IMPLEMENTATION NOTES
The endianess of the UTF-16 strings manipulated by unac must always be
big endian. When using iconv(3) to translate strings, UTF-16BE should
be used instead of UTF-16 to make sure it is big endian (BE). On some
systems where UTF-16BE is not available, unac will rely on UTF-16 and
hope it is properly big endian encoded. For more information check
RFC2781 (http://www.faqs.org/rfcs/rfc.html: UTF-16, an encoding of
ISO 10646).
The unac library uses the Unicode database to map accented letters to
their unaccented equivalent. Mapping tables are generated from the
UnicodeData-4.0.0.txt file (as found at
http://www.unicode.org/Public/4.0-Update/) by the builder perl script.
The builder script inserts these tables in the unac.h and unac.c files,
replacing the existing ones. Looking for the ’Generated by builder’
string in the unac.[ch] files allows to spot the various parts handled
by the builder script.
Some desirable decompositions may not be included in the UnicodeData
file, such as AE. To complement the standard decompositions for the
purpose of the unac library, the unaccent-local-map.perl script is
used. It maps character names (such as LATIN SMALL LETTER AE) to an
array of character names into which it will be decomposed. This script
is used by the builder script and has precendence over decomposition
rules defined in the Unicode data file.
The library data occupies 30KB where a simple minded table would occupy
around 512Kbytes. The idea used to compress the tables is that many
Unicode characters do not have unaccented equivalent. Instead of
relying on a table mapping each Unicode character to the corresponding
unaccented character, an intermediate array of pointers is created. In
the drawing below, the range of UTF-16 character is not accurate but
illustrates the method. The unac_data_table points to a set of
unac_dataXX arrays. Each pointer covers a range of UTF-16 characters (4
in the example below). When a range of character does not contain any
accented character, unac_data_table always points to the same array :
unac_data0. Since there are many characters without accents, this is
enough to achieve a good compression.
unac_data15 unac_data16
[ NULL, NULL, NULL, e ] <---- /------> [ a, NULL, NULL, NULL ]
| |
| |
^ ^
|-----| |-----| |-----| |-----| |-----| |-----|
[ ... a b c d e f g h i j k é à 0 1 2 3 4 5 6 7 8 9 A... ] unac_data_table
|-----| |-----| |-----| |-----| |-----| |-----|
v v v v
| | | |
| | | |
--------------------------------------/
|
V
[ NULL, NULL, NULL, NULL ]
unac_data0
Beside this simple optimization, a table (unac_positions) listing the
actual position of the unaccented replacement within a block
(unac_dataXX) is necessary because they are not of fixed length. Some
characters such as æ will be replaced by two characters a and e
therefore unac_dataXX has a variable size.
The unaccented equivalent of an UTF-16 character is calculated by
applying a compatibility decomposition and then stripping all
characters that belong to the mark category. For a precise definition
see the Unicode-4.0 normalization forms at
http://www.unicode.org/unicode/reports/tr15/.
All original Unicode data files were taken from
http://www.unicode.org/Public and are subject to the UCD Terms of Use.
http://www.unicode.org/Public/4.0-Update/UCD-4.0.0.html#UCD_Terms
Disclaimer
The Unicode Character Database is provided as is by Unicode, Inc. No
claims are made as to fitness for any particular purpose. No warranties
of any kind are expressed or implied. The recipient agrees to determine
applicability of information provided. If this file has been purchased
on magnetic or optical media from Unicode, Inc., the sole remedy for
any claim will be exchange of defective media within 90 days of
receipt.
This disclaimer is applicable for all other data files accompanying the
Unicode Character Database, some of which have been compiled by the
Unicode Consortium, and some of which have been supplied by other
sources.
Limitations on Rights to Redistribute This Data
Recipient is granted the right to make copies in any form for internal
distribution and to freely use the information supplied in the creation
of products supporting the UnicodeTM Standard. The files in the Unicode
Character Database can be redistributed to third parties or other
organizations (whether for profit or not) as long as this notice and
the disclaimer notice are retained. Information can be extracted from
these files and used in documentation or programs, as long as there is
an accompanying notice indicating the source.
The file Unihan.txt contains older and inconsistent Terms of Use. That
language is overridden by these terms.
BUGS
The input string must not contain partially formed characters, there is
no support for this case.
UTF-16 surrogates are not handled.
Unicode may contain bugs in the decomposition of characters. When you
suspect such a bug on a given string, add a test case with the faulty
string in the t_unac.in test script (you will find it in the source
distribution) and run make check. It will describe, in a very verbose
way, how the string was unaccented. You may then fix the
UnicodeData-4.0.0.txt file and run make check again to make sure the
problem is solved. Please send such fixes to the author and to the
Unicode consortium.
SEE ALSO
unaccent(1), iconv(3)
http://www.unicode.org/
http://oss.software.ibm.com/icu/
http://www.gnu.org/manual/glibc-2.2.5/libc.html
AUTHOR
Loic Dachary loic@senga.org
http://www.senga.org/unac/
local unac(3)