iconv(3)iconv(3)NAME
iconv - charset conversion function
SYNOPSIS
#include <iconv.h>
size_t iconv(iconv_t cd, const char **inbuf,
size_t *inbytesleft, char **outbuf,
size_t *outbytesleft);
DESCRIPTION
The iconv() function converts the sequence of characters from one
charset, in the array specified by inbuf, into a sequence of corre‐
sponding characters in another charset, in the array specified by out‐
buf. The charsets are those specified in the iconv_open() call that
returned the conversion descriptor, cd. The inbuf argument points to a
variable that points to the first character in the input buffer and
inbytesleft indicates the number of bytes to the end of the buffer to
be converted. The outbuf argument points to a variable that points to
the first available byte in the output buffer and outbytesleft indi‐
cates the number of the available bytes to the end of the buffer.
For state-dependent encodings, the conversion descriptor cd is placed
into its initial shift state by a call for which inbuf is a null
pointer, or for which inbuf points to a null pointer. When iconv() is
called in this way, and if outbuf is not a null pointer or a pointer to
a null pointer, and outbytesleft points to a positive value, iconv()
will place, into the output buffer, the byte sequence to change the
output buffer to its initial shift state. If the output buffer is not
large enough to hold the entire reset sequence, iconv() will fail and
set errno to E2BIG. Subsequent calls with inbuf as other than a null
pointer or a pointer to a null pointer cause the conversion to take
place from the current state of the conversion descriptor.
If a sequence of input bytes does not form a valid character in the
specified charset, conversion stops after the previous successfully
converted character. If the input buffer ends with an incomplete char‐
acter or shift sequence, conversion stops after the previous success‐
fully converted bytes. If the output buffer is not large enough to
hold the entire converted input, conversion stops just prior to the
input bytes that would cause the output buffer to overflow. The vari‐
able pointed to by inbuf is updated to point to the byte following the
last byte successfully used in the conversion. The value pointed to by
inbytesleft is decremented to reflect the number of bytes still not
converted in the input buffer. The variable pointed to by outbuf is
updated to point to the byte following the last byte of converted out‐
put data. The value pointed to by outbytesleft is decremented to
reflect the number of bytes still available in the output buffer. For
state-dependent encodings, the conversion descriptor is updated to
reflect the shift state in effect at the end of the last successfully
converted byte sequence.
If iconv() encounters a character in the input buffer that is legal,
but for which an identical character does not exist in the target
charset, iconv() performs an implementation-defined conversion on this
character.
RETURN VALUES
The iconv() function updates the variables pointed to by the arguments
to reflect the extent of the conversion and returns the number of non-
identical conversions performed. If the entire string in the input
buffer is converted, the value pointed to by inbytesleft will be 0. If
the input conversion is stopped due to any conditions mentioned above,
the value pointed to by inbytesleft will be non-zero and errno is set
to indicate the condition. If an error occurs iconv() returns (size_t)
-1 and sets errno to indicate the error.
ERRORS
The iconv() function will fail if:
EILSEQ Input conversion stopped due to an input byte that does
not belong to the input charset.
E2BIG Input conversion stopped due to lack of space in the
output buffer.
EINVAL Input conversion stopped due to an incomplete character
or shift sequence at the end of the input buffer.
The iconv() function may fail if:
EBADF The cd argument is not a valid open conversion descrip‐
tor.
APPLICATION USAGE
The inbuf argument indirectly points to the memory area which contains
the conversion input data. The outbuf argument indirectly points to the
memory area which is to contain the result of the conversion. The
objects indirectly pointed to by inbuf and outbuf are not restricted to
containing data that is directly representable in the ISO C language
char data type. The type of inbuf and outbuf, char **, does not imply
that the objects pointed to are interpreted as null-terminated C
strings or arrays of characters. Any interpretation of a byte sequence
that represents a character in a given character set encoding scheme is
done internally within the codeset converters. For example, the area
pointed to indirectly by inbuf and/or outbuf can contain all zero
octets that are not interpreted as string terminators but as coded
character data according to the respective codeset encoding scheme. The
type of the data (char, short int, long int, and so on) read or stored
in the objects is not specified, but may be inferred for both the input
and output data by the converters determined by the from_charset and
to_charset arguments of iconv_open().
Regardless of the data type inferred by the converter, the size of the
remaining space in both input and output objects (the intbytesleft and
outbytesleft arguments) is always measured in bytes.
IMPLEMENTATION DETAILS
Conversions between different charsets are done via the UCS-4 universal
character set. Conversions between the same charset (e.g. when two
different aliases of the same charset are used) are done by direct
copying from the input buffer to the output one. The libiconv library
itself usually contains only a small set of (built-in) charsets.
Tables for conversion between UCS-4 and particular charsets are mapped
to memory from binary table files, or C methods are loaded dynamically
from shared modules:
Coded character sets (CCS)
Each CCS file contains tables for convertion between exactly one
character of a corresponding charset and one UCS-4 character,
and vice versa, a UCS-4 character to the character of the CCS
charset. About 200 character sets are supported (only those used
in FreeBSD distribution is provided in this package) including
ASCII and the following standards: ISO-8859, KOI8, Windows, IBM-
DOS, Macintosh, CJK national charsets and EBCDIC. CCS files are
accessed via memory mapping.
Character encoding schemes (CES)
Each CES module contains functions converting a byte sequence
of a corresponding encoding scheme to exactly one UCS-4 32-bit
character, and vice versa, a UCS-4 character to a byte sequence
of the CES. The following CES groups are supported in the
iconv-1.0: ISO-10646 (UCS-4 and UCS-2, each in both architec‐
ture independent (network) and dependent (internal) byte order
versions), Unicode (UTF-16, UTF-8 and UTF-7), ISO-2022 and
Extended Unix Code (EUC) (both for Chinese (CN and TW), Japa‐
nese and Korean languages). A special table-driven CES module
providing conversion for all CCS tables is always built in into
the library. ISO-2022, EUC and table-driven modules use one or
more memory-mapped CCS tables.
Any CCS table or CES module can be built in into the library at compi‐
lation time.
A CCS or CES charset can have zero or more aliases (alternative names)
which are listed in charset.aliases file located in the same directory
as CCS tables. The library maps the aliases file to memory to find
canonical charset names.
If iconv() encounters a character in the input buffer that is legal,
but for which an identical character does not exist in the target
charset, iconv() replaces the source character with the '_' (under‐
score) character and tries to convert it into the target charset. If
there is no underscore character in the target charset, no bytes are
written to the target buffer for the source character. In any case,
iconv() increments the number of non-identical conversions performed
(the value being returned as the function result).
FILES
/usr/local/share/iconv/charset.aliases
Charset aliases file
/usr/local/share/iconv/*.cct
CCS conversion tables
/usr/local/libexec/iconv/*.so
CES conversion modules
SEE ALSOiconv(1), iconv_close(3), iconv_open(3)
7 Sep 2000 iconv(3)
