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NAME
iconv - perform character set conversion
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <iconv.h>
size_t iconv(iconv_t cd,
char **restrict inbuf, size_t *restrict inbytesleft,
char **restrict outbuf, size_t *restrict outbytesleft);
DESCRIPTION
The iconv() function converts a sequence of characters in one character encoding to a sequence of
characters in another character encoding. The cd argument is a conversion descriptor, previously created
by a call to iconv_open(3); the conversion descriptor defines the character encodings that iconv() uses
for the conversion. The inbuf argument is the address of a variable that points to the first character
of the input sequence; inbytesleft indicates the number of bytes in that buffer. The outbuf argument is
the address of a variable that points to the first byte available in the output buffer; outbytesleft
indicates the number of bytes available in the output buffer.
The main case is when inbuf is not NULL and *inbuf is not NULL. In this case, the iconv() function
converts the multibyte sequence starting at *inbuf to a multibyte sequence starting at *outbuf. At most
*inbytesleft bytes, starting at *inbuf, will be read. At most *outbytesleft bytes, starting at *outbuf,
will be written.
The iconv() function converts one multibyte character at a time, and for each character conversion it
increments *inbuf and decrements *inbytesleft by the number of converted input bytes, it increments
*outbuf and decrements *outbytesleft by the number of converted output bytes, and it updates the
conversion state contained in cd. If the character encoding of the input is stateful, the iconv()
function can also convert a sequence of input bytes to an update to the conversion state without
producing any output bytes; such input is called a shift sequence. The conversion can stop for five
reasons:
• An invalid multibyte sequence is encountered in the input. In this case, it sets errno to EILSEQ and
returns (size_t) -1. *inbuf is left pointing to the beginning of the invalid multibyte sequence.
• A multibyte sequence is encountered that is valid but that cannot be translated to the character
encoding of the output. This condition depends on the implementation and on the conversion
descriptor. In the GNU C library and GNU libiconv, if cd was created without the suffix //TRANSLIT or
//IGNORE, the conversion is strict: lossy conversions produce this condition. If the suffix
//TRANSLIT was specified, transliteration can avoid this condition in some cases. In the musl C
library, this condition cannot occur because a conversion to '*' is used as a fallback. In the
FreeBSD, NetBSD, and Solaris implementations of iconv(), this condition cannot occur either, because a
conversion to '?' is used as a fallback. When this condition is met, iconv() sets errno to EILSEQ and
returns (size_t) -1. *inbuf is left pointing to the beginning of the unconvertible multibyte
sequence.
• The input byte sequence has been entirely converted, that is, *inbytesleft has gone down to 0. In
this case, iconv() returns the number of nonreversible conversions performed during this call.
• An incomplete multibyte sequence is encountered in the input, and the input byte sequence terminates
after it. In this case, it sets errno to EINVAL and returns (size_t) -1. *inbuf is left pointing to
the beginning of the incomplete multibyte sequence.
• The output buffer has no more room for the next converted character. In this case, it sets errno to
E2BIG and returns (size_t) -1.
A different case is when inbuf is NULL or *inbuf is NULL, but outbuf is not NULL and *outbuf is not NULL.
In this case, the iconv() function attempts to set cd's conversion state to the initial state and store a
corresponding shift sequence at *outbuf. At most *outbytesleft bytes, starting at *outbuf, will be
written. If the output buffer has no more room for this reset sequence, it sets errno to E2BIG and
returns (size_t) -1. Otherwise, it increments *outbuf and decrements *outbytesleft by the number of
bytes written.
A third case is when inbuf is NULL or *inbuf is NULL, and outbuf is NULL or *outbuf is NULL. In this
case, the iconv() function sets cd's conversion state to the initial state.
RETURN VALUE
The iconv() function returns the number of characters converted in a nonreversible way during this call;
reversible conversions are not counted. In case of error, iconv() returns (size_t) -1 and sets errno to
indicate the error.
ERRORS
The following errors can occur, among others:
E2BIG There is not sufficient room at *outbuf.
EILSEQ An invalid multibyte sequence has been encountered in the input.
EINVAL An incomplete multibyte sequence has been encountered in the input.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌─────────────────────────────────────────────────────────────────────┬───────────────┬─────────────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────────────────────────────────────┼───────────────┼─────────────────┤
│ iconv() │ Thread safety │ MT-Safe race:cd │
└─────────────────────────────────────────────────────────────────────┴───────────────┴─────────────────┘
The iconv() function is MT-Safe, as long as callers arrange for mutual exclusion on the cd argument.
STANDARDS
POSIX.1-2008.
HISTORY
glibc 2.1. POSIX.1-2001.
NOTES
In each series of calls to iconv(), the last should be one with inbuf or *inbuf equal to NULL, in order
to flush out any partially converted input.
Although inbuf and outbuf are typed as char **, this does not mean that the objects they point can be
interpreted as C strings or as arrays of characters: the interpretation of character byte sequences is
handled internally by the conversion functions. In some encodings, a zero byte may be a valid part of a
multibyte character.
The caller of iconv() must ensure that the pointers passed to the function are suitable for accessing
characters in the appropriate character set. This includes ensuring correct alignment on platforms that
have tight restrictions on alignment.
SEE ALSO
iconv_close(3), iconv_open(3), iconvconfig(8)
Linux man-pages 6.9.1 2024-05-02 iconv(3)