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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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iconv(3) Library Functions Manual iconv(3)
iconv - perform character set conversion
Standard C library (libc, -lc)
#include <iconv.h>
size_t iconv(iconv_t cd,
char **restrict inbuf, size_t *restrict inbytesleft,
char **restrict outbuf, size_t *restrict outbytesleft);
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.
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.
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.
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.
POSIX.1-2008.
glibc 2.1. POSIX.1-2001.
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.
iconv_close(3), iconv_open(3), iconvconfig(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 iconv(3)
Pages that refer to this page: iconv(1), iconv_close(3), iconv_open(3), mbsnrtowcs(3), mbsrtowcs(3), wcsnrtombs(3), wcsrtombs(3), wprintf(3), locale(7), iconvconfig(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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