iconv(3) Library Functions Manual iconv(3) NAME iconv - perform character set conversion LIBRARY Standard C library (libc, -lc) SYNOPSIS #include 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 en- coding 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; in- bytesleft indicates the number of bytes in that buffer. The outbuf argu- ment 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 *in- buf 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 decre- ments *outbytesleft by the number of converted output bytes, and it updates the conversion state contained in cd. If the character encoding of the in- put 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 de- pends 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 pro- duce this condition. If the suffix //TRANSLIT was specified, translit- eration 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 be- ginning of the unconvertible multibyte sequence. * The input byte sequence has been entirely converted, that is, *in- bytesleft 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 begin- ning 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 *out- buf, 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 nonre- versible 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). allbox; lbx lb lb l l l. Interface Attribute Value T{ iconv() T} Thread safety MT-Safe race:cd The iconv() function is MT-Safe, as long as callers arrange for mutual ex- clusion 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 charac- ters: 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 re- strictions on alignment. SEE ALSO iconv_close(3), iconv_open(3), iconvconfig(8) Linux man-pages 6.18 2026-02-08 iconv(3)