mbsrtowcs - Man Page

convert a multibyte string to a wide-character string


Standard C library (libc, -lc)


#include <wchar.h>

size_t mbsrtowcs(wchar_t dest[restrict .len], const char **restrict src,
                 size_t len, mbstate_t *restrict ps);


If dest is not NULL, the mbsrtowcs() function converts the multibyte string *src to a wide-character string starting at dest. At most len wide characters are written to dest. The shift state *ps is updated. The conversion is effectively performed by repeatedly calling mbrtowc(dest, *src, n, ps) where n is some positive number, as long as this call succeeds, and then incrementing dest by one and *src by the number of bytes consumed. The conversion can stop for three reasons:

If dest is NULL, len is ignored, and the conversion proceeds as above, except that the converted wide characters are not written out to memory, and that no length limit exists.

In both of the above cases, if ps is NULL, a static anonymous state known only to the mbsrtowcs() function is used instead.

The programmer must ensure that there is room for at least len wide characters at dest.

Return Value

The mbsrtowcs() function returns the number of wide characters that make up the converted part of the wide-character string, not including the terminating null wide character. If an invalid multibyte sequence was encountered, (size_t) -1 is returned, and errno set to EILSEQ.


For an explanation of the terms used in this section, see attributes(7).

mbsrtowcs()Thread safetyMT-Unsafe race:mbsrtowcs/!ps


POSIX.1-2001, POSIX.1-2008, C99.


The behavior of mbsrtowcs() depends on the LC_CTYPE category of the current locale.

Passing NULL as ps is not multithread safe.

See Also

iconv(3), mbrtowc(3), mbsinit(3), mbsnrtowcs(3), mbstowcs(3)

Referenced By

mbrtowc(3), mbsinit(3), mbsnrtowcs(3), mbstowcs(3), unicode(7), utf-8(7).

2023-02-05 Linux man-pages 6.03