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NAME
mbsnrtowcs - convert a multibyte string to a wide-character string
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <wchar.h>
size_t mbsnrtowcs(size_t size;
wchar_t dest[restrict size], const char **restrict src,
size_t nms, size_t size, mbstate_t *restrict ps);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mbsnrtowcs():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_GNU_SOURCE
DESCRIPTION
The mbsnrtowcs() function is like the mbsrtowcs(3) function, except that the number of bytes to be
converted, starting at *src, is limited to at most nms bytes.
If dest is not NULL, the mbsnrtowcs() function converts at most nms bytes from the multibyte string *src
to a wide-character string starting at dest. At most size 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:
• An invalid multibyte sequence has been encountered. In this case, *src is left pointing to the
invalid multibyte sequence, (size_t) -1 is returned, and errno is set to EILSEQ.
• The nms limit forces a stop, or size non-L'\0' wide characters have been stored at dest. In this
case, *src is left pointing to the next multibyte sequence to be converted, and the number of wide
characters written to dest is returned.
• The multibyte string has been completely converted, including the terminating null wide character
('\0') (which has the side effect of bringing back *ps to the initial state). In this case, *src is
set to NULL, and the number of wide characters written to dest, excluding the terminating null wide
character, is returned.
According to POSIX.1, if the input buffer ends with an incomplete character, it is unspecified whether
conversion stops at the end of the previous character (if any), or at the end of the input buffer. The
glibc implementation adopts the former behavior.
If dest is NULL, size is ignored, and the conversion proceeds as above, except that the converted wide
characters are not written out to memory, and that no destination size limit exists.
In both of the above cases, if ps is NULL, a static anonymous state known only to the mbsnrtowcs()
function is used instead.
The programmer must ensure that there is room for at least size wide characters at dest.
RETURN VALUE
The mbsnrtowcs() 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌──────────────┬───────────────┬────────────────────────────────────────────────────────────────────────┐
│ Interface │ Attribute │ Value │
├──────────────┼───────────────┼────────────────────────────────────────────────────────────────────────┤
│ mbsnrtowcs() │ Thread safety │ MT-Unsafe race:mbsnrtowcs/!ps │
└──────────────┴───────────────┴────────────────────────────────────────────────────────────────────────┘
STANDARDS
POSIX.1-2008.
NOTES
The behavior of mbsnrtowcs() 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), mbsrtowcs(3)
Linux man-pages 6.15 2025-06-28 mbsnrtowcs(3)