mbsrtowcs(3) Library Functions Manual mbsrtowcs(3)
NAME
mbsrtowcs - convert a multibyte string to a wide-character string
(restartable)
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <wchar.h>
size_t mbsrtowcs(wchar_t dest[restrict .dsize],
const char **restrict src,
size_t dsize, mbstate_t *restrict ps);
DESCRIPTION
If dest is not NULL, convert the multibyte string *src to a wide-charac-
ter string starting at dest. At most dsize 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 increment-
ing dest by one and *src by the number of bytes consumed. The conver-
sion 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.
• dsize non-L'\0' wide characters have been stored at dest. In this
case, *src is left pointing to the next multibyte sequence to be con-
verted, and the number of wide characters written to dest is re-
turned.
• 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.
If dest is NULL, dsize 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.
In order to avoid the case 2 above, the programmer should make sure
dsize is greater than or equal to mbsrtowcs(NULL,src,0,ps)+1.
The programmer must ensure that there is room for at least dsize wide
characters at dest.
This function is a restartable version of mbstowcs(3).
RETURN VALUE
The number of wide characters that make up the converted part of the
wide-character string, not including the terminating null wide charac-
ter. 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 │
├─────────────┼───────────────┼────────────────────────────────────────┤
│ mbsrtowcs() │ Thread safety │ MT-Unsafe race:mbsrtowcs/!ps │
└─────────────┴───────────────┴────────────────────────────────────────┘
STANDARDS
C11, POSIX.1-2008.
HISTORY
POSIX.1-2001, C99.
NOTES
The behavior of mbsrtowcs() depends on the LC_CTYPE category of the cur-
rent locale.
Passing NULL as ps is not multithread safe.
SEE ALSO
iconv(3), mbrtowc(3), mbsinit(3), mbsnrtowcs(3), mbstowcs(3)
Linux man-pages 6.9.1 2024-06-15 mbsrtowcs(3)
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