size_t mbsrtowcs(wchar_t *dest, const char **src,
size_t len, mbstate_t *ps);
If dest is not a NULL pointer, 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:
1. 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.
2. len 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
3. 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, len is ignored, and the conversion proceeds as above,
except that the converted wide characters are not written out to mem-
ory, and that no length limit exists.
In both of the above cases, if ps is a NULL pointer, 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.
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.
The behavior of mbsrtowcs() depends on the LC_CTYPE category of the
GNU 2011-09-28 MBSRTOWCS(3)
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