The mbsnrtowcs function is like the mbsrtowcs function, except
that the number of bytes to be converted, starting at *src, is limited
If dest is not a NULL pointer, the mbsnrtowcs function converts at
most nms bytes from 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. The nms limit forces a stop, or 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 converted, and the number of wide characters
written to dest is returned.
3. The multibyte string has been completely converted, including the terminating
'\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 L'\0' character,
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 destination length limit exists.
In both of the above cases, if ps is a NULL pointer, a static anonymous
state only known to the mbsnrtowcs function is used instead.
The programmer must ensure that there is room for at least len wide
characters at dest.
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.