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mbstowcs - convert a multibyte string to a wide character string
size_t mbstowcs (wchar_t *dest, const char *src, size_t n);
If dest is not a NULL pointer, the mbstowcs function converts the
multibyte string src to a wide-character string starting at dest. At
most n wide characters are written to dest. The conversion starts in
the initial state. The conversion can stop for three reasons:
1. An invalid multibyte sequence has been encountered. In this case
(size_t)(-1) is returned.
2. n non-L'\0' wide characters have been stored at dest. In this case
the number of wide characters written to dest is returned, but the
shift state at this point is lost.
3. The multibyte string has been completely converted, including the
terminating '\0'. In this case the number of wide characters written to
dest, excluding the terminating L'\0' character, is returned.
The programmer must ensure that there is room for at least n wide
characters at dest.
If dest is NULL, n 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 order to avoid the case 2 above, the programmer should make sure n
is greater or equal to mbstowcs(NULL,src,0)+1.
The mbstowcs 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.
ISO/ANSI C, UNIX98
The behaviour of mbstowcs depends on the LC_CTYPE category of the
The function mbsrtowcs provides a better interface to the same