size_t wcrtomb(char *s, wchar_t wc, mbstate_t *ps);
The main case for this function is when s is not NULL and wc is not a
null wide character (L'\0'). In this case, the wcrtomb() function con-
verts the wide character wc to its multibyte representation and stores
it at the beginning of the character array pointed to by s. It updates
the shift state *ps, and returns the length of said multibyte represen-
tation, that is, the number of bytes written at s.
A different case is when s is not NULL, but wc is a null wide character
(L'\0'). In this case the wcrtomb() function stores at the character
array pointed to by s the shift sequence needed to bring *ps back to
the initial state, followed by a '\0' byte. It updates the shift state
*ps (i.e., brings it into the initial state), and returns the length of
the shift sequence plus one, that is, the number of bytes written at s.
A third case is when s is NULL. In this case wc is ignored, and the
function effectively returns
wcrtomb(buf, L'\0', ps)
where buf is an internal anonymous buffer.
In all of the above cases, if ps is a NULL pointer, a static anonymous
state known only to the wcrtomb() function is used instead.
The wcrtomb() function returns the number of bytes that have been or
would have been written to the byte array at s. If wc can not be rep-
resented as a multibyte sequence (according to the current locale),
(size_t) -1 is returned, and errno set to EILSEQ.
The behavior of wcrtomb() depends on the LC_CTYPE category of the cur-
Passing NULL as ps is not multithread safe.
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