btowc
extern wint_t btowc(int);
# define __btowc btowc
extern wint_t btowc (int __c) __THROW;
B_DEFINE_WEAK_ALIAS(__btowc, btowc);
assert (btowc (EOF) == WEOF);
assert (btowc (c) == (wint_t)c);
assert (btowc (c) != WEOF);
assert (btowc (c) == (wint_t)c);
assert (btowc (c) == WEOF);
ret = wcrtomb (buf, btowc (c), NULL);
ret = wcrtomb (NULL, btowc ('x'), NULL);
wint_t wc = btowc(c);
wint_t wc = btowc(c);
wint_t wc = btowc(EOF);