__wcsnlen
extern size_t __wcsnlen(const wchar_t *wcs, size_t maxLength);
extern size_t __wcsnlen (__const wchar_t *__s, size_t __maxlen)
len = __wcsnlen (string, prec); \
size_t destLength = __wcsnlen(dest, maxLength);
B_DEFINE_WEAK_ALIAS(__wcsnlen, wcsnlen);