The btowc function converts a single-byte character into a corresponding wide character. If the character is EOF or not valid in the initial shift state, btowc returns WEOF.
The wctob function converts a wide character into a corresponding single-byte character. If the wide character is WEOF or not able to be represented as a single byte in the initial shift state, wctob returns WEOF.
mbrtowc(3), multibyte(3), wcrtomb(3)