The btowc function converts c, interpreted as a multibyte sequence
of length 1, starting in the initial shift state, to a wide character and
returns it. If c is EOF or not a valid multibyte sequence of length 1,
the btowc function returns WEOF.
The behaviour of btowc depends on the LC_CTYPE category of the current
This function should never be used. It does not work for encodings which have
state, and unnecessarily treats single bytes differently from multibyte
sequences. Use the function mbtowc instead.