text: NAME
  mbtowc - convert a multibyte sequence to a wide character
  SYNOPSIS
  #include <stdlib.h> int mbtowc (wchar_t *pwc, const char *s, size_t n);
  DESCRIPTION only known to the mbtowc function. It s does not point to a ’\0’ byte, it returns the number of bytes that were consumed from s, otherwise it returns 0.s-zero if the encoding has non-trivial shift state, or zero if the encoding is stateless.
  RETURN VALUE.
  CONFORMING TO
  ISO/ANSI C, UNIX98
  SEE ALSO
  mbrtowc(3), mbstowcs(3), MB_CUR_MAX(3)
  NOTES
  The behaviour of mbtowc depends on the LC_CTYPE category of the current locale. This function is not multi-thread safe. The function mbrtowc provides a better interface to the same functionality.