The mbsrtowcs function converts a sequence of multibyte
    characters, beginning in the conversion state described by the
    object pointed to by ps, from the array indirectly pointed to by
    src, into a sequence of corresponding wide characters.

    If dst is not a NULL pointer, the converted characters are stored
    into the array pointed to by dst. Conversion continues up to and
    including a terminating null character, which is also stored.

    Conversion stops earlier for one of the following reasons:

    o  A sequence of bytes is encountered that does not form a valid
       multibyte character.

    o  If dst is not a NULL pointer, when len codes have been stored
       into the array pointed to by dst.

    If dst is not a NULL pointer, the pointer object pointed to by
    src is assigned either a NULL pointer (if the conversion stopped
    because of reaching a terminating null wide character), or the
    address just beyond the last multibyte character converted (if
    any). If conversion stopped because of reaching a terminating
    null wide character, the resulting state described is the initial
    conversion state.