The wcstombs function converts a sequence of codes corresponding
    to multibyte characters from the array pointed to by pwcs to a
    sequence of multibyte characters that are stored into the array
    pointed to by s, up to a maximum of n bytes. The value returned
    is equal to the number of characters converted or a -1 if an
    error occurred.

    This function is affected by the LC_CTYPE category of the
    program's current locale.

    If s is NULL, this function call is a counting operation and n is
    ignored.

    See also wctomb.