Function darts_save 

pub unsafe extern "C" fn darts_save(
    darts: DartsT,
    file_name: *const c_char,
    mode: *const c_char,
    offset: size_t,
) -> c_int

Writes the array of units into the specified file. `offset’ specifies the number of bytes to be skipped before writing the array. Returns 0 iff the operation succeeds. Otherwise, returns a non-zero value.