Function gmp_mpfr_sys::mpfr::mpfr_get_str

pub unsafe extern fn mpfr_get_str(str: *mut c_char,
                                  expptr: *mut mpfr_exp_t,
                                  b: c_int,
                                  n: usize,
                                  op: *const __mpfr_struct,
                                  rnd: mpfr_rnd_t)
                                  -> *mut c_char