Function as_float_helper

system/lib/libcxx/src/string.cpp:191–205

template <typename V, typename S, typename F>
inline V as_float_helper(const string& func, const S& str, size_t* idx, F f) {
  typename S::value_type* ptr                             = nullptr;
  const typename S::value_type* const p                   = str.c_str();
  __libcpp_remove_reference_t<decltype(errno)> errno_save = errno;
  errno                                                   = 0;
  V r                                                     = f(p, &ptr);
  swap(errno, errno_save);
  if (errno_save == ERANGE)
    throw_from_string_out_of_range(func);
  if (ptr == p)
    throw_from_string_invalid_arg(func);
  if (idx)
    *idx = static_cast<size_t>(ptr - p);
  return r;
}

template <typename V, typename S>
inline V as_float(const string& func, const S& s, size_t* idx = nullptr);