Function parse_format_specs

include/fmt/base.h:1444–1579

// Parses standard format specifiers.
template <typename Char>
FMT_CONSTEXPR auto parse_format_specs(const Char* begin, const Char* end,
                                      dynamic_format_specs<Char>& specs,
                                      parse_context<Char>& ctx, type arg_type)
    -> const Char* {
  auto c = '\0';
  if (end - begin > 1) {
    auto next = to_ascii(begin[1]);
    c = parse_align(next) == align::none ? to_ascii(*begin) : '\0';
  } else {
    if (begin == end) return begin;
    c = to_ascii(*begin);
  }

  struct {
    state current_state = state::start;
    FMT_CONSTEXPR void operator()(state s, bool valid = true) {
      if (current_state >= s || !valid)
        report_error("invalid format specifier");
      current_state = s;
    }
  } enter_state;

  using pres = presentation_type;
  constexpr auto integral_set = sint_set | uint_set | bool_set | char_set;
  struct {
    const Char*& begin;
    format_specs& specs;
    type arg_type;

    FMT_CONSTEXPR auto operator()(pres pres_type, int set) -> const Char* {
      if (!in(arg_type, set)) report_error("invalid format specifier");
      specs.set_type(pres_type);
      return begin + 1;
    }
  } parse_presentation_type{begin, specs, arg_type};

  for (;;) {
    switch (c) {
    case '<':
    case '>':
    case '^':
      enter_state(state::align);
      specs.set_align(parse_align(c));
      ++begin;
      break;
    case '+':
    case ' ':
      specs.set_sign(c == ' ' ? sign::space : sign::plus);
      FMT_FALLTHROUGH;
    case '-':
      enter_state(state::sign, in(arg_type, sint_set | float_set));
      ++begin;
      break;
    case '#':
      enter_state(state::hash, is_arithmetic_type(arg_type));
      specs.set_alt();
      ++begin;
      break;