20 General utilities library [utilities]

20.20 Formatting [format]

20.20.5 Formatter [format.formatter]

20.20.5.3 Class template basic_­format_­parse_­context [format.parse.ctx]

namespace std {
  template<class charT>
  class basic_format_parse_context {
  public:
    using char_type = charT;
    using const_iterator = typename basic_string_view<charT>::const_iterator;
    using iterator = const_iterator;

  private:
    iterator begin_;                                    // exposition only
    iterator end_;                                      // exposition only
    enum indexing { unknown, manual, automatic };       // exposition only
    indexing indexing_;                                 // exposition only
    size_t next_arg_id_;                                // exposition only
    size_t num_args_;                                   // exposition only

  public:
    constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt,
                                                  size_t num_args = 0) noexcept;
    basic_format_parse_context(const basic_format_parse_context&) = delete;
    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;

    constexpr const_iterator begin() const noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr void advance_to(const_iterator it);

    constexpr size_t next_arg_id();
    constexpr void check_arg_id(size_t id);
  };
}
1
#
An instance of basic_­format_­parse_­context holds the format string parsing state consisting of the format string range being parsed and the argument counter for automatic indexing.
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constexpr explicit basic_format_parse_context(basic_string_view<charT> fmt, size_t num_args = 0) noexcept;
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#
Effects: Initializes begin_­ with fmt.begin(), end_­ with fmt.end(), indexing_­ with unknown, next_­arg_­id_­ with 0, and num_­args_­ with num_­args.
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constexpr const_iterator begin() const noexcept;
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Returns: begin_­.
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constexpr const_iterator end() const noexcept;
4
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Returns: end_­.
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constexpr void advance_to(const_iterator it);
5
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Preconditions: end() is reachable from it.
6
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Effects: Equivalent to: begin_­ = it;
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constexpr size_t next_arg_id();
7
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Effects: If indexing_­ != manual, equivalent to: 
if (indexing_ == unknown)
  indexing_ = automatic;
return next_arg_id_++;
8
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Throws: format_­error if indexing_­ == manual which indicates mixing of automatic and manual argument indexing.
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constexpr void check_arg_id(size_t id);
9
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Effects: If indexing_­ != automatic, equivalent to: 
if (indexing_ == unknown)
  indexing_ = manual;
10
#
Throws: format_­error if indexing_­ == automatic which indicates mixing of automatic and manual argument indexing.
11
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Remarks: Call expressions where id >= num_­args_­ are not core constant expressions ([expr.const]).