22 General utilities library [utilities]

22.14 Formatting [format]

22.14.6 Formatter [format.formatter]

22.14.6.5 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) 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); template<class... Ts> constexpr void check_dynamic_spec(size_t id) noexcept; constexpr void check_dynamic_spec_integral(size_t id) noexcept; constexpr void check_dynamic_spec_string(size_t id) noexcept; }; }

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) noexcept;

Effects: Initializes begin_ with fmt.begin(), end_ with fmt.end(), indexing_ with unknown, next_arg_id_ with 0, and num_args_ with 0.

[Note 1:

Any call to next_arg_id, check_arg_id, or check_dynamic_spec on an instance of basic_format_parse_context initialized using this constructor is not a core constant expression.

— end note]

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constexpr const_iterator begin() const noexcept;

Returns: begin_.

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constexpr const_iterator end() const noexcept;

Returns: end_.

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constexpr void advance_to(const_iterator it);

Preconditions: end() is reachable from it.

Effects: Equivalent to: begin_ = it;

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constexpr size_t next_arg_id();

Effects: If indexing_ != manual is true, equivalent to: if (indexing_ == unknown) indexing_ = automatic; return next_arg_id_++;

Throws: format_error if indexing_ == manual is true.

[Note 2:

This indicates mixing of automatic and manual argument indexing.

— end note]

Remarks: Let cur-arg-id be the value of next_arg_id_ prior to this call.

Call expressions where cur-arg-id >= num_args_ is true are not core constant expressions ([expr.const]).

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constexpr void check_arg_id(size_t id);

Effects: If indexing_ != automatic is true, equivalent to: if (indexing_ == unknown) indexing_ = manual;

Throws: format_error if indexing_ == automatic is true.

[Note 3:

This indicates mixing of automatic and manual argument indexing.

— end note]

Remarks: A call to this function is a core constant expression ([expr.const]) only if id < num_args_ is true.

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template<class... Ts>
  constexpr void check_dynamic_spec(size_t id) noexcept;

Mandates: The types in Ts... are unique.

Each type in Ts... is one of bool, char_type, int, unsigned int, long long int, unsigned long long int, float, double, long double, const char_type*, basic_string_view<char_type>, or const void*.

Remarks: A call to this function is a core constant expression only if

(14.1)
id < num_args_ is true and
(14.2)
the type of the corresponding format argument (after conversion to basic_format_arg<Context>) is one of the types in Ts....

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constexpr void check_dynamic_spec_integral(size_t id) noexcept;

Effects: Equivalent to: check_dynamic_spec<int, unsigned int, long long int, unsigned long long int>(id);

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constexpr void check_dynamic_spec_string(size_t id) noexcept;

Effects: Equivalent to: check_dynamic_spec<const char_type*, basic_string_view<char_type>>(id);