std::formatter<pair-or-tuple>

 

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format (C++20)

format_to (C++20)

format_to_n (C++20)

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vformat (C++20)

vformat_to (C++20)

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basic_format_stringformat_stringwformat_string (C++20)(C++20)(C++20)

runtime_format (C++26)

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formattable (C++23)

Formatter

formatter (C++20)

formatter<pair-or-tuple> (C++23)

formatter<range> (C++23)

range_formatter (C++23)

enable_nonlocking_formatter_optimization (C++23)

basic_format_parse_contextformat_parse_contextwformat_parse_context (C++20)(C++20)(C++20)

basic_format_contextformat_contextwformat_context (C++20)(C++20)(C++20)

range_format (C++23)

format_kind (C++23)

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basic_format_arg (C++20)

basic_format_arg::handle (C++20)

basic_format_argsformat_argswformat_args (C++20)(C++20)(C++20)

visit_format_arg (C++20)(deprecated in C++26)

make_format_argsmake_wformat_args (C++20)(C++20)

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format_error (C++20)

 

Defined in header <format>
template<class CharT, std::formattable<CharT>... Ts> struct formatter</*pair-or-tuple*/<Ts...>, CharT>;		(since C++23)

The template specialization of std::formatter for the std::pair and std::tuple allows users to convert a pair or a tuple to its textual representation as a collection of elements using formatting functions.

The exposition-only name /*pair-or-tuple*/ denotes either class template std::pair or std::tuple.

This specialization meets the Formatter requirements if (std::formattable<const Ts, CharT>&& ...) is true. It always meets the BasicFormatter requirements.

Format specification

The syntax of tuple-format-spec is:

tuple-fill-and-align (optional)width (optional)tuple-type (optional)

The tuple-fill-and-align is interpreted the same way as a fill-and-align except that the fill in tuple-fill-and-align is any character other than {, }, or :.

The width is described in standard format width specification.

The tuple-type changes the way a tuple is formatted, with certain options only valid with certain argument types.

The available tuple presentation types are:

• m: Indicates that both opening and closing brackets should be "" while the separator should be ": ".

• If m is chosen as the tuple-type, the program is ill-formed unless sizeof...(Ts)==2 is true.

• n: Indicates that separator, opening and closing brackets should be "".

Member objects

Member name	Definition
underlying_(private)	tuple of underlying formatters of type std::tuple<std::formatter<std::remove_cvref_t<Ts>, CharT>...> (exposition-only member object*)
separator_(private)	a string representing the separator of the tuple formatted result (defaults to ", ") (exposition-only member object*)
opening-bracket_(private)	a string representing the opening bracket of the tuple formatted result (defaults to "(") (exposition-only member object*)
closing-bracket_(private)	a string representing the closing bracket of the tuple formatted result (defaults to ")") (exposition-only member object*)

Member functions

set_separator	sets a specified separator for the tuple formatted result (public member function)
set_brackets	sets a specified opening and closing brackets for the tuple formatted result (public member function)
parse	parses the format specifier as specified by tuple-format-spec (public member function)
format	writes the tuple formatted output as specified by tuple-format-spec (public member function)

std::formatter<pair-or-tuple>::set_separator

constexprvoid set_separator(std::basic_string_view<CharT> sep )noexcept;

Assigns sep to separator_.

std::formatter<pair-or-tuple>::set_brackets

constexprvoid set_brackets(std::basic_string_view<CharT> opening,                              std::basic_string_view<CharT> closing )noexcept;

Assigns opening and closing to opening-bracket_ and closing-bracket_, respectively.

std::formatter<pair-or-tuple>::parse

template<class ParseContext > constexprauto parse( ParseContext& ctx )-> ParseContext::iterator;

Parses the format specifiers as a tuple-format-spec and stores the parsed specifiers in the current object.

If tuple-type or the n option is present, the values of opening-bracket, closing-bracket, and separator are modified as required.

For each element e in underlying_, calls e.parse(ctx) to parse an empty format-spec and, if e.set_debug_format() is a valid expression, calls e.set_debug_format().

Returns an iterator past the end of the tuple-format-spec.

std::formatter<pair-or-tuple>::format

template<class FormatContext > FormatContext::iterator format(/*maybe-const-pair-or-tuple*/<Ts...>& elems, FormatContext& ctx )const;

/*maybe-const-pair-or-tuple*/ denotes:

• const/*pair-or-tuple*/, if (std::formattable<const Ts, CharT>&& ...) is true,
• /*pair-or-tuple*/ otherwise.

Writes the following into ctx.out() as specified by tuple-format-spec, in order:

• opening-bracket_,
• for each index I in [​0​, sizeof...(Ts)):

• if I !=0, separator_,
• the result of writing std::get<I>(elems) via std::get<I>(underlying_), and

• closing-bracket_.

Returns an iterator past the end of the output range.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3892	C++23	the formatting of nested tuples was incorrect	corrected

See also

formatter (C++20)

defines formatting rules for a given type (class template)