std::formatter - cppreference.com (original) (raw)

| | | | | ----------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | 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.

Contents

• 1 Format specification
• 2 Member objects
• 3 Member functions
• 4 std::formatter<_pair-or-tuple_>::set_separator
• 5 std::formatter<_pair-or-tuple_>::set_brackets
• 6 std::formatter<_pair-or-tuple_>::parse
• 7 std::formatter<_pair-or-tuple_>::format
  • 7.1 Defect reports
  • 7.2 See also

[edit] 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 "".

[edit] Member objects

[edit] Member functions

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

std::formatter<_pair-or-tuple_>::set_separator

Assigns sep to _separator_.

std::formatter<_pair-or-tuple_>::set_brackets

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

std::formatter<_pair-or-tuple_>::parse

| template< class ParseContext > constexpr auto 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.

[edit] Defect reports

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

[edit] See also

| | defines formatting rules for a given type (class template) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |