std::range_formatter

template< class T, class CharT = char >
  requires std::same_as<std::remove_cvref_t<T>, T> && std::formattable<T, CharT>
class range_formatter;

The std::range_formatter is a helper class template for implementing std::formatter specializations for range types.

Range format specification

The syntax of range-format-spec is:

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

The width is described in standard format width specification.

The n option causes the range to be formatted without the opening and closing brackets.

The format-spec in a range-underlying-spec (its syntax is equivalent to : format-spec), if any, is interpreted by the range element formatter std::formatter<T, CharT>.

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

The available range presentation types are:

• m: Indicates that the opening bracket should be "{", the closing bracket should be "}", the separator should be ", ", and each range element should be formatted as if m were specified for its tuple-type (in tuple-format-spec).
• If m is chosen as the range-type, the program is ill-formed unless T is either a specialization of:
• std::pair, or
• std::tuple such that std::tuple_size_v<T> == 2 is true.
• s: Indicates that the range should be formatted as a string.
• ?s: Indicates that the range should be formatted as an escaped string.
• If s or ?s is chosen as the range-type, both n option and range-underlying-spec should not be included in the format specifier, and
• the program is ill-formed unless T is CharT.

Member objects

Member functions

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

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

constexpr std::formatter<T, CharT>& underlying();

constexpr const std::formatter<T, CharT>& underlying() const;

std::range_formatter::parse

template< class ParseContext >
constexpr auto parse( ParseContext& ctx ) -> typename ParseContext::iterator;

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

Calls underlying_.parse(ctx) to parse format-spec in range-format-spec or, if the latter is not present, an empty format-spec.

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

It calls underlying_.set_debug_format() if:

• the range-type is neither s nor ?s,
• underlying_.set_debug_format() is a valid expression, and
• there is no range-underlying-spec.

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

std::range_formatter::format

template< ranges::input_range R, class FormatContext >
  requires std::formattable<ranges::range_reference_t<R>, CharT> &&
           std::same_as<std::remove_cvref_t<ranges::range_reference_t<R>>, T>
auto format( R&& r, FormatContext& ctx ) const -> typename FormatContext::iterator;

If the range-type was either s or ?s, it writes the formatted std::basic_string<CharT>(std::from_range, r) as a string or an escaped string, respectively, into ctx.out().

Otherwise, it writes the following into ctx.out() as specified by range-format-spec, in order:

• opening-bracket_,
• for each formattable element e of the range r:
• the result of writing e view underlying_, and
• separator_, unless e is the last element of r, 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.

See also