NAME¶

std::range_formatter - std::range_formatter

Synopsis¶

Defined in header <format>
template< class T, class CharT = char >

requires std::same_as<std::remove_cvref_t<T>, T> && (since C++23)
std::formattable<T, CharT>

class range_formatter;

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

Member objects¶

Member name Definition
underlying_ (private) the underlying formatter of type std::formatter<T, CharT>
(exposition-only member object*)
a string representing the separator of the range
separator_ (private) formatted result. The default separator is ", ".
(exposition-only member object*)
a string representing the opening bracket of the range
opening-bracket_ (private) formatted result. The default opening bracket is "[".
(exposition-only member object*)
a string representing the closing bracket of the range
closing-bracket_ (private) formatted result. The default closing bracket is "]".
(exposition-only member object*)

Member functions¶

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

std::range_formatter::set_separator

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

Assigns sep to separator_.

std::range_formatter::set_brackets

constexpr void 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::range_formatter::underlying

constexpr std::formatter<T, CharT>& underlying(); (1)
constexpr const std::formatter<T, CharT>& underlying() const; (2)

Returns underlying_ (the underlying formatter).

std::range_formatter::parse

template< class ParseContext >
constexpr auto parse( ParseContext& ctx ) -> 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 -> 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 via 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.

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

See also¶

formatter defines formatting rules for a given type
(C++20) (class template)