std::formattable

Defined in header `<format>`
template < class T, class CharT > concept formattable = /* formattable_with / < std::remove_reference_t <T>, std::basic_format_context < / fmt_iter_for */ <CharT>, CharT> > ;	(1)	(since C++23)
Helper templates
template < class CharT > using /* fmt_iter_for / = / unspecified */ ;	(2)	(exposition only*)
template < class T, class Context, class Formatter = typename Context:: template formatter_type< std::remove_const_t <T>> > concept /* formattable_with */ = std::semiregular <Formatter> && requires (Formatter& f, const Formatter& cf, T&& t, Context fc, std::basic_format_parse_context < typename Context:: char_type > pc) { { f.parse (pc) } - > std::same_as < typename decltype(pc) :: iterator > ; { cf.format (t, fc) } - > std::same_as < typename Context:: iterator > ; } ;	(3)	(exposition only*)

The concept formattable specifies that std::formatter < std::remove_cvref_t <T>, CharT> meets the requirements of BasicFormatter and Formatter (if std::remove_reference_t<T>

The exposition-only alias template /* fmt_iter_for */ yields an unspecified type that satisfies std::output_iterator < const CharT& >

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

DR	Applied to	Behavior as published	Correct behavior
LWG 3925	C++23	the second template argument of std::basic_format_context was not provided	provided

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

Standard format specification
Formatting functions
format (C++20)
format_to (C++20)
format_to_n (C++20)
formatted_size (C++20)
vformat (C++20)
vformat_to (C++20)
Format strings
basic_format_stringformat_stringwformat_string (C++20)(C++20)(C++20)
runtime_format (C++26)
Formatting concepts
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)
Formatting arguments
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)
Format error
format_error (C++20)

formatter (C++20)	defines formatting rules for a given type (class template)
BasicFormatter (C++20)	abstracts formatting operations for a given formatting argument type and character type (named requirement)
Formatter (C++20)	defines functions used by the formatting library (named requirement)