< cpp‎ | utility‎ | format
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Formatting library (C++20)
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Defined in header <format>
template< class T, class CharT >

concept formattable = /* formattable_with */<
  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,
                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> is const-qualified).

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

[edit] 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 3925 C++23 the second template argument of std::basic_format_context was not provided provided

[edit] See also

defines formatting rules for a given type
(class template) [edit]
abstracts formatting operations for a given formatting argument type and character type
(named requirement)
defines functions used by the formatting library
(named requirement)