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std::enable_nonlocking_formatter_optimization

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enable_nonlocking_formatter_optimization
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Defined in header <format>
template< class T >
constexpr bool enable_nonlocking_formatter_optimization = false;
 (since C++23)

This template can be used by implementations to enable efficient implementations of std::print and std::println.

If std::enable_nonlocking_formatter_optimization<T> is true, printing an argument of type T can be performed in a more efficient way (see std::print for details). std::enable_nonlocking_formatter_optimization specializations can be true in the following cases:

Contents

[edit] Basic standard specializations

In the following list, CharT is either char or wchar_t, ArithmeticT is any cv-unqualified arithmetic type other than char, wchar_t, char8_t, char16_t, or char32_t:

Nonlocking flag for character formatters
template<>
constexpr bool enable_nonlocking_formatter_optimization<CharT> = true;
 (1)
Nonlocking flag for string formatters
template<>
constexpr bool enable_nonlocking_formatter_optimization<CharT*> = true;
 (2)
template<>
constexpr bool enable_nonlocking_formatter_optimization<const CharT*> = true;
 (3)
template< std::size_t N >
constexpr bool enable_nonlocking_formatter_optimization<CharT[N]> = true;
 (4)
template< class Traits, class Alloc >

constexpr bool enable_nonlocking_formatter_optimization

    <std::basic_string<CharT, Traits, Alloc>> = true;
 (5)
template< class Traits >

constexpr bool enable_nonlocking_formatter_optimization

    <std::basic_string_view<CharT, Traits>> = true;
 (6)
Nonlocking flag for arithmetic formatters
template<>
constexpr bool enable_nonlocking_formatter_optimization<ArithmeticT> = true;
 (7)
Nonlocking flag for pointer formatters
template<>
constexpr bool enable_nonlocking_formatter_optimization<std::nullptr_t> = true;
 (8)
template<>
constexpr bool enable_nonlocking_formatter_optimization<void*> = true;
 (9)
template<>
constexpr bool enable_nonlocking_formatter_optimization<const void*> = true;
 (10)

[edit] Standard specializations for library types

Specializations of enable_nonlocking_formatter_optimization for all specializations of the following standard templates are defined as true:

Specializations of enable_nonlocking_formatter_optimization for all specializations of the following standard templates are defined as conditionally true:

Specialization of enable_nonlocking_formatter_optimization for all formattable range types are always defined as false for which the range format kind is not std::range_format::disabled.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_print 202403L (C++26)
(DR23)		 Formatted output with stream locking
202406L (C++26)
(DR23)		 Enabling nonlocking formatter optimization for more formattable types

[edit] See also

(C++20)
 defines formatting rules for a given type
(class template) [edit]
(C++23)
 prints to stdout or a file stream using formatted representation of the arguments
(function template) [edit]
(C++23)
 same as std::print except that each print is terminated by additional new line
(function template) [edit]
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