Feature Test Recommendations

To track progress of partial implementation of C++ standards and experimental features, the feature test recommendations provide a set of preprocessor macros which, if defined by the implementation, give a simple and portable way to detect the presence of said features.

Function Macros

Feature test function macros can be expanded in the expression of #if and #elif. They will be treated as defined macros by #ifdef, #ifndef and defined but cannot be used anywhere else.

Finding Headers

__has_include( header-name )	(1)

Perform a check on the header file name in the same way a #include directive would interpret it.

If the header is found, it expands to 1, 0 otherwise.

Note: __has_include is part of C++17.

Attributes

__has_cpp_attribute( attribute-token )

Checks for the presence of an attribute.

For standard attributes, it will expand to the year and month in which the attribute was added to the working draft, the presence of vendor-specific attributes is determined by a non-zero value.

Language Features

The following macros expand to a numeric value corresponding to the year and month when the feature has been included in the working draft.

When a feature changes significantly, the macro will be updated accordingly.

Macro name	Feature	Value	Header	Standard/TS
__cpp_aggregate_bases	Extension to aggregate initialization	201603	predefined	(C++17)
__cpp_aggregate_nsdmi	Member initializers and aggregates	201304	predefined	(C++14)
__cpp_alias_templates	Template aliases	200704	predefined	(C++11)
__cpp_aligned_new	Dynamic memory allocation for over-aligned data	201606	predefined	(C++17)
__cpp_attributes	Attributes	200809	predefined	(C++11)
__cpp_binary_literals	Binary Literals in the C++ Core Language	201304	predefined	(C++14)
__cpp_capture_star_this	Lambda Capture of *this by Value as [=,*this]	201603	predefined	(C++17)
__cpp_concepts	constraints and concepts	201507	predefined	(concepts TS)
__cpp_constexpr	constexpr	200704	predefined	(C++11)
	Relaxing constraints on constexpr functions / constexpr member functions and implicit const	201304	predefined	(C++14)
	Constexpr Lambda	201603	predefined	(C++17)
__cpp_decltype	decltype	200707	predefined	(C++11)
__cpp_decltype_auto	Return type deduction for normal functions	201304	predefined	(C++14)
__cpp_deduction_guides	Template argument deduction for class templates	201606	predefined	(C++17)
	Class Template Argument Deduction Assorted NB resolution and issues	201611	predefined	(C++17)
__cpp_delegating_constructors	Delegating Constructors	200604	predefined	(C++11)
__cpp_enumerator_attributes	Attributes for enumerators	201411	predefined	(C++17)
__cpp_exceptions	Exception handling	199711	predefined	(c++98)
__cpp_fold_expressions	Fold expressions	201411	predefined	(C++17)
	Unary Folds and Empty Parameter Packs	201603	predefined	(C++17)
__cpp_generic_lambdas	Generic (Polymorphic) Lambda Expressions	201304	predefined	(C++14)
__cpp_hex_float	Hexadecimal floating literals	201603	predefined	(C++17)
__cpp_if_constexpr	constexpr if	201606	predefined	(C++17)
__cpp_inheriting_constructors	Inheriting Constructors	200802	predefined	(C++11)
	Rewording inheriting constructors	201511	predefined	(C++17)
__cpp_init_captures	Generalized Lambda-capture	201304	predefined	(C++14)
__cpp_initializer_lists	Initializer lists	200806	predefined	(C++11)
__cpp_inline_variables	Inline Variables	201606	predefined	(C++17)
__cpp_lambdas	Lambda expressions	200907	predefined	(C++11)
__cpp_lib_addressof_constexpr	constexpr std::addressof	201603	<memory>	(C++17)
__cpp_lib_allocator_traits_is_always_equal	std::allocator_traits::is_always_equal	201411	<memory> <scoped_allocator> <string> <deque> <forward_list> <list> <vector> <map> <set> <unordered_map> <unordered_set>	(C++17)
__cpp_lib_any	Library Fundamentals V1 TS Components: any	201603	<any>	(C++17)
__cpp_lib_apply	Library Fundamentals V1 TS Components: apply	201603	<tuple>	(C++17)
__cpp_lib_array_constexpr	Adding Constexpr Modifiers to std::reverse_iterator, std::move_iterator, std::array and Range Access	201603	<iterator> <array>	(C++17)
__cpp_lib_as_const	std:as_const	201510	<utility>	(C++17)
__cpp_lib_atomic_is_always_lock_free	constexpr atomic<T>::is_always_lock_free	201603	<atomic>	(C++17)
__cpp_lib_bool_constant	std::bool_constant	201505	<type_traits>	(C++17)
__cpp_lib_boyer_moore_searcher	Library Fundamentals V1 TS Components: Searchers	201603	<functional>	(C++17)
__cpp_lib_byte	A byte type definition	201603	<cstddef>	(C++17)
__cpp_lib_chrono	rounding functions for std::chrono::duration and std::chrono::time_point	201510	<chrono>	(C++17)
	making all the member functions of std::chrono::duration and std::chrono::time_point constexpr	201611	<chrono>	(C++17)
__cpp_lib_chrono_udls	User-defined Literals for Time Types	201304	<chrono>	(C++14)
__cpp_lib_clamp	An algorithm to "clamp" a value between a pair of boundary values (std::clamp)	201603	<algorithm>	(C++17)
__cpp_lib_complex_udls	User-defined Literals for std::complex	201309	<complex>	(C++14)
__cpp_lib_enable_shared_from_this	Re-enabling shared_from_this	201603	<memory>	(C++17)
__cpp_lib_exchange_function	exchange() utility function	201304	<utility>	(C++14)
__cpp_lib_experimental_any	class any	201411	<experimental/any>	(library fundamentals TS)
__cpp_lib_experimental_apply	apply() call a function with arguments from a tuple	201402	<experimental/tuple>	(library fundamentals TS)
__cpp_lib_experimental_boyer_moore_searching	Extending std::search to use Additional Searching Algorithms	201411	<experimental/functional>	(library fundamentals TS)
__cpp_lib_experimental_filesystem	Filesystem library	201406	<experimental/filesystem>	(filesystem TS)
__cpp_lib_experimental_function_erased_allocator	Type-erased allocator for std::function	201406	<experimental/functional>	(library fundamentals TS)
__cpp_lib_experimental_invocation_type	Invocation type traits	201406	<experimental/type_traits>	(library fundamentals TS)
__cpp_lib_experimental_memory_resources	Polymorphic Memory Resources	201402	<experimental/memory_resource>	(library fundamentals TS)
__cpp_lib_experimental_optional	optional objects	201411	<experimental/optional>	(library fundamentals TS)
__cpp_lib_experimental_packaged_task_erased_allocator	Type-erased allocator for std::packaged_task	201406	<experimental/future>	(library fundamentals TS)
__cpp_lib_experimental_promise_erased_allocator	Type-erased allocator for std::promise	201406	<experimental/future>	(library fundamentals TS)
__cpp_lib_experimental_sample	sample	201402	<experimental/algorithm>	(library fundamentals TS)
__cpp_lib_experimental_shared_ptr_arrays	Extending shared_ptr to Support Arrays	201406	<experimental/memory>	(library fundamentals TS)
__cpp_lib_experimental_string_view	string_view: a non-owning reference to a string	201411	<experimental/string_view>	(library fundamentals TS)
__cpp_lib_experimental_type_trait_variable_templates	Variable templates For type traits	201402	<experimental/type_traits>	(library fundamentals TS)
__cpp_lib_filesystem	Adopt the File System TS for C++17	201603	<filesystem>	(C++17)
__cpp_lib_gcd	Library Fundamentals V2 Components: std::gcd	201606	<numeric>	(C++17)
__cpp_lib_generic_associative_lookup	Adding heterogeneous comparison lookup to associative containers	201304	<map> <set>	(C++14)
__cpp_lib_hardware_interference_size	constexpr std::hardware_{constructive, destructive}_interference_size	201703	<new>	(C++17)
__cpp_lib_has_unique_object_representations	std::has_unique_object_representations	201606	<type_traits>	(C++17)
__cpp_lib_hypot	Introduce a 3-Argument Overload to std::hypot	201603	<cmath>	(C++17)
__cpp_lib_incomplete_container_elements	Minimal incomplete type support for standard containers	201505		(C++17)
__cpp_lib_integer_sequence	Compile-time integer sequences	201304	<utility>	(C++14)
__cpp_lib_integral_constant_callable	std::integral_constant::operator()	201304	<type_traits>	(C++14)
__cpp_lib_invoke	std::invoke function template	201411	<functional>	(C++17)
__cpp_lib_is_aggregate	std::is_aggregate type trait	201703	<type_traits>	(C++17)
__cpp_lib_is_final	std::is_final	201402	<type_traits>	(C++14)
__cpp_lib_is_invocable	std::is_invocable, std::invoke_result	201703	<type_traits>	(C++17)
__cpp_lib_is_swappable	[nothrow-]swappable traits	201603	<type_traits>	(C++17)
__cpp_lib_is_null_pointer	std::is_null_pointer	201309	<type_traits>	(C++14)
__cpp_lib_launder	Core Issue 1776: Replacement of class objects containing reference members (std::launder)	201606	<new>	(C++17)
__cpp_lib_lcm	Library Fundamentals V2 Components: std::lcm	201606	<numeric>	(C++17)
__cpp_lib_logical_traits	Logical operator type traits	201510	<type_traits>	(C++17)
__cpp_lib_make_from_tuple	make_from_tuple: apply for construction	201606	<tuple>	(C++17)
__cpp_lib_make_unique	std::make_unique	201304	<memory>	(C++14)
__cpp_lib_make_reverse_iterator	std::make_reverse_iterator	201402	<iterator>	(C++14)
__cpp_lib_map_try_emplace	std::map::try_emplace, std::map::insert_or_assign	201411	<map>	(C++17)
__cpp_lib_math_special_functions	Mathematical Special Functions for C++17	201603	<cmath>	(C++17)
__cpp_lib_memory_resource	Library Fundamentals V1 TS Components: memory_resource	201603	<memory_resource>	(C++17)
__cpp_lib_node_extract	Splicing Maps and Sets (std::map::extract, std::map::merge, std::map::insert(node_type), etc)	201606	<map> <set> <unordered_map> <unordered_set>	(C++17)
__cpp_lib_nonmember_container_access	Non-member size() and more (uniform container access)	201411	<iterator> <array> <deque> <forward_list> <list> <map> <regex> <set> <string> <unordered_map> <unordered_set> <vector>	(C++17)
__cpp_lib_not_fn	Adopt not_fn from Library Fundamentals 2 for C++17	201603	<functional>	(C++17)
__cpp_lib_null_iterators	Null ForwardIterators	201304	<iterator>	(C++14)
__cpp_lib_experimental_parallel_algorithm	Extensions for parallelism	201505	<experimental/algorithm> <experimental/exception_list> <experimental/execution_policy> <experimental/numeric>	(parallelism TS)
__cpp_lib_optional	Library Fundamentals V1 TS Components: optional	201603	<optional>	(C++17)
__cpp_lib_parallel_algorithm	Adopt the Parallelism TS for C++17	201603	<algorithm> <numeric>	(C++17)
__cpp_lib_quoted_string_io	std::quoted	201304	<iomanip>	(C++14)
__cpp_lib_result_of_sfinae	std::result_of and SFINAE	201210	<type_traits>	(C++14)
__cpp_lib_robust_nonmodifying_seq_ops	Making non-modifying sequence operations more robust (two-range overloads for std::mismatch, std::equal and std::is_permutation)	201304	<algorithm>	(C++14)
__cpp_lib_sample	Library Fundamentals V1 TS Components: sample	201603	<algorithm>	(C++17)
__cpp_lib_scoped_lock	Variadic std::lock_guard (std::scoped_lock)	201703	<mutex>	(C++17)
__cpp_lib_shared_mutex	std::shared_mutex (untimed)	201505	<shared_mutex>	(C++17)
__cpp_lib_shared_ptr_arrays	Library Fundamentals V1 TS Components: shared_ptr<T[]>	201603	<memory>	(C++17)
	Fixes to shared_ptr support for arrays	201611	<memory>	(C++17)
__cpp_lib_shared_ptr_weak_type	shared_ptr::weak_type	201606	<memory>	(C++17)
__cpp_lib_shared_timed_mutex	Rename shared_mutex to shared_timed_mutex	201402	<shared_mutex>	(C++14)
__cpp_lib_string_udls	User-defined Literals for String Types	201304	<string>	(C++14)
__cpp_lib_string_view	Library Fundamentals V1 TS Components: string_view	201603	<string_view>	(C++17)
__cpp_lib_to_chars	Elementary string conversions (std::to_chars, std::from_chars)	201611	<utility>	(C++17)
__cpp_lib_transformation_trait_aliases	TransformationTraits Redux	201304	<type_traits>	(C++14)
__cpp_lib_tuple_element_t	Consistent Metafunction Aliases	201402	<utility>	(C++14)
__cpp_lib_tuples_by_type	Addressing Tuples by Type	201304	<utility>	(C++14)
__cpp_lib_transparent_operators	Making Operator Functors greater<>	201210	<functional>	(C++14)
	Making std::owner_less more flexible (std::owner_less<void>)	201510	<memory> <functional>	(C++17)
__cpp_lib_type_trait_variable_templates	Adopt Type Traits Variable Templates from Library Fundamentals TS for C++17 (std::is_void_v, etc)	201510	<type_traits>	(C++17)
__cpp_lib_uncaught_exceptions	std::uncaught_exceptions	201411	<exception>	(C++17)
__cpp_lib_unordered_map_try_emplace	std::unordered_map::try_emplace, std::unordered_map::insert_or_assign	201411	<unordered_map>	(C++17)
__cpp_lib_variant	std::variant: a type-safe union for C++17	201606	<variant>	(C++17)
__cpp_lib_void_t	std::void_t	201411	<type_traits>	(C++17)
__cpp_namespace_attributes	Attributes for namespaces	201411	predefined	(C++17)
__cpp_nested_namespace_definitions	Nested namespace definition	201411	predefined	(C++17)
__cpp_noexcept_function_type	Make exception specifications be part of the type system	201510	predefined	(C++17)
__cpp_nontype_template_args	Allow constant evaluation for all non-type template arguments	201411	predefined	(C++17)
__cpp_nsdmi	Non-static data member initializers	200809	predefined	(C++11)
__cpp_range_based_for	Range-for loop	200907	predefined	(C++11)
	Generalized Range-Based For Loop	201603	predefined	(C++17)
__cpp_raw_strings	Raw String Literals	200710	predefined	(C++11)
__cpp_ref_qualifiers	ref-qualifiers	200710	predefined	(C++11)
__cpp_return_type_deduction	Return type deduction for normal functions	201304	predefined	(C++14)
__cpp_rtti	Run-time type identification (dynamic_cast, typeid)	199711	predefined	(c++98)
__cpp_rvalue_references	Rvalue reference	200610	predefined	(C++11)
__cpp_sized_deallocation	Sized Deallocation	201309	predefined	(C++14)
__cpp_static_assert	static_assert	200410	predefined	(C++11)
	Extended static_assert	201411	predefined	(C++17)
__cpp_structured_bindings	structured bindings	201606	predefined	(C++17)
__cpp_template_auto	Declaring non-type template parameters with auto	201606	predefined	(C++17)
__cpp_template_template_args	Matching of template template-arguments	201611	predefined	(C++17)
__cpp_threadsafe_static_init	Dynamic Initialization and Destruction with Concurrency	200806	predefined	(C++11)
__cpp_transactional_memory	Transactional Memory	201505	predefined	(TM TS)
__cpp_unicode_characters	New character types (char16_t and char32_t)	200704	predefined	(C++11)
__cpp_unicode_literals	Unicode String Literals	200710	predefined	(C++11)
__cpp_user_defined_literals	User-defined Literals	200809	predefined	(C++11)
__cpp_variable_templates	Variable Templates	201304	predefined	(C++14)
__cpp_variadic_templates	Variadic templates	200704	predefined	(C++11)
__cpp_variadic_using	Pack expansions in using-declarations	201611	predefined	(C++17)
__lib_cpp_execution	Adopt the Parallelism TS for C++17	201603	<execution>	(C++17)

Example

Run this code

#ifdef __has_include                           // Check if __has_include is present
#  if __has_include(<optional>)                // Check for a standard library
#    include<optional>
#  elif __has_include(<experimental/optional>) // Check for an experimental version
#    include <experimental/optional>
#  elif __has_include(<boost/optional.hpp>)    // Try with an external library
#    include <boost/optional.hpp>
#  else                                        // Not found at all
#     error "Missing <optional>"
#  endif
#endif
 
#ifdef __has_cpp_attribute                      // Check if __has_cpp_attribute is present
#  if __has_cpp_attribute(deprecated)           // Check for an attribute
#    define DEPRECATED(msg) [[deprecated(msg)]]
#  endif
#endif
#ifndef DEPRECATED
#    define DEPRECATED(msg)
#endif
 
DEPRECATED("foo() has been deprecated") void foo();
 
#if __cpp_constexpr >= 201304                   // Check for a specific version of a feature
#  define CONSTEXPR constexpr
#else
#  define CONSTEXPR
#endif
 
CONSTEXPR int bar(unsigned i)
{
#ifdef __cpp_binary_literals                    // Check for the presence of a feature
    unsigned mask1 = 0b11000000;
    unsigned mask2 = 0b00000111;
#else
    unsigned mask1 = 0xC0;
    unsigned mask2 = 0x07;
#endif
    if ( i & mask1 )
        return 1;
    if ( i & mask2 )
        return 2;
    return 0;
}
 
int main()
{
}

See Also

Standing Document 6

The official document on Feature Test Recommendations