Feature Test Recommendations

To track progress of partial implementation of C++ standards and experimantal 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_nsdmi	Member initializers and aggregates	201304	predefined	(C++14)
__cpp_alias_templates	Template aliases	200704	predefined	(C++11)
__cpp_attributes	Attributes	200809	predefined	(C++11)
__cpp_binary_literals	Binary Literals in the C++ Core Language	201304	predefined	(C++14)
__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)
__cpp_decltype	decltype	200707	predefined	(C++11)
__cpp_decltype_auto	Return type deduction for normal functions	201304	predefined	(C++14)
__cpp_delegating_constructors	Delegating Constructors	200604	predefined	(C++11)
__cpp_exceptions	Exception handling	199711	predefined	(c++98)
__cpp_generic_lambdas	Generic (Polymorphic) Lambda Expressions	201304	predefined	(C++14)
__cpp_inheriting_constructors	Inheriting Constructors	200802	predefined	(C++11)
__cpp_init_captures	Generalized Lambda-capture	201304	predefined	(C++14)
__cpp_initializer_lists	Initializer lists	200806	predefined	(C++11)
__cpp_lambdas	Lambda expressions	200907	predefined	(C++11)
__cpp_lib_chrono_udls	User-defined Literals for Time Types	201304	<chrono>	(C++14)
__cpp_lib_complex_udls	User-defined Literals for std::complex	201309	<complex>	(C++14)
__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_generic_associative_lookup	Adding heterogeneous comparison lookup to associative containers	201304	<map> <set>	(C++14)
__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_is_final	std::is_final	201402	<type_traits>	(C++14)
__cpp_lib_is_null_pointer	std::is_null_pointer	201309	<type_traits>	(C++14)
__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_null_iterators	Null Template:concepts	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_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_shared_timed_mutex	A proposal to 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_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)
__cpp_nsdmi	Non-static data member initializers	200809	predefined	(C++11)
__cpp_range_based_for	Range-for loop	200907	predefined	(C++11)
__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)
__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)

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 = 0xA0;
    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