Feature Test Recommendations

To track progress of partial implementation of 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( filename )	(1)
__has_include( <filename> )	(2)
__has_include( "filename" )	(3)

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

1) filename is treated as a preprocessor token and expanded as usual before checking

2,3) Perform a check on the header file name in the same way a #include directive would interpret it.

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.

C++14

Feature	Macro name	Value	Header
Binary Literals in the C++ Core Language	__cpp_binary_literals	201304	predefined
Single-Quotation-Mark as a Digit Separator	__cpp_digit_separators	201309	predefined
Wording Changes for Generalized Lambda-capture	__cpp_init_captures	201304	predefined
Generic (Polymorphic) Lambda Expressions	__cpp_generic_lambdas	201304	predefined
C++ Sized Deallocation	__cpp_sized_deallocation	201309	predefined
Relaxing constraints on constexpr functions / constexpr member functions and implicit const	__cpp_constexpr	201304	predefined
Return type deduction for normal functions	__cpp_decltype_auto	201304	predefined
Return type deduction for normal functions	__cpp_return_type_deduction	201304	predefined
Member initializers and aggregates	__cpp_aggregate_nsdmi	201304	predefined
Variable Templates	__cpp_variable_templates	201304	predefined
Compile-time integer sequences	__cpp_lib_integer_sequence	201304	<utility>
exchange() utility function	__cpp_lib_exchange_function	201304	<utility>
Wording for Addressing Tuples by Type	__cpp_lib_tuples_by_type	201304	<utility>
Consistent Metafunction Aliases	__cpp_lib_tuple_element_t	201402	<utility>
make_unique	__cpp_lib_make_unique	201304	<memory>
Making Operator Functors greater<>	__cpp_lib_transparent_operators	201210	<functional>
std::result_of and SFINAE	__cpp_lib_result_of_sfinae	201210	<functional>
An Incremental Improvement to integral_constant	__cpp_lib_integral_constant_callable	201304	<type_traits>
TransformationTraits Redux	__cpp_lib_transformation_trait_aliases	201304	<type_traits>
User-defined classes that cannot be derived from	__cpp_lib_is_final	201402	<type_traits>
Type traits and std::nullptr_t	__cpp_lib_is_null_pointer	201309	<type_traits>
User-defined Literals for Time Types	__cpp_lib_chrono_udls	201304	<chrono>
User-defined Literals for String Types	__cpp_lib_string_udls	201304	<string>
Adding heterogeneous comparison lookup to associative containers	__cpp_lib_generic_associative_lookup	201304	<map> <set>
Null Forward Iterators	__cpp_lib_null_iterators	201304	<iterator>
make_reverse_iterator	__cpp_lib_make_reverse_iterator	201402	<iterator>
Making non-modifying sequence operations more robust	__cpp_lib_robust_nonmodifying_seq_ops	201304	<algorithm>
User-defined Literals for std::complex	__cpp_lib_complex_udls	201309	<complex>
Quoted Strings Library Proposal	__cpp_lib_quoted_string_io	201304	<iomanip>
A proposal to rename shared_mutex to shared_timed_mutex	__cpp_lib_shared_timed_mutex	201402	<shared_mutex>

C++11

Feature	Macro name	Value	Header
New character types (char16_t and char32_t)	__cpp_unicode_characters	200704	predefined
Raw and Unicode String Literals	__cpp_raw_strings	200710	predefined
	__cpp_unicode_literals	200710	predefined
User-defined Literals	__cpp_user_defined_literals	200809	predefined
Lambda expressions	__cpp_lambdas	200907	predefined
constexpr	__cpp_constexpr	200704	predefined
Range-for loop	__cpp_range_based_for	200907	predefined
static_assert	__cpp_static_assert	200410	predefined
decltype	__cpp_decltype	200707	predefined
Forward declaration of enumerations	__cpp_forward_decl_enum	200809	predefined
Attributes	__cpp_attributes	200809	predefined
Rvalue reference	__cpp_rvalue_references	200610	predefined
Variadic templates	__cpp_variadic_templates	200704	predefined
Initializer lists	__cpp_initializer_lists	200806	predefined
Explicit conversion operators	__cpp_explicit_conversion	200710	predefined
Delegating Constructors	__cpp_delegating_constructors	200604	predefined
Non-static data member initializers	__cpp_nsdmi	200809	predefined
Inheriting Constructors	__cpp_inheriting_constructors	200802	predefined
ref-qualifiers	__cpp_ref_qualifiers	200710	predefined
Template aliases	__cpp_alias_templates	200704	predefined
noexcept	__cpp_noexcept	201003	predefined

C++98

Feature	Macro name	Value	Header
Run-time type identification (dynamic_cast, typeid)	__cpp_rtti	199711	predefined
Exception handling	__cpp_exceptions	199711	predefined

File System TS

Feature	Macro name	Value	Header
Filesystem library	__cpp_lib_experimental_filesystem	201406	<experimental/filesystem>

Library Fundamentals TS

Feature	Macro Name	Value	Header
apply() call a function with arguments from a tuple	__cpp_lib_experimental_apply	201402	<experimental/tuple>
Variable templates For type traits	__cpp_lib_experimental_type_trait_variable_templates	201402	<experimental/type_traits>
Invocation type traits	__cpp_lib_experimental_invocation_type	201406	<experimental/type_traits>
Type-erased allocator for std::function	__cpp_lib_experimental_function_erased_allocator	201406	<experimental/functional>
Extending std::search to use Additional Searching Algorithms	__cpp_lib_experimental_boyer_moore_searching	201411	<experimental/functional>
optional objects	__cpp_lib_experimental_optional	201411	<experimental/optional>
class any	__cpp_lib_experimental_any	201411	<experimental/any>
string_view: a non-owning reference to a string	__cpp_lib_experimental_string_view	201411	<experimental/string_view>
Extending shared_ptr to Support Arrays	__cpp_lib_experimental_shared_ptr_arrays	201406	<experimental/memory>
Polymorphic Memory Resources	__cpp_lib_experimental_memory_resources	201402	<experimental/memory_resource>
Type-erased allocator for std::promise	__cpp_lib_experimental_promise_erased_allocator	201406	<experimental/future>
Type-erased allocator for std::packaged_task	__cpp_lib_experimental_packaged_task_erased_allocator	201406	<experimental/future>
sample	__cpp_lib_experimental_sample	201402	<experimental/algorithm>

Concepts TS

Feature	Macro name	Value	Header
constraints and concepts	__cpp_experimental_concepts	201501	predefined

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