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    Feature testing (since C++20)

    From cppreference.com
    < cpp
     
    C++
     
    Feature testing
     

    The standard defines a set of preprocessor macros corresponding to C++ language and library features introduced in C++11 or later. They are intended as a simple and portable way to detect the presence of said features.

    Attributes

    __has_cpp_attribute( attribute-token )

    Checks for the support of an attribute named by attribute-token (after macro expansion).

    For each standard attribute, it is implementation-defined whether __has_cpp_attribute expands to the value given in the table below (which is the year and month in which the attribute was added to the working draft) or 0. It will expand to given value in the table if and only if the standard attribute causes the implementation to behave as recommended (issuing diagnostic messages, affecting class layout, etc.).

    The presence of vendor-specific attributes is determined by a non-zero value.

    __has_cpp_attribute can be expanded in the expression of #if and #elif. It is treated as a defined macro by #ifdef, #ifndef, #elifdef, #elifndef(since C++23) and defined but cannot be used anywhere else.

    attribute-token Attribute Value Std Paper(s)
    assume [[assume]] 202207L (C++23) P1774R8
    carries_dependency [[carries_dependency]] 200809L (C++11)
    (until C++26)     		N2556
    N2643
    P3475R2
    deprecated [[deprecated]] 201309L (C++14) N3760
    fallthrough [[fallthrough]] 201603L (C++17) P0188R1
    indeterminate [[indeterminate]] 202403L (C++26) P2795R5
    likely [[likely]] 201803L (C++20) P0479R5
    maybe_unused [[maybe_unused]] 201603L (C++17) P0212R1
    no_unique_address [[no_unique_address]] 201803L (C++20) P0840R2
    nodiscard [[nodiscard]] 201603L (C++17) P0189R1
    [[nodiscard]] with reason 201907L (C++20) P1301R4
    noreturn [[noreturn]] 200809L (C++11) N2761
    unlikely [[unlikely]] 201803L (C++20) P0479R5
    Total number of attributes: 11

    Language features

    The following macros can be used to detect whether a language feature is implemented by the current implementation. They are predefined in every translation unit.

    Each macro expands to an integer literal corresponding to the year and month when the corresponding feature has been included in the working draft. When a feature changes significantly, the macro will be updated accordingly.

    [edit]
    Macro name Feature Value Std Paper(s)
    __cpp_aggregate_bases Aggregate classes with base classes 201603L (C++17) P0017R1
    __cpp_aggregate_nsdmi Aggregate classes with default member initializers 201304L (C++14) N3653
    __cpp_aggregate_paren_init Aggregate initialization in the form of direct initialization 201902L (C++20) P0960R3
    __cpp_alias_templates Alias templates 200704L (C++11) N2258
    __cpp_aligned_new Dynamic memory allocation for over-aligned data 201606L (C++17) P0035R4
    __cpp_attributes Attributes 200809L (C++11) N2761
    __cpp_auto_cast Casting an expression to a prvalue (auto(x)) 202110L (C++23) P0849R8
    __cpp_binary_literals Binary literals 201304L (C++14) N3472
    __cpp_capture_star_this Lambda capture of *this by value as [=,*this] 201603L (C++17) P0018R3
    __cpp_char8_t char8_t 201811L (C++20) P0482R6
    char8_t compatibility and portability fix (allow initialization of (unsigned) char arrays from UTF-8 string literals) 202207L (C++23)
    (DR20)     		P2513R4
    __cpp_concepts Concepts 201907L (C++20) P0734R0
    P1084R2
    P1452R2
    Conditional trivial special member functions 202002L P0848R3
    P2493R0
    __cpp_conditional_explicit Conditional explicit specifier 201806L (C++20) P0892R2
    __cpp_consteval Immediate functions 201811L (C++20) P1073R3
    Making consteval propagate up 202211L (C++23)
    (DR20)     		P2564R3
    __cpp_constexpr constexpr 200704L (C++11) N2235
    Relaxed constexpr, non-const constexpr methods 201304L (C++14) N3652
    Constexpr lambda 201603L (C++17) P0170R1
    Virtual function calls in constant expressions; try blocks in constexpr functions, dynamic_cast and polymorphic typeid in constant expressions; trivial default initialization and asm-declaration in constexpr functions 201907L (C++20) P1064R0
    P1002R1
    P1327R1
    P1331R2
    P1668R1
    Changing the active member of a union in constant evaluation 202002L P1330R0
    P2493R0
    Non-literal variables, labels, and goto statements in constexpr functions 202110L (C++23) P2242R3
    Relaxing some restrictions on constexpr functions and function templates 202207L P2448R2
    Permitting static constexpr variables in constexpr functions 202211L P2647R1
    Constexpr cast from void*: towards constexpr type-erasure 202306L (C++26) P2738R1
    Constexpr placement new 202406L P2747R2
    __cpp_constexpr_dynamic_alloc Operations for dynamic storage duration in constexpr functions 201907L (C++20) P0784R7
    __cpp_constexpr_exceptions Constexpr exceptions 202411L (C++26) P3068R6
    __cpp_constexpr_in_decltype Generation of function and variable definitions when needed for constant evaluation 201711L (C++20)
    (DR11)     		P0859R0
    __cpp_constinit constinit 201907L (C++20) P1143R2
    __cpp_contracts Contracts 202502L (C++26) P2900R14
    __cpp_decltype decltype 200707L (C++11) N2343
    __cpp_decltype_auto Return type deduction for normal functions 201304L (C++14) N3638
    __cpp_deduction_guides Template argument deduction for class templates (CTAD) 201703L (C++17) P0091R3
    P0512R0
    P0620R0
    CTAD for aggregates and aliases 201907L (C++20) P1814R0
    P1816R0
    __cpp_delegating_constructors Delegating constructors 200604L (C++11) N1986
    __cpp_deleted_function Deleted function definitions with messages (= delete("should have a reason");) 202403L (C++26) P2573R2
    __cpp_designated_initializers Designated initializers 201707L (C++20) P0329R4
    __cpp_enumerator_attributes Attributes for enumerators 201411L (C++17) N4266
    __cpp_explicit_this_parameter Explicit object parameter 202110L (C++23) P0847R7
    __cpp_fold_expressions Fold expressions 201603L (C++17) N4295
    P0036R0
    __cpp_generic_lambdas Generic lambda expressions 201304L (C++14) N3649
    Explicit template parameter list for generic lambdas 201707L (C++20) P0428R2
    __cpp_guaranteed_copy_elision Guaranteed copy elision through simplified value categories 201606L (C++17) P0135R1
    __cpp_hex_float Hexadecimal floating literals 201603L (C++17) P0245R1
    __cpp_if_consteval if consteval 202106L (C++23) P1938R3
    __cpp_if_constexpr if constexpr 201606L (C++17) P0292R2
    __cpp_impl_coroutine Coroutines (compiler support) 201902L (C++20) P0912R5
    LWG3393
    __cpp_impl_destroying_delete Destroying operator delete (compiler support) 201806L (C++20) P0722R3
    __cpp_impl_three_way_comparison Three-way comparison (compiler support) 201907L (C++20) P0515R3
    P0768R1
    P1185R2
    P1630R1
    __cpp_implicit_move Simpler implicit move 202207L (C++23) P2266R3
    __cpp_inheriting_constructors Inheriting constructors 200802L (C++11) N2540
    New specification for inheriting constructors 201511L (C++17)
    (DR11)     		P0136R1
    __cpp_init_captures Lambda init-capture 201304L (C++14) N3648
    Allow pack expansion in lambda init-capture 201803L (C++20) P0780R2
    __cpp_initializer_lists List-initialization and std::initializer_list 200806L (C++11) N2672
    __cpp_inline_variables Inline variables 201606L (C++17) P0386R2
    __cpp_lambdas Lambda expressions 200907L (C++11) N2927
    __cpp_modules Modules 201907L (C++20) P1103R3
    P1811R0
    __cpp_multidimensional_subscript Multidimensional subscript operator 202110L (C++23) P2128R6
    Static operator[] 202211L P2589R1
    __cpp_named_character_escapes Named universal character escapes 202207L (C++23) P2071R2
    __cpp_namespace_attributes Attributes for namespaces 201411L (C++17) N4266
    __cpp_noexcept_function_type Make exception specifications be part of the type system 201510L (C++17) P0012R1
    __cpp_nontype_template_args Allow constant evaluation for all non-type template arguments 201411L (C++17) N4268
    Class types and floating-point types in non-type template parameters 201911L (C++20) P1907R1
    __cpp_nontype_template_parameter_auto Declaring non-type template parameter with auto 201606L (C++17) P0127R2
    __cpp_nsdmi Non-static data member initializers 200809L (C++11) N2756
    __cpp_pack_indexing Pack indexing 202311L (C++26) P2662R3
    __cpp_placeholder_variables A nice placeholder with no name 202306L (C++26) P2169R4
    __cpp_pp_embed #embed 202502L (C++26) P1967R14
    __cpp_range_based_for Range-based for loop 200907L (C++11) N2930
    Range-based for loop with different begin/end types 201603L (C++17) P0184R0
    Lifetime extension in range-based for 202211L (C++23) P2644R1
    P2718R0
    CWG2659
    __cpp_raw_strings Raw string literals 200710L (C++11) N2442
    __cpp_ref_qualifiers ref-qualifiers 200710L (C++11) N2439
    __cpp_return_type_deduction Return type deduction for normal functions 201304L (C++14) N3638
    __cpp_rvalue_references Rvalue reference 200610L (C++11) N2118
    __cpp_size_t_suffix Literal suffixes for std::size_t and its signed version 202011L (C++23) P0330R8
    __cpp_sized_deallocation Sized deallocation 201309L (C++14) N3778
    __cpp_static_assert static_assert 200410L (C++11) N1720
    Single-argument static_assert 201411L (C++17) N3928
    User-generated static_assert messages 202306L (C++26) P2741R3
    __cpp_static_call_operator Static operator() 202207L (C++23) P1169R4
    __cpp_structured_bindings Structured bindings 201606L (C++17) P0217R3
    Attributes for structured binding 202403L (C++26) P0609R3
    Structured bindings can introduce a pack 202411L P1061R10
    __cpp_template_parameters Concept and variable-template template-parameters 202502L (C++26) P2841R7
    __cpp_template_template_args Matching of template template arguments 201611L (C++17) P0522R0
    __cpp_threadsafe_static_init Dynamic initialization and destruction with concurrency 200806L (C++11) N2660
    __cpp_trivial_union Trivial unions 202502L (C++26) P3074R7
    __cpp_unicode_characters New character types (char16_t and char32_t) 200704L (C++11) N2249
    __cpp_unicode_literals Unicode string literals 200710L (C++11) N2442
    __cpp_user_defined_literals User-defined literals 200809L (C++11) N2765