---

features:

- desc: "Reflection for C++26 (`<meta>`)"

paper: P2996

lib: true

support:

- GCC 16

ftm:

- name: __cpp_impl_reflection

value: 202506L

content: p2996_reflection.md

- desc: "Annotations for Reflection"

paper: P3394

support:

- GCC 16

- desc: "Splicing a base class subobject"

paper: P3293

support:

- GCC 16

keywords: ["reflection"]

- desc: "`define_static_{string,object,array}`"

paper: P3491

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_define_static

value: 202506L

keywords: ["reflection"]

- desc: "Function Parameter Reflection in Reflection for C++26"

paper: P3096

lib: true

support:

- GCC 16

- desc: "Expansion Statements (`template for`)"

paper: P1306

support:

- GCC 16

ftm:

- name: __cpp_expansion_statements

value: 202506L

keywords: ["reflection"]

- desc: "Error Handling in Reflection"

paper: P3560

lib: true

ftm:

- name: __cpp_lib_reflection

value: 202506L

- desc: "`constexpr` virtual inheritance"

paper: P3533

support:

- GCC 16

ftm:

- name: __cpp_constexpr_virtual_inheritance

value: 202506L

content: p3533.md

- desc: "Contracts for C++ (`<contracts>`)"

paper: P2900

ftm:

- name: __cpp_contracts

value: 202502L

desc: "Core language feature"

- name: __cpp_lib_contracts

value: 202502L

desc: "Library API is available. This is a separate macro to allow for mixing language (compiler) support with different standard library implementations, where this macro specifies the level of support for contracts by that standard library implementation."

keywords: ["safety"]

content: p2900.md

- desc: "Standard library hardening"

paper: P3471

lib: true

support:

- GCC 15 (partial)

- Clang 18 (partial)

- MSVC 19.44 (partial)

- Xcode 16 (partial)

hints:

- target: GCC 15

msg: "Calls `abort()` instead of using C++26 contracts when a hardened precondition is violated."

- target: Clang 18

msg: "Calls `__builtin_expect(false, ...)` instead of using C++26 contracts when a hardened precondition is violated."

- target: MSVC 19.44

msg: "Calls `__fastfail()` instead of using C++26 contracts when a hardened precondition is violated."

- target: Xcode 16

msg: "Calls `__builtin_expect(false, ...)` instead of using C++26 contracts when a hardened precondition is violated."

ftm:

- name: __cpp_lib_hardened_array

desc: "Hardened `std::array`"

value: 202502L

- name: __cpp_lib_hardened_basic_string

desc: "Hardened `std::basic_string`"

value: 202502L

- name: __cpp_lib_hardened_basic_string_view

desc: "Hardened `std::basic_string_view`"

value: 202502L

- name: __cpp_lib_hardened_bitset

desc: "Hardened `std::bitset`"

value: 202502L

- name: __cpp_lib_hardened_deque

desc: "Hardened `std::deque`"

value: 202502L

- name: __cpp_lib_hardened_expected

desc: "Hardened `std::expected`"

value: 202502L

- name: __cpp_lib_hardened_forward_list

desc: "Hardened `std::forward_list`"

value: 202502L

- name: __cpp_lib_hardened_inplace_vector

desc: "Hardened `std::inplace_vector`"

value: 202502L

- name: __cpp_lib_hardened_list

desc: "Hardened `std::list`"

value: 202502L

- name: __cpp_lib_hardened_mdspan

desc: "Hardened `std::mdspan`"

value: 202502L

- name: __cpp_lib_hardened_optional

desc: "Hardened `std::optional`"

value: 202502L

- name: __cpp_lib_hardened_span

desc: "Hardened `std::span`"

value: 202502L

- name: __cpp_lib_hardened_valarray

desc: "Hardened `std::valarray`"

value: 202502L

- name: __cpp_lib_hardened_vector

desc: "Hardened `std::vector`"

value: 202502L

keywords: ["safety"]

content: "p3471_hardening.md"

- desc: "Minor additions to C++26 standard library hardening"

paper: P3697

lib: true

content: p3697_minor_additions_to_hardening.md

support:

- MSVC 19.50 (partial)

hints:

- target: MSVC 19.50

msg: Partial support only due to the lack of Contracts. Support starting with Visual Studio 2026 18.0 Preview 2. ([GitHub Issue](https://github.com/microsoft/STL/pull/5650))

keywords: ["safety"]

- desc: "[Pack indexing](https://en.cppreference.com/w/cpp/language/pack_indexing.html)"

paper: P2662

support:

- GCC 15

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_pack_indexing

value: 202311L

- desc: "`constexpr` cast from `void*`: towards `constexpr` type-erasure"

paper: P2738

support:

- GCC 14

- Clang 17

- Xcode 16.3

ftm:

- name: __cpp_constexpr

value: 202306L

- desc: "Static storage for braced initializers"

paper: P2752

support:

- GCC 14

- desc: "User-generated `static_assert` messages"

paper: P2741

support:

- GCC 14

- Clang 17

- Xcode 16.3

ftm:

- name: __cpp_static_assert

value: 202306L

content: p2741_static_assert_msgs.md

- desc: "A nice placeholder with no name (using `_` as a variable name)"

paper: P2169

support:

- GCC 14

- Clang 18

- Xcode 16.3

ftm:

- name: __cpp_placeholder_variables

value: 202306L

content: p2169_placeholder_with_no_name.md

- desc: "`#embed` - a scannable, tooling-friendly binary resource inclusion mechanism"

paper: P1967

support:

- GCC 15 (hint)

- Clang 19 (hint)

- Xcode 16.3 (hint)

hints:

- target: GCC 15

msg: >

Although this is a C++26 feature, this is available in GCC starting with C++20 (`-std=c++20`).

- target: Clang 19

msg: >

Supported as an extension.<br>

Use the flag `-Wno-c23-extensions` to suppress warnings related to `#embed`.<br>

Although this is a C++26 feature, this is available in Clang starting with C++20 (`-std=c++20`).<br>

Clang does not define the `__cpp_pp_embed` feature-testing macro yet.

- target: Xcode 16.3

msg: >

Supported as an extension.<br>

Use the flag `-Wno-c23-extensions` to suppress warnings related to `#embed`.<br>

Although this is a C++26 feature, this is available in Apple Clang starting with C++20 (`-std=c++20`).<br>

Apple Clang does not define the `__cpp_pp_embed` feature-testing macro yet.

ftm:

- name: __cpp_pp_embed

value: 202502L

content: p1967_embed.md

- desc: "On the ignorability of standard attributes"

paper: P2552

support:

- GCC 15

- Clang

- Xcode 16.3

- desc: "Remove deprecated arithmetic conversion on enumerations"

paper: P2864

support:

- GCC 14

- Clang 18

- Xcode 16.3

- desc: "UB? In My Lexer? (Remove undefined behavior from lexing)"

paper: P2621

support:

- GCC

- Clang 3.3

- Xcode 16

- desc: "Template parameter initialization"

paper: P2308

support:

- GCC 9

- Clang 18

- Xcode 16.3

- desc: "Disallow binding a returned [glvalue](https://en.cppreference.com/w/cpp/language/value_category.html#glvalue) to a temporary"

paper: P2748

support:

- GCC 14

- Clang 19

- Xcode 16.3

- desc: "Attributes for [structured bindings](https://en.cppreference.com/w/cpp/language/structured_binding.html)"

paper: P0609

support:

- GCC 15

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_structured_bindings

value: 202403L

- desc: "Making non-encodable string literals ill-formed"

paper: P1854

support:

- GCC 14

- Clang 14

- Xcode 16

- desc: "[Unevaluated strings](https://en.cppreference.com/w/cpp/language/string_literal.html#Unevaluated_strings)"

paper: P2361

support:

- GCC 14

- Clang 17 (partial)

- Clang 18

- Xcode 16

hints:

- target: Clang 17

msg: "Attributes arguments don't yet parse as unevaluated string literals."

- desc: "Add @, $, and ` to the [basic character set](https://en.cppreference.com/w/cpp/language/charset.html#Basic_character_set)"

paper: P2558

support:

- GCC 15

- Clang

- Xcode 15

- desc: "Erroneous behavior for uninitialized reads (and `[[indeterminate]]` attribute)"

paper: P2795

support:

- GCC 16

keywords: ["safety"]

- desc: '= delete("should have a reason");'

paper: P2573

support:

- GCC 15

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_deleted_function

value: 202403L

content: p2573.md

- desc: "Clarifying rules for brace elision in [aggregate initialization](https://en.cppreference.com/w/cpp/language/aggregate_initialization.html)"

paper: P3106

support:

- GCC

- Clang 17

- Xcode 16.3

- desc: "Module declarations shouldn't be macros"

paper: P3034

support:

- GCC 15

- desc: "`constexpr` `std::shared_ptr` and friends"

paper: P3037

lib: true

ftm:

- name: __cpp_lib_constexpr_memory

value: 202506L

- desc: "Trivial infinite loops are not undefined behavior"

paper: P2809

support:

- GCC 14

- Clang 19

- Xcode 16.3

content: p2809_trivial_infinite_loops_ub.md

keywords: ["safety"]

- desc: "`constexpr` placement `new`"

paper: P2747

support:

- GCC 15

- Clang 20

- Xcode 26

ftm:

- name: __cpp_constexpr

value: 202406L

- name: __cpp_lib_constexpr_new

value: 202406L

- desc: "Structured binding declaration as a condition"

paper: P0963

support:

- GCC 15

- Clang 6 (partial)

- Clang 21

hints:

- target: Clang 6

msg: "Supported as an extension, not fully conforming to standardized version."

ftm:

- name: __cpp_structured_bindings

value: 202406L

keywords: ["decompose"]

- desc: "`std::optional<T&>`"

paper: P2988

lib: true

support:

- GCC 16

- Clang 22

ftm:

- name: __cpp_lib_freestanding_optional

value: 202506L

- name: __cpp_lib_optional

value: 202506L

content: p2988_optional_ref.md

- desc: "Debugging support (`<debugging>`)"

paper:

- P2546

- P2810

lib: true

support:

- GCC 16 (hint)

hints:

- target: GCC 16

msg: "Requires linking with `-lstdc++exp`."

ftm:

- name: __cpp_lib_debugging

value: 202311L

keywords: ["debugger", "breakpoint"]

content: p2546_debugging.md

- desc: "Variadic friends"

paper: P2893

support:

- GCC 15

- Clang 20

ftm:

- name: __cpp_variadic_friend

value: 202403L

- desc: "`std::mdspan::at()`"

paper: P3383

lib: true

- desc: "dextents index type parameter (`std::dims`)"

paper: P2389

lib: true

support:

- GCC 16

- Clang 19

ftm:

- name: __cpp_lib_mdspan

value: 202406L

- desc: "Padded `std::mdspan` layouts"

paper: P2642

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_submdspan

value: 202403L

- desc: "Better `std::mdspan`'s [CTAD](https://en.cppreference.com/w/cpp/language/class_template_argument_deduction.html)"

paper: P3029

lib: true

support:

- GCC 16

- Clang 19

- desc: "Inspecting `std::exception_ptr`"

paper: P2927

lib: true

support:

- GCC 16

- desc: "Inspecting `std::exception_ptr` should be `constexpr`"

paper: P3748

lib: true

ftm:

- name: __cpp_lib_exception_ptr_cast

value: 202506L

support:

- GCC 16

- desc: "Standardized `constexpr` type ordering"

paper: P2830

lib: true

ftm:

- name: __cpp_lib_type_order

value: 202506L

support:

- GCC 16

- desc: "`execution::write_env` and unstoppable sender adaptors"

paper: P3284

lib: true

- desc: "Parallel range algorithms"

paper: P3179

lib: true

ftm:

- name: __cpp_lib_parallel_algorithm

value: 202506L

- desc: "Reconsider parallel `ranges::rotate_copy()` and `ranges::reverse_copy()`"

paper: P3709

lib: true

- desc: "Rename `std::observable()` to `std::observable_checkpoint()`, and add a feature-test macro"

paper: P3641

lib: true

- desc: "`std::string::subview()`"

paper: P3044

lib: true

ftm:

- name: __cpp_lib_string_subview

value: 202506L

support:

- GCC 16

- Clang 22

- desc: "Interleaved complex values support in `std::simd`"

paper: P2663

lib: true

ftm:

- name: __cpp_lib_simd_complex

value: 202502L

- desc: "Extend `<bit>` header function with overloads for `std::simd`"

paper: P2933

lib: true

ftm:

- name: __cpp_lib_simd

value: 202506L

- desc: "Proposal to extend `std::simd` with more constructors and accessors"

paper: P2876

lib: true

- desc: "`std::simd` is a range"

paper: P3480

lib: true

ftm:

- name: __cpp_lib_simd

value: 202506L

- desc: "Extend `std::simd` with permutation API"

paper: P2664

lib: true

ftm:

- name: __cpp_lib_simd_permutations

value: 202506L

- desc: "Reconsider naming of the namespace for `std::simd`"

paper: P3691

lib: true

- desc: "`std::optional` variants in sender/receiver"

paper: P3570

lib: true

ftm:

- name: __cpp_lib_senders

value: 202506L

- desc: "`std::execution::bulk()` issues"

paper: P3481

lib: true

- desc: "Allocator support for operation states"

paper: P3433

lib: true

- desc: "`async_scope` - Creating scopes for non-sequential concurrency"

paper: P3149

lib: true

ftm:

- name: __cpp_lib_counting_scope

value: 202506L

- desc: "Remove `std::execution::split()`"

paper: P3682

lib: true

- desc: "Parallel scheduler"

paper: P2079

lib: true

ftm:

- name: __cpp_lib_parallel_scheduler

value: 202506L

- desc: "Make type-erased allocator use in `std::promise` and `std::packaged_task` consistent"

paper: P3503

lib: true

support:

- MSVC 19.51

- desc: "Atomic floating-point min/max"

paper: P3008

lib: true

ftm:

- name: __cpp_lib_atomic_min_max

value: 202506L

- desc: "Atomic reduction operations"

paper: P3111

lib: true

ftm:

- name: __cpp_lib_atomic_reductions

value: 202506L

- desc: "Add `std::views::indices(n)`"

paper: P3060

lib: true

support:

- GCC 16

- Clang 22

ftm:

- name: __cpp_lib_ranges_indices

value: 202506L

- desc: "Prevent path presentation problems"

paper: P2319

lib: true

ftm:

- name: __cpp_lib_format_path

value: 202506L

- desc: "Making `std::istream::ignore` less surprising"

paper: P3223

lib: true

support:

- GCC 16

- Clang 22

- MSVC 19.50

- desc: "`std::constant_wrapper`"

paper: P2781

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_constant_wrapper

value: 202506L

- desc: "High-quality sender diagnostics with `constexpr` exceptions"

paper: P3557

lib: true

- desc: "Preprocessing is never undefined"

paper: P2843

support:

- GCC 16

- desc: "Add a coroutine task type"

paper: P3552

lib: true

ftm:

- name: __cpp_lib_task

value: 202506L

- desc: "Remove return type deduction in `std::apply()`"

paper: P1317

lib: true

ftm:

- name: __cpp_lib_apply

value: 202506L

- desc: "Ordering of constraints involving fold expressions"

paper: P2963

support:

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_fold_expressions

value: 202406L

- desc: "Deleting a pointer to an incomplete type should be ill-formed"

paper: P3144

support:

- GCC 15

- Clang 19

- Xcode 16.3

- desc: "[Structured bindings](https://en.cppreference.com/w/cpp/language/structured_binding.html) can introduce a pack"

paper: P1061

support:

- GCC 16

- Clang 21

ftm:

- name: __cpp_structured_bindings

value: 202411L

- desc: "`constexpr` structured bindings and references to `constexpr` variables"

paper: P2686

support:

- GCC 16 (partial)

- Clang 22 (partial)

hints:

- target: GCC 16

msg: 'No [references to constexpr variables](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117784).'

- target: Clang 22

msg: "References to `constexpr` and decomposition of tuple-like types are not supported (only arrays and aggregates are)."

- desc: "Allowing exception throwing in constant-evaluation (`constexpr` exceptions)"

paper: P3068

support:

- GCC 16

ftm:

- name: __cpp_constexpr_exceptions

value: 202411L

- desc: "The Oxford variadic comma"

paper: P3176

support:

- GCC 15

- Clang 20

- desc: "Remove deprecated array comparisons from C++26"

paper: P2865

support:

- GCC 15

- Clang 20

- Xcode 16

keywords: ["safety"]

- desc: "C++26 should refer to C23 not C17"

paper: P3348

lib: true

- desc: "Concept and variable-template template-parameters"

paper: P2841

ftm:

- name: __cpp_template_parameters

value: 202502L

- desc: "Trivial unions (was `std::uninitialized<T>`)"

paper: P3074

ftm:

- name: __cpp_trivial_union

value: 202502L

- desc: "Partial program correctness (`std::observable()`)"

paper: P1494

support:

- GCC 16

keywords: ["safety"]

- desc: "Testing for success or failure of `<charconv>` functions"

lib: true

paper: P2497

support:

- GCC 14

- Clang 18

ftm:

- name: __cpp_lib_to_chars

value: 202306L

- desc: "`std::text_encoding`: text encodings identification"

paper:

- P1885

- P2862

lib: true

support:

- GCC 14

ftm:

- name: _cpp_lib_text_encoding

value: 202306L

- desc: "Arithmetic overloads of `std::to_string()` and `std::to_wstring()` use `std::format()`"

paper: P2587

lib: true

support:

- GCC 14

ftm:

- name: __cpp_lib_to_string

value: 202306L

- desc: "Type-checking format args"

paper: P2757

lib: true

support:

- GCC 15

ftm:

- name: __cpp_lib_format

value: 202305L

- desc: "Formatting pointers"

paper: P2510

lib: true

support:

- GCC 14

- Clang 17

- MSVC 19.40

ftm:

- name: __cpp_lib_format

value: 202304L

- desc: "Hashing support for `chrono` value classes"

paper: P2592

lib: true

support:

- GCC 16

- Clang 22

ftm:

- name: __cpp_lib_chrono

value: 202306L

- desc: "Read-copy update (RCU) (`<rcu>`)"

paper: P2545

lib: true

ftm:

- name: __cpp_lib_rcu

value: 202306L

- desc: "Hazard pointers (`<hazard_pointer>`)"

paper: P2530

lib: true

ftm:

- name: __cpp_lib_hazard_pointer

value: 202306L

- desc: "ADL-proof `std::projected`"

paper: P2538

lib: true

support:

- GCC 14

- Clang 18

- MSVC 19.38

- Xcode 16

- desc: "`constexpr` stable sorting"

paper: P2562

lib: true

support:

- GCC 15

- Clang 21

ftm:

- name: __cpp_lib_constexpr_algorithms

value: 202306L

- desc: "Member `visit` (`std::variant::visit()`)"

paper: P2637

lib: true

support:

- GCC 15

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_lib_variant

value: 202306L

- name: __cpp_lib_format

value: 202306L

- desc: "Checking if a union alternative is active (`std::is_within_lifetime()`)"

paper: P2641

lib: true

ftm:

- name: __cpp_lib_is_within_lifetime

value: 202306L

support:

- Clang 22

- desc: "Extending associative containers with the remaining heterogeneous overloads"

paper: P2363

lib: true

ftm:

- name: __cpp_lib_associative_heterogeneous_insertion

value: 202306L

keywords: ["insert", "insert_or_assign", "bucket", "map", "set", "unordered", "emplace", "multiset", "multimap"]

- desc: "Enabling the use of `std::weak_ptr` as keys in unordered associative containers"

paper: P1901

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_smart_ptr_owner_equality

value: 202306L

- desc: "Native handles and file streams"

paper: P1759

lib: true

support:

- GCC 14

- Clang 18

- Xcode 16

ftm:

- name: __cpp_lib_fstream_native_handle

value: 202306L

- desc: "Interfacing `std::stringstream` with `std::string_view`"

paper: P2495

lib: true

support:

- GCC 16

- Clang 19

- Xcode 16.3

ftm:

- name: __cpp_lib_sstream_from_string_view

value: 202306L

- desc: "Interfacing `std::bitset` with `std::string_view`"

paper: P2697

lib: true

support:

- Clang 18

- Xcode 16

- GCC 16

ftm:

- name: __cpp_lib_bitset

value: 202306L

- desc: "More constexpr for `<cmath>` and `<complex>`"

paper: P1383

lib: true

support:

- GCC 4.6

ftm:

- name: __cpp_lib_constexpr_cmath

value: 202306L

- name: __cpp_lib_constexpr_complex

value: 202306L

- desc: "Adding the new 2022 SI prefixes (`std::quecto`, `std::ronto`, `std::ronna`, `std::quetta`)"

paper: P2734

lib: true

support:

- GCC 14

- Clang 17 (partial)

ftm:

- name: __cpp_lib_ratio

value: 202306L

hints:

- target: Clang 17

msg: "Only the feature-testing macro has been added (`__cpp_lib_ratio`)."

- desc: "`std::function_ref`: type-erased callable reference"

paper: P0792

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_function_ref

value: 202306L

- desc: "`std::copyable_function`"

paper: P2548

lib: true

ftm:

- name: __cpp_lib_copyable_function

value: 202306L

support:

- GCC 16

- desc: "Bind front and back to NTTP callables (`std::bind_front()`, `std::bind_back()`, `std::not_fn`)"

paper: P2714

lib: true

support:

- GCC 16

- Clang 20 (partial)

ftm:

- name: __cpp_lib_bind_front

value: 202306L

desc: "`std::bind_front()` is available"

- name: __cpp_lib_bind_back

value: 202306L

desc: "`std::bind_back()` is available"

- name: __cpp_lib_not_fn

value: 202306L

desc: "`std::not_fn` is available"

- desc: "`std::submdspan()`"

paper:

- P2630

- P3355

lib: true

support:

- GCC 16

ftm:

- name: __cpp_lib_submdspan

value: 202306L

- desc: "Freestanding language: Optional `::operator new`"

paper: P2013

lib: true

support:

- MSVC 19.38

- desc: "Freestanding `std::char_traits`, `std::errc` and facilities in: `<charconv>`, `<cstdlib>`, `<cstring>`, `<cwchar>`"

paper: P2338

lib: true

support:

- MSVC 19.38

ftm:

- name: __cpp_lib_freestanding_char_traits

value: 202306L

- name: __cpp_lib_freestanding_charconv

value: 202306L

- name: __cpp_lib_freestanding_cstdlib

value: 202306L

- name: __cpp_lib_freestanding_cstring

value: 202306L

- name: __cpp_lib_freestanding_cwchar

value: 202306L

- name: __cpp_lib_freestanding_errc

value: 202306L

- desc: "Freestanding Feature-Test Macros and Implementation-Defined Extensions"

paper: P2198

lib: true

support:

- MSVC 19.38

ftm:

- name: __cpp_lib_freestanding_feature_test_macros

value: 202306L

- name: __cpp_lib_freestanding_functional

value: 202306L

- name: __cpp_lib_freestanding_iterator

value: 202306L

- name: __cpp_lib_freestanding_memory

value: 202306L

- name: __cpp_lib_freestanding_operator_new

value: 202306L

- name: __cpp_lib_freestanding_ranges

value: 202306L

- name: __cpp_lib_freestanding_ratio

value: 202306L

- name: __cpp_lib_freestanding_tuple

value: 202306L

- name: __cpp_lib_freestanding_utility

value: 202306L

- desc: "Saturation arithmetic"

paper: P0543

lib: true