Clang - C++ Programming Language Status

# C++ Support in Clang

Clang implements the following published and upcoming ISO C++ standards:

Language Standard | Flag | Available in Clang?
--- | --- | ---
C++2c | `-std=c++2c` | Partial
C++23 | `-std=c++23` | Partial
C++20 | `-std=c++20` | Partial
C++17 | `-std=c++17` | Clang 5
C++14 | `-std=c++14` | Clang 3.4
C++11 | `-std=c++11` | Clang 3.3
C++98 / C++03 | `-std=c++98` | Yes (other than `export`)

The Clang community is continually striving to improve C++ standards compliance between releases by submitting and tracking C++ Defect Reports and implementing resolutions as they become available.

Experimental work is also under way to implement C++ Technical Specifications that will help drive the future of the C++ programming language.

The LLVM bug tracker uses the "c++" label, as well as mode-specific labels such as "c++11", "c++14", and so on, to track known bugs with Clang's language conformance.

## C++2c implementation status

Clang has support for some of the features of the C++ standard following C++23, informally referred to as C++26.

You can use Clang in C++2c mode with the `-std=c++2c` option.

List of features and minimum Clang version with support

Language Feature | C++26 Proposal | Available in Clang?
--- | --- | ---
Remove undefined behavior from lexing | P2621R2 (DR) | Clang 3.3
Making non-encodable string literals ill-formed | P1854R4 (DR) | Clang 14
Unevaluated strings | P2361R6 | Clang 18
Add @, $, and ` to the basic character set | P2558R2 | Yes
constexpr cast from `void*` | P2738R1 | Clang 17
On the ignorability of standard attributes | P2552R3 (DR) | No
Static storage for braced initializers | P2752R3 (DR) | No
User-generated `static_assert` messages | P2741R3 | Clang 17
Placeholder variables with no name | P2169R4 | Clang 18
Template parameter initialization | P2308R1 (DR) | Clang 18
Pack Indexing | P2662R3 | No
Remove Deprecated Arithmetic Conversion on Enumerations | P2864R2 | Clang 18

## C++23 implementation status

Clang has support for some of the features of the ISO C++ 2023 standard.

You can use Clang in C++23 mode with the `-std=c++23` option.

List of features and minimum Clang version with support

Language Feature | C++23 Proposal | Available in Clang?
--- | --- | ---
Literal suffix `uz`, `z` for `size_t`, `ssize_t` | P0330R8 | Clang 13
Make `()` in lambdas optional in all cases | P1102R2 | Clang 13
Simpler implicit move | P2266R1 | Clang 13
`if consteval` | P1938R3 | Clang 14
Allow duplicate attributes | P2156R1 | Clang 13
Narrowing contextual conversions to bool | P1401R5 | Clang 14
Trimming whitespaces before line splicing | P2223R2 | Yes
Make declaration order layout mandated | P1874R4 | Yes
C++ identifier syntax using UAX 31 | P1949R7 | Clang 14
Mixed string literal concatenation | P2201R1 | Yes
Deducing this | P0847R7 | Clang 18
P2797R0 | No
Change scope of lambda trailing-return-type | P2036R3 | Clang 17
P2579R0
Multidimensional subscript operator | P2128R6 | Clang 15
Non-literal variables (and labels and gotos) in constexpr functions | P2242R3 | Clang 15
Character encoding of diagnostic text | P2246R1 | Yes
Character sets and encodings | P2314R4 | Yes
Consistent character literal encoding | P2316R2 | Yes
Add support for preprocessing directives elifdef and elifndef | P2334R1 | Clang 13
Extend init-statement to allow alias-declaration | P2360R0 | Clang 14
auto(x): decay-copy in the language | P0849R8 | Clang 15
Attributes on Lambda-Expressions | P2173R1 | Clang 13
`constexpr` for `<cmath>` and `<cstdlib>` | P0533R9 | No
Type trait to determine if a reference binds to a temporary | P2255R2 | Partial Clang provides `__reference_constructs_from_temporary` type trait builtin, with which `std::reference_constructs_from_temporary` is implemented. `__reference_converts_from_temporary` needs to be provided, following the normal cross-vendor convention to implement traits requiring compiler support directly.
The Equality Operator You Are Looking For | P2468R2 | Clang 16
De-deprecating volatile compound operations | P2327R1 | Clang 15
Support for `#warning` | P2437R1 | Yes
Remove non-encodable wide character literals and multicharacter wide character literals | P2362R3 | Clang 14
Labels at the end of compound statements | P2324R2 | Clang 16
Delimited escape sequences | P2290R3 | Clang 15
Named universal character escapes | P2071R2 | Clang 15
Relaxing some constexpr restrictions | P2448R2 | Clang 17 (Partial) We do not support outside of defaulted special memeber functions the change that constexpr functions no longer have to be constexpr compatible but rather support a less restricted requirements for constexpr functions. Which include allowing non-literal types as return values and parameters, allow calling of non-constexpr functions and constructors.
Using unknown pointers and references in constant expressions | P2280R4 (DR) | No
static `operator()` | P1169R4 | Clang 16
Extended floating-point types and standard names | P1467R9 | No
Class template argument deduction from inherited constructors | P2582R1 | No
Portable assumptions | P1774R8 | No
Support for UTF-8 as a portable source file encoding | P2295R6 | Clang 15
`char8_t` Compatibility and Portability Fix | P2513R3 | Clang 16
Relax requirements on `wchar_t` to match existing practices | P2460R2 | Yes
Explicit lifetime management | P2590R2 | No
static `operator[]` | P2589R1 | Clang 16
Permitting static constexpr variables in constexpr functions | P2647R1 | Clang 16
consteval needs to propagate up | P2564R3 (DR) | Clang 17
Lifetime extension in range-based for loops | P2718R0 | No
Referencing The Unicode Standard | P2736R2 | Yes

## C++20 implementation status

Clang has support for some of the features of the ISO C++ 2020 standard.

You can use Clang in C++20 mode with the `-std=c++20` option (use `-std=c++2a` in Clang 9 and earlier).

List of features and minimum Clang version with support

Language Feature | C++20 Proposal | Available in Clang?
--- | --- | ---
Default member initializers for bit-fields | P0683R1 | Clang 6
`const&`-qualified pointers to members | P0704R1 | Clang 6
Allow lambda-capture `[=, this]` | P0409R2 | Clang 6
`__VA_OPT__` for preprocessor comma elision | P0306R4 | Clang 6
P1042R1 | Clang 9
Designated initializers | P0329R4 | Clang 10
template-parameter-list for generic lambdas | P0428R2 | Clang 9
Concepts | P0734R0 | Clang 10
P0857R0 | Clang 16
P1084R2 | Clang 10
P1141R2
P0848R3 | Clang 16 (Partial) Because of other concepts implementation deficits, the __cpp_concepts macro is not yet set to 202002L. Also, the related defect reports DR1496 and DR1734 are not yet implemented. Accordingly, deleted special member functions are treated as eligible even though they shouldn't be.
P1616R1 | Clang 10
P1452R2
P1972R0 | Clang 10
P1980R0
P2103R0
P2493R0
P2092R0 | Clang 16
P2113R0 | Clang 16
Range-based for statements with initializer | P0614R1 | Clang 8
ADL and function templates that are not visible | P0846R0 | Clang 9
`const` mismatch with defaulted copy constructor | P0641R2 | Clang 8
Consistent comparison (`operator<=>`) | P0515R3 | Clang 10
P0905R1
P1120R0
P1185R2
P1186R3
P1630R1
P1946R0
P1959R0
P2002R1 | Clang 17
P2085R0 | Clang 14
Access checking on specializations | P0692R1 | Clang 14
Default constructible and assignable stateless lambdas | P0624R2 | Clang 8
Lambdas in unevaluated contexts | P0315R4 | Clang 17
`[[no_unique_address]]` attribute | P0840R2 | Clang 9
`[[likely]]` and `[[unlikely]]` attributes | P0479R5 | Clang 12
`typename` optional in more contexts | P0634R3 | Clang 16
Pack expansion in lambda init-capture | P0780R2 | Clang 9
Class types as non-type template parameters | P0732R2 | Clang 12
Generalized non-type template parameters of scalar type | P1907R1 | Clang 18 (Partial) Reference type template arguments referring to instantiation-dependent objects and subobjects (i.e. declared inside a template but neither type- nor value-dependent) aren't fully supported.
Destroying operator delete | P0722R3 | Clang 6
Relaxations of `constexpr` restrictions | P1064R0 | Clang 9
P1002R1 | Clang 8
P1327R1 | Clang 9
P1330R0
P1331R2 | Clang 10
P1668R1
P0784R7
Prohibit aggregates with user-declared constructors | P1008R1 | Clang 8
Feature test macros | P0941R2 | (see below)
`explicit(bool)` | P0892R2 | Clang 9
Signed integers are two's complement | P1236R1 | Clang 9
`char8_t` | P0482R6 | Clang 7 (11)
Immediate functions (`consteval`) | P1073R3 | Clang 17
P1937R2 | Clang 14
`std::is_constant_evaluated` | P0595R2 | Clang 9
Nested inline namespaces | P1094R2 | Clang 8
Structured binding extensions | P1091R3 | Clang 16
P1381R1
Stronger Unicode requirements | P1041R4 | Yes
P1139R2
Parenthesized initialization of aggregates | P0960R3 | Clang 16
P1975R0
Modules | P1103R3 | Clang 15
P1766R1 (DR) | Clang 11
P1811R0 | No
P1703R1 | Subsumed by P1857
P1874R1 | Clang 15
P1979R0 | No
P1779R3 | Clang 15
P1857R3 | No
P2115R0 | Partial
P1815R2 | Partial
P2615R1 (DR) | No
P2788R0 (DR) | No
Coroutines | P0912R5 | Partial Fully supported on all targets except Windows, which still has some stability and ABI issues.
Deprecate `a[b,c]` | P1161R3 | Clang 9
Deprecate some problematic uses of `volatile` | P1152R4 | Clang 10
`[[nodiscard("with reason")]]` | P1301R4 | Clang 9
`using enum` | P1099R5 | Clang 13
Class template argument deduction for aggregates | P1816R0 | Clang 17
P2082R1
Class template argument deduction for alias templates | P1814R0 | No
Permit conversions to arrays of unknown bound | P0388R4 | Clang 14
`constinit` | P1143R2 | Clang 10
Pseudo-destructors end object lifetimes | P0593R6 (DR) | Clang 11
More implicit moves | P1825R0 (DR) | Clang 13

(11): Prior to Clang 8, this feature is not enabled by `-std=c++20`, but can be enabled with `-fchar8_t`.

## C++17 implementation status

Clang 5 and later implement all the features of the ISO C++ 2017 standard.

By default, Clang 16 or later builds C++ code according to the C++17 standard. You can use Clang in C++17 mode with the `-std=c++17` option (use `-std=c++1z` in Clang 4 and earlier).

List of features and minimum Clang version with support

Language Feature | C++17 Proposal | Available in Clang?
--- | --- | ---
`static_assert` with no message | N3928 | Clang 3.5
Disabling trigraph expansion by default | N4086 | Clang 3.5
`typename` in a template template parameter | N4051 | Clang 3.5
New `auto` rules for direct-list-initialization | N3922 | Clang 3.8 (8)
Fold expressions | N4295 | Clang 3.6
P0036R0 | Clang 3.9
`u8` character literals | N4267 | Clang 3.6
Nested namespace definition | N4230 | Clang 3.6
Attributes for namespaces and enumerators | N4266 | Clang 3.6
Allow constant evaluation for all non-type template arguments | N4268 | Clang 3.6
Remove deprecated `register` storage class | P0001R1 | Clang 3.8
Remove deprecated `bool` increment | P0002R1 | Clang 3.8
Make exception specifications part of the type system | P0012R1 | Clang 4
`__has_include` in preprocessor conditionals | P0061R1 | Yes
`[[fallthrough]]` attribute | P0188R1 | Clang 3.9
`[[nodiscard]]` attribute | P0189R1 | Clang 3.9
P1771R1 (DR) | Clang 9
`[[maybe_unused]]` attribute | P0212R1 | Clang 3.9
Aggregate initialization of classes with base classes | P0017R1 | Clang 3.9
`constexpr` lambda expressions | P0170R1 | Clang 5
Differing `begin` and `end` types in range-based `for` | P0184R0 | Clang 3.9
Lambda capture of `*this` | P0018R3 | Clang 3.9
Direct-list-initialization of `enum`s | P0138R2 | Clang 3.9
Hexadecimal floating-point literals | P0245R1 | Yes
Using attribute namespaces without repetition | P0028R4 | Clang 3.9
Dynamic memory allocation for over-aligned data | P0035R4 | Clang 4
Template argument deduction for class templates | P0091R3 | Clang 5
P0512R0
P0620R0 (DR) | Clang 7
P0702R1 (DR) | Clang 6
Non-type template parameters with `auto` type | P0127R2 | Clang 4
Guaranteed copy elision | P0135R1 | Clang 4
Stricter expression evaluation order | P0145R3 | Clang 4 (9)
P0400R0
Requirement to ignore unknown attributes | P0283R2 | Yes
`constexpr` if-statements | P0292R2 | Clang 3.9
Inline variables | P0386R2 | Clang 3.9
Structured bindings | P0217R3 | Clang 4
P0961R1 (DR) | Clang 8
P0969R0 (DR) | Clang 8
Separate variable and condition for `if` and `switch` | P0305R1 | Clang 3.9
Matching template template parameters to compatible arguments | P0522R0 | Partial (10)
Removing deprecated dynamic exception specifications | P0003R5 | Clang 4
Pack expansions in using-declarations | P0195R2 | Clang 4

(8): This is a backwards-incompatible change that is applied to all language versions that allow type deduction from `auto` (per the request of the C++ committee). In Clang 3.7, a warning is emitted for all cases that would change meaning.
(9): Under the MS ABI, function parameters are destroyed from left to right in the callee. As a result, function parameters in calls to `operator<<`, `operator>>`, `operator->*`, `operator&&`, `operator||`, and `operator,` functions using expression syntax are no longer guaranteed to be destroyed in reverse construction order in that ABI. This is not fully supported during constant expression evaluation until Clang 12.
(10): Despite being the resolution to a Defect Report, this feature is disabled by default in all language versions, and can be enabled explicitly with the flag `-frelaxed-template-template-args` in Clang 4 onwards. The change to the standard lacks a corresponding change for template partial ordering, resulting in ambiguity errors for reasonable and previously-valid code. This issue is expected to be rectified soon.

## C++14 implementation status

Clang 3.4 and later implement all of the ISO C++ 2014 standard.

You can use Clang in C++14 mode with the `-std=c++14` option (use `-std=c++1y` in Clang 3.4 and earlier).

List of features and minimum Clang version with support

Language Feature | C++14 Proposal | Available in Clang?
--- | --- | ---
Tweak to certain C++ contextual conversions | N3323 | Clang 3.4
Binary literals | N3472 | Clang 2.9
decltype(auto) | N3638 | Clang 3.3
Return type deduction for normal functions | Clang 3.4
Initialized lambda captures | N3648 | Clang 3.4
Generic lambdas | N3649 | Clang 3.4
Variable templates | N3651 | Clang 3.4
Relaxing requirements on constexpr functions | N3652 | Clang 3.4
Member initializers and aggregates | N3653 | Clang 3.3
Clarifying memory allocation | N3664 | Clang 3.4
`[[deprecated]]` attribute | N3760 | Clang 3.4
Single quotation mark as digit separator | N3781 | Clang 3.4
C++ Sized Deallocation | N3778 | Clang 3.4 (7)

(7): In Clang 3.7 and later, sized deallocation is only enabled if the user passes the `-fsized-deallocation` flag. The user must supply definitions of the sized deallocation functions, either by providing them explicitly or by using a C++ standard library that does. `libstdc++` added these functions in version 5.0, and `libc++` added them in version 3.7.

## C++11 implementation status

Clang 3.3 and later implement all of the ISO C++ 2011 standard.

You can use Clang in C++11 mode with the `-std=c++11` option. Clang's C++11 mode can be used with libc++ or with gcc's libstdc++.

List of features and minimum Clang version with support

Language Feature | C++11 Proposal | Available in Clang?
--- | --- | ---
Rvalue references | N2118 | Clang 2.9
P1825R0 (DR) | Clang 13
Rvalue references for `*this` | N2439 | Clang 2.9
Initialization of class objects by rvalues | N1610 | Clang 2.9
Non-static data member initializers | N2756 | Clang 3.0
Variadic templates | N2242 | Clang 2.9
Extending variadic template template parameters | N2555 | Clang 2.9
Initializer lists | N2672 | Clang 3.1
P1009R2 (DR) | Clang 9
P1957R2 (DR) | Clang 11
Static assertions | N1720 | Clang 2.9
`auto`-typed variables | N1984 | Clang 2.9
Multi-declarator `auto` | N1737 | Clang 2.9
Removal of auto as a storage-class specifier | N2546 | Clang 2.9
New function declarator syntax | N2541 | Clang 2.9
Lambda expressions | N2927 | Clang 3.1
P0588R1 (DR) | No
Declared type of an expression | N2343 | Clang 2.9
Incomplete return types | N3276 | Clang 3.1
Right angle brackets | N1757 | Clang 2.9
Default template arguments for function templates | DR226 | Clang 2.9
Solving the SFINAE problem for expressions | DR339 | Clang 2.9
Alias templates | N2258 | Clang 3.0
Extern templates | N1987 | Clang 2.9
Null pointer constant | N2431 | Clang 3.0
Strongly-typed enums | N2347 | Clang 2.9
Forward declarations for enums | N2764 DR1206 | Clang 3.1
Standardized attribute syntax | N2761 | Clang 3.3 (1)
Generalized constant expressions | N2235 | Clang 3.1
P0859R0 (DR) | Clang 8
Alignment support | N2341 | Clang 3.3
Conditionally-support behavior | N1627 | Clang 2.9
Changing undefined behavior into diagnosable errors | N1727 | Clang 2.9
Delegating constructors | N1986 | Clang 3.0
Inheriting constructors | N2540 | Clang 3.3
P0136R1 (DR) | Clang 3.9
Explicit conversion operators | N2437 | Clang 3.0
New character types | N2249 | Clang 2.9
Unicode string literals | N2442 | Clang 3.0
Raw string literals | N2442 | Clang 3.0
Universal character names in literals | N2170 | Clang 3.1
User-defined literals | N2765 | Clang 3.1
Standard Layout Types | N2342 | Clang 3.0
Defaulted functions | N2346 | Clang 3.0
P1286R2 (DR) | Clang 9
Deleted functions | N2346 | Clang 2.9
Extended friend declarations | N1791 | Clang 2.9
Extending `sizeof` | N2253 DR850 | Clang 3.1
Inline namespaces | N2535 | Clang 2.9
Unrestricted unions | N2544 | Clang 3.1
Local and unnamed types as template arguments | N2657 | Clang 2.9
Range-based for | N2930 | Clang 3.0
P0962R1 (DR) | Clang 8
Explicit virtual overrides | N2928 N3206 N3272 | Clang 3.0
Minimal support for garbage collection and reachability-based leak detection | N2670 | N/A (2)
Allowing move constructors to throw [noexcept] | N3050 | Clang 3.0
Defining move special member functions | N3053 | Clang 3.0
Concurrency
Sequence points | N2239 | Clang 3.3
Atomic operations | N2427 | Clang 3.1
Strong Compare and Exchange | N2748 | Clang 3.1 (3)
Bidirectional Fences | N2752 | Clang 3.1
Memory model | N2429 | Clang 3.2
Data-dependency ordering: atomics and memory model | N2664 | Clang 3.2 (4)
Propagating exceptions | N2179 | Clang 2.9
Allow atomics use in signal handlers | N2547 | Clang 3.1
Thread-local storage | N2659 | Clang 3.3 (5)
Dynamic initialization and destruction with concurrency | N2660 | Clang 2.9
C99 Features in C++11
`__func__` predefined identifier | N2340 | Clang 2.9
C99 preprocessor | N1653 | Clang 2.9
`long long` | N1811 | Clang 2.9
Extended integral types | N1988 | N/A (6)

(1): The `[[carries_dependency]]` attribute has no effect.
(2): No compiler changes are required for an implementation such as Clang that does not provide garbage collection.
(3): All compare-exchange operations are emitted as strong compare-exchanges.
(4): `memory_order_consume` is lowered to `memory_order_acquire`.
(5): `thread_local` support requires a C++ runtime library providing `__cxa_thread_atexit`, such as libc++abi 3.6 or later, or libsupc++ 4.8 or later.
(6): No compiler changes are required for an implementation such as Clang that does not provide any extended integer types. `__int128` is not treated as an extended integer type, because changing `intmax_t` would be an ABI-incompatible change.

## C++98 implementation status

Clang implements all of the ISO C++ 1998 standard (including the defects addressed in the ISO C++ 2003 standard) except for `export` (which was removed in C++11).

## Defect reports

Clang generally aims to implement resolutions to Defect Reports (bug fixes against prior standards) retroactively, in all prior standard versions where the fix is meaningful. Significant Defect Report changes to language features after the publication of the relevant standard are marked (DR) in the above table.

Clang also has a test suite for conformance to resolutions for issues on the C++ core issues list, most of which are considered Defect Reports. Implementation status for C++ core issues based on that test suite is tracked on a separate page.

## Technical specifications and standing documents

ISO C++ also publishes a number of documents describing additional language and library features that are not part of standard C++.

List of features and minimum Clang version with support

Document | Latest draft | Compiler flag | Available in Clang?
--- | --- | --- | ---
SD-6: SG10 feature test recommendations | SD-6 | N/A | Clang 3.4 (N3745)
Clang 3.6 (N4200)
Clang 4 (P0096R3)
Clang 5 (P0096R4)
Clang 7 (P0096R5)
Clang 9 (P1353R0)
Clang 10 (P1902R1)
[TS] Concepts | P0121R0 |  | Superseded by P0734R0
[TS] Coroutines | N4663 | `-fcoroutines-ts -stdlib=libc++` | Clang 5
`-std=c++20 -stdlib=libc++` | Superseded by P0912R5
[TS] Library Fundamentals, Version 1 (invocation type traits) | N4480 | N/A | No
[TS] Library Fundamentals, Version 2 (`source_location`) | N4617 | N/A | Clang 9 (documentation)
[TS] Modules | N4720 | `-fmodules-ts` | Superseded by P1103R3
[DRAFT TS] Reflection | N4818 |  | No
[TS] Transactional Memory | N4514 |  | No