C++ Support in Clang

Last updated: $Date$

Clang fully implements all published ISO C++ standards (C++98 / C++03, C++11, and C++14), and most of the upcoming C++17 standard.

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 contains Clang C++ components that track known bugs with Clang's language conformance in each language mode.

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).

C++11 implementation status

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

By default, Clang builds C++ code according to the C++98 standard, with many C++11 features accepted as extensions. 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
    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
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
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
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
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
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
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++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++17 implementation status

Clang SVN implements all the features of the C++ 2017 Draft International Standard.

You can use Clang in C++17 mode with the -std=c++1z option.

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
New specification for inheriting constructors (DR1941 et al) P0136R1 Clang 3.9 (9)
[[fallthrough]] attribute P0188R1 Clang 3.9
[[nodiscard]] attribute P0189R1 Clang 3.9
[[maybe_unused]] attribute P0212R1 Clang 3.9
Aggregate initialization of classes with base classes P0017R1 Clang 3.9
constexpr lambda expressions P0170R1 SVN
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 enums 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 SVN
P0512R0
Non-type template parameters with auto type P0127R2 Clang 4
Guaranteed copy elision P0135R1 Clang 4
Stricter expression evaluation order P0145R3 Clang 4 (10)
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
Separate variable and condition for if and switch P0305R1 Clang 3.9
Matching template template parameters to compatible arguments P0522R0 Partial (12)
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): This is the resolution to a Defect Report, so is applied to all language versions supporting inheriting constructors.
(10): 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.
(12): Despite being the 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. 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++2a implementation status

Clang does not yet support any of the proposed features of the C++ standard following C++17, provisionally named C++2a. Note that support for these features may change or be removed without notice, as the draft C++2a standard evolves.

List of features and minimum Clang version with support
Language Feature C++2a Proposal Available in Clang?
Default member initializers for bit-fields P0683R1 No
const&-qualified pointers to members P0704R1 No
Allow lambda-capture [=, this] P0409R2 No
__VA_OPT__ for preprocessor comma elision P0306R4 No
Designated initializers P0329R4 Partial (extension)
template-parameter-list for generic lambdas P0428R2 No
Initializer list constructors in class template argument deduction P0702R1 No
Concepts P0734R0 No

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)
[TS] Concepts P0121R0 WIP
[DRAFT TS] Coroutines N4663 -fcoroutines-ts
-stdlib=libc++		 SVN
[TS] Library Fundamentals, Version 1 (invocation type traits) N4480 N/A No
[DRAFT TS] Library Fundamentals, Version 2 (source_location) N4600 N/A No
[DRAFT TS] Modules N4667 -fmodules-ts WIP
[TS] Transactional Memory N4514 No