C++ Support in Clang

Last updated: $Date: 2018/07/17 18:31:55 $

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
	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)	No
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
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)	No
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 5 and later implement all the features of the ISO C++ 2017 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
[[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 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	Clang 5
	P0512R0
	P0620R0 (DR)	SVN
	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)	No
	P0969R0 (DR)	No
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.
(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++2a implementation status

Clang has experimental support for some 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.

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

List of features and minimum Clang version with support

Language Feature	C++2a 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	Partial
Designated initializers	P0329R4	Partial (extension)
template-parameter-list for generic lambdas	P0428R2	No
Concepts	P0734R0	No
	P0857R0
Range-based for statements with initializer	P0614R1	No
ADL and function templates that are not visible	P0846R0	No
const mismatch with defaulted copy constructor	P0641R2	No
Consistent comparison (operator<=>)	P0515R3	Partial
	P0905R1
	P1120R0
Access checking on specializations	P0692R1	Partial
Default constructible and assignable stateless lambdas	P0624R2	No
Lambdas in unevaluated contexts	P0315R4	No
[[no_unique_address]] attribute	P0840R2	No
[[likely]] and [[unlikely]] attributes	P0479R5	No
typename optional in more contexts	P0634R3	No
Pack expansion in lambda init-capture	P0780R2	No
Class types as non-type template parameters	P0732R2	No
Destroying operator delete	P0722R3	Clang 6
Virtual function calls in constant expressions	P1064R0	No
Prohibit aggregates with user-declared constructors	P1008R1	No
Contracts	P0542R5	No
Feature test macros	P0941R2	(see below)
explicit(bool)	P0892R2	No

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)
			SVN (P0096R5)
[TS] Concepts	P0121R0		Superseded by P0734R0
[DRAFT TS] Coroutines	N4663	-fcoroutines-ts -stdlib=libc++	Clang 5
[TS] Library Fundamentals, Version 1 (invocation type traits)	N4480	N/A	No
[TS] Library Fundamentals, Version 2 (source_location)	N4617	N/A	No
[TS] Modules	N4720	-fmodules-ts	WIP
[DRAFT TS] Reflection	N4746		No
[TS] Transactional Memory	N4514		No