C++ Support in Clang

Last updated: $Date: 2016-03-28 01:08:37 -0500 (Mon, 28 Mar 2016) $

Clang fully implements all published ISO C++ standards including C++11, as well as the upcoming C++14 standard, and some parts of the fledgling C++1z standard, and is considered a production-quality C++ compiler.

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. The following table describes the Clang version in which each feature became available.

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++, but patches are needed to make libstdc++-4.4 work with Clang in C++11 mode. Patches are also needed to make libstdc++-4.6 and libstdc++-4.7 work with Clang releases prior to version 3.2 in C++11 mode.

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
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
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
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
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 Draft International Standard (see most recent publicly available draft) of the upcoming C++14 language standard. The following table describes the Clang version in which each feature became available.

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

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++1z implementation status

Clang has experimental support for some proposed features of the C++ standard following C++14, provisionally named C++1z. The following table describes which C++1z features have been implemented in Clang and in which Clang version they became available.

Note that support for these features may change or be removed without notice, as the draft C++1z standard evolves.

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

Language Feature C++1z 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 SVN
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 No
__has_include in preprocessor conditionals P0061R1 Yes
New specification for inheriting constructors (DR1941 et al) P0136R1 No
[[fallthrough]] attribute P0188R1 SVN
[[nodiscard]] attribute P0189R1 SVN
[[maybe_unused]] attribute P0212R1 SVN
Aggregate initialization of classes with base classes P0017R1 SVN
constexpr lambda expressions P0170R1 No
Differing begin and end types in range-based for P0184R0 SVN
Lambda capture of *this P0018R3 SVN
Direct-list-initialization of enums P0138R2 SVN
Hexadecimal floating-point literals P0245R1 Yes

(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.

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++. The following table describes which language features have been implemented in Clang and in which Clang version they became available:

Document Latest draft Available in Clang?
SD-6: SG10 feature test recommendations SD-6 Clang 3.4 (N3745)
Clang 3.6 (N4200)
[TS] Concepts P0121R0 No
[TS] Library Fundamentals, Version 1 (invocation type traits) N4480 No
[DRAFT TS] Library Fundamentals, Version 2 (source_location) N4529 No
[TS] Modules P0143R2 No
[TS] Transactional Memory N4514 No