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
(1): 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)
No
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
Static assertions
N1720
Clang 2.9
auto
-typed variablesN1984
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
DR1206Clang 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
DR850Clang 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
N3272Clang 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 identifierN2340
Clang 2.9
C99 preprocessor
N1653
Clang 2.9
long long
N1811
Clang 2.9
Extended integral types
N1988
N/A (6)
[[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 |
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 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) | 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.
(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++20 implementation status
Clang has support for some of the features of the ISO C++ 2020 Draft International Standard.
You can use Clang in C++20 mode with the -std=c++20
option
(use -std=c++2a
in Clang 10 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 | SVN |
template-parameter-list for generic lambdas | P0428R2 | Clang 9 |
Concepts | P0734R0 | SVN |
P0857R0 | ||
P1084R2 | ||
P1141R2 | ||
P0848R3 | No | |
P1616R1 | SVN | |
P1452R2 | ||
P1972R0 | No | |
P1980R0 | ||
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 | SVN |
P0905R1 | ||
P1120R0 | ||
P1185R2 | ||
P1186R3 | ||
P1630R1 | ||
P1946R0 | ||
P1959R0 | ||
Access checking on specializations | P0692R1 | Partial |
Default constructible and assignable stateless lambdas | P0624R2 | Clang 8 |
Lambdas in unevaluated contexts | P0315R4 | No |
[[no_unique_address]] attribute | P0840R2 | Clang 9 |
[[likely]] and [[unlikely]] attributes | P0479R5 | No |
typename optional in more contexts | P0634R3 | No |
Pack expansion in lambda init-capture | P0780R2 | Clang 9 |
Class types as non-type template parameters | P0732R2 | No |
P1907R1 | ||
Destroying operator delete | P0722R3 | Clang 6 |
Relaxations of constexpr restrictions | P1064R0 | Clang 9 |
P1002R1 | Clang 8 | |
P1327R1 | Clang 9 | |
P1330R0 | ||
P1331R2 | SVN | |
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 | No |
std::is_constant_evaluated | P0595R2 | Clang 9 |
Nested inline namespaces | P1094R2 | Clang 8 |
Structured binding extensions | P1091R3 | Partial |
P1381R1 | ||
Stronger Unicode requirements | P1041R4 | Yes |
P1139R2 | ||
Parenthesized initialization of aggregates | P0960R3 | No |
P1975R0 | ||
Modules | P1103R3 | Partial |
P1766R1 (DR) | No | |
P1811R0 | ||
P1703R1 | ||
P1874R1 | Partial | |
P1979R0 | No | |
Coroutines | P0912R5 | Partial |
Deprecate a[b,c] | P1161R3 | Clang 9 |
Deprecate some problematic uses of volatile | P1152R4 | SVN |
[[nodiscard("with reason")]] | P1301R4 | Clang 9 |
using enum | P1099R5 | No |
Class template argument deduction for aggregates | P1816R0 | No |
Class template argument deduction for alias templates | P1814R0 | No |
Permit conversions to arrays of unknown bound | P0388R4 | No |
constinit | P1143R2 | SVN |
(11): Prior to Clang 8, this feature is not enabled by -std=c++20, but can be enabled with -fchar8_t.
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) | |||
SVN (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 | N4746 | No | |
[TS] Transactional Memory | N4514 | No |