C++ Standards Support in GCC

GCC supports different dialects of C++, corresponding to the multiple published ISO standards. Which standard it implements can be selected using the -std= command-line option.

For information about the status of the library implementation, please see this page.

C++2a Support in GCC

GCC has experimental support for the next revision of the C++ standard, which is expected to be published in 2020.

C++2a features are available as part of "mainline" GCC in the trunk of GCC's repository and will be available in GCC 8 and later. To enable C++2a support, add the command-line parameter -std=c++2a to your g++ command line. Or, to enable GNU extensions in addition to C++2a features, add -std=gnu++2a.

Important: Because the ISO C++2a standard is still evolving, GCC's support is experimental. No attempt will be made to maintain backward compatibility with implementations of C++2a features that do not reflect the final standard.

C++2a Language Features

The following table lists new language features that have been accepted into the C++2a working draft. The "Proposal" column provides a link to the ISO C++ committee proposal that describes the feature, while the "Available in GCC?" column indicates the first version of GCC that contains an implementation of this feature (if it has been implemented).

Language Feature Proposal Available in GCC? SD-6 Feature Test
Default member initializers for bit-fields P0683R1 8
Fixing const-qualified pointers to members P0704R1 8
Allow lambda capture [=, this] P0409R2 8
__VA_OPT__ for preprocessor comma elision P0306R4 8 (partial, no #__VA_OPT__ support)
Designated initializers P0329R4 8
Familiar template syntax for generic lambdas P0428R2 8
List deduction of vector P0702R1 8
Concepts P0734R0
P0857R0 		TS with -fconcepts
Range-based for statements with initializer P0614R1 9
Simplifying implicit lambda capture P0588R1 8
ADL and function templates that are not visible P0846R0 No
const mismatch with defaulted copy constructor P0641R2 9
Less eager instantiation of constexpr functions P0859R0 5.2 (mostly)
9 (P0859R0)
Consistent comparison (operator<=>) P0515R3
P0905R1		 No
Access checking on specializations P0692R1 No
Default constructible and assignable stateless lambdas P0624R2 9
Lambdas in unevaluated contexts P0315R4 No
Language support for empty objects P0840R2 No
Relaxing the range-for loop customization point finding rules P0962R1 8
Allow structured bindings to accessible members P0969R0 8
Relaxing the structured bindings customization point finding rules P0961R1 8
Down with typename! P0634R3 No
Allow pack expansion in lambda init-capture P0780R2 No
Proposed wording for likely and unlikely attributes P0479R5 No

C++17 Support in GCC

GCC has experimental support for the latest revision of the C++ standard, which was published in 2017.

C++17 features are available as part of "mainline" GCC in the trunk of GCC's repository and in GCC 5 and later. To enable C++17 support, add the command-line parameter -std=c++17 to your g++ command line. Or, to enable GNU extensions in addition to C++17 features, add -std=gnu++17.

Important: Because the final ISO C++17 standard is still new, GCC's support is experimental. No attempt will be made to maintain backward compatibility with implementations of C++17 features that do not reflect the final standard.

C++17 Language Features

The following table lists new language features that have been accepted into the C++17 working draft. The "Proposal" column provides a link to the ISO C++ committee proposal that describes the feature, while the "Available in GCC?" column indicates the first version of GCC that contains an implementation of this feature (if it has been implemented).

Language Feature Proposal Available in GCC? SD-6 Feature Test
Removing trigraphs N4086 5
u8 character literals N4267 6 __cpp_unicode_characters >= 201411
Folding expressions N4295 6 __cpp_fold_expressions >= 201411
Attributes for namespaces and enumerators N4266 4.9 (namespaces)
6 (enumerators) 		__cpp_namespace_attributes >= 201411
__cpp_enumerator_attributes >= 201411
Nested namespace definitions N4230 6 __cpp_nested_namespace_definitions >= 201411
Allow constant evaluation for all non-type template arguments N4268 6 __cpp_nontype_template_args >= 201411
Extending static_assert N3928 6 __cpp_static_assert >= 201411
New Rules for auto deduction from braced-init-list N3922 5
Allow typename in a template template parameter N4051 5
[[fallthrough]] attribute P0188R1 7 __has_cpp_attribute(fallthrough)
[[nodiscard]] attribute P0189R1 4.8 ([[gnu::warn_unused_result]])
7 (P0189R1)		 __has_cpp_attribute(nodiscard)
[[maybe_unused]] attribute P0212R1 4.8 ([[gnu::unused]])
7 (P0212R1)		 __has_cpp_attribute(maybe_unused)
Extension to aggregate initialization P0017R1 7 __cpp_aggregate_bases >= 201603
Wording for constexpr lambda P0170R1 7 __cpp_constexpr >= 201603
Unary Folds and Empty Parameter Packs P0036R0 6 __cpp_fold_expressions >= 201603
Generalizing the Range-Based For Loop P0184R0 6 __cpp_range_based_for >= 201603
Lambda capture of *this by Value P0018R3 7 __cpp_capture_star_this >= 201603
Construction Rules for enum class variables P0138R2 7
Hexadecimal floating literals for C++ P0245R1 3.0 __cpp_hex_float >= 201603
Dynamic memory allocation for over-aligned data P0035R4 7 __cpp_aligned_new >= 201606
Guaranteed copy elision P0135R1 7
Refining Expression Evaluation Order for Idiomatic C++ P0145R3 7
constexpr if P0292R2 7 __cpp_if_constexpr >= 201606
Selection statements with initializer P0305R1 7
Template argument deduction for class templates P0091R3
P0512R0		 7
8		 __cpp_deduction_guides >= 201606
__cpp_deduction_guides >= 201611
Declaring non-type template parameters with auto P0127R2 7 __cpp_template_auto >= 201606
Using attribute namespaces without repetition P0028R4 7
Ignoring unsupported non-standard attributes P0283R2 Yes
Structured bindings P0217R3 7 __cpp_structured_bindings >= 201606
Remove Deprecated Use of the register Keyword P0001R1 7
Remove Deprecated operator++(bool) P0002R1 7
Make exception specifications be part of the type system P0012R1 7 __cpp_noexcept_function_type >= 201510
__has_include for C++17 P0061R1 5
Rewording inheriting constructors (core issue 1941 et al) P0136R1 7 __cpp_inheriting_constructors >= 201511
Inline variables P0386R2 7 __cpp_inline_variables >= 201606
DR 150, Matching of template template arguments P0522R0 7 __cpp_template_template_args >= 201611
Removing dynamic exception specifications P0003R5 7
Pack expansions in using-declarations P0195R2 7 __cpp_variadic_using >= 201611
A byte type definition P0298R0 7

Technical Specifications

GCC also implements experimental support for some language Technical Specifications published by the C++ committee.

Important: Because these Technical Specifications are still evolving toward future inclusion in a C++ standard, GCC's support is experimental. No attempt will be made to maintain backward compatibility with implementations of features that do not reflect the final standard.

Technical Specification Document Available in GCC? Compiler Option SD-6 Feature Test
Concepts N4377 6 -fconcepts __cpp_concepts >= 201507
Transactional Memory N4514 6 (no atomic_cancel) -fgnu-tm __cpp_transactional_memory >= 201505
Coroutines N4649 No
Modules N4720 In progress

C++14 Support in GCC

GCC has full support for the previous revision of the C++ standard, which was published in 2014.

This mode is the default in GCC 6.1 and above; it can be explicitly selected with the -std=c++14 command-line flag, or -std=gnu++14 to enable GNU extensions as well.

C++14 Language Features

The following table lists new language features that are part of the C++14 standard. The "Proposal" column provides a link to the ISO C++ committee proposal that describes the feature, while the "Available in GCC?" column indicates the first version of GCC that contains an implementation of this feature.

Language Feature Proposal Available in GCC? SD-6 Feature Test
Tweak to certain C++ contextual conversions N3323 4.9
Binary literals N3472 4.3 (GNU)
4.9 (N3472)		 __cpp_binary_literals >= 201304
Return type deduction for normal functions N3638 4.8 (N3386)
4.9 (N3638)		 __cpp_decltype_auto >= 201304
Generalized lambda capture (init-capture) N3648 4.5 (partial)
4.9 (N3648)		 __cpp_init_captures >= 201304
Generic (polymorphic) lambda expressions N3649 4.9 __cpp_generic_lambdas >= 201304
Variable templates N3651 5 __cpp_variable_templates >= 201304
Relaxing requirements on constexpr functions N3652 5 __cpp_constexpr >= 201304
Member initializers and aggregates N3653 5 __cpp_aggregate_nsdmi >= 201304
Clarifying memory allocation N3664 N/A
Sized deallocation N3778 5 __cpp_sized_deallocation >= 201309
[[deprecated]] attribute N3760 4.9 (N3797) __has_cpp_attribute(deprecated) >= 201309
Single-quotation-mark as a digit separator N3781 4.9 (N3797) __cpp_digit_separator >= 201309

This feature was briefly part of the C++14 working paper, but was not part of the published standard; as a result, it has been removed from the compiler.

Language Feature Proposal Available in GCC? SD-6 Feature Test
Runtime-sized arrays with automatic storage duration
(Removed from the standard)		 N3639 ?.? (GNU VLAs)
4.9 (N3639)
5 (GNU VLAs)		 __cpp_runtime_arrays >= 198712

C++11 Support in GCC

GCC 4.8.1 was the first feature-complete implementation of the 2011 C++ standard, previously known as C++0x.

This mode can be selected with the -std=c++11 command-line flag, or -std=gnu++11 to enable GNU extensions as well.

For information about C++11 support in a specific version of GCC, please see:

Language Feature Proposal Available in GCC? SD-6 Feature Test
Rvalue references N2118 GCC 4.3 __cpp_rvalue_references >= 200610
    Rvalue references for *this N2439 GCC 4.8.1 __cpp_ref_qualifiers >= 200710
Initialization of class objects by rvalues N1610 Yes
Non-static data member initializers N2756 GCC 4.7 __cpp_nsdmi >= 200809
Variadic templates N2242 GCC 4.3 __cpp_variadic_templates >= 200704
    Extending variadic template template parameters N2555 GCC 4.4
Initializer lists N2672 GCC 4.4 __cpp_initializer_lists >= 200806
Static assertions N1720 GCC 4.3 __cpp_static_assert >= 200410
auto-typed variables N1984 GCC 4.4
    Multi-declarator auto N1737 GCC 4.4
    Removal of auto as a storage-class specifier N2546 GCC 4.4
    New function declarator syntax N2541 GCC 4.4
New wording for C++0x lambdas N2927 GCC 4.5 __cpp_lambdas >= 200907
Declared type of an expression N2343 GCC 4.3 __cpp_decltype >= 200707
    decltype and call expressions N3276 GCC 4.8.1
Right angle brackets N1757 GCC 4.3
Default template arguments for function templates DR226 GCC 4.3
Solving the SFINAE problem for expressions DR339 GCC 4.4
Template aliases N2258 GCC 4.7 __cpp_alias_templates >= 200704
Extern templates N1987 Yes
Null pointer constant N2431 GCC 4.6
Strongly-typed enums N2347 GCC 4.4
Forward declarations for enums N2764 GCC 4.6
Generalized attributes N2761 GCC 4.8 __cpp_attributes >= 200809;
__has_cpp_attribute(noreturn) >= 200809;
__has_cpp_attribute(carries_dependency) == 0 (not implemented)
Generalized constant expressions N2235 GCC 4.6 __cpp_constexpr >= 200704
Alignment support N2341 GCC 4.8
Delegating constructors N1986 GCC 4.7 __cpp_delegating_constructors >= 200604
Inheriting constructors N2540 GCC 4.8 __cpp_inheriting_constructors >= 200802
Explicit conversion operators N2437 GCC 4.5
New character types N2249 GCC 4.4 __cpp_unicode_characters >= 200704
Unicode string literals N2442 GCC 4.5 __cpp_unicode_literals >= 200710
Raw string literals N2442 GCC 4.5 __cpp_raw_strings >= 200710
Universal character name literals N2170 GCC 4.5
User-defined literals N2765 GCC 4.7 __cpp_user_defined_literals >= 200809
Standard Layout Types N2342 GCC 4.5
Defaulted and deleted functions N2346 GCC 4.4
Extended friend declarations N1791 GCC 4.7
Extending sizeof N2253 GCC 4.4
Inline namespaces N2535 GCC 4.4
Unrestricted unions N2544 GCC 4.6
Local and unnamed types as template arguments N2657 GCC 4.5
Range-based for N2930 GCC 4.6 __cpp_range_based_for >= 200907
Explicit virtual overrides N2928
N3206
N3272		 GCC 4.7
Minimal support for garbage collection and reachability-based leak detection N2670 No
Allowing move constructors to throw [noexcept] N3050 GCC 4.6
Defining move special member functions N3053 GCC 4.6
Concurrency
Sequence points N2239 Yes
Atomic operations N2427 GCC 4.4
Strong Compare and Exchange N2748 GCC 4.5
Bidirectional Fences N2752 GCC 4.8
Memory model N2429 GCC 4.8
Data-dependency ordering: atomics and memory model N2664 GCC 4.4
(memory_order_consume)
Propagating exceptions N2179 GCC 4.4
Abandoning a process and at_quick_exit N2440 GCC 4.8
Allow atomics use in signal handlers N2547 Yes
Thread-local storage N2659 GCC 4.8
Dynamic initialization and destruction with concurrency N2660 GCC 4.3 __cpp_threadsafe_static_init >= 200806
C99 Features in C++11
__func__ predefined identifier N2340 GCC 4.3
C99 preprocessor N1653 GCC 4.3
long long N1811 GCC 4.3
Extended integral types N1988 Yes

C++98 Support in GCC

GCC has full support for the 1998 C++ standard as modified by the 2003 technical corrigendum and some later defect reports, excluding the export feature which was later removed from the language.

This mode is the default in GCC versions prior to 6.1; it can be explicitly selected with the -std=c++98 command-line flag, or -std=gnu++98 to enable GNU extensions as well.

For questions related to the use of GCC, please consult these web pages and the GCC manuals. If that fails, the gcc-help@gcc.gnu.org mailing list might help. Comments on these web pages and the development of GCC are welcome on our developer list at gcc@gcc.gnu.org. All of our lists have public archives.

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These pages are maintained by the GCC team. Last modified 2018-06-14.