C++ Standards Support in GCC - GCC 对 C++ 标准的支持

C++ Standards Support in GCC - 2019-2-20

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.

参考地址：https://gcc.gnu.org/projects/cxx-status.html

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 P1042R1	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 P1084R2 P1141R2	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	9
`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 P1120R0	No	__cpp_impl_three_way_comparison >= 201711
Access checking on specializations	P0692R1	Yes
Default constructible and assignable stateless lambdas	P0624R2	9
Lambdas in unevaluated contexts	P0315R4	9
Language support for empty objects	P0840R2	9
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	9
Allow pack expansion in lambda init-capture	P0780R2	9
Proposed wording for likely and unlikely attributes	P0479R5	9
Deprecate implicit capture of this via [=]	P0806R2	9
Class Types in Non-Type Template Parameters	P0732R2	9	__cpp_nontype_template_parameter_class >= 201806
Atomic Compare-and-Exchange with Padding Bits	P0528R3	No (PR 88101)
Efficient sized delete for variable sized classes	P0722R3	9	__cpp_impl_destroying_delete >= 201806
Allowing Virtual Function Calls in Constant Expressions	P1064R0	9
Prohibit aggregates with user-declared constructors	P1008R1	9
Support for contract based programming in C++	P0542R5 P1289R1	No (PR 88102)
explicit(bool)	P0892R2	9	__cpp_conditional_explicit >= 201806
Signed integers are two's complement	P1236R1	9
char8_t	P0482R6	9	__cpp_char8_t >= 201811
Immediate functions (consteval)	P1073R3	No
std::is_constant_evaluated	P0595R2	9
Nested inline namespaces	P1094R2	9
Relaxations of constexpr restrictions	P1002R1 P1327R1 P1330R0	No
Feature test macros	P0941R2	4.9 (`__cpp_` macros) 5 (`__has_cpp_attribute`)

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	__cpp_guaranteed_copy_elision >= 201606
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 __cpp_nontype_template_parameter_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 2019-02-07.