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.
- C 98
- C 11
- C 14
- C 17
- C 2a
- Technical Specifications
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 | P0306R4P1042R1 | 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 | P0734R0P0857R0P1084R2P1141R2 | 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<=>) | P0515R3P0905R1P1120R0 | 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 | P0542R5P1289R1 | 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 | P1002R1P1327R1P1330R0 | 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 | P0091R3P0512R0 | 78 | __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:
- GCC 4.3 C 0x Status
- GCC 4.4 C 0x Status
- GCC 4.5 C 0x Status
- GCC 4.6 C 0x Status
- GCC 4.7 C 11 Status
- GCC 4.8 C 11 Status
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.
Copyright (C) Free Software Foundation, Inc. Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.
These pages are maintained by the GCC team. Last modified 2019-02-07.
参考地址：https://gcc.gnu.org/projects/cxx-status.html
