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  • C++ Standards Support in GCC

    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.

    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 FeatureProposalAvailable 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 FeatureProposalAvailable 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
    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 SpecificationDocumentAvailable in GCC?Compiler OptionSD-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 FeatureProposalAvailable 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 FeatureProposalAvailable 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 FeatureProposalAvailable 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.

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  • 原文地址:https://www.cnblogs.com/xuyaowen/p/gcc-cxx-support.html
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