C++ Standards Support in GCC

Warning

The page was automatically converted by pandoc tool!

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++20

• C++23

• Technical Specifications

For information about the status of C++ defect reports, please see this page.

For information about the status of the library implementation, please see the Implementation Status section of the Libstdc++ manual.

C++23 Support in GCC

GCC has experimental support for the next revision of the C++ standard, which is expected to be published in 2023.

C++23 features are available since GCC 11. To enable C++23 support, add the command-line parameter -std=c++2b to your g++ command line. Or, to enable GNU extensions in addition to C++23 features, add -std=gnu++2b.

Important: Because the ISO C++23 standard is still evolving, GCC’s support is experimental. No attempt will be made to maintain backward compatibility with implementations of C++23 features that do not reflect the final standard.

C++23 Language Features

Language Feature	Proposal	Available in GCC?	SD-6 Feature Test
Literal Suffix for (signed) size_t	P0330R8	11	__cpp_size_t_suffix >= 202006L
Make () more optional for lambdas	P1102R2	11
DR: Declarations and where to find them	P1787R6	No
if consteval	P1938R3	12	__cpp_if_consteval >= 202106L
C++ Identifier Syntax using Unicode Standard Annex 31	P1949R7	12
Allow Duplicate Attributes	P2156R1	11
Narrowing contextual conversions to bool	P1401R5	9
Trimming whitespaces before line splicing	P2223R2	Yes
Mixed string literal concatenation	P2201R1	Yes
Make declaration order layout mandated	P1847R4	Yes
Removing Garbage Collection Support	P2186R2	12
Simpler implicit move	P2266R3	13	__cpp_implicit_move >= 202207L
Deducing this	P0847R7	No	__cpp_explicit_this_parameter >= 202110L
	CWG2586
Change scope of lambda trailing-return-type	P2036R3	No
	P2579R0
Multidimensional subscript operator	P2128R6	12	__cpp_multidimensional_subscript >= 202110L
	CWG2507	13
Non-literal variables (and labels and gotos) in constexpr functions	P2242R3	12	__cpp_constexpr >= 202110L
Character encoding of diagnostic text	P2246R1	No
Character sets and encodings	P2314R4	No
Consistent character literal encoding	P2316R2	Yes
Add support for preprocessing directives elifdef and elifndef	P2334R1	12
Extend init-statement to allow alias-declaration	P2360R0	12
auto(x): decay-copy in the language	P0849R8	12
Labels at the end of compound statements	P2324R1	13
CWG 2397: auto specifier for pointers and references to arrays	CWG2397	12
CWG 2481: Cv-qualification of temporary to which a reference is bound	CWG2481	Yes
Attributes on lambda-expressions	P2173R1	9
A type trait to detect reference binding to temporary	P2255R2	13
The Equality Operator You Are Looking For	P2468R2	No
De-deprecating volatile compound operations	P2327R1	13
Support for #warning	P2437R1	Yes (extension) 13 (P2437R1)
Remove non-encodable wide character literals and multicharacter wide character literals	P2362R3	13
Delimited escape sequences	P2290R3	13
Named universal character escapes	P2071R2	13	__cpp_named_character_escapes >= 202207L
Relaxing some constexpr restrictions	P2448R2	No	__cpp_constexpr >= 202207L
Using unknown references in constant expressions	P2280R4	No
static operator()	P1169R4	13	__cpp_static_call_operator >= 202207L
Extended floating-point types and standard names	P1467R9	No
Class template argument deduction from inherited constructors	P2582R1	No
Portable assumptions	P1774R8	13
Support for UTF-8 as a portable source file encoding	P2295R6	13
char8_t Compatibility and Portability Fix	P2513R3	13	__cpp_char8_t >= 202207L
Relax requirements on wchar_t to match existing practices	P2460R2	Yes
Explicit lifetime management	P2590R2	No

C++20 Support in GCC

GCC has experimental support for the latest revision of the C++ standard, which was published in 2020.

C++20 features are available since GCC 8. To enable C++20 support, add the command-line parameter -std=c++20 (use -std=c++2a in GCC 9 and earlier) to your g++ command line. Or, to enable GNU extensions in addition to C++20 features, add -std=gnu++20.

Important: Because the ISO C++20 standard is very recent, GCC’s support is experimental.

C++20 Language Features

The following table lists new language features that have been accepted into the C++20 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) 10 (partial, no placemarker token handling changes) 12
Designated initializers	P0329R4	8	__cpp_designated_initializers >= 201707
Familiar template syntax for generic lambdas	P0428R2	8	__cpp_generic_lambdas >= 201707
List deduction of vector	P0702R1	8
Concepts	P0734R0	10	__cpp_concepts >= 201907
	P0857R0
	P1084R2
	P1141R2
	P0848R3		__cpp_concepts >= 202002
	P1616R1		__cpp_concepts >= 201907
	P1452R2
	P1972R0
	P1980R0
	P2092R0
	P2103R0
	P2113R0	10.2 (no reversed operator handling)
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)	__cpp_constexpr_in_decltype >= 201711
Consistent comparison (operator<=>)	P0515R3	10	__cpp_impl_three_way_comparison >= 201711
	P0905R1
	P1120R0
	P1185R2
	P1186R3	11
	P1630R1	10
	P1946R0
	P1959R0
	P2002R1	10.2
	P2085R0
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	__cpp_init_captures >= 201803
	P2095R0	10
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
Inconsistencies with non-type template parameters	P1907R1	10 (no floating point, union, or subobject template args) 11 (complete)	__cpp_nontype_template_args >= 201911
Atomic Compare-and-Exchange with Padding Bits	P0528R3	11 (compiler side only) 13 (full)
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
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	10 (no consteval virtual) 11 (full)	__cpp_consteval >= 201811
	P1937R2	10
std::is_constant_evaluated	P0595R2	9
Nested inline namespaces	P1094R2	9
Relaxations of constexpr restrictions	P1002R1	9
	P1327R1	10
	P1330R0	9	__cpp_constexpr >= 202002
	P1331R2	10	__cpp_constexpr >= 201907
	P1668R1	10
	P0784R7	10	__cpp_constexpr_dynamic_alloc >= 201907
Feature test macros	P0941R2	4.9 (__cpp_ macros) 5 (__has_cpp_attribute)
Modules	P1103R3	11 (requires -fmodules-ts) (No Private Module Fragment, Parser-level Global Module Entity Merging, Global Module Implications of extern "C/C++", or Partition-specific Definition Visibility)	__cpp_modules >= 201810L (Date of p1103r3)
	P1766R1	No
	P1811R0	11
	P1703R1 (superceded by p1857)	11
	P1874R1	11
	P1979R0	11
	P1779R3	11
	P1857R3	11
	P2115R0	11
	P1815R2	No
Coroutines	P0912R5 as applied to n4861	10 (requires -fcoroutines)	__cpp_impl_coroutine >= 201902
Parenthesized initialization of aggregates	P0960R3	10	__cpp_aggregate_paren_init >= 201902
	P1975R0	11
DR: array size deduction in new-expression	P1009R2	11
DR: Converting from T* to bool should be considered narrowing	P1957R2	10 (C++20 mode only), 11 (all modes)
Stronger Unicode requirements	P1041R4 P1139R2	10
Structured binding extensions	P1091R3 P1381R1	10 8
Deprecate a[b,c]	P1161R3	10
Deprecating some uses of volatile	P1152R4	10
[[nodiscard("with reason")]]	P1301R4	10
using enum	P1099R5	11
Class template argument deduction for aggregates	P1816R0	10	__cpp_deduction_guides >= 201907L
	P2082R1	11
Class template argument deduction for alias templates	P1814R0	10
Permit conversions to arrays of unknown bound	P0388R4	10
constinit	P1143R2	10	__cpp_constinit >= 201907
Layout-compatibility and Pointer-interconvertibility Traits	P0466R5	12	(in library)
DR: Checking for abstract class types	P0929R2	11
DR: More implicit moves (merge P0527R1 and P1155R3)	P1825R0	11 (C++20 mode)
DR: Pseudo-destructors end object lifetimes	P0593R6	11

C++17 Support in GCC

GCC has almost full support for the previous revision of the C++ standard, which was published in 2017. Some library features are missing or incomplete, as described in the library documentation.

C++17 features are available since GCC 5. This mode is the default in GCC 11; it can be explicitly selected with the -std=c++17 command-line flag, or -std=gnu++17 to enable GNU extensions as well.

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	10	-fcoroutines	__cpp_impl_coroutine >= 201902L
Modules	N4720	11	-fmodules-ts	__cpp_modules >= 201810L

C++14 Support in GCC

GCC has full support for the of the 2014 C++ standard.

This mode is the default in GCC 6.1 up until GCC 10 (including); 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 2022-10-21.