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C++20 is a version of the ISO/IEC 14882 standard for the C++ programming language. C++20 replaced the prior version of the C++ standard, called C++17, and was later replaced by C++23.cite-ref-1[1] The standard was technically finalizedcite-ref-2[2] by WG21 at the meeting in Prague in February 2020,cite-ref-3[3] had its final draft version announced in March 2020,cite-ref-n4859-4-0[4] was approved on 4 September 2020,cite-ref-5[5]cite-ref-6[6] and published in December 2020.cite-ref-7[7]

• Features

• Language

• Library

• New and changed keywords

• Removed and deprecated

• Published as Technical Specifications

• Deferred to a later standard

• Compiler support

• History

• References

• External links

C++20 adds more new major features than C++14 or C++17.cite-ref-8[8] Changes that have been accepted into C++20 include:cite-ref-9[9]

• concepts,cite-ref-10[10] with terse syntaxcite-ref-11[11]

• modulescite-ref-12[12]

• designated initializerscite-ref-13[13] (based on the C99 feature, and common g++ extension)

• [=, this] as a lambda capturecite-ref-14[14]

• template parameter lists on lambdascite-ref-15[15]

• three-way comparison using the "spaceship operator", operator <=>

• initialization of an additional variable within a range-based for statementcite-ref-16[16]

• lambdas in unevaluated contextscite-ref-0-17-0[17]cite-ref-18[18]

• default constructible and assignable stateless lambdascite-ref-0-17-1[17]cite-ref-19[19]

• allow pack expansions in lambda init-capturecite-ref-0-17-2[17]cite-ref-20[20]

• class types in non-type template parameters, also allowing string literals as template parameterscite-ref-21[21]

• removing the need for typename in certain circumstancescite-ref-22[22]

• new standard attributes [[no_unique_address]],cite-ref-23[23] [[likely]] and [[unlikely]]cite-ref-24[24]

• conditional explicit, allowing the explicit modifier to be contingent on a Boolean expressioncite-ref-25[25]

• expanded constexpr: virtual functions,cite-ref-26[26] union,cite-ref-27[27] try and catch,cite-ref-28[28] dynamic_cast and typeid,cite-ref-29[29] std::pointer_traitscite-ref-30[30]

• immediate functions using the new consteval keywordcite-ref-31[31]

• signed integers are now defined to be represented using two's complement (signed integer overflow remains undefined behavior)cite-ref-32[32]

• a revised memory modelcite-ref-33[33]

• various improvements to structured bindings (interaction with lambda captures, static and thread_local storage duration)cite-ref-34[34]cite-ref-35[35]

• coroutinescite-ref-36[36]

• using on scoped enumscite-ref-p1099r5-using-enum-37-0[37]

• constinit keywordcite-ref-constinit-38-0[38]

• ranges (The One Ranges Proposal)cite-ref-39[39]

• std::make_shared and std::allocate_shared for arrayscite-ref-40[40]

• atomic smart pointers (such as std::atomic<shared_ptr<T>> and std::atomic<weak_ptr<T>>)cite-ref-41[41]

• std::to_address to convert a pointer to a raw pointercite-ref-42[42]

• calendar and time-zone additions to <chrono>cite-ref-43[43]

• std::span, providing a view to a contiguous array (analogous to std::string_view but span can mutate the referenced sequence)cite-ref-44[44]

• std::erase and std::erase_if, simplifying element erasure for most standard containerscite-ref-45[45]

• <version> headercite-ref-46[46]

• std::bit_cast<> for type casting of object representations, with less verbosity than memcpy() and more ability to exploit compiler internalscite-ref-47[47]

• feature test macroscite-ref-48[48]

• various constexpr library bitscite-ref-49[49]

• smart pointer creation with default initializationcite-ref-50[50]

• contains-method for associative containerscite-ref-51[51]

• prefix and suffix checking for stringscite-ref-52[52]

• bit operations, such as leading/trailing zero/one count,cite-ref-p0553r4-bit-operations-53-0[53] and log2 operationscite-ref-54[54]cite-ref-55[55]cite-ref-56[56]

• std::bind_frontcite-ref-57[57]

• std::atomic::wait, std::atomic::notify_one, andstd::atomic::notify_all were added, giving the standard library futex-like capabilitiescite-ref-58[58]

Eight new keywords added (plus the new "spaceship operator", operator <=>), such as concept, constinit,cite-ref-constinit-38-1[38] consteval, requires (plus changed meaning for export), and char8_t (for UTF-8 support); of the eight new these three co_await, co_return, co_yield, are only for the new coroutine supportcite-ref-59[59] (additionally six previously existing keywords have changed or new meaning added); explicit can take an expression since C++20.cite-ref-60[60] Most of the uses of the volatile keyword have been deprecated.cite-ref-volatile-61-0[61]

In addition to keywords, there are identifiers with special meaning (effectively keywords in certain contexts), including new import and module.

New attributes in C++20: [[likely]], [[unlikely]], and [[no_unique_address]]cite-ref-62[62]

Removed features:cite-ref-63[63]

• The C-derived headers <ccomplex>, <ciso646>, <cstdalign>, <cstdbool> and <ctgmath> were removed, as they serve no purpose in C++. (The corresponding <*.h> headers remain, for compatibility with C.)

• The use of throw clauses was removed.

• Some previously deprecated library features were removed, including std::uncaught_exception, std::raw_storage_iterator, std::is_literal_type, std::is_literal_type_v, std::result_of and std::result_of_t.

Deprecated features:

• Use of comma operator in subscript expressions has been deprecatedcite-ref-open-std-org-64-0[64]

• (most of) volatile has been deprecatedcite-ref-volatile-61-1[61]

• Parallelism TS v2cite-ref-65[65] (including task blocks)

• Reflection TS v1cite-ref-66[66]

• Networking TS v1cite-ref-67[67]

• Contracts – a new study group (SG21) has been formed to work on a new proposalcite-ref-68[68]

• Reflectioncite-ref-69[69]cite-ref-70[70]

• Metaclassescite-ref-71[71]

• Executorscite-ref-72[72]

• Networking extensions,cite-ref-73[73]cite-ref-74[74] including async, basic I/O services, timers, buffers and buffer-oriented streams, sockets, and Internet protocols (blocked by executors)

• Propertiescite-ref-75[75]

• Extended futurescite-ref-76[76]

Full supportcite-ref-77[77]

• Visual Studio 2019 supports all C++20 features through its /std:c++latest option, as of version 16.10.0.cite-ref-78[78] An option /std:c++20 to enable C++20 mode is added in version 16.11.0.cite-ref-79[79]cite-ref-80[80]

Microsoft's compiler supports not only Windows but also Linux, Android, and iOS. However, for Linux development, it requires the "Visual C++ for Linux Development" extension. cite-ref-81[81]

• Clang has partial C++20 support that can be enabled with the option -std=c++20 (version 10 and later) or -std=c++2a (version 9 and earlier).cite-ref-82[82]

• EDG started implementing C++20 features in version 5.0 and as of version 6.1 supports most C++20 core language features.cite-ref-83[83]

• GCC added partial, experimental C++20 support in 2017cite-ref-84[84] in version 8 through the option -std=c++2a. Like Clang, GCC replaced this option with -std=c++20 in version 10. It also has an option to enable GNU extensions in addition to the experimental C++20 support, -std=gnu++20.cite-ref-85[85]

Changes applied to the C++20 working draft in July 2017 (Toronto) include:cite-ref-86[86]

• concepts (what made it into the standard is a cut-down version; also described as "Concepts Lite"cite-ref-87[87])

• designated initializers

• [=, this] as a lambda capture

• template parameter lists on lambdas

• std::make_shared and std::allocate_shared for arrays

Changes applied to the C++20 working draft in the fall meeting in November 2017 (Albuquerque) include:cite-ref-88[88]cite-ref-89[89]

• three-way comparison using the "spaceship operator", operator <=>

• initialization of an additional variable within a range-based for statement

• lambdas in unevaluated contexts

• default constructible and assignable stateless lambdas

• allow pack expansions in lambda init-capture

• string literals as template parameters

• atomic smart pointers (such as std::atomic<shared_ptr<T>> and std::atomic<weak_ptr<T>>)

• std::to_address to convert a pointer to a raw pointer

Changes applied to the C++20 working draft in March 2018 (Jacksonville) include:cite-ref-90[90]

• removing the need for typename in certain circumstances

• new standard attributes [[no_unique_address]], [[likely]] and [[unlikely]]

• calendar and time-zone additions to <chrono>

• std::span, providing a view to a contiguous array (analogous to std::string_view but span can mutate the referenced sequence)

• <version> header

Changes applied to the C++20 working draft in the summer meeting in June 2018 (Rapperswil) include:cite-ref-91[91]

• contracts (later deferred to a later standard)cite-ref-92[92]

• feature test macros

• bit-casting of object representations, with less verbosity than memcpy() and more ability to exploit compiler internals

• conditional explicit, allowing the explicit modifier to be contingent on a Boolean expression

• constexpr virtual functions

Changes applied to the C++20 working draft in the fall meeting in November 2018 (San Diego) include:cite-ref-93[93]

• ranges (The One Ranges Proposal)

• concept terse syntax

• constexpr union, try and catch, dynamic_cast, typeid and std::pointer_traits.

• various constexpr library bits

• immediate functions using the new consteval keyword

• signed integers are now defined to be represented using two's complement (signed integer overflow remains undefined behavior)

• refinements of the contracts facility (access control in contract conditions)cite-ref-94[94] (see list of features deferred to a later standard)

• a revised memory model

• smart pointer creation with default initialization

Changes applied to the C++20 working draft in the winter meeting in February 2019 (Kona) include:cite-ref-95[95]cite-ref-96[96]cite-ref-97[97]

• coroutines

• modules

• various improvements to structured bindings (interaction with lambda captures, static and thread_local storage duration)

Changes applied to the C++20 working draft in the summer meeting in July 2019 (Cologne) include:cite-ref-98[98]cite-ref-99[99]cite-ref-100[100]cite-ref-101[101]

• contracts were removed (see list of features deferred to a later standard)cite-ref-102[102]

• use of comma operator in subscript expressions has been deprecatedcite-ref-open-std-org-64-1[64]

• constexpr additions (trivial default initialization,cite-ref-103[103] unevaluated inline-assemblycite-ref-104[104])

• using scoped enumscite-ref-p1099r5-using-enum-37-1[37]

• various changes to the spaceship operatorcite-ref-105[105]cite-ref-106[106]

• DR: minor changes to modulescite-ref-107[107]

• constinit keyword

• changes to concepts (removal of -> Type return-type-requirementscite-ref-108[108])

• (most of) volatile has been deprecatedcite-ref-volatile-61-2[61]

• DR: [[nodiscard]] effects on constructorscite-ref-109[109]

• The new standard library concepts will not use PascalCase (rather standard_case, as the rest of the standard library)cite-ref-110[110]

• text formatting (std::format, cite-ref-111[111]cite-ref-112[112] chrono integration,cite-ref-113[113] corner case fixescite-ref-114[114])

• bit operationscite-ref-p0553r4-bit-operations-53-1[53]

• constexpr INVOKEcite-ref-115[115]

• math constantscite-ref-116[116]

• consistency additions to atomics (std::atomic_ref<T>,cite-ref-117[117] std::atomic<std::shared_ptr<T>>cite-ref-118[118])

• add the <=> operator to the standard librarycite-ref-119[119]

• header units for the standard librarycite-ref-120[120]

• synchronization facilitiescite-ref-121[121] (merged from: Efficient atomic waiting and semaphores,cite-ref-122[122] latches and barriers,cite-ref-123[123] Improving atomic_flag,cite-ref-124[124] Don't Make C++ Unimplementable On Small CPUscite-ref-125[125])

• std::source_locationcite-ref-126[126]

• constexpr containers (std::string,cite-ref-127[127] std::vectorcite-ref-128[128])

• std::stop_token and joining thread (std::jthread)cite-ref-129[129]

Changes applied during the NB comment resolution in the fall meeting in November 2019 (Belfast) include:cite-ref-130[130]cite-ref-131[131]cite-ref-132[132]cite-ref-133[133]

• Class Types in Non-Type Template Parameters (NTTP): The restriction of no user-defined operator== allowed has been removed as the meaning of template argument equality has been divorced from operator==.cite-ref-134[134] This allows also for array members in class-type NTTP.

• Floating-point types,cite-ref-135[135] pointers and references and unions and union-like classes (class types containing anonymous unions) are now allowed as NTTP.

• Function identity now also includes trailing requires-clauses (P1971)

• Constrained non-template functions have been removed

• <compare> is now available in freestanding implementationscite-ref-136[136]

• std::spans typedef was changed from index_type to size_type to be consistent with the rest of the standard librarycite-ref-137[137]

• Concept traits have been renamed to follow the renaming of the concepts as a result from the Cologne meeting

• Several fixes and additions to ranges (P1456R1: Move-only views,cite-ref-138[138] P1391R4: Range constructor for std::string_view (constructor from iterator-pair of characters),cite-ref-139[139] P1394R4: Range constructor for std::span<ref>,cite-ref-140[140] P1870R1: forwarding-range<T> is too subtlecite-ref-141[141])

• Initialization for std::atomic<T> has been changed to make it work with default and list initialization,cite-ref-142[142] std::latch and std::barrier can now report the maximum number of threads that the implementation supports through the new member function max()

• std::weak_equality and std::strong_equality have been removed as they are not used anymore

• Algorithms in <numeric> have been made constexpr

• Missing feature-test macros for new or changed features of C++20 have been addedcite-ref-143[143]

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cite-note-n4859-44. ↑ "N4859 Editors' Report -- Programming Languages -- C++". Archived from the original on 2022-12-09. Retrieved 2023-09-22.

cite-note-55. ↑ "Current Status". isocpp.org. Archived from the original on 8 September 2020. Retrieved 7 September 2020.

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cite-note-1515. ↑ "Familiar template syntax for generic lambdas". Archived from the original on 2018-11-21. Retrieved 2017-07-16.

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cite-note-2222. ↑ citerefnina-rannsdaveed-vandevoordeNina Ranns; Daveed Vandevoorde. "Down with typename!". Archived from the original on 2018-04-22. Retrieved 2019-05-18.

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cite-note-3333. ↑ "P0668R4: Revising the C++ memory model". Archived from the original on 2018-11-11. Retrieved 2018-11-11.

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cite-note-4646. ↑ citerefalan-talbotAlan Talbot. "<version>". Archived from the original on 2019-05-18. Retrieved 2019-05-18.

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cite-note-5151. ↑ citerefmikhail-maltsevMikhail Maltsev. "P0458R2: Checking for Existence of an Element in Associative Containers". Archived from the original on 2022-01-16. Retrieved 2022-01-02.

cite-note-5252. ↑ citerefmikhail-maltsevMikhail Maltsev. "P0457R2: String Prefix and Suffix Checking". Archived from the original on 2022-05-18. Retrieved 2025-06-22.

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cite-note-volatile-6161. ↑ "P1152R4: Deprecating volatile". www.open-std.org. 2019-07-20. Archived from the original on 2019-06-23. Retrieved 2019-07-20.

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cite-note-6868. ↑ citerefsutter2019Sutter, Herb (2019-07-20). "Trip report: Summer ISO C++ standards meeting (Cologne)". Sutter's Mill. Archived from the original on 2020-04-17. Retrieved 2019-07-21.

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• Link to purchase ISO/IEC 14882:2020 from the ISO online store.

• N4860, the final draft version of the standard.

• JTC1/SC22/WG21 – the ISO/IEC C++ Standard Working Group (a.k.a. the C++ Standards Committee)

• Ranges (range-v3) GitHub repository, by Eric Niebler