C++17 - cppreference.com (original) (raw)

C++17 is a major version that follows the minor version C++14 and introduces new language and library features. The standard was published in December 2017.

The following features were merged into C++17:

• From the File System TS: the filesystem library.
• From the Library fundamentals v1 TS: features, including std::any, std::optional, std::string_view, std::apply, polymorphic allocators, searchers.
• From Library fundamentals v2 TS: std::void_t, std::conjunction, std::disjunction, std::negation, std::not_fn, std::gcd, std::lcm.
• From Parallelism v1 TS: features, including execution policies, std::reduce, std::inclusive_scan, std::exclusive_scan, but removing exception_list.
• From Mathematical special functions IS: mathematical special functions.
• From C11: std::aligned_alloc, std::timespec_get.

Contents

• 1 Obsolete features
  • 1.1 Removed features
  • 1.2 Deprecated features
• 2 New language features
• 3 New headers
• 4 New library features
  • 4.1 Utility types
  • 4.2 Memory management
  • 4.3 Compile-time programming
  • 4.4 Algorithms
  • 4.5 Iterators and containers
  • 4.6 Numerics
  • 4.7 Others
• 5 Defect reports
• 6 Compiler support
  • 6.1 C++17 core language features
  • 6.2 C++17 library features
    * 6.2.1 Notes
  • 6.3 External links

[edit] Obsolete features

[edit] Removed features

• std::auto_ptr,
• deprecated function objects,
• std::random_shuffle,
• std::unexpected,
• the obsolete iostreams aliases,
• trigraphs,
• the register keyword,
• bool increment,
• dynamic exception specification

[edit] Deprecated features

• std::iterator,
• std::raw_storage_iterator,
• std::get_temporary_buffer,
• std::is_literal_type,
• std::result_of,
• all of

[edit] New language features

• u8 character literal
• made noexcept part of type system
• new order of evaluation rules
• lambda capture of *this
• constexpr
  compile-time if constexpr
  constexpr lambda
• Variables
  inline variables
  structured bindings
  initializers for if and switch
  guaranteed copy elision
  temporary materialization
• Templates
  fold-expressions ( ... )
  class template argument deduction tuple t(4, 3, 2.5)
  constant template parameters declared with auto
• Namespaces
  simplified nested namespaces
  using-declaration declaring multiple names
  attribute namespaces don't have to repeat
• new attributes:
  • [[[fallthrough](language/attributes/fallthrough.html "cpp/language/attributes/fallthrough")]]
  • [[[maybe_unused](language/attributes/maybe%5Funused.html "cpp/language/attributes/maybe unused")]]
  • [[[nodiscard](language/attributes/nodiscard.html "cpp/language/attributes/nodiscard")]]
• __has_include

[edit]

• <memory_resource>
• <string_view>

[edit] New library features

[edit] Utility types

• std::tuple:
  • std::apply
  • std::make_from_tuple
  • deduction guides
• std::any
• std::optional
• std::variant
• searchers
• std::as_const
• std::not_fn

[edit] Memory management

• uninitialized memory algorithms
  • std::destroy_at
  • std::destroy
  • std::destroy_n
  • std::uninitialized_move
  • std::uninitialized_value_construct
• weak_from_this
• std::pmr::memory_resource and std::polymorphic_allocator
• std::aligned_alloc
• transparent std::owner_less
• array support for std::shared_ptr
• allocation functions with explicit alignment

[edit] Compile-time programming

• std::byte
• std::conjunction/std::disjunction/std::negation
• type trait variable templates (_xxx__+v)
• std::is_swappable
• std::is_invocable
• std::is_aggregate
• std::has_unique_object_representations

[edit] Algorithms

• std::clamp
• parallel algorithms and execution policies
• std::inclusive_scan
• std::exclusive_scan
• std::gcd
• std::lcm
• std::reduce

[edit] Iterators and containers

• map/set extract and map/set merge
• map/unordered_map try_emplace and insert_or_assign
• contiguous iterators (LegacyContiguousIterator)
• non-member std::size/std::empty/std::data

[edit] Numerics

• mathematical special functions
• 3D std::hypot

[edit] Others

• cache line interface
• std::launder
• std::uncaught_exceptions
• std::to_chars/std::from_chars
• std::atomic::is_always_lock_free
• std::scoped_lock
• std::timespec_get
• rounding functions for std::chrono::duration and std::chrono::time_point

[edit] Defect reports

[edit] Compiler support

[edit] C++17 core language features

| C++17 feature | Paper(s) | GCC | Clang | MSVC | Apple Clang | EDG eccp | Intel C++ | Nvidia HPC C++ (ex PGI)* | Nvidia nvcc | Cray | Embarcadero C++ Builder | IBM Open XL C++ for AIX | | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------ | ---------------- | ----- | ----------------- | ----------- | -------- | --------- | ------------------------- | ----------- | ---- | ----------------------- | ----------------------- | | | DR11: New auto rules for direct-list-initialization | N3922 | 5 | 3.8 | 19.0 (2015)* | Yes | 4.10.1 | 17.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | typename in a template template parameter | N4051 | 5 | 3.5 | 19.0 (2015)* | Yes | 4.10.1 | 17.0 | 17.7 | Yes* | 11.0 | 10.3 | 17.1.0 | | | Removing trigraphs | N4086 | 5 | 3.5 | 16.0* | Yes | 5.0 | | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Nested namespace definition | N4230 | 6 | 3.6 | 19.0 (Update 3)* | Yes | 4.12 | 17.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | static_assert with no message (FTM)* | N3928 | 6 | 2.5 | 19.10* | Yes | 4.12 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Attributes for namespaces and enumerators (FTM)* (FTM)* | N4266 | 4.9 (partial)*6 | 3.6 | 19.0 (2015)* | Yes | 4.11 | 17.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | u8 character literals | N4267 | 6 | 3.6 | 19.0 (2015)* | Yes | 4.11 | 17.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Allow constant evaluation for all constant template arguments (FTM)* | N4268 | 6 | 3.6 | 19.12* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Unary fold expressions and empty parameter packs | P0036R0 | 6 | 3.9 | 19.12* | Yes | 4.14 | 19.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Remove deprecated use of the register keyword | P0001R1 | 7 | 3.8 | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Remove deprecated operator++(bool) | P0002R1 | 7 | 3.8 | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Make exception specifications part of the type system (FTM)* | P0012R1 | 7 | 4 | 19.12* | Yes | 4.14 | 19.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | __has_include in preprocessor conditionals | P0061R1 | 5 | Yes | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | DR11: New specification for inheriting constructors (DR1941 et al) (FTM)* | P0136R1 | 7 | 3.9 | 19.14** | Yes | 6.1 | | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Aggregate classes with base classes (FTM)* | P0017R1 | 7 | 3.9 | 19.14* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Fold Expressions (FTM)* | N4295 | 6 | 3.6 | 19.12* | Yes | 4.14 | 19.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Lambda capture of *this (FTM)* | P0018R3 | 7 | 3.9 | 19.11* | Yes | 4.14 | 19.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Direct-list-initialization of enumerations | P0138R2 | 7 | 3.9 | 19.11* | Yes | 4.14 | 18.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | constexpr lambda expressions (FTM)* | P0170R1 | 7 | 5 | 19.11* | Yes | 4.14 | 19.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Differing begin and end types in range-based for (FTM)* | P0184R0 | 6 | 3.9 | 19.10* | Yes | 4.12 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | [[fallthrough]] attribute | P0188R1 | 7 | 3.9 | 19.10* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | [[nodiscard]] attribute | P0189R1 | 7 | 3.9 | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | [[maybe_unused]] attribute | P0212R1 | 7 | 3.9 | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Hexadecimal floating-point literals (FTM)* | P0245R1 | 3.0 | Yes | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Using attribute namespaces without repetition | P0028R4 | 7 | 3.9 | 19.11* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Dynamic memory allocation for over-aligned data (FTM)* | P0035R4 | 7 | 4 | 19.12* | 10.0.0* | 4.14 | 19.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Constant template parameters with auto type (FTM)* | P0127R2 | 7 | 4 | 19.14* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Guaranteed copy elision (FTM)* | P0135R1 | 7 | 4 | 19.13* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Replacement of class objects containing reference members | P0137R1 | 7 | 6 | 19.14* | Yes | 5.0 | | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Stricter expression evaluation order | P0145R3 | 7 | 4 | 19.14* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Structured Bindings (FTM)* | P0217R3 | 7 | 4 | 19.11* | Yes | 4.14 | 19.0 | 18.1 | 11.0* | 11.0 | 10.3 | 17.1.0 | | | Ignore unknown attributes | P0283R2 | Yes | 3.9 | 19.0 (2015)* | Yes | 4.13 | 18.0 | 17.7 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | constexpr if statements (FTM)* | P0292R2 | 7 | 3.9 | 19.11* | Yes | 4.14 | 19.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Init-statements for if and switch | P0305R1 | 7 | 3.9 | 19.11* | Yes | 4.14 | 18.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Inline variables (FTM)* | P0386R2 | 7 | 3.9 | 19.12* | Yes | 4.14 | 19.0 | 18.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Removing dynamic exception specifications | P0003R5 | 7 | 4 | 19.12* | Yes | 4.14 | 19.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Pack expansions in using-declarations (FTM)* | P0195R2 | 7 | 4 | 19.14* | Yes | 5.0 | 19.0 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | DR98: Matching of template template-arguments excludes compatible templates (FTM)* | P0522R0 | 7 | 4 | 19.12* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | Class template argument deduction (FTM)* | P0091R3 | 7 | 5 | 19.14* | Yes | 5.0 | 19.0.1 | 19.1 | 11.0 | 11.0 | 10.3 | 17.1.0 | | | C++17 feature | Paper(s) | GCC | Clang | MSVC | Apple Clang | EDG eccp | Intel C++ | Nvidia HPC C++ (ex PGI)* | Nvidia nvcc | Cray | Embarcadero C++ Builder | IBM Open XL C++ for AIX | |

[edit] C++17 library features

| C++17 feature | Paper(s) | GCC libstdc++ | Clang libc++ | MSVC STL | Apple Clang* | IBM Open XL C/C++ for AIX* | Intel Parallel STL | Embarcadero C++ Builder* | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------- | ---------------- | ---------------------------- | ------------- | --------------------------- | ------------------ | ------------------------- | | | std::void_t (FTM)* | N3911 | 6.1 | 3.6 | 19.0 (2015)* | Yes | 17.1.0 | N/A | 10.3 | | | std::uncaught_exceptions() (FTM)* | N4259 | 6.1 | 3.7 | 19.0 (2015)* | Yes | 17.1.0 | N/A | 10.3 | | | std::size(), std::empty() and std::data() (FTM)* | N4280 | 6 | 3.6 | 19.0 (2015)* | Yes | 17.1.0 | N/A | 10.3 | | | std::allocator_traits::is_always_equal, noexcept cleanups (FTM)* | N4258 | 6.1 | 3.7 | 19.0 (2015)* | | 17.1.0 | N/A | | | | std::invoke (FTM)* | N4169 | 6.1 | 3.7 | 19.0 (2015)* | Yes | 17.1.0 | N/A | | | | std::map::try_emplace, std::map::insert_or_assign (FTM)* | N4279 | 6.1 | 3.7 | 19.0 (2015)* | Yes | 17.1.0 | N/A | | | | std::unordered_map::try_emplace, std::unordered_map::insert_or_assign (FTM)* | N4279 | 6.1 | 3.7 | 19.0 (2015)* | Yes | 17.1.0 | N/A | | | | Improving std::pair and std::tuple | N4387 | 6.1 | 4 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | 10.3 | | | std::bool_constant (FTM)* | N4389 | 6.1 | 3.7 | 19.0 (2015)* | Yes | 17.1.0 | N/A | 10.3 | | | std::shared_mutex (untimed) (FTM)* | N4508 | 6 | 3.7 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | 10.3 | | | Minimal incomplete type support for std::forward_list, std::list, and std::vector (FTM)* | N4510 | 3.0 | 3.6 | 18.0* | Yes | 17.1.0 | N/A | | | | Type traits variable templates (FTM)* | P0006R0 | 7.1 | 3.8 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | 10.3 | | | Logical operator type traits (FTM)* | P0013R1 | 6.1 | 3.8 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | 10.3 | | | std::as_const (FTM)* | P0007R1 | 7.1 | 3.8 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | | | | Rounding functions for std::chrono::duration and std::chrono::time_point (FTM)* | P0092R1 | 7.1 | 3.8 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | | | | Transparent std::owner_less (std::owner_less) (FTM)* | P0074R0 | 7.1 | 3.8 | 19.0 (Update 2)* | Yes | 17.1.0 | N/A | | | | std::not_fn (FTM)* | P0005R4P0358R1 | 7.1 | 3.9 | 19.12* | Yes | 17.1.0 | N/A | 10.3 | | | Parallel algorithms and execution policies (FTM)* (FTM)* | P0024R2 | 9* | 17(partial)* | 19.14* | | | 18.0* | | | | std::clamp() (FTM)* | P0025R1 | 7 | 3.9 | 19.0 (Update 3)* | 10.0.0* | 17.1.0 | N/A | 10.3 | | | (nothrow-)swappable traits (FTM)* | P0185R1 | 7.1* | 3.9 | 19.0 (Update 3)* | 10.0.0* | 17.1.0 | N/A | 10.3 | | | Polymorphic memory resources (FTM)* | P0220R1 | 9.1 | 16 | 19.13* | 15.0.0* | 17.1.1 | N/A | 10.3 | | | std::apply (FTM)* | P0220R1 | 7.1 | 16 | 19.13* | Yes | 17.1.0 | N/A | | | | Searchers (FTM)* | P0220R1 | 7.1 | 16 | 19.13* | Yes | 17.1.0 | N/A | | | | std::sample (FTM)* | P0220R1 | 7.1 | 16 | 19.13* | Yes | 17.1.0 | N/A | | | | Mathematical special functions (FTM)* | P0226R1 | 7 | | 19.14* | | 17.1.1 | N/A | 10.3 | | | constexpr std::addressof (FTM)* | LWG2296 | 7.1 | Yes | 19.0 (Update 3)* | | 17.1.0 | N/A | | | | constexpr for std::reverse_iterator, std::move_iterator, std::array and range access (FTM)* | P0031R0 | 7.1 | 4 | 19.11* | Yes | 17.1.0 | N/A | | | | constexpr std::atomic<T>::is_always_lock_free (FTM)* | P0152R1 | 7.1 | 3.9 | 19.11* | Yes | 17.1.0 | N/A | | | | std::enable_shared_from_this::weak_from_this (FTM)* | P0033R1 | 7.1 | 3.9 | 19.12* | Yes | 17.1.0 | N/A | | | | 3-argument overload of std::hypot (FTM)* | P0030R1 | 7.1 | 3.9 | 19.14* | Yes | 17.1.0 | N/A | | | | std::byte (FTM)* | P0298R3 | 7 | 5 | 19.11* | Yes | 17.1.1 | N/A | 10.3 | | | std::string_view (FTM)* | N3921P0220R1P0254R2P0403R1 | 7.1 | 4 | 19.10* (partial)*19.11** | 10.0.0* | 17.1.0 | N/A | 10.3 | | | std::any (FTM)* | P0220R1P0032R3 | 7.1 | 4 | 19.10* | 10.0.0* | 17.1.0 | N/A | 10.3 | | | std::optional (FTM)* | P0220R1 | 7.1 | 4 | 19.10* | 10.0.0* | 17.1.0 | N/A | 10.3 | | | Major portion of C11 standard library | P0063R3 | 9.1 | 7 | 19.0 (2015)*(partial)* | 10.0.0* | 17.1.1 | N/A | | | | Splicing Maps and Sets (FTM)* | P0083R3 | 7 | 8 | 19.12* | 10.0.0* | 17.1.1 | N/A | | | | return type of emplace* functions of some containers changed from void to reference | P0084R2 | 7.1 | 4.0 | 19.11* | Yes | 17.1.0 | N/A | | | | std::variant (FTM)* | P0088R3 | 7.1 | 4 | 19.10* | 10.0.0* | 17.1.0 | N/A | 10.3 | | | std::make_from_tuple() (FTM)* | P0209R2 | 7.1 | 3.9 | 19.10* | Yes | 17.1.0 | N/A | 10.3 | | | std::has_unique_object_representations (FTM)* | P0258R2 | 7.1 | 6 | 19.11* | Yes | 17.1.1 | N/A | 10.3 | | | std::gcd() and std::lcm() (FTM)* | P0295R0 | 7 | 4 | 19.11* | Yes | 17.1.0 | N/A | 10.3 | | | CWG issue 1776: Replacement of class objects containing reference members (std::launder) (FTM)* | P0137R1 | 7.1 | 6 | 19.14* | Yes | 17.1.0 | N/A | | | | Extending memory management tools (FTM)* | P0040R3 | 7.1 | 4 | 19.11* | | 17.1.0 | N/A | | | | shared_ptr::weak_type (FTM)* | P0163R0 | 7.1 | 3.9 | 19.10* | Yes | 17.1.0 | N/A | | | | Elementary string conversions: std::to_chars / std::from_chars (FTM)* | P0067R5 | 8*11 | 7*14*20* | 19.14**19.24* | 10.0.0** | 17.1.1* | N/A | 10.3* | | | std::shared_ptr and std::weak_ptr with array support | P0414R2 | 7 | 11 | 19.12* | 12.0.0* | 17.1.1 | N/A | 10.3 | | | Constexpr for all the member functions of std::chrono::duration and std::chrono::time_point (FTM)* | P0505R0 | 7.1 | 4 | 19.11* | Yes | 17.1.1 | N/A | | | | std::shared_ptr<T[]> (FTM)* | P0497R0 | 7.1 | 11 | 19.12* | | 17.1.1 | N/A | | | | constexpr std::char_traits (FTM)* | P0426R1 | 8.1 | 4 | 19.14* | Yes | 17.1.1 | N/A | | | | File system library (std::filesystem) (FTM)* | P0218R1P0219R1 | 8 | 7 | 19.14* | 11.0.0* | 17.1.1 | N/A | 10.3 | | | Hardware interference size (FTM)* | P0154R1 | 12.1 | 15 (partial)*19 | 19.11* | | | N/A | 10.3 | | | std::scoped_lock (FTM)* | P0156R2 | 7 | 5 | 19.11* | Yes | 17.1.1 | N/A | 10.3 | | | std::is_aggregate (FTM)* | LWG2911 | 7 | 5 | 19.15* | Yes | 17.1.1 | N/A | 10.3 | | | std::is_invocable, std::invoke_result (FTM)* | P0604R0 | 7.1 | Yes | 19.11* | Yes | 17.1.1 | N/A | | | | DR17: std::hashstd::filesystem::path | LWG3657 | 11.4 | 17 | 19.32* | | | N/A | | | | C++17 feature | Paper(s) | GCC libstdc++ | Clang libc++ | MSVC STL | Apple Clang* | IBM Open XL C/C++ for AIX* | Intel Parallel STL | Embarcadero C++ Builder* | |

[edit] Notes

• As of 2020-11-20, the latest release of Oracle Developer Studio is 12.6. Its documentation does not mention C++17.
• Cray compiler may have support for some features earlier than 11.0. That version is when it became a derivative of Clang, gaining all of the attendant language feature support of the base compiler. See Cray/HPE document S-2179.

* - hover over a cell marked with the star * to see additional pop-up notes.
DR_nn_ - the number nn after "DR" denotes target C++ revision the Defect Report is applied to, e.g., DR20 → C++20.

[edit] External links