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As of 2018, C++17 is the name for the most recent revision of the ISO/IEC 14882 standard for the C++ programming language.

Contents

HistoryEdit

Before the C++ Standards Committee fixed a 3-year release cycle, C++17's release date was uncertain. In that time period, the C++17 revision was also called C++1z, following C++0x or C++1x for C++11 and C++1y for C++14. The C++17 specification reached the Draft International Standard (DIS) stage in March 2017.[1][2] This DIS was unanimously approved, with only editorial comments,[3] and the final standard was published in December 2017.[4] Few changes were made to the C++ Standard Template Library, although some algorithms in the <algorithm> header were given support for explicit parallelization and some syntactic enhancements were made.

Next standardEdit

Removed featuresEdit

This revision of C++ not only added new features but also removed a few.

New featuresEdit

C++17 introduces many new features. The following lists may not be complete.

LanguageEdit

  • Making the text message for static_assert optional[12]
  • Allow typename (as an alternative to class) in a template template parameter[13]
  • Nested namespace definitions, e.g., namespace X::Y { … } instead of namespace X { namespace Y { … }}[10][15]
  • New standard attributes [[fallthrough]], [[maybe_unused]] and [[nodiscard]][18]
  • UTF-8 (u8) character literals[16][19] (UTF-8 string literals have existed since C++11; C++17 adds the corresponding character literals for consistency, though as they are restricted to a single byte they can only store ASCII)
  • Constant evaluation for all non-type template arguments[16][22]
  • Fold expressions, for variadic templates[16][23]
  • A compile-time static if with the form if constexpr(expression)[24]
  • Structured binding declarations, allowing auto [a, b] = getTwoReturnValues();[25]
  • Initializers in if and switch statements[26]
  • copy-initialization and direct-initialization of objects of type T from prvalue expressions of type T (ignoring top-level cv-qualifiers) shall result in no copy or move constructors from the prvalue expression. See copy elision for more information.
  • Some extensions on over-aligned memory allocation[27]
  • Template deduction of constructors, allowing std::pair(5.0, false) instead of std::pair<double, bool>(5.0, false)
  • __has_include, allowing the availability of a header to be checked by preprocessor directives[28]
  • The keyword register is now reserved and unused (formerly deprecated)[29]
  • Value of __cplusplus changed to 201703L[30]

LibraryEdit

  • Most of Library Fundamentals TS I, including:[31][32]
    • std::string_view, a read-only non-owning reference to a character sequence or string-slice[33]
    • std::optional, for representing optional objects, a data type that may not be always be returned by a given algorithm with support for non-return
    • std::any, for holding single values of any type
  • std::byte, allowing char to be replaced for data types intending to model a byte of data as a byte rather than a character[43]
  • Logical operator traits: std::conjunction, std::disjunction and std::negation[44]

Compiler supportEdit

  • GCC 8 has complete (but experimental)[clarification needed] support for C++17.[45][46]
  • Clang 5 and later implement all the features of C++17.[47]
  • Visual Studio 2017 15.7 (MSVC 19.14) supports almost all of C++17.[48][49]

See alsoEdit

ReferencesEdit

  1. ^ "N4661 Editors' Report -- Programming Languages -- C++". 21 March 2017. Retrieved 2017-03-21.
  2. ^ "ISO/IEC DIS 14882: Programming Languages — C++" (PDF). Archived from the original (PDF) on 2017-03-25.
  3. ^ Herb Sutter. "C++17 is formally approved".
  4. ^ "ISO/IEC 14882:2017".
  5. ^ https://herbsutter.com/2016/06/30/trip-report-summer-iso-c-standards-meeting-oulu/ "the next standard after C++17 will be C++20"
  6. ^ "Current Status : Standard C++".
  7. ^ "Trip Report: C++ Standards Meeting in Toronto, July 2017". 2 August 2017. Retrieved 11 January 2018.
  8. ^ "N3981: Removing trigraphs??! (Richard Smith)". 2014-05-06.
  9. ^ IBM comment on preparing for a Trigraph-adverse future in C++17, IBM paper N4210, 2014-10-10. Authors: Michael Wong, Hubert Tong, Rajan Bhakta, Derek Inglis
  10. ^ a b c "Updates to my trip report".
  11. ^ "N4190: Removing auto_ptr, random_shuffle(), And Old <functional> Stuff (Stephan T. Lavavej)".
  12. ^ "N3928: Extending static_assert, v2 (Walter E. Brown)" (PDF).
  13. ^ "N4051: Allow typename in a template template parameter (Richard Smith)".
  14. ^ "N3922: New Rules for auto deduction from braced-init-list (James Dennett)".
  15. ^ "N4230: Nested namespace definition (Robert Kawulak, Andrew Tomazos)".
  16. ^ a b c d e "New core language papers adopted for C++17".
  17. ^ "N4266: Attributes for namespaces and enumerators (Richard Smith)".
  18. ^ "N4640: Working Draft, Standard for Programming Language C++" (PDF). pp. 193–195.
  19. ^ "N4267: Adding u8 character literals (Richard Smith)".
  20. ^ Thomas Köppe. "Hexadecimal floating literals for C++".
  21. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §5.13.4.
  22. ^ "N4268: Allow constant evaluation for all non-type template arguments (Richard Smith)".
  23. ^ "N4295: Folding expressions (Andrew Sutton, Richard Smith)".
  24. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §9.4.1.
  25. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §11.5.
  26. ^ "Selection statements with initializer".
  27. ^ "Dynamic memory allocation for over-aligned data".
  28. ^ "N4640: Working Draft, Standard for Programming Language C++" (PDF). pp. 431–433.
  29. ^ "C++ Keywords: register".
  30. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §19.8.
  31. ^ "Adopt Library Fundamentals V1 TS Components for C++17 (R1)".
  32. ^ "Current Status".
  33. ^ "std::basic_string_view - cppreference.com". en.cppreference.com. Retrieved 2016-06-23.
  34. ^ "N4259: Wording for std::uncaught_exceptions (Herb Sutter)" (PDF).
  35. ^ "N4279: Improved insertion interface for unique-key maps (Thomas Köppe)".
  36. ^ a b c "New standard library papers adopted for C++17".
  37. ^ "N4280: Non-member size() and more (Riccardo Marcangelo)" (PDF).
  38. ^ "N4284: Contiguous Iterators (Jens Maurer)".
  39. ^ "Filesystem Library Proposal (Beman Dawes)".
  40. ^ "The Parallelism TS Should be Standardized".
  41. ^ "Mathematical Special Functions for C++17, v5" (PDF).
  42. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §23.7.
  43. ^ "A byte type definition" (PDF).
  44. ^ "N4659: Working Draft, Standard for Programming Language C++" (PDF). §23.15.8.
  45. ^ "C++ Standards Support in GCC - GNU Project - Free Software Foundation (FSF)". gcc.gnu.org.
  46. ^ "Chapter 1. Status". gcc.gnu.org.
  47. ^ "Clang - C++17, C++14, C++11 and C++98 Status". clang.llvm.org.
  48. ^ corob-msft. "Visual C++ Language Conformance". docs.microsoft.com.
  49. ^ "Announcing: MSVC Conforms to the C++ Standard".