What are the Key New Features and Enhancements Introduced in C 17?

What are the new features in C 17?

C 17 introduces a range of new features and improvements to the language, including:

• Language Features:

  • Template argument deduction for class templates
  • template to represent values of any non-type template argument type
  • Fixes to non-type template arguments
  • Support for template templates
  • Extended folding and ... expressions
  • auto x{8} as an integer
  • Modernizing using with ... and lists
  • Constexpr lambdas
  • Capturing this in lambdas
  • Attributes such as [[fallthrough]], [[nodiscard]], [[maybe_unused]]
  • Attributes on namespaces and enumerators
  • Using in attributes to avoid repeating attribute namespaces
  • Requiring compilers to ignore non-standard attributes they don't recognize
  • Inline variables
  • Namespace aliases (e.g., namespace A::B)
  • Simple static_assert(expression); without a string
  • Eliminating no throw and replacing it with throw() and noexcept(true)

• Cleaner multi-return and flow control:

  • Structured bindings to simplify multi-return values
  • if (init; condition) and switch (init; condition) for extended if and switch statements
  • Generalizing range-based for loops for sentinels and custom iterators
  • if constexpr for almost-generic code

• Misc:

  • Hexadecimal float point literals
  • Dynamic memory allocation for over-aligned data
  • Guaranteed copy elision
  • Fixed order-of-evaluation for expressions
  • Direct list-initialization of enums
  • Forward progress guarantees (FPGs)
  • Character literals u8'U', u8'T', u8'F', u8'8'
  • noexcept in the type system
  • __has_include to test for header file inclusion errors
  • Arrays of pointer conversion fixes
  • Fixes to inherited constructors and aggregate initialization with inheritance
  • Utility functions for std type punning

• Library Additions:

  • Data types:

    • std::variant for tagged union types
    • std::optional for nullable values
    • std::any for any type of value
    • std::string_view as a reference to a character array or substring
    • std::byte as neither an integer nor a character, but just data

  • Invoke stuff:

    • std::invoke for generic function calling
    • std::apply for unpacking tuples into function calls
    • std::make_from_tuple and std::apply for object construction
    • is_invocable, is_invocable_r, and invoke_result for function invocation functionality
  • File System TS v1: Improved file system operations
  • New algorithms: for_each_n, reduce, transform_reduce, exclusive_scan, inclusive_scan, transform_exclusive_scan, and transform_inclusive_scan
  • Threading: std::shared_mutex, atomic::is_always_lockfree, and scoped_lock
  • Parallelism TS v1: Parallel versions of algorithms and related machinery
  • Library Fundamentals TS v1: Searching algorithms, polymorphic allocator (pmr), sampling
  • Container Improvements: try_emplace and insert_or_assign, splicing for maps and sets, non-const .data() for strings, non-member std::size, std::empty, std::data, minimal incomplete type support in containers, contiguous iterator "concept", constexpr iterators, updated constructors for emplace family of functions
  • Smart pointer changes: Fixes to unique_ptr and tweaks to weak_from_this and shared from this
  • Other std datatype improvements: Construction of std::tuple with curly braces, trivially copyable reference_wrapper

  • Misc:

    • C 17 library is based on C11 instead of C99
    • Reserved std[0-9] for future standard libraries
    • Utility functions like destroy, uninitialized_move, uninitialized_value_construct, and uninitialized_default_construct
    • Special math functions
    • std::clamp()
    • GCD and LCM calculations
    • std::uncaught_exceptions for throwing within destructors
    • std::as_const and std::bool_constant types
    • std::void_t and std::void_t types
    • std::owner_less for smart pointers to sort based on contents
    • Improvements to std::chrono
    • std::conjunction, std::disjunction, std::negation
    • std::not_fn
    • Rules for noexcept within std
    • std::is_contiguous_layout
    • High performance number conversion with std::to_chars and std::from_chars

• Traits:

  • swap, is_aggregate, has_unique_object_representations

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