C++23

Modern "Hello, world" Example

Features

Language

• explicit this object parameter
• if consteval
• multidimensional subscript operator
• static call and subscript operators and static lambdas
• simplifying implicit move
• auto and auto
• new preprocessor directives:
• *#elifdef and #elifndef
• *#warning
• extending the lifetime of some temporaries in range-based for loop
• new standard attribute assume
• class template argument deduction from inherited constructors
• labels at the end of the compound statement
• alias declarations in init-statements
• literal suffixes for size_t and the corresponding signed type:
• extended floating-point types with literals
• optional from nullary lambda expressions
• attributes on lambda expressions
• constexpr changes:
• *non-literal variables, labels, and gotos in constexpr functions
• *allowing static and thread_local variables that are usable in constant expressions in constexpr functions
• *constexpr function does not need its return type and parameter types to be literal type
• *it is now possible to write a constexpr function for which no invocation satisfies the requirements of a core constant expression
• narrowing contextual conversions to bool in static_assert and if constexpr
• trimming whitespaces before line splicing
• make declaration order layout mandated
• delimited escape sequences
• named universal character escapes
• text encoding changes:
• *support for UTF-8 as a portable source file encoding
• *consistent character literal encoding
• *character sets and encodings
• New meaning added to some keywords, such as for this.

  Library

Standard Library Module Support

• standard library modules std and std.compat

  Coroutine Library Support

• synchronous coroutine std::generator for ranges

  General Utilities Support

• result type std::expected
• monadic operations for std::optional and std::expected
• utility function std::to_underlying to get the underlying value of enum
• move-only callable wrapper std::move_only_function
• std::forward_like
• std::invoke_r
• std::bind_back
• std::byteswap
• std::unreachable: a function to mark unreachable code
• made std::tuple compatible with other tuple-like objects
• std::basic_common_reference specialization for std::reference_wrapper yielding reference types
• adding default arguments for std::pair's forwarding constructor

  Compile-time Support

• constexpr support for:
• *std::type_info::operator
• * std::bitset
• * std::unique_ptr
• * for some functions
• * for integral overloads of std::to_chars and std::from_chars
• metaprogramming utilities:
• *type traits std::is_scoped_enum, std::is_implicit_lifetime, std::reference_constructs_from_temporary, and std::reference_converts_from_temporary.
• adding move-only types support for comparison concepts

  Iterators, Ranges, and Algorithm Support

• new range conversion function std::ranges::to
• new constrained ranges algorithm:
• *std::ranges::starts_with
• *std::ranges::ends_with
• *std::ranges::contains
• *std::ranges::contains_subrange
• *std::ranges::find_last and other variants
• *rangified versions of iota, shift_left, and shift_right
• *range fold algorithms
• new std::ranges::range_adaptor_closure, a helper for defining user-defined range adaptor closures
• new range adaptors:
• *std::views::zip and other variants
• *std::views::adjacent and other variants
• *std::views::join_with
• *std::views::slide
• *std::views::chunk
• *std::views::chunk_by
• *std::views::as_rvalue
• *std::views::as_const
• *std::views::repeat
• *std::views::stride
• *std::views::cartesian_product
• *std::views::enumerate
• rectifying constant iterators, sentinels, and ranges, that is, std::ranges::cbegin and other similar utilities returning constant iterators should be fully guaranteed even for shallow-const views
• ranges iterators as inputs to non-ranges algorithms
• relaxing range adaptors to allow for move only types
• making multi-param constructors of some views explicit

  Memory Management Support

• std::out_ptr and std::inout_ptr for C interoperability
• std::allocate_at_least and std::allocator::allocate_at_least
• explicit lifetime management function std::start_lifetime_as for implicit-lifetime types
• disallowing user specialization of std::allocator_traits

  String and Text Processing Support

• new member functions and changes in string types:
• *std::basic_string_view::contains and std::basic_string::contains
• *disabling construction from nullptr for std::basic_string and std::basic_string_view
• *explicit range constructor for std::basic_string_view
• *std::basic_string::resize_and_overwrite
• *rvalue reference overload of std::basic_string::substr for efficient slicing
• formatting ranges, tuples, escaped presentation of characters and strings, std::thread::id, and stacktraces.

  Diagnostic Support

• stacktrace library, header and class std::stacktrace

  I/O Support

• formatted output functions std::print and std::println from new header
• spanstream library from new header
• a support for exclusive mode in std::fstreams

  Containers Support

• multidimensional-span std::mdspan
• constructability and assignability of containers from other compatible ranges
• flat set and flat map container adapters
• non-deduction context for allocators in container deduction guides
• heterogeneous erasure overloads for associative containers
• allowing iterator pair construction in stack and queue
• requiring std::span and std::basic_string_view to be trivially copyable

  C-Compatibility Support

• new header

  Language defect reports

• C++ identifier syntax using Unicode Standard Annex 31
• allowing duplicate attributes
• changing scope of lambda trailing return type
• making overloaded comparison operators less breaking change
• undeprecating volatile compound assignments
• fixing the compatibility and portability of char8_t
• relaxing requirements on wchar_t to match existing practices
• allowing some pointers and references of this or unknown origin in constant expressions
• introduction of immediate-escalating functions promoted to immediate functions
• allowing static_assert in uninstantiated template contexts

  Library defect reports

• changes in ranges library:
• *conditionally borrowed ranges
• *repairing input range adaptors and std::counted_iterator
• *relaxing the constraint on std::ranges::join_view
• *renamed std::ranges::split_view to std::ranges::lazy_split_view and new split_view
• *removed std::default_initializable constraint from concept std::ranges::view
• *view with ownership and new std::ranges::owning_view
• *fixed std::ranges::istream_view
• changes in text formatting library:
• *std::basic_format_string
• *compile-time format string checks
• *reducing binary code size of std::format_to
• *fixing locale handling in chrono formatters
• *improving width estimation and fill character allowances of std::format
• *use of forwarding references in format arguments to allow non-const-formattable types
• fully constexpr std::variant and std::optional
• supporting types derived from std::variant in std::visit

  Removed features and deprecation

• Garbage Collection Support and Pointer Safety. This minimal garbage collection support, was added to C++11 but no compilers have ever supported it so the support was removed in C++23. However, that doesn't mean many GC implementations haven't been used, and continue to be used with C++, such as Boehm GC, and such GC is often implemented in C++, for other languages to use.
• Mixed wide-string literal concatenation.
• Non-encodable wide character literals and multicharacter wide character literals.

• std::aligned_storage and std::aligned_union
• std::numeric_limits::has_denorm

• Use of comma operator in subscript expressions was no longer deprecated but the semantics has been changed to support overloadable n-adic operator.
• C headers