C++20 标准改动汇总

TODO

New language features

• Feature test macros (opens new window)

• 3-way comparison (opens new window) operator and <=>operator==() = default (opens new window)

• designated initializers (opens new window)

• init-statements and initializers in range-for (opens new window)

• char8_t (opens new window)

• New attributes (opens new window): , , [[no_unique_address]]``[[likely]]``[[unlikely]]

• pack-expansions (opens new window) in lambda init-captures (opens new window)

• removed the requirement to use to disambiguate types in many contexts typename

• consteval (opens new window), constinit (opens new window)

• further relaxed constexpr

• signed integers are 2's complement

• aggregate initialization (opens new window) using parentheses

• Coroutines (opens new window)

• Modules (opens new window)

• Constraints and concepts (opens new window)

• Abbreviated function templates (opens new window)

• DR: array new (opens new window) can deduce array size

• New library features

  New headers

  • concepts (opens new window)
  • coroutine (opens new window)
  • compare (opens new window)
  • version (opens new window)
  • source_location (opens new window)
  • format (opens new window)
  • span (opens new window)
  • ranges (opens new window)
  • bit (opens new window)
  • numbers (opens new window)
  • syncstream (opens new window)

  in Thread support library (opens new window):

  • stop_token (opens new window)
  • semaphore (opens new window)
  • latch (opens new window)
  • barrier (opens new window)

  Library features

• Library feature-test macros (opens new window)

• Formatting library (opens new window)

• Calendar (opens new window) and Time Zone (opens new window) library

• source_location (opens new window)

• span (opens new window)

• endian (opens new window)

• array support for make_shared (opens new window)

• remove_cvref (opens new window)

• to_address (opens new window)

• floating-point atomics (opens new window), shared_ptr atomics (opens new window)

• thread-coordination classes: barrier (opens new window), latch (opens new window), and counting_semaphore (opens new window)

• jthread (opens new window) and thread cancellation (opens new window) classes: stop_token (opens new window), stop_source (opens new window), and stop_callback (opens new window)

• basic_osyncstream (opens new window)

• u8string (opens new window) and other char8_t (opens new window) uses

• constexpr for ](https://en.cppreference.com/w/cpp/header/algorithm), [ (opens new window), `` (opens new window)

• string::starts_with (opens new window) / ends_with (opens new window) and string_view::starts_with (opens new window) / ends_with (opens new window)

• assume_aligned (opens new window)

• bind_front (opens new window)

• c8rtomb (opens new window)/mbrtoc8 (opens new window)

• make_obj_using_allocator (opens new window) etc

• make_shared_for_overwrite (opens new window)/make_unique_for_overwrite (opens new window)

• heterogeneous lookup in unordered associative containers

• polymorphic_allocator (opens new window) with additional member functions and byte (opens new window) as its default template argument

• execution::unseq (opens new window)

• midpoint (opens new window) and lerp (opens new window)

• ssize (opens new window)

• is_bounded_array (opens new window), is_unbounded_array (opens new window)

• Ranges (opens new window)

• uniform container erasure: std::erase (opens new window)/std::erase_if (opens new window), e.g. std::erase(std::list) (opens new window) or erase_if(std::map) (opens new window) etc

• Mathematical constants (opens new window) in `` (opens new window)