C++20

C++20 is a major version after C++17, featuring major features (concepts, modules, coroutines, and ranges) and other language and library features. The standard was published in December 2020.

New language features

• Feature test macros
• Three-way comparison operator <=> and operator==() = default
• Designated initializers
• Init-statements and initializers in range-for
• char8_t
• New attributes: [[no_unique_address]], [[likely]], [[unlikely]]
• Pack-expansions in lambda init-captures
• Removed the requirement to use typename to disambiguate types in many contexts
• consteval, constinit
• Further relaxed constexpr
• Signed integers are 2's complement
• Bitwise shift operators unified behavior
• aggregate initialization using parentheses
• coroutines
• modules
• Constraints and concepts
• Abbreviated function template
• DR11: array new can deduce array size

New library features

New headers

• <bit>
• <compare>
• <concepts>
• <coroutine>
• <format>
• <numbers>
• <ranges>
• <source_location>
• <span>
• <syncstream>
• <version>

in Thread support library:

• <barrier>
• <latch>
• <semaphore>
• <stop_token>

Library features

• Library feature-test macros
• Formatting library
• Concepts library
• Calendar and Time zone library in <chrono>
• std::source_location
• std::span
• std::endian: big / little / native
• Integral power-of-2 operations and std::bit_cast in <bit>
• Array support for std::make_shared
• std::remove_cvref
• std::to_address
• Floating-point atomics, std::shared_ptr atomics
• Thread-coordination classes: std::barrier, std::latch, and std::counting_semaphore
• std::jthread and thread cancellation classes: std::stop_token, std::stop_source, and std::stop_callback
• std::basic_osyncstream
• std::basic_string and other char8_t uses
• constexpr for <algorithm>, <utility>, <complex>
• string::starts_with / ends_with and string_view::starts_with / ends_with
• std::assume_aligned
• std::bind_front
• std::c8rtomb / std::mbrtoc8
• std::make_obj_using_allocator etc
• std::make_shared_for_overwrite / std::make_unique_for_overwrite
• Heterogeneous lookup in unordered associative containers
• std::pmr::polymorphic_allocator with additional member functions and std::byte as its default template argument
• execution::unseq
• std::midpoint and std::lerp
• std::ssize
• std::is_bounded_array, std::is_unbounded_array
• Ranges
• Uniform container erasure: std::erase / std::erase_if, e.g. std::erase(std::list) or erase_if(std::map) etc
• Mathematical constants in <numbers>

Defect reports

Compiler support

Main Article: C++20 compiler support

C++20 core language features

C++20 library features

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

External links