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C++20

From cppreference.com
< cpp

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.

This section is incomplete

Contents

[edit] New language features

[edit] New library features

[edit] New headers

in Thread support library:

[edit] Library features

[edit] Defect reports

Defect Reports fixed in C++20 (158 core, 345 library)

[edit] Compiler support

Main Article: C++20 compiler support

[edit] C++20 core language features

C++20 feature

  		Paper(s)

 
GCC
Clang
MSVC
Apple Clang
EDG eccp
Intel C++
Nvidia HPC C++ (ex PGI)*
Nvidia nvcc
Cray
Allow Lambda capture [=, this] P0409R2 8 6 19.22* 10.0.0* 5.1 2021.1 20.7 12.0 11.0
__VA_OPT__ P0306R4
P1042R1 		8 (partial)*
10 (partial)*
12 		9 19.25* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Designated initializers  (FTM)* P0329R4 4.7 (partial)*
8 		3.0 (partial)*
10 		19.21* 12.0.0* 5.1 2021.1 20.7 12.0 11.0
template-parameter-list for generic lambdas  (FTM)* P0428R2 8 9 19.22* 11.0.0* 5.1 2021.1 20.7 12.0 11.0
Default member initializers for bit-fields P0683R1 8 6 19.25* 10.0.0* 5.1 2021.1 20.7 12.0 11.0
Initializer list constructors in class template argument deduction P0702R1 8 6 19.14* Yes 5.0 2021.1 20.7 12.0 11.0
const&-qualified pointers to members P0704R1 8 6 19.0 (2015)* 10.0.0* 5.1 2021.1 20.7 12.0 11.0
Concepts  (FTM)* P0734R0 5*
10 		10 19.23* (partial)*
19.30* 		12.0.0* (partial) 6.1 2023.1* 20.11 12.0 11.0
Lambdas in unevaluated contexts P0315R4 9 13 (partial)*
14 (partial)*
17 		19.28 (16.8)* 13.1.6* (partial) 6.2 2023.1 (partial)
2024.0 		20.7 12.0
Three-way comparison operator  (FTM)* P0515R3 10 8 (partial)
10 		19.20* 12.0.0* 5.1 2021.1 20.7 12.0 11.0
DR11: Simplifying implicit lambda capture P0588R1 8 19.24* 5.1 2021.1 20.7 12.0
init-statements for range-based for P0614R1 9 8 19.25* 11.0.0* 6.0 2021.7 20.11 12.0 11.0
Default constructible and assignable stateless lambdas P0624R2 9 8 19.22* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
Type mismatch of defaulted special member functions P0641R2 9 (partial)* 8 19.0 (2015)* (partial)* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
Access checking on specializations P0692R1 Yes 8 (partial)
14 		19.26* 14.0.0* 5.1 2021.1 20.7 12.0
ADL and function templates that are not visible P0846R0 9 9 19.21* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
DR11: Specify when constexpr function definitions are needed for constant evaluation  (FTM)* P0859R0 5.2 (partial)*
9 		8 19.27* (partial)*
19.31** 		11.0.0* (partial) 12.0 11.0
Attributes [[likely]] and [[unlikely]] P0479R5 9 12 19.26* 13.0.0* 5.1 2021.7 20.7 12.0
Make typename more optional P0634R3 9 16 19.29 (16.10)* 16.0.0* 5.1 2023.1 20.7 12.0
Pack-expansions in lambda init-captures  (FTM)* P0780R2 9 9 19.22* 11.0.3* 6.1 2021.7 20.11 12.0 11.0
Attribute [[no_unique_address]] P0840R2 9 9 19.28 (16.9)** 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Conditionally trivial special member functions  (FTM)* P0848R3 10 16 19.28 (16.8)* 6.1 2021.7 20.11 12.0
DR17: Relaxing the structured bindings customization point finding rules P0961R1 8 8 19.20* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
DR11: Relaxing the range-for loop customization point finding rules P0962R1 8 8 19.25* 11.0.0* 5.1 2021.1 20.7 12.0 11.0
DR17: Allow structured bindings to accessible members P0969R0 8 8 19.20* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
Destroying operator delete  (FTM)* P0722R3 9 6 19.27* 10.0.0* 6.1 2023.1 20.11 12.0 11.0
Class types in Constant template parameters P0732R2 9 12 (partial) 19.26*(partial)*
19.28 (16.9)* 		13.0.0* (partial) 6.2 2023.1 (partial) 21.3 12.0
Deprecate implicit capture of this via [=] P0806R2 9 7 19.22* 10.0.1* 5.1 20.7 12.0 11.0
explicit(bool)  (FTM)* P0892R2 9 9 19.24* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Integrating feature-test macros P0941R2 5 3.4 19.15* (partial)
19.20* 		Yes 5.0 2021.1 20.7 12.0 11.0
Prohibit aggregates with user-declared constructors P1008R1 9 8 19.20* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
constexpr virtual function  (FTM)* P1064R0 9 9 19.28 (16.9)* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Consistency improvements for comparisons P1120R0 10 8 (partial)
10 		19.22* 12.0.0* 5.1 2023.1 20.7 12.0 11.0
char8_t   (FTM)* P0482R6 9 7* 19.22* 10.0.0* 5.1 2021.1 20.7 12.0 11.0
std::is_constant_evaluated()  (FTM)* P0595R2 9 9 19.25* 11.0.3* 5.1 19.1 21.1 12.0 11.0
constexpr try-catch blocks P1002R1 9 8 19.25* 10.0.1* 5.1 2023.1 20.7 12.0 11.0
Immediate functions (consteval)  (FTM)* P1073R3 10 (partial)*
11 		11 (partial)
14 (partial)*
17 		19.28 (16.8)*
(partial)*
19.29 (16.10)* 		11.0.3* (partial)
15.0.0* 		5.1 2021.1 20.7 12.0
Nested inline namespaces P1094R2 9 8 19.27* 10.0.1* 5.1 2021.1 20.7 12.0 11.0
Yet another approach for constrained declarations P1141R2 10 10 19.26* (partial)
19.28 (16.9)* 		12.0.5* 6.1 2023.1 20.11 12.0 11.0
Signed integers are two's complement P1236R1 9 9 Yes 11.0.3* N/A 2023.1* yes* 12.0 11.0
dynamic_cast and polymorphic typeid in constant expressions P1327R1 10 9 19.28 (16.9)* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Changing the active member of a union inside constexpr  (FTM)* P1330R0 9 9 19.10* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Coroutines  (FTM)*  (FTM)* P0912R5
LWG3393 		10 8 (partial)
17 (partial)* 		19.0 (2015)* (partial)
19.10**
19.28 (16.8)* 		10.0.1* (partial) 5.1 2021.1 23.3* 12.0 (host code only)
Parenthesized initialization of aggregates  (FTM)* P0960R3 10 16 19.28 (16.8)* 16.0.0* 5.1 2021.1 20.7 12.0
DR11: Array size deduction in new-expressions P1009R2 11 9 19.27* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Modules  (FTM)* P1103R3 11 (partial) 8 (partial) 19.0 (2015)* (partial)
19.10**
19.28 (16.8)* 		10.0.1* (partial) 2023.1 (partial)
Stronger Unicode requirements P1041R4
P1139R2 		10 Yes 19.0 (2015)**
19.26** 		Yes N/A 2023.1* Yes 12.0 11.0
<=> != == P1185R2 10 10 19.22* 12.0.0* 5.1 2021.1 20.7 12.0 11.0
DR11: Explicitly defaulted functions with different exception specifications P1286R2 10 9 19.28 (16.8)* 11.0.3* 5.1 2021.1 20.7 12.0 11.0
Lambda capture and storage class specifiers of structured bindings P1091R3
P1381R1 		10 8 (partial)
16 		19.11**
19.24** 		16.0.0* 5.1 2021.1 20.7 12.0
Permit conversions to arrays of unknown bound P0388R4 10 14 19.27* 14.0.0* 6.0 2021.5 20.11 12.0
constexpr container operations  (FTM)* P0784R7 10 10 19.28 (16.9)* 12.0.0* 6.0 2021.5 20.11 12.0 11.0
Deprecating some uses of volatile P1152R4 10 10 19.27* 12.0.0* 6.0 2021.5 20.11 12.0 11.0
constinit  (FTM)* P1143R2 10 10 19.29 (16.10)* 12.0.0* 6.1 2021.7 20.11 12.0 11.0
Deprecate comma operator in subscripts P1161R3 10 9 19.25* 11.0.3* 6.0 2021.7 20.11 12.0 11.0
[[nodiscard]] with message P1301R4 10 9 19.25* 11.0.3* 6.0 2021.5 20.11 12.0 11.0
Trivial default initialization in constexpr functions P1331R2 10 10 19.27* 12.0.0* 6.1 2021.7 20.11 12.0 11.0
Unevaluated asm-declaration in constexpr functions P1668R1 10 10 19.28 (16.9)* 12.0.0* 6.1 2021.7 20.11 12.0 11.0
using enum  (FTM)* P1099R5 11 13 19.24* 13.1.6* 6.3 2023.1 22.5 12.0
Synthesizing Three-way comparison for specified comparison category P1186R3 11 10 19.24* 12.0.0* 6.0 2021.5 20.11 12.0 11.0
DR17: [[nodiscard]] for constructors P1771R1 10 9 19.24* 11.0.3* 6.0 2021.5 20.11 12.0 11.0
class template argument deduction for alias templates  (FTM)* P1814R0 10 19 19.27* 6.5 23.9 12.0
class template argument deduction for aggregates  (FTM)* P1816R0
P2082R1 		10*
11* 		17 19.27* 6.3 2023.1 (partial)*
2024.1 		23.3 12.0
DR11: Implicit move for more local objects and rvalue references P1825R0 11* 13 19.24* 13.1.6* 6.0 2021.5 20.11 12.0
Allow defaulting comparisons by value P1946R0 10 10 19.25* 12.0.0* 6.1 2021.7 20.11 12.0 11.0
Remove std::weak_equality and std::strong_equality P1959R0 10 10 19.25* 12.0.0* 6.1 2021.7 20.11 12.0 11.0
Inconsistencies with constant template parameters  (FTM)* P1907R1 10 (partial)
11 		18 (partial)* 19.26* 13.1.6* (partial) 6.2 2023.1 (partial) 21.3 12.0
DR98: Pseudo-destructors end object lifetimes P0593R6 11 11 Yes 12.0.5* N/A 2023.1* Yes 12.0 11.0
DR11: Converting from T* to bool should be considered narrowing P1957R2 10*
11* 		11 19.27* 12.0.5* 6.1 12.0 11.0
 

C++20 feature 		 

Paper(s)
GCC
Clang
MSVC
Apple Clang
EDG eccp
Intel C++
Nvidia HPC C++ (ex PGI)*
Nvidia nvcc
Cray

[edit] C++20 library features

C++20 feature

  		Paper(s)

 
GCC libstdc++
Clang libc++
MSVC STL
Apple Clang*
std::endian  (FTM)* P0463R1 8 7 19.22* 10.0.0*
Extending std::make_shared() to support arrays  (FTM)* P0674R1 12 15 19.27* 14.0.3*
Floating-point atomic  (FTM)* P0020R6 10 18 19.22* 16.0.0*
Synchronized buffered (std::basic_osyncstream)  (FTM)* P0053R7 11 18 19.29 (16.10)*
constexpr for <algorithm> and <utility>  (FTM)* P0202R3 10 8 (partial)
12 		19.26* 10.0.1* (partial)
13.0.0*
More constexpr for <complex>  (FTM)* P0415R1 9 7 (partial)
16 		19.27* 10.0.0* (partial)
15.0.0*
Make std::memory_order a scoped enumeration P0439R0 9 9 19.25* 11.0.3*
String prefix and suffix checking: string (_view) ::starts_with / ends_with  (FTM)* P0457R2 9 6 19.21* 10.0.0*
Library support for operator<=> <compare>  (FTM)* P0768R1 10 7 (partial)
12 (partial)*
17 		19.20* (partial)
19.28 (16.9)* 		13.0.0*
std::remove_cvref  (FTM)* P0550R2 9 6 19.20* 10.0.0*
[[nodiscard]] in the standard library P0600R1 9 7 (partial)
16 		19.13* (partial)
19.22* 		10.0.0* (partial)
15.0.0*
Using std::move in numeric algorithms P0616R0 9 12 19.23* 13.0.0*
Utility to convert a pointer to a raw pointer  (FTM)* P0653R2 8 6 19.22* Yes
Atomic std::shared_ptr and std::weak_ptr  (FTM)* P0718R2 12 19.27*
std::span  (FTM)* P0122R7 10 7 19.26* 10.0.0*
Calendar and Time zone  (FTM)* P0355R7 11 (partial)*
13 (partial)*
14 		7 (partial)
19 (partial)* 		19.29 (16.10)* 10.0.0* (partial)
<version> P0754R2 9 7 19.22* 10.0.0*
Comparing unordered containers P0809R0 Yes Yes 16.0* Yes
ConstexprIterator requirements  (FTM)*  (FTM)* P0858R0 9 12 19.11* 13.0.0*
std::basic_string::reserve() should not shrink P0966R1 11 8 19.25* 10.0.1*
Atomic Compare-And-Exchange with padding bits P0528R3 13 19.28 (16.8)*
std::atomic_ref  (FTM)* P0019R8 10 19 19.28 (16.8)*
contains() member function of associative containers, e.g. std::map::contains() P0458R2 9 13 19.21* 13.1.6*
DR11: Guaranteed copy elision for piecewise construction P0475R1 9 Yes 19.29 (16.10)* Yes
std::bit_cast()  (FTM)* P0476R2 11 14 19.27* 14.0.3*
Integral power-of-2 operations:

std::bit_ceil(), std::bit_floor(), std::bit_width(), std::has_single_bit()  (FTM)*

P0556R3
P1956R1 		9*
10* 		9*
12* 		19.25**
19.27**
19.28 (16.8)* 		11.0.3**
13.0.0**
Improving the return value of erase-like algorithms  (FTM)* P0646R1 9 10 19.21* 12.0.0*
std::destroying_delete_t  (FTM)* P0722R3 9 9 19.27* 11.0.3*
std::is_convertible  (FTM)* P0758R1 9 9 19.23* 11.0.3*
Add std::shift_left/right to <algorithm>  (FTM)* P0769R2 10 12 19.21* 13.0.0*
Constexpr for std::swap() and swap related functions P0879R0 10 13 19.26* 13.1.6*
std::type_identity  (FTM)* P0887R1 9 8 19.21* 10.0.1*
Concepts library  (FTM)* P0898R3 10 13 19.23* 13.1.6*
constexpr comparison operators for std::array P1023R0 10 8 19.27* 10.0.1*
std::unwrap_ref_decay and std::unwrap_reference  (FTM)* P0318R1 9 8 19.21* 10.0.1*
std::bind_front()  (FTM)* P0356R5 9 13 19.25* 13.1.6*
std::reference_wrapper for incomplete types P0357R3 9 8 19.26* 10.0.1*
Fixing operator>>(basic_istream&, CharT*) P0487R1 11 8 19.23* 10.0.1*
Library support for char8_t   (FTM)* P0482R6 9 8 (partial)
16 		19.22* 10.0.1* (partial)
15.0.0*
Utility functions to implement uses-allocator construction P0591R4 9 16 19.29 (16.10)* 15.0.0*
DR17: std::variant and std::optional should propagate copy/move triviality P0602R4 8.3 8 19.11* 10.0.1*
DR17: A sane std::variant converting constructor P0608R3 10 9 19.29 (16.10)**
19.42** 		11.0.3*
std::function 's move constructor should be noexcept P0771R1 7.2 6 19.22* Yes
The One Ranges Proposal  (FTM)* P0896R4 10 13 (partial)
15* 		19.29 (16.10)* 14.0.3*
Heterogeneous lookup for unordered associative containers  (FTM)* P0919R3
P1690R1 		11 12 19.23* (P0919R3)
19.25* (P1690R1) 		13.0.0*
<chrono> zero(), min(), and max() should be noexcept P0972R0 9 8 19.14* 10.0.1*
constexpr in std::pointer_traits   (FTM)* P1006R1 9 8 19.26* 10.0.1*
std::assume_aligned()  (FTM)* P1007R3 9*
11 		15 19.28 (16.9)* 14.0.3*
Smart pointer creation with default initialization (e.g. make_unique_for_overwrite)  (FTM)* P1020R1
P1973R1 		11*
12* 		16 19.28 (16.9)* 15.0.0*
Misc constexpr bits  (FTM)*  (FTM)*  (FTM)*  (FTM)*  (FTM)*  (FTM)* P1032R1 10 13 19.28 (16.8)* 13.1.6*
Remove comparison operators of std::span P1085R2 10 8 19.26* 10.0.1*
Make stateful allocator propagation more consistent for operator+(basic_string) P1165R1 10 15 19.26* 14.0.3*
Consistent container erasure, e.g. std::erase(std::vector), or std::erase_if(std::map)  (FTM)* P1209R0
P1115R3 		9*
10* 		8*
11* 		19.25**
19.27** 		10.0.1**
12.0.5**
Standard library header units P1502R1 11 19.29 (16.10)*
polymorphic_allocator<> as a vocabulary type  (FTM)* P0339R6 9 16 19.28 (16.9)* 15.0.0*
std::execution::unseq  (FTM)* P1001R2 9 17 19.28 (16.8)*
std::lerp() and std::midpoint()  (FTM)* P0811R3 9 9 19.23* (partial)
19.28 (16.8)* 		11.0.3*
Usability enhancements for std::span P1024R3 10 9*
14 		19.26* 11.0.3*
DR17: Make std::create_directory() intuitive P1164R1 8.3 12 19.20* 13.0.0*
std::ssize() and unsigned extent for std::span  (FTM)* P1227R2 10 9 19.25* 11.0.3*
Traits for (un)bounded arrays  (FTM)* P1357R1 9 9 19.25* 11.0.3*
std::to_array()  (FTM)* P0325R4 10 10 19.25* 12.0.0*
Efficient access to std::basic_stringbuf ’s buffer P0408R7 11 17 19.29 (16.10)* 15.0.0*
Layout-compatibility and pointer-interconvertibility traits  (FTM)*  (FTM)* P0466R5 12 19.29 (16.10)**
Bit operations: std::

rotl(), rotr(), countl_zero(), countl_one(), countr_zero(), countr_one(), popcount()  (FTM)*

P0553R4 9 9 19.25**
19.28 (16.8)* 		11.0.3*
Mathematical constants  (FTM)* P0631R8 10 11 19.25* 12.0.5*
Text formatting  (FTM)* P0645R10 13 14**
17 		19.29 (16.10)* 15.0.0*
std::stop_token and std::jthread  (FTM)* P0660R10 10 17
(partial)*
20* 		19.28 (16.9)*
constexpr std::allocator and related utilities  (FTM)* P0784R7 10 12 19.29 (16.10)* 13.0.0*
constexpr std::string   (FTM)* P0426R1
P1032R1
P0980R1 		12 15 19.29 (16.10)*
19.30** 		14.0.3*
constexpr std::vector   (FTM)* P1004R2 12 15 19.29 (16.10)*
19.30** 		14.0.3*
Input range adaptors P1035R7 10 16 19.29 (16.10)* 15.0.0*
constexpr std::invoke() and related utilities P1065R2 10 12 19.28 (16.8)* 13.0.0*
Atomic waiting and notifying, std::counting_semaphore, std::latch and std::barrier  (FTM)*  (FTM)*  (FTM)*  (FTM)*  (FTM)*  (FTM)* P1135R6 11 11 19.28 (16.9)* 13.1.6*
std::source_location  (FTM)* P1208R6 11 15*
(partial)
16 		19.29 (16.10)* 15.0.0*
Adding <=> to the standard library P1614R2 10 14*
(partial)
17*
(partial)
19 		19.29 (16.10)* 13.1.6* (partial)
constexpr default constructor of std::atomic and std::atomic_flag   (FTM)* P0883R2 10 13 19.26* 13.1.6*
constexpr for numeric algorithms  (FTM)* P1645R1 10 12 19.26* 13.0.0*
Safe integral comparisons  (FTM)* P0586R2 10 13 19.27* 13.1.6*
 

C++20 feature 		 

Paper(s)
GCC libstdc++
Clang libc++
MSVC STL
Apple Clang*

* - 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.

[edit] External links

1.  C++20 - Wikipedia
2.  Working C++20 examples
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