set> ` ](/w/cpp/header/unordered_set "cpp/header/unordered set") |  (C++26)  |  [ P2363R5 ](https://wg21.link/P2363R5)  
` __cpp_lib_assume_aligned ` |  [ std::assume_aligned ](/w/cpp/memory/assume_aligned "cpp/memory/assume aligned") |  201811L  |  [ ` <memory> ` ](/w/cpp/header/memory "cpp/header/memory") |  (C++20)  |  [ P1007R3 ](https://wg21.link/P1007R3)  
` __cpp_lib_atomic_flag_test ` |  std::atomic_flag::test  |  201907L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++20)  |  [ P1135R6 ](https://wg21.link/P1135R6)  
` __cpp_lib_atomic_float ` |  [ Floating-point atomic ](/w/cpp/atomic/atomic "cpp/atomic/atomic") |  201711L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++20)  |  [ P0020R6 ](https://wg21.link/P0020R6)  
` __cpp_lib_atomic_  is_always_lock_free ` |  [ ` constexpr atomic<T>::is_always_lock_free ` ](/w/cpp/atomic/atomic/is_always_lock_free "cpp/atomic/atomic/is always lock free") |  201603L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++17)  |  [ P0152R1 ](https://wg21.link/P0152R1)  
` __cpp_lib_atomic_  lock_free_type_aliases ` |  atomic lockfree integral types (  [ std::atomic_signed_lock_free ](/w/cpp/atomic/atomic "cpp/atomic/atomic") ,  [ std::atomic_unsigned_lock_free ](/w/cpp/atomic/atomic "cpp/atomic/atomic") )  |  201907L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++20)  |  [ P1135R6 ](https://wg21.link/P1135R6)  
` __cpp_lib_atomic_ref ` |  [ ` std::atomic_ref ` ](/w/cpp/atomic/atomic_ref "cpp/atomic/atomic ref") |  201806L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++20)  |  [ P0019R8 ](https://wg21.link/P0019R8)  
` __cpp_lib_atomic_shared_ptr ` |  [ ` std::atomic<std::shared_ptr> ` ](/w/cpp/memory/shared_ptr/atomic2 "cpp/memory/shared ptr/atomic2") |  201711L  |  [ ` <memory> ` ](/w/cpp/header/memory "cpp/header/memory") |  (C++20)  |  [ P0718R2 ](https://wg21.link/P0718R2)  
` __cpp_lib_atomic_  value_initialization ` |  Fixing atomic initialization (value-initialize  [ std::atomic ](/w/cpp/atomic/atomic "cpp/atomic/atomic") by default)  |  201911L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") [ ` <memory> ` ](/w/cpp/header/memory "cpp/header/memory") |  (C++20)  |  [ P0883R2 ](https://wg21.link/P0883R2)  
` __cpp_lib_atomic_wait ` |  Efficient  [ std::atomic ](/w/cpp/atomic/atomic "cpp/atomic/atomic") waiting  |  201907L  |  [ ` <atomic> ` ](/w/cpp/header/atomic "cpp/header/atomic") |  (C++20)  |  [ P1135R6 ](https://wg21.link/P1135R6)  
` __cpp_lib_barrier ` |  [ ` std::barrier ` ](/w/cpp/thread/barrier "cpp/thread/barrier") |  201907L  |  [ ` <barrier> ` ](/w/cpp/header/barrier "cpp/header/barrier") |  (C++20)  |  [ P1135R6 ](https://wg21.link/P1135R6)  
[ ` std::barrier ` ](/w/cpp/thread/barrier "cpp/thread/barrier") 's phase completion guarantees  |  202302L  |  [ ` <barrier> ` ](/w/cpp/header/barrier "cpp/header/barrier") |  (C++23)  |  [ P2588R3 ](https://wg21.link/P2588R3)  
` __cpp_lib_bind_back ` |  std::bind_back  |  202202L  |  [ ` <functional> ` ](/w/cpp/header/functional "cpp/header/functional") |  (C++23)  |  [ P2387R3 ](https://wg21.link/P2387R3)  
Allow passing callable objects as non-type template arguments to  std::bind_back  |  202306L  |  [ ` <functional> ` ](/w/cpp/header/functional "cpp/header/functional") |  (C++26)  |  [ P2714R1 ](https://wg21.link/P2714R1)  
` __cpp_lib_bind_front ` |  [ ` std::bind_front ` ](/w/cpp/utility/functional/bind_front "cpp/utility/functional/bind front") |  201907L  |  [ ` <functional> ` ](/w/cpp/header/functional "cpp/header/functional") |  (C++20)  |  [ P0356R5 ](https://wg21.link/P0356R5)   
[ P1651R0 ](https://wg21.link/P1651R0)  
Allow passing callable objects as non-type template arguments to  [ std::bind_front ](/w/cpp/utility/functional/bind_front "cpp/utility/functional/bind front") |  202306L  |  [ ` <functional> ` ](/w/cpp/header/functional "cpp/header/functional") |  (C++26)  |  [ P2714R1 ](http