# Standard library header <atomic> (C++11)

From cppreference.com
< cpp‎ | header

This header is part of the concurrency support library.

### Classes
atomic (C++11) | atomic class template and specializations for bool, integral, and pointer types (class template)
atomic_ref (C++20) | provides atomic operations on non-atomic objects (class template)
atomic_flag (C++11) | the lock-free boolean atomic type (class)
memory_order (C++11) | defines memory ordering constraints for the given atomic operation (enum)
atomic_bool (C++11) | std::atomic<bool> (typedef)
atomic_char (C++11) | std::atomic<char> (typedef)
atomic_schar (C++11) | std::atomic<signed char> (typedef)
atomic_uchar (C++11) | std::atomic<unsigned char> (typedef)
atomic_short (C++11) | std::atomic<short> (typedef)
atomic_ushort (C++11) | std::atomic<unsigned short> (typedef)
atomic_int (C++11) | std::atomic<int> (typedef)
atomic_uint (C++11) | std::atomic<unsigned int> (typedef)
atomic_long (C++11) | std::atomic<long> (typedef)
atomic_ulong (C++11) | std::atomic<unsigned long> (typedef)
atomic_llong (C++11) | std::atomic<long long> (typedef)
atomic_ullong (C++11) | std::atomic<unsigned long long> (typedef)
atomic_char8_t (C++20) | std::atomic<char8_t> (typedef)
atomic_char16_t (C++11) | std::atomic<char16_t> (typedef)
atomic_char32_t (C++11) | std::atomic<char32_t> (typedef)
atomic_wchar_t (C++11) | std::atomic<wchar_t> (typedef)
atomic_int8_t (C++11)(optional) | std::atomic<std::int8_t> (typedef)
atomic_uint8_t (C++11)(optional) | std::atomic<std::uint8_t> (typedef)
atomic_int16_t (C++11)(optional) | std::atomic<std::int16_t> (typedef)
atomic_uint16_t (C++11)(optional) | std::atomic<std::uint16_t> (typedef)
atomic_int32_t (C++11)(optional) | std::atomic<std::int32_t> (typedef)
atomic_uint32_t (C++11)(optional) | std::atomic<std::uint32_t> (typedef)
atomic_int64_t (C++11)(optional) | std::atomic<std::int64_t> (typedef)
atomic_uint64_t (C++11)(optional) | std::atomic<std::uint64_t> (typedef)
atomic_int_least8_t (C++11) | std::atomic<std::int_least8_t> (typedef)
atomic_uint_least8_t (C++11) | std::atomic<std::uint_least8_t> (typedef)
atomic_int_least16_t (C++11) | std::atomic<std::int_least16_t> (typedef)
atomic_uint_least16_t (C++11) | std::atomic<std::uint_least16_t> (typedef)
atomic_int_least32_t (C++11) | std::atomic<std::int_least32_t> (typedef)
atomic_uint_least32_t (C++11) | std::atomic<std::uint_least32_t> (typedef)
atomic_int_least64_t (C++11) | std::atomic<std::int_least64_t> (typedef)
atomic_uint_least64_t (C++11) | std::atomic<std::uint_least64_t> (typedef)
atomic_int_fast8_t (C++11) | std::atomic<std::int_fast8_t> (typedef)
atomic_uint_fast8_t (C++11) | std::atomic<std::uint_fast8_t> (typedef)
atomic_int_fast16_t (C++11) | std::atomic<std::int_fast16_t> (typedef)
atomic_uint_fast16_t (C++11) | std::atomic<std::uint_fast16_t> (typedef)
atomic_int_fast32_t (C++11) | std::atomic<std::int_fast32_t> (typedef)
atomic_uint_fast32_t (C++11) | std::atomic<std::uint_fast32_t> (typedef)
atomic_int_fast64_t (C++11) | std::atomic<std::int_fast64_t> (typedef)
atomic_uint_fast64_t (C++11) | std::atomic<std::uint_fast64_t> (typedef)
atomic_intptr_t (C++11)(optional) | std::atomic<std::intptr_t> (typedef)
atomic_uintptr_t (C++11)(optional) | std::atomic<std::uintptr_t> (typedef)
atomic_size_t (C++11) | std::atomic<std::size_t> (typedef)
atomic_ptrdiff_t (C++11) | std::atomic<std::ptrdiff_t> (typedef)
atomic_intmax_t (C++11) | std::atomic<std::intmax_t> (typedef)
atomic_uintmax_t (C++11) | std::atomic<std::uintmax_t> (typedef)
atomic_signed_lock_free (C++20) | a signed integral atomic type that is lock-free and for which waiting/notifying is most efficient (typedef)
atomic_unsigned_lock_free (C++20) | an unsigned integral atomic type that is lock-free and for which waiting/notifying is most efficient (typedef)
### Functions
atomic_is_lock_free (C++11) | checks if the atomic type's operations are lock-free (function template)
atomic_store atomic_store_explicit (C++11)(C++11) | atomically replaces the value of the atomic object with a non-atomic argument (function template)
atomic_load atomic_load_explicit (C++11)(C++11) | atomically obtains the value stored in an atomic object (function template)
atomic_exchange atomic_exchange_explicit (C++11)(C++11) | atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic (function template)
atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit (C++11)(C++11)(C++11)(C++11) | atomically compares the value of the atomic object with non-atomic argument and performs atomic exchange if equal or atomic load if not (function template)
atomic_fetch_add atomic_fetch_add_explicit (C++11)(C++11) | adds a non-atomic value to an atomic object and obtains the previous value of the atomic (function template)
atomic_fetch_sub atomic_fetch_sub_explicit (C++11)(C++11) | subtracts a non-atomic value from an atomic object and obtains the previous value of the atomic (function template)
atomic_fetch_and atomic_fetch_and_explicit (C++11)(C++11) | replaces the atomic object with the result of bitwise AND with a non-atomic argument and obtains the previous value of the atomic (function template)
atomic_fetch_or atomic_fetch_or_explicit (C++11)(C++11) | replaces the atomic object with the result of bitwise OR with a non-atomic argument and obtains the previous value of the atomic (function template)
atomic_fetch_xor atomic_fetch_xor_explicit (C++11)(C++11) | replaces the atomic object with the result of bitwise XOR with a non-atomic argument and obtains the previous value of the atomic (function template)
atomic_wait atomic_wait_explicit (C++20)(C++20) | blocks the thread until notified and the atomic value changes (function template)
atomic_notify_one (C++20) | notifies a thread blocked in atomic_wait (function template)
atomic_notify_all (C++20) | notifies all threads blocked in atomic_wait (function template)
atomic_flag_test atomic_flag_test_explicit (C++20)(C++20) | atomically returns the value of the flag (function)
atomic_flag_test_and_set atomic_flag_test_and_set_explicit (C++11)(C++11) | atomically sets the flag to true and returns its previous value (function)
atomic_flag_clear atomic_flag_clear_explicit (C++11)(C++11) | atomically sets the value of the flag to false (function)
atomic_flag_wait atomic_flag_wait_explicit (C++20)(C++20) | blocks the thread until notified and the flag changes (function)
atomic_flag_notify_one (C++20) | notifies a thread blocked in atomic_flag_wait (function)
atomic_flag_notify_all (C++20) | notifies all threads blocked in atomic_flag_wait (function)
atomic_init (C++11)(deprecated in C++20) | non-atomic initialization of a default-constructed atomic object (function template)
kill_dependency (C++11) | removes the specified object from the std::memory_order_consume dependency tree (function template)
atomic_thread_fence (C++11) | generic memory order-dependent fence synchronization primitive (function)
atomic_signal_fence (C++11) | fence between a thread and a signal handler executed in the same thread (function)
### Macros
ATOMIC_VAR_INIT (C++11)(deprecated in C++20) | constant initialization of an atomic variable of static storage duration (function macro)
ATOMIC_FLAG_INIT (C++11) | initializes an std::atomic_flag to false (macro constant)

### Synopsis

    namespace std {
      /* until C++20:
      typedef enum memory_order {
        memory_order_relaxed,
        memory_order_consume,
        memory_order_acquire,
        memory_order_release,
        memory_order_acq_rel,
        memory_order_seq_cst
      } memory_order;
      */

      enum class memory_order : /* unspecified */ {
        relaxed, consume, acquire, release, acq_rel, seq_cst
      };
      inline constexpr memory_order memory_order_relaxed = memory_order::relaxed;
      inline constexpr memory_order memory_order_consume = memory_order::consume;
      inline constexpr memory_order memory_order_acquire = memory_order::acquire;
      inline constexpr memory_order memory_order_release = memory_order::release;
      inline constexpr memory_order memory_order_acq_rel = memory_order::acq_rel;
      inline constexpr memory_order memory_order_seq_cst = memory_order::seq_cst;

      template<class T>
        T kill_dependency(T y) noexcept;

      // lock-free property
      #define ATOMIC_BOOL_LOCK_FREE /* unspecified */
      #define ATOMIC_CHAR_LOCK_FREE /* unspecified */
      #define ATOMIC_CHAR8_T_LOCK_FREE /* unspecified */
      #define ATOMIC_CHAR16_T_LOCK_FREE /* unspecified */
      #define ATOMIC_CHAR32_T_LOCK_FREE /* unspecified */
      #define ATOMIC_WCHAR_T_LOCK_FREE /* unspecified */
      #define ATOMIC_SHORT_LOCK_FREE /* unspecified */
      #define ATOMIC_INT_LOCK_FREE /* unspecified */
      #define ATOMIC_LONG_LOCK_FREE /* unspecified */
      #define ATOMIC_LLONG_LOCK_FREE /* unspecified */
      #define ATOMIC_POINTER_LOCK_FREE /* unspecified */

      // class template atomic_ref
      template<class T> struct atomic_ref;
      // partial specialization for pointers
      template<class T> struct atomic_ref<T*>;

      // class template atomic
      template<class T> struct atomic;
      // partial specialization for pointers
      template<class T> struct atomic<T*>;

      // non-member functions
      template<class T>
        bool atomic_is_lock_free(const volatile atomic<T>*) noexcept;
      template<class T>
        bool atomic_is_lock_free(const atomic<T>*) noexcept;
      template<class T>
        void atomic_store(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        void atomic_store(atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        void atomic_store_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        void atomic_store_explicit(atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        T atomic_load(const volatile atomic<T>*) noexcept;
      template<class T>
        T atomic_load(const atomic<T>*) noexcept;
      template<class T>
        T atomic_load_explicit(const volatile atomic<T>*, memory_order) noexcept;
      template<class T>
        T atomic_load_explicit(const atomic<T>*, memory_order) noexcept;
      template<class T>
        T atomic_exchange(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_exchange(atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_exchange_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        T atomic_exchange_explicit(atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        bool atomic_compare_exchange_weak(volatile atomic<T>*,
                                          typename atomic<T>::value_type*,
                                          typename atomic<T>::value_type) noexcept;
      template<class T>
        bool atomic_compare_exchange_weak(atomic<T>*,
                                          typename atomic<T>::value_type*,
                                          typename atomic<T>::value_type) noexcept;
      template<class T>
        bool atomic_compare_exchange_strong(volatile atomic<T>*,
                                            typename atomic<T>::value_type*,
                                            typename atomic<T>::value_type) noexcept;
      template<class T>
        bool atomic_compare_exchange_strong(atomic<T>*,
                                            typename atomic<T>::value_type*,
                                            typename atomic<T>::value_type) noexcept;
      template<class T>
        bool atomic_compare_exchange_weak_explicit(volatile atomic<T>*,
                                                   typename atomic<T>::value_type*,
                                                   typename atomic<T>::value_type,
                                                   memory_order, memory_order) noexcept;
      template<class T>
        bool atomic_compare_exchange_weak_explicit(atomic<T>*,
                                                   typename atomic<T>::value_type*,
                                                   typename atomic<T>::value_type,
                                                   memory_order, memory_order) noexcept;
      template<class T>
        bool atomic_compare_exchange_strong_explicit(volatile atomic<T>*,
                                                     typename atomic<T>::value_type*,
                                                     typename atomic<T>::value_type,
                                                     memory_order, memory_order) noexcept;
      template<class T>
        bool atomic_compare_exchange_strong_explicit(atomic<T>*,
                                                     typename atomic<T>::value_type*,
                                                     typename atomic<T>::value_type,
                                                     memory_order, memory_order) noexcept;

      template<class T>
        T atomic_fetch_add(volatile atomic<T>*, typename atomic<T>::difference_type) noexcept;
      template<class T>
        T atomic_fetch_add(atomic<T>*, typename atomic<T>::difference_type) noexcept;
      template<class T>
        T atomic_fetch_add_explicit(volatile atomic<T>*, typename atomic<T>::difference_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_add_explicit(atomic<T>*, typename atomic<T>::difference_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_sub(volatile atomic<T>*, typename atomic<T>::difference_type) noexcept;
      template<class T>
        T atomic_fetch_sub(atomic<T>*, typename atomic<T>::difference_type) noexcept;
      template<class T>
        T atomic_fetch_sub_explicit(volatile atomic<T>*, typename atomic<T>::difference_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_sub_explicit(atomic<T>*, typename atomic<T>::difference_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_and(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_and(atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_and_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_and_explicit(atomic<T>*, typename atomic<T>::value_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_or(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_or(atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_or_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        T atomic_fetch_or_explicit(atomic<T>*, typename atomic<T>::value_type,
                                   memory_order) noexcept;
      template<class T>
        T atomic_fetch_xor(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_xor(atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        T atomic_fetch_xor_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
                                    memory_order) noexcept;
      template<class T>
        T atomic_fetch_xor_explicit(atomic<T>*, typename atomic<T>::value_type,
                                    memory_order) noexcept;

      template<class T>
        void atomic_wait(const volatile atomic<T>*, typename atomic<T>::value_type);
      template<class T>
        void atomic_wait(const atomic<T>*, typename atomic<T>::value_type);
      template<class T>
        void atomic_wait_explicit(const volatile atomic<T>*, typename atomic<T>::value_type,
                                  memory_order);
      template<class T>
        void atomic_wait_explicit(const atomic<T>*, typename atomic<T>::value_type,
                                  memory_order);
      template<class T>
        void atomic_notify_one(volatile atomic<T>*);
      template<class T>
        void atomic_notify_one(atomic<T>*);
      template<class T>
        void atomic_notify_all(volatile atomic<T>*);
      template<class T>
        void atomic_notify_all(atomic<T>*);

      // type aliases
      using atomic_bool           = atomic<bool>;
      using atomic_char           = atomic<char>;
      using atomic_schar          = atomic<signed char>;
      using atomic_uchar          = atomic<unsigned char>;
      using atomic_short          = atomic<short>;
      using atomic_ushort         = atomic<unsigned short>;
      using atomic_int            = atomic<int>;
      using atomic_uint           = atomic<unsigned int>;
      using atomic_long           = atomic<long>;
      using atomic_ulong          = atomic<unsigned long>;
      using atomic_llong          = atomic<long long>;
      using atomic_ullong         = atomic<unsigned long long>;
      using atomic_char8_t        = atomic<char8_t>;
      using atomic_char16_t       = atomic<char16_t>;
      using atomic_char32_t       = atomic<char32_t>;
      using atomic_wchar_t        = atomic<wchar_t>;

      using atomic_int8_t         = atomic<int8_t>;
      using atomic_uint8_t        = atomic<uint8_t>;
      using atomic_int16_t        = atomic<int16_t>;
      using atomic_uint16_t       = atomic<uint16_t>;
      using atomic_int32_t        = atomic<int32_t>;
      using atomic_uint32_t       = atomic<uint32_t>;
      using atomic_int64_t        = atomic<int64_t>;
      using atomic_uint64_t       = atomic<uint64_t>;

      using atomic_int_least8_t   = atomic<int_least8_t>;
      using atomic_uint_least8_t  = atomic<uint_least8_t>;
      using atomic_int_least16_t  = atomic<int_least16_t>;
      using atomic_uint_least16_t = atomic<uint_least16_t>;
      using atomic_int_least32_t  = atomic<int_least32_t>;
      using atomic_uint_least32_t = atomic<uint_least32_t>;
      using atomic_int_least64_t  = atomic<int_least64_t>;
      using atomic_uint_least64_t = atomic<uint_least64_t>;

      using atomic_int_fast8_t    = atomic<int_fast8_t>;
      using atomic_uint_fast8_t   = atomic<uint_fast8_t>;
      using atomic_int_fast16_t   = atomic<int_fast16_t>;
      using atomic_uint_fast16_t  = atomic<uint_fast16_t>;
      using atomic_int_fast32_t   = atomic<int_fast32_t>;
      using atomic_uint_fast32_t  = atomic<uint_fast32_t>;
      using atomic_int_fast64_t   = atomic<int_fast64_t>;
      using atomic_uint_fast64_t  = atomic<uint_fast64_t>;

      using atomic_intptr_t       = atomic<intptr_t>;
      using atomic_uintptr_t      = atomic<uintptr_t>;
      using atomic_size_t         = atomic<size_t>;
      using atomic_ptrdiff_t      = atomic<ptrdiff_t>;
      using atomic_intmax_t       = atomic<intmax_t>;
      using atomic_uintmax_t      = atomic<uintmax_t>;

      using atomic_signed_lock_free   = /* see description */;
      using atomic_unsigned_lock_free = /* see description */;

      // flag type and operations
      struct atomic_flag;

      bool atomic_flag_test(const volatile atomic_flag*) noexcept;
      bool atomic_flag_test(const atomic_flag*) noexcept;
      bool atomic_flag_test_explicit(const volatile atomic_flag*, memory_order) noexcept;
      bool atomic_flag_test_explicit(const atomic_flag*, memory_order) noexcept;
      bool atomic_flag_test_and_set(volatile atomic_flag*) noexcept;
      bool atomic_flag_test_and_set(atomic_flag*) noexcept;
      bool atomic_flag_test_and_set_explicit(volatile atomic_flag*, memory_order) noexcept;
      bool atomic_flag_test_and_set_explicit(atomic_flag*, memory_order) noexcept;
      void atomic_flag_clear(volatile atomic_flag*) noexcept;
      void atomic_flag_clear(atomic_flag*) noexcept;
      void atomic_flag_clear_explicit(volatile atomic_flag*, memory_order) noexcept;
      void atomic_flag_clear_explicit(atomic_flag*, memory_order) noexcept;

      void atomic_flag_wait(const volatile atomic_flag*, bool) noexcept;
      void atomic_flag_wait(const atomic_flag*, bool) noexcept;
      void atomic_flag_wait_explicit(const volatile atomic_flag*,
                                     bool, memory_order) noexcept;
      void atomic_flag_wait_explicit(const atomic_flag*,
                                     bool, memory_order) noexcept;
      void atomic_flag_notify_one(volatile atomic_flag*) noexcept;
      void atomic_flag_notify_one(atomic_flag*) noexcept;
      void atomic_flag_notify_all(volatile atomic_flag*) noexcept;
      void atomic_flag_notify_all(atomic_flag*) noexcept;

      // fences
      extern "C" void atomic_thread_fence(memory_order) noexcept;
      extern "C" void atomic_signal_fence(memory_order) noexcept;
    }
    // deprecated
    namespace std {
      template<class T>
        void atomic_init(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
      template<class T>
        void atomic_init(atomic<T>*, typename atomic<T>::value_type) noexcept;

      #define ATOMIC_VAR_INIT(value) /* see description */

      #define ATOMIC_FLAG_INIT /* see description */
    }

#### Class template std::atomic

    namespace std {
      template<class T> struct atomic {
        using value_type = T;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;

        // operations on atomic types
        constexpr atomic() noexcept(is_nothrow_default_constructible_v<T>);
        constexpr atomic(T) noexcept;
        atomic(const atomic&) = delete;
        atomic& operator=(const atomic&) = delete;
        atomic& operator=(const atomic&) volatile = delete;

        T load(memory_order = memory_order::seq_cst) const volatile noexcept;
        T load(memory_order = memory_order::seq_cst) const noexcept;
        operator T() const volatile noexcept;
        operator T() const noexcept;
        void store(T, memory_order = memory_order::seq_cst) volatile noexcept;
        void store(T, memory_order = memory_order::seq_cst) noexcept;
        T operator=(T) volatile noexcept;
        T operator=(T) noexcept;

        T exchange(T, memory_order = memory_order::seq_cst) volatile noexcept;
        T exchange(T, memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_weak(T&, T, memory_order, memory_order) volatile noexcept;
        bool compare_exchange_weak(T&, T, memory_order, memory_order) noexcept;
        bool compare_exchange_strong(T&, T, memory_order, memory_order) volatile noexcept;
        bool compare_exchange_strong(T&, T, memory_order, memory_order) noexcept;
        bool compare_exchange_weak(T&, T,
                                   memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_weak(T&, T, memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_strong(T&, T,
                                     memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_strong(T&, T, memory_order = memory_order::seq_cst) noexcept;

        void wait(T, memory_order = memory_order::seq_cst) const volatile noexcept;
        void wait(T, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() volatile noexcept;
        void notify_one() noexcept;
        void notify_all() volatile noexcept;
        void notify_all() noexcept;
      };
    }

#### Specializations of std::atomic for integral types

    namespace std {
      template<> struct atomic</* integral */> {
        using value_type = /* integral */;
        using difference_type = value_type;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;

        constexpr atomic() noexcept;
        constexpr atomic(/* integral */) noexcept;
        atomic(const atomic&) = delete;
        atomic& operator=(const atomic&) = delete;
        atomic& operator=(const atomic&) volatile = delete;

        void store(/* integral */, memory_order = memory_order::seq_cst) volatile noexcept;
        void store(/* integral */, memory_order = memory_order::seq_cst) noexcept;
        /* integral */ operator=(/* integral */) volatile noexcept;
        /* integral */ operator=(/* integral */) noexcept;
        /* integral */ load(memory_order = memory_order::seq_cst) const volatile noexcept;
        /* integral */ load(memory_order = memory_order::seq_cst) const noexcept;
        operator /* integral */() const volatile noexcept;
        operator /* integral */() const noexcept;

        /* integral */ exchange(/* integral */,
                            memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ exchange(/* integral */,
                            memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order, memory_order) volatile noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order, memory_order) noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order, memory_order) volatile noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order, memory_order) noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order = memory_order::seq_cst) noexcept;

        /* integral */ fetch_add(/* integral */,
                             memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ fetch_add(/* integral */,
                             memory_order = memory_order::seq_cst) noexcept;
        /* integral */ fetch_sub(/* integral */,
                             memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ fetch_sub(/* integral */,
                             memory_order = memory_order::seq_cst) noexcept;
        /* integral */ fetch_and(/* integral */,
                             memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ fetch_and(/* integral */,
                             memory_order = memory_order::seq_cst) noexcept;
        /* integral */ fetch_or(/* integral */,
                             memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ fetch_or(/* integral */,
                             memory_order = memory_order::seq_cst) noexcept;
        /* integral */ fetch_xor(/* integral */,
                             memory_order = memory_order::seq_cst) volatile noexcept;
        /* integral */ fetch_xor(/* integral */,
                             memory_order = memory_order::seq_cst) noexcept;

        /* integral */ operator++(int) volatile noexcept;
        /* integral */ operator++(int) noexcept;
        /* integral */ operator--(int) volatile noexcept;
        /* integral */ operator--(int) noexcept;
        /* integral */ operator++() volatile noexcept;
        /* integral */ operator++() noexcept;
        /* integral */ operator--() volatile noexcept;
        /* integral */ operator--() noexcept;
        /* integral */ operator+=(/* integral */) volatile noexcept;
        /* integral */ operator+=(/* integral */) noexcept;
        /* integral */ operator-=(/* integral */) volatile noexcept;
        /* integral */ operator-=(/* integral */) noexcept;
        /* integral */ operator&=(/* integral */) volatile noexcept;
        /* integral */ operator&=(/* integral */) noexcept;
        /* integral */ operator|=(/* integral */) volatile noexcept;
        /* integral */ operator|=(/* integral */) noexcept;
        /* integral */ operator^=(/* integral */) volatile noexcept;
        /* integral */ operator^=(/* integral */) noexcept;

        void wait(/* integral */,
                  memory_order = memory_order::seq_cst) const volatile noexcept;
        void wait(/* integral */, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() volatile noexcept;
        void notify_one() noexcept;
        void notify_all() volatile noexcept;
        void notify_all() noexcept;
      };
    }

#### Specializations of std::atomic for floating-point types

    namespace std {
      template<> struct atomic</* floating-point */> {
        using value_type = /* floating-point */;
        using difference_type = value_type;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;

        constexpr atomic() noexcept;
        constexpr atomic(/* floating-point */) noexcept;
        atomic(const atomic&) = delete;
        atomic& operator=(const atomic&) = delete;
        atomic& operator=(const atomic&) volatile = delete;

        void store(/* floating-point */,
                   memory_order = memory_order_seq_cst) volatile noexcept;
        void store(/* floating-point */,
                   memory_order = memory_order_seq_cst) noexcept;
        /* floating-point */ operator=(/* floating-point */) volatile noexcept;
        /* floating-point */ operator=(/* floating-point */) noexcept;
        /* floating-point */ load(memory_order = memory_order_seq_cst) volatile noexcept;
        /* floating-point */ load(memory_order = memory_order_seq_cst) noexcept;
        operator /* floating-point */() volatile noexcept;
        operator /* floating-point */() noexcept;

        /* floating-point */ exchange(/* floating-point */,
                                memory_order = memory_order_seq_cst) volatile noexcept;
        /* floating-point */ exchange(/* floating-point */,
                                memory_order = memory_order_seq_cst) noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order, memory_order) volatile noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order, memory_order) noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order, memory_order) volatile noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order, memory_order) noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order = memory_order_seq_cst) volatile noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order = memory_order_seq_cst) noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order = memory_order_seq_cst) volatile noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order = memory_order_seq_cst) noexcept;

        /* floating-point */ fetch_add(/* floating-point */,
                                 memory_order = memory_order_seq_cst) volatile noexcept;
        /* floating-point */ fetch_add(/* floating-point */,
                                 memory_order = memory_order_seq_cst) noexcept;
        /* floating-point */ fetch_sub(/* floating-point */,
                                 memory_order = memory_order_seq_cst) volatile noexcept;
        /* floating-point */ fetch_sub(/* floating-point */,
                                 memory_order = memory_order_seq_cst) noexcept;

        /* floating-point */ operator+=(/* floating-point */) volatile noexcept;
        /* floating-point */ operator+=(/* floating-point */) noexcept;
        /* floating-point */ operator-=(/* floating-point */) volatile noexcept;
        /* floating-point */ operator-=(/* floating-point */) noexcept;

        void wait(/* floating-point */,
                  memory_order = memory_order::seq_cst) const volatile noexcept;
        void wait(/* floating-point */,
                  memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() volatile noexcept;
        void notify_one() noexcept;
        void notify_all() volatile noexcept;
        void notify_all() noexcept;
      };
    }

#### Specializations of std::atomic for pointer types

    namespace std {
      template<class T> struct atomic<T*> {
        using value_type = T*;
        using difference_type = ptrdiff_t;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;

        constexpr atomic() noexcept;
        constexpr atomic(T*) noexcept;
        atomic(const atomic&) = delete;
        atomic& operator=(const atomic&) = delete;
        atomic& operator=(const atomic&) volatile = delete;

        void store(T*, memory_order = memory_order::seq_cst) volatile noexcept;
        void store(T*, memory_order = memory_order::seq_cst) noexcept;
        T* operator=(T*) volatile noexcept;
        T* operator=(T*) noexcept;
        T* load(memory_order = memory_order::seq_cst) const volatile noexcept;
        T* load(memory_order = memory_order::seq_cst) const noexcept;
        operator T*() const volatile noexcept;
        operator T*() const noexcept;

        T* exchange(T*, memory_order = memory_order::seq_cst) volatile noexcept;
        T* exchange(T*, memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_weak(T*&, T*, memory_order, memory_order) volatile noexcept;
        bool compare_exchange_weak(T*&, T*, memory_order, memory_order) noexcept;
        bool compare_exchange_strong(T*&, T*, memory_order, memory_order) volatile noexcept;
        bool compare_exchange_strong(T*&, T*, memory_order, memory_order) noexcept;
        bool compare_exchange_weak(T*&, T*,
                                   memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_weak(T*&, T*,
                                   memory_order = memory_order::seq_cst) noexcept;
        bool compare_exchange_strong(T*&, T*,
                                     memory_order = memory_order::seq_cst) volatile noexcept;
        bool compare_exchange_strong(T*&, T*,
                                     memory_order = memory_order::seq_cst) noexcept;

        T* fetch_add(ptrdiff_t, memory_order = memory_order::seq_cst) volatile noexcept;
        T* fetch_add(ptrdiff_t, memory_order = memory_order::seq_cst) noexcept;
        T* fetch_sub(ptrdiff_t, memory_order = memory_order::seq_cst) volatile noexcept;
        T* fetch_sub(ptrdiff_t, memory_order = memory_order::seq_cst) noexcept;

        T* operator++(int) volatile noexcept;
        T* operator++(int) noexcept;
        T* operator--(int) volatile noexcept;
        T* operator--(int) noexcept;
        T* operator++() volatile noexcept;
        T* operator++() noexcept;
        T* operator--() volatile noexcept;
        T* operator--() noexcept;
        T* operator+=(ptrdiff_t) volatile noexcept;
        T* operator+=(ptrdiff_t) noexcept;
        T* operator-=(ptrdiff_t) volatile noexcept;
        T* operator-=(ptrdiff_t) noexcept;

        void wait(T*, memory_order = memory_order::seq_cst) const volatile noexcept;
        void wait(T*, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() volatile noexcept;
        void notify_one() noexcept;
        void notify_all() volatile noexcept;
        void notify_all() noexcept;
      };
    }

#### Class template std::atomic_ref

    namespace std {
      template<class T> struct atomic_ref {
      private:
        T* ptr;             // exposition only
      public:
        using value_type = T;
        static constexpr size_t required_alignment = /* implementation-defined */;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const noexcept;

        explicit atomic_ref(T&);
        atomic_ref(const atomic_ref&) noexcept;
        atomic_ref& operator=(const atomic_ref&) = delete;

        void store(T, memory_order = memory_order_seq_cst) const noexcept;
        T operator=(T) const noexcept;
        T load(memory_order = memory_order_seq_cst) const noexcept;
        operator T() const noexcept;

        T exchange(T, memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_weak(T&, T,
                                   memory_order, memory_order) const noexcept;
        bool compare_exchange_strong(T&, T,
                                     memory_order, memory_order) const noexcept;
        bool compare_exchange_weak(T&, T,
                                   memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_strong(T&, T,
                                     memory_order = memory_order_seq_cst) const noexcept;

        void wait(T, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() const noexcept;
        void notify_all() const noexcept;
      };
    }

#### Specializations of std::atomic_ref for integral types

    namespace std {
      template<> struct atomic_ref</* integral */> {
      private:
        /* integral */* ptr;        // exposition only
      public:
        using value_type = /* integral */;
        using difference_type = value_type;
        static constexpr size_t required_alignment = /* implementation-defined */;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const noexcept;

        explicit atomic_ref(/* integral */&);
        atomic_ref(const atomic_ref&) noexcept;
        atomic_ref& operator=(const atomic_ref&) = delete;

        void store(/* integral */, memory_order = memory_order_seq_cst) const noexcept;
        /* integral */ operator=(/* integral */) const noexcept;
        /* integral */ load(memory_order = memory_order_seq_cst) const noexcept;
        operator /* integral */() const noexcept;

        /* integral */ exchange(/* integral */,
                          memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order, memory_order) const noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order, memory_order) const noexcept;
        bool compare_exchange_weak(/* integral */&, /* integral */,
                                   memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_strong(/* integral */&, /* integral */,
                                     memory_order = memory_order_seq_cst) const noexcept;

        /* integral */ fetch_add(/* integral */,
                           memory_order = memory_order_seq_cst) const noexcept;
        /* integral */ fetch_sub(/* integral */,
                           memory_order = memory_order_seq_cst) const noexcept;
        /* integral */ fetch_and(/* integral */,
                           memory_order = memory_order_seq_cst) const noexcept;
        /* integral */ fetch_or(/* integral */,
                          memory_order = memory_order_seq_cst) const noexcept;
        /* integral */ fetch_xor(/* integral */,
                           memory_order = memory_order_seq_cst) const noexcept;

        /* integral */ operator++(int) const noexcept;
        /* integral */ operator--(int) const noexcept;
        /* integral */ operator++() const noexcept;
        /* integral */ operator--() const noexcept;
        /* integral */ operator+=(/* integral */) const noexcept;
        /* integral */ operator-=(/* integral */) const noexcept;
        /* integral */ operator&=(/* integral */) const noexcept;
        /* integral */ operator

#### Specializations of std::atomic_ref for floating-point types

    namespace std {
      template<> struct atomic_ref</* floating-point */> {
      private:
        /* floating-point */* ptr;  // exposition only
      public:
        using value_type = /* floating-point */;
        using difference_type = value_type;
        static constexpr size_t required_alignment = /* implementation-defined */;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const noexcept;

        explicit atomic_ref(/* floating-point */&);
        atomic_ref(const atomic_ref&) noexcept;
        atomic_ref& operator=(const atomic_ref&) = delete;

        void store(/* floating-point */, memory_order = memory_order_seq_cst) const noexcept;
        /* floating-point */ operator=(/* floating-point */) const noexcept;
        /* floating-point */ load(memory_order = memory_order_seq_cst) const noexcept;
        operator /* floating-point */() const noexcept;

        /* floating-point */ exchange(/* floating-point */,
                                memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order, memory_order) const noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order, memory_order) const noexcept;
        bool compare_exchange_weak(/* floating-point */&, /* floating-point */,
                                   memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_strong(/* floating-point */&, /* floating-point */,
                                     memory_order = memory_order_seq_cst) const noexcept;

        /* floating-point */ fetch_add(/* floating-point */,
                                 memory_order = memory_order_seq_cst) const noexcept;
        /* floating-point */ fetch_sub(/* floating-point */,
                                 memory_order = memory_order_seq_cst) const noexcept;

        /* floating-point */ operator+=(/* floating-point */) const noexcept;
        /* floating-point */ operator-=(/* floating-point */) const noexcept;

        void wait(/* floating-point */, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() const noexcept;
        void notify_all() const noexcept;
      };
    }

#### Specializations of std::atomic_ref for pointer types

    namespace std {
      template<class T> struct atomic_ref<T*> {
      private:
        T** ptr;        // exposition only
      public:
        using value_type = T*;
        using difference_type = ptrdiff_t;
        static constexpr size_t required_alignment = /* implementation-defined */;

        static constexpr bool is_always_lock_free = /* implementation-defined */;
        bool is_lock_free() const noexcept;

        explicit atomic_ref(T*&);
        atomic_ref(const atomic_ref&) noexcept;
        atomic_ref& operator=(const atomic_ref&) = delete;

        void store(T*, memory_order = memory_order_seq_cst) const noexcept;
        T* operator=(T*) const noexcept;
        T* load(memory_order = memory_order_seq_cst) const noexcept;
        operator T*() const noexcept;

        T* exchange(T*, memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_weak(T*&, T*,
                                   memory_order, memory_order) const noexcept;
        bool compare_exchange_strong(T*&, T*,
                                     memory_order, memory_order) const noexcept;
        bool compare_exchange_weak(T*&, T*,
                                   memory_order = memory_order_seq_cst) const noexcept;
        bool compare_exchange_strong(T*&, T*,
                                     memory_order = memory_order_seq_cst) const noexcept;

        T* fetch_add(difference_type, memory_order = memory_order_seq_cst) const noexcept;
        T* fetch_sub(difference_type, memory_order = memory_order_seq_cst) const noexcept;

        T* operator++(int) const noexcept;
        T* operator--(int) const noexcept;
        T* operator++() const noexcept;
        T* operator--() const noexcept;
        T* operator+=(difference_type) const noexcept;
        T* operator-=(difference_type) const noexcept;

        void wait(T*, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() const noexcept;
        void notify_all() const noexcept;
      };
    }

#### Class std::atomic_flag

    namespace std {
      struct atomic_flag {
        constexpr atomic_flag() noexcept;
        atomic_flag(const atomic_flag&) = delete;
        atomic_flag& operator=(const atomic_flag&) = delete;
        atomic_flag& operator=(const atomic_flag&) volatile = delete;

        bool test(memory_order = memory_order::seq_cst) const volatile noexcept;
        bool test(memory_order = memory_order::seq_cst) const noexcept;
        bool test_and_set(memory_order = memory_order::seq_cst) volatile noexcept;
        bool test_and_set(memory_order = memory_order::seq_cst) noexcept;
        void clear(memory_order = memory_order::seq_cst) volatile noexcept;
        void clear(memory_order = memory_order::seq_cst) noexcept;

        void wait(bool, memory_order = memory_order::seq_cst) const volatile noexcept;
        void wait(bool, memory_order = memory_order::seq_cst) const noexcept;
        void notify_one() volatile noexcept;
        void notify_one() noexcept;
        void notify_all() volatile noexcept;
        void notify_all() noexcept;
      };
    }

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/header/atomic&oldid=143442"