# Standard library header <atomic>

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This header is part of the atomic operations 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)

### Typedefs

std::atomic_bool | std::atomic<bool>
std::atomic_char | std::atomic<char>
std::atomic_schar | std::atomic<signed char>
std::atomic_uchar | std::atomic<unsigned char>
std::atomic_short | std::atomic<short>
std::atomic_ushort | std::atomic<unsigned short>
std::atomic_int | std::atomic<int>
std::atomic_uint | std::atomic<unsigned int>
std::atomic_long | std::atomic<long>
std::atomic_ulong | std::atomic<unsigned long>
std::atomic_llong | std::atomic<long long>
std::atomic_ullong | std::atomic<unsigned long long>
std::atomic_char16_t | std::atomic<char16_t>
std::atomic_char32_t | std::atomic<char32_t>
std::atomic_wchar_t | std::atomic<wchar_t>
std::atomic_int8_t | std::atomic<std::int8_t>
std::atomic_uint8_t | std::atomic<std::uint8_t>
std::atomic_int16_t | std::atomic<std::int16_t>
std::atomic_uint16_t | std::atomic<std::uint16_t>
std::atomic_int32_t | std::atomic<std::int32_t>
std::atomic_uint32_t | std::atomic<std::uint32_t>
std::atomic_int64_t | std::atomic<std::int64_t>
std::atomic_uint64_t | std::atomic<std::uint64_t>
std::atomic_int_least8_t | std::atomic<int_least8_t>
std::atomic_uint_least8_t | std::atomic<uint_least8_t>
std::atomic_int_least16_t | std::atomic<int_least16_t>
std::atomic_uint_least16_t | std::atomic<uint_least16_t>
std::atomic_int_least32_t | std::atomic<int_least32_t>
std::atomic_uint_least32_t | std::atomic<uint_least32_t>
std::atomic_int_least64_t | std::atomic<int_least64_t>
std::atomic_uint_least64_t | std::atomic<uint_least64_t>
std::atomic_int_fast8_t | std::atomic<int_fast8_t>
std::atomic_uint_fast8_t | std::atomic<uint_fast8_t>
std::atomic_int_fast16_t | std::atomic<int_fast16_t>
std::atomic_uint_fast16_t | std::atomic<uint_fast16_t>
std::atomic_int_fast32_t | std::atomic<int_fast32_t>
std::atomic_uint_fast32_t | std::atomic<uint_fast32_t>
std::atomic_int_fast64_t | std::atomic<int_fast64_t>
std::atomic_uint_fast64_t | std::atomic<uint_fast64_t>
std::atomic_intptr_t | std::atomic<intptr_t>
std::atomic_uintptr_t | std::atomic<uintptr_t>
std::atomic_size_t | std::atomic<size_t>
std::atomic_ptrdiff_t | std::atomic<ptrdiff_t>
std::atomic_intmax_t | std::atomic<intmax_t>
std::atomic_uintmax_t | std::atomic<uintmax_t>

### 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_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_init (C++11) | 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)

### Preprocessor macros

ATOMIC_VAR_INIT (C++11) | 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 {

        /* before C++17:

        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_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*>;

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

        // named typedefs
        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_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>;

        // 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_init(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
        template<class T>
        void atomic_init(atomic<T>*, typename atomic<T>::value_type) 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;

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

        // flag type and operations
        struct atomic_flag;

        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;

        #define ATOMIC_FLAG_INIT /*see description*/

        // fences
        extern "C" void atomic_thread_fence(memory_order) noexcept;
        extern "C" void atomic_signal_fence(memory_order) noexcept;

#### Class std::atomic

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

        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;
        void store(T, memory_order = memory_order_seq_cst) volatile noexcept;
        void store(T, memory_order = memory_order_seq_cst) 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;

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

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

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

        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;
        void store(/*integral*/,
                   memory_order = memory_order_seq_cst) volatile noexcept;
        void store(/*integral*/,
                   memory_order = memory_order_seq_cst) 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;

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

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

    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;
        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*/ 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;

        atomic() noexcept = default;
        constexpr atomic(/*floating-point*/) noexcept;

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

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

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

        bool is_lock_free() const volatile noexcept;
        bool is_lock_free() const noexcept;
        void store(T*, memory_order = memory_order_seq_cst) volatile noexcept;
        void store(T*, memory_order = memory_order_seq_cst) 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;

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

#### Class std::atomic_ref

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

        atomic_ref() = delete;
        atomic_ref& operator=(const atomic_ref&) = delete;

        explicit atomic_ref(T&);
        atomic_ref(const atomic_ref&) noexcept;

        T operator=(T) const noexcept;
        operator T() const noexcept;

        bool is_lock_free() const noexcept;
        void store(T, memory_order = memory_order_seq_cst) const noexcept;
        T load(memory_order = memory_order_seq_cst) 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;
    };

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

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

        atomic_ref() = delete;
        atomic_ref& operator=(const atomic_ref&) = delete;

        explicit atomic_ref(/*integral*/&);
        atomic_ref(const atomic_ref&) noexcept;

        /*integral*/ operator=(/*integral*/) const noexcept;
        operator /*integral*/() const noexcept;

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

    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 bool is_always_lock_free = /*implementation-defined*/;
        static constexpr size_t required_alignment = /*implementation-defined*/;

        atomic_ref() = delete;
        atomic_ref& operator=(const atomic_ref&) = delete;

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

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

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

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

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

        atomic_ref() = delete;
        atomic_ref& operator=(const atomic_ref&) = delete;

        explicit atomic_ref(T*&);
        atomic_ref(const atomic_ref&) noexcept;

        T* operator=(T*) const noexcept;
        operator T*() const noexcept;

        bool is_lock_free() const noexcept;
        void store(T*, memory_order = memory_order_seq_cst) const noexcept;
        T* load(memory_order = memory_order_seq_cst) 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;
    };

#### Class std::atomic_flag

    typedef struct atomic_flag {
        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;
        atomic_flag() noexcept = default;
        atomic_flag(const atomic_flag&) = delete;
        atomic_flag& operator=(const atomic_flag&) = delete;
        atomic_flag& operator=(const atomic_flag&) volatile = delete;
    } atomic_flag;

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