Standard library header <atomic>

 

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Technical Specifications

 

Standard Library headers

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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_storeatomic_store_explicit (C++11)(C++11)	atomically replaces the value of the atomic object with a non-atomic argument (function template)
atomic_loadatomic_load_explicit (C++11)(C++11)	atomically obtains the value stored in an atomic object (function template)
atomic_exchangeatomic_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_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_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_addatomic_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_subatomic_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_andatomic_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_oratomic_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_xoratomic_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_setatomic_flag_test_and_set_explicit (C++11)(C++11)	atomically sets the flag to true and returns its previous value (function)
atomic_flag_clearatomic_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;