# Standard library header <stdatomic.h>

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This header was originally in the C standard library.

This header is part of the concurrency support library.

It is unspecified whether `<stdatomic.h>` provides any declarations in namespace `std`.

### Macros

_Atomic (C++23) | compatibility macro such that _Atomic(T) is identical to std::atomic <T> (function macro)
ATOMIC_FLAG_INIT (C++11) | initializes an std::atomic_flag to false (macro constant)

### Types

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)

### 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_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)

### Synopsis

    template<class T>
      using __std_atomic = std::atomic<T>;        // exposition only

    #define _Atomic(T) __std_atomic<T>

    #define ATOMIC_BOOL_LOCK_FREE /* see description */
    #define ATOMIC_CHAR_LOCK_FREE /* see description */
    #define ATOMIC_CHAR16_T_LOCK_FREE /* see description */
    #define ATOMIC_CHAR32_T_LOCK_FREE /* see description */
    #define ATOMIC_WCHAR_T_LOCK_FREE /* see description */
    #define ATOMIC_SHORT_LOCK_FREE /* see description */
    #define ATOMIC_INT_LOCK_FREE /* see description */
    #define ATOMIC_LONG_LOCK_FREE /* see description */
    #define ATOMIC_LLONG_LOCK_FREE /* see description */
    #define ATOMIC_POINTER_LOCK_FREE /* see description */

    using std::memory_order;                // see description
    using std::memory_order_relaxed;        // see description
    using std::memory_order_consume;        // see description
    using std::memory_order_acquire;        // see description
    using std::memory_order_release;        // see description
    using std::memory_order_acq_rel;        // see description
    using std::memory_order_seq_cst;        // see description

    using std::atomic_flag;                 // see description

    using std::atomic_bool;                 // see description
    using std::atomic_char;                 // see description
    using std::atomic_schar;                // see description
    using std::atomic_uchar;                // see description
    using std::atomic_short;                // see description
    using std::atomic_ushort;               // see description
    using std::atomic_int;                  // see description
    using std::atomic_uint;                 // see description
    using std::atomic_long;                 // see description
    using std::atomic_ulong;                // see description
    using std::atomic_llong;                // see description
    using std::atomic_ullong;               // see description
    using std::atomic_char8_t;              // see description
    using std::atomic_char16_t;             // see description
    using std::atomic_char32_t;             // see description
    using std::atomic_wchar_t;              // see description
    using std::atomic_int8_t;               // see description
    using std::atomic_uint8_t;              // see description
    using std::atomic_int16_t;              // see description
    using std::atomic_uint16_t;             // see description
    using std::atomic_int32_t;              // see description
    using std::atomic_uint32_t;             // see description
    using std::atomic_int64_t;              // see description
    using std::atomic_uint64_t;             // see description
    using std::atomic_int_least8_t;         // see description
    using std::atomic_uint_least8_t;        // see description
    using std::atomic_int_least16_t;        // see description
    using std::atomic_uint_least16_t;       // see description
    using std::atomic_int_least32_t;        // see description
    using std::atomic_uint_least32_t;       // see description
    using std::atomic_int_least64_t;        // see description
    using std::atomic_uint_least64_t;       // see description
    using std::atomic_int_fast8_t;          // see description
    using std::atomic_uint_fast8_t;         // see description
    using std::atomic_int_fast16_t;         // see description
    using std::atomic_uint_fast16_t;        // see description
    using std::atomic_int_fast32_t;         // see description
    using std::atomic_uint_fast32_t;        // see description
    using std::atomic_int_fast64_t;         // see description
    using std::atomic_uint_fast64_t;        // see description
    using std::atomic_intptr_t;             // see description
    using std::atomic_uintptr_t;            // see description
    using std::atomic_size_t;               // see description
    using std::atomic_ptrdiff_t;            // see description
    using std::atomic_intmax_t;             // see description
    using std::atomic_uintmax_t;            // see description

    using std::atomic_is_lock_free;                         // see description
    using std::atomic_load;                                 // see description
    using std::atomic_load_explicit;                        // see description
    using std::atomic_store;                                // see description
    using std::atomic_store_explicit;                       // see description
    using std::atomic_exchange;                             // see description
    using std::atomic_exchange_explicit;                    // see description
    using std::atomic_compare_exchange_strong;              // see description
    using std::atomic_compare_exchange_strong_explicit;     // see description
    using std::atomic_compare_exchange_weak;                // see description
    using std::atomic_compare_exchange_weak_explicit;       // see description
    using std::atomic_fetch_add;                            // see description
    using std::atomic_fetch_add_explicit;                   // see description
    using std::atomic_fetch_sub;                            // see description
    using std::atomic_fetch_sub_explicit;                   // see description
    using std::atomic_fetch_or;                             // see description
    using std::atomic_fetch_or_explicit;                    // see description
    using std::atomic_fetch_xor;                            // see description
    using std::atomic_fetch_xor_explicit;                   // see description
    using std::atomic_fetch_and;                            // see description
    using std::atomic_fetch_and_explicit;                   // see description
    using std::atomic_flag_test_and_set;                    // see description
    using std::atomic_flag_test_and_set_explicit;           // see description
    using std::atomic_flag_clear;                           // see description
    using std::atomic_flag_clear_explicit;                  // see description

    #define ATOMIC_FLAG_INIT /* see description */

    using std::atomic_thread_fence;                         // see description
    using std::atomic_signal_fence;                         // see description

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