C++11 并發指南六( <atomic> 類型詳解二 std::atomic ) 介紹了基本的原子類型 std::atomic 的用法，本節我會給大家介紹C++11 標準庫中的 std::atomic 針對整形(integral)和指針類型的特化版本做了哪些改進。

總地來說，C++11 標準庫中的 std::atomic 針對整形(integral)和指針類型的特化版本新增了一些算術運算和邏輯運算操作。具體如下：

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integral fetch_add(integral, memory_order = memory_order_seq_cst)volatile; integral fetch_add(integral, memory_order = memory_order_seq_cst); integral fetch_sub(integral, memory_order = memory_order_seq_cst)volatile; integral fetch_sub(integral, memory_order = memory_order_seq_cst); integral fetch_and(integral, memory_order = memory_order_seq_cst)volatile; integral fetch_and(integral, memory_order = memory_order_seq_cst); integral fetch_or(integral, memory_order = memory_order_seq_cst)volatile; integral fetch_or(integral, memory_order = memory_order_seq_cst); integral fetch_xor(integral, memory_order = memory_order_seq_cst)volatile; integral fetch_xor(integral, memory_order = memory_order_seq_cst); integral operator++(int)volatile; integral operator++(int); integral operator--(int)volatile; integral operator--(int); integral operator++()volatile; integral operator++(); integral operator--()volatile; integral operator--(); integral operator+=(integral)volatile; integral operator+=(integral); integral operator-=(integral)volatile; integral operator-=(integral); integral operator&=(integral)volatile; integral operator&=(integral); integral operator|=(integral)volatile; integral operator|=(integral); integral operator^=(integral)volatile; integral operator^=(integral);

?下面我們來簡單介紹以上的 std::atomic 特化版本的成員函數。

fetch_add if T is integral (1)if T is pointer (2)

T fetch_add (T val, memory_order sync = memory_order_seq_cst) volatile noexcept; T fetch_add (T val, memory_order sync = memory_order_seq_cst) noexcept;

T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) volatile noexcept; T fetch_add (ptrdiff_t val, memory_order sync = memory_order_seq_cst) noexcept;

將原子對象的封裝值加 val，并返回原子對象的舊值（適用于整形和指針類型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序： Memory Order 值Memory Order 類型

memory_order_relaxed	Relaxed
memory_order_consume	Consume
memory_order_acquire	Acquire
memory_order_release	Release
memory_order_acq_rel	Acquire/Release
memory_order_seq_cst	Sequentially consistent

另外，如果第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_add 相當與 std::atomic::operator+=。 fetch_sub if T is integral (1)if T is pointer (2)

T fetch_sub (T val, memory_order sync = memory_order_seq_cst) volatile noexcept; T fetch_sub (T val, memory_order sync = memory_order_seq_cst) noexcept;

T fetch_sub (ptrdiff_t val, memory_order sync = memory_order_seq_cst) volatile noexcept; T fetch_sub (ptrdiff_t val, memory_order sync = memory_order_seq_cst) noexcept;

將原子對象的封裝值減 val，并返回原子對象的舊值（適用于整形和指針類型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序： Memory Order 值Memory Order 類型

memory_order_relaxed	Relaxed
memory_order_consume	Consume
memory_order_acquire	Acquire
memory_order_release	Release
memory_order_acq_rel	Acquire/Release
memory_order_seq_cst	Sequentially consistent

另外，如果第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_sub 相當與 std::atomic::operator-=。 fetch_and ?

T fetch_and (T val, memory_order sync = memory_order_seq_cst)volatile noexcept; T fetch_and (T val, memory_order sync = memory_order_seq_cst)noexcept;

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將原子對象的封裝值按位與 val，并返回原子對象的舊值（只適用于整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序： Memory Order 值Memory Order 類型

memory_order_relaxed	Relaxed
memory_order_consume	Consume
memory_order_acquire	Acquire
memory_order_release	Release
memory_order_acq_rel	Acquire/Release
memory_order_seq_cst	Sequentially consistent

另外，如果第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_add 相當與 std::atomic::operator&=。 fetch_or ?

T fetch_or (T val, memory_order sync = memory_order_seq_cst)volatile noexcept; T fetch_or (T val, memory_order sync = memory_order_seq_cst)noexcept;

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將原子對象的封裝值按位或 val，并返回原子對象的舊值（只適用于整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序： Memory Order 值Memory Order 類型

memory_order_relaxed	Relaxed
memory_order_consume	Consume
memory_order_acquire	Acquire
memory_order_release	Release
memory_order_acq_rel	Acquire/Release
memory_order_seq_cst	Sequentially consistent

另外，如果第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_or 相當與 std::atomic::operator|=。 fetch_xor ?

T fetch_xor (T val, memory_order sync = memory_order_seq_cst)volatile noexcept; T fetch_xor (T val, memory_order sync = memory_order_seq_cst)noexcept;

將原子對象的封裝值按位異或 val，并返回原子對象的舊值（只適用于整型的 std::atomic 特化版本），整個過程是原子的。sync 參數指定內存序： Memory Order 值Memory Order 類型

memory_order_relaxed	Relaxed
memory_order_consume	Consume
memory_order_acquire	Acquire
memory_order_release	Release
memory_order_acq_rel	Acquire/Release
memory_order_seq_cst	Sequentially consistent

另外，如果第二個參數不指定（取默認參數 memory_order_seq_cst），則 fetch_xor 相當與 std::atomic::operator^=。 operator++ pre-increment (1)post-increment (2)

T operator++() volatile noexcept; T operator++() noexcept;

T operator++ (int) volatile noexcept; T operator++ (int) noexcept;

自增運算符重載， 第一種形式 (1) 返回自增后的值（即前綴++），第二種形式(2) 返回自增前的值（即后綴++），適用于整形和指針類型的 std::atomic 特化版本。 operator--自減運算符重載， 第一種形式 (1) 返回自減后的值（即前綴--），第二種形式(2) 返回自減前的值（即后綴--），適用于整形和指針類型的 std::atomic 特化版本。 atomic::operator (comp. assign.)復合賦值運算符重載，主要包含以下形式：
if T is integral (1)if T is pointer (2)

T operator+= (T val) volatile noexcept; T operator+= (T val) noexcept; T operator-= (T val) volatile noexcept; T operator-= (T val) noexcept; T operator&= (T val) volatile noexcept; T operator&= (T val) noexcept; T operator|= (T val) volatile noexcept; T operator|= (T val) noexcept; T operator^= (T val) volatile noexcept; T operator^= (T val) noexcept;

T operator+= (ptrdiff_t val) volatile noexcept; T operator+= (ptrdiff_t val) noexcept; T operator-= (ptrdiff_t val) volatile noexcept; T operator-= (ptrdiff_t val) noexcept;

以上各個 operator 都會有對應的 fetch_* 操作，詳細見下表：

操作符成員函數支持類型復合賦值等價于整型指針類型其他類型

+	atomic::operator+=	atomic::fetch_add	是	是	否
-	atomic::operator-=	atomic::fetch_sub	是	是	否
&	atomic::operator&=	atomic::fetch_and	是	否	否
|	atomic::operator|=	atomic::fetch_or	是	否	否
^	atomic::operator^=	atomic::fetch_xor	是	否	否

好了，本節先介紹這里，下一節我會介紹 C++11 中 C 風格的原子操作 API。

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