3.1 原子 C 类型的大小和对齐
下表显示了原子数据类型及其表示方法。 对齐（align 列）以字节为单位。
表 7 原子 C 类型的大小和对齐
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整型
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_Atomic _Bool
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1
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1
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1
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1
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1
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1
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1
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1
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_Atomic char
_Atomic signed char
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1
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1
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1
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1
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1
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1
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1
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1
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_Atomic unsigned char
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1
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1
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1
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1
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1
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1
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1
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1
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_Atomic short
_Atomic signed short
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2
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2
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2
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2
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2
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2
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2
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2
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_Atomic unsigned short
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2
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2
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2
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2
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2
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2
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2
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2
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_Atomic int
_Atomic signed int
_Atomic enum
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4
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4
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4
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4
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4
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4
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4
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4
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_Atomic unsigned int
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4
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4
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4
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4
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4
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4
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4
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4
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_Atomic long
_Atomic signed long
_Atomic unsigned long
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8
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8
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4
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4
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8
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8
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4
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4
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_Atomic long long
_Atomic signed long long
_Atomic unsigned long long
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8
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8
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8
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8
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8
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8
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8
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8
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指针
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any-type _Atomic *
_Atomic( any-type (*) () )
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8
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8
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4
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4
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8
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8
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4
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4
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浮点
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_Atomic float
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4
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4
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4
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4
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4
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4
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4
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4
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_Atomic double
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8
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8
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8
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8
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8
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8
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8
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8
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_Atomic long double
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16
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16
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12
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4
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16
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16
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16
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8
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复数
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_Atomic float _Complex
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8
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8
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8
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8
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8
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8
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8
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8
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_Atomic double _Complex
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16
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16
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16
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16
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16
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16
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16
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8
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_Atomic long double _Complex
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32
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16
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24
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4
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32
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16
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32
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8
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虚数
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_Atomic float _Imaginary
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4
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4
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4
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4
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4
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4
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4
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4
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_Atomic double _Imaginary
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8
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8
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8
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8
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8
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8
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8
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8
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_Atomic long double _Imaginary
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16
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16
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12
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4
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16
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16
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16
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8
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结构（有选择性的示例）
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_Atomic struct {char a[2];}
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2
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2
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2
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2
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2
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2
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2
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2
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_Atomic struct {short a[2];}
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4
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4
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4
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4
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4
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4
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4
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4
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_Atomic struct {int a[2];}
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8
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8
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8
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8
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8
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8
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8
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8
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_Atomic struct {char a[16];}
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16
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16
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16
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16
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16
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16
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16
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8
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原子 struct 类型的一般对齐规则如下：如果 struct 类型的大小为 2、4、8 或 16 之一，且对应非原子类型的对齐小于该大小，则增大原子 struct 类型的对齐以便与该大小匹配。
位字段不允许原子类型。