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Union declaration

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C++
 
C + +语言
大会的主题
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General topics
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流量控制
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Flow control
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条件执行语句
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Conditional execution statements
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迭代语句
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Iteration statements
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跳转语句
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Jump statements
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功能
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Functions
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函数声明
lambda函数的声明
函数模板
的历史。内嵌说明
异常规范 （过时了）
noexcept说明 （C++11）
例外
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Exceptions
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命名空间
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Namespaces
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类型
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Types
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联合类型
函数类型
decltype specifier （C++11）
规范
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Specifiers
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CV符
存储时间说明符
constexpr说明 （C++11）
汽车符 （C++11）
alignas说明 （C++11）
初始化
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Initialization
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常
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Literals
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布尔文字
nullptr （C++11）
用户定义的 （C++11）
表达式
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Expressions
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另一种表示形式
实用工具
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Utilities
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类型
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Types
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typedef declaration
声明类型别名 （C++11）
属性 （C++11）
施放
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Casts
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隐式转换
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-风格和功能转换
内存分配
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Memory allocation
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类
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Classes
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类特定的功能特性
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Class-specific function properties
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虚函数
覆盖说明 （C++11）
最后说明 （C++11）
明确的 （C++11）
静态的
特殊的成员函数
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Special member functions
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模板
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Templates
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类模板
函数模板
模板特化
参数包 （C++11）
杂项
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Miscellaneous
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内联汇编
 
本节是不完整的
原因: Expand description and example
工会是一类特殊类型的存储的所有数据成员在相同的内存位置.
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A union is a special class type that stores all of its data members in the same memory location.
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工会不能有虚函数，继承或继承其他类.
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Unions cannot have virtual functions, be inherited or inherit other classes.
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（至 C++11），工会只能包含POD（普通的旧数据）类型.
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（至 C++11） Unions can only contain POD（普通的旧数据） types.
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（C++11 起）如果一个union中包含一个非POD的成员，其中有一个用户定义的特殊功能，该功能是默认情况下，在工会中删除，并需要明确定义的用户（构造函数，析构函数，拷贝构造函数或复制赋值）.
Original:
（C++11 起） If a union contains a non-POD member, which has a user-defined special function (constructor, destructor, copy constructor or copy assignment) that function is deleted by default in the union and needs to be defined explicitly by the user.
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目录

[编辑] 语法

union name { member_declarations } object_list （可选的） ; (1)
union { member_declarations } ; (2)

[编辑] 解释

＃命名的工会
Original:
#Named union
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＃无名氏工会
Original:
#Anonymous union
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[编辑] 匿名工会

一个匿名的工会成员从封闭的范围作为单一变量.
Original:
Members of an anonymous union are accessible from the enclosing scope as single variables.
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匿名工会有进一步的限制：他们必须有唯一的公共成员，不能有成员函数.
Original:
Anonymous unions have further restrictions: they must have only public members and cannot have member functions.
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命名空间的匿名工会必须是静态的.....
Original:
Namespace-scope anonymous unions must be static.
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[编辑] 为例

union foo
{
  int x;
  signed char y;
};
 
int main()
{
  foo.x = 128 + 896;
  std::cout << "as int: "  << (int)foo.x << '\n';
  std::cout << "as char: " << (int)foo.y << '\n';
  return 0;
}

Output: 

as int: 1024
as char: 128
（little-endian处理器）
Original:
(for little-endian processors)
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来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/language/union&oldid=28560”