联合

介绍联合类型的定义。

// Example is from POSIX
union sigval {
    int     sival_int;
    void   *sival_ptr;
};

引入*详细的类型说明符，*它指定以下名称是联合类型的名称。如果已经声明了联合名称，即使被其他名称隐藏也可以找到它。如果联合名称尚未声明，则为前向声明。

union foo; // elaborated type specifier -> forward declaration
class bar {
  public:
    bar(foo& f);
};
void baz();
union baz; // another elaborated type specifer; another forward declaration
           // note: the class has the same name as the function void baz()
union foo {
    long l;
    union baz* b; // elaborated type specifier refers to the class,
                  // not the function of the same name
};