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这段代码在C下面可以直接写B1 B2 B3, 但是在C++下，不允许白字直接访问，必须放在对应的namespace里，但对应的namespace是什么呢？
struct A { int X; union { struct B { enum { B1, B2, B3 } ABCD; }v2; } v; };
业精于勤，荒于嬉;行成于思，毁于随。
A:：B::B1A:：B::B2A:：B::B3
int main(){
A::B::ABCD dd = A:：B::B1; return 0;
}
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
A:：B::B1
A:：B::B2
A:：B::B3
int main()
{
}