公共嵌套类和普通类有什么区别吗？
假设我有：
class A {
public:
class B {
};
};
公共嵌套类和在其自己的 cpp 文件中定义的常规 B 类之间有什么区别，除了 A::B 必须在第一个选项中使用这一事实之外？
Let's say I have:
class A {
public:
class B {
};
};
Is there any difference between that public nested class and just a regular B class which is defined in its own cpp file, except for the fact that A::B must be used in the first option?
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本质上没有区别，只是
A::B是A的成员，因此拥有A私有成员的所有访问权限> 任何其他成员都会有的。There is essentially no difference, except that
A::Bis a member ofA, and so has all the access rights to private members ofAthat any other member would have.除了“B”的范围规则之外没有任何区别。使用“B”的客户端必须使用“A::”限定其范围。当您想要转发引用“B”时，嵌套“B”有时可能会出现问题，因为 C++ 编译器通常不允许您转发引用类中的类（但它允许您转发引用命名空间中的类）。
There isn't any difference other than the scoping rules for "B". Clients that use "B" must qualify its scope with "A::". Nesting the "B" can sometimes be problematic when you want to forward reference it, since C++ compilers typically do not allow you to forward reference a class within a class (it does allow you to forward reference a class within a namespace though).