您只需要使 B 模板：

template <typename T>
class B {
    A<T>* a;
public:
    B(A<T>* ar) : a(ar) {}
};

这是基于共享指针的问题。作为读者，我尚不清楚 B 是否取决于外部的 A * 所有权，或者如果 A< * 的所有权也正在转移到 B< T> 。 C ++ 11为您提供了一些共享指针的出色工具，我强烈建议您利用它们。

This runs upon the problem of shared pointers. It's unclear to me as the reader if B<T> will depend upon an A<T>* that is externally owned, or if the ownership of A<T>* is also being transfered to B<T>. C++11 has provided you some great tools for sharing pointers, and I'd strongly recommend that you take advantage of them.

如果要共享 A&T; * ，但它将使用 shared_ptr 。

如果您转让 A< T> * 的所有权>在构造上，请使用 unique_ptr 。

If you want to share A<T>* but it will be owned externally use a shared_ptr.
If you transferring ownership of A<T>* on construction, signify that by using a unique_ptr.

编辑：

B< T> 包含成员对象 A< T> 。但是它是由指针持有的。 通过指针或引用持有成员表示对象的使用是共享的，或者所有权是外部的。

B<T> contains a member object A<T>. But it is held by pointer. Holding a member by pointer or reference indicates that the objects use is shared or ownership is external.

在不知道您的设计的情况下，很难展示好的设计原则，因此我在这里给出一些可选的情况，并建议您遵循与您的情况相符的建议：

Without knowing your design it's hard to present a good design principle, so I'll give some optional situations here with the recommendation that you adhere to the one that matches your situation:

1. 如果 B< T> 的 A< T> 成员仅在单个 B&lt ; T> 对象，该成员需要在 B< T> 的构造函数或Emplace构建的内部创建


2. 如果 all之间共享 B 的 A< code>成员 B< T> 它应该是 B 类的静态成员


3. 如果 A< 将由 B< T> 拥有，但只能由指针使用来接收 unique_ptr< A< T>> c而不是 A< T> * 作为成员类型i>

4. 如果 A&T; 将在外部共享并且不会被删除，只要至少保留了对其的一个引用，请使用 shared_ptr< A< T>> 而不是 A&T; * 作为成员类型


5. 如果 A< T> 是外部拥有的，并且可能已被销毁或未被销毁，请使用 weak_ptr< A< T>> 而不是 A< T ** 作为成员类型

1. If B<T>'s A<T> member is only used within the single B<T> object, that member needs to be created within B<T>'s constructor or emplace constructed
2. If B<T>'s A<T> member is shared among all B<T> it should be a static member of the B class
3. If A<T> will be owned by B<T> but may only be received by pointer use a unique_ptr<A<T>> rather than A<T>* as the member type
4. If A<T> will be shared externally and will not be deleted as long as at least one reference to it is maintained use use shared_ptr<A<T>> rather than A<T>* as the member type
5. If A<T> is owned externally and may or may not have been destroyed use weak_ptr<A<T>> rather than A<T>* as the member type