“不完整类型"在具有与类本身相同类型的成员的类中
我有一个类应该有同一个类的私有成员，例如:
I have a class that should have a private member of the same class, something like:
class A {
private:
A member;
}
但它告诉我成员是一个不完整的类型.为什么?如果我使用指针，它不会告诉我不完整的类型，但我宁愿不使用指针.任何帮助表示赞赏
But it tells me that member is an incomplete type. Why? It doesn't tell me incomplete type if I use a pointer, but I'd rather not use a pointer. Any help is appreciated
推荐答案
在你声明你的成员时，你还在定义 A 类，所以类型A 仍未定义.
At the time you declare your member, you are still defining the A class, so the type A is still undefined.
然而，当你写A*时，编译器已经知道A代表一个类名，所以指向A的指针"的类型是定义.这就是为什么您可以嵌入指向您正在定义的类型的指针的原因.
However, when you write A*, the compiler already knows that A stands for a class name, and so the type "pointer to A" is defined. That's why you can embed a pointer to the type your are defining.
同样的逻辑也适用于其他类型，所以如果你只写:
The same logic applies also for other types, so if you just write:
class Foo;
您声明了类 Foo，但您从未定义过它.你可以写:
You declare the class Foo, but you never define it. You can write:
Foo* foo;
但不是:
Foo foo;
另一方面，如果编译器允许递归定义，您希望类型 A 的内存结构是什么?
On another hand, what memory structure would you expect for your type A if the compiler allowed a recursive definition ?
但是，有时在逻辑上是有效的类型以某种方式引用同一类型的另一个实例.人们通常为此使用指针，甚至更好:智能指针(如 boost::shared_ptr)以避免必须处理手动删除.
However, its sometimes logically valid to have a type that somehow refer to another instance of the same type. People usually use pointers for that or even better: smart pointers (like boost::shared_ptr) to avoid having to deal with manual deletion.
类似于:
class A
{
private:
boost::shared_ptr<A> member;
};
相关文章