C ++如何将对象移至nullptr [英] C++ how to move object to a nullptr

问题描述

我正在考虑一个奇怪的用例，我想将对象移至nullptr.也许我应该给一个代码片段:

I am thinking a strange use case where I want to move an object to a nullptr. Maybe I should give an code fragment:

class Objpair {
   public:
      Objpair(Obj&& a, Obj&&b) : first(&a), second(&b) { }
   private:
       Obj* first;
       Obj* second;
};

问题在于，当a和b超出范围时，第一个和第二个指针将悬空.如果我可以将Object a移到第一个指针上，那么就不会有双重释放和作用域问题.如果首先将成员声明为Obj而不是Obj *指针，则直接的first(std :: move(a))将完成此工作.我在这里一定做错了.我正在考虑移动而不是复制，因为我试图将控制权从另一个对象转移到当前对象，并提高性能.

The problem is that when a and b is out of scope, the first and second pointer will be dangling. If I can move Object a onto the first pointer then there should be no problem of double free and scoping issues. If the member first were declared as Obj not Obj* pointer, then the straight first(std::move(a)) would do the job. I must be doing something wrong here. I am thinking of move instead of copying because I am trying to transfer of control from another object to the current object and improve on performance.

使用指针版本是因为我正在考虑成员对象的多态行为.

The pointer version is used because I am thinking about polymorphic behavior for the member object.

推荐答案

您可以做的是从您的参数中移动构造对象，如下所示:

What you can do is move construct objects from your parameters like this:

class Objpair {
   public:
      Objpair(Obj&& a, Obj&& b)
      : first(new Obj(std::move(a)))
      , second(new Obj(std::move(b)))
      {}

   private:
       Obj* first;
       Obj* second;
};

我建议您使用 std :: unique_ptr :

class Objpair {
   public:
      Objpair(Obj&& a, Obj&& b)
      : first(std::make_unique<Obj>(std::move(a)))
      , second(std::make_unique<Obj>(std::move(b)))
      {}

   private:
       std::unique_ptr<Obj> first;
       std::unique_ptr<Obj> second;
};

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