访问其他类中多个对象的私有成员向量 [英] Access private member vector of multiple objects in other class

问题描述

我有两个结构相似的类(A和B)，都包含一个结构向量.

I have two classes (A & B) with a similar structure, which both contain a vector of structs.

class A/B{
private: std::vector<DataStruct> vec_A/vec_B;
...
public:
...
}

要创建/更新B对象，我必须组合来自A类多个对象的矢量的数据(将矢量中的相似条目组合到对象B的矢量中的一个条目，然后在B中进行数据转换)

To create/update an object of B, I have to combine the data from the vectors of multiple objects of class A (combining similar entries in the vector into one entry in the vector of object B and do data transformations in B).

我该怎么做?

我的想法是:

• 让B类成为A的朋友.但是我听说，在C ++中成为类的朋友只是万不得已，应该避免.
• 在类A中编写一个 getVector()函数，该函数返回对Vector vec_A 的引用，以便类B可以对数据进行操作.对我来说，这似乎只是绕过了数据封装.将载体设置为公开有什么好处?
• 在类A中编写一个 getVector()函数，该函数返回 vec_A 的副本.但是由于 vec_A 并不是那么小，所以效率似乎很低(好，只有几kB.应该可以，但总的来说...)
• 为A类编写一个函数，该函数进行计算并创建B类的对象.然后将B的多个对象连接到B的一个最终对象中.但是，这似乎给我带来了很多开销.

• Making class B a friend of A. But I've heard, that making classes friends in C++ is only the last resort and should be avoided.
• Writing a getVector() function in class A, which returns a reference to the Vector vec_A, so that class B can operate on the data. For me this seems to simply bypass the data encapsulation. What would be the advantage to setting the vector to public?
• Writing a getVector() function in class A, which returns a copy of vec_A. But as vec_A is not that small, this seems to be inefficient (ok, only a few kB. Should work but in general...)
• Write a function for class A, which does the calculation and creates an object of class B. Then concatenate multiple objects of B into one final object of B. However, this seems to be a lot of overhead to me.

推荐答案

在类A中编写一个 getVector()函数，该函数返回一个引用到 Vector vec_A 上，以便B类可以对数据进行操作.为我这似乎只是绕过了数据封装.那会是什么将向量设置为公开有什么好处?

Writing a getVector() function in class A, which returns a reference to the Vector vec_A, so that class B can operate on the data. For me this seems to simply bypass the data encapsulation. What would be the advantage to setting the vector to public?

如果B只是需要观察 vec_A 的内容，请考虑返回一个 const 参考( const& ):

If B just needs to observe the content of vec_A, consider returning a const reference (const &):

class A {
 ...
  public:

    // Give read-only access to vec_A
    const std::vector<DataStruct> & getVector() const {
        return vec_A;
    }
};

我更喜欢这种解决方案，而不是仅仅公开矢量数据成员:使用访问器(getter/setter)，您可以更好地进行控制.例如，您可以实现只读访问(如上图所示).或者，如果您想提供设置器，还可以对输入参数进行一些检查，等等.

I prefer this solution to just making the vector data member public: with accessors (getter/setter) you have better control. For example you can implement a read-only access (like shown above). Or, if you want to provide a setter, you can also implement some checking on the input argument, etc.

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