c++ - 访问类 obj 的私有(private)数据

Question

这是代码，其中函数 operator+ 重载正在使用 . 运算符访问类的私有(private)成员。这有效吗？实际上我的问题是使用. operator .他们可以用来直接访问私有(private)成员吗？

   #include <iostream>
using namespace std;

class Box
{
   public:

      double getVolume(void)
      {
         return length * breadth * height;
      }
        void setLength( double len )
      {
          length = len;
      }

      void setBreadth( double bre )
      {
           breadth = bre;
      }

      void setHeight( double hei )
      {
      height = hei;
      }
                        // Overload + operator to add two Box objects.
  Box operator+(const Box& b)
      {
         Box box;
         box.length = this->length + b.length;     //These are my problem
         box.breadth = this->breadth + b.breadth;  //These are my problem
         box.height = this->height + b.height;     //These are my problem
         return box;
      }
   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};
// Main function for the program
int main( )
{
   Box Box1;                // Declare Box1 of type Box
   Box Box2;                // Declare Box2 of type Box
   Box Box3;                // Declare Box3 of type Box
   double volume = 0.0;     // Store the volume of a box here

   // box 1 specification
   Box1.setLength(6.0); 
   Box1.setBreadth(7.0); 
   Box1.setHeight(5.0);

   // box 2 specification
   Box2.setLength(12.0); 
   Box2.setBreadth(13.0); 
   Box2.setHeight(10.0);

   // volume of box 1
   volume = Box1.getVolume();
   cout << "Volume of Box1 : " << volume <<endl;

   // volume of box 2
    volume = Box2.getVolume();
    cout << "Volume of Box2 : " << volume <<endl;

   // Add two object as follows:
   Box3 = Box1 + Box2;

   // volume of box 3
   volume = Box3.getVolume();
   cout << "Volume of Box3 : " << volume <<endl;

   return 0;
    }

我不明白函数运算符重载如何使用 . 运算符来访问私有(private)成员。我了解到只有成员函数才能访问类的私有(private)成员。它们不是直接访问的accessible , 比那个函数如何访问它？谢谢你。

Answer 1

因为他们是同一类型，所以他们是天然的 friend 。

C++ 允许 friend 访问另一个类的私有(private)方法和属性。

参见 here了解更多信息。