c++ - 如何访问类对象的每个实例的静态变量值

Question

#include <iostream>

using namespace std;

class Box {
   public:
      static int objectCount;
      // Constructor definition
      Box(double l = 2.0, double b = 2.0, double h = 2.0) {
         cout <<"Constructor called." << endl;
         length = l;
         breadth = b;
         height = h;
         // Increase every time object is created
         this->objectCount++;
      }

      double Volume() {
         return length * breadth * height;
      }

      static int getID()
      {
          return objectCount;
      }

   private:
      double length;     // Length of a box
      double breadth;    // Breadth of a box
      double height;     // Height of a box
};

// Initialize static member of class Box
int Box::objectCount = 0;

int main(void) {
   Box Box1(3.3, 1.2, 1.5);    // Declare box1
   Box Box2(8.5, 6.0, 2.0);    // Declare box2

   // Print total number of objects.
   cout << "Total objects: " << Box::objectCount << endl;
   cout << "Box1 ID: " << Box1.getID() << endl;
   cout << "Box2 ID: " << Box2.getID() << endl;

   return 0;
}

如何访问“Box1”和“Box2”的 objectCount。 “Box1”的 objectCount 应该为 1，而“Box2”仍为 2。例如

它打印:

Constructor called.
Constructor called.
Total objects: 2
Box1 ID: 2
Box2 ID: 2

代替:

Constructor called.
Constructor called.
Total objects: 2
Box1 ID: 1
Box2 ID: 2

Answer 1

类只有一个objectCount。根据定义，这就是 static 类成员。

您需要做的是向类中添加一个非静态成员，并在构造函数中对其进行初始化。

 static int objectCount;
 int my_objectCount;

  // Constructor definition
  Box(double l = 2.0, double b = 2.0, double h = 2.0)
     : my_objectCount(++objectCount)
  {
    // ...
  }

然后，对于类的第一个实例，my_objectCount 将为 1，对于第二个实例为 2，依此类推。