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网上看了很多说明，还是处于半知半解的状态，看了下面这个例子才算是明白了

this

指针

#include <iostream>
 
using namespace std;

class Box {
   public:
      // 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;
      }
      double Volume() {
         return length * breadth * height;
      }
      int compare(Box box) {
         return this->Volume() > box.Volume();
      }
      
   private:
      double length;     // Length of a box
      double breadth;    // Breadth of a box
      double height;     // Height of a box
};

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

   if(Box1.compare(Box2)) {
      cout << "Box2 is smaller than Box1" <<endl;
   } else {
      cout << "Box2 is equal to or larger than Box1" <<endl;
   }
   
   return 0;
}

Constructor called.
Constructor called.
Box2 is equal to or larger than Box1
[Finished in 1.9s]

说明：

表达式

Box1.compare(Box2)

，

Box1

调用了

compare

函数，

compare

函数中的

this

指针此时指向的是

Box1

，因此

compare

函数中的表达式

return this->Volume() > box.Volume()

变成了

return Box1->Volume() > box.Volume()


以上例子也可以写成指针的形式，如下

#include <iostream>
 
using namespace std;

class Box {
   public:
      // 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;
      }
      double Volume() {
         return length * breadth * height;
      }
      int compare(Box box) {
         return this->Volume() > box.Volume();
      }
      
   private:
      double length;     // Length of a box
      double breadth;    // Breadth of a box
      double height;     // Height of a box
};

int main(void) {
   Box *b1 = new Box(3.3, 1.2, 1.5);    // Declare b1
   Box *b2 = new Box(8.5, 6.0, 2.0);    // Declare b2

   if(b1 ->compare(*b2)) {
      cout << "b2 is smaller than b1" <<endl;
   } else {
      cout << "b2 is equal to or larger than b1" <<endl;
   }
   
   return 0;
}