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()