老师这里我不太明白，我写出来了

就是这个*this = obj;
这一句是不是说把obj的值给现在这个实例，按照道理他们不是应该是一样的嘛，为啥加上这句就不行了

#include <iostream>

using namespace std;

class Test{
public:
   Test(int size){
       cout << "Test(int size)" << endl;
       data = new int[size];
        
   }
   Test(const Test &obj){
       cout << "Test(const Test obj)" << endl;
       if(obj.data){

      
       
       int size=sizeof(obj.data)/sizeof(obj.data[0])+1;
       
       this->data=new int[size];
      // cout << data << endl;
       //this->data=obj.data;
       for(int i=0; i<size; i++){
           this->data[i]=obj.data[i];
       }
       
       
       
       //*this = obj;


    }else {
        this->data=NULL;
    }
   }
   
   ~Test(void){
       cout << "~Test()" << endl;
      // cout << data << endl;
       if(data!=NULL) {
        delete [] data;
       }
       
   }
   
private:
   int *data;
};

Test function(Test obj)
{
   Test tmp = obj;
   return tmp;
}

int main(void)
{
   Test obj1(3);
   Test obj2 = function(obj1);
   
   return 0;
}