This pointer, shallow and deep copy

This pointer

• this pointer holds the address of the current object.
• In simple words, you can say that this pointer points to the current object of the class.
• This pointer is accessible within non-static member functions of a class. Static member functions do not have a this pointer.

This pointer can be used to,

• refer to a current class instance variable.
• pass the current object as a parameter to another method.
• declare indexers.

Example:

class mobile
{
    string model;
    int year_of_manufacture;

public:
    void set_details(string model, int year_of_manufacture)
    {
        this->model = model;
        this->year_of_manufacture = year_of_manufacture;
    }
    void print()
    {
        cout << this->model << endl;
        cout << this->year_of_manufacture << endl;
    }
};

int main()
{
    mobile redmi;
    redmi.set_details("Note 7 Pro", 2019);
    redmi.print();
}

// Output:
// Note 7 Pro
// 2019

---

Shallow copy

• An object is created by simply copying the data of all variables of the original object.
• Both objects will reference the exact memory location, then change made by one will reflect those change in another object as well.
• Default copy constructor is a shallow copy constructor.
• It is not recommended to use shallow copy.

• A shallow copy can be made by simply copying the reference.

  class students()
  {
      int age;
      char* names; // names is a pointer to a char array
  
  public:
      students(int age, char* names)
      {
          this->age = age;
          // shallow copy
          this->names = names;
          // here we are putting the same array.
          // we are just copying the reference
      }
  };
  

Deep copy

• A deep copy is a copy of an object in which the copied object is completely independent of the original object.
• Separate memory is allocated for the copied object. So changes made in any object will not affect the other object.
• An object is created by copying all the fields, and it also allocates similar memory resources with the same value to the object.

• To perform Deep copy, we need to** explicitly define the copy constructor** and assign dynamic memory as well if required. Also, it is necessary to allocate memory to the other constructors’ variables dynamically.

  class student()
  {
      int age;
      char* names;
  
  public:
      student(int age, char* names)
      {
          this->age = age; // deep copy
          this->names = new char[strlen(names) + 1];
          strcopy(this->names, names);
          // Created new array and copied data
      }
  };
  

Interview questions

• Interview questions

Resources

• Codestudio - This pointer, shallow and deep copy