What is deep copy constructor?

What is deep copy constructor?

Overriding default copy constructor with a constructor which copies all the members including all dynamically allocated members is called deep copy constructor.


Example:

#include <iostream>
#include <string>
#include <conio.h>
using namespace std;
  
class Student
{
public:
      Student(char* szName,int nAge)
      {
           m_szName =new char[20];
           strcpy(m_szName,szName);
           m_nAge=nAge;
      }
       Student(const Student &obj )
      {
           m_szName =new char[20];
           strcpy(m_szName,obj.m_szName);
           m_nAge=obj.m_nAge;
      }
      ~Student()
      {
           delete[] m_szName;
           m_szName=NULL;
           cout<<"Memory destroyed \r\n";
      };
      int m_nAge;
      char *m_szName;
};
  
int main()
{
     Student *ptr=new Student("John",12);
     cout<<"Name: "<<ptr->m_szName<<"\r\n"<<"Age: "<< ptr->m_nAge<<"\r\n";
     {
          Student obj( *ptr);
          cout<<"Name: "<<obj.m_szName<<"\r\n"<<"Age: "<< obj.m_nAge<<"\r\n";
          //obj scope ends and ~Student() will be called
     }
     cout<<"Name: "<<ptr->m_szName<<"\r\n"<<"Age: "<< ptr->m_nAge<<"\r\n";
     delete ptr;
     getch();
     return 0;
}

Result:

Name: John
Age: 12
Name: John
Age: 12
Memory destroyed
Name: John
Age: 12
Memory destroyed

What is shallow copy?

What is shallow copy?

Default copy constructor of compiler copies all the member variables
from source to destination object. This is called shallow copy
constructor.

Example:

#include <iostream>
#include <string>
#include <conio.h>
using namespace std;
class Student
{

public:
     Student(int nAge)
     {
          m_nAge=nAge;
     }               
     int m_nAge;     
};
int main()
{
     Student obj(13);
     cout<<"Age1: "<< obj.m_nAge<<"\r\n";     
     Student obj1(obj);
     cout<<"Age2: "<<obj1.m_nAge<<"\r\n";
     getch();
     return 0;
}

Result:
Age1: 13
Age2: 13

Example 2:

#include <iostream>
#include <string>
#include <conio.h>
using namespace std;
  
class Student
{
public:
      Student(char* szName,int nAge)
      {
           m_szName =new char[20];
           strcpy(m_szName,szName);
           m_nAge=nAge;
      }
      ~Student()
      {
           delete[] m_szName;
           m_szName=NULL;
           cout<<"Memory destroyed \r\n";
      };
      int m_nAge;
      char *m_szName;
};
  
int main()
{
     Student *ptr=new Student("John",12);
     cout<<"Name: "<<ptr->m_szName<<"\r\n"<<"Age: "<< ptr->m_nAge<<"\r\n";
     {
          Student obj( *ptr);
          cout<<"Name: "<<obj.m_szName<<"\r\n"<<"Age: "<< obj.m_nAge<<"\r\n";

          //obj scope ends and ~Student() will be called
     }
     //Will Crash here
     //because m_szName is already freed in destructor.
     // this is the problem with shallow copy
     cout<<"Name: "<<ptr->m_szName<<"\r\n"<<"Age: "<< ptr->m_nAge<<"\r\n";
     delete ptr;
     getch();
     return 0;
}

Result:

Crash!!!!!!!!!!!

What is copy constructor?

What is copy constructor?
In addition to providing a default constructor and a destructor, the compiler also provides a default copy constructor which is called each time a copy of an object is made. When a program passes an object by value, either into the function or as a function return value, a temporary copy of the object is made. This work is done by the copy constructor.

All copy constructors take one argument or parameter which is the reference to an object of the same class. The default copy constructor copies each data member from the object passed as a parameter to the data member of the new object.

Example:

#include <iostream>
#include <string>
#include <conio.h>
using namespace std;
class Student
{
public:

     Student()

     {
          cout << "Default constructor\r\n";          
     }

     Student(int nAge)

     {

          cout<<"Overloaded Constructor Called \r\n";     

          m_nAge=nAge;

     }     
     Student(Student &a)
     {
          cout << "Copy constructor\r\n";
          m_nAge = a.m_nAge;         
     }

     int m_nAge;     

};
int main()

{
     
     Student obj(13);
     cout<<"Age: "<< obj.m_nAge<<"\r\n";
    
     Student obj1(obj);
     cout<<"Age: "<<obj1.m_nAge<<"\r\n";

     
     getch();
     return 0;

}

Result:

Overloaded Constructor Called
Age: 13
Copy constructor
Age: 13