• By default, each member of one object is copied to its counterpart in the other object
• Called when two objects have been already exist
  • Object o1;
  • Object o2;
  • o2 = o1;

#ifndef V_H
#define V_H
class V
{
	private:
		int size;
	public:
		V(int s):size(s){}
		int getSize() const {return size;}
};
#endif

#include <iostream>
#include "V.h"

int main(int argc, char *argv[])
{
	V v(10);
	V v2(20);

	std::cout<<"Size: "<<v.getSize()<<" "<<v2.getSize()<<std::endl;

	v2 = v;
	std::cout<<"Size: "<<v.getSize()<<" "<<v2.getSize()<<std::endl;

	return 0;
}
			

//V.h
#ifndef V_H
#define V_H
class V
{
	private:
		int size;
		int *array;
	public:
		V(int s):size(s)
		{
			array = new int[size];
			for(int i = 0; i < size; i++)
				array[i] = 10*i;
		}

		int *getAddress() const {return array;}

		void display() const
		{
			for(int i = 0; i < size; i++)
				std::cout<<array[i]<<" ";
			std::cout<<std::endl;
		}

		~V()
		{
			delete [] array;
			array = 0;
			size = 0;
		}
};
#endif
			

#include <iostream>
#include "V.h"

int main(int argc, char *argv[])
{
	V *v = new V(10);
	V *v2 = new V(20);

	*v2 = *v;

	//both objects have same dynamic memory
	std::cout<<"Address: "<<v->getAddress()<<" "<<v2->getAddress()<<std::endl;

	v->display();
	v2->display();

	delete v;

	v2->display();

	return 0;
}
			

• Default assignmetn constructor does not work anymore, copy assignment cause two objects share the same memory

//g++ *.cpp -std=c++11
//V.h
#ifndef V_H
#define V_H
class V
{
	private:
		int size;
		int *array;
	public:
		//constructor
		V(int s):size(s)
		{
			array = new int[size];
			for(int i = 0; i < size; i++)
				array[i] = 10*i;
		}

		//copy constructor
		V(const V &right):size(right.size), array(size?new int[size]:nullptr)
		{
			std::cout<<"Copy Constructor ..."<<std::endl;
			std::copy(right.array, right.array+size, array);
			std::cout<<"End Constructor ..."<<std::endl;
		}

		int *getAddress() const {return array;}

		void display() const
		{
			for(int i = 0; i < size; i++)
				std::cout<<array[i]<<" ";
			std::cout<<std::endl;
		}

		//copy assignment
		const V & operator=(const V &right)//not calll copy constructor
		//const V operator=(const V &right)//calll copy constructor
		{
			std::cout<<"Copy Assignment ..."<<std::endl;
			delete [] array;//release the current memory
			array = new int[right.size];
			for(int i = 0; i < right.size; i++)
				array[i] = right.array[i];
			size = right.size;
			return *this;
		}

		~V()
		{
			std::cout<<"Destructor ..."<<std::endl;
			delete [] array;
			array = 0;
			size = 0;
		}
};
#endif

//main.cpp
#include <iostream>
#include "V.h"

int main(int argc, char *argv[])
{
	V *v = new V(10);
	V *v2 = new V(20);
	V *v3 = new V(30);

	*v3 = *v2 = *v;

	v->display();
	v2->display();
	v3->display();
	
	delete v;
	delete v2;
	delete v3;

	return 0;
}
			

#include <iostream>
#include "V.h"

V getObject()
{
	std::cout<<"Inside function ..."<<std::endl;
	V v(10);

	std::cout<<"Return from function ..."<<std::endl;
	return v;
}

int main(int argc, char *argv[])
{
	std::cout<<"Before calling function ..."<<std::endl;
	V v(20);
	v = getObject();
	std::cout<<"After calling function ..."<<std::endl;

	v.display();

	return 0;
}
			

//g++ *.cpp -std=c++11
#ifndef V_H
#define V_H
class V
{
	private:
		int size;
		int *array;
	public:
		//constructor
		V(int s):size(s)
		{
			std::cout<<"Constructor ..."<<std::endl;
			array = new int[size];
			for(int i = 0; i < size; i++)
				array[i] = 10*i;
		}

		//copy constructor
		V(const V &right):size(right.size), array(size?new int[size]:nullptr)
		{
			std::cout<<"Copy Constructor ..."<<std::endl;
			std::copy(right.array, right.array+size, array);
			std::cout<<"End Copy Constructor ..."<<std::endl;
		}

		int *getAddress() const {return array;}
		int getSize() const {return size;}

		void display() const
		{
			for(int i = 0; i < size; i++)
				std::cout<<array[i]<<" ";
			std::cout<<std::endl;
		}

		//copy assignment
		const V& operator=(const V &right)
		{
			std::cout<<"Copy Assignment ..."<<size<<std::endl;
			if (this != &right)//sef-assignment check
			{
				delete [] array;
				array = nullptr;

				//code duplication
				size = right.size;
				array = size?new int[size]:nullptr;
				std::copy(right.array, right.array+size, array);
			}
			std::cout<<"Return from Assignment ..."<<std::endl;
			return *this;
		}

		~V()
		{
			std::cout<<"Destructor ..."<<size<<std::endl;
			delete [] array;
			array = 0;
			size = 0;
		}
};
#endif
			

• Self-assignment check
• if new[size] fail, *this could have been modified; or copy only succesfully copied several elements and fail
• Stackoverflow
• cpluplus.com

#ifndef V_H
#define V_H
class V
{
	private:
		int size;
		int *array;
	public:
		//constructor
		V(int s):size(s)
		{
			std::cout<<"Constructor ..."<<std::endl;
			array = new int[size];
			for(int i = 0; i < size; i++)
				array[i] = 10*i;
		}

		//copy constructor
		V(const V &right):size(right.size), array(size?new int[size]:nullptr)
		{
			std::cout<<"Copy Constructor ..."<<std::endl;
			std::copy(right.array, right.array+size, array);
			std::cout<<"End Copy Constructor ..."<<std::endl;
		}

		int *getAddress() const {return array;}
		int getSize() const {return size;}

		void display() const
		{
			for(int i = 0; i < size; i++)
				std::cout<<array[i]<<" ";
			std::cout<<std::endl;
		}

		//copy assignment
		const V& operator=(const V &right)
		{
			std::cout<<"Copy Assignment -----------------------"<<size<<std::endl;
			V temp(right);
			std::swap(size, temp.size);
			std::swap(array, temp.array);
			std::cout<<"Ending Assignment ---------------------"<<std::endl;

			return *this;
		}

		~V()
		{
			std::cout<<"Destructor ..."<<size<<std::endl;
			delete [] array;
			array = 0;
			size = 0;
		}
};
#endif
			

• Starting out with C++, Tony Gaddis