C++: Objects as Function arguments

Objects as Function arguments

Objects can also be passed as arguments to a member function just like any other data type of C++. Objects can also be passed in both ways

(1) Pass By Value

(2) Pass By Reference

Pass By Value

When an object is passed by value the function creates its own copy of the object and works on it . Therefore any changes made to the object inside the function do not affect the original object.

Illustration 14.9 C++ program to illustrate how the pass by value method work

we can assign one object to another object, Similar to structure object

#include <iostream>

using namespace std;

class Sample

{

private:

      int num;         

public:

      void set (int x)

      {

      num = x;

      }

void pass(Sample obj1, Sample obj2) //objects are passed

{

      obj1.num=100;        // value of the object is changed inside the function

      obj2.num=200;        // value of the object is changed inside the function

      cout<<"\n\n Changed value of object1 "<<obj1.num;

      cout<<"\n\n Changed value of object2 "<<obj2.num;

}

      void print( )

      {

           cout<<num;

      }

};

int main()

{

      //object declarations

      Sample s1;

      Sample s2;

      Sample s3;

      //assigning values to the data member of objects

      s1.set(10);

      s2.set(20);

      cout<<"\n\t\t Example program for pass by value\n\n\n"; //printing the values before passing the object

      cout<<"\n\nValue of object1 before passing";

      s1.print();

      cout<<"\n\nValue of object2 before passing ";

      s2.print();

      passing object s1 and s2

      s3.pass(s1,s2);

      //printing the values after returning to main

      cout<<"\n\nValue of object1 after passing ";

      s1.print();

      cout<<"\n\nValue of object2 after passing ";

      s2.print();

      return 0;

}

Output:

Example program for PASS BY VALUE

Value of object1 before passing 10

Value of object2 before passing 20

Changed value of object 1 100

Changed value of object 200

Value of object 1 after passing 10

Value of object 2 after passing 20

In the above program the objects s1,and s2 are passed to pass( ) method. They are copied to obj1 and obj2 respectively. The data member num’s value is changed inside the function. But it didn’t affected the s1 and s2 objects data member.

Pass By Reference

When an object is passed by reference , its memory address is passed to the function so the called function works directly on the original object used in the function call. So any changes made to the object inside the function definition are reflected in original object.

Illustration 14.10 C++ program to illustrate how the pass by reference method work

#include <iostream>

using namespace std;

class Sample

{

private:

      int num;

public:

void set (int x)

{

      num = x;

}

void pass(Sample &obj1, Sample &obj2) //objects are passed

{

      obj1.num=100;            // value of the object is changed inside the function

      obj2.num=200;            // value of the object is changed inside the function

      cout<<"\n\n Changed value of object1 "<<obj1.num;

      cout<<"\n\n Changed value of object2 "<<obj2.num;

}

      void print()

      {

           cout<<num;

      }

};

int main()

{

      clrscr();

      //object declarations

      Sample s1;

      Sample s2;

      Sample s3;

      //assigning values to the data member of objects

      s1.set(10);

      s2.set(20);

      cout<<"\n\t\t Example program for pass by reference\n\n\n";

      //printing the values before passing the object

      cout<<"\n\nValue of object1 before passing"; s1.print();

      cout<<"\n\nValue of object2 before passing "; s2.print();

      //passing object s1 and s2 s3.pass(s1,s2);

      //printing the values after returning to main

      cout<<"\n\nValue of object1 after passing "; s1.print();

      cout<<"\n\nValue of object2 after passing ";

      s2.print();

      return 0;

}

Output:

Example program for PASS BY REFERENCE

Value of object1 before passing10

Value of object 2 before passing 20

Changed value of object1 100

Changed value of object2 200

Value of object1 after passing 100

Value of object2 after passing 200

In the above program the objects s1,and s2 are passed as reference to pass( ) method. So obj1 and obj2 become reference(alias name) for s1 and s2 respectively. The data member num’s value is changed inside the function affected s1 and s2 objects data member.