Operator overloading:-

  • Operator overloading is a syntactic sugar.
  • It is the type of compile time polymorphism.
  • Overloaded operators are used for class objects or other data members other than basic data types.
  • When we overload an operator we do not have to call explicitly that overloaded function.
  • It is a rule that,

1)    Do not change the meaning of previously defined operator (but we can change the meaning).

2)    Do not change precedence and associatively of that operator.

  • We can provide an overloaded function of an operator as a member function or a friend function.

e.g.

class demo

{

public:

int i;

int operator +(demo &d)

{

return i+d.i;

}

demo d1,d2;

int no;

no = d1 + d2;

d1.+(d2);

int operator -(demo &d)

{

return i-d.i;

}

int operator *(demo &d)

{

return i*d.i;

}

int operator /(demo &d)

{

return i/d.i;

}

};

int main()

{

demo d1;

demo d2;

cout<<d1+d2;

cout<<d1-d2;

cout<<d1*d2;

cout<<d1/d2;

}

  • In operator overloading,

d1+d2 is replaced as

d1.+(d2);

  • In this, ‘+’ operator, 1st operand is considered as a caller object and 2nd operand is considered as a parameter.

d1-d2 is replaced as

d1.-(d2);

d1*d2 is replaced as

d1.*(d2);

d1/d2 is replaced as

d1./(d2);

  • When to provide an operator overloaded function as friend function:

1)    In case of binary operator, if both the operands are of different class object then provide a friend function.

e.g.

class A;

class B

{

public:

int i;

A()

{

i=10;

}

friend int operator +(A &a,B &b);

friend int operator +(A &b,B &a);

};

class A

{

public:

int j;

B()

{

j=20;

}

friend int operator +(A &a,B &b);

friend int operator +(A &b,B &a);

};

int operator +(A &a,B &b)

{

return a.i+b.j;

}

int operator +(B &b, A &a)

{

return b.j+a.i;

}

int main()

{

A a;

B b;

cout<<a+b;

cout<<b+a;

}

  • Provide a definition for overloaded operator ‘+’ which accepting object of a same class.

e.g.

int operator +(A &a1,A &a2)

{

return a1.j+a2.j;

}

int operator +(B &b1,B &b2)

{

return b1.i+b2.i;

}

Operator Overloading

2)    In case of a binary operator if the 1st operand is not a type of an object (it is not an invoker) in that case we have to provide a friend function.

e.g.

class demo

{

public:

int i,j;

demo()

{

i=10;

j=20;

}

friend int operator +(int x,demo &d);

};

int operator +(int x,demo d)

{

return x+d.i+d.j;

}

int main()

{

demo d;

cout<<2+d;

return 0;

}

  • If we want to provide a definition d+7 then we can provide operator overloaded function as a member function, because, in this case an invoker is of an object type.
  • Definition for that member function is,

int operator +(int x)

{

return x+i+j;

}

Overloading of increment and decrement operator:-

  • Overloading for this operator is different than normal overloading.
  • Because, both the increment and decrement operator can be worked as pre and post.
  • Due to which we have to write a function which distinguishes difference between pre-increment and post-increment or pre decrement and post-decrement.
  • To provide this function, the compiler provides a different mechanism like a hidden argument which is not passed by the caller but which is used for distinguishing between pre and post operator.

e.g.

class demo

{

public;

int i;

demo()

{

i=10;

}

friend int operator ++(demo &d); // pre-increment

friend int operator ++(demo &d,int dummy); // post-increment

friend int operator –(demo &d); // pre-decrement

friend int operator –(demo &d,int dummy); // post-decrement

};

int operator ++(demo &d)

{

d.i++;

return d.i;

} // this is for pre-increment

int operator ++(demo &d,int dummy)

{

int temp;

temp=d.i;

d.i++;

return temp;

} // this is for post-increment

demo operator ++(demo &d,int dummy)

{

demo temp;

temp.i=d.i;

d.i++;

return temp;

} // this is for post-increment

int operator –(demo &d)

{

return d.i;

}

int operator –(demo &d,int dummy)

{

int no=d.i;

d.i–;

return no;

}

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Written by Sourabh Bhunje

Sourabh Bhunje, B.E. IT from Pune University. Currently Working at Techliebe. Professional Skills: Programming - Software & Mobile, Web & Graphic Design, Localization, Content Writing, Sub-Titling etc. http://techliebe.com/about-us

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