C++ Tutorial/Operator Overloading/overload operator with friend

+ is overloaded using friend function

<source lang="cpp">#include <iostream> using namespace std; class Point {

 int x, y;

public:

 Point() {} // needed to construct temporaries
 Point(int px, int py) {
   x = px;
   y = py;
 }
 void show() {
   cout << x << " ";
   cout << y << "\n";
 }
 friend Point operator+(Point op1, Point op2); // now a friend
 Point operator-(Point op2);
 Point operator=(Point op2);
 Point operator++();

}; // Now, + is overloaded using friend function. Point operator+(Point op1, Point op2) {

 Point temp;
 temp.x = op1.x + op2.x;
 temp.y = op1.y + op2.y;
 return temp;

} // Overload - for Point. Point Point::operator-(Point op2) {

 Point temp;
 // notice order of operands
 temp.x = x - op2.x;
 temp.y = y - op2.y;
 return temp;

} // Overload assignment for Point. Point Point::operator=(Point op2) {

 x = op2.x;
 y = op2.y;
 return *this; // i.e., return object that generated call

} // Overload ++ for Point. Point Point::operator++() {

 x++;
 y++;
 return *this;

} int main() {

 Point ob1(10, 20), ob2( 5, 30);
 ob1 = ob1 + ob2;
 ob1.show();
 return 0;

}</source>

15 50

Make op-- a friend; use reference

<source lang="cpp">#include <iostream> using namespace std; class Point {

 int x, y;

public:

 Point() {}
 Point(int px, int py) {
   x = px;
   y = py;
 }
 void show() {
   cout << x << " ";
   cout << y << "\n";
 }
 Point operator=(Point op2);
 friend Point operator++(Point &op);
 friend Point operator--(Point &op);

}; // Overload assignment for Point. Point Point::operator=(Point op2) {

 x = op2.x;
 y = op2.y;
 return *this; // i.e., return object that generated call

} // Now a friend; use a reference parameter. Point operator++(Point &op) {

 op.x++;
 op.y++;
 return op;

} // Make op-- a friend; use reference. Point operator--(Point &op) {

 op.x--;
 op.y--;
 return op;

} int main() {

 Point ob1(10, 20), ob2;
 ob1.show();
 ++ob1;
 ob1.show(); // displays 11 21
 ob2 =  ++ob1;
 ob2.show(); // displays 12 22
 --ob2;
 ob2.show(); // displays 11 21
 return 0;

}</source>

10 20
11 21
12 22
11 21