Object-Oriented Programming In C++: Operator Overloading

Submitted by PhoeniciansSy on Tuesday, September 23, 2014 - 10:40.

1. Introduction.

2. Basic Principles in Operator Overloading.

Introduction:

Calling function in some classes may be annoying, especially mathematical classes, for example:

a = 2 + 3
assign(a, add(2,3));

In C++ the overloading principle applies not only to functions, but to operators too. - Operators can be extended to work not just with built-in types but also classes. - Operator is used on objects of that class. - Operator Overloading makes it very easy to write code that feels natural. - It requires special care, can be abused to make code unreadable.

Basic Principles in Operator Overloading:

When using operator overloading, you have to: - use it to increase readability of your program. - avoid exaggeration in use. To use operator overloading, follow those steps: 1- write the definition of your function as usual. 2- your function name is consist of operator keyword Followed by the operation symbol which you overload. For example to overloading addition operation (+) your function name will be :

operator+

It is possible to overloading almost all operators in C++. This list contains all operators we can overloading :

+ - * / % ^ & | ~ ! = += -= *= /= %= ^= &= |= > >>= = && || ++ -- ->* , -> [] () new delete new[] delete[]

In the following example, we will overload > operators:

// Overloading the stream-insertion and 
// stream-extraction operators.
#include <iostream>
 
using std::cout;
using std::cin;
using std::endl;
using std::ostream;
using std::istream;
 
#include <iomanip>
 
using std::setw;
 
class PhoneNumber 
{
   friend ostream &operator<<( ostream&, const PhoneNumber& );
   friend istream &operator>>( istream&, PhoneNumber &);
 
   private:
     char areaCode[ 4 ];  // 3-digit area code and null 
     char exchange[ 4 ];  // 3-digit exchange and null
     char line[ 5 ];  // 4-digit line and null
};
 
// Overloaded stream-insertion operator (cannot be 
// a member function if we would like to invoke it with
//cout <<somePhoneNumber;).
ostream &operator<<( ostream &output, constPhoneNumber &num )
{
     output << "(" << num.areaCode << ") "
     << num.exchange << "-" << num.line;
     return output;  // enables cout << a << b << c;
}
 
istream &operator>>( istream &input, PhoneNumber &num )
{
   input.ignore();  // skip (
   input >> setw( 4 ) >> num.areaCode; // input area code
   input.ignore( 2 );  // skip ) and space
   input >> setw( 4 ) >> num.exchange; // input exchange
   input.ignore();  // skip dash (-)
   input >>setw( 5 ) >> num.line;  // input line
   return input;  // enables cin >> a >> b >> c;
}
 
int main()
{
   PhoneNumber phone; // create object phone
 
   cout << "Enter phone number in the form (123) 456-7890:\n";
 
   // cin >> phone invokes operator>> function by 
   // issuing the call operator>>(cin, phone ).
   cin >> phone;
 
   // cout<< phone invokes operator<< function by
   // issuing the call operator<<(cout, phone ). 
   cout << "The phone number entered was: " << phone << endl;
   return 0;
}

The Output:

Enter phone number in the form (123) 456-7890: (800) 555-1212 The phone number entered was: (800) 555-1212

Note: You can find the full source code of this example in code.zip file.

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