Object-Oriented Programming In C++: Operator Overloading

[samaduske]

1. Introduction.

2. Basic Principles in Operator Overloading.

Introduction:

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

1. a =
   
   2
   
   +
   
   3
   
2. 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 and >> operators:

1. // Overloading the stream-insertion and
   
2. // stream-extraction operators.
   
3. #include <iostream>
   
4. 
   
5. using
   
   std::
   
   cout
   
   ;
   
6. using
   
   std::
   
   cin
   
   ;
   
7. using
   
   std::
   
   endl
   
   ;
   
8. using
   
   std::
   
   ostream
   
   ;
   
9. using
   
   std::
   
   istream
   
   ;
   
10. 
    
11. #include <iomanip>
    
12. 
    
13. using
    
    std::
    
    setw
    
    ;
    
14. 
    
15. class
    
    PhoneNumber
    
16. {
    
17. friend
    
    ostream &
    
    operator<<
    
    (
    
    ostream&
    
    , const
    
    PhoneNumber&
    
    )
    
    ;
    
18. friend
    
    istream &
    
    operator>>
    
    (
    
    istream&
    
    , PhoneNumber &
    
    )
    
    ;
    
19. 
    
20. private
    
    :
    
21. char
    
    areaCode[
    
    4
    
    ]
    
    ;
    
    // 3-digit area code and null
    
22. char
    
    exchange[
    
    4
    
    ]
    
    ;
    
    // 3-digit exchange and null
    
23. char
    
    line[
    
    5
    
    ]
    
    ;
    
    // 4-digit line and null
    
24. }
    
    ;
    
25. 
    
26. // Overloaded stream-insertion operator (cannot be
    
27. // a member function if we would like to invoke it with
    
28. //cout <<somePhoneNumber;).
    
29. ostream &
    
    operator<<
    
    (
    
    ostream &
    
    output, constPhoneNumber &
    
    num )
    
30. {
    
31. output <<
    
    "("
    
    <<
    
    num.areaCode
    
    <<
    
    ") "
    
32. <<
    
    num.exchange
    
    <<
    
    "-"
    
    <<
    
    num.line
    
    ;
    
33. return
    
    output;
    
    // enables cout << a << b << c;
    
34. }
    
35. 
    
36. istream &
    
    operator>>
    
    (
    
    istream &
    
    input, PhoneNumber &
    
    num )
    
37. {
    
38. input.ignore
    
    (
    
    )
    
    ;
    
    // skip (
    
39. input >>
    
    setw(
    
    4
    
    )
    
    >>
    
    num.areaCode
    
    ;
    
    // input area code
    
40. input.ignore
    
    (
    
    2
    
    )
    
    ;
    
    // skip ) and space
    
41. input >>
    
    setw(
    
    4
    
    )
    
    >>
    
    num.exchange
    
    ;
    
    // input exchange
    
42. input.ignore
    
    (
    
    )
    
    ;
    
    // skip dash (-)
    
43. input >>
    
    setw(
    
    5
    
    )
    
    >>
    
    num.line
    
    ;
    
    // input line
    
44. return
    
    input;
    
    // enables cin >> a >> b >> c;
    
45. }
    
46. 
    
47. int
    
    main(
    
    )
    
48. {
    
49. PhoneNumber phone;
    
    // create object phone
    
50. 
    
51. cout
    
    <<
    
    "Enter phone number in the form (123) 456-7890:\n
    
    "
    
    ;
    
52. 
    
53. // cin >> phone invokes operator>> function by
    
54. // issuing the call operator>>(cin, phone ).
    
55. cin
    
    >>
    
    phone;
    
56. 
    
57. // cout<< phone invokes operator<< function by
    
58. // issuing the call operator<<(cout, phone ).
    
59. cout
    
    <<
    
    "The phone number entered was: "
    
    <<
    
    phone <<
    
    endl;
    
60. return
    
    0
    
    ;
    
61. }
    

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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