1. Programming with ANSI C ++
A Step-by-Step Approach
Prof. Bhushan Trivedi
Director
GLS Institute of Computer Technology

2. and User Defined Conversions
Chapter 6
Operator Overloading
and User Defined Conversions

3. Introduction Give an additional meaning to an existing operator
A Meaningful meaning! Is important
The operator functions

4. Operator Overloading and User Defined Conversions
Comparison of both the methods of conversion
Which method is to be used?
Conversion and OO should not be changing the semantics of use
The stack example for + and –
The employee example for + and -

5. Introduction Give an additional meaning to an existing operator
A Meaningful meaning! Is important
The operator functions

6. Restrictions on use of OO
Cannot change the original meaning
New operators cannot be devised
Ops will not have additional precedence.
cannot change number of arguments
at least one argument as user defined type
Except (), no other operator can have a default argument.
same return type for new, delete and ->

7. Operators which can not be overloaded
The dot operator for member access
The dereference member to class operator .*
Scope resolution operator ::
Size of operator sizeof
Conditional ternary operator ?:
Casting operators static_cast<>, dynamic_cast<>, reinterpret_cast<>, const_cast<>
# and ## tokens for macro preprocessors

8. Operators which can not be overloaded as friends
Assignment Operator =
Function call operator ()
Array Subscript operator []
Access to class member using pointer to object operator ->
To ensure their first operand is lvalue!
= has global meaning as well!

9. The operator function
The need for word operator preceding the real operator like operator +
No explicit call!
Better as a library function!
Users do not need to remember function names
No ambiguity about parameters and call
Readability increases
No misspelled functions

10. Types of operators Unary Operators Binary Operators
The dummy arguments for postfix versions of increment and decrement operators
Binary Operators
Overloading shorthand operators while overloading arithmetic operators
The single ternery operator is not available

11. Using Friends
The lvalue problem for cases like Object + scaler and Scaler + Object calls to +
The body for both the cases can be different!
The operator << and >> case
The need to return reference

12. Overloading other Operators
The = operator
Normal Overloading
Extending = in the derived class
The [] operator
The safearray class example
The need to have reference as return type
Can be extended using templates

13. Overloading other Operators
The () operator
The function object vs. Function pointers
Inlining is possible
May have cache info and help
The new and delete using malloc and free
The New and delete using ::new and ::delete

14. Overloading new and delete
Before
Insertion
After First Insertion
Old Pointer
Table Space pointer
Current Pointer
Null
After 8th Insertion
Overloading new and delete

15. User Defined Conversions
Conversion from built-in data type to an object
Object to a built-in data type
The need for such operator: the wrapper class example
Object to Object Conversion
using constructors
using conversion functions

16. Operator Overloading and User Defined Conversions
Comparison of both the methods of conversion
Which method is to be used?
Conversion and OO should not be changing the semantics of use
The stack example for + and –
The employee example for + and -