Lec 28 - operator overloading

Chapter: 08

Operator Overloading
Customised behaviour of operators

Lecture: 28
Date: 25.09.2012

Objectives
 Overloading in C++
 Function overloading
 Operator overloading

 Different types of operators and their overloading
 Operators that cannot be overloaded
 Data conversion
 Automatic type conversion
 User-defined type conversion

C++ Overloading
 Overloading in C++ allows to specify more than one
definition for a function name or an operator in the same
scope, which is called function overloading and operator
overloading respectively.

C++ OVERLAODING

Function Operator

 An overloaded declaration is the one that had been declared
with exactly the same name as the previous declaration in
the same scope, except that both declarations have different
arguments and also different definition (implementation).

C++ Function Overloading
 An overloaded function can have multiple definitions for
the same function name in the same scope.

 The definition of the function must differ from each other
by the types and/or the number of arguments in the
argument list.

 Function declarations cannot be overloaded if they differ
only by return type.

C++ Operator Overloading
 It simplifies the program listing, e.g.,
d3.addobjects(d1, d2)
or the similar but equally obscure
d3 = d1.addobjects(d2)
can be changed to much more readable form
d3 = d1 + d2
 Operator overloading refers to giving normal C++
operators such as +, *, and <= so on, an additional
meaning when they are applied to user defined data types,
e.g.,
d3 = d1 + d2 (legal when d1, d2, and d3 are basic types)

C++ Operator Overloading (Syntax)
returnType operator*(parameters);
↑ ↑ ↑
any type keyword operator symbol

 Return type may be whatever the operator returns
 Including a reference to the object of the operand

 Operator symbol may be any valid operator allowed
by the language compiler (see the following list)

Operators that can be overloaded
+ - * / % ^

& | ~ ! = <

> += -= *= /= %=

^= &= |= << >> >>=

<<= == != <= >= &&

|| ++ -- ->* , ->

[] () new delete new[] delete[]

Operators that cannot be overloaded

. .* :: ?:

Types of Operators

OPERATORS

Unary Binary
(+, <, =, …)

Prefix Postfix
(!, & , ~ , …) (++, --, …)

Unary Operators

 Operators attached to a single operand,
e.g., -a, +a, --a, a--, ++a, a++

Example: Unary Operators (Prefix)
class UnaryExample
{ private:
int m_LocalInt;
public:
UnaryExample(int j)
{ m_LocalInt = j; }

int operator++ ()
{ return (++m_LocalInt); }
};
int main()
{ UnaryExample object1(10);
cout << ++object1; // overloaded operator
getch();
return 0;
}

Example: Unary Operators (Postfix)
class UnaryExample
{ private:
int m_LocalInt;
public:
UnaryExample(int j)
{ m_LocalInt = j; }

int operator++ (int) // “int” argument for postfix operator
{ return m_LocalInt++; }
};
int main()
{ UnaryExample object1(10);
cout << object1++; // overloaded operator
getch();
return 0;
}

Binary Operators

 Operators attached to two operands,
e.g.,
a-b, a+b, a*b, a/b, a%b, a>b, a>=b,
a<b, a<=b, a==b

Example: Binary Operators
class BinaryExample
{
private:
int m_LocalInt;
public:
BinaryExample(int j)
{ m_LocalInt = j; }

int operator+ (BinaryExample& rhsObj)
{ return (m_LocalInt + rhsObj.m_LocalInt); }
};
int main()
{ BinaryExample object1(10), object2(20);
cout << object1 + object2; // overloaded operator called
getch();
return 0;
}

Non-Overloadable Operators
 Operators that cannot be overloaded due to
safety reasons:
 Member Selection ‘.’ operator
 Member dereference ‘.*’ operator

 Exponential ‘**’ operator

 User-defined operators

 Operator precedence rules

Data Conversion
 Assignment operator assigns a value from one side to
another, e.g.,
intvar1 = intvar2
 But what happens when the variables on different
sides of the = sign are of different types?
 Two possibilities:
 Automatic data conversion
 User-defined data conversion

Conversion Between basic Types
#include<iostream>
#include<conio.h>
using namespace std;

int main()
{
int intvar;
float floatvar;

intvar = static_cast<int>(floatvar); //casting provides explicit conversion

getch();
return 0;
}

Conversion between User-defined
and Basic Types

 Built-in conversion routines can’t be relied while
converting b/w user-defined data types and basic
types; since the compiler doesn’t know anything
about user-defined types besides what we tell it.

Conversion between User-defined
and Basic Types
 Create a member function that takes the current type
 Converts it to the desired type using the operator
keyword followed by the type you want to convert to.
 Return type is the name of the operator overloaded
 Reflexivity - global overloading instead of member
overloading; for code saving.
 Syntax:
operator type_name()
{ }

Conversion Between C-String and String
Objects

Lecture Summary
Lecture covered …
 Overloading in C++
 Function overloading
 Operator overloading

 Different types of operator
 Operators that cannot be overloaded
 Data conversion:
 Automatic type conversion
 User-defined type conversion

Lecture Summary

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Lec 28 - operator overloading

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