Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 16

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 16

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Object-Oriented Programming

(OOP)Lecture No. 16


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Operator overloadingConsider the following class:

class Complex{

private:

double real, img;

public:

Complex Add(const Complex &);

Complex Subtract(const Complex &);

Complex Multiply(const Complex &);

}


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Operator overloadingFunction implementation:

Complex Complex::Add(

const Complex & c1){Complex t;

t.real = real + c1.real;

t.img = img + c1.img;

return t;

}


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Operator overloadingThe following statement:

Complex c3 = c1.Add(c2);

Adds the contents of c2to c1and

assigns it to c3(copy constructor)


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Operator overloadingTo perform operations in asingle mathematical statement

e.g:c1+c2+c3+c4

We have to explicitly write:c1.Add(c2.Add(c3.Add(c4)))


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Operator overloadingAlternative way is:

t1 = c3.Add(c4);

t2 = c2.Add(t1);

t3 = c1.Add(t2);


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Operator overloadingIf the mathematical expression isbig:

Converting it to C++ code will involvecomplicated mixture of function calls

Less readable

Chances of human mistakes are veryhigh

Code produced is very hard to maintain


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Operator overloadingC++ provides a very elegantsolution:

Operator overloading

C++ allows you to overloadcommon operators like +, -or *etc

Mathematical statements dont haveto be explicitly converted into functioncalls


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Operator overloadingAssume that operator + hasbeenoverloaded

Actual C++ code becomes:

c1+c2+c3+c4

The resultant code is very easyto read, write and maintain


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Operator overloadingC++ automatically overloadsoperators for pre-defined types

Example of predefined types:

int

float

double

char

long


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Operator overloadingExample:

float x;

int y;

x = 102.02 + 0.09;Y = 50 + 47;


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Operator overloadingThe compiler probably calls the correctoverloaded low level function for additioni.e:

// for integer addition:

Add(int a, int b)

// for float addition:

Add(float a, float b)


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Operator overloadingOperator functions are not usuallycalled directly

They are automatically invoked toevaluate the operations theyimplement


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Operator overloadingList of operators that can beoverloaded in C++:


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Operator overloadingList of operators that cant beoverloaded:

Reason: They take name, ratherthan value in their argument except

for ?:

?:is the only ternary operator inC++ and cant be overloaded


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Operator overloadingAssociativity is NOTchangeddue to overloading

Following arithmetic expressionalways is evaluated from left to

right:c1 + c2 + c3 + c4


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Operator overloadingUnary operators and assignmentoperator are right associative, e.g:

a=b=cis same as a=(b=c)

All other operators are leftassociative:

c1+c2+c3is same as

(c1+c2)+c3


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Operator overloadingCreating a new operator is a syntax

error (whether unary, binary orternary)

You cannot create $


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Operator overloadingArity of an operator is NOT affected

by overloadingExample:

Division operator will take exactly two operandsin any case:

b = c / d


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inary operatorsBinary operators act on twoquantities

Binary operators:


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inary operatorsGeneral syntax:

Member function:

TYPE1CLASS::operator B_OP(

TYPE2rhs){

...

}


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inary operatorsGeneral syntax:

Non-member function:

TYPE1operator B_OP(TYPE2lhs,TYPE3rhs){

...

}


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inary operatorsThe operator OP must have at

least one formal parameter of typeclass (user defined type)

Following is an error:int operator + (int, int);


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inary operatorsOverloading + operator:

class Complex{

private:

double real, img;

public:

Complex operator +(const

Complex & rhs);

};


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inary operatorsComplex Complex::operator +( const Complex & rhs){

Complex t;t.real = real + rhs.real;

t.img = img + rhs.img;

return t;}


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inary operatorsIf the return type was void,

class Complex{

...

public:

void operator+(

const Complex & rhs);

};


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inary operatorsvoid Complex::operator+(const

Complex & rhs){

real = real + rhs.real;

img = img + rhs.img;

};


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inary operatorswe have to do the same operationc1+c2+c3as:

c1+c2

c1+c3

// final result is stored in c1


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inary operatorsDrawback of void return type:

Assignments and cascaded expressionsare not possible

Code is less readable

Debugging is tough

Code is very hard to maintain

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Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 16