Operator overloading lecture1

Object-Oriented Object-Oriented Programming (OOP)Programming (OOP)

Lecture No. 16Lecture No. 16

Operator overloadingOperator overloading►Consider the following class:Consider the following class:

class Complex{class Complex{

private:private:

double real, img;double real, img;

public:public:

Complex Add(const Complex &);Complex Add(const Complex &);

Complex Subtract(const Complex &);Complex Subtract(const Complex &);

Complex Multiply(const Complex &);Complex Multiply(const Complex &);

……

}}

Operator overloadingOperator overloading►Function implementation:Function implementation:

Complex Complex::Add(Complex Complex::Add(

const Complex & c1){const Complex & c1){

Complex t;Complex t;

t.real = real + c1.real;t.real = real + c1.real;

t.img = img + c1.img;t.img = img + c1.img;

return t;return t;

}}

Operator overloadingOperator overloading

►The following statement:The following statement:

Complex c3 = c1.Add(c2);Complex c3 = c1.Add(c2);

Adds the contents of Adds the contents of c2c2 to to c1c1 and assigns it to and assigns it to c3c3 (copy (copy constructor)constructor)


►To perform operations in a To perform operations in a single mathematical single mathematical statement e.g:statement e.g:

c1+c2+c3+c4c1+c2+c3+c4

►We have to explicitly write:We have to explicitly write:

c1.Add(c2.Add(c3.Add(c4)))c1.Add(c2.Add(c3.Add(c4)))


►Alternative way is:Alternative way is:

t1 = c3.Add(c4);t1 = c3.Add(c4);

t2 = c2.Add(t1);t2 = c2.Add(t1);

t3 = c1.Add(t2);t3 = c1.Add(t2);


►If the mathematical expression If the mathematical expression is big:is big:

Converting it to C++ code will Converting it to C++ code will involve complicated mixture of involve complicated mixture of function callsfunction callsLess readableLess readableChances of human mistakes are Chances of human mistakes are very highvery highCode produced is very hard to Code produced is very hard to maintainmaintain


►C++ provides a very elegant C++ provides a very elegant solution:solution:

““Operator overloadingOperator overloading””►C++ allows you to overload C++ allows you to overload common operators like common operators like ++, , -- or or ** etc…etc…►Mathematical statements don’t Mathematical statements don’t have to be explicitly converted have to be explicitly converted into function callsinto function calls


►Assume that operator Assume that operator + has+ has been overloadedbeen overloaded►Actual C++ code becomes:Actual C++ code becomes:

c1+c2+c3+c4c1+c2+c3+c4

►The resultant code is very The resultant code is very easy to read, write and easy to read, write and maintainmaintain

Operator overloading Operator overloading ►C++ automatically overloads C++ automatically overloads operators for pre-defined typesoperators for pre-defined types►Example of predefined types:Example of predefined types:

intint

floatfloat

doubledouble

charchar

longlong

Operator overloading Operator overloading

►Example:Example:

float x;float x;

int y;int y;

x = 102.02 + 0.09;x = 102.02 + 0.09;

Y = 50 + 47;Y = 50 + 47;

Operator overloading Operator overloading

The compiler probably calls the The compiler probably calls the correct overloaded low level function correct overloaded low level function for addition i.e:for addition i.e:

// // for integer addition:for integer addition:

Add(int a, int b)Add(int a, int b)

// // for float addition:for float addition:

Add(float a, float b)Add(float a, float b)


►Operator functions are not Operator functions are not usually called directlyusually called directly

►They are automatically invoked They are automatically invoked to evaluate the operations they to evaluate the operations they implementimplement


►List of operators that can be List of operators that can be overloaded in C++:overloaded in C++:


►List of operators that can’t be List of operators that can’t be overloaded:overloaded:

►Reason: They take name, rather Reason: They take name, rather than value in their argument than value in their argument except for except for ?:?:►?:?: is the only ternary operator is the only ternary operator in C++ and can’t be overloadedin C++ and can’t be overloaded


►The precedence of an The precedence of an operator is operator is NOTNOT affected due affected due to overloadingto overloading

►Example:Example:

c1*c2+c3c1*c2+c3

c3+c2*c1c3+c2*c1

both yield the same answerboth yield the same answer


►Associativity is Associativity is NOTNOT changed due to overloadingchanged due to overloading

►Following arithmetic Following arithmetic expression always is expression always is evaluated from left to right:evaluated from left to right:

c1 + c2 + c3 + c4c1 + c2 + c3 + c4


►Unary operators and Unary operators and assignment operator are right assignment operator are right associative, e.g:associative, e.g:

a=b=ca=b=c is same as is same as a=(b=c)a=(b=c)

►All other operators are left All other operators are left associative:associative:

c1+c2+c3c1+c2+c3 is same as is same as

(c1+c2)+c3(c1+c2)+c3


►Always write code Always write code representing the operatorrepresenting the operator

►Example:Example:

Adding subtraction code inside Adding subtraction code inside the + operator will create the + operator will create chaoschaos


►Creating a new operator is a Creating a new operator is a syntax error (whether unary, syntax error (whether unary, binary or ternary)binary or ternary)

► You cannot create You cannot create $$


►Arity of an operator is NOT Arity of an operator is NOT affected by overloadingaffected by overloading

►Example:Example:

Division operator will take exactly two Division operator will take exactly two operands in any case:operands in any case:

b = c / db = c / d

Binary operatorsBinary operators►Binary operators act on two Binary operators act on two quantitiesquantities►Binary operators:Binary operators:

Binary operatorsBinary operators

►General syntax:General syntax:

Member function:Member function:

TYPETYPE11 CLASS::operator B_OP( CLASS::operator B_OP(

TYPETYPE22 rhs){ rhs){

......

}}


►General syntax:General syntax:

Non-member function:Non-member function:

TYPETYPE11 operator B_OP(TYPE operator B_OP(TYPE22 lhs, lhs, TYPETYPE33 rhs) rhs)

{{

......

}}


►The “The “operator OPoperator OP” must have at ” must have at least one formal parameter of type least one formal parameter of type class (user defined type)class (user defined type)

►Following is an error:Following is an error:

int operator + (int, int);int operator + (int, int);

Binary operatorsBinary operators►Overloading + operator:Overloading + operator:

class Complex{class Complex{

private:private:

double real, img;double real, img;

public:public:

……

Complex operator +Complex operator +(const (const Complex & Complex & rhs);rhs);

};};


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

Complex t;Complex t;

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

t.img = img + rhs.img;t.img = img + rhs.img;

return t;return t;

}}

Binary operatorsBinary operators►The return type is Complex so The return type is Complex so as to facilitate complex as to facilitate complex statements like:statements like:

Complex t = c1 + c2 + c3;Complex t = c1 + c2 + c3;

►The above statement is The above statement is automatically converted by the automatically converted by the compiler into appropriate compiler into appropriate function calls:function calls:

((c1.operator +(c2)c1.operator +(c2))).operator +.operator +(c3);(c3);


►If the return type was If the return type was voidvoid, , class Complex{class Complex{

......

public:public:

void operator+(void operator+(

const Complex & rhs);const Complex & rhs);

};};


void Complex::operator+(const void Complex::operator+(const Complex & rhs){Complex & rhs){

real = real + rhs.real;real = real + rhs.real;

img = img + rhs.img;img = img + rhs.img;

};};


►we have to do the same we have to do the same operation operation c1+c2+c3c1+c2+c3 as: as:

c1+c2c1+c2

c1+c3c1+c3

// final result is stored in c1// final result is stored in c1


►Drawback of void return type:Drawback of void return type:Assignments and cascaded Assignments and cascaded expressions are not possibleexpressions are not possibleCode is less readableCode is less readableDebugging is toughDebugging is toughCode is very hard to maintainCode is very hard to maintain

Operator overloading lecture1

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