Operator Overloading - Object Oriented Programming - Lecture Slides, Slides of Object Oriented Programming

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Object-Oriented Programming

(OOP)

Lecture No. 16

• Consider the following class:

class Complex{ private: double real, img; public: Complex Add(const Complex &); Complex Subtract(const Complex &); Complex Multiply(const Complex &); … } Docsity.com

• Function implementation:

Complex Complex::Add(

const Complex & c1){

Complex t;

t.real = real + c1.real;

t.img = img + c1.img;

return t;

}

• The following statement:

Complex c3 = c1.Add(c2);

Adds the contents of c2 to c1 and assigns it to c3 (copy constructor)

• To perform operations in a single

mathematical statement e.g:

c1+c2+c3+c

• We have to explicitly write:

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

• Alternative way is:

t1 = c3.Add(c4);

t2 = c2.Add(t1);

t3 = c1.Add(t2);

• If the mathematical expression is big:
  • Converting it to C++ code will involve complicated mixture of function calls
  • Less readable
  • Chances of human mistakes are very high
  • Code produced is very hard to maintain

• C++ provides a very elegant solution:

“ Operator overloading ”

• C++ allows you to overload common operators like + , - or ***** etc…
• Mathematical statements don’t have to be explicitly converted into function calls

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

c1+c2+c3+c

• The resultant code is very easy

to read, write and maintain

• C++ automatically overloads operators for pre-defined types
• Example of predefined types:

int float double char long

• Example:

float x;

int y;

x = 102.02 + 0.09;

Y = 50 + 47;

The compiler probably calls the correct

overloaded low level function for addition

i.e:

// for integer addition: Add(int a, int b)

// for float addition: Add(float a, float b)

• Operator functions are not usually

called directly

• They are automatically invoked to

evaluate the operations they

implement

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

• List of operators that can’t be overloaded:
• Reason: They take name, rather than

value in their argument except for ?:

• ?: is the only ternary operator in

C++ and can’t be overloaded

• The precedence of an operator is

NOT affected due to overloading

• Example:

c1c2+c*

c3+c2c*

both yield the same answer

• Associativity is NOT changed due

to overloading

• Following arithmetic expression

always is evaluated from left to

right:

c1 + c2 + c3 + c

• Unary operators and assignment

operator are right associative, e.g:

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

• All other operators are left

associative:

c1+c2+c3 is same as

(c1+c2)+c

• Always write code representing

the operator

• Example:

Adding subtraction code inside the

• operator will create chaos

• Creating a new operator is a syntax

error (whether unary, binary or ternary)

• You cannot create $

• Arity of an operator is NOT affected by

overloading

• Example:

Division operator will take exactly two operands in any case:

b = c / d

Binary operators

• Binary operators act on two quantities
• Binary operators:

Binary operators

• General syntax:

Member function:

TYPE 1 CLASS::operator B_OP(

TYPE 2 rhs){

...

}

Binary operators

• General syntax:

Non-member function:

TYPE 1 operator B_OP(TYPE 2 lhs, TYPE 3 rhs){

...

}

Binary operators

• The “ operator OP ” must have at

least one formal parameter of type

class (user defined type)

• Following is an error:

int operator + (int, int);